February 11, 2021

What Makes Humans So Different from Other Animals?

ESSENTIALS OF PHYSICAL ANTHROPOLOGY

Bn W. W. NORTON & COMPANY NEW YORK • LONDON

ESSENTIALS OF PHYSICAL ANTHROPOLOGY D I S C O V E R I N G O U R O R I G I N S

CLARK SPENCER LARSEN T H E O H I O S T A T E U N I V E R S I T Y

T H I R D E D I T I O N

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Library of Congress Cataloging- in- Publication Data

Larsen, Clark Spencer. Essentials of physical anthropology : discovering our origins / Clark Spencer Larsen, The Ohio State University.—Third edition. pages cm Includes index. ISBN 978-0-393-93866-1 (pbk.) 1. Physical anthropology. I. Title. GN50.4.L367 2015 599.9—dc23 2015023645

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TO CHRIS AND SPENCER, WITH MY DEEPEST THANKS FOR THEIR HELP, ENCOURAGEMENT, AND

(UNWAVERING) PATIENCE

CLARK SPENCER LARSEN heads the Department of Anthropology at The Ohio State University, Columbus. A native of Nebraska, he received his B.A. from Kansas State University and M.A. and Ph.D. from the Uni- versity of Michigan. Clark’s research is in bioarchaeology, skeletal biol- ogy, and paleoanthropology. He has worked in North America, Europe, and Asia. He has taught at the University of Massachusetts, Northern Illi- nois University, Purdue University, and the University of North Carolina. Since 2001, he has been a member of the faculty at Ohio State, where he is Distinguished Professor of Social and Behavioral Sciences. He teaches introductory physical anthropology, osteology, bioarchaeology, and paleoanthropology. Clark has served as president of the American Association of Physical Anthropologists and as editor- in- chief of the American Journal of Physical Anthropology. In addition to Our Origins, he has authored or edited 30 books and monographs, including Bioar- chaeology: Interpreting Behavior from the Human Skeleton, Skeletons in Our Closet, Advances in Dental Anthropology, and A Companion to Biological Anthropology.

ABOUT THE AUTHOR

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To the Instructor xx To the Student xxviii

CHAPTER 1 What Is Physical Anthropology? 2

PART I The Present: Foundation for the Past 19

CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory 20

CHAPTER 3 Genetics: Reproducing Life and Producing Variation 42

CHAPTER 4 Genes and Their Evolution: Population Genetics 70

CHAPTER 5 Biology in the Present: Living People 100

CHAPTER 6 Biology in the Present: The Other Living Primates 132

CHAPTER 7 Primate Sociality, Social Behavior, and Culture 164

PART II The Past: Evidence for the Present 183

CHAPTER 8 Fossils and Their Place in Time and Nature 184

CHAPTER 9 Primate Origins and Evolution: The First 50 Million Years 216

CHAPTER 10 Early Hominin Origins and Evolution: The Roots of Humanity 244

CHAPTER 11 The Origins and Evolution of Early Homo 282

CHAPTER 12 The Origins, Evolution, and Dispersal of Modern People 306

CHAPTER 13 Our Last 10,000 Years: Agriculture, Population, Biology 350

BASIC TABLE OF CONTENTS

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TABLE OF CONTENTS

Two-Page Spreads xix

To the Instructor xx

Tools for Teaching and Learning xxiii

Who Helped xxv

To the Student xxviii

CHAPTER 1 WHAT IS PHYSICAL ANTHROPOLOGY? 2

Big Questions 3 What Is Anthropology? 5 What Is Physical Anthropology? 7

What Do Physical Anthropologists Do? 7 What Makes Humans So Different from Other Animals?: The Six Steps to

Humanness 8 How We Know What We Know: The Scientific Method 14 Answering the Big Questions 16 Key Terms 17 Evolution Review 17 Additional Readings 17

x Table of Contentsx Table of Contents

PART I THE PRESENT: FOUNDATION FOR THE PAST 19

CHAPTER 2 EVOLUTION: CONSTRUCTING A FUNDAMENTAL SCIENTIFIC THEORY 20

Big Questions 21 The Theory of Evolution: The Context for Darwin 23

Geology: Reconstructing Earth’s Dynamic History 24 Paleontology: Reconstructing the History of Life on Earth 25 Taxonomy and Systematics: Classifying Living Organisms and Identifying Their

Biological Relationships 26 Concept Check Pre-Darwinian Theory and Ideas: Groundwork for

Evolution 27 Demography: Influences on Population Size and Competition for Limited

Resources 28 Evolutionary Biology: Explaining the Transformation of Earlier Life-Forms into

Later Life-Forms 28 Concept Check Darwin Borrows from Malthus 30 The Theory of Evolution: Darwin’s Contribution 31 Since Darwin: Mechanisms of Inheritance, the Evolutionary Synthesis, and the

Discovery of DNA 33 Mechanisms of Inheritance 33 The Evolutionary Synthesis, the Study of Populations, and the Causes of

Evolution 36 DNA: Discovery of the Molecular Basis of Evolution 37

Answering the Big Questions 39 Key Terms 39 Evolution Review: Past, Present, and Future of a Fundamental Scientific

Theory 40 Additional Readings 41

CHAPTER 3 GENETICS: REPRODUCING LIFE AND PRODUCING VARIATION 42

Big Questions 43 The Cell: Its Role in Reproducing Life and Producing Variation 44 The DNA Molecule: The Genetic Code 46

DNA: The Blueprint of Life 48 The DNA Molecule: Replicating the Code 48 How Do We Know? Ancient DNA Opens New Windows on the Past 50 Concept Check The Two Steps of DNA Replication 51

Chromosome Types 51 Mitosis: Production of Identical Somatic Cells 52 Meiosis: Production of Gametes (Sex Cells) 54 Producing Proteins: The Other Function of DNA 56

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Concept Check The Two Steps of Protein Synthesis 60 Genes: Structural and Regulatory 61 Polymorphisms: Variations in Specific Genes 61

Genotypes and Phenotypes: Genes and Their Expression 63 The Complexity of Genetics 65 Answering the Big Questions 67 Key Terms 68 Evolution Review: Insights from Genetics 68 Additional Readings 69

CHAPTER 4 GENES AND THEIR EVOLUTION: POPULATION GENETICS 70

Big Questions 71 Demes, Reproductive Isolation, and Species 72 Hardy-Weinberg Law: Testing the Conditions of Genetic Equilibrium 76 Mutation: The Only Source of New Alleles 77 Natural Selection: Advantageous Characteristics, Survival, and

Reproduction 80 Patterns of Natural Selection 81 Natural Selection in Animals: The Case of the Peppered Moth and Industrial

Melanism 82 Natural Selection in Humans: Abnormal Hemoglobins and Resistance to

Malaria 84 The Geography of Sickle-Cell Anemia and the Association with Malaria 86 The Biology of Sickle-Cell Anemia and Malarial Infection 87 The History of Sickle-Cell Anemia and Malaria 87 Other Hemoglobin and Enzyme Abnormalities 89

Genetic Drift: Genetic Change due to Chance 90 Founder Effect: A Special Kind of Genetic Drift 93

Gene Flow: Spread of Genes across Population Boundaries 93 Concept Check What Causes Evolution? 97 Answering the Big Questions 97 Key Terms 98 Evolution Review: The Four Forces of Evolution 99 Additional Readings 99

CHAPTER 5 BIOLOGY IN THE PRESENT: LIVING PEOPLE 100

Big Questions 101 Is Race a Valid, Biologically Meaningful Concept? 102

Brief History of the Race Concept 102 Debunking the Race Concept: Franz Boas Shows that Human Biology Is Not

Static 103

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xii Table of Contentsxii Table of Contents

So-Called Racial Traits Are Not Concordant 103 Human Variation: Geographic Clines, Not Racial Categories 103

Life History: Growth and Development 104 The Growth Cycle: Conception through Adulthood 105 Prenatal Stage: Sensitive to Environmental Stress, Predictive of Adult Health

105 Postnatal Stage: The Maturing Brain, Preparing for Adulthood 106 Adult Stage: Aging and Senescence 109 Evolution of Human Life History: Food, Sex, and Strategies for Survival and

Reproduction 111 Concept Check Life History Stages in Humans: Prenatal, Postnatal, and

Adult 111 Prolonged Childhood: Fat-Bodied Moms and Their Big-Brained Babies 112 Grandmothering: Part of Human Adaptive Success 112

Adaptation: Meeting the Challenges of Living 113 Climate Adaptation: Living on the Margins 114

Heat Stress and Thermoregulation 114 Body Shape and Adaptation to Heat Stress 114 Cold Stress and Thermoregulation 115 Solar Radiation and Skin Color 116 Solar Radiation and Vitamin D Synthesis 117 Solar Radiation and Folate Protection 118 High Altitude and Access to Oxygen 118

Concept Check Adaptation: Heat, Cold, Solar Radiation, High Altitude 119 Nutritional Adaptation: Energy, Nutrients, and Function 120

Macronutrients and Micronutrients 120 Human Nutrition Today 121 Overnutrition and the Consequences of Dietary Excess 123

Concept Check Nutritional Adaptation 126 Workload Adaptation: Skeletal Homeostasis and Function 126 Excessive Activity and Reproductive Ecology 128

Answering the Big Questions 129 Key Terms 130 Evolution Review: Human Variation Today 130 Additional Readings 131

CHAPTER 6 BIOLOGY IN THE PRESENT: THE OTHER LIVING PRIMATES 132

Big Questions 133 What Is a Primate? 135

Arboreal Adaptation—Primates Live in Trees and Are Good at It 138 Primates Have a Versatile Skeletal Structure 138 Primates Have an Enhanced Sense of Touch 140

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Primates Have an Enhanced Sense of Vision 141 Primates Have a Reduced Reliance on Senses of Smell and Hearing 141

Concept Check What Makes Primates Good at Living in Trees? 142 Dietary Plasticity—Primates Eat a Highly Varied Diet, and Their Teeth Reflect This

Adaptive Versatility 142 Primates Have Retained Primitive Characteristics in Their Teeth 142 Primates Have a Reduced Number of Teeth 142 Primates Have Evolved Different Dental Specializations and Functional

Emphases 143 Concept Check What Gives Primates Their Dietary Flexibility? 143

Parental Investment—Primate Parents Provide Prolonged Care for Fewer but Smarter, More Socially Complex, and Longer-Lived Offspring 146

Concept Check Primate Parenting 148 What Are the Kinds of Primates? 148

The Strepsirhines 153 Concept Check Monkey or Ape? Differences Matter 154

The Haplorhines 155 Concept Check Strepsirhines and Haplorhines Differ in Their Anatomy and

Senses 161 Answering the Big Questions 162 Key Terms 162 Evolution Review: Our Closest Living Relatives 163 Additional Readings 163

CHAPTER 7 PRIMATE SOCIALITY, SOCIAL BEHAVIOR, AND CULTURE 164

Big Questions 165 Primate Societies: Diverse, Complex, Long-Lasting 166

Diversity of Primate Societies 166 Primate Social Behavior: Enhancing Survival and Reproduction 167 Primate Residence Patterns 168 Primate Reproductive Strategies: Males’ Differ from Females’ 169

Concept Check Male and Female Reproductive Strategies 170 The Other Side of Competition: Cooperation in Primates 170

Getting Food: Everybody Needs It, but the Burden Is on Mom 172 Acquiring Resources and Transmitting Knowledge: Got Culture? 173 Vocal Communication Is Fundamental Behavior in Primate Societies 175 Answering the Big Questions 181 Key Terms 181 Evolution Review: Primate Social Organization and Behavior 182 Additional Readings 182

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PART II THE PAST: EVIDENCE FOR THE PRESENT 183

CHAPTER 8 FOSSILS AND THEIR PLACE IN TIME AND NATURE 184

Big Questions 185 Fossils: Memories of the Biological Past 188

What Are Fossils? 188 Taphonomy and Fossilization 188 Types of Fossils 188 Limitations of the Fossil Record: Representation Is Important 191

Just How Old Is the Past? 192 Time in Perspective 192 Geologic Time: Earth History 193 Relative and Numerical Age 195 Relative Methods of Dating: Which Is Older, Younger, the Same Age? 196

Stratigraphic Correlation 196 Chemical Dating 196 Biostratigraphic (Faunal) Dating 197 Cultural Dating 198

Absolute Methods of Dating: What Is the Numerical Age? 198 The Radiometric Revolution and the Dating Clock 198 The Revolution Continues: Radiopotassium Dating 203 Non-Radiometric Absolute Dating Methods 205

Genetic Dating: The Molecular Clock 207 Concept Check How Old Is It? 208 Reconstruction of Ancient Environments and Landscapes 209

The Driving Force in Shaping Environment: Temperature 210 Chemistry of Animal Remains and Ancient Soils: Windows onto Diets and

Habitats 211 Answering the Big Questions 213 Key Terms 214 Evolution Review: The Fossil Record 214 Additional Readings 215

CHAPTER 9 PRIMATE ORIGINS AND EVOLUTION: THE FIRST 50 MILLION YEARS 216

Big Questions 217 Why Did Primates Emerge? 218 The First True Primate: Visual, Tree-Dwelling, Agile, Smart 220

Primates in the Paleocene? 220 Eocene Euprimates: The First True Primates 220 The Anthropoid Ancestor: Euprimate Contenders 224 The First Anthropoids 225

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Early Anthropoids Evolve and Thrive 227 Concept Check When Were They Primates?: Anatomy through Time 227 Coming to America: Origin of New World Higher Primates 230

How Anthropoids Got to South America 230 Apes Begin in Africa and Dominate the Miocene Primate World 231 Apes Leave Africa: On to New Habitats and New Adaptations 234

Apes in Europe: The Dryopithecids 234 Apes in Asia: The Sivapithecids 235 Dead End in Ape Evolution: The Oreopithecids 235 Climate Shifts and Habitat Changes 238 Miocene Ape Survivors Give Rise to Modern Apes 238

Apes Return to Africa? 238 Concept Check The First Apes: A Remarkable Radiation 239 Monkeys on the Move 239 Answering the Big Questions 241 Key Terms 242 Evolution Review: Primate Social Organization and Behavior:

The Deep Roots of the Order Primates 242 Additional Readings 243

CHAPTER 10 EARLY HOMININ ORIGINS AND EVOLUTION: THE ROOTS OF HUMANITY 244

Big Questions 245 What Is a Hominin? 246

Bipedal Locomotion: Getting Around on Two Feet 248 Nonhoning Chewing: No Slicing, Mainly Grinding 248

Why Did Hominins Emerge? 251 Charles Darwin’s Hunting Hypothesis 251

Concept Check What Makes a Hominin a Hominin? 252 Peter Rodman and Henry McHenry’s Patchy Forest Hypothesis 254 Owen Lovejoy’s Provisioning Hypothesis 254 Sexual Dimorphism and Human Behavior 255 Bipedality Had Its Benefits and Costs: An Evolutionary Trade-Off 255

What Were the First Hominins? 256 The Pre-Australopithecines 256

Sahelanthropus tchadensis (7–6 mya) 257 Orrorin tugenensis (6 mya) 257 Ardipithecus kadabba and Ardipithecus ramidus (5.8–4.4 mya) 258

Concept Check The Pre-Australopithecines 263 The Australopithecines (4–1 mya) 264

Australopithecus anamensis (4 mya) 265 Australopithecus afarensis (3.6–3.0 mya) 266 Australopithecus (Kenyanthropus) platyops (3.5 mya) 269

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Diversification of the Homininae: Emergence of Multiple Evolutionary Lineages from One (3–1 mya) 269

Australopithecus garhi (2.5 mya) 270 The First Tool Makers and Users: Australopithecus or Homo? 270

Evolution and Extinction of the Australopithecines 273 Concept Check The Australopithecines 276 Answering the Big Questions 280 Key Terms 280 Evolution Review: The First Hominins 281 Additional Readings 281

CHAPTER 11 THE ORIGINS AND EVOLUTION OF EARLY HOMO 282

Big Questions 283 Homo habilis: The First Species of the Genus Homo 285

The Path to Humanness: Bigger Brains, Tool Use, and Adaptive Flexibility 285

Homo habilis and Australopithecus: Similar in Body Plan 287 Homo habilis’s Adaptation: Intelligence and Tool Use Become Important 287 Habitat Changes and Increasing Adaptive Flexibility 288

Concept Check Homo habilis: The First Member of Our Lineage 288 Homo erectus: Early Homo Goes Global 289

Homo erectus in Africa (1.8–.3 mya) 290 Homo erectus in Asia (1.8–.3 mya) 293 Homo erectus in Europe (1.2 million–400,000 yBP) 296 Evolution of Homo erectus: Biological Change, Adaptation, and Improved

Nutrition 297 Patterns of Evolution in Homo erectus 302

Concept Check Homo erectus: Beginning Globalization 303 Answering the Big Questions 304 Key Terms 305 Evolution Review: The Origins of Homo 305 Additional Readings 305

CHAPTER 12 THE ORIGINS, EVOLUTION, AND DISPERSAL OF MODERN PEOPLE 306

Big Questions 307 What Is So Modern about Modern Humans? 309 Modern Homo sapiens: Single Origin and Global Dispersal or Regional

Continuity? 309 What Do Homo sapiens Fossils Tell Us about Modern Human Origins? 311

Early Archaic Homo sapiens 311 Archaic Homo sapiens in Africa (350,000–200,000 yBP) 312

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Early Archaic Homo sapiens in Asia (350,000–130,000 yBP) 312 Early Archaic Homo sapiens in Europe (500,000–130,000 yBP) 313 Early Archaic Homo sapiens’ Dietary Adaptations 313

Late Archaic Homo sapiens 314 Late Archaic Homo sapiens in Asia (60,000–40,000 yBP) 315 Late Archaic Homo sapiens in Europe (130,000–30,000 yBP) 316 The Neandertal Body Plan: Aberrant or Adapted? 319 Neandertal Hunting: Inefficient or Successful? 321 Neandertals Buried Their Dead 324 Neandertals Talked 325 Neandertals Used Symbols 327

Early Modern Homo sapiens 327 Concept Check Archaic Homo sapiens 328

Early Modern Homo sapiens in Africa (200,000–6,000 yBP) 329 Early Modern Homo sapiens in Asia (90,000–18,000 yBP) 331 Early Modern Homo sapiens in Europe (35,000–15,000 yBP) 332

Modern Behavioral and Cultural Transitions 334 How Has the Biological Variation in Fossil Homo sapiens Been

Interpreted? 335 Ancient DNA: Interbreeding between Neandertals and Early Modern People? 336

Concept Check Early Modern Homo sapiens 337 Living People’s Genetic Record: Settling the Debate on Modern Human Origins 338

Assimilation Model for Modern Human Variation: Neandertals Are Still with Us 339

Concept Check Models for Explaining Modern Homo sapiens’ Origins 340 Modern Humans’ Other Migrations: Colonization of Australia, the Pacific, and

the Americas 340 Down Under and Beyond: The Australian and Pacific Migrations 342 Arrival in the Western Hemisphere: The First Americans 344

Answering the Big Questions 348 Key Terms 349 Evolution Review: The Origins of Modern People 349 Additional Readings 349

CHAPTER 13 OUR LAST 10,000 YEARS: AGRICULTURE, POPULATION, BIOLOGY 350

Big Questions 351 The Agricultural Revolution: New Foods and New Adaptations 353

Population Pressure 354 Regional Variation 355 Survival and Growth 359

Agriculture: An Adaptive Trade-Off 360 Population Growth 360 Environmental Degradation 361

Concept Check The Good and Bad of Agriculture 362

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How Did Agriculture Affect Human Biology? 362 The Changing Face of Humanity 363

Two Hypotheses 363 Implications for Teeth 365

Concept Check Soft Food and Biological Change 365 Building a New Physique: Agriculture’s Changes to Workload/Activity 366 Health and the Agricultural Revolution 369

Population Crowding and Infectious Disease 369 Concept Check Labor, Lifestyle, and Adaptation in the Skeleton 370

The Consequences of Declining Nutrition: Tooth Decay 371 Nutritional Consequences Due to Missing Nutrients: Reduced Growth and

Abnormal Development 371 Nutritional Consequences of Iron Deficiency 373

Concept Check Health Costs of Agriculture 374 Nutritional Consequences: Heights on the Decline 375

If It Is So Bad for You, Why Farm? 375 The Past Is Our Future 375 Our Ongoing Evolution 376 Answering the Big Questions 378 Key Terms 379 Evolution Review: Setting the Stage for the Present and Future 379 Additional Readings 380

Appendix: The Skeleton A1

Glossary A11

Glossary of Place Names A19

Bibliography A21

Permissions Acknowledgments A47

Index A51

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T WO- PAGE SPRE ADS

ENHANCED TOUCH

Primates have an enhanced sense of touch. This sensitivity is due in part to the presence of dermal ridges (fingerprints and toe prints) on the inside surfaces of the hands and feet. The potto, a prosimian, has primitive dermal ridges, whereas the human, a higher primate, has more derived ridges, which provide better gripping ability.

Em er

gi ng

c an

op y

M ai

n ca

no py

U nd

er st

or y

GENERALIZED SKELETAL STRUCTURE

Primates have a generalized skeletal structure. The bones that make up the shoulders, upper limbs, lower limbs, and other major joints such as the hands and feet are separate, giving primates a great deal of flexibility when moving in trees. In this monkey skeleton, note the grasping hands and feet, the long tail, and the equal length of the front and hind limbs relative to each other.

REDUCED SMELL

Primates have a reduced sense of smell. The smaller and less projecting snouts of most primates indicate their decreased reliance on smell.

DIETARY VERSATILITY

Primates have dietary plasticity. Part of the record of primate dietary adaptation is found in the teeth. The red colobus monkey dentition shown here is typical of a catarrhine dentition with a 2/1/2/3 dental formula. Note the differences in morphology of the four different tooth types: incisors (I1, I2), canines (C), premolars (P3, P4), and molars (M1, M2, M3).

ENHANCED VISION

Primates have an enhanced sense of vision. Evolution has given primates better vision, including increased depth perception and seeing in color. The eyes’ convergence provides significant overlap in the visual fields and thus greater sense of depth.

Human Potto

Overlapping visual fields

Taï Forest

MonkeyDog

Reduced snout length

I1 I2I2

P3P3 P4P4 M1

I1I1 I2I2 CC

P3P3

P4P4

Black-and-white colobus

Campbell’s

Chimpanzee

Demidoff’s galago

Diana monkey

Human

Lesser spot-nosed

Olive colobus

Potto

Putty-nosed

Red colobus

Sooty mangabey

Thomas’s galago

Eagle

F I G U R E

6.2 Primate Adaptation in Microcosm: The Taï Forest, Ivory Coast, West Africa

Apes Leave Africa: On to New Habitats and New Adaptations | 237236 | CHAPTER 9 Primate Origins and Evolution: The First 50 Million Years

Primate evolution began with primitive primates in the Eocene, setting the stage for the origin of all hominoids. Euprimates of the Eocene had the basic characteristics of living primates, such as convergent eye orbits and grasping digits. In the last 20 million years, primates diversified in appearance and behavior. These changes included the shift, for some, from life in the trees to life on the ground, and eventually the beginning of bipedality in the late miocene. (Based on Fleagle, J. G. Primate Adaptation and Evolution, 2nd ed. 1999. Academic Press.)

Scenes from the late Eocene in the Paris Basin. Top: The diurnal Adapis is feeding on leaves. Bottom: Several taxa of omomyids (Pseudoloris, Necrolemur, Microchoerus). Note the large eyes, a nocturnal adaptation, typical of both ancient and modern prosimians who are active at night.

Scene from the early Miocene of Rusinga Island, Kenya. Apes first appeared during this period, and these are the first apes (two species of Proconsul, Dendropithecus, Limnopithecus). These and other taxa form the ancestry of all later apes and hominins. Note the range of habitats occupied by these primates within the forest, including some in the middle and lower canopies and some on the forest floor. These primates show a combination of monkeylike and apelike features, in the skeleton and skull, respectively.

Scenes from the early Oligocene of the Fayum, Egypt. These anthropoid ancestors include Aegyptopithecus, Propliopithecus, and Apidium. These primates were adept arborealists, using their hands and feet for climbing and feeding.

Convergent eyes and grasping hands

Large eyes for nocturnal vision

Eocene 34–56 mya

Oligocene 23–34 mya Miocene 5.3–23 mya

Quadrupedal, monkeylike primate with superb arboreal skills

Quadrupedal, apelike primate. Note the lack of a tail, an ape characteristic.

Eocene-Oligocene-Miocene Habitats and Their Primates

F I G U R E

9.21

Figure 1.3 The Six Big Events of Human Evolution: Bipedalism, Nonhoning Chewing, Dependence on Material Culture, Speech, Hunting, and Domestication of Plants and Animals pp. 10–11

Figure 3.17 Protein Synthesis pp. 58–59

Figure 6.2 Primate Adaptation in Microcosm: The Taï Forest, Ivory Coast, West Africa pp. 136–137

Figure 9.21 Eocene– Oligocene– Miocene Habitats and Their Primates pp. 236–237

Figure 10.16 From Discovery to Understanding: Ardipithecus of Aramis pp. 260–261

TO THE INSTRUCTOR

HOW THIS BOOK CAN HELP YOUR STUDENTS DISCOVER PHYSICAL ANTHROPOLOGY

IT IS ABOUT ENGAGEMENT

Teaching is about engagement— connecting the student with knowledge, making it real to the student, and having the student come away from the course with an understanding of core concepts. Essentials of Physical Anthropology seeks to engage the student in the learning process. Engaging the student is perhaps more of a challenge in the study of phys- ical anthropology than in the study of other sciences, mainly because the student has likely never heard of the subject. The average student has probably taken a precollege course in chemistry, physics, or biology. Physical anthropology, though, is rarely mentioned or taught in precollege settings. Commonly, the student first finds out about the subject when an academic advisor explains that physical anthro- pology is a popular course that fulfills the college’s natural science requirement.

Once taking the course, however, that same student usually connects quickly with the subject because so many of the topics are familiar— fossils, evolution, race, genet- ics, DNA, monkeys, forensic investigations, and origins of speech, to name a few. The student simply had not real- ized that these separately engaging topics come under the umbrella of one discipline, the subject of which is the study of human evolution and human variability.

Perhaps drawn to physical anthropology because it focuses on our past and our present as a species, the student quickly sees the fundamental importance of the discipline. In Discover magazine’s 100 top stories of 2009, 18 were from physical anthropology. Three topics from the field were in the top 10, including the remarkable new discovery of our earliest human ancestor, Ardipithecus. So important was this discovery that Science, the leading international professional science journal, called it the “Breakthrough of the Year” for

2009. The discussions in this textbook of topics familiar and unfamiliar give the student stepping- stones to science and to the centrality of physical anthropology as a window into understanding our world. Whether the students find the material familiar or unfamiliar, they will see that the book relates the discipline to human life: real concerns about human bodies and human identity. They will see themselves from an entirely different point of view and gain new awareness.

In writing this book, I made no assumptions about what the reader knows, except to assume that the reader— the stu- dent attending your physical anthropology class— has very little or no background in physical anthropology. As I wrote the book, I constantly reflected on the core concepts of phys- ical anthropology and how to make them understandable. I combined this quest for both accuracy and clarity with my philosophy of teaching— namely, engage the student to help the student learn. Simply, teaching is about engagement. While most students in an introductory physical anthro- pology class do not intend to become professional physical anthropologists, some of these students become interested enough to take more courses. So this book is written for stu- dents who will not continue their study of physical anthro- pology, those who get “hooked” by this fascinating subject (a common occurrence!), and those who now or eventually decide to become professionals in the field.

The book is unified by the subject of physical anthropol- ogy. But equally important is the central theme of science— what it is, how it is done, and how scientists (in our case, anthropologists) learn about the natural world. I wrote the book so as to create a picture of who humans are as organ- isms, how we got to where we are over the last millions of years of evolution, and where we are going in the future in light of current conditions. In regard to physical anthro- pology, the student should finish the book understanding human evolution and how it is studied, how the present helps us understand the past, the diversity of organisms living and past, and the nature of biological change over

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time and across geography. Such knowledge should help the student answer questions about the world. For example, how did primates emerge as a unique group of mammals? Why do people look different from place to place around the world? Why is it important to gain exposure to sunlight yet unsafe to prolong that exposure? Why is it unhealthy to be excessively overweight? Throughout their history, what have humans eaten, and why is it important to know?

I have presented such topics so that the student can come to understand the central concepts and build from them a fuller understanding of physical anthropology. Throughout the book, I emphasize hypothesis testing, the core of the scientific method, and focus on that process and the excite- ment of discovery. The narrative style is personalized. Often I draw on my own experiences and those of scientists I know or am familiar with through their teaching and writing, to show the student how problems are addressed through field- work or through laboratory investigations.

Scientists do not just collect facts. Rather, they collect data and make observations that help them answer questions about the complex natural world we all inhabit. Reflecting this practice, Essentials of Physical Anthropology is a collec- tion not of facts for the student to learn but of answers to questions that help all of us understand who we are as living organisms and our place in the world. Science is a way of knowing, it is a learning process, and it connects our lives with our world. In these ways, it is liberating.

HOW THE BOOK IS ORGANIZED

The book is divided into two parts. Following an introduc- tory overview of anthropology and physical anthropology, Part I presents the key principles and concepts in biology, especially from an evolutionary perspective. This material draws largely on the study of living organisms, including humans and nonhuman primates. Because much of our understanding of the past is drawn from what we have learned from the present, this part lays the foundation for the presentation in Part II— the past record of primate and human evolution. In putting the record of the living up front, this book departs from the style of most other introductory physical anthropology textbooks, which start out with the earliest record and end with the living. This book takes the position that most of what we learn about the past is based on theory and principles learned from the living record. Just as all of Charles Darwin’s ideas were first derived from seeing living plants and animals, much of our understanding of function and adaptation comes from living organisms as models. Therefore, this book views the living as the window

into what came before— the present contextualizes and informs our understanding of the past. It is no mistake, then, that Discovering Our Origins is the subtitle of the book. The origins of who we are today do not just lie in the record of the past, but are very much embodied in the living. Our origins are expressed in our physical makeup (bone, teeth, and muscles), in our behavior, and in so many other ways that the student taking this course will learn about from this book and from you. You can teach individual chapters in any order, and that is partly because each chapter reinforces the central point: we understand our past via what we see in the living.

Part II presents evidence of the past, covering more than 50 million years of primate and human evolution. Most textbooks of this kind end the record of human evolution at about 25,000 years ago, when modern Homo sapiens evolved worldwide. This textbook also provides the record since the appearance of modern humans, showing that important bio- logical changes occurred in just the last 10,000 years, largely relating to the shift from hunting and gathering to the domestication of plants and animals. Food production was a revolutionary development in the human story, and Part II presents this remarkable record, including changes in health and well- being that continue today. A new subdiscipline of physical anthropology, bioarchaeology, is contributing pro- found insights into the last 10,000 years, one of the most dynamic periods of human evolution.

During this period, a fundamental change occurred in how humans obtained food. This change set the stage for our current environmental disruptions and modern living conditions, including global warming, the alarming global increase in obesity, and the rise of health threats such as newly emerging infectious diseases, of which there is little under- standing and for which scientists are far from finding cures.

CHANGES IN THE THIRD EDITION

Reflecting the dynamic nature of physical anthropology, there are numerous revisions and updates throughout this new, third edition of Essentials of Physical Anthropology. These updates provide content on the cutting- edge developments in the discipline, give new ways of looking at older findings, and keep the book engaging and timely for both you and your students. Although the core principle of the book remains the same, namely the focus on evolution, the revi- sions throughout the book present new insights, new discov- eries, and new perspectives. Other changes are intended to give added focus and clarity and to increase the visual appeal that supports the pedagogy of engagement and learning:

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• New content on biocultural adaptation. Anthropol- ogists provide important insights into how humans’ remarkable intelligence is related to their evolution- ary success. This third edition presents new research on the role of social learning and the retention of knowledge— the accumulation of information— over many generations.

• New primate taxonomy. In order to inform students about the latest developments in primate classifica- tion, the third edition has shifted from the tradi- tional, grade- based approach used in the previous editions to the cladistics, or phylogenetic, approach. This approach provides students with a classifica- tion based on ancestor- descendant evolutionary relationships.

• New content on developments in genetics that are altering our understanding of phenotype. We are learning that non- protein coding DNA, often considered “junk” DNA, has important implications for various other instructions in the genome. Similarly, the rapidly expanding field of epigenetics is revealing evolution- ary change without alteration of DNA.

• New content on race and human variation in Chapter 5. • New content on maladaptive human behavior and health

outcomes such as obesity. The role of environment is fundamental in understanding patterns of health in very recent human evolution, including the impacts of the creation of obesogenic environments, the alarming rise in obesity globally, and the causes and consequences of these changing circumstances and outcomes.

• New content on fossil primate and hominin discoveries. Exciting new discoveries in early primate evolution from Africa and Asia are revealing the enormous variety and complexity of species. New discoveries from East Africa reveal that although all australo- pithecines were bipedal, some retained arboreal behavior relatively late in the evolution of these early hominins. New discovery of stone tools dat- ing to 3.3 million years ago—700,000 years earlier than previously known—from East Africa shows the beginnings of humankind’s reliance on material culture. Once thought to be the domain of Homo, these early dates show use of tools by earlier aus- tralopithecines, long before the origins of our genus. These discoveries continue to illustrate the com- plexity of early hominin evolution. New evidence from chemical and tooth wear analyses reveals that at least some later australopithecines were eating significant quantities of low- quality vegetation,

including grasses on the African savanna, confirming the long- held notion that some had highly specialized diets.

• New findings on the origins of cooking and its importance in human evolution. Controlled use of fire dates to as early as 1 mya in South Africa. This innovation provided a means for cooking meats and starches, thereby increasing the digestibility of these foods. New research suggests that cooking and nutri- tional changes associated with cooking may have “fueled” the increase in brain and body size in early hominins.

• New content on the appearance and evolution of modern Homo sapiens and the Neandertal genome. Analysis of the direction and pattern of scratches on the incisors of Neandertals reveals that they were pre- dominantly right- handed. In addition to showing this modern characteristic, this finding reveals that this earlier form of H. sapiens had brain laterality, a feature linked to speech. Neandertals talked. New genetic evidence reveals the presence of Neander- tal genes in modern humans, consistent with the hypothesis that modern H. sapiens interbred with Neandertals. Newly discovered hominin fossils from Denisova, Siberia, dating to the late Pleistocene represent a genome that is different from Neander- tals’ and modern H. sapiens’. This newly discovered “Denisovan” genome is also found in people living today in East Asia, suggesting that modern H. sapiens encountered Neandertals as well as other populations once in Europe.

• New findings on the future of humankind. The study of melting ice caps and glaciers around the world today reveals a dramatic warming trend. As temperatures rise, habitats are in the process of changing. These environmental changes will provide a context for evolution, both in plants and in animals. These fac- tors, coupled with reduction in species diversity, are creating new health challenges for humans today and for the foreseeable future.

• Revision of content to enhance clarity. I have contin- ued to focus on helping students understand core concepts, with considerable attention given to cell biology, genetics, DNA, race and human variation, primate taxonomy, locomotion, and dating methods. As in previous editions, I paid careful attention to the clarity of figure captions. The captions do not simply repeat text. Instead, they offer the student additional details relevant to the topic and occasional questions about concepts that the figures convey.

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• Greatly enhanced art program. The new edition con- tains over 100 new or revised figures, often using a new “photorealistic” style. The book adds several full- color two- page spreads developed by Mauri- cio Antón, a world- renowned artist with expertise in conveying past life through wonderful visual presentations.

• “Evolution Review” sections. At the end of each chapter, an “Evolution Review” section summarizes material on evolution in that chapter and includes assignable questions about concepts and content. Suggested answers appear in the Instructor’s Manual.

• InQuizitive. Norton’s new formative and adaptive online learning resource improves student under- standing of the big picture concepts of physical anthropology. Students receive personalized quiz questions on the topics they need the most help with. Engaging, game- like elements motivate students as they learn. These are intended for use in teaching face- to- face, blended, or online class formats.

• New lab manual. This text now has a new lab manual, the Lab Manual for Biological Anthropology—Engaging with Human Evolution by K. Elizabeth Soluri and Sabrina C. Agarwal. This flexible and richly illus- trated manual is designed to support or enhance your current labs and collections, or work on its own. Attractively priced, discount bundles can be pur- chased including this text.

AIDS TO THE LEARNING PROCESS

Each chapter opens with a vignette telling the story of one person’s discovery that relates directly to the central theme of the chapter. This vignette is intended to draw your stu- dents into the excitement of the topic and to set the stage for the Big Questions that the chapter addresses.

BIG QUESTION learning objectives are introduced early in the chapter to help your students organize their reading and understand the topic.

CONCEPT CHECKS are scattered throughout each chap- ter and immediately follow a major section. These aids are intended to help your students briefly revisit the key points they have been reading about.

LOCATOR MAPS are placed liberally throughout the book. College- level instructors tend to hope that students have a good sense of geography, but like a lot of people who do not

look at places around the world on a daily basis, students often need reminders about geography. In recognition of this, locator maps in the book’s margins show the names and locations of places that are likely not common knowledge.

PHOTOREALISTIC ART YOU CAN “TOUCH”: Designed to give students an even better appreciation for the feel of the discipline, the art program has been substantially reworked. Now most illustrations of bones and skeletons have an almost photorealistic feel, and most primates were redrawn for a high degree of realism. This book helps your students visualize what they are reading about by including hundreds of images, many specially prepared for the book. These illustrations tell the story of physical anthropology, including key processes, central players, and important con- cepts. As much thought went into the pedagogy behind the illustration program as into the writing of the text.

DEFINITIONS are also presented in the text’s margins, giving your students ready access to what a term means generally in addition to its use in the associated text. For convenient reference, defined terms are signaled with bold- face page numbers in the index.

At the end of each chapter, ANSWERING THE BIG QUESTIONS presents a summary of the chapter’s central points organized along the lines of the Big Questions pre- sented at the beginning of the chapter.

The study of evolution is the central core concept of physical anthropology. The newly introduced EVOLUTION REVIEW section at the end of each chapter discusses topics on evolution featured in the chapter and asks questions that will help the student develop a focused understanding of content and ideas.

INQUIZITIVE is our new game- like, formative, adaptive assessment program featuring visual and conceptual ques- tions keyed to each chapter’s learning objectives from the text. InQuizitive helps you track and report on your students’ progress to make sure they are better prepared for class.

Join me now in engaging your students in the excitement of discovering physical anthropology.

TOOLS FOR TEACHING AND LEARNING

The Essentials of Physical Anthropology teaching and learning package provides instructors and students with all the tools they need to visualize anthropological concepts, learn key vocabulary, and test knowledge.

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FOR INSTRUCTORS

InQuizitive

New InQuizitive online formative and adaptive assessment is available for use with Essentials of Physical Anthropology, Third Edition, featuring interactive and engaging questions with answer- specific feedback. InQuizitive features ques- tions designed to help students better understand the core objectives of each chapter. Built to be intuitive and easy to use, InQuizitive makes it a snap to assign, assess, and report on student performance and help keep your class on track. Options are available to integrate InQuizitive into your LMS or Coursepack. Contact your local W. W. Norton representative for details.

Lab Manual and Workbook for Biological Anthropology— Engaging with Human Evolution by K. Elizabeth Soluri and Sabrina C. Agarwal.

This new manual captures student interest and illustrates the discipline with the vivid images— every chapter contains large detailed figures, photographs that are properly scaled, and drawings of bones and fossils with an almost three- dimensional appearance. The labs are grouped into four units of four chapters each: 1) genetics/evolutionary theory; 2) human osteology and forensics; 3) primatology; and 4) paleoanthropology. No topic is over- or underemphasized, and the manual is flexibly designed to be used as a whole, or as individual labs, and with a school’s cast and photo collec- tion or with the sample photos provided. Each lab has unique Critical Thinking Questions to go with Chapter Review and Lab Exercises. This manual is available at student friendly prices, either as a stand- alone volume or bundled with this text, or as a custom volume.

Coursepacks

Available at no cost to professors or students, Norton Coursepacks for online or hybrid courses are available in a variety of formats, including all versions of Blackboard and WebCT. Content includes review quizzes, flash cards, and links to animations and videos. Coursepacks are available from wwnorton.com/instructors.

New Animations

These new animations of key concepts from each chapter are available in either the Coursepacks, or from wwnorton.com/ instructors. Animations are brief, easy to use, and great for explaining concepts either in class or in a distance- learning environment.

New Videos

This new streaming video service is now available through Norton Coursepacks and at wwnorton.com/instructors. These one- to seven- minute educational film clips from across the discipline but with an emphasis on paleoanthro- pology and primatology help students see and think like anthropologists and make it easy for instructors to illustrate key concepts and spark classroom discussion.

Update PowerPoint Service

To help cover what is new in the discipline, each semester we will provide a new set of supplemental lectures, notes, and assessment material covering current and breaking research. Prepared by Laurie Reitsema (University of Georgia) and with previous updates from Kathy Droesch (Suffolk County Community College), this material is available for download at wwnorton.com/instructors.

PowerPoint Slides and Art JPEGs

Designed for instant classroom use, these slides prepared by Jeremy DeSilva (Boston University) using art from the text are a great resource for your lectures. All art from the book is also available in PowerPoint and JPEG formats. Download these resources from wwnorton.com/instructors.

Instructor’s Manual

Prepared by Nancy Tatarek (Ohio University) and Greg Laden, this innovative resource provides chapter summaries, chapter outlines, lecture ideas, discussion topics, suggested reading lists for instructors and students, a guide to “Writ- ing about Anthropology,” suggested answers to Evolution Matters questions, and teaching materials for each video.

Test Bank

Prepared by Renee Garcia (Saddleback College) and Greg Laden, this Test Bank contains multiple- choice and essay questions for each chapter. It is downloadable from Norton’s Instructor’s Website and available in Word, PDF, and ExamView® Assessment Suite formats. Visit wwnorton.com/ instructors.

Ebook

An affordable and convenient alternative, Norton ebooks retain the content and design of the print book and allow students to highlight and take notes with ease, print chap- ters as needed, and search the text.

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http://wwnorton.com/instructors

WHO HELPED

I owe much to the many people who made this book possible, from the planning and writing of the first and sec- ond editions, and now this third edition. First and foremost, I thank my wife, Christine, and son, Spencer, who helped in innumerable ways. They were my captive audience: without protest, they listened to my ideas at the dinner table, on family trips, and in other places where we probably should have been talking about other things. Chris read many drafts of chapters and gave great advice on when and where to cut, add, or rethink. I thank my parents, the late Leon and Patricia Larsen, who introduced me to things old and sparked my interest in the human past.

Jack Repcheck first approached me about writing a text- book on introductory physical anthropology. His power of persuasion, combined with my own interest in the discipline and its presentation to college students, was instrumental in reeling me in and getting the project off the ground. Jack and others at W. W. Norton & Company made the process of writing the book a great experience in all ways, from writ- ing to publication. On the first edition, I began work with editors John Byram and then Leo Wiegman. I am indebted to Pete Lesser, who took on the project after Leo. Pete gave direction on writing and production, provided very helpful feedback on presentation and pedagogy, and orchestrated the process of review, revision, and production— all without a hitch. Under Pete’s guidance, the first edition became the most widely used textbook in physical anthropology. Jack Repcheck continued the project in preparation for the sec- ond edition. The preparation of the third edition was over- seen by editor Eric Svendsen. His advice and guidance were central to seeing the book come to fruition. Tacy Quinn recently joined the team and has spearheaded the develop- ment of new media for this edition including InQuizitive. Marina Rozova does an excellent job developing the core supplement package for each edition. Kurt Wildermuth edited the entire manuscript for the first two editions. His skill as an editor and staying on top of content from begin- ning to end added enormously to the book’s presentation and readability. Sunny Hwang has now taken Kurt’s place and has especially helped with revisions in the end- of- chapter mate- rial and the on- line supplements program. Diane Cipollone was instrumental in producing these pages and directing a wide variety of editing issues that arose, and the entire team is now supported by Rachel Goodman. Ben Reynolds guided the process of production from beginning to end. I am also grateful to Mauricio Antón for his wonderful new illustra- tions of six “big events” of human evolution in chapter 1, the new rendition of the Taï Forest primates as a microcosm of

primate adaptation in chapter 6, and the Eocene, Oligocene, and Miocene primates and their habitats in chapter 9. Greg Laden, Renee Garcia, and Nancy Tatarek’s timely and effi- cient completion of the Test Bank and Instructor’s Manual is much appreciated. Laurie Reitsema has been recently added to the team producing our valuable update PowerPoints each semester, and I thank Kathy Droesch for her past work on these updates.

With the input of instructors and focus group attendees who are included in the reviewer list, we have created an extensive new media and assessment suite for the third edi- tion. However, my thanks for extensive work in developing InQuizitive and our new animations go to Tracy Betsinger of SUNY Oneonta, Ashley Hurst of University of Texas at San Antonio, Kristina Killgrove of University of West Florida, Greg Laden, Joanna Lambert of the University of Colorado, and Heather Worne of University of Kentucky, with further thanks to contributors Jaime Ullinger, Quinnipiac University, and Nancy Cordell, South Puget Sound Community College. And thanks to Sandra Wheeler of University of Central Flor- ida, Ellen Miller of Wake Forest University, Bonnie Yoshida of Grossmont College, Jacqueline Eng of Western Michigan University, Jeremy DeSilva of Boston University, K. Eliza- beth Soluri of College of Marin, and again Nancy Cordell of South Puget Sound Community College for their important feedback and reviews of these resources.

Thanks go to former and current graduate students and faculty colleagues at the Ohio State University who helped in so many ways. I offer a very special thanks to Tracy Betsinger, who assisted in a number of aspects of the book. For the first edition, she read drafts of chapters at various stages and helped in figure selection, in glossary compilation, and as a sounding board in general for ideas that went into the book. For the second edition, she offered very helpful suggestions for revisions. Thanks to Jaime Ullinger, who provided the content and data for the box on PTC tasting. Tracy, Jaime, Jim Gosman, Dan Temple, Haagen Klaus, and Josh Sadvari read parts or all of the manuscript and offered great advice. For all three editions, I had many helpful discussions with Scott McGraw about primate behavior, evolution, and tax- onomy. Scott also provided advice on the production of the two- page spreads on both primate diversity and eagle predation in the Taï Forest, Ivory Coast (chapters 6 and 7). For this edition, John Fleagle provided valuable support reviewing details in most of the new primate illustrations, in particular the two- page spreads, and every new piece of art was first reviewed in the larger Our Origins volume by Arthur Durband, Andrew Kramer, and Sandra Wheeler. Doug Crews gave advice on the complexities of primate (including human) biology and life history. Haagen Klaus

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provided materials for and help on the two- page spread on the biological consequences of the agricultural revolution and many other helpful comments and suggestions for revision. Barbara Piperata advised me on key aspects of modern human biology and nutrition science, and Dawn Kitchen provided discussion and help on the fundamentals of primate communication and how best to present it. Josh Sadvari was indispensable in the creation of the Evolution Review sections at the end of each chapter.

Over the years, I have had helpful conversations with my teachers, colleagues, and students about areas of their exper- tise, and these people have influenced the development of the book in so many ways. I am grateful to Patricia J. O’Brien and Milford H. Wolpoff, my respective undergraduate and graduate advisors. Both were instrumental in developing my interest in science and the wonderful profession I work in. I thank Barry Bogin, Kristen Hawkes, Jim O’Connell, David Thomas, Bob Kelly, Jerry Milanich, Bruce Smith, Kris Gremillion, Bonnie McEwan, Matt Cartmill, Dale Hutchinson, Chris Ruff, Simon Hillson, Michael Schultz, Sam Stout, Doug Ubelaker, Dan Sellen, Clark Howell, Rick Steckel, Phil Walker, John Relethford, Mark Weiss, Mar- garet Schoeninger, Karen Rosenberg, Lynne Schepartz, Fred Smith, Brian Hemphill, Bruce Winterhalder, Meg Conkey, Desmond Clark, Erik Trinkaus, Katherine Russell, Vin Steponaitis, Mark Teaford, Richard Wrangham, Jerry Rose, Mark Cohen, William Bass, Loring Brace, Stanley Garn, Frank Livingstone, Phil Gingerich, T. Dale Stew- art, Larry Angel, Mike Finnegan, Harriet Ottenheimer, Marty Ottenheimer, Roberto Frisancho, Randy Susman, Karen Strier, Joanna Lambert, Jim Hijiya, Cecil Brown, Bill Fash, Rich Blanton, Henry Wright, James Griffin, Bill Jungers, David Frayer, Bill Pollitzer, George Armelagos, Jane Buikstra, Elwyn Simons, Steve Churchill, Neil Tubbs, Bob Bettinger, Tim White, Dean Falk, Owen Lovejoy, Scott Simpson, David Carlson, Alan Goodman, Bill Dancey, Debbie Guatelli- Steinberg, Sam Stout, Clark Mallam, and Chris Peebles.

I would like to thank Joanna E. Lambert, University of Colorado–Boulder and Friderun Ankel-Simons, Duke Uni- versity for their help and their words used to prepare the back cover description. Their response was helpful, timely, and their suggested wording was perfect.

The book benefited from the expertise of many anthro- pologists and other experts. I especially acknowledge the fol- lowing reviewers for their insights, advice, and suggestions for revision of the text and creation of the support package:

Sabrina Agarwal, University of California, Berkeley Paul Aiello, Ventura College Lon Alterman, North Carolina State University

Tara Devi Ashok, University of Massachusetts Boston Diana Ayers- Darling, Mohawk Valley Community

College Philip de Barros, Palomar College Thad Bartlett, University of Texas at San Antonio Cynthia Beall, Case Western Reserve University Owen Beattie, University of Alberta Anna Bellisari, Wright State University Daniel Benyshek, University of Nevada, Las Vegas Tracy Betsinger, State University of New York at Oneonta Deborah Blom, University of Vermont Amy Bogaard, Oxford University Günter Bräuer, University of Hamburg Emily Brunson, University of Washington Victoria Buresch, Glendale Community College Isabelle Champlin, University of Pittsburgh at Bradford Joyce Chan, California State University, Dominguez

Hills Chi- hua Chiu, Kent State University David Clark, Catholic University of America Robert Corruccini, Southern Illinois University Herbert Covert, University of Colorado Douglas Crews, Ohio State University Eric Delson, Lehman College, City University of

New York Katherine Dettwyler, University of Delaware Joanne Devlin, University of Tennessee Paul Erickson, St. Mary’s University Becky Floyd, Cypress College David Frayer, University of Kansas Daniel Gebo, Northern Illinois University Anne Grauer, Loyola University of Chicago Mark Griffin, San Francisco State University Michael Grimes, Western Washington University Gregg Gunnell, Duke University Lesley Harrington, University of Alberta Lauren Hasten, Las Positas College John Hawks, University of Wisconsin– Madison Samantha Hens, California State University, Sacramento James Higham, New York University Madeleine Hinkes, San Diego Mesa College Homes Hogue, Ball State University Nina Jablonski, Pennsylvania State University Karin Enstam Jaffe, Sonoma State University Gabriela Jakubowska, Ohio State University Gail Kennedy, University of California, Los Angeles Dawn Kitchen, Ohio State University Haagen Klaus, George Mason University Patricia Lambert, Utah State University Michael Little, Binghamton University Chris Loeffler, Irvine Valley College

xxvi Instructor

Sara Lynch, Queens College, City University of New York Lorena Madrigal, University of South Florida Ann Magennis, Colorado State University Stephen Marshak, University of Illinois at

Urbana– Champaign Debra Martin, University of Nevada, Las Vegas Thomas McDade, Northwestern University William McFarlane, Johnson County Community

College Scott McGraw, Ohio State University Rachel Messinger, Moorpark College Ellen Miller, Wake Forest University Leonor Monreal, Fullerton College Ellen Mosley- Thompson, Ohio State University Michael Muehlenbein, Indiana University Dawn Neill, California Polytechnic State University, San

Luis Obispo Wesley Niewoehner, California State University, San

Bernardino Kevin Nolan, Ball State University Rachel Nuger, Hunter College, City University of

New York Dennis O’Rourke, University of Utah Janet Padiak, McMaster University Amanda Wolcott Paskey, Cosumnes River College Michael Pilakowski, Butte College Janine Pliska, Golden West College Deborah Poole, Austin Community College Leila Porter, Northern Illinois University Frances E. Purifoy, University of Louisville Mary Ann Raghanti, Kent State University Lesley M. Rankin- Hill, University of Oklahoma Jeffrey Ratcliffe, Penn State Abington Laurie Reitsema, University of Georgia Melissa Remis, Purdue University Analiese Richard, University of the Pacific Charles Roseman, University of Illinois Karen Rosenberg, University of Delaware John Rush, Sierra College Andrew Scherer, Brown University Timothy Sefczek, Ohio State University Lynette Leidy Sievert, University of Massachusetts

Scott W. Simpson, Case Western Reserve University Cynthia Smith, Ohio State University Fred Smith, Illinois State University Richard Smith, Washington University Sara Smith, Delta College Lilian Spencer, Glendale Community College Sara Stinson, Queens College, City University of

New York Christopher Stojanowski, Arizona State University Margaret Streeter, Boise State University Karen Strier, University of Wisconsin– Madison Nancy Tatarek, Ohio University Lonnie Thompson, Ohio State University Victor Thompson, University of Georgia Christopher Tillquist, University of Louisville Sebina Trumble, Hartnell College Lisa Valkenier, Merritt College Dennis Van Gerven, University of Colorado Boulder Ronald Wallace, University of Central Florida David Webb, Kutztown University Daniel Wescott, Texas State University Tim White, University of California, Berkeley Janet Wiebold, Spokane Community College Caleb Wild, Mira Costa College Leslie Williams, Beloit College Sharon Williams, Purdue University Kristen Wilson, Cabrillo College Milford Wolpoff, University of Michigan Thomas Wynn, University of Colorado Colorado Springs

Thanks, everyone, for your help! Lastly, a very special thanks goes to all of the faculty around the globe who adopted the previous two editions of Essentials of Physical Anthropology for their introductory physical anthropology classes. I am also grateful to the hundreds of students who connected with the book— many of whom have written me with their comments. Please continue to send me your com- ments ([email protected]).

Columbus, Ohio August 10, 2015

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http://[email protected]

xxviii

TO THE STUDENT

PHYSICAL ANTHROPOLOGY IS ABOUT DISCOVERING WHO WE ARE

THINKING LIKE AN ANTHROPOLOGIST

Who are we? Where do we come from? Why do we look and act the way we do? This book is a journey that addresses these and other big questions about us, Homo sapiens. This journey emphasizes humans’ discovery of the fascinating record of our diversity and of our evolution, a record that serves as a collective memory of our shared biological pres- ence on Earth. From here to the end of the book, I will share with you all kinds of ideas that add up to our current understanding of human beings as living organisms. Along the way, you will experience scientific breakthroughs such as the Human Genome Project and forensics (you might even watch CSI and Bones in a whole new way). You will gain new understandings of phenomena such as race and human diversity, global warming and its impact on our evolution and our well- being, the origins of human violence, global disease, and the growing worldwide obesity epidemic. Like an anthropologist tackling important questions, you will discover places on nearly every continent and come to see what life was like for millions of years before the present, before the emergence and evolution of humans.

Neither your instructor nor I can expect you as an intro- ductory student to understand all the developments in phys- ical anthropology. Both of us can, however, present you with a clear and concise framework of the field. By the time you are finished reading this book and completing this course, you will have a solid background in the basic tenets of the discipline. This knowledge will help you understand your place in nature and the world that we— more than 7 billion of us and growing— live in. The framework for developing your understanding of physical anthropology is the scien- tific method, a universal approach to understanding the very complex natural world. You should not assume that this book and this course are about only knowing the right

answers, the “facts” of physical anthropology. Rather, they are also about seeing how physical anthropologists know what they know— understanding the scientific method. So as you read, keep in mind the key questions that scientists try to answer, their processes and methods for finding the answers, and the answers themselves.

In writing this book, I have focused on the big ques- tions in physical anthropology, how scientists have tackled them, and what key discoveries have been made. I have not shied away from identifying the scientists who made these discoveries— real people, young and old, from all over the world. Whether you need to learn all these individuals’ names and what they contributed to the growth of physical anthropology and to our knowledge of human evolution and variation is up to your instructor. But in the introductory physical anthropology class that I teach, I encourage my stu- dents to learn about the people behind the ideas. By seeing the field through these people’s eyes, you can start thinking like an anthropologist.

SEEING LIKE AN ANTHROPOLOGIST

Thinking like an anthropologist includes seeing what anthropologists see. We anthropologists are constantly looking at things— fossilized human teeth, ancient DNA, excavated stone tools, primate skeletons, and much more— and using what we see to understand biology in the past and in the present. The photos and drawn art throughout this book have been chosen to help you see what anthropologists see. I strongly encourage you to pay close attention to the visuals in the book and their captions because much of our anthropological understanding is in the art program.

THE STRUCTURE OF THE BOOK

The book is divided into two parts. Following an overview of anthropology and physical anthropology (chapter 1), Part I provides the basic context for how we understand human (and our nonhuman primate relatives’) biology in the present

(and how that helps us understand the past). From this section of the book you should come away with an under- standing of evolution and the biology associated with it. Evolution as an idea has a long history (chapter 2). You will need to fully grasp the meaning and power of this theory, which explains humans’ biological variation today and in the past. Part I also has the important job of providing you with an understanding of genetics (chapters 3 and 4). This information is a central part of the evidence for evolution, from the level of the molecule to the level of the population.

Part I also looks at the biology of living people, that of the other living primates, and the variation among primate spe- cies. I am keen on debunking the common notion that there are discrete categories— races— of human beings (chapter 5). In fact, nothing about the biology of people, present or past, indicates that we can be divided into distinct groups. After looking at how environment and culture help shape the way humans look and behave, I will look similarly at nonhuman primates (chapters 6 and 7). Because nonhuman primates’ appearances are much more categorical than humans’ are, nonhuman primate appearance lends itself to classification or taxonomy. In these chapters, we will look at what nonhu- man primates do in the wild, what they are adapted to, and especially the environment’s role in shaping their behavior and biology. By looking at living people and living nonhu- man primates, we will be better equipped to understand the biological evidence drawn from the past.

Part II examines the processes and evidence physical anthropologists and other scientists use to understand the past (chapter 8), the evolution of prehuman primate ances- tors that lived more than 50 million years ago (chapter 9), and both the emergence of our humanlike ancestors and their evolution into modern humans (chapters 10, 11, and 12). Contrary to popular (and some scientific) opinion, human evolution did not stop when anatomically modern people first made their appearance in various corners of the globe. Rather, even into the last 10,000 years a considerable amount of biological change has occurred. Anthropologists have learned that agriculture, which began some 10,000 years ago, has been a fundamental force behind population increase. The downside of this shift to new kinds of food and the resulting population increase was a general decline in health. The later section of Part II (chapter 13) explores the nature and cause of biological change, including the changes associated with health and well- being that led to the biological and environmental conditions we face today.

With this book in hand and our goals— thinking and see- ing like anthropologists— in mind, let us set off on this excit- ing journey. Consider it a voyage of discovery, on which our shipmates include your instructor and your fellow students. If we work hard and work together, we will find perhaps the most interesting thing on Earth: ourselves.

To the Student xxix

Gorilla meets hominin and author of Essentials of Physical Anthropology Clark Larsen.

ESSENTIALS OF PHYSICAL ANTHROPOLOGY

THE GEORGIA COAST WAS A FOCAL point for Spanish colonization in the sixteenth and seventeenth centuries. European colo- nization set in motion changes in human living conditions that eventually affected human biology on a global scale.

3 3

1 What is anthropology?

What is physical anthropology?

What makes us human and different from other animals?

How do physical anthropologists know what they know?

What Is Physical Anthropology?

In the heat of the midday summer sun, our boat slowly made its way across the five miles of water that separate mainland Georgia from St. Catherines Island, one of a series of barrier islands dotting the Atlantic seaboard. Today, the island is covered by dense vegetation typical of the subtropical American South— palmettos and other palm trees, pines, hickories, and live oaks— and is infested with a wide array of stinging and biting insects. It is hard to imagine that this setting was once a focal point of the Span- ish colonial “New World,” representing the northernmost extension of Spain’s claim on eastern North America. This was the location of the Roman Catholic church and mis- sion Santa Catalina de Guale, where several hundred Indians and a dozen Spaniards lived and worked during the late 1500s and most of the 1600s.

What could possibly have motivated my field team and me to work for months under a blazing sun, fighting insects? Like any scientific investigation, our fieldwork was moti- vated by specific questions that we keenly wanted to answer. Buried in the sands of St. Catherines were the mortal remains— skeletons— of the native people who had lived at this long- abandoned place. These remains held answers to questions about the biology of modern people. Native Americans had lived in this area of the world for most of the last 10,000 years. We wanted to know about their biological evolution and vari- ation: How had these people changed biologically over this time span? What caused these changes? What circumstances led to the changes that we hoped to identify and interpret?

When we first set foot on St. Catherines Island in the summer of 1982 to begin our work at Mission Santa Catalina, we were excited about our project, but little did we

B I G Q U E S T I O N S ?

4 | CHAPTER 1 What Is Physical Anthropology?

realize just what a spectacular scientific journey we were undertaking. The skel- etons we sought turned out to provide wonderfully rich biological details about a little- understood region of the world, especially relating to the health consequences and behavioral consequences of European contact on native peoples. In setting up the research project, I had envisioned that our findings would provide a microcosm of what had unfolded globally— in the Americas, Asia, Africa, and Australia— during the previous 500 years of human history. During this period, significant biological changes had taken place in humans. Some of these changes were evolutionary— they resulted in genetic change. Other biological changes, nonevolutionary ones, reflected significant alterations in health and lifestyle, alterations that had left impressions on the skeletons we studied. Such study— of genetic and nongenetic changes— here and elsewhere in the world has proven fundamental to human beings’ understanding of their biology in the early twenty- first century.

Like any scientific investigation, the research project at Mission Santa Catalina did not develop in a vacuum. Prior to our work there, my team and I had devoted nearly a decade to studying hundreds of skeletons we had excavated from the region, dating from before the arrival of Spaniards. We had learned from archaeological evidence that before AD 1000 or so the people there ate exclusively wild animals, fish, and wild plants— they were hunters and gatherers. Never settling into one place for any period of time, they moved from place to place over the year, hunting animals, fishing on the coastline, and collecting plants. Then, their descendants— the ancestors of the mission Indians— acquired corn agriculture, becoming the first farmers in the region. These people did lots of fishing, but farming produced the mainstay of their diet. This major shift in lifestyle led to the establishment of semipermanent villages. In comparison with the hunter– gatherers living before AD 1000, the later agricultural people were shorter, their skulls and limb bones were smaller, and they had more dental disease and more infections. All of this information— scientific discoveries about the prehistoric people, their biological changes, and their adaptations— set the stage for our return to the island to study the people who lived at Santa Catalina, the descendants of the prehistoric hunter– gatherers and later farmers. From our study of their remains, we learned that after the Spaniards’ arrival the native people worked hard, they became more focused on producing and eating corn, and their health declined. The combination of declining quality of life and new diseases introduced by the Spaniards led to the native people’s extinction in this area of North America.

The research just described is one small part of the broader discipline known as physical anthropology. My work concerns life on the southeastern United States Atlantic coast, but physical anthropologists explore and study everywhere how humans and their ancestors lived. This enterprise covers a lot of ground and a lot of time, basi- cally the entire world and the last 50 million years or so! The territorial coverage of physical anthropology is so widespread and so diverse because the field addresses broad issues, seeking to understand human evolution— what we were in the past, who we are today, and where we will go in the future. Physical anthropologists seek answers to questions about why we are what we are as biological organisms. How we answer these questions is oftentimes difficult. The questions, though, motivate physical anthropologists to spend months in the subtropics of coastal Georgia, learning about an extinct native people; in the deserts of central Ethiopia, finding and studying the remains of people who lived hundreds, thousands, or even millions

What Is Anthropology? | 5

of years ago; or at the high altitudes of the Andes Mountains, studying living people and their responses and long- term adaptation to low oxygen and extreme cold, to name just a few of the settings you will learn about in this book. In this chapter, we will explore in more detail the nature of physical anthropology and its subject matter.

What Is Anthropology? When European explorers first undertook transcontinental travel (for example, Marco Polo into Asia in the late 1200s) or transoceanic voyages to faraway lands (for example, Christopher Columbus to the Americas in the late 1400s and early 1500s), they encountered people that looked, talked, dressed, and behaved very differently from themselves. When these travelers returned to their home coun- tries, they described the peoples and cultures they saw. Building on these accounts, early scholars speculated on the relationships between humans living in Europe and those encountered in distant places. Eventually, later scholars developed new ideas about other cultures, resulting in the development of the discipline of anthropology.

Anthropology is the study of humankind, viewed from the perspective of all people and all times. As it is practiced in the United States, it includes four branches or subdisciplines: cultural anthropology, archaeology, linguistic anthropology, and physical anthropology, also called biological anthropology (Figure 1.1).

Cultural anthropologists typically study present- day societies in non- Western settings, such as in Africa, South America, or Australia. Culture— defined as learned behavior that is transmitted from person to person— is the unifying theme of study in cultural anthropology.

Archaeologists study past human societies, focusing mostly on their material remains— such as animal and plant remains and places where people lived in the past. Archaeologists are best known for their study of material objects— artifacts— from past cultures, such as weaponry and ceramics. Archaeologists study the processes behind past human behaviors— for example, why people lived where they did, why some societies were simple and others complex, and why people shifted from hunting and gathering to agriculture beginning more than 10,000 years ago. Archaeologists are the cultural anthropologists of the past— they seek to reassemble cultures of the past as though those cultures were alive today.

Linguistic anthropologists study the construction and use of language by human societies. Language— defined as a set of written or spoken symbols that refer to things (people, places, concepts, etc.) other than themselves— makes possible the transfer of knowledge from one person to the next and from one gen- eration to the next. Popular among linguistic anthropologists is a subfield called sociolinguistics, the investigation of language’s social contexts.

Physical (or biological) anthropologists study all aspects of present and past human biology. As we will explore in the next section, physical anthropology deals with the evolution of and variation among human beings and their living and past relatives.

No anthropologist is expected to be an expert in all four branches. Anthropol- ogists in all four areas and with very different interests, however, acknowledge the diversity of humankind in all contexts. No other discipline embraces the breadth of the human condition in this manner. In fact, this remarkably diverse discipline

anthropology The study of humankind, viewed from the perspectives of all peo- ple and all times.

cultural anthropology The study of modern human societies through the analysis of the origins, evolution, and variation of culture.

archaeology The study of historic of pre- historic human populations through the analysis of material remains.

linguistic anthropology The study of the construction, use, and form of language in human populations.

physical anthropology The original term for biological anthropology.

biological (physical) anthropology The study of the evolution, variation, and adaptation of humans and their past and present relatives.

culture Learned behavior that is transmit- ted from person to person.

artifacts Material objects from past cultures.

language A set of written or spoken sym- bols that refer to things (people, places, concepts, etc.) other than themselves.

sociolinguistics The science of investigat- ing language’s social contexts.

6 | CHAPTER 1 What Is Physical Anthropology?

differs from other disciplines in its commitment to the notion that, unlike other animals, humans are biocultural— both biological and cultural beings. Anthro- pologists are interested in the interrelationship between biology and culture. Anthropologists call this focus the biocultural approach. Anthropology also differs from other disciplines in emphasizing a broad comparative approach to the study of biology and culture, looking at all people (and their ancestors) and all cultures in all times and all places. Anthropologists are interested in people and their ancestors, wherever or whenever they lived. Simply, you are studying a field that is holistic, unlike any you have studied before.

biocultural approach The scientific study of the interrelationship between what humans have inherited genetically and culture.

The Four Branches of Anthropology

Cultural Anthropology Archaeology Linguistic Anthropology Physical Anthropology

The study of cultures and societies of human beings and their very recent past.

Traditional cultural anthropologists study

living cultures and present their observations in

an ethnography.

The study of past societies and their cultures,

especially the material remains of the past, such

as tools, food remains, and places where people lived.

The study of language, especially how language

is structured, the evolution of language, and the social

and cultural contexts for language.

Also called biological anthropology, physical

anthropology is the study of human evolution and variation, both past and current.

FIGURE 1.1 The Four Branches of Anthropology (a) Cultural anthropologists, who study living populations, often spend time living with cultural groups to gain more intimate perspectives on those cultures. The American anthropologist Margaret Mead (1901–1978), one of the most recognizable names in cultural anthropology, studied the peoples of the Admiralty Islands, near Papua New Guinea. (b) Archaeologists study past human behaviors by investigating material remains that humans leave behind, such as buildings and other structures. In the Peruvian Andes, this archaeologist examines the remnants of a brewery used by the Wari Empire (ca. AD 750–1000). (c) Linguistic anthropologists study all aspects of language and language use. Here, Leslie Moore, a linguistic anthropologist working in a Fulbe community in northern Cameroon, records as a teacher guides a boy in memorizing Koranic verses. (d) Physical anthropologists study human evolution and variation. Some physical anthropologists study skeletons from the past to investigate evolution and variation throughout human history. Those working in forensic anthropology, a specialty within physical anthropology, examine skeletons to identify who they were in life. Such an identification may be of a single person or of thousands. For example, the forensic anthropologist pictured here was called on to help identify the estimated 30,000 victims of Argentina’s “Dirty War,” which followed the country’s 1976 coup.

(a) (b) (c) (d)

forensic anthropology The scientific exam- ination of skeletons in hope of identifying the people whose bodies they came from.

What Is Physical Anthropology? | 7

What Is Physical Anthropology? The short answer to this question is, Physical anthropology is the study of human biologi- cal evolution and human biocultural variation. Two key concepts underlie this definition.

Number one, every person is a product of evolutionary history, or all the bio- logical changes that have brought humanity to its present form. The remains of humanlike beings, or hominins, indicate that the earliest human ancestors, in Africa, date to sometime around 6–8 million years ago (mya). Since that time, the physical appearance of hominins and their descendants, including modern humans, has changed dramatically. Our physical appearance, our intelligence, and everything else that makes us distinctive biological organisms evolved in our predecessors, whose genes led to the species we are today. (Genes and species are among the subjects of chapters 3 and 4.)

Number two, each of us is the product of his or her own individual life history. From the moment you were conceived, your biological makeup has been deter- mined mostly by your genes. (The human genome— that is, all the genetic mate- rial in a person— includes some 20,000–25,000 genes.) Your biological makeup is also strongly influenced by your environment. Environment here refers not just to the obvious factors such as climate but to everything that has affected you— the physical activities you have engaged in (which have placed stress on your muscles and bones), the food you have eaten, and many other factors that affect overall health and well- being. Environment also includes social and cultural factors. A disadvantaged social environment, such as one in which infants and children receive poor- quality nutrition, can result in negative consequences such as poor health, reduced height, and shortened life expectancy. The Indian child who lived after the shift from foraging to farming on the Georgia coast ate more corn than did the Indian child who lived in the same place before AD 1000. Because of the corn- rich diet, the later child’s teeth had more cavities. Each child’s condition reflects millions of years of evolution as well as more immediate circumstances, such as diet, exposure to disease, and the stresses of day- to- day living.

WHAT DO PHYSICAL ANTHROPOLOGISTS DO? Physical anthropologists routinely travel to places throughout the United States and around the world to investigate populations. Some physical anthropologists study living people, while others study extinct and living species of our nearest biological relatives, primates such as lemurs, monkeys, and apes. I am among the physical anthropologists who travel to museum collections and archaeological localities to study past societies. When I tell people outside the field what I do for a living, they often think physical anthropology is quite odd, bizarre even. Frequently they ask, “Why would anyone want to study dead people and old bones and teeth?” Everyone has heard of physics, chemistry, and biology; but the average person has never heard of this field. Compared to other areas of science, physical anthropology is small. But smallness does not make it unimportant. It is practical and important, providing answers to fundamental questions that have been asked by scholars and scientists for centuries, such as Who are we as a species? What does it mean to be human? Where did we come from? Moreover, physical anthropology plays a vital role in address- ing questions that are central to our society, sometimes involving circumstances that all of us wish had never come about. For example, the tragedy that Americans identify as 9/11 called immediately for the assistance of specialists from forensic anthropology.

hominin Humans and humanlike ancestors.

genome The complete set of genetic information— chromosomal and mito- chondrial DNA— for an organism or spe- cies that represents all of the inheritable traits.

primates A group of mammals in the order Primates that have complex behavior, varied forms of locomotion, and a unique suite of traits, including large brains, forward- facing eyes, fingernails, and reduced snouts.

8 | CHAPTER 1 What Is Physical Anthropology?

The discipline as practiced in the United States began in the first half of the twentieth century, especially under the guidance of three key figures: Franz Boas for American anthropology generally; Czech- born Aleš HrdliČka, who started the professional scientific journal and professional society devoted to the field; and Earnest Hooton, who trained most of the first generation of physical anthro- pologists. While the theory and methods of physical anthropologists today have changed greatly since the early 1900s, the same basic topics first envisioned by these founders form what we do.

Physical anthropologists study all aspects of human biology, specifically looking at the evolution and variation of human beings and their living and past relatives. This focus on biology means that physical anthropologists practice a biological science. But they also practice a social science, in that they study biology within the context of culture and behavior. Depending on their areas of interest, physical anthropologists might examine molecular structure, bones and teeth, blood types, breathing capacity and lung volume, genetics and genetic history, infectious and other types of disease, origins of language and speech, nutrition, reproduction, growth and development, aging, primate origins, primate social behavior, brain biology, and many other topics dealing with variation in both the living and the dead— sometimes the very long dead (Figure 1.2)!

In dealing with such topics, physical anthropologists apply methods and theo- ries developed in other disciplines as well as in their own as they answer questions that help us understand who we are, a point that I will raise over and over again throughout this book. The very nature of their discipline and their constant borrowing from other disciplines mean that physical anthropologists practice an interdisciplinary science. For example, they might draw on the work of geologists who study the landforms and layering of deposits of soil and rock that tell us when earlier humans lived. Or they might obtain information from paleontologists, who study the evolution of life- forms in the distant past and thus provide the essential context for understanding the world in which earlier humans lived. Some physical anthropologists are trained in chemistry, so they can analyze the chemical properties of bones and teeth to determine what kinds of foods were eaten by those earlier humans. Or to learn how living humans adapt to reduced- oxygen settings, such as in the high altitudes of the Peruvian Andes Mountains, physical anthropologists might work with physiologists who study the lungs’ ability to absorb oxygen. The firm yet flexible identity of their science allows physical anthropologists to gather data from other disciplines in order to address key questions. Questions drive what they do.

What Makes Humans So Different from Other Animals?: The Six Steps to Humanness Human beings clearly differ from other animals. From humanity’s earliest origin— about 6–8 mya, when an apelike primate began walking on two feet— to the period beginning about 10,000 years ago, when modern climates and environments emerged following what is commonly known as the Ice Age, six key attributes developed that make us unique. These attributes are bipedalism, nonhoning chewing, complex material culture and tool use, hunting, speech, and dependence on domesticated foods (Figure 1.3, pp. 10–11). The first development represents

FIGURE 1.2 A Sample of What Physical Anthropologists Do (a) Human remains excavated at Bactia Pozzeveri, a medieval church cemetery in Tuscany, Italy, provide a window onto health and living conditions in Europe. (b) Geneticists analyze samples of human DNA for various anthropological purposes. DNA studies are used to determine how closely related humans are to other primate species, to examine human origins, and to determine individual identities. (c) A human biologist records the physical activities of a lactating woman (right, weaving basket) living in a rural community in the eastern Amazon, Brazil. These data will be used to calculate the woman’s energy expenditure and to understand how she copes with reproduction’s great energy demands. (d) In a lab, a forensic anthropologist measures and assesses human bones. If the bones came from a contemporary grave, this forensic information might help to identify the victim. If the bones belonged to a past population, physical anthropologists might use these data to gain insight into the population’s health and lifestyle. (e) Laboratory investigations of human ancestors’ bones help paleoanthropologists to determine where these ancestors fit in the human family tree. (f) Primatologists, such as the British researcher Jane Goodall (b. 1934), study our closest living relatives, nonhuman primates. The behavior and lifestyle of chimpanzees, for example, help physical anthropologists to understand our evolutionary past.

(c)

(a)

(e)

(b)

(d)

(f)

What Makes Humans So Different from Other Animals?: The Six Steps to Humanness | 9

(c)

(a)

(e)

(b)

(d)

(f)

BIPEDALISM 6 MYA

The upright, bipedal (two-footed) gait was the first hallmark feature of our hominin ancestors.

SPEECH 2.5 MYA

In the entire animal kingdom, only humans can speak and, through speech, express complex thoughts and ideas. The shape of the hyoid bone is unique to hominins and reflects their ability to speak. Speech is part of the overall package in the human lineage of increased cognition, intelligence, and brain-size expansion.

HUNTING 1 MYA

Humans’ relatively large brains require lots of energy to develop and function. Animal protein is an ideal source of that energy, and humans obtained it for most of their evolution by eating animals they hunted. To increase their chances of success in hunting, humans employed tools they made and cooperative strategies.

NONHONING CHEWING 5.5 MYA

Humans’ nonhoning chewing complex (below) lacks large, projecting canines in the upper jaw and a diastema, or gap, between the lower canine and the third premolar.

The chewing complex of apes such as gorillas (below) has large, projecting upper canines and a diastema in the lower jaw to accommodate them.

MATERIAL CULTURE AND TOOLS 3.3 MYA

Humans’ production and use of stone tools is one example of complex material culture. The tools of our closest living relatives, the chimpanzees, do not approach the complexity and diversity of modern and ancestral humans’ tools

DOMESTICATED FOODS 11,000 YEARS AGO

In recent evolution—within the last 10,000 years or so—humans domesticated a wide variety of plants and animals, controlling their life cycles and using them for food and other products, such as clothing and shelter.

Human Ape Diastema

Hyoid bone

F I G U R E

1.3 The Six Big Events of Human Evolution: Bipedalism, Nonhoning Chewing, Dependence on Material Culture, Speech, Hunting, and Domestication of Plants and Animals

BIPEDALISM 6 MYA

The upright, bipedal (two-footed) gait was the first hallmark feature of our hominin ancestors.

SPEECH 2.5 MYA

HUNTING 1 MYA

NONHONING CHEWING 5.5 MYA

Humans’ nonhoning chewing complex (below) lacks large, projecting canines in the upper jaw and a diastema, or gap, between the lower canine and the third premolar.

The chewing complex of apes such as gorillas (below) has large, projecting upper canines and a diastema in the lower jaw to accommodate them.

MATERIAL CULTURE AND TOOLS 3.3 MYA

DOMESTICATED FOODS 11,000 YEARS AGO

Human Ape Diastema

Hyoid bone

12 | CHAPTER 1 What Is Physical Anthropology?

the most profound physical difference between humans and other animals, namely the manner in which we get around: we are committed to bipedalism, that is, walking on two feet. The next development was the loss of a large, honing canine tooth, like the one that apes typically use to shred their food (mostly plants), to the simple nonhoning canine, with which we simply process food. Our ancestors’ honing canine disappeared because they developed the ability to make and use tools for processing food.

Today, our species completely depends on culture— and especially material culture— for its day- to- day living and its very survival. Culture is a complex human characteristic that facilitates our survival by enabling us to adapt to different settings. Material culture is the part of culture that is expressed as objects that humans use to manipulate environments. For example, hammers and nails are forms of material culture that enable us to make cabinets, tables, and countless other forms of material culture. The material remains of past cultures go back hundreds of thousands of years, to the first simple tools made from rocks 3.3 mya (Figure 1.4). Material culture today makes our lifestyles possible. Can you imag- ine your life without it? We could survive without modern additions to material culture, such as cars, computers, TVs, plumbing, and electricity, as our ancestors did before the last century. What about living without basic material culture, such as shelter and clothing, especially in climates where it can be very, very cold in the winter? Without material culture, how would any of us get food? The answer to both questions is simple: we could not make it without some forms of technology— to regulate temperature, to acquire food, and so on. Some societies are much less technologically complex than others, but no society functions with- out any technology.

Anthropologists and animal behaviorists have shown that human beings are not, however, the only type of animal that has or can employ material culture. Primatologists have observed some chimpanzee societies in Africa, for example, making simple tools from twigs (Figure 1.5). In laboratories, chimpanzees have been taught to use physical symbols that approximate human communication. Still, these and other forms of material culture used by nonhuman species are nowhere near as complex as those created by humans.

The other three key attributes of humanness— hunting, speech, and depen- dence on domesticated foods— appeared much later in human evolution than bipedalism, nonhoning chewing, and complex material culture and tool use. Hunting here refers to the social behavior whereby a group, adult men in general, organize themselves to pursue animals for food. This behavior likely dates back to a million or more years ago. Some nonhuman primates organize to pursue prey, but they do not use tools or travel long distances as humans distinctively do when they hunt.

An equally distinctive human behavior is speech. We are the only animal that communicates by talking. Unfortunately for research purposes, recording- and- listening technology was invented only about a century ago. For information about long- past speech, anthropologists rely on indirect evidence within the skeleton. For example, the hyoid bone, in the neck, is part of the vocal structure that helps produce words. The unique appearance of the human hyoid helps anthropologists conjecture about the origins of speech.

The most recently developed unique human behavior is the domesticated manner in which we acquire our food. About 10,000–11,000 years before the pres- ent (yBP), humans began to raise animals and grow plants. This development led

bipedalism Walking on two feet.

nonhoning canine An upper canine that, as part of a nonhoning chewing mechanism, is not sharpened against the lower third premolar.

material culture The part of culture that is expressed as objects that humans use to manipulate environments.

FIGURE 1.4 First Tools The earliest stone tools date to 3.3 mya and are associated with early human ancestors in East Africa. The example shown here is from Lomekwi, West Turkana, Kenya. This tool had various functions, including the processing of plants and meat for food.

What Makes Humans So Different from Other Animals?: The Six Steps to Humanness | 13

to our current reliance on domesticated species. This reliance has had a profound impact on human biology and behavior and represents a pivotal step in human evolution.

Human beings’ unique behaviors and survival mechanisms, and the anatomical features related to them, arose through the complex interaction of biology and culture. Indeed, our ancestors’ increasing dependence on culture for survival has made us entirely culture- dependent for survival. The behaviors that are unique to humans— speech, tool use, and dependence on culture— are also related to the fact that humans are very smart. Our remarkable intelligence is reflected in our abilities to think and interact in the ways we do (and take for granted), to communicate in complex ways, and to accomplish diverse tasks on a daily basis to survive. Our brains are bigger and have more complex analytical skills than do the brains of both other primates and animals in general. These biological advantages enable us to figure out complex problems, including how to survive in a wide range of environments.

The American anthropologist Robert Boyd and his colleagues argue that while humans are the smartest animals, in no way are we individually smart enough to acquire all the complex information necessary to survive in any particular envi- ronment. Today and through much of human evolution, our species has survived owing to our complex culture, including tool use and technology generally, prac- tices, and beliefs. For hundreds of thousands of years, humans have had a record of unique ways of learning from other humans. Retaining new knowledge, we pass this information to our offspring and other members of our societies, and this pro- cess extends over many generations. That is, social learning makes it possible for humans to accumulate an amazing amount of information over long time periods.

In the following chapters, you will be looking at these processes and behaviors— the particulars of physical anthropology— from a biocultural perspective. It is the unique and phenomenal interplay between biology, culture, and behavior that makes us human.

FIGURE 1.5 Tool- Making Once thought to be a uniquely human phenomenon, tool- making has been observed in chimpanzees, the closest biological relatives of humans. As seen here, chimpanzees have modified twigs to scoop termites from nests. Other chimpanzees have used two rocks as a hammer and anvil to crack open nuts. More recently, gorillas were seen using a stick to test the depth of a pool of water they wanted to cross. Tool use such as this likely preceded the first identified tools (see Figure 1.4).

social learning The capacity to learn from other humans, enabling the accu- mulation of knowledge across many generations.

14 | CHAPTER 1 What Is Physical Anthropology?

How We Know What We Know: The Scientific Method How do physical anthropologists make decisions about what their subject matter means? More specifically, how do we know what we know about human evolution and human variation? Like all other scientists, physical anthropologists carefully and systematically observe and ask questions about the natural world around them. These observations and questions form the basis for identifying problems and gath- ering evidence— data— that will help answer questions and solve problems— that is, fill gaps in scientific knowledge about how the natural world operates. These data are used to test hypotheses, possible explanations for the processes under study. Scientists observe and then reject or accept these hypotheses. This process of determining whether ideas are right or wrong is called the scientific method (Figure 1.6). It is the foundation of science.

Science (Latin scientia, meaning “knowledge”), then, is more than just knowl- edge of facts about the natural world. Science is also much more than technical details. Certainly, facts and technical details are important in developing answers to questions, but facts and technical skills are not science. Rather, science is a process that provides new discoveries that connect our lives with the world we live in— it is a way of knowing through observation of natural phenomena. This repeated acquisition results in an ever- expanding knowledge base, one built from measurable, repeatable, and highly tangible observations. In this way, science is empirical, or based on observation or experiment. After the systematic collection of observations, the scientist develops a theory— an explanation as to why a natural phenomenon takes place. For many nonscientists, a theory is simply a guess or a hunch; but for a scientist, a theory is not just some stab at an explanation. Rather, a theory is an explanation grounded in a great deal of evidence, or what a lawyer calls the “evidentiary record.” A scientist builds a case by identifying incontrovertible facts. To arrive at these facts, the scientist examines and reexamines the evidence, putting it through many tests.

The scientist thus employs observation, documentation, and testing to gener- ate hypotheses and, eventually, to construct a theory based on those hypotheses. Hypotheses explain observations, predict the results of future investigation, and can be refuted by new evidence.

data Evidence gathered to help answer questions, solve problems, and fill gaps in scientific knowledge.

hypotheses Testable statements that potentially explain specific phenomena observed in the natural world.

scientific method An empirical research method in which data are gathered from observations of phenomena, hypotheses are formulated and tested, and conclu- sions are drawn that validate or modify the original hypotheses.

empirical Verified through observation and experiment.

theory A set of hypotheses that have been rigorously tested and validated, leading to their establishment as a gen- erally accepted explanation of specific phenomena.

Observations

Hypothesis supported Hypothesis rejected

Hypothesis

Predictions (“If… then…”)

Test (observations, experiments)

Further tests

New or revised

hypothesis

FIGURE 1.6 The Scientific Method: How We Know What We Know

How We Know What We Know: The Scientific Method | 15

For example, the great English naturalist Charles Robert Darwin (1809–1882) (Figure 1.7) developed the hypothesis that the origin of human bipedalism was linked to the shift from life in the trees to life on the ground (Figure 1.8). Darwin’s hypothesis was based on his own observations of humans walking, other scientists’ then- limited observations of nonhuman primate behavior, and other scientists’ anatomical evidence, or information (about structural makeup) drawn from dis- sections, in this case of apes. Darwin’s hypothesis led to an additional hypothesis, based on evidence that accumulated over the following century and a half, that the first hominins arose in the open grasslands of Africa from some apelike animal that was formerly arboreal— that is, had once lived in trees.

Support for Darwin’s hypothesis about human origins— and in particular the origin of bipedal locomotion— began to erode in 2001, when a group of scientists discovered early hominins, from 5.2 to 5.8 mya, in the modern country of Ethiopia. Contrary to expectation and accepted wisdom, these hominins had lived not in grasslands but in woodlands. Moreover, unlike modern humans, whose fingers and toes are straight because we are fully terrestrial— we live on the ground—the early hominins had slightly curved fingers and toes. The physical shape and appearance, what physical anthropologists call morphology, of the hominins’ finger and toe bones indicate a lot of time spent in trees, holding on to branches, moving from limb to limb. These findings forced scientists to reject Darwin’s hypothesis, to toss out what had been a fundamental tenet of physical anthropology.

This story does not end, however, with the understanding that the earliest hominins lived in forests. Instead, this new hypothesis generated new questions. For example, why did the earliest hominins arise in a wooded setting, and why did they “come out of the woods” as time went on? Later in this book, we will consider these questions. For now, the point is that science is a self- correcting approach to knowledge acquisition. Scientists develop new hypotheses as new findings are made. Scientists use these hypotheses to build theories. And like the hypotheses that underlie them, theories can be modified or even replaced by better theories, depending on findings made through meticulous observation. As new observations are made and hypotheses and theories are subjected to the test of time, science revises its own errors.

A scientific law is a statement of irrefutable truth of some action or actions occurring in the natural world. Among the few scientific laws, the well- known ones are the laws of gravity, thermodynamics, and motion. But scientific truth seldom gets finalized into law. Rather, truth is continuously developed— new facts are discovered and new understandings about natural phenomena are made. Unlike theories, scientific laws do not address the larger questions as to why a natural action or actions take place.

FIGURE 1.7 Charles Darwin George Richmond painted this portrait of Darwin in 1840.

anatomical Pertaining to an organism’s physical structure.

arboreal Tree- dwelling, adapted to living in the trees.

terrestrial Life- forms, including humans, that live on land versus living in water or in trees.

morphology Physical shape and appearance.

scientific law A statement of fact describ- ing natural phenomena.

FIGURE 1.8 Bipedalism These 1887 photographs by Eadweard Muybridge capture humans’ habitual upright stance. Other animals, such as chimpanzees, occasionally walk on two feet; but humans alone make bipedalism their main form of locomotion. As Darwin observed, this stance frees the hands to hold objects. What are some other advantages of bipedalism?

As my crew and I traveled to St. Catherines Island, we were intent on discovering new facts and forming new understandings about the prehistoric farmers’ descen- dants who were first encountered by Spaniards in the late 1500s. These facts and understandings would enable us to test hypotheses about human evolution and human variation. Once we completed the months of arduous fieldwork and the years of laboratory investigations on the remains that fieldwork uncovered, we would have some answers. The scientific method would guide us in provid- ing insights into this part of the human lineage— human beings’ most recent evolution— and how our species came to be what it is in the early twenty- first century.

C H A P T E R 1 R E V I E W

A N S W E R I N G T H E B I G Q U E S T I O N S

What is anthropology? • Anthropology is the study of humankind. In two

major ways, it differs from other sciences that study humankind. First, anthropology views humans as both biological and cultural beings. Second, anthropology emphasizes a holistic, comparative approach, encompassing all people at all times and all places.

• The four branches of anthropology are cultural anthropology (study of living cultures), archaeology (study of past cultures), linguistic anthropology (study of language), and physical anthropology.

What is physical anthropology? • Physical (or biological) anthropology is the study

of human biology, specifically of the evolution and variation of humans (and their relatives, past and present).

• Physical anthropology is an eclectic field, deriving theory and method both from within the discipline and from other sciences that address important questions about human evolution and human variation.

What makes us human and different from other animals? • Humans living today are the product of millions of

years of evolutionary history and their own personal life histories.

• Humans have six unique physical and behavioral characteristics: bipedalism, nonhoning chewing, complex material culture and tool use, hunting, speech, and dependence on domesticated foods.

How do physical anthropologists know what they know? • Physical anthropologists derive knowledge via the

scientific method. This method involves observations, the development of questions, and the answering of those questions. Scientists formulate and test hypotheses that they hope will lead to theories about the natural world.

REVIEW THIS CHAPTER WITH PERSONALIZED, INTERACTIVE QUESTIONS THROUGH IJK, INQUIZITIVE.WWNORTON.COM q

http://inquizitive.wwnorton.com

K E Y T E R M S anatomical anthropology arboreal archaeology artifacts biocultural approach biological anthropology bipedalism cultural anthropology culture

data empirical forensic anthropology genome hominin hypotheses language linguistic anthropology material culture morphology

nonhoning canine physical anthropology primates scientific law scientific method social learning sociolinguistics terrestrial theory

E V O L U T I O N R E V I E W Physical Anthropology as Science

Synopsis Anthropology is a holistic discipline in that it views humankind from the perspectives of all people and all times. Anthropology is also an interdisciplinary science in that it both draws on and influences research in many related fields. Physi- cal anthropology is one of the four subfields (along with cultural anthropology, archaeology, and linguistic anthropology) that make up anthropology as both a biological and a social science. The two main concepts that define physical anthropology are human biological evo- lution and human biocultural variation. Through the employment of the scientific method, physical anthropologists study many different aspects of living humans, modern and extinct nonhuman primates, and fossil hominins, among other lines of research. Through all of these different ways of gathering knowledge about the human con- dition, physical anthropologists ultimately address research questions related to the two broad themes of evolution and variation.

Q1. Define the biocultural approach—a hallmark of physical anthropology.

Q2. Focusing on Figure 1.3, The Six Big Events of Human Evolution, identify which two of these events were caused primarily by biological changes in humans and which four were caused by changes in both human biology and human culture.

Q3. Over time, has culture had more or less of an effect on human evolution? Focusing on Figure 1.3, briefly explain your answer.

Q4 . As a species, humans are unique in the degree to which culture influences our evolution. Consider Figure 1.3 again. How might aspects of human culture have affected the evolution of other species, such as livestock or wild animals?

Q5. Many nonscientists often critique evolution as “just a theory.” What does it mean for evolution to be a theory in the context of the scientific method? How does the study of evolution illustrate the interdisciplinary nature of physical anthropology?

Hint What other scientific fields might contribute data that are used to test hypotheses related to biological evolution?

A D D I T I O N A L R E A D I N G S

Larsen, C. S., ed. 2010. A Companion to Biological Anthropology. Chichester, UK: Wiley- Blackwell.

Molnar, S. 2005. Human Variation: Races, Types, and Ethnic Groups. Upper Saddle River, NJ: Prentice Hall.

Moore, J. A. 1999. Science as a Way of Knowing: The Foundations of Modern Biology. Cambridge, MA: Harvard University Press.

Spencer, F., ed. 1997. History of Physical Anthropology: An Ency- clopedia. New York: Garland.

Stocking, G., ed. 1974. The Shaping of American Anthropology, 1883–1911: A Franz Boas Reader. New York: Basic Books.

Some Periodicals in Anthropology

Physical anthropology: American Journal of Human Biology, Amer- ican Journal of Physical Anthropology, American Journal of Prima- tology, Evolutionary Anthropology, Human Biology, International

Journal of Paleopathology, Journal of Human Evolution, Yearbook of Physical Anthropology.

Archaeology: American Antiquity, Antiquity, Archaeology, Journal of Archaeological Science, Latin American Antiquity, World Archaeology.

Cultural anthropology: American Anthropologist, Cultural Anthro pology.

General anthropology: American Anthropologist, Annual Review of Anthropology, Current Anthropology.

A D D I T I O N A L R E A D I N G S

The Present: Foundation for the Past

Some physical anthropologists learn about human evolution by studying living plants and animals, including humans. Other physical anthropologists learn about human evolution by investigating the past, now represented mostly by fossilized bones and fossilized teeth. Together, living and past enable us to understand evolution in the largest context. The fossil record provides us with the history of humans and of humanlike ancestors, while the living record provides the essential picture through which to view that history. Charles Darwin, the pioneering force behind our knowledge about evolution and natural selection, developed his ideas by studying living plants and animals. He had the extraordinary insight to realize that his

theories and hypotheses applied to past organisms. For Darwin, living organisms were key to interpreting the past because they displayed evidence of evolution’s elements and mechanics. In the same way, living organisms pro- vide insights— into fundamental forces such as reproduc- tion, DNA synthesis, protein synthesis, and behavior— that are not available, at least in the same way, within the past record. Part I of this book lays out observations and princi- ples based on the study of living populations, the essential background for understanding evolution. Part II then digs into the past, into the study of ancestors whose descen- dants are present in the world (all of us now living) and of those evolutionary lineages that did not survive.

The living primates— such as, here, orangutans and humans— have much in common, biological and behavioral. Their study provides essential context for understanding variation and evolution, now and in the past.

P A R T I

CHARLES DARWIN’S OBSERVATIONS provided the groundwork for his theory of natural selection, the basis of his 1859 book On the Origin of Species.

21 21

2 How did the theory of evolution come to be?

What was Darwin’s contribution to the theory of evolution?

What has happened since Darwin in the development of our understanding of evolution?

Evolution Constructing a Fundamental Scientific Theory

T he nineteenth century was the century of scientific collecting. During the 1800s, the world discovered itself through collections. Expeditions large and small— involving scientists, explorers, and adventurers— crossed the continents and investigated landmasses around the globe. These teams collected hundreds of thou- sands of samples: plants, animals, rocks, and preserved remains (or fossils— the sub- ject of chapter 8). If it seemed worth picking off the ground or exposing in some other fashion, it was fair game. This kind of work, on one of these international expeditions, helped lay the foundation for the most important biological theory, arguably among the half- dozen most important scientific theories— the theory of evolution.

In 1831, a 22- year- old Englishman and recent graduate of Cambridge University, Charles Darwin, was appointed the naturalist for a five- year voyage around the world on the ship HMS Beagle (Figure 2.1). Imagine that as your first job right out of col- lege! Young Mr. Darwin, who was trained in medicine and theology, accepted a difficult task. He was to collect, document, and study the natural world— plants and animals, especially— everywhere the ship harbored. By the end of that voyage, Darwin had amassed a wonderfully comprehensive collection of plants, insects, birds, shells, fossils, and lots of other materials. The specimens he collected and the observations he made about the things he saw on that trip would form the basis of his lifetime of research. His discoveries would do no less than shape the future of the biological sciences, including physical anthropology. His ideas would provide the key to understanding the origin and evolution of life itself.

Soon after returning home from the voyage, Darwin began to formulate questions about the origins of plants and animals living in the many lands he and his shipmates

B I G Q U E S T I O N S ?

fossils Physical remains of part or all of once- living organisms, mostly bones and teeth, that have become mineralized by the replacement of organic with inorganic materials.

22 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

had explored. His most prominent observations concerned the physical differences, or variation, between and among members of species, or like animals and like plants. He articulated the phenomenon best in his notes on finches that live in the Galápagos, a small cluster of islands 965 km (600 mi) off the coast of Ecuador. Not only did these birds differ from island to island, but even within a single island they seemed to vary according to habitat, or surroundings. For example, finches living on an island’s coast had a different beak shape from finches living in an island’s inte- rior (Figure 2.2). These observations raised two questions for Darwin: Why were the birds different from island to island and from habitat to habitat? How did differ- ent species of finches arise? After years of study, Darwin answered these questions with an idea called “descent with modification,” or the theory of evolution.

Darwin also came to realize that the variations in physical characteristics of the different species of finches and other organisms were adaptations— physical characteristics that enhance an organism’s ability to survive and reproduce. Dar- win recognized many other adaptations in the natural world, and he concluded that adaptation was the crux of evolution. To connect these processes, he coined the term natural selection. According to this principle, biological characteristics that enhance survival increase in frequency from generation to generation. Members of a population endowed with these characteristics produce more offspring that survive to reproductive age than members that are not endowed with these characteristics. Natural selection is thus the primary driver of evolution. Recognizing that the differ- ent species of finches all derived from a single common ancestor that had originated in South America, Darwin also postulated the process of adaptive radiation: out of one species branch multiple closely related species.

FIGURE 2.1 Darwin’s Voyage (a) Charles Darwin ca. 1855, about 25 years after he set out on HMS Beagle. (b) In this illustration, the ship is passing through the Strait of Magellan, during the South American stretch of (c) its worldwide journey, whose ports of call are here mapped.

(a)

(b)

Galápagos Islands

Western Islands Canary

Islands

Marquesas

Cape Horn

Strait of Magellan

Madagascar Bay of Islands

N O R T H A M E R I C A

B R I T I S H I S L E S

E U R O P E

A F R I C A

A U S T R A L I A

A S I A

S O U T H A M E R I C A

P A C I F I C O C E A N

K I N G G E O R G E ’ S S O U N D

AT L A N T I C O C E A N

Rio de Janeiro

Bahia

Falkland Islands

Montevideo Valparaiso

Hobart

SydneyCape of Good Hope

(c)

species A group of related organisms that can interbreed and produce fertile, viable offspring.

habitat The specific area of the natural environment in which an organism lives.

adaptations Changes in physical struc- ture, function, or behavior that allow an organism or species to survive and repro- duce in a given environment.

natural selection The process by which some organisms, with features that enable them to adapt to the environment, preferentially survive and reproduce, thereby increasing the frequency of those features in the population.

adaptive radiation The diversification of an ancestral group of organisms into new forms that are adapted to specific environmental niches.

The Theory of Evolution: The Context for Darwin | 23

Darwin regarded evolution as simply biological change from generation to gener- ation. Many evolutionary biologists today limit their definition of evolution to genetic change only. However, nongenetic developmental change— biological change occurring within an individual’s lifetime— can give an adaptive advantage (or disad- vantage) to an individual or individuals within a population. Moreover, genes control developmental processes, which likewise influence other genes.

In subsequent chapters, we will further explore these and other aspects of evolu- tion. Although the core of this book is human evolution or how human biology came to be, understanding human evolution requires understanding the term evolution as it applies to all living organisms. In this chapter, we will take a historical approach to the term and the theory behind it. After reading about its intellectual history before Darwin, Darwin’s contribution, and developments since Darwin, you should have a clear idea of what physical anthropologists and other evolutionary biologists mean by evolution.

The Theory of Evolution: The Context for Darwin Before Darwin’s time, Western scientists’ understanding of Earth and the organ- isms that inhabit it was strongly influenced by religious doctrine. In the Judeo- Christian view, the planet was relatively young, and both its surface and the life- forms on it had not changed since their miraculous creation. By the late 1700s, scientists had realized three key things about the world and its inhabitants: Earth is quite ancient, its surface is very different from what it was in the past, and plants

FIGURE 2.2 Darwin’s Finches Darwin studied the physical variation in finches living on different islands of the Galápagos. Among other attributes, he studied beak shape, which varied from island to island. Eventually, Darwin related each beak shape to diet, especially to the texture of food and how the food was acquired. Finches with larger beaks typically consumed harder foods, such as seeds and nuts, while finches with smaller beaks ate softer foods, such as berries. Darwin concluded that each finch species had adapted to the particular environment and food resources of its island.

24 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

and animals have changed over time. These realizations about the natural world provided the context for Darwin’s theory of evolution.

To generate his theory, Darwin drew on information from five scientific dis- ciplines: geology, paleontology, taxonomy and systematics, demography, and what is now called evolutionary biology. Geology is the study of Earth, especially with regard to its composition, activity, and history. This discipline has demonstrated the great age of our planet and the development of its landscape. Paleontology is the study of fossils. This discipline has detailed past life- forms, many now extinct. Taxonomy is the classification of past and living life- forms. This disci- pline laid the foundation for systematics, the study of biological relationships over time. Demography is the study of population, especially with regard to birth, survival, and death and the major factors that influence these three key parts of life. Evolutionary biology is the study of organisms and their changes. By investigating the fundamental principles by which evolution operates, Darwin founded this discipline. In the following sections, we will look at these fields in more detail.

GEOLOGY: RECONSTRUCTING EARTH’S DYNAMIC HISTORY We now know that our planet is 4.6 billion years old and that over time its surface has changed dramatically. If you had espoused these ideas in, say, the late 1600s, you would not have been believed, and you would have been condemned by the Church because you had contradicted the Bible. According to a literal interpre- tation of the Bible, Earth is a few thousand years old and its surface is static. The Scottish scientist James Hutton (1726–1797) became dissatisfied with the biblical interpretation of the planet’s history (Figure 2.3). He devoted his life to studying natural forces, such as wind and rain, and how they affected the landscape in Scotland. Hutton inferred from his observations that these forces changed Earth’s surface in the past just as they do in the present. Wind and rain created erosion, which provided the raw materials— sand, rock, and soil— for the formation of new land surfaces. Over time, these surfaces became stacked one on top of the other, forming layers, or strata, of geologic deposits (Figure 2.4). From the (very long) time it took for these strata to build up, he calculated Earth’s age in the millions of years. This was a revolutionary, indeed heretical, realization.

FIGURE 2.3 James Hutton Hutton (here depicted ca. 1790) founded modern geology with his theory of Earth’s formation. Hutton realized that the same natural processes he observed in Scotland had occurred in the past.

geology The study of Earth’s physical history.

paleontology The study of extinct life- forms through the analysis of fossils.

taxonomy The classification of organisms into a system that reflects degree of relatedness.

systematics The study and classification of living organisms to determine their evo- lutionary relationships with one another.

demography The study of a population’s features and vital statistics, including birth rate, death rate, population size, and population density.

evolutionary biology A specialty within the field of biology; the study of the process of change in organisms.

FIGURE 2.4 Geologic Strata The succession of strata from oldest at the bottom to youngest at the top (as here, in Utah’s Bryce Canyon) marks the formation of new land surfaces over time.

The Theory of Evolution: The Context for Darwin | 25

Hutton’s idea— that the natural processes operating today are the same as the natural processes that operated in the past— is called uniformitarianism. Few paid much attention to Hutton’s important contribution to our understanding of Earth’s history until the rediscovery of the idea by the Scottish geologist Charles Lyell (1797–1875; Figure 2.5). Lyell devoted considerable energy to thinking and writing about uniformitarianism and its implications for explaining the history of our planet. His calculations of how long it would have taken for all known strata to build up created a mountain of evidence, an undeniable record, that Earth was millions of years old. Hutton and Lyell, relying on empirical evidence and personal observation to develop their ideas and to test clear hypotheses about the natural world, had revised the timescale for the study of past life.

PALEONTOLOGY: RECONSTRUCTING THE HISTORY OF LIFE ON EARTH For hundreds of years, people have been finding the preserved— that is, fossilized— remains of organisms all over the world (see also the full discussion in chapter 8). To test his hypothesis that fossils are the remains of past life, the English scientist Robert Hooke (1635–1703) studied the microscopic structure of fossil wood. After observing that the tissue structure of the fossil wood was identical to the tissue structure of living trees, Hooke concluded that the fossil wood derived from once- living trees (Figure 2.6).

Fossils’ potential to illuminate the past was demonstrated by the French nat- uralist and zoologist Georges Cuvier (1769–1832). Cuvier devoted considerable effort to learning the anatomy, or structural makeup, of many kinds of animals (Figure 2.7). Pioneering what we now call paleontology and comparative anat- omy, he applied his extensive knowledge of comparative anatomy to fossils. By doing so, he reconstructed the physical characteristics of past animals— their appearance, physiology, and behavior. Although not very accurate by today’s standards, these efforts provided early tools for understanding past life- forms as once- living organisms. Through detailed reconstructions, Cuvier demonstrated

FIGURE 2.5 Charles Lyell Lyell (here depicted ca. 1845) rediscovered Hutton’s work and the idea of uniformitarianism. Lyell’s research, based on examinations of geologic strata, confirmed Hutton’s estimate of Earth’s very old age.

uniformitarianism The theory that pro- cesses that occurred in the geologic past are still at work today.

FIGURE 2.6 Robert Hooke (a) Hooke did pioneering biological research using a very simple microscope. He was the first to identify cells; in fact, he coined the term cell. (b) This illustration of cork wood cells appeared in Hooke’s Micrographia (1667), the first major book on microscopy. His examinations of cells like this enabled Hooke to determine that fossils represented past life- forms.(a) (b)

26 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

that fossils found in geologic strata in France were the remains of animals that had gone extinct at some point in the remote past. Cuvier’s work provided the first basic understanding of the history of life, from the earliest forms to recent ones.

Cuvier observed that each stratum seemed to contain a unique set of fos- sils. What happened to the animals represented by each set, each layer? Cuvier concluded that they must have gone extinct due to some powerful catastrophe, such as an earthquake or a volcanic eruption. He surmised that following each catastrophe, the region was vacant of all life and was subsequently repopulated by a different group of animals moving into it from elsewhere. This perspective is called catastrophism.

We now know that Earth’s history does not consist of sequential catastrophes and resulting extinctions. Past catastrophes, such as the extinction of the dinosaurs at around 65 mya, have profoundly affected the direction of evolution, but they were not the leading factor in evolution.

However, such events are rare and do not explain even the sequence of fossils Cuvier observed, mostly in the region called the Paris Basin. In addition to con- firming that fossils were the remains of life in the distant past, though, Cuvier revealed that the most recent geologic strata contain mostly mammals and earlier geologic strata contain mostly reptiles, including the dinosaurs.

TAXONOMY AND SYSTEMATICS: CLASSIFYING LIVING ORGANISMS AND IDENTIFYING THEIR BIOLOGICAL RELATIONSHIPS In the pre- Darwinian world, most scientists who studied life- forms realized the importance of developing a taxonomy— a classification of life- forms— for identifying biological relationships. Early efforts at taxonomy took a commonsense approach. Animals were placed within major groups such as dogs, cats, horses, cattle, and people. Plants were placed within major groups such as trees, shrubs, vines, and weeds.

(b)(a)

FIGURE 2.7 Georges Cuvier (a) One of Cuvier’s most important contributions to science was the concept of extinction. Here, Cuvier is depicted examining a fish fossil. (b) In his 1796 paper on fossil and living elephants, Cuvier suggested that mammoth remains— such as those shown here, from one of his many publications— represented a species different from any living elephant species and, therefore, were from a species that had gone extinct. This idea was revolutionary because the common perception was that God had created all species, none of which had ever gone extinct.

catastrophism The doctrine asserting that cataclysmic events (such as volcanoes, earthquakes, and floods), rather than evolutionary processes, are responsible for geologic changes throughout Earth’s history.

The Theory of Evolution: The Context for Darwin | 27

As late as the seventeenth century, scientists generally believed that species were immutable. In their view, life had changed very little, or not at all, since the time of the single Creation. Thus, early taxonomists were not motivated by an interest in evolution. Rather, they were motivated by their desire to present the fullest and most accurate picture of the Creator’s intentions for His newly created world. To construct the best possible taxonomy, the English naturalist John Ray (1627–1705) advocated personal observation, careful description, and consideration of plants’ and animals’ many attributes. Ray’s attention to detail laid the

Pre- Darwinian Theory and Ideas: Groundwork for Evolution

Charles Darwin first presented his theory of evolution in his book On the Origin of Species (1859). Based on years of personal observation and of study, this unifying biological theory drew on geology, paleontology, taxonomy and systematics, and demography.

Scientist Contribution (and year of publication) Significance

James Hutton Calculated Earth’s age as millions of years (1788)

Provided geologic evidence necessary for calculating time span of evolution

Charles Lyell Rediscovered and reinforced Hutton’s ideas (1830)

Provided more geologic evidence

Robert Hooke Proved that fossils are organisms’ remains (1665)

Revealed that fossils would provide the history of past life

Georges Cuvier

Extensively studied fossils (1796)

Revealed much variation in the fossil record

John Ray Pioneered taxonomy based on physical appearance (1660)

Created the first scientific classification of plants and animals

Carolus Linnaeus

Wrote Systems of Nature (1735)

Presented the binomial nomenclature taxonomy of plants and animals

Thomas Malthus

Founded demography: only some will find enough food to survive (1798)

Provided the concept of characteristics advantageous for survival

Jean- Baptiste de Lamarck

Posited characteristics acquired via inheritance (Lamarckism) (1809)

Provided first serious model of physical traits’ passing from parents to offspring

Erasmus Darwin

Also posited characteristics (determined by wants and needs) acquired via inheritance (1794)

Advanced the notion that physical changes occurred in the past

C O N C E P T C H E C K !

28 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

groundwork for later taxonomy, especially for the binomial nomenclature ( two- name) system developed by the Swedish naturalist Carl von Linné (1707–1778). Von Linné, better known by his Latinized name, Carolus Linnaeus, gave each plant and animal a higher- level genus (plural, genera) name and a lower- level species (plural is also species) name (Figure 2.8). A single genus could include one or more spe- cies. For example, when Linnaeus named human beings Homo sapiens— Homo being the genus, sapiens being the species— he thought there were species and subspecies of living humans (an idea discussed further in chapter 5). The presence of more than one level in his taxonomy acknowledged different degrees of physical simi- larity. Today, we recognize that sapiens is the one living species in the genus Homo.

Linnaeus presented the first version of his taxonomy in his book Systema Naturae (1735), or System of Nature. As he revised the taxonomy— his book would eventually go through 10 editions— he added more and more levels to the hierarchy. He clas- sified groups of genera into orders and groups of orders into classes. For example, he named the order “Primates,” the group of mammals that includes humans, apes, monkeys, and prosimians. Since the eighteenth century, this taxonomic system has evolved into multiple levels of classification, going from the subspecies at the bottom to the kingdom at the top (Figure 2.9).

Like Ray, Linnaeus was committed to the notion that life- forms were static, fixed at the time of the Creation. In later editions of his book, he hinted at the pos- sibility that some species may be related to each other because of common descent, but he never developed these ideas. His taxonomy is still used today, although viewed with a much stronger sense of present and past variation. The system’s flexibility aided evolutionary biologists in their study of biological diversity, and the focus on taxonomic relationships over time is now called systematics.

DEMOGRAPHY: INFLUENCES ON POPULATION SIZE AND COMPETITION FOR LIMITED RESOURCES After returning to England and while developing his ideas on natural selection, Darwin read the works of all the great scientists of the time. Probably the most important influence on his ideas was An Essay on the Principle of Population, by the English political economist Thomas Malthus (1766–1834). First published in 1798, Malthus’s book made the case that an abundance of food— enough to feed anyone born— would allow the human population to increase geometrically and indefinitely. In reality, the Essay argued, there simply is not enough food for every- one born, so population is limited by food supply (Figure 2.10). Who survives to reproductive age? Those who can successfully compete for food. Whose children thrive? Those of survivors who manage to feed their offspring. Applying Malthus’s demographic ideas to human and nonhuman animals, Darwin concluded that some members of any species successfully compete for food because they have some special attribute or attributes. That an individual characteristic could facilitate survival was a revelation!

EVOLUTIONARY BIOLOGY: EXPLAINING THE TRANSFORMATION OF EARLIER LIFE- FORMS INTO LATER LIFE- FORMS By the late 1700s, a handful of scientists had begun to argue that, contrary to religious doctrine, organisms are not fixed— they change over time, sometimes in dramatic ways. Simply, life evolved in the past and evolution is an ongoing,

genus A group of related species.

FIGURE 2.8 Carolus Linnaeus Linnaeus, a botanist, zoologist, and physician, is known for his contributions to the system of classification used today by all biological scientists, including physical anthropologists. He is also a founder of modern ecology.

FIGURE 2.10 Thomas Malthus Malthus, the founder of demography, theorized that population size was limited by food supply.

TAXONOMIC CATEGORY

Subfamily Homininae

Homo

sapiens

sapiens Modern humans alone.

Tribe Hominini

Genus

Species

Subspecies

TAXONOMIC LEVEL COMMON CHARACTERISTICS

Group of hominins including modern humans, their direct ancestors, and extinct relatives (e.g., Neandertals). They have the largest brains in the Hominini.

Modern and ancestral modern humans. They have culture, use language, and inhabit every continent except Antarctica.

Chimpanzees, humans, and humanlike ancestors

Family Hominidae Great apes, humans, and humanlike ancestors.

Superfamily Hominoidea Group of anthropoids, including humans, great apes, lesser apes, and humanlike ancestors. They have the largest bodies and brains of all primates.

Parvorder Catarrhini Group of anthropoids, including humans, apes, and Old World monkeys.

Infraorder Anthropoidea Group of haplorhines, including humans, apes, and monkeys.

Suborder

Order Primates

Haplorhini Group of primates, including monkeys, apes, humans, and tarsiers. They have in general long life cycles and are relatively large-bodied.

Group of mammals specialized for life in the trees, with large brains, stereoscopic vision, opposable thumbs, and grasping hands and feet.

Subclass Theria Group of mammals that produce live young without a shelled egg (including placental and marsupial mammals).

Class Mammalia Group of warm-blooded vertebrate animals that produce milk for their young in mammary glands. They have hair or fur and specialized teeth.

Superclass Tetrapoda Vertebrate animals with four feet or legs, including amphibians, birds, dinosaurs, and mammals.

Subphylum Vertebrata Animals with vertebral columns or backbones (including fish, amphibians, reptiles, birds, and mammals).

Phylum Chordata Group of vertebrate and invertebrate animals that have a notochord, which becomes the vertebral column in humans and other primates.

Subkingdom Eumetazoa All major animals (except sponges) that contain true tissue layers, organized as germ layers, which develop into organs in humans.

Kingdom Animalia Mobile multicellular organisms that consume other organims for food and develop during an embryo stage.

Commonly called “hominins,” this level includes humans and humanlike ancestors, all of which are obligate bipeds.

FIGURE 2.9 The Place of Humans in Linnaeus’s Taxonomy Linnaeus’s system organized living things into various levels of hierarchical classification. Kingdom, at the top of the taxonomy, is the largest classification. The five kingdoms of the natural world— animals, plants, fungi, protists, monera— include all living organisms. Through descending taxonomic levels, each group’s size gets progressively smaller. For example, there are fewer organisms in a genus than there are in a phylum. Additionally, these classifications reflect organisms’ relationships to one another. For example, organisms within a genus are more closely related than are those from different genera.

30 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

undirected process. Building on this concept, the French naturalist Jean- Baptiste de Monet (1744–1829), better known by his title, Chevalier de Lamarck, speculated that plants and animals not only change in form over time but do so for purposes of self- improvement. Lamarck believed that in response to new demands or needs, life- forms develop new anatomical modifications, such as new organs. His central idea— that when life- forms reproduce, they pass on to their offspring the modifications they have acquired to that point— is called Lamarckian inheritance of acquired characteristics, or Lamarckism (Figure 2.11). We now know Lamarck’s mechanism for evolution to be wrong— offspring do not inherit traits acquired by their parents— but his work was the first major attempt to develop a theory built on the premise that living organisms arose from precursor species. Lamarck was also convinced that humans evolved from some apelike animal.

Among the other scholars who believed that life had changed over time was the English physician, naturalist, and poet Erasmus Darwin (1731–1802), grandfather of Charles Darwin. Like Lamarck, he hypothesized about the inheritance of char- acteristics acquired thanks to wants and needs; but he, too, was wrong about the mechanism for change.

Lamarckism First proposed by Lamarck, the theory of evolution through the inheritance of acquired characteristics in which an organism can pass on features acquired during its lifetime.

Darwin Borrows from Malthus

Five of Malthus’s observations inspired Darwin’s principle of natural selection.

Observation 1 For most organisms, every pair of parents produces multiple (sometimes many) offspring.

Observation 2 For most organisms, the population size remains the same. No increase occurs over time.

Observation 3 Population is limited by the food supply.

Observation 4 Members of populations compete for access to food.

Observation 5 No two members of a species are alike in their physical attributes— variation exists.

Theory: Evolution by Means of Natural Selection Individuals having variation that is advantageous for survival to reproductive age produce more offspring (and more offspring that survive) than individuals lacking this variation.

C O N C E P T C H E C K !

The Theory of Evolution: Darwin’s Contribution | 31

The Theory of Evolution: Darwin’s Contribution Darwin’s remarkable attention to detail enabled him to connect his voluminous reading with his personal observations from the Beagle voyage. For example, while in Chile, Darwin had observed firsthand the power of earthquakes in shaping the

(a)

Original short-necked ancestor.

Descendants keep stretching to reach leaves higher up on tree …

… and stretching until neck becomes progressively longer in descendants.

… and stretching …

(b)

FIGURE 2.11 Jean- Baptiste Lamarck (a) Lamarck developed an early theory of evolution involving the inheritance of acquired characteristics. Although his mechanism of evolution was wrong, Lamarck’s recognition of the dynamic nature of life in the past made an important contribution to the development of evolutionary theory. (b) According to the classic (though incorrect) example of Lamarckism, giraffes stretched to reach food at the tops of trees, their necks grew as a result, and they passed on these long necks to their offspring.

32 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

landscape. Hutton’s and Lyell’s uniformitarianism led him to recognize that the accumulation of such catastrophes over a long period of time explains, at least in part, the appearance of the present- day landscape. This understanding of Earth’s remarkably dynamic geologic history laid the groundwork for Darwin’s view of evolution as a long, gradual process.

That process, he saw, could be reconstructed through the fossil record. He had read carefully Cuvier’s studies of fossils, and in South America he saw fossils first- hand. Some of these fossils resembled living animals native to South America, such as the armadillo, ground sloth, and llama. This evidence strongly suggested that an earlier species had transformed into the modern species, most likely through a succession of species over time. Drawing on Malthus’s ideas about reproduction, population, and variation, Darwin wrote, “it at once struck me that under these circumstances [i.e., specific environmental conditions] favorable variations would

(a)

(b)

FIGURE 2.12 Writing a Masterpiece (a) Darwin wrote most of On the Origin of Species at his beloved home, Down House, in Kent, England. (b) He generally worked in his study there.

Since Darwin: Mechanisms of Inheritance, the Evolutionary Synthesis, and the Discovery of DNA | 33

tend to be preserved and unfavorable ones to be destroyed. The result of this would be the formation of new species.” Another revelation.

Darwin hypothesized that surviving offspring had attributes advantageous for acquiring food. Because these offspring survived, the frequency of their advanta- geous characteristics increased over time. Meanwhile, as environmental conditions changed— such as when rainfall decreased— offspring lacking adaptive attributes suited to their survival in the new environment died off. Building on these obser- vations and their implications, Darwin deduced that natural selection was the primary mechanism of evolution. Over a long period of time, through generations’ adaptation to different environments and different foods, a common ancestor gave rise to related species. Darwin’s hypothesis was revolutionary, undermining the mid- nineteenth- century consensus that species were fixed types in a defined natural order of life. Now, species would have to be considered as populations with no predetermined limit on variation.

Darwin’s background research had begun in the 1830s. It was not until 1856, however— fully two decades after his voyage around the world— that Darwin had gathered enough evidence and developed his ideas enough to begin writing his great work about evolution by means of natural selection, On the Origin of Species (Figure 2.12). His colleagues had warned him that if he did not write his book soon, someone else might receive credit for the idea. Indeed, in 1858, Darwin received from the English naturalist and explorer Alfred Russel Wallace (1823–1913) a letter and a 20-page report outlining Wallace’s theory of evolution by means of natural selection (Figure 2.13). Independently from Darwin, Wallace had arrived at most of the same conclusions that Darwin had. Both men had been aware of their shared interest in the subject, and both men formulated their theories independently. Concerned that Wallace would publish first, Darwin completed Origin over the next 15 months and published it in London in 1859. Who, then, “discovered” natu- ral selection, the key mechanism that explains evolution? Some argue that Wallace should be given primary credit for the theory. However, because Wallace had not amassed the extensive body of evidence needed to support the theory, Darwin is generally recognized as the discoverer.

Darwin and Wallace made monumental discoveries, but neither man could come up with a compelling explanation of the physical mechanisms by which evolution takes place. That is, what mechanisms result in evolutionary change? Half a continent away, a series of novel experiments led to the discovery of these biological mechanisms, paving the way for remarkable new insights into evolution.

Since Darwin: Mechanisms of Inheritance, the Evolutionary Synthesis, and the Discovery of DNA MECHANISMS OF INHERITANCE Having articulated and supported his theory of evolution by means of natural selection, Darwin turned to the next fundamental question about natural selec- tion: How do the traits that are being selected for (or against) pass from parent to offspring? Like other scientists of his day, Darwin believed that each body part contained invisible particles called gemmules. Darwin hypothesized that

FIGURE 2.13 Alfred Russel Wallace Although Darwin often gets sole credit for the development of the theory of evolution through natural selection, Wallace (here depicted ca. 1860) contributed substantially to evolutionary theory. Wallace was the leading authority on the geographic distribution of animals, for example, and was the first to recognize the concept of warning coloration in animals. In addition, he raised the issue of human impact on the environment a full century before it became a concern for the general public.

gemmules As proposed by Darwin, the units of inheritance, supposedly accu- mulated in the gametes so they could be passed on to offspring.

34 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

representative gemmules for all body parts resided in the reproductive organs. During fertilization, each parent contributed his or her gemmules to the poten- tial offspring. The father’s and the mother’s gemmules then intermingled to form the characteristics observed in their progeny. Called blending inheritance, this process was a popular notion at the time.

Unknown to Darwin, research elsewhere in Europe was calling into question the idea of blending inheritance. In 1865, just six years after the publication of On the Origin of Species, Gregor Mendel (1822–1884), an Augustinian monk living in a mon- astery in what is now Brno, Czech Republic, published in an obscure local scientific journal the results of his work on inheritance (Figure 2.14). Mendel had spent the previous eight years crossbreeding different varieties of garden pea plants. Over the course of his experiments, he grew some 28,000 plants. These plants enabled him to identify and carefully observe seven characteristics, or traits, that were especially informative about breeding and its outcome over generations (Figure 2.15). From his results, Mendel inferred that a discrete physical unit was responsible for each characteristic. This unit passed from parent to offspring, and in this way the charac- teristic was inherited. In fact, the discrete unit could be traced through generations, and its passage (the inheritance) was determined by mathematical laws.

Mendel also discovered that the garden peas’ traits did not blend. For example, plants and their offspring were either tall or short. Over time, the short plants diminished in frequency and eventually disappeared. Later scientists determined that the physical unit of inheritance— now known as a gene— has two subunits, one from the father and one from the mother, each called an allele. Each allele is either dominant or recessive. In garden peas, the allele for tallness is dominant and the allele for shortness is recessive. If one parent provides a “tall” allele (T ) and the other parent provides a “short” allele (t), then the offspring having one of each allele (Tt) would be tall because of the presence of the “tall” allele— the dominant allele is physically expressed, whereas the recessive allele is hidden. The pure strain for tall (TT ) includes one tall maternal allele (T ) and one tall paternal allele (T ). The pure strain for short (tt) includes one short maternal allele (t) and one short paternal allele (t) (Figure 2.16).

FIGURE 2.14 Gregor Mendel Mendel, the father of modern genetics, was a Christian monk by profession but a scientist by nature. His observations provided the foundation for our understanding of genetics (the subject of chapters 3 and 4).

FIGURE 2.15 Mendel’s Peas (a) This illustration— from the 1876 catalog of one of Mendel’s seed suppliers— shows some of (b) the seven characteristics Mendel studied, each of which had two variants. Flower position, for example, could be axial or terminal, while flower color could be white or purple.

Flower Position Flower Color Plant Height Pea Shape Pea Color Pod Shape Pod Color

Axial White Tall Round Yellow In ated Yellow

Terminal Purple Short Wrinkled Green Constricted Green

(a) (b)

Parent 1 (TT ): Tall

Generation 1

Parent 2 (tt): Short

100% Tt = Tall

25% TT = Tall 50% Tt = Tall 25% tt = Short

3:1 Tall:Short

Tt Tt

Parent 1 (Tt): Tall

Generation 2

Parent 2 (Tt): Tall

t Tt tt

TT Tt

If the tallness allele is expressed as T and the shortness allele is expressed as t, the pure strain for tall is TT (one T is the maternal allele, the other T is the paternal allele), and the pure strain for short is tt (one t is the maternal allele, and the other t is the paternal allele).

When a TT plant is crossbred with a tt plant, one allele must come from the father (paternal) and one allele (maternal) must come from the mother, thereby producing a Tt offspring.

When the offspring from the TT and tt parental plants are bred, the offspring’s alleles independently redistribute, producing about equal numbers of the four possible combinations of T and t alleles: TT, Tt, tT, and tt.

Thus, three of the four plants (75%) will be tall owing to the dominance of the T allele and one plant (25%) will be short owing to the recessiveness of the t allele. Note, however, that 25% of the offspring are tall with two dominant tall alleles (TT ), while 50% are tall with one of each allele (Tt).

Because T is dominant, the offspring is tall.

FIGURE 2.16 Mendel’s Genetics

blending inheritance An outdated, dis- reputed theory that the phenotype of an offspring was a uniform blend of the parents’ phenotypes.

gene The basic unit of inheritance; a sequence of DNA on a chromosome, coded to produce a specific protein.

allele One or more alternative forms of a gene.

dominant Refers to an allele that is expressed in an organism’s phenotype and that simultaneously masks the effects of another allele, if another one is present.

recessive An allele that is expressed in an organism’s phenotype if two copies are present but is masked if the dominant allele is present.

Since Darwin: Mechanisms of Inheritance, the Evolutionary Synthesis, and the Discovery of DNA | 35

Flower Position Flower Color Plant Height Pea Shape Pea Color Pod Shape Pod Color

Axial White Tall Round Yellow In ated Yellow

Terminal Purple Short Wrinkled Green Constricted Green

(a) (b)

Parent 1 (TT ): Tall

Generation 1

Parent 2 (tt): Short

100% Tt = Tall

25% TT = Tall 50% Tt = Tall 25% tt = Short

3:1 Tall:Short

Tt Tt

Parent 1 (Tt): Tall

Generation 2

Parent 2 (Tt): Tall

t Tt tt

TT Tt

When a TT plant is crossbred with a tt plant, one allele must come from the father (paternal) and one allele (maternal) must come from the mother, thereby producing a Tt offspring.

Because T is dominant, the offspring is tall.

FIGURE 2.16 Mendel’s Genetics

blending inheritance An outdated, dis- reputed theory that the phenotype of an offspring was a uniform blend of the parents’ phenotypes.

gene The basic unit of inheritance; a sequence of DNA on a chromosome, coded to produce a specific protein.

allele One or more alternative forms of a gene.

dominant Refers to an allele that is expressed in an organism’s phenotype and that simultaneously masks the effects of another allele, if another one is present.

recessive An allele that is expressed in an organism’s phenotype if two copies are present but is masked if the dominant allele is present.

36 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

While Darwin’s theory generated immediate excitement in the scientific com- munity and among the public and was supported by leading scientists of the time such as Thomas Henry Huxley (Figure 2.17), Mendel’s crucial discovery (now known as Mendelian inheritance) went unnoticed. His writing was not widely distributed, and his work was simply ahead of its time. But in 1900, three scientists working independently— the German botanist Carl Erich Correns (1864–1933), the Austrian botanist Erich Tschermak von Seysenegg (1871–1962), and the Dutch botanist Hugo de Vries (1848–1935)—discovered Mendel’s research and replicated his findings. The Danish botanist Wilhelm Ludvig Johannsen (1857–1927) called the pair of alleles (e.g., TT, Tt, tt) the genotype and the actual physical appearance (tall, short) the phenotype.

Mendel’s theory of inheritance forms the basis of the modern discipline of genetics (the subject of chapters 3 and 4). It makes clear that the physical units— the genes and the two component alleles of each gene— responsible for physical attributes are located in the reproductive cells, eggs and sperm. When microscope technology improved in the late nineteenth century, the cell structure and the units of inheritance were defined (see chapter 3).

Beginning in 1908, the American geneticist Thomas Hunt Morgan (1866–1945) and his associates bred the common fruit fly in experiments that built on Mendel’s pea breeding. All genes, they discovered, are transmitted from parents to offspring in the ratios identified by Mendel. The genes are on chromosomes, and both the hereditary material and its carriers are duplicated during reproductive cell division.

THE EVOLUTIONARY SYNTHESIS, THE STUDY OF POPULATIONS, AND THE CAUSES OF EVOLUTION The combination of Darwin’s theory of evolution and Mendel’s theory of heredity resulted in an evolutionary synthesis. Darwin’s theory provided the mechanism for evolution (natural selection), and Mendel’s theory showed how traits are passed on systematically and predictably (Mendelian inheritance). The melding of natural selection and Mendelian inheritance led biologists to ask further questions about evolution, specifically about the origins of particular genes, genetic variation in general, and change in physical characteristics over time. Why do some genes increase in frequency, some decrease in frequency, and some show no change? How do completely new genes appear? These questions and a focus on population— viewed as the gene pool— provided the basis for a newly emerging field in evolution- ary biology called population genetics (among the subjects of chapter 4).

Natural selection, the guiding force of evolution, could operate only on variation that already existed in a population. How did new variation— new characteristics— arise in a population? Through his experiments with fruit flies, Morgan showed that a new gene could appear as a result of spontaneous change in an existing gene. This kind of genetic change is called mutation (Figure 2.18). The only source of new genetic material, mutation is another cause of evolution.

Gene flow, a third cause of evolution, is the diffusion, or spread, of new genetic material from one population to another of the same species. In other words, via reproduction, genes from one gene pool are transferred to another gene pool. Take, for example, the gene that causes sickle- cell anemia (this disorder is discussed extensively in chapter 4). Among West African blacks, it has a frequency of about 10%. Among American whites, it has a frequency of 0%. Because West African blacks and their descendants have long reproduced with American whites, the

FIGURE 2.17 Thomas Henry Huxley Huxley (1825–1895), an English biologist, was known as “Darwin’s bulldog” because he so forcefully promoted Darwin’s theory of evolution by natural selection. Among Huxley’s contributions to evolutionary theory was the concept that humans evolved from an apelike animal.

Mendelian inheritance The basic principles associated with the transmission of genetic material, forming the basis of genetics, including the law of segregation and the law of independent assortment.

genotype The genetic makeup of an organism; the combination of alleles for a given gene.

phenotype The physical expression of the genotype; it may be influenced by the environment.

chromosomes The strand of DNA found in the nucleus of eukaryotes that contains hundreds or thousands of genes.

evolutionary synthesis A unified theory of evolution that combines genetics with natural selection.

population genetics A specialty within the field of genetics; it focuses on the changes in gene frequencies and the effects of those changes on adaptation and evolution.

frequency among people descended from both West African blacks and American whites of the gene that causes sickle- cell anemia is approximately 5%, halfway between that of the two original populations. Over time, as the two populations have mixed, gene flow has decreased genetic difference.

Genetic drift, the fourth cause of evolution, is random change in the frequency of alleles— that is, of the different forms of a gene. Such change affects a small population more powerfully than it affects a large population (Figure 2.19). Over time, it increases the genetic difference between two genetically related but not interbreeding populations.

By the mid- twentieth century, the four causes of evolution— natural selection, mutation, gene flow, and genetic drift— were well defined, thanks to a synthesis of ideas drawn from the full range of sciences that deal with biological variation. In effect, evolutionary synthesis unified the branches of biology and its affiliated sci- ences, including genetics, taxonomy, morphology, comparative anatomy, paleontol- ogy, and the subject of this book, physical anthropology. Similarly, evolution unites living and past worlds. All organisms are related through common descent, and organisms more closely related than others share a more recent common ancestor.

DNA: DISCOVERY OF THE MOLECULAR BASIS OF EVOLUTION Once chromosomes were recognized as the carriers of genes, scientists sought to understand the structure of deoxyribonucleic acid (DNA), the chemical that makes up chromosomes. In 1953, the American geneticist James Watson (b. 1928) and the British biophysicist Francis Crick (1916–2004) published their discovery that DNA molecules have a ladderlike, double- helix structure. Crucial to their discovery was the work of the British X- ray crystallographer Rosalind Franklin (1920–1958), who used a special technique, X- ray diffraction, to produce high- quality images of DNA. The combined efforts of Franklin, Watson, and Crick opened up a whole new vista for biology by helping explain how chromosomes are replicated.

Analysis of the DNA from a wide variety of organisms, including primates, has provided both new perspectives on biological relationships and a molecular “clock” with which to time the branches of evolution (based on the similarity of species within those branches). In addition, DNA analysis has begun to shed light on a growing list of illnesses such as viral and bacterial infections, cancer, heart disease, and stroke.

mutation A random change in a gene or chromosome, creating a new trait that may be advantageous, deleterious, or neutral in its effects on the organism.

gene flow Admixture, or the exchange of alleles between two populations.

genetic drift The random change in allele frequency from one generation to the next, with greater effect in small populations.

deoxyribonucleic acid (DNA) A double- stranded molecule that provides the genetic code for an organism, consisting of phosphate, deoxyribose sugar, and four types of nitrogen bases.

(a) (b)

FIGURE 2.18 Fruit Fly Mutations (a) The normal fruit fly has two wings, while (b) the four- wing mutation has two wings on each side.

Since Darwin: Mechanisms of Inheritance, the Evolutionary Synthesis, and the Discovery of DNA | 37

38 | CHAPTER 2 Evolution: Constructing a Fundamental Scientific Theory

Little did Darwin realize just what a powerful foundation his evolutionary theory would build for science, ushering in modern biology and its allied disciplines, including physical anthropology. Long after his death, Darwin’s search for the biological mechanisms involved in evolution would continue to inspire scientists. The questions Darwin and his colleagues asked, especially about how physical attributes pass from parents to offspring, laid the foundation for the study of inheritance— the science of genetics— and eventually the DNA revolution. Darwin would have been impressed.

One month later

One red fish lost from each population

1:5 8:16

A B A B

0:5 7:16

16.6% Red 33.3% Red 0% Red 32.8% Red

Two populations of fish include red and gold varieties.

In the smaller population (6 fish), the ratio of red to gold is 1:5. Red fish represent 16.6% of the total.

In the smaller population (now 5 fish), the ratio of red to gold changes to 0:5. Red fish represent 0% of the total, a substantial change in the makeup of the population.

In the larger population (24 fish), the ratio of red fish to gold fish is 8:16 or 1:2. Red fish represent 33.3% of the total.

Over time, each population loses one red fish.

In the larger population (now 23 fish), the ratio of red to gold changes to 7:16. Red fish represent 32.8% of the total, a very small change in the makeup of the population.

FIGURE 2.19 Genetic Drift’s Effects on Small and Large Populations

A N S W E R I N G T H E B I G Q U E S T I O N S

C H A P T E R 2 R E V I E W

How did the theory of evolution come to be? • In developing his theory of evolution by means

of natural selection, Darwin drew on geology, paleontology, taxonomy and systematics, demography, and what is now called evolutionary biology.

• Scientists working in these disciplines had shown that — Earth is quite old and has changed considerably

over its history — fossils represent the remains of once- living, often

extinct organisms and thus provide a record of the history of life on the planet

— life evolves over time — groups of related species provide insight into

evolutionary history — the number of adults in a population tends to

remain the same over time

What was Darwin’s contribution to the theory of evolution? • Darwin’s key contribution was the principle of natural

selection. Three observations and inferences allowed him to deduce that natural selection is the primary driver of evolution: — the number of adults in a population tends to

remain the same over time even though, for most

organisms, parents tend to produce multiple and sometimes many offspring

— variation exists among members of populations — individuals having variation that is advantageous

for survival and reproduction increase in relative frequency over time

What has happened since Darwin in the development of our understanding of evolution? • Gregor Mendel discovered the principles of

inheritance, the basis for our understanding of how physical attributes are passed from parents to offspring.

• Mendel’s revelation that attributes are passed as discrete units, which we now know as genes, laid the groundwork for our understanding of cell biology, our understanding of chromosomes, and eventually the field of population genetics.

• We now know that evolution— genetic change in a population or species— is caused by one or a combination of four forces: natural selection, mutation, gene flow, and genetic drift.

• We now know that each chromosome in an organism’s cells consists of DNA molecules. DNA is the blueprint for all biological characteristics and functions.

REVIEW THIS CHAPTER WITH PERSONALIZED, INTERACTIVE QUESTIONS THROUGH IJK, INQUIZITIVE.WWNORTON.COM q

K E Y T E R M S adaptations adaptive radiation allele

blending inheritance catastrophism chromosomes

demography deoxyribonucleic acid (DNA) dominant

http://inquizitive.wwnorton.com

K E Y T E R M S

evolutionary biology evolutionary synthesis fossils gemmules gene gene flow genetic drift genotype

genus geology habitat Lamarckism Mendelian inheritance mutation natural selection paleontology

phenotype population genetics recessive species systematics taxonomy uniformitarianism

E V O L U T I O N R E V I E W Past, Present, and Future of a Fundamental Scientific Theory

Synopsis The theory of evolution forms the foundation of all the biological sciences, including physical anthropology. Although Charles Darwin is the most famous contributor to the formulation of this theory, his innovative idea of natural selection was partly influenced by the work of scientists across a number of disciplines, including geology, paleontology, taxonomy, and demography. The work of Gregor Mendel, rediscovered years after his death, provided a genetic basis for the evolutionary processes envisioned by Darwin and showed how evolution can occur in the natural world. Darwin’s principle of natural selection and Mendel’s principles of inheritance are intertwined in the modern evolutionary synthesis, the frame- work by which physical anthropologists address research questions related to human biological evolution and biocultural variation.

Q1. Charles Darwin is one of the most admired scientists of all time, and his principle of natural selection laid the foundations for all future biological thinking and discoveries. However, other scientists before Darwin argued in favor of biological evolution. Who is credited with one of the first major attempts at explaining the process of evolutionary change through time? What is the name of the erroneous mechanism hypothesized by this scientist to be a driving force of evolution?

Q2. Before the discoveries of Gregor Mendel, Darwin hypothesized that the characteristics of the father and mother intermingled

in the offspring. What was this idea called at the time? What discovery, first made by Mendel and later by scientists such as Thomas Hunt Morgan, proved this hypothesis to be wrong?

Q3. In formulating his principle of natural selection, Darwin was inspired by the idea of the demographer Thomas Malthus that population is limited by food supply. How is this idea a concern for human populations today? What steps might be taken to address this issue in the future?

Q4 . Darwin originally did not publish his theory of evolution by means of natural selection as he was well aware of the con- troversy it would generate. Over 150 years later, and backed by massive amounts of evidence spanning many scientific disciplines, evolution remains a subject of controversy among the general public. Why has evolution always been the subject of fierce debate?

Q5. Darwin gathered information from the fields of geology, paleontology, taxonomy, demography, and what is now called evolutionary biology to develop his theory of evolution, which includes the idea of variation and natural selection. What are the five most important ideas from these other fields (described in this chapter) that contributed to Darwin’s devel- opment of his theory of evolution?

A D D I T I O N A L R E A D I N G S

Alvarez, W. 1997. T. rex and the Crater of Doom. Princeton: Prince- ton University Press.

Berra, T. M. 2009. Charles Darwin: The Concise Story of an Extraor- dinary Man. Baltimore: Johns Hopkins University Press.

Bowler, P. J. 2003. Evolution: The History of an Idea. Berkeley: University of California Press.

Carroll, S. B. 2009. Remarkable Creatures: Epic Adventures in the Search for the Origins of Species. Boston: Houghton Mifflin Harcourt.

Gould, S. J. 1992. Ever since Darwin: Reflections on Natural History. New York: Norton.

Huxley, R. 2007. The Great Naturalists. New York: Thames & Hudson.

Repcheck, J. 2003. The Man Who Found Time: James Hutton and the Discovery of the Earth’s Antiquity. Cambridge, MA: Perseus Publishing.

Ridley, M. 2004. Evolution. Malden, MA: Blackwell Science.

Stott, R. 2012. Darwin’s Ghosts: The Secret History of Evolution. New York: Spiegel & Grau.

Wilson, E. O. 2006. From So Simple a Beginning: Darwin’s Four Great Books [Voyage of the H.M.S. Beagle, The Origin of Species, The Descent of Man, The Expression of Emotions in Man and Ani- mals]. New York: Norton.

ON THE SURFACE, A HUMAN BEING and a chimpanzee might not seem to have much in common. However, they share 98% of their DNA. Chimpanzees are humans’ closest living relatives, and both primates often have similar facial expres- sions, emotions, and body movements. In these and many other ways, these two primates share a considerable amount of biology.

43 43

3 What is the genetic code?

What does the genetic code (DNA) do?

What is the genetic basis for human variation?

Genetics Reproducing Life and Producing Variation

There is a revolution going on in science: the discovery of DNA and the identifi-cation of its molecular structure have brought about a “DNA Revolution.” At no time in history have humans learned so much so quickly about the biology of plants and animals. In addition to bringing about developments in agriculture and food production, medicine, and other areas that affect billions of people every day, the infor- mation derived from DNA has transformed a number of scientific disciplines. Consider forensic science, where fingerprints and blood types were once the primary evidence. Thanks to DNA, far smaller samples— of tissue, bone, hair, and blood— can be used to identify victims’ remains and to identify criminals with far greater accuracy. DNA in samples saved from old crime scenes has helped free scores of individuals con- victed of crimes they had not committed. Beyond forensics, DNA analysis has helped determine family relationships. It has helped genealogists reach into the past to chart ancestry. It has even been used to detect the presence of diseases, such as leprosy and syphilis, in ancient skeletons. Given the long and growing list of ways in which DNA can be used, no wonder former US president Bill Clinton referred to the human DNA sequence, right after it was presented to the public in 2003, as “the most important, most wondrous map ever produced by mankind.”

When I studied introductory biology in college, in the early 1970s, knowledge of DNA was just a tiny fraction of what it is today. Evolution was understood in terms of entire organisms and their biological history. Now, DNA provides us with the information— a whole new window— whereby we can see how organisms are put together and what is actually evolving. Powerful stuff! In anthropology, it has meant new insights into

B I G Q U E S T I O N S ?

44 | CHAPTER 3 Genetics: Reproducing Life and Producing Variation

primate and human evolution. Before we can tie together the growing strands of DNA and evolution, though, we need to back up and examine the foundational work in genetics— the study of heredity.

Although the great nineteenth- century biologists discussed in chapter 2 knew a lot about variation in species, they did not fully understand how this variation is produced or how it is transmitted from parents to offspring. For example, how do an organism’s attributes grow from a fertilized egg? The answers to questions about variation— its ori- gin and continuation— lie in the cell, its structures, and the myriad functions it performs from conception through full maturity. And governing each cell is the genetic code.

The Cell: Its Role in Reproducing Life and Producing Variation The cell is the basic unit of life for all organisms (Figure 3.1). Every organism has at least one cell (that is the baseline definition of an organism). Organisms having cells with no internal compartments are called prokaryotes. These were likely the first life on Earth, appearing about 3.5 billion years ago (bya). Today, the prokaryotes are single- cell bacteria. Organisms with internal compartments sepa- rated by membranes are called eukaryotes. The membranes enclose the two main

prokaryotes Single- celled organisms with no nuclear membranes or organelles and with their genetic material as a single strand in the cytoplasm.

eukaryotes Multicelled organisms that have a membrane- bound nucleus con- taining both the genetic material and specialized organelles.

The nucleus is the largest organelle in a cell. It houses one copy of nearly all the genetic material, or DNA, of that organism. It is covered by a nuclear membrane, or nuclear envelope, which keeps the contents of the nucleus separate from the rest of the cell. The cell membrane is a semipermeable

membrane surrounding the entire cell, separating one cell from the next.

The mitochondrion is considered the “powerhouse” of the cell, because it generates most of the energy. The number of mitochondria per cell varies by tissue type and by organism.

The endoplasmic reticulum is an organelle that usually surrounds the nucleus. It plays an especially important role in protein synthesis (a process discussed later in this chapter).

The cytoplasm is fluid that fills the cell and maintains the cell’s shape. Organelles are suspended in the cytoplasm, which can also store chemical substances. The extranuclear DNA is in the mitochondria.

FIGURE 3.1 Cells and Their Organelles This illustration depicts the many components of cells found in plants and animals. Among the components are organelles, specialized parts analogous to organs.

The Cell: Its Role in Reproducing Life and Producing Variation | 45

parts of individual cells, the nucleus and the cytoplasm, between which various communications and activities happen (Figure 3.2). Eukaryotes evolved much later than prokaryotes, appearing some 1.2 bya. Their quite complex structures require enormous amounts of energy to survive and reproduce. As they did in the past, eukaryotes come in many different forms, ranging from single- cell yeasts to large, complex, multicellular organisms, such as us.

nucleus A membrane- bound structure in eukaryotic cells that contains the genetic material.

cytoplasm The jellylike substance inside the cell membrane that surrounds the nucleus and in which the organelles are suspended.

FIGURE 3.2 Prokaryotes and Eukaryotes (a) The many types of bacteria that we encounter in our daily lives are prokaryotic cells like this one. (b) For example, Escherichia coli (E. coli), two single cells of which are shown here, is a bacterium that aids digestion in the intestines of mammals, including humans. (c) This image shows the eukaryotic cells of a primate’s kidney.

Outer membrane

FlagellaeRibosome

Fimbriae

Cell wall Plasma membrane

Cytoplasm

The nucleoid region houses the genetic material of the prokaryotic cell, but unlike the nucleus of a eukaryotic cell it is not contained within a membrane. A prokaryotic cell has about one- thousandth the genetic material of a eukaryotic cell.

The cell wall provides a rigid shape and controls the movement of molecules into and out of the cell.

The flagellum is a whiplike structure attached to some prokaryotes. Rotated by a motorlike system located in the outer layers of the cell, the flagellum enables locomotion.

(a)

Nucleus Cytoplasm Plasma membrane (also called cell membrane)

(c)(b)

46 | CHAPTER 3 Genetics: Reproducing Life and Producing Variation

In all animals and plants, there are two types of eukaryotic cells. Somatic cells, also called body cells, comprise most tissues, such as bone, muscle, skin, brain, lung, fat, and hair (Figure 3.3). Gametes are the sex cells, sperm in males and ova (or eggs) in females (Figure 3.4). The root of somatic cell and gamete production is in the chromosomes, located in the nucleus of each cell. In humans, somatic cells have 46 chromosomes and gametes have 23 (Figure 3.5).

The DNA Molecule: The Genetic Code The chemical that makes up each chromosome, DNA, is the body’s genetic code. Because chromosomal DNA is contained in the nucleus of the cell, it is referred to as nuclear DNA, or nDNA. Within each chromosome, DNA molecules form a sequence, or code, that is a template for the production of a protein, or part of a protein, in the body. Each protein has a specific function, and collectively the proteins determine all physical characteristics and govern the functions of all cells, tissues, and organs. Each DNA sequence, each protein- generating code, is a gene; and the complete set of genes in an individual cell is called the genome.

Although the number of chromosomes varies according to species (see Figure 3.5), all organisms share much the same genome. Chimpanzees have two more chromosomes than humans, but the DNA in chimpanzees and in humans is about 98% identical. Even the DNA in baker’s yeast is 45% similar to human DNA. Within any organism, nDNA is homoplasmic, meaning it is the same in each and every cell— the DNA in a skin cell matches the DNA in a bone cell. (An exception to the rule is mature red blood cells, which have no nuclei and, hence, no nuclear DNA.)

FIGURE 3.3 Somatic Cells Somatic cells in different tissues have different characteristics, but most somatic cells share a number of features. Every somatic cell has a nucleus, which contains a complete copy of the organism’s DNA. As a result, throughout the organism’s body there are millions of copies of that DNA. Note the nuclei in these images of human anatomy: (a) brain tissue, (b) red blood cells (the larger cells are white blood cells, and the small dots are platelets), (c) osteocyte (bone cell), (d) skin cells.

(a) (b)

FIGURE 3.4 Gametes Only one of the sperm surrounding this ovum will penetrate the external membrane and fertilize the ovum.

somatic cells Diploid cells that form the organs, tissues, and other parts of an organism’s body.

gametes Sexual reproductive cells, ova and sperm, that have a haploid number of chromosomes and that can unite with a gamete of the opposite type to form a new organism.

homoplasmic Refers to nuclear DNA, which is identical in the nucleus of each cell type (except red blood cells).

The DNA Molecule: The Genetic Code | 47

A small but significant amount of DNA is contained in tiny organelles, called mitochondria, within each cell’s cytoplasm. These structures use oxygen to turn food molecules, especially sugar and fat, into adenosine triphosphate (ATP), a high- energy molecule that powers cells and, in turn, powers every tissue in the body. The number of mitochondria in a cell varies according to the cell’s

Organism Chromosome

Number Organism Chromosome

Number

FIGURE 3.5 Chromosomes (a) To get an idea of the incredibly minute size of chromosomes, consider that this pair has been magnified 35,000 times. If a penny (approximately 2 cm, or .8 in, in diameter) were magnified 35,000 times, it would be approximately .7 km, or .44 mi, in diameter. (b) An organism’s complexity is not related to its number of chromosomes, as this comparison illustrates. While humans have 46 chromosomes, other primates have more (e.g., ring- tailed lemurs) or fewer (e.g., black- and- white colobus monkeys).

Camel: 70

Guinea pig: 64

Salamander: 24

Housefly: 12

Apple: 34

Potato: 48

Petunia: 14

Algae: 148

Ring-tailed lemur: 56

Black-and- white colobus monkey: 44

Orangutan: 48

(b)

(a)

Camel: 70

Guinea pig: 64

Salamander: 24

Housefly: 12

Apple: 34

Potato: 48

Petunia: 14

Algae: 148

Ring-tailed lemur: 56

Black-and- white colobus monkey: 44

Orangutan: 48

(b)

(a)

mitochondria Energy- producing (ATP) organelles in eukaryotic cells; they pos- sess their own independent DNA.

adenosine triphosphate (ATP) An import- ant cellular molecule, created by the mitochondria and carrying the energy necessary for cellular functions.

48 | CHAPTER 3 Genetics: Reproducing Life and Producing Variation

activity level. For example, the cells in highly active body tissues, such as muscles, contain far more mitochondria than do cells in relatively inactive tissues, such as hair.

The mitochondrial DNA (mtDNA), a kind of miniature chromosome contain- ing 37 genes, is inherited just from the mother. That is, the mtDNA comes from the ovum. Each of us, then, carries our mother’s mtDNA, she carries or carried her mother’s mtDNA, and so on for generation after generation. In theory, a maternal lineage, or matriline, can be traced back hundreds of thousands of years. (Ancient matrilines in fossil hominins are discussed in chapter 10.) Unlike nDNA, mtDNA is heteroplasmic, meaning it can differ among different parts of a person’s body or even within the same kinds of cells.

DNA: THE BLUEPRINT OF LIFE The DNA molecule is the blueprint of life. It serves as the chemical template for every aspect of biological organisms. As Watson and Crick discovered, the molecule has a right- twisted, double- helix structure (see “DNA: Discovery of the Molecular Basis of Evolution” in chapter 2). Understanding this structure is key to understanding the growth of any organism and the transmission of genes from parents to offspring. The starting point for looking at the DNA molecule in any detail is to unravel a chromosome and look at a tiny segment of it under supermagnification. Its helical, ladderlike structure consists of two uprights and many rungs. The uprights of the structure are made up of alternating sugar and phosphate molecules, while the rungs are composed of paired nitrogen bases linked by a weak hydrogen bond (Figure 3.6).

On each side of the ladder, every unit of sugar, phosphate, and nitrogen base forms a single nucleotide (Figure 3.7). While the sugar and phosphate are the same throughout DNA, the base can be adenine (A), thymine (T), guanine (G), or cytosine (C). Owing to the bases’ unvarying chemical configurations, adenine and thymine always pair with each other and guanine and cytosine always pair up. In other words, apart from the rare errors in matching, adenine and thymine are complementary bases and guanine and cytosine are complementary bases. This means that if on one side of the ladder the sequence is ATGCAG, on the other side the sequence will be complementary, TACGTC. This predictability of base pair- ings assures the high reliability of one key function of the DNA molecule, that of self- reproduction. Anthropologists and geneticists investigate the many thousands of single DNA base pairings that produce genetic differences between individuals. Known as single nucleotide polymorphisms (SNPs, pronounced “snips”), these pairings are spread uniformly throughout the genome. Groups of SNPs play a crit- ical role in determining various attributes, such as hair color and blood type (see “Polymorphisms: Variations in Specific Genes,” later in this chapter).

The DNA Molecule: Replicating the Code One function of the DNA molecule is to replicate itself. Replication takes place in the nucleus and is part of cell division, leading to the production of new somatic cells (mitosis) or the production of new gametes (meiosis). Replication thus results

matriline DNA, such as mitochondrial DNA, whose inheritance can be traced from mother to daughter or to son.

heteroplasmic Refers to a mixture of more than one type of organellar DNA, such as mitochondrial DNA, within a cell or a single organism’s body, usually due to the mutation of the DNA in some organelles but not in others.

FIGURE 3.6 The Structure of DNA

The compact chromo- somal packaging of DNA enables thousands of genes to be housed inside a cell’s nucleus. The unwinding of this packaging reveals the genetic material.

DNA includes four different types of nitrogen bases. A gene is a specific and unique sequence of these bases.

DNA includes only one type of sugar (deoxyribose, the first part of the chemical name of DNA) and one type of phosphate group.

A T

G C

S S

The DNA Molecule: Replicating the Code | 49

in continued cell production, from the single- celled zygote (the fertilized egg) to two cells, then four cells, and so on, to the fully mature body with all of its many different tissues and organs— within which cells are continuously dying and being replaced.

In replication, DNA makes identical copies of itself, going from one double- stranded parent molecule of DNA to two double strands of daughter DNA. This means that where there was one chromosome, now there are two (Figure 3.8).

Nitrogen baseSugar

Phosphate

FIGURE 3.7 Nucleotide A nucleotide is the building block of DNA, made up of a phosphate group, a sugar, and a single nitrogen base.

complementary bases The predictable pairing of nitrogen bases in the structure of DNA and RNA, such that adenine and thymine always pair together (adenine and uracil in RNA) and cytosine and guanine pair together.

single nucleotide polymorphisms (SNPs) Variations in the DNA sequence due to the change of a single nitrogen base.

replication The process of copying nuclear DNA prior to cell division so that each new daughter cell receives a com- plete complement of DNA.

mitosis The process of cellular and nuclear division that creates two identical diploid daughter cells.

meiosis The production of gametes through one DNA replication and two cell (and nuclear) divisions, creating four haploid gametic cells.

zygote The cell that results from a sperm’s fertilization of an ovum.

C T TA

G A AT

C T TA

G A AT

C T TA

G A AT

C T

T A

C T

T A

G A

A T

G A

A TC

T T

G A

A T

Old strand

New strand

Old strand

New strand

The two strands of DNA become the parent template strands for replication. Each strand will replicate, using its nitrogen bases to synthesize a complementary strand.

Replication begins with the separation of the two strands of DNA. Enzymes break the relatively weak hydrogen bonds that hold together the paired nitrogen bases. In effect, the DNA is “unzipped,” creating the two parent template strands.

Each parent strand serves as a template for the creation of a new complementary DNA strand. The exposed, unpaired nitrogen bases on the parent strands attract complementary free-floating nucleotides. The nitrogen bases of these nucleotides form hydrogen bonds with the existing nitrogen bases—for example, a free-floating nucleotide with a cytosine base will attach itself to a guanine base.

New strands

New strands forming

When all the nitrogen bases of the parent strands are paired with (formerly free-floating) nucleotides, replication is complete. There are now two complete DNA molecules, each consisting of one parent strand and one new strand.

FIGURE 3.8 The Steps of DNA Replication

Imagine if we could look at ancient organisms’ DNA to understand their evolution. In fact, new tech- nology is enabling anthropologi- cal geneticists to routinely extract DNA from the tissues (mostly bones and teeth) of ancient remains. This emerging field, called paleoge- netics, has been made possible by the development of polymerase chain reaction (PCR), a method of amplifying a tiny sequence of DNA for study by incrementally increas- ing the sizes of a billion copies made from a single template of DNA. PCR has opened new windows onto the genetics of ancient populations, including the identification of sex chromosomes, the documentation of diseases, and the isolation of unique repetitions of DNA segments. It has yielded insight into the genetic dis- similarity of Neandertals and modern humans, and it has enabled explora- tion into population origins and move- ments (both subjects are among the topics of chapter 12).

Anthropologists have long specu- lated about the origins of Native Ameri- cans (where they came from is another subject of chapter 12). Key to under- standing their origins is their genetic diversity. Studies have revealed that the haplogroups of mtDNA— A, B, C, and D— in living Native Americans are quite similar to the haplogroups of their ancestors. This resemblance strongly suggests that Native Amer- icans’ genetic structure is quite

By examining the distribution of haplogroups A, B, C, and D in North and South America as well as eastern Asia, researchers have estimated that Native Americans arrived in the West- ern Hemisphere between 15,000 and 40,000 yBP. The presence of the same haplogroups in the northeastern part of Asia suggests that Native Americans originated from this area.

A B

CD A

D C AB

Ancient DNA Opens New Windows on the Past

old. Based on current assumptions about mutation rates in mtDNA, anthropologists and geneticists have estimated that people arrived in the Americas sometime between 15,000 and 40,000 yBP, earlier than what is documented in the archaeo- logical record (among the subjects of chapter 13). But a new variant of haplogroup D, discovered in the DNA of a 10,300- year- old skeleton from Alaska by paleogeneticist Brian Kemp and his collaborators, sug- gests that the molecular clock may be off and that humans first arrived

in the New World around 13,500 yBP, a date that jibes well with the archaeological evidence.

In addition, the presence of all four haplogroups and their variants in the skeletons of Native Ameri- cans dating to before 1492 tells us that the widespread decline of the Native American population after Columbus’s arrival did not reduce their genetic, and therefore biologic, diversity. Native Americans living today are likely as diverse genetically as were their ancestors living hun- dreds and thousands of years ago.

H O W D O W E K N O W ?

CHROMOSOME TYPES Within somatic cells, chromosomes occur in homologous, or matching, pairs (Figure 3.9). Each pair includes the father’s contribution (the paternal chromo- some) and the mother’s contribution (the maternal chromosome). These nonsex chromosomes are called autosomes.

The karyotype, or complete set of chromosomes, includes all of the autosomes and one pair of sex chromosomes, so called because they determine an individ- ual’s biological sex. Females have two X chromosomes, and males have one X and one Y chromosome (Figure 3.10). The Y chromosome contains a small amount of genetic material, which determines only male characteristics. The interaction of

FIGURE 3.9 Chromosome Pairs Homologous chromosomes are virtually identical in their physical and chemical structure. Each pair of chromosomes has the same genes, but the pair may have different alleles for specific genes.

FIGURE 3.10 Karyotype Contained within each somatic cell, the human karyotype typically consists of 46 chromosomes of various sizes in 23 pairs. Of those 23, one pair determines the person’s sex. Here, the label “X” means that these sex chromosomes are both Xs and thus belong to a human female.

free- floating nucleotides Nucleotides (the basic building block of DNA and RNA) that are present in the nucleus and are used during DNA replication and mRNA synthesis.

homologous Refers to each set of paired chromosomes in the genome.

autosomes All chromosomes, except the sex chromosomes, that occur in pairs in all somatic cells (not the gametes).

karyotype The characteristics of the chro- mosomes for an individual organism or a species, such as number, size, and type. The karyotype is typically presented as a photograph of a person’s chromosomes that have been arranged in homologous pairs and put in numerical order by size.

sex chromosomes The pair of chromo- somes that determine an organism’s biological sex.

The Two Steps of DNA Replication

The first function of DNA is to replicate itself. Templates from the original (parental) strand of DNA yield two exact (daughter) copies.

Step Activity

1. Strand of DNA unzips to form templates.

Weak nucleotide bonds between bases break, exposing two parental strands of DNA.

2. Templates plus nucleotides yield daughters.

Free- floating nucleotides in the nucleus match with the newly exposed template strands of DNA.

C O N C E P T C H E C K !

The DNA Molecule: Replicating the Code | 51

52 | CHAPTER 3 Genetics: Reproducing Life and Producing Variation

gametes during fertilization determines the combination of chromosomes in the offspring. If an X- carrying sperm fertilizes an egg (which always carries an X), the offspring will be female. If a Y- carrying sperm fertilizes an egg, the offspring will be male. Therefore, the male parent’s gamete determines the sex of his offspring because the Y chromosome is present in males only; it is passed from father to son.

The Y chromosome can be highly informative about paternity over many gen- erations. This patriline is in part analogous to the matriline- based mtDNA, which is passed on only by females. However, mtDNA goes to all of a woman’s children, whereas the Y chromosome is passed only to a man’s son.

Mitosis: Production of Identical Somatic Cells An organism starts life as a single cell, the zygote, which then produces identical copies of itself many, many times. A single human zygote, for example, even- tually results in more than 10 trillion cells, each having the exact same DNA (Figure 3.11). Here, the production of identical daughter cells from an original

patriline DNA whose inheritance can be traced from father to son via the Y chromosome.

Fertilization occurs when one sperm penetrates the outer membrane of the ovum, or egg.

A zygote is the single cell that forms at the beginning of an organism’s life. This cell must replicate itself millions of times to form a fully developed fetus.

After the regions of the body are established and different types of tissue have formed, the fetus grows until it reaches full-term size.

Following many replications, the embryo begins to differentiate different types of tissues and separate regions of the body, such as the head and limbs.

FIGURE 3.11 Prenatal Development The stages of human development from fertilization to a full- term infant.

diploid cell A cell that has a full comple- ment of paired chromosomes.

parental cell, mitosis, involves one DNA replication followed by one cell division (Figure 3.12). In this kind of cell division, a diploid cell— a cell having its organ- ism’s full set of chromosomes— divides to produce two cells, each of which also has the full set of chromosomes.

Chromatin

46 chromosomes

Chromosome duplication

Line up, spindle forms

The DNA in the cell is replicated, as described in Figure 3.8. This parent cell has a full set (23 pairs) of chromosomes.

The replicated DNA lines up in the middle of the cell.

As the cell divides, the DNA sep- arates. One complete complement of DNA goes into one new cell, and the other full complement goes into the second new cell.

Each new cell has a full set of DNA, with 23 pairs of chromosomes.

(b)

(a)

FIGURE 3.12 Mitosis (a) The steps of mitosis in humans. (b) A human skin cell undergoing mitosis, dividing into two new daughter cells.

46 chromo- somes

Chromo- some

duplication

Homologous chromosome

pairing

The pairs are separated and pulled to opposite sides as the cell divides.

The cell divides, forming two daughter cells.

The chromosomes line up in the middle of the cell, but are not paired.

A second cell division follows, without DNA replication. The chromosomes are separated into single strands and are pulled to opposite sides as the cell divides.

Four haploid daughter cells result, each with 23 chromosomes, but no pairs.

The parent cell is diploid, hav- ing 23 pairs of chromosomes.

Meiosis begins like mitosis. Initially, the cell’s DNA is replicated.

Homologous pairs of chromosomes line up in the middle of the cell.

FIGURE 3.13 Meiosis The steps of meiosis in humans. Compare this process to mitosis, shown in Figure 3.12.

Mitosis: Production of Identical Somatic Cells | 53

54 | CHAPTER 3 Genetics: Reproducing Life and Producing Variation

Meiosis: Production of Gametes (Sex Cells) The genetic code is transmitted from parents to offspring via the female and male gametes. Gametes, remember, have only half the chromosomes that are in somatic cells— they are haploid, containing one chromosome from each pair. Unlike mito- sis, the production of these cells, meiosis, does not result in identical copies of the parent cell and the parent cell’s DNA. Meiosis involves one DNA replication followed by two cell divisions (Figure 3.13).

Meiosis plays a critical role in the inheritance of biological characteristics and the variation seen in offspring. Because each gamete contains just one chromosome from a homologous pair and just one sex chromosome, during reproduction each parent contributes only half of his or her genetic material. For example, in your somatic cells, each homologous pair includes one chromosome from your mother and one chromosome from your father. Whether a particular gamete contains your mother’s chromosome or your father’s chromosome is completely random. In addition, homologous chromosomes often exchange parts when they pair up and intertwine. This exchange of parts is called crossing- over. The outcome of such reshuffling is that gene variants originally on the maternal chromosome are now on the paternal chromosome (or vice versa), a common development called recombination. Genes that are close together on a chromosome are much less likely to recombine. These units or blocks of genetic material are called haplo- types. Geneticists prefer to study haplotypes because they do not recombine and are passed on for many generations, potentially hundreds, over time. Groups of related haplotypes, called haplogroups, are an important tool for studying both long- term evolution and populations’ histories.

In rare instances, during meiosis nonhomologous chromosomes exchange seg- ments. These rare exchanges are called translocations. The most common form in humans, involving both chromosome 13 and chromosome 14, affects about 1 in 1,300 people. Translocations may cause infertility, Down syndrome (when one- third of chromosome 21 joins onto chromosome 14), and a number of diseases, including several forms of cancer (some leukemias). On occasion, chromosome pairs fail to separate during meiosis or mitosis. These nondisjunctions result in an incorrect number of chromosomes in the person’s genome. A loss in number of chromosomes is a monosomy. A gain in number of chromosomes is a trisomy, the most common being trisomy- 21, or Down syndrome (in this form, caused by an extra or part of an extra chromosome 21). As with many chromosomal abnor- malities, the age of the mother determines the risk of the offspring’s having Down syndrome. For 20- to 24- year- old mothers, the risk is 1/1,490. It rises to 1/106 by age 40 and 1/11 beyond age 49.

As Mendel had recognized (see “Since Darwin: Mechanisms of Inheritance, the Evolutionary Synthesis, and the Discovery of DNA” in chapter 2), each physical unit (that is, gene) passes from parent to offspring independently of other physical units. This independent inheritance— often called Mendel’s law of independent assortment (Figure 3.14)—applies to genes from different chromosomes. How- ever, what happens when genes are on the same chromosome? Because meiosis involves the separation of chromosome pairs (homologous chromosomes), genes on the same chromosome, especially ones near each other on that chromosome, have a greater chance of being inherited as a package. They are less subject to

haploid cell A cell that has a single set of unpaired chromosomes; half of the num- ber of chromosomes as a diploid cell.

crossing- over The process by which homologous chromosomes partially wrap around each other and exchange genetic information during meiosis.

recombination The exchange of genetic material between homologous chromo- somes, resulting from a cross- over event.

haplotypes A group of alleles that tend to be inherited as a unit due to their closely spaced loci on a single chromosome.

haplogroups A large set of haplotypes, such as the Y chromosome or mitochon- drial DNA, that may be used to define a population.

translocations Rearrangements of chromosomes due to the insertion of genetic material from one chromosome to another.

nondisjunctions Refers to the failure of the chromosomes to properly segregate during meiosis, creating some gametes with abnormal numbers of chromosomes.

monosomy Refers to the condition in which only one of a specific pair of chro- mosomes is present in a cell’s nucleus.

trisomy Refers to the condition in which an additional chromosome exists with the homologous pair.

law of independent assortment Mendel’s second law, which asserts that the inher- itance of one trait does not affect the inheritance of other traits.

F1 GgYy

GGYy GGyy

Gy gY gy

GGYY GGYy

GgYy Ggyy

GgYY GgYy

GgYy Ggyy

GgYY GgYy

ggYy ggyy

ggYY ggYy

This Punnett square shows all possible combinations of two different genes, pod color and seed color: G = green pod g = yellow pod Y = yellow seed y = green seed

Since both parents have two different alleles for both traits, there are 16 possible combinations.

Of the 16 combinations, nine have green pods and yellow seeds. The genotypes vary and include: GGYY, GGYy, GgYY, GgYy.

Three of the resulting combinations have green pods and green seeds. They have one of two genotypes: GGyy or Ggyy.

Three of the resulting combinations have yellow pods and yellow seeds. There are two possible genotypes: ggYY or ggYy.

One of the resulting combinations has yellow pods and green seeds, with the genotype ggyy.

FIGURE 3.14 Law of Independent Assortment Through his research with pea plants, Mendel created several laws pertaining to inheritance. (a) His second law, the law of independent assortment, asserts that traits linked to different chromosomes are inherited independently from one another. (b) Hair color, for example, is inherited independently from eye color.

Two equally probable chromosome arrangements in

meiosis I: OR

meiosis II: OR

gametes OR

with genotypes OR

The large chromosomes have a gene that determines eye color: red represents brown eyes, and blue represents blue eyes.

Alternatively, following the first cell division of meiosis, one cell has genes for brown eyes and blond hair, while the second has genes for blue eyes and brown hair.

Again, the four daughter cells, or gametes, follow suit: two gametes have genes for brown eyes and blond hair, while the other two gametes have genes for blue eyes and brown hair.

The small chromosomes have a gene that determines hair color: red represents brown hair, and blue represents blond hair.

Following the first cell division of meiosis, one cell has genes for brown eyes and brown hair, while the second cell has genes for blue eyes and blond hair.

The four daughter cells, or gametes, follow suit: two gametes have genes for brown eyes and brown hair, while the other two gametes have genes for blue eyes and blond hair.