Comparisons of Neanderthal mitochondrial DNA with that of modern humans indicate that the Neanderthals are not related to modern humans and did not contribute to our mitochondrial heritage. However, because Neanderthals and modern humans are separated by at least 25,000 years, this does not rule out that some forms of interbreeding may have caused the modern European gene pool to be derived from both Neanderthals and early humans (called Cro-Magnons). To resolve this question, researchers analyzed mitochondrial DNA sequences from 25,000-year-old Cro-Magnon remains and compared them to four Neanderthal specimens and a large data set derived from modern humans (Caramelli et al., 2003. Proc. Natl. Acad. Sci. [USA] 100: 6593–6597). The results are shown in the graph below.

(a) What can you conclude about the relationship between CroMagnons and modern Europeans? What about the relationship between Cro-Magnons and Neanderthals?

(b) From these data, does it seem likely that Neanderthals made any contributions to the Cro-Magnon gene pool or the modern European gene pool?