Chapter 22, Problem 26PDQ

Comparisons of Neanderthal mitochondrial DNA with that of modern humans indicate that they 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 some forms of interbreeding causing the modern European gene pool to be derived from both Neanderthals and early humans (called Cro-Magnons). To resolve this question, Caramelli et al. (2003. Proc. Natl Acad Sci. [USA] 100: 6593–6597) analyzed mitochondrial DNA sequences from 25,000–year-old Cro-Magnon remains and compared them to four Neanderthal specimens and a large dataset derived from modern humans. The results are shown in the graph.

The x-axis represents the age of the specimens in thousands of years; the y-axis represents the average genetic distance. Modern humans are indicated by filled squares; Cro-Magnons, open squares; and Neanderthals, diamonds.

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

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