The phylogenetic relationships among Homo, Pan and Gorilla: a population genetics perspective

Abstract

The phylogenetic relationships among Homo, Gorilla and Pan are still controversial. Some anatomical and genetic comparisons suggest that Pan is more closely related to Gorilla than it is to Homo. A larger number of genetic comparisons, and a recent analysis of morphology, suggest that Pan and Homo share the most recent common ancestry among these genera. The inconsistency across genetic studies can be explained by hypothesizing that (a) the last common ancestor of all three lineages was polymorphic at a number of loci and (b) that the two divergences that gave rise to these three lineages occurred close together in time. If these two hypotheses are correct, then a model based on the random loss or retention of alternative alleles segregating at polymorphic loci in the last common ancestor can explain the apparent discrepancies. Observed levels of DNA polymorphism in extant primates and the consensus time frame for this diversification indicate this is a plausible model. The available DNA sequence data are best explained by inferring that all three lineages diverged from a single common ancestor over a brief period of time, i.e., that the diversification was effectively a trichotomy. This model challenges the common assumption that two independent and temporally separate speciation events occurred during the diversification of the African hominoids.