A Genetic Perspective on the Origin and History of Humans

Recent topics in molecular anthropology are reviewed with special reference to hominoid DNA sequences and population genetics theory. To cover a wide range of possible demographic situations in the human lineage since the Mio- cene, a model is introduced that allows temporal changes in population struc- ture and size. The coalescence process of neutral genes is formulated and used to make quantitative inferences on the origin and history of humans. Nuclear DNA sequence data support the theory that humans and chimpanzees diverged from each other 4.6 million years (mya) and the gorilla lineage branched off as early as 7.0-7.4 mya. The same data estimate the effective size of the Pliocene hominoid population as i05, a figure similar to that obtained inde- pendently from alleles that have persisted in the human population for more than 5 my. Hypotheses about the origin of Homo sapiens, genetic differentia- tion among human populations, and changes in population size are quantified. None of the hypotheses seems compatible with the observed DNA variation. The effective population size decreased to 104 in the Pleistocene, suggesting an important role of extinction/restoration in H. sapiens populations. Natural selection against protein variation might be relaxed in the Pleistocene. The history of H. sapiens appears to have been more dynamical than is postulated by the hypotheses.