Fossil and molecular evidence have hitherto suggested that the cercopithecoids (Old-World monkeys) and hominoid (ape and human) lineages diverged around the Oligocene/ Miocene boundary, 23 to 25 million years ago (Ma). In a challenge to the recentness of this estimate, Steiper et al. adopt a molecular approach called quartet analysis, which uses sequence data from two pairs of species from two clades to assess divergence dates with greater precision. For the hominoid branch, chimpanzee and human were chosen, and for the cercopithecoids, baboon and macaque; the divergence dates between the members of each pair were calibrated from fossil data. The resulting model suggests that the hominoid/cercopithecoid divergence took place in the Early Oligocene, 29 to 34.5 Ma. The implication of this result is that several million years of early hominoid history have yet to be sampled paleontologically and that Proconsul--hitherto considered the earliest of all hominoids--may have had earlier hominoid ancestors. -- AMS
Proc. Natl. Acad. Sci. U.S.A. 101, 17021 (2004).
