Turn back the clock

Abstract

It’s easy to forget, as the universal currency of DNA sequence data continues to drive the field of molecular evolution, that the exchange rate between sequence differences and times of species divergence is ultimately set by that less fashionable commodity, the bone. Through the work of paleontologists and taxonomists, dates of divergence between pairs of animal groups are established; molecular divergence data between the groups’ living descendants then provide a reference by which other species splits can be dated. The validity of these reference dates is therefore crucial, and attention has now been turned to one that has implications for our own species, as it profoundly affects the timings of divergences among the primates. For over 30 years these have rested on an uncertain dating of ⩾30 MYBP (million years before present) for the split between Old World Monkeys (e.g. baboon), and apes and humans. The primate fossil record is particularly poor, so it makes sense to apply other references where it is better: these are the split between artiodactyls (e.g. cow) and cetaceans (whales), at 60 MYBP, and that between equids (e.g. horse) and rhinoceroses (50 MYBP). Contributing a baboon mtDNA sequence as molecular calibrator, Arnason et al.1xMolecular timing of primate divergences as estimated by two nonprimate calibration points. Arnason, U. et al. J. Mol. Evol. 1998; 47: 718–727Crossref | PubMed | Scopus (111)See all References1 recalculate the Old World Monkey – hominoid split at 50 MYBP, thus doubling the times of divergences among the primates: the human – chimp split increases from 5 MYBP to ⩾10 MYBP. All of the dates in human evolution that rely on this divergence will need extending accordingly.