Category Archives: paleontology

Chimps and humans diverged some eight million years ago

I have said that several times. So I’m not going to miss the opportunity of saying it once more: the 5 million year figure for the Pan-Homo divergence is a total nonsense: it’s more like 8-10 million years. Even the less exaggerated hunch (not sure on what is based) of 7 million years is too short.
New research, using mathematical-statistic analysis with not one but several cross-references, produces an older figure: some 8 million years.


Estimation of divergence times is usually done using either the fossil record or sequence data from modern species. We provide an integrated analysis of palaeontological and molecular data to give estimates of primate divergence times that utilize both sources of information. The number of preserved primate species discovered in the fossil record, along with their geological age distribution, is combined with the number of extant primate species to provide initial estimates of the primate and anthropoid divergence times. This is done by using a stochastic forwards-modeling approach where speciation and fossil preservation and discovery are simulated forward in time. We use the posterior distribution from the fossil analysis as a prior distribution on node ages in a molecular analysis. Sequence data from two genomic regions (CFTR on human chromosome 7 and the CYP7A1 region on chromosome 8) from 15 primate species are used with the birth–death model implemented in mcmctree in PAML to infer the posterior distribution of the ages of 14 nodes in the primate tree. We find that these age estimates are older than previously reported dates for all but one of these nodes. To perform the inference, a new approximate Bayesian computation (ABC) algorithm is introduced, where the structure of the model can be exploited in an ABC-within-Gibbs algorithm to provide a more efficient analysis. 

Press article at Science Daily.
A central issue is that fossils are seldom preserved and discovered, so fossil evidence can well be five or 5.5 million years old and the divergence be in fact older.
But combining fossil and genetic data it is possible to refine the equation and get to much more accurate estimates. That’s what the authors have done in what should be celebrated as a the convergence of genetics and archaeology (paleontology in this particular case), a convergence much needed indeed. 

One of the particular fossils which find new room into the potential Human ancestry is Sahelanthropus tchadensis, Toumaï, which fits well in the evolutionary line of Homo sp. but was earlier thought by many as too old for that.
Another aspect vindicated by this study is that primates lived in the late era of the dinosaurs, what really allows them to have reached South America without need of swimming across an ocean which did not actually exist yet. 
This was actually addressed by the same team in 2002 but its obvious implications in human evolution were ignored. So they have now decided to address the matter themselves, what is very much appreciated, because they must be damn right.

Related posts (also from my old blog Leherensuge):