Sunday, January 22, 2012

Chris Stringer on Modern Human Origins

Chris Stringer was one of the original progenitors of the Out of Africa model of modern human origins, which posited that anatomically modern Homo sapiens arose in sub-Saharan Africa as a speciation event1 and then replaced the archaic humans that they came into contact in other areas of the Old World. Needless to say, this perspective has been rocked by a number of astonishing studies that have come out in the last few years, including but not limited to these reports:
These have cast considerable doubt on the integrity of anatomically modern humans as a separate species but suggest, instead that despite the timing of some of these trysts, Homo sapiens was a much more polytypic species then met the eye.

Now the grand don of the replacement model is undergoing a re-think. The Edge provides us with a wonderful trek through the history of the origins of modern humans debate and the current evidence for it. He hasn't given up the ship yet, though. He notes:
In my view the Neanderthals were closely related and probably potentially able to interbreed with modern humans, but until recently I considered that while there could have been interbreeding forty or fifty thousand years ago, it was on such a small scale that all trace of it vanished in the intervening years. But it now seems from Neanderthal genome studies that that was not so. We do have a bit of Neanderthal in us, you and I—it's a small amount, but certainly not negligible..

Does that mean Neanderthals are a different species or does it mean we should include them in Homo sapiens? Well, they are still only a small part of our makeup now, reflecting something like a 2.5% input of their DNA. Physically, however, they went extinct about 30,000 years ago. They had distinct behavior and they evolved under different conditions from us, so I still think it's useful to keep them as a separate species, even if we remember that that doesn't necessarily preclude interbreeding.
The percentage of Neandertal genes ranges from a low of 2% to a high of 9%, depending on who you read. The problem here is that, while we currently only have the small percentages, what can be said of the early modern Europeans, or of the people in Europe even as late as the Neolithic? It is almost certain that they would have had much higher percentages.

Further, do these genes explain the traits that Dave Frayer has been seeing for years in the earliest modern humans, such as the extended hemi-buns of the central European sample from Předmosti or archaic characteristics of the Mladeč crania?

The talk is quite long but worth every minute to get the full understanding of how vexing the search for the origins of modern humans has been. As Glenn Reynolds would say: Read the Whole Thing.

1Stringer, C. B., & Andrews, P. (1988). Genetic and Fossil Evidence for the Origin of Modern Humans. Science, 239(4845), 1263-1268.

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