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:

• Researchers say Neanderthals interbred with modern humans
• Shared Genes With Neanderthal Relatives: Modern East Asians Share Genetic Material With Prehistoric Denisovans
• Non-Africans Are Part Neanderthal, Genetic Research Shows
• A New Human Relative from the Siberian Mountains
• Skull suggests Stone Age humans interbred with more primitive relatives
• Ancient Humans Were Mixing It Up: Anatomically Modern Humans Interbred With More Archaic Hominin Forms While in Africa
  

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.
http://www.jstor.org/stable/1700885

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Archaeological Evidence: Neandertals and Modern Humans Interacted and Interbred

The Newsroom at the University of Colorado has released news of a study that links the archaeological evidence in Europe with Neandertal/early modern human interaction and, probably, interbreeding. They write:

Anthropologists using computer modeling to determine how early hominins adapted to climate change during the last Ice Age, have gained new insights into why Neanderthals disappeared as a distinct population some 30,000 years ago.

The scientists believe Neanderthals interbred with more numerous modern humans until they ceased to exist as their own population.

This is called "gene swamping" and is not uncommon. The authors further argue:

“Neanderthal genes make up between one and four percent of today’s human genome, especially in those of European descent. Their legacy lives on in our genome and possibly in our cultural knowledge.”

Modern humans begin to show up in Europe during the Early Würm/Late Würm glaciation, between 35 and 40 thousand years B.P. A good representation of these hominins are those from the cave of Mladeč, which, while being classified as modern humans, have characteristics reminiscent of Neandertals. Even the later hominins such as those from the central European site of Dolní Vĕstonice, show archaic characteristics such as expanded occipital buns (a bulge at the rear of the vault). This all makes sense within the context of hybridization between the two groups of people. Fred Smith was right.

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“Out-of-Africa Replacement Model”: Piling On

On the heels of the recent DNA arguments supporting hybridization between early modern Homo sapiens and archaic Homo sapiens in Africa comes fossil skeletal evidence.  As the Telegraph reports:

A study on human remains found in the Iwo Eleru cave in Nigeria, West Africa, shows that Stone Age humans in the area shared characteristics with much older human relatives. Palaeontologists leading the study believe their findings provide evidence that modern humans and older subspecies of human might have coexisted and even crossbred in Africa. The findings add weight to theories that ancient species of human lived alongside the anatomically modern humans after they first appeared in Africa 200,000 years ago.

Quoted in the article is Chris Stringer, one of the progenitors of the Out-of-Africa replacement model of modern human origins which was based on mitochondrial DNA studies done in the late 1980s.The article continues:

Professor Stringer said: "The majority view was that once modern humans emerged in Africa 150,000 years ago, it was kind of the end of the story and modern humans took over. "I think the reality is that the ancestral forms didn't just disappear but hung around alongside those that had evolved into modern humans. "Somewhere lurking in bits of Africa were these more archaic people and we are starting to get a picture of that."

I suspect that it is going to get very hard to pin down exactly where Homo sapiens starts. It is becoming more and more clear that anatomically modern Homo sapiens and archaic Homo sapiens went for the occasional “roll in the hay.” If so, as I pointed out earlier, there simply was no “speciation event.” This goes more to supporting the multiregional evolution model, as it applies to Africa, in which there was selection for more modern genes. This model may also apply to Europe, with the mixing of modern humans and archaic humans there. I suspect that this will spur reexamination of the early modern material from there, such as Mladeč, where the material dates from the Early Würm/Late Würm interglacial period.