EarthSky: Twenty years of discoveries changing story of human evolution

EarthSky has an interesting article that summarizes twenty years of human evolution discoveries.  They write:

Perspectives on our own species have also changed. Archaeologists previously thought Homo sapiens evolved in Africa around 200,000 years ago, but the story has become more complicated. Fossils discovered in Morocco have pushed that date back to 300,000 years ago, consistent with ancient DNA evidence. This raises doubts that our species emerged in any single place.

This century has also brought unexpected discoveries from Europe and Asia. From enigmatic “hobbits” on the Indonesian island of Flores to the Denisovans in Siberia, our ancestors may have encountered a variety of other hominins when they spread out of Africa. Just this year, researchers reported a new species from the Philippines.

All of these discoveries point to the idea that there was considerable population mixing throughout the Middle to Late Pleistocene not just in Africa but throughout the Old World. We know that it took place in China around 120,000 years ago by the evidence from Linjing.  These particular hominins have characteristics found in modern humans, Neandertals and Homo erectus.

Interestingly, the idea that our species did not originate in any single place was an idea pursued by Rachel Caspari almost two decades ago, at a paper given at one of the American Association of Physical Anthropologists conventions.  At the time, it was still thought that the “Out of Africa” replacement model was still the best explanation for modern human origins.We now know that it is not.

More Trouble for the Complete "Out-of-Africa" Model

Science Daily is reporting on research done on migration patterns involving early anatomically modern humans.  They write:

The team, led by Johannes Krause from Tübingen University, was able to reconstruct more than ten mitochondrial genomes (mtDNAs) from modern humans from Eurasia that span 40,000 years of prehistory. The samples include some of the oldest modern human fossils from Europe such as the triple burial from Dolni Vestonice in the Czech Republic, as well as the oldest modern human skeletons found in Germany from the site of Oberkassel close to Bonn.

The researchers show that pre-ice age hunter-gatherers from Europe carry mtDNA that is related to that seen in post-ice age modern humans such as the Oberkassel fossils. This suggests that there was population continuity throughout the last major glaciation event in Europe around 20,000 years ago. Two of the Dolni Vestonice hunter-gatherers also carry identical mtDNAs, suggesting a close maternal relationship among these individuals who were buried together.

It was also suggested that the split between non-Africans and Africans was much later in time, between 62 and 95 ky BP. This would mean that the window of hybridization would be much larger than originally thought and that archaic and modern hybridization was a good deal more common until a later time than thought.  The first moderns that we have are from the site of Bouri, in the Afar Triangle, and date to around 160 ky BP.  Maddeningly, what we are lacking is good material between that time and around 100 ky BP, when the Near Eastern Skhul and Qafzeh material are found.  A friend of mine and I argued that the archaic traits in those skulls represent African archaic traits and not hybridization with Neandertals.  This would seem to support that.  They suggest that there are discrepancies between these results and previous ones but, critically, that these results tend to support both the palaeoanthropological and archaeological evidence.    Here is the citation:

Fu et al., A Revised Timescale for Human Evolution Based on Ancient Mitochondrial Genomes,
Current Biology (2013), http://dx.doi.org/10.1016/j.cub.2013.02.044

New Chinese Hominid Fossil Supports Multiregional Evolution?

China National News has a story about a hominid find in Guangxi that suggests that there was not replacement of archaic humans by modern humans in this area. The author writes:

The mandible has a protruding chin like that of Homo sapiens, but the thickness of the jaw is indicative of more primitive hominins, suggesting that the fossil could derive from interbreeding.

If confirmed, the finding would lend support to the "multiregional hypothesis", which says that modern humans descend from Homo sapiens coming out of Africa who then interbred with more primitive humans on other continents.

In contrast, the prevailing "out of Africa" hypothesis holds that modern humans are the direct descendants of people who spread out of Africa to other continents around 100,000 years ago.

"This paper acts to reject the theory that modern humans are of uniquely African origin and supports the notion that emerging African populations mixed with natives they encountered," said Milford Wolpoff, a proponent of the multiregional hypothesis at the University of Michigan.

Most Chinese Palaeoanthropologists, pointing to the unique features of remains like Dali and Maba have long believed that there is a continuous line from Homo erectus to the later remains and going to the material found in the Upper Cave at Zhoukoudian, which is dated at around 30 ky BP. This should prove interesting.

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Neandertal Population Size: The Cause for Extinction?

The Max Planck institute has released findings that suggest that Neandertals became extinct because they were below effective population size. Live Science reports that:

Neanderthals are of course extinct. But there never were very many of them, new research concludes.

In fact, new genetic evidence from the remains of six Neanderthals (Homo neanderthalensis) suggests the population hovered at an average of 1,500 females of reproductive age in Europe between 38,000 and 70,000 years ago, with the maximum estimate of 3,500 such female Neanderthals.

"It seems they never really took off in Eurasia in the way modern humans did later," said study researcher Adrian Briggs of the Max-Planck Institute for Evolutionary Anthropology in Germany.

The research, which will be published in the July 17 issue of the journal Science, suggests the small population size of our ancestral cousins may have been a factor in their demise.

It wasn't for lack of intelligence. As the story notes, Neandertals were far from stupid:

Rather than the dumb cavemen characters starring in Geico car insurance ads, accumulating archaeological and genetic evidence shows Neanderthals were pretty sophisticated. They apparently hunted with blades and spear tips rivaling those of modern humans, ate marine mammals like seals and dolphins and sported brains that grew like ours. Their bodies likely looked similar to ours, and some Neanderthals showed off red locks on their heads.

I am still of the mind that Neandertals did interbreed with the arriving moderns, based on evidence at Arcy Sur-Cure where you have Aurignacian and Chatelperronian tool industries interdigitated, suggesting a somewhat fluid landscape for these hominids. The evidence at Lagar Velho, in Portugal, also suggests interbreeding. But if that didn't happen all over, or if there were conflicts regarding land or food resources, it is easy to see that there may have been a time of admixing and replacement, subsequent to which the Neandertal genome disappeared in the wake of selective pressures for that of modern humans.


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