Saturday, December 16, 2017

Modern Humans Came Out of Africa Earlier Than Thought and Did So Multiple Times

If you have been studying human evolution, this story is not new.We have suspected for some time that humans migrated out of Africa in waves, beginning with Homo heidelbergensis, up through archaic Homo sapiens and, now, modern Homo sapiens.  As the story notes, there have likely been multiple migrations of Homo sapiens, as well. 

From the story in Science Daily:
A review of recent research on dispersals by early modern humans from Africa to Asia by researchers from the Max Planck Institute for the Science of Human History and the University of Hawai'i at Manoa confirms that the traditional view of a single dispersal of anatomically modern humans out of Africa around 60,000 years ago can no longer be seen as the full story. The analysis, published in the journal Science, reviews the plethora of new discoveries being reported from Asia over the past decade, which were made possible by technological advances and interdisciplinary collaborations, and shows that Homo sapiens reached distant parts of the Asian continent, as well as Near Oceania, much earlier than previously thought. Additionally, evidence that modern humans interbred with other hominins already present in Asia, such as Neanderthals and Denisovans, complicates the evolutionary history of our species.
Here is the graphic from the story:

What is only hinted at in the article is that when these waves of moderns came out of Africa, they interbred with the archaic hominins that they encountered. Further, this genome was remarkably stable, since there is genetic evidence that there was at least 500 thousand years of separation between them.Also missing from the story is the range of variation that these hybridizations display.  For example, as noted by the triangle on the map, the Xuchang fossils from China seem to show a mix of modern, Neandertal and late Homo erectus morphologies.  As I noted at the time:
The implications of these skulls are stark: there has been widespread population mixing and regional continuity in Europe and Asia for at least 400 thousand years. Not only did the Neandertals feel enough cultural kinship to mate and have children with these East Asian people, the early modern humans coming out of Africa did, as well.
The other peculiar thing about the graphic is that there seems to be no migration pattern through the strait of Gibraltar. This seems odd since this is likely at least one of the routes that were taken by H. ergaster between 1.5 and 2.0 mya, and since it is thought that the Levallois tool technology comes from the Middle Stone Age of Africa, this would have been a likely route of introduction.  There may have been a barrier of sorts, suggested by the fact that the latest surviving Neandertals are from Spain

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