Out of Africa II Refined

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October 05, 2011

The fossil evidence has long indicated there were two great migrations out of Africa. Although there is a minority view some australopithecines may have reached what is now Indonesia, placing this 1st migration well before 2 million years ago,  many paleoanthropologists say there is no fossil evidence of hominin occupation outside of Africa until about 1.8 million years ago when bands of Homo erectus were moving along the eastern Mediterranean littoral. These various populations gradually expanded East and West and this first wave of  migration is called out of Africa I.

Our species, Homo sapiens, appears to have originated in Eastern Africa around 200,000 years ago and there is strong evidence small populations of H. sapiens were moving north out of Africa and pressing into the near East around 100,000 years ago. This has been called Out of Africa II. Until very recently there appeared to be a gap in this migration for we find the first evidence of Homo sapiens in what is now eastern Europe around 40 to 50,000 years ago and fuzzier dating for migrations eastward into Asia.

Scientists are quick to point out that both migrations most likely comprised many separate bands, moving at their own pace over many generations, seeking food resources and with no destination in mind.   We must avoid jumping to the conclusion these migrations moved purposefully on a course of territorial conquest.

Recent announcements in the journal Science reveal a picture with more nuance.

First came the evidence from the cave called Denisova in central Asia, with  genetic evidence of interbreeding among Neanderthals and modern humans and the possible emergence of a third species, not yet given a taxonomic classification but referred to as the “Denisovans”.  the scientist working on this say there is a genetic connection between these Dennis opens and modern-day Homo sapiens in the Far East. See thearticle in our NEWS section,”Neanderthals in the News”

The journal Science in its September 22, 2011 issue  has two articles discussing the possibility of at least two separate waves of migration across Asia, based on the DNA analysis of a small sample of hair first recovered from an aboriginal Australian a century ago.  Danish researchers Morten Rasmussen et al., in an article entitled “An Aboriginal Australian Genome Reveals Separate Human Dispersals into Asia” state

“We present an Aboriginal Australian genomic sequence obtained from a 100-year-old lock of hair donated by an Aboriginal man from southern Western Australia... We detect no evidence of European admixture and estimate contamination levels to be below 0.5%. We show that Aboriginal Australians are descendants of an early human dispersal into eastern Asia, possibly 62,000 to 75,000 years ago. This dispersal is separate from the one that gave rise to modern Asians 25,000 to 38,000 years ago. We also find evidence of gene flow between populations of the two dispersal waves prior to the divergence of Native Americans from modern Asian ancestors. Our findings support the hypothesis that present-day Aboriginal Australians descend from the earliest humans to occupy Australia, likely representing one of the oldest continuous populations outside Africa.”

Read the Rasmussen paper. Additionally, Science writer Ann Gibbons comments.

Thus, the Danish researchers posit two widely separated waves of migration comprising the eastward flow of Out of Africa II. Strictly speaking, they have identified two distinct genetic strains of our Homo sapiens ancestors, out of what most likely were many small bands moving across the landscape in an uncoordinated manner, some pausing, some moving on and the overall migration spanning tens of thousands of years.