Within the same wave out of Africa (??), Aborigines diverged from Eurasians between 50,000 and 70,000 years ago

For anyone who has visited the Outback (sometimes seen also in cities), you know that Australian Aborigines appear “quite distinct” in appearance––often displaying blue eyes and blonde hair while having brown skin and small stature. They have long been cast as a people apart. In fact, in an Aboriginal Museum in Cairns, one can watch videos of early-20th-century films showing Australians hunting and shooting Aborigines, not unlike some hunters today would shoot deer and elk.

Although Australia is distant from the accepted origins of Homo sapiens in Southeast Africa, the continent is nevertheless home to some of the earliest undisputed signs of modern humans outside Africa. Aborigines have unique languages and cultural adaptations. Some researchers have proposed that ancestors of the Aborigines were the first modern humans to move in a migration Out of Africa––spreading rapidly eastward along the coasts of southern Asia––thousands of years before a second wave of migrants populated Eurasia.

This proposal has now been challenged by researchers analyzing whole genomes from Australia and New Guinea [see attached]. They conclude that, like most other living Eurasians, Aborigines descended from a single group of modern humans who migrated Out of Africa 50,000 to 60,000 years ago and then spread in different directions. Recent studies suggest that the vast majority of non-Africans alive today trace their ancestry back to a single Out-of-Africa event. Yet, the case isn’t closed. One study argues that an earlier wave of modern humans contributed traces to the genomes of people today populating Papua New Guinea.

And perhaps both sides are right. A decade ago, some researchers proposed the controversial idea that an early wave of modern humans left Africa more than 60,000 years ago via a coastal route. These people would have launched their migration from Ethiopia, crossing the Red Sea at its narrowest point to the Arabian Peninsula, then rapidly pushing east along the south Asian coastline––all the way to Australia. Some genetic studies, many on mitochondrial DNA (mtDNA) of living people, supported this hypothesis by indicating a relatively early split between Aborigines and other non-Africans.

However, analysis of whole genomes––the gold standard for population studies––has been scanty for individuals from many key parts of the world. Three large groups of geneticists independently set out to fill the gaps [see attached], adding hundreds of fully sequenced genomes from Africa, Australia, and Papua New Guinea to existing databases. Each team used complex computer models and statistical analyses to interpret the population history behind the patterns of similarity and difference in the genomes.

By comparing Aboriginal genomes to other groups, they conclude that Aborigines diverged from Eurasians between 50,000 and 70,000 years ago, after the entire group had already diverged from Africans. These data indicate that Aborigines and all other non-African people descended from the same Out-of-Africa sweep, and that Australia was initially settled only once––rather than twice, as some earlier evidence had suggested. Patterns in the Aboriginal DNA also point to a genetic bottleneck about 50,000 years ago: which resulted in the lasting legacy of the small group that first colonized the ancient Australian continent.

Science  23 Sept 2o16; 353: 1352–1354

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