Genetic Studies Reveal Diversity Of Early Human Populations – And Pin Down When We Left Africa

Genetic studies reveal diversity of early human populations – and pin down when we left Africa

Danielle Andrew 21 Sep 2016, 19:46

More migrations?

Following the move out of the continent, the pioneers must then have journeyed incredibly quickly to Australia. The Danish study, the most comprehensive analysis of Aboriginal Australian and Papuan genomes to date, is the first to really examine the position of Australia at the end of the migration.

They found that the ancestors of populations from “Sahul” – Tasmania, Australia and New Guinea – split from the common ancestor of Europeans and Asians 51,000-72,000 years ago. This is prior to their split from each other around 29,000-55,000 years ago, and almost immediately after the move out of Africa. This implies that the group of people who ended up in the Sahul split away from others almost as soon as the initial group left Africa. Substantial mixing with Denisovans is only seen in Sahulians, which is consistent with this early split.

Crucially, because the ancestors of modern-day Europeans and Asians hadn’t split in two at this point, we think that they must have still been somewhere in western Eurasia at this point. This means that there must have been a second migration from west Eurasia into east Asia later on. The Simons Genome Diversity Project study, by contrast, albeit with a far smaller sample of Sahulian genomes, found no evidence for such an early Sahulian split. It instead shows that the ancestors of East Asians and Sahulians split from western Eurasians before they split from each other, and therefore that Denisovan admixture occurred after the former split from each other.

A graphic representation of the interaction between modern and archaic human lines, showing traces of an early out of Africa (xOoA) expansion within the genome of modern Sahul populations. Dr Mait Metspalu at the Estonian Biocentre, Tartu, Estonia

Meanwhile, a third paper proposes an earlier, “extra” migration out of Africa, some 120,000 years ago. This migration is only visible in the genomes of a separate set of Sahulians sequenced as part of the Estonian Biocentre Human Genome Diversity Panel. Only around 2% per cent of these genomes can be traced to this earlier migration event, which implies that this wave can’t have many ancestors left in the present day. If true (the two other papers find little support for it), this suggests that there must have been a migration across Asia prior to the big one about 60,000 years ago, and that anatomically modern human populations left Africa earlier than many think.

Whatever the reality of the detail of the Out of Africa event, these studies provide some benchmarks for the timings of some of the key events. Importantly, they are also a huge resource of over 600 new and diverse human genomes that provide the genomics community with the opportunity for further understanding of the paths our ancestors took towards the Anthropocene.

 

George Busby, Research Associate in Statistical Genomics, University of Oxford

This article was originally published on The Conversation. Read the original article.

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