DNA Hints at Earlier Human Migration Out of Africa –“Faded Signal Points to About 90,000 Years Ago”



Hints of an early exodus of modern humans from Africa may have been detected in living humans. Present-day people outside Africa were thought to descend from a group that left their homeland 60,000 years ago, crossing through Egypt into the Arabian Peninsula. Now, analysis of nearly 500 human genomes appears to have turned up the faded signal of an earlier migration of Homo sapiens that has all but vanished. So the genetic evidence has shown that every non-African alive today could trace their origins to this fateful dispersal, still holds.

Reporting in the journal Nature, Luca Pagani, Mait Metspalu and colleagues describe hints of this pioneer group in their analysis of DNA in people from the Oceanian nation of Papua New Guinea.

In order to reconcile the faint signature of an earlier migration out of Africa evidence may be found in people from Papua New Guineawith the genetic data from living populations, the prevailing view advanced by scientists was of a wave of pioneer settlement that ended in extinction.

But the latest results suggest some descendents of these pioneers survived long enough to get swept up in the later, ultimately more successful migration that led to the settling of Oceania. “The first instance when we thought we were seeing something was when we used a technique called MSMC, which allows you to look at split times of populations,” said co-author Dr Mait Metspalu, director of the Estonian Biocentre in Tartu, told BBC News. “All the other Eurasians we had were very homogenous in their split times from Africans.

“This suggests most Eurasians diverged from Africans in a single event… about 75,000 years ago, while the Papuan split was more ancient – about 90,000 years ago,” said first author Dr Luca Pagani, also from the Estonian Biocentre. “So we thought there must be something going on.”

It was already known that Papuans, along with other populations from Oceania and Asia, possess some ancestry from Denisovans, an enigmatic sister group to the Neanderthals. The researchers tried to remove this component, but were left with a third segment of the genome which was different from the Denisovan segment and the overwhelming majority which represents the main out of Africa migration 60,000 years ago.

“This third component had intermediate properties which we concluded must have originated as an independent expansion out of Africa about 120,000 years ago,” Dr Pagani told BBC News. “We believe this at least 2% of the genome of modern Papuans.”

More information: Luca Pagani et al. Genomic analyses inform on migration events during the peopling of Eurasia, Nature (2016). DOI: 10.1038/nature19792

The Daily Galaxy via BBC Science 

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