Population genomics: Human genomes across diverse populations inform migration out of Africa

High-quality genomes of individuals from more than 280 diverse populations around the world are reported in three papers published this week in Nature. The studies describe genetic diversity from typically understudied regions and together provide new insight into the migration of modern humans out of Africa.

The timing and route of human population expansion from our evolutionary birthplace in Africa to Europe, Asia and Oceania is hotly debated. Some models suggest that all present-day non-Africans can trace their ancestry back to a single population while others suggest that migration out of Africa took place in distinct waves at different times.

David Reich and colleagues report genome sequences of 300 people from 142 different populations usually under-represented in large-scale studies to describe a range of human variation. They find that the population that gave rise to all present-day humans began to diverge at least 200,000 years ago, and since then the accumulation of genetic mutations has accelerated by about 5% in non-Africans. The authors suggest a possible explanation for this could be that the time between generations decreased in non-Africans after separation, thereby increasing the rate of change in genetic material.

Eske Willerslev and colleagues sequenced the genomes of 83 Aboriginal Australians from across the Australian mainland and 25 individuals from the highlands of Papua New Guinea. The data, which represent the first comprehensive population-level whole-genome study of human genetic diversity in Australia, suggests that the ancestors of Aboriginal Australians and Papua New Guineans diverged from Eurasian populations between 51,000 and 72,000 years ago and reveals traces of genetic material from ancient humans such as Denisovans and an unknown hominin group.

Luca Pagani, Mait Metspalu and colleagues added 379 new genomes from 125 populations focused on European populations to an existing dataset and find that at least 2% of the genome of modern Papuans reflects ancestry from a distinct population that diverged from Africans earlier than Eurasians. This finding provides evidence for an early, distinct wave of human expansion out of Africa, approximately 120,000 years ago, that led to the peopling of Papua New Guinea.

“The high-resolution portrait of human genetic diversity afforded by these studies allows new inferences to be made about our migration out of Africa,” write Serena Tucci and Joshua Akey in an accompanying News & Views article. "Although these studies fill in some missing pieces in the puzzle of human history, many fascinating questions remain…to fully retrace the steps taken by our ancestors as they explored and colonized the world.”

doi: 10.1038/nature18299

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