Whole genome sequencing (WGS) studies in humans––such as the 1000 Genomes Project, which was completed last year––have contributed to a catalog of genetic variation and genomic regions that have allowed humans the ability to adapt (genetically) to diverse environments (diet, predators, weather/climate). However, existing genetic data are often constrained by several factors––including limited breadth of population sampling and low-coverage data (in which each region of the genome is sequenced only a few times, leading to high error rates and missed variants). To address this issue, the three attached publications are able to show that new information be inferred by collecting high-coverage sequence data for individuals from more than 270 populations across the globe. By studying all the genetic diversity within and between these populations, … these groups of scientists can tackle many questions about The Great Human Diaspora.
The high-resolution portrait of human genetic diversity afforded by these studies allows new inferences to be made about our migration Out-of-Africa. There are currently two conflicting models for such human dispersal.
The first hypothesizes a single event that occurred around 40,000–80,000 years ago. Under this scenario, all present-day non-Africans trace their ancestry to a single population.
In contrast, the multiple-dispersal model proposes that an initial migration out of Africa occurred as early as 120,000–130,000 years ago, culminating in the peopling of southeast Asia and Australasia––possibly via a southern migration route along the coastline of the Arabian peninsula and the Indian subcontinent. This early dispersal was followed by a second migration from Africa, through the Levant, which resulted in the peopling of mainland Eurasia.
The first full-length article (p 201) shows that indigenous Australians, New Guineans and Andamanese are not derived from substantial ancestry (i.e. an early dispersal of modern humans). Instead, their modern human ancestry is consistent with coming from the same source as that of other non-Africans.
The 2nd article (p 207) suggests that Aboriginal Australians and Papuans diverged from Eurasians 51,000–72,000 years ago, following a single Out-of-Africa dispersal, which subsequently admixed with archaic populations. They also report evidence of selection in Aboriginal Australians potentially associated with living in the desert.
The 3rd article (p 238) reports evidence of a ‘genetic signature’ in present-day Papuans––suggesting that at least 2% of their genome originates from an early and largely extinct expansion of anatomically modern humans (AMHs) out of Africa. Together with evidence from the western Asian fossil record and admixture between AMHs and Neanderthals predating the main Eurasian expansion, these findings contribute to the mounting evidence for the presence of AMHs out of Africa earlier than 75,000 years ago.
Nature 13 Oct 2o16; 538: 201–206 & 207–214 & 238–242 [3 articles] and 179–180 [News-N-Views editorial]