"Great Surprise"—Native Americans Have West Eurasian Origins.Oldest human genome reveals less of an East Asian ancestry than thought.
Nearly one-third of Native American genes come from west Eurasian people linked to the Middle East and Europe, rather than entirely from East Asians as previously thought, according to a newly sequenced genome.
Putting the Research in ContextRaghavan's research did not appear in a vacuum. It adds another detail to a broad scientific understanding of the timing and route our ancestors took as they colonised the globe. The common ancestors of all humans lived in sub-Saharan Africa. They began migrating "out of Africa" about 80,000 years ago and by about 50,000 years ago had colonized Western Asia, India and Southeast Asia and Australia (Fig.1). Eastern Asia was colonised by people derived from this southern migration event. By about 40,000 years ago people arrived in Europe and Central Asia via a northern route, finally reaching the Americas between 15 and 25,000 years ago.
|Fig.1. Major routes and timing of human colonisation of the world |
(Wellcome Trust, www.sanger.ac.uk)
|Fig. 2. The extent of human colonization of the world 25,000 years ago |
and the location of Raghavan's Siberian sample.
The major finding of the study is that the Siberian individual is not closely related to East Asians and much more closely related to Native Americans (red dots). In addition, this Siberian appears to be related to people now living in Europe and Western Asia (yellow, light blue-green dots). This suggests that this Siberian individual's ancestors had migrated from Western Eurasia into Siberia, but when they arrived they did not mix very much with Asian populations living further east. Consequently, when some of this Siberian's descendants migrated on to the Americas, they didn't carry many DNA markers found in East Asian populations.
Another way of describing the results of the study is shown in Fig. 4 below. All Eurasians and Native Americans descend from people who lived in West Asia (near modern day Afghanistan and Pakistan) about 50,000 years ago (see also Fig. 1.). These people carried with them large numbers of DNA markers that can be defined as West Asian. When the ancestors of the Siberians and Europeans/Middle Easterners migrated away from each other, both groups carried the same set of West Asian (blue) DNA markers with them. This is why the Siberian individual carried DNA markers also found in Europeans and Middle Easterners. They shared common ancestors about 15,000 years earlier (50,000 years ago).
However, once they became separated from each other, each group began to accumulate DNA markers that were unique to each group. This is indicated by the green (Eur/ME) and purple (Siberian) shading on the tree (Fig. 4). Once the Siberian groups encountered East Asians some of their DNA lineages (red) also entered Siberian populations, and some of these DNA markers found their way to the Americas.
|Fig. 4. Origin of DNA markers in Native Americans and some Eurasian populations |
and the approximate timing of their occurrence