Tuesday, February 19, 2013
Ancient Amerindian-like admixture in Europe - something doesn't add up
It seems quite certain now that all Europeans carry non-trivial ancient admixture from somewhere east of the Urals. We mostly share this genetic component with South Amerindians, but also with Siberians and East Asians. However, possibly because of its age, the precise levels of this influence across Europe are difficult to measure, and it's not yet clear who brought it to Europe and when.
The mystery deepened recently when it was shown by Kamberov et al. that Europeans lack a ~30,000-year-old, East Asian-derived variant of the EDAR gene which appears at high frequencies in all East Asian and Amerindian populations, and is also present in groups with well documented minor East Asian and Amerindian ancestry. For more background on that see this post at Gene Expression.
So something definitely doesn't add up. Perhaps the analyses showing Amerindian-like admixture in Europeans are flawed? Or maybe this EDAR mutation is actually much younger than 30,000 YBP, and the eastern groups that apparently migrated to Europe came at a time when it didn't exist or was still very rare?
Then again, maybe Europeans don't carry this mutation because by and large we don't have East Asian admixture? In other words, perhaps the mysterious eastern component shared by Europeans, Amerindians and East Asians came from a now extinct population in Siberia? If so, this component might have been picked up by the (East Asian EDAR carrying) ancestors of Amerindians as they moved into the Americas. In fact, perhaps whoever carried this component blocked the entry of any (East Asian EDAR carrying) East Eurasians proper into Europe at a critical time when population densities in West Eurasia were very low?
So the other thing I'm getting at is that Amerindians and East Asians might be ancient hybrid groups, just like Europeans and South Asians. Indeed, David Reich has made some comments to that effect, and it seems we might soon see a paper on the topic.
In any case, what is certain is that we're still in for some major surprises when it comes to our deep genetic ancestry. That's because no matter how many statistically sound studies come out showing signals of various types of prehistoric admixture in Europeans and others, only ancient DNA from C14 dated remains can ultimately verify and explain such results.
Gene Expression: Is Girls’ Generation the outcome of the Pleistocene mind?
Yana G. Kamberov et al., Modeling Recent Human Evolution in Mice by Expression of a Selected EDAR Variant, Cell, Volume 152, Issue 4, 691-702, 14 February 2013, 10.1016/j.cell.2013.01.016
Europeans are a three-way mix, with a whopping 20-40% ancient North Asian ancestry
ADMIXTURE and STRUCTURE tests aren’t formal mixture tests