Sunday, November 24, 2013

Upper Palaeolithic Siberian genome reveals dual ancestry of Native Americans

Maanasa Raghavan, Pontus Skoglund et al.

There has been a lot of discussion on this recently announced paper.  First, I will say that I think the title is a little unfortunate and I am surprised that Nature let this one get by them.  We don't really know how many migrations into the Americans there were.  We also don't have a good understanding of back migrations from Beringia into Eurasia.  Many hunter gatherers were migratory and highly mobile groups, so I really disagree with the "dual ancestry of Native Americans" phrase in the title.

Beringia was a huge area, now submerged, 20,000 thousand years ago.  It would have supported animal and human diversity.  The paper I posted a few days ago on The Black Dog at the River of Tears myth well illustrates that migrations in Siberia, Beringia and into the Americans were comprised of people of different backgrounds and cultures.

That being said, I think the result is interesting in that it shows that people carrying both Y-chromosome R and mtDNA U were present in Beringia during the last Ice Age.  It's likely that the boy from which the main sample was taken, had freckles. 

The link with this sample and paleo Amerindian populations is also interesting, but it should be said that many more ancient DNA samples of Ameridian, Beringian, and Eurasian populations would be needed to understand the timing and dynamic of these population movements.

One further effect of having only one reliable ancient DNA sample is that the sample in this paper is likely subject to genotyping error.  That's according to Joe Pickrell who developed the software package Treemix, as shown in this Twitter exchange:

The comment refers to the long arm of the Siberian sample in the Treemix diagram in the paper.

When I hear geneticists who are expert in the field discussing the source of error in a paper, and they are clearly unsure of the source of error, it's a concern that the conclusions of the paper title are overstated.

There is probably additional error because the sample is old.

I don't have much to say except that I wish the genetics community would do a more considered job conveying the limitations of these results to the curious public.


terryt said...

"so I really disagree with the 'dual ancestry of Native Americans' phrase in the title".

The 'dual' in the title doesn't refer to the number of migrations but to the two populations that mixed before the Americans arrived.

I agree with joe that all populations have admixed but I disagree to the extent that I don't believe such admixing has been confined to just the last 20,000 years. In fact it seems to go at least as far back as to when H. erectus first left Africa. see Dienekes:

Marnie said...

Yes, admixing hasn't been confined to the last 20,000 years. I'm tired of reading about "Interbreeding with Neanderthals", "Interbreeding with Denisovans", "Interbreeding with the unknown mystery guy related to Denisovans", like it was a novelty. It certainly generates a lot of press every time one of these prima donas gets a moment in the spotlight to talk about "interbreeding". Let's face it, people had and have sex! And sometimes, they had and have sex with the guy with the big nose and the different skin color in the next valley. Who cares?! Some of these guys are like children, gleeful every time they get a chance to have a conference that lets them talk about INTERBREEDING. No wonder the public, and even the scientific community, is confused.

Regarding this paper specifically, we're talking ONE workable ancient DNA sample here. Also, the "modern" comparison populations in the Americas are limited. I'll be more interested once we approach something like ten geographically distributed ancient DNA samples in each of Siberia and the Americans. Until then, I guess the feeding frenzy will continue, and I'm not just talking about the lay public.

In particular, David Reich's statement that this MA1 sample might be "the missing link" is truly regrettable. As a professor at Harvard, you'd think he would at least try to convey to the public that real scientists no longer construct hypotheses from single data points or very limited data sets, especially regarding a topic that is politically and ethically fraught. Furthermore, a "missing link" statement would lead the public to think that Amerindians are a deeply separated population from Eurasians, which they are not.

For the record, I wouldn't be surprised at all if five or ten years down the road it turns out to be true that populations closely related to Ice Age Europeans were one of the early founding populations that crossed into the Americas. Frankly, having grown up in Canada close to many First Nations people, I've always thought that at least in Canada, many of my native compatriots looked somewhat like Europeans. But then again, native peoples to my eye always seemed to look inhomogeneous.

Out of respect, First Nations people are entitled to a well constructed, considerate and detailed account of their history. They should be the first to speak and should be included in the scientific process as well as the announcement of the results.