The initial native Americans were quite inbred

From Science vol. 365 pp. 138, eaat 5447 pp.  1 —> 9 ’19  12 July ‘19

“Genetic studies of contemporary Indigenous people and ancient individuals from Asia and the Americas reveal an outline of the ancestry of the first humans to settle the Americas, providing age estimates for the timing of population contact, divergence, and migration. Studies of contemporary mitochondrial DNA (mtDNA) and Y-chromosome DNA lineages gave the first genetic insights into Indigenous American population history (6). These studies demonstrated that the ancestors of all contemporary Indigenous people had descended from only five maternal lineages (haplogroups A, B, C, D, and X) and two paternal lineages (haplogroups C and Q). These lineages also showed that the founding population came from Asia and experienced a severe genetic bottleneck, in which a small number of people with limited genetic diversity gave rise to all Indigenous people who occupied the continent before European arrival.”

Interesting that the authors of the papers discussed below didn’t know this (or weren’t telling) when I wrote them last December asking if there was limited genetic diversity in the ancestors of today’s native Americans (or Indians as they called themselves when we lived in Montana in the 70s and 80s).

 

Usually when I eMail the author(s) of a paper or a math book with a question or a comment I get a quick response.  My cynical wife says thing this is because mathematicians don’t have much to do.  Not so in this case. Hence the hopefully attention getting title of this post.

I refer to the following papers [ Cell vol. 175 pp. 1173 – 1174, 1185 – 1197 ’18 ]  Nature vol. 563 pp. 303 – 304 ’18,Science vol. 362 pp. 1128 eaav2621  1 –> 11 ’18 ] I’ve sent a bunch letters to the authors and have heard nothing back in a week.

So what is all this about?  It’s about population bottlenecks and founder effects in the ancestors of what are now called ‘native Americans’ — although while living in Montana from ’72 – ’87, if you called an Indian, a Native American, you would have received some strange looks.

I am not a population geneticist, so I wonder just how many people made it over the Bering land bridge during the last ice age, and just how genetically diverse they were.  Northern Siberia today is a rather forbidding place, and I doubt that hordes of genetically different people lived here.  I’m not sure how long the land bridge was open and how many people crossed it.

So modern native Americans may be quite genetically homogeneous.  How to tell?  This is where the papers come in.  They sequenced genomes from a variety of locations in the western hemisphere, all dying over a thousand years ago (before the Europeans came and interbred with them).  It seems that they have around 100 such genomes.

I wrote to ask how similar these genomes are.  No response.  Is it because the answer might be politically incorrect?

I don’t think the question is idiotic.  Possibly we don’t have enough genomes to make a sensible statement, but if they’re all really close (however defined) we could say something.

Anybody out there have any thoughts (or even better)  knowledge about these matters?

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Comments

  • Peter Shenkin  On July 16, 2019 at 4:41 pm

    No deep thoughts or deep knowledge, but that’s a really interesting article. I don’t know enough about the history of the the field to understand what the deviations from previous belief are. Many years ago, I recall Jared Diamond pooh-poohing some then fashionable conclusions that the settlement of the Americas could have occurred as long as 30k years ago, rather than the <20k years ago which was the contemporary mainstream belief, based on dating of the Clovis settlements. He viewed earlier dates as outlying results that may be hard to understand, but are unlikely to be real. This article is certainly in agreement with the classical thinking, with somewhat more specific, and somewhat later, dates. The genomic similarities are good to know, but if I had had to guess, I would have placed my bet on a small founding population, though I'd have been hard-pressed to define exactly what "small" means. The more ramified picture of when and among whom various gene flows and splits took place seem to be new in this article, but unsurprising, and I'm sure aficionados will have plenty of opportunity to question the details.

    You raise the question why you got no response from the authors of the earlier articles, perhaps because, concerning genetic diversity, "the answer might be politically incorrect." I don't know why they didn't respond, but I have to say I have trouble imagining any answer being politically incorrect. Is the new article's answer (closely related groups, small founding population) the politically correct or the politically incorrect one? I really have no idea.

  • NEIL  On July 16, 2019 at 5:51 pm

    The term ‘inbred’ will raise a few eyebrows. I think the geneticists prefer ‘limited genetic variability.’ As an aside, this is a very real issue facing cheetahs. A lack of variation in MHC was one suggested reason for a declining population (touched on in an old Sci Am article).

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