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Sunday, April 17, 2016

More on the loss of genetic diversity in the Americas after European discovery


A post that I wrote in July 2014 regarding the Loss of Amerindian genetic diversity post 1492, has now more evidence to support it, as shown by a paper by Bastien Llama et al., Ancient mitochondrial DNA provides high-resolution time scale of the peopling of the Americas Science Advances 01 Apr 2016:Vol. 2, no. 4, e1501385, DOI: 10.1126/sciadv.1501385.


The paper states that "As a result, our ancient mitochondrial data suggest that European colonization was followed by local mass mortality and extinction of lineages associated with major population centers of the pre-Columbian past. Our results contrast with previous observations that Native American genetic diversity has been temporally and geographically stable for at least the past 2000 years".


And has some interesting graphs showing the loss of lineages.


I disagree with the timeline and the Beringian standstill notion, but I must admit it is an interesting paper.


The following image, from the paper, shows the magnitude of this loss of diversity, but the magnitude is surely bigger as the sampling of archaic genomes is quite small: the paper only includes one (1) sample from the US and Canada, one from Northern Mexico (none from Yucatan or Central America, Venezuela, Guyanas, Colombia, Ecuador,Brazil, Southern Chile, Paraguay or Uruguay, and only 2 from Argentina, excluding Patagonia... (see Fig. S1 in the paper)


loss of amerindian genetic diversity
Fig. S6 in the Supplementary Materials of the paper. The Red lineages are extinct, the blue ones have survived. (this is one of 3 simulations in the Fig. all three are very similar.

Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2014 by Austin Whittall © 

2 comments:

  1. Marcelo BruyereApril 23, 2016 at 9:58 PM

    I think it is indeed an interesting paper. But, as you have rightly commented, the sampling space is somewhat limited and perhaps not so representative of some regions. I would add that the human fossil record in America (at least the certified one), which goes no further in dating than 10/11 Kya or so, surely places another limitation for this study.
    Anyway, it is a very respectable research in ancient DNA, matter in which, honestly, I am “less than” an amateur,.and therefore not capable to perform a proper critical judgement. Despite this, it really claryfies me on how lost are american ancient linneages,... and on how powerful can be this approach as a complement of a global study of our origins, in the case of having enough and reliable data.
    My complaints may be similar to yours, and are the timing of the events, and the conclusions that they (surely) will be tempted to arrive to...”now there is sufficient evidence that there is “nothing” in South America beyond the 14,5 Kya dating of Monteverde II”...
    Of course is not a surprise that this resulting human dispersal model would definitively exclude the well known non certified earlier archaeological sites.
    But, even seen from their conservative optics, that is to say, no previous inmigrations through Bering other than the described one, my modest opinion is that;
    -1) The timing of the events is extremely tight, only is enough for Monteverde II...and by means a very fast (and may be questionably fast) inmigration to the South which demanded not more than 1,4 Kya or so.
    -2) Unexpectedly (or perhaps not??) they leave no room for a very serious research, recently done by Tom Dillehay, precisely in the same place, Monteverde/Chinchihuapi, Chile, where he returned in 2015, and found in situ new archaeologycal evidence of human presence, that is conservatively dated to 18/19 Kya. The evidence shows ephemeral, but real at all, ocupation in these sites,...and is not to be denied, taking into account the rigourosity employed by the author and his team, and the extreme caution of his statements.

    So, It would be imprudent to draw “final conclusions” about early peopling (at least in South América) from this paper which, I agree with you, is a very interesting research.

    I include the link for the full paper, available free at PLOS ONE.
    http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141923

    Best regards
    Marcelo

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  2. AWApril 26, 2016 at 9:54 PM

    Thanks for your comment Marcelo. Indeed the "quick" push into South America and the rather "early" date for occupying the area is in my layman opinion, pushing things a bit too far.
    What if someone comes up with a site dated 30 Ky ago? The whole structure of all these papers would just tumble to the ground. It is very similar to physics in 1899. All was neat and tidy and then Planck came up with the quantum theory and Einstein tore down the ether hypothesis....

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