February 24, 2012

Late West European Neanderthals had very low matrilineal genetic diversity

According to the new paper, this diversity was lower than modern day Iceland, however it had been larger before 48,000 years ago.

Love Dalén et al., Partial genetic turnover in neandertals: continuity in the east and population replacement in the west. MBE 2012. Pay per view.

Abstract

Remarkably little is known about the population-level processes leading up to the extinction of the neandertal. To examine this, we use mtDNA sequences from 13 neandertal individuals, including a novel sequence from northern Spain, to examine neandertal demographic history. Our analyses indicate that recent western European neandertals (<48 kyr) constitute a tightly defined group with low mitochondrial genetic variation in comparison to both eastern and older (>48 kyr) European neandertals. Using control region sequences, Bayesian demographic simulations provide higher support for a model of population fragmentation followed by separate demographic trajectories in subpopulations over a null model of a single stable population. The most parsimonious explanation for these results is that of a population turnover in western Europe during early Marine Isotope Stage 3, predating the arrival of anatomically modern humans in the region.

Other sources: Pileta[es], NeanderFollia[cat].

I do not have access to the paper so I remain in doubt about the details, however I wonder if this genetic bottleneck or founder effect may be related to the formation of Chatelperronian culture (oldest dates (ref: direct download): Grotte du Renne since c. 52 Ka calBP, Roc de Combe since c. 49 Ka calBP). It'd be interesting to know how these Western Neanderthal individuals correlate with the cultural mosaic of the MP-UP transition period c. 50-35 Ka BP.

4 comments:

  1. Maju,

    I tried to post this @ Razib's - but that site currently doesn't work for me.

    I have a hard time with the authors' interpretation. It all hinges on a very small number of early western specimen, and their dating.

    If one believes the timing, there was an expansion of the tight group (blue in the figure) ~60,000ya. The other branches may have expanded as well - we have simply insufficient data prior to ~42,000ya.

    Now, all or nearly all of the finds of the tight group are dated to when AMHs were already present in the region. Since the expansion occurred beforehand, I don't see a bottleneck, but rather a very strong selection event. Could this group have had physiological features that spared them? Were they resistant to newly brought-in diseases?

    I also miss a discussion of the archeological context. Surely, instead of relying on the very few specimen we have, one should compare to known sites and occupation timings. IIRC, there indeed were expansions at some sites ~60,000ya and shortly before AMHs arrived.

    Interesting also that none of the tight group survived the Phlegraean Fields eruption...

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  2. "the Phlegraean Fields eruption... "

    What group? Isn't this eruption (the Campanian Ignimbrite one, right?) supposed to pre-date Vindija and the rest?

    "I also miss a discussion of the archeological context".

    Sure. I plan to write something but I haven't got time. I only got the paper yesterday, you know. ;)

    I was previously working on some MP-UP transition maps, which are almost finished in draft form, but again, I need some more time...

    ReplyDelete
  3. You may want to check this database (direct download, excel file), which was mentioned last year by Millán and came again to my attention recently thanks to Neanderthalerin and David.

    I mean in relation to the archaeological context.

    I am rather in agreement with what you say: it seems that Mousterian-Micoquian group might have expanded from Italy or the Balcans in NW direction, maybe in relation to the earliest Aurignacoid expansion (but without mode 4 tech, at least not these), replacing their predecessors.

    However I'd like to see data from South Iberian late Neanderthals, like those from Gibraltar, which may well belong to a different, older group (??)

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  4. Maju,

    Thanks for the link to the database. My main point was that one must be very careful with the interpretation of the data, because there is a strong ascertainment bias: the vast majority of specimen from which mtDNA has been extracted is of course the most recent material (<42kya). If, on the one hand, the analysis indicates a population expansion 60-50kya, but on the other hand we have almost no data from that time period nor from the time to 42kya, then we cannot say much about the makeup of the population during that time.

    A reasonable conjecture would be that all then existing branches expanded - because one that we have data from shows this pattern. Then, the only conclusion one is left with is that all but the "blue" branch vanished with the arrival of AMHs.

    As to the Campanian Ignimbrite deposits (~39kya), two of the Vindija samples seem to post date it, I guess for the remainder the age uncertainty is too large to say much.

    ReplyDelete

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