Different Neandertal strokes

By Razib Khan | March 21, 2011 11:38 pm

John Hawks, Europe and China have different Neandertal genes:

This is very striking. China and Europe by and large have different Neandertal-derived haplotypes. Haplotypes from Neandertals that are common in Europe — say, with more than two or three copies — are mostly rare in China. And vice-versa; haplotypes that are common in CHB are rare in CEU.

Why should this be? Green and colleagues…hypothesized an early population mixture of Africans and Neandertals in West Asia, before that population dispersed throughout the rest of Eurasia. This hypothesis was meant to explain why China and Europe have the same proportion of Neandertal genes.

I think that is also consistent with the fact that China and Europe have different Neandertal genes. If the population mixture was followed by substantial genetic drift as the West Asian population dispersed in different geographic directions, drift would randomly increase the frequency of some haplotypes in one direction, others in the other direction. Europe and China would end up with the same proportion of Neandertal ancestry, but it would be distributed very differently among loci.

Next, we’ll examine whether this pattern is the same for the rest of the chromosomes. Or maybe something even more interesting…

Guesses? I’m assuming it has something to do with adaptation.

MORE ABOUT: Neandertal

Comments (8)

  1. What about Papua New Guinea: does it have different Neanderthal genes, too? As for Amerindians, Green et al. didn’t even bother including them in the sample.

  2. “Guesses? I’m assuming it has something to do with adaptation.”

    Panadaptationist. ;

  3. The possibility of West Eurasian and East Eurasian populations admixing separately would be even more interesting, and would fit emerging evidence that there were probably multiple than one wave of pre-Neolithic human expansion in Asia, not all of which had West Eurasian counterparts (most notably the expansions that spread mtDNA macrohaplogroup M and Y-DNA haplogroup D did not have West Eurasian counterparts).

    While you could have a common set of Neaderthal genes from a single admixed population that then splits, the more time elapsed between the admixture events and the ultimate population split, and the larger the effective population sizes of the diverging populations at the time of divergence, the less likely the kind of distribution Hawks describes seems. If a single admixed population were a single population genetic population for several thousands years before dividing, the Neanderthal components would have reached very close to uniform distributions in the entire population – you’d need admixture to be something less than several hundred years old and quite small diverging effective population (closer to several hundred than ten thousand), or strongly endogamous tribal structures prior to divergence, to get the kinds of genetic drift effects Hawks is suggesting.

    There are lots of mechanisms that could keep the percentage of admixture similar without the source population being a common one. After all, the social structure of the modern human population and the Neanderthal populations would be very similar to each other in a two admixing population scenario, so the level of and nature of their interactions would have been similar, thus producing similar admixture percentages from independent events.

    In the same vein, assimilation patterns of immigrant Hispanics in the United States today are quite similar to the assimilation patterns of Irish and Italian immigrants a century and a half earlier.

    Also striking is the near absence of Neanderthal genes that are common in both Europe and China. This argues against adaptative value being important. Adaptive genes for modern humans in general would likely be high frequency in both populations. Whether there was one admixing population, or more than one, I would agree that Hawks is on target in suggesting genetic drift from the X chomosome data set as opposed to something else.

  4. AG

    Or Multiregionalism for neandertal also?

  5. gcochran

    “the less likely the kind of distribution Hawks describes seems”

    You’re wrong. This is exactly what you’d expect to see for neutral Neanderthal alleles. The overall amount of admixture does not change – law of large numbers – but the frequency of individual alleles drifts. Since the base frequency is only about 2.5%, most Neanderthal alleles drift to zero frequency, while a few drift to high frequency. If two populations have been separated for a long time, the high-frequency Neanderthal alleles in the two populations will mostly be different ones.

    This requires that the effective population sizes be small enough that drift matters, but that seems to have been the case for much of the period we’re talking about, considering the low population density of hunter-gatherers, nasty glacial climates, intertribal warfare, Triffids, etc. This drift effectively stops when populations become large, as they are today. Assuming that they stay large.

    The story would be quite different for Neanderthal alleles with a noticeable selective advantage.

  6. DK

    I’m assuming it has something to do with adaptation.

    Or with a lack of it.

  7. dave chamberlin

    Responding to #6 gchochran.

    The triffids would have eaten everybody if it wasn’t for those neanderthal alleles that made us a bit smarter. Oh wait a minute, that can’t be, we are all equal.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com


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