Admixture mapping in Northern Europeans?

By Razib Khan | September 19, 2013 7:46 pm

Dienekes has a post up highlighting a preprint out of Pontus Skoglund’s group. It is titled Ancient genomes mirror mode of subsistence rather than geography in prehistoric Europe. It doesn’t seem to be online (fingers crossed that it shows up linked at Haldane’s Sieve soon). In any case I am not surprised by the broad outlines of the thesis. And, it is not as if Skoglund’s group is the only one working in this area, I have suspicions that others are finding something very similar. These results out of Europe are probably reflective of the fact that much of the model in Peter Bellwood’s First Farmers is generally correct, the emergence of an agriculture revolution in a few select world societies produced a cultural and demographic revolution.

But one can take things too far, and I think Bellwood did. The results above, and elsewhere, also confirm that there was not total demographic replacement. In many regions the agriculturalists absorbed the hunter-gatherers. Using light coverage of whole genomes Skoglund’s group inferred that the farmers who arrived in prehistoric Europe from the Middle East seem to have contributed most of the ancestry of Southern Europeans, and also match nearly perfectly the genetic profiles of farming populations in Scandinavia. In contrast, ancient hunter-gatherers in Scandinavia and prehistoric Spain resemble contemporary  Baltic groups (e.g., Lithuanians, Finns, and Scanadinavians). Finally, they conclude that modern Scandinavians are slightly more close to ancient hunter-gatherers than the farmers. This implies substantial farmer admixture in demographic terms. The group notes that previous inferences of Middle Eastern admixture were compromised  by the fact that modern groups often exhibit African admixture. When you look only at the non-African portion, they are a much better proxy. One reason I am curious about the preprint in full is that I believe that even removing African admixture, one might be biased by selection of ‘reference’ populations. It seems likely that there were major eruptions from Arabia in antiquity and the medieval period (inferred by comparing religious isolates such as Arab Christians with their Muslim neighbors).

Setting aside that a two-way admixture seems unlikely to be the whole story*, it does offer up a way to explore an interesting question: on what sort of genes do hunter-gatherers and farmers differ? Specifically I’m wondering about utilizing admixture mapping. In Scandinavian populations regions of the genome where there are adaptations for farming are localized should be enriched for farmer ancestry, and vice versa for hunter-gathering. In the case of Northern Europeans farmers moved up latitudinal clines, and adapted to local conditions only halting.  This explains in part that it seems Iberia and parts of Western Europe have more farmer ancestry than regions of Northeast Europe which are closer to the original zone of expansion as the crow flies.  Not only did the hunter-gatherers have some cultural traits which conferred benefits in the deep north, but likely there were particular adaptations in these climes which aided their survival.

I understand that admixture mapping for populations which have mixed (and frankly were not that genetically different in the first place) may be difficult. But linkage disequilibrium based methods have been pushed much further back than I could have imagined, and it has been done with South Asians in regards to “Ancestral Northern Indian” vs. “Ancestral South Indian” ancestry and genetic functionality (specifically disease risk alleles).

* In addition, I am more skeptical of a simple demic diffusion model than I was in the past. I think there may have been multiple demographic pulses, followed by equilibration phases.

CATEGORIZED UNDER: Agriculture, History, Human Genetics
  • Charles Nydorf

    Its funny that hunter gatherer cultural traits are still with us in civilized societies. Many people still like to hunt, fish or just forage for wild plants. Cooking without pots as in a clam bake still has a lot of attraction. I like to have a conversation with people who like me retain a paleolithic cognitive style.

    • Elzbieta Dagne

      A hunter gatherer part would prefer us live in a country with a lots of free space, near a forest, walk a lot of foot, work as a freelancer and have lots of spare time … And also, you must have a passion for mushroom gathering!

  • http://blogs.discovermagazine.com Apple Pie

    If we moderns are a mix of these farmer + hunter types, then I am curious about the differences in social strategies + cognitive adaptations in HG vs Neolithic contexts.

    EO Wilson said that the most advanced eusocial insect societies usually involve symbiosis of multiple specialist types. In ants/termites this includes highly flexible workers cooperating with hypertrophic defense specialists.

    For humans (a tool using primate), the specializations will be more cognitive than physical. Not just “G” or general intelligence, but differentiated / mutually exclusive (in individuals) forms of cognition.

    Ex: the “autistic spectrum” ability to coldly follow isolated concepts with crystal clarity, versus the “social intelligence” of negotiating and understanding the subtler nuance of complex mass society. Or another ex: the cognitive/behavioral adaptations of a “dauntless warrior” versus a “sensitive social adapter.”

    Pop sci writers like Bellwood usually fail to notice this and glom everything together in blurry narratives about development of “the” modern cognitive/behavioral toolkit. But folklorically, cognitive “types” vary by culture/subculture (even today in America) and have difficulty communicating with each other sometimes (each type sees the other as “bad”). It would be illuminating to see a joint reading of EO Wilson “Sociobiology” (everything but the last chapter) together with Jonathan Haidt “The Righteous Mind” (for the human part).

    • http://blogs.discovermagazine.com Gene Partlow

      Agreed… To the extent that some recent studies suggesting
      actual brain tissue differences between so-called self-described conservatives and liberals (whatever that means) may hold up, it seems obvious to me that any adaptively successful human populations would have a rich psycho-social ‘tool-kit’ for encountering the usual slings-and-arrows. One can imagine the usefulness of having a partial hereditary basis for both conservative and liberal responses to very different survival scenarios in a
      population, over generations. Differentials along other behavioral axes would plausibly be important also.

  • Lank

    Were there really major expansions from Arabia in the medieval period? I know that in the recent Lebanese study, Christian Arabs actually had a higher “Arab” component than Muslims. Muslims had more African, which is why they pull toward peninsular Arabs in PCA plots. But I don’t know how the intermixture that followed the Arab conquest may have differed in other parts of West Asia.

  • GuestOfGuests

    “It seems likely that there were major eruptions from Arabia in antiquity and the medieval period (inferred by comparing religious isolates such as Arab Christians with their Muslim neighbors).”

    Well, it certainly seems likely.

    If you check Dienekes’ blog, he linked a recent study about Kuwait (Alsmadi et al 2013)… It basically confirms Moorjani et al 2011′s find that there’s been non-trivial, recent African admixture in Arabians.
    And the interesting part, is that the Palestinian samples included within the study have non-negligible amounts of African admixture, similar to “Kuwaiti 2″ and “Bedouin” samples (basically half of the “Kuwaiti 3″ samples’ African admix, so more or less similar to Yemeni Jews… There’s a clear pattern here)

    So yeah, the odds are growing in favour of a more Mediterranean-leaning (Cypriot-leaning? Sardinian-clining?!) pre-Islamic Levant… Either that, or a more West Asian/Anatolian-like Levant, which definitely makes sense given the region’s prehistorical (and historical) links to Anatolia and the Zagros (as well as the Caucasus).

    But much of it is still speculation, we need actual genome-wide studies about West Asian aDNA to settle up this issue (or, to be more precise, get to ask relevant questions).

  • andrew oh-willeke

    I seem to recall for a long time that the argument was between the 80% Paleolithic contribution camp and the 20% camp. It seems like the latter is closer to the mark than the former.

  • kiiski

    How does the spread of lactase persistence in Northern Europe fit in time-wise? Did the first farmers also bring the cattle?

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

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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