European man perhaps not a Middle Eastern farmer

By Razib Khan | April 30, 2010 1:20 am

A few months ago I blogged a paper in PLoS Biology which suggested that a common Y chromosomal haplogroup, in fact the most common in Europe and at modal frequency along the Atlantic fringe, is not pre-Neolithic. Rather their analysis of the data implied that the European variants were derived from an Anatolian variant. The implication was that a haplogroup which had previously been diagnostic of “Paleolithicness,” so to speak, of a particular population may in fact be an indication of the proportion of Neolithic Middle Eastern ancestry. The most interesting case were the Basques, who have a high frequency of this haplogroup, and are often conceived of as “ur-Europeans,” Paleolithic descendants of the Cro-Magnons in the most romantic tellings. I was somewhat primed to accept this finding because of confusing results from ancient DNA extraction which implies a lot of turnover in maternal lineages, the mtDNA. My logic being that if the mtDNA exhibited rupture, then the Y lineages should too, as demographic revolutions are more likely to occur among men.

But perhaps not. A new paper in PLoS ONE takes full aim at the paper I blogged above. It is in short a purported refutation of the main finding of the previous paper, and a reinstatement of what had been the orthodoxy (note the citations to previous papers). A Comparison of Y-Chromosome Variation in Sardinia and Anatolia Is More Consistent with Cultural Rather than Demic Diffusion of Agriculture:

Two alternative models have been proposed to explain the spread of agriculture in Europe during the Neolithic period. The demic diffusion model postulates the spreading of farmers from the Middle East along a Southeast to Northeast axis. Conversely, the cultural diffusion model assumes transmission of agricultural techniques without substantial movements of people. Support for the demic model derives largely from the observation of frequency gradients among some genetic variants, in particular haplogroups defined by single nucleotide polymorphisms (SNPs) in the Y-chromosome. A recent network analysis of the R-M269 Y chromosome lineage has purportedly corroborated Neolithic expansion from Anatolia, the site of diffusion of agriculture. However, the data are still controversial and the analyses so far performed are prone to a number of biases. In the present study we show that the addition of a single marker, DYSA7.2, dramatically changes the shape of the R-M269 network into a topology showing a clear Western-Eastern dichotomy not consistent with a radial diffusion of people from the Middle East. We have also assessed other Y-chromosome haplogroups proposed to be markers of the Neolithic diffusion of farmers and compared their intra-lineage variation—defined by short tandem repeats (STRs)—in Anatolia and in Sardinia, the only Western population where these lineages are present at appreciable frequencies and where there is substantial archaeological and genetic evidence of pre-Neolithic human occupation. The data indicate that Sardinia does not contain a subset of the variability present in Anatolia and that the shared variability between these populations is best explained by an earlier, pre-Neolithic dispersal of haplogroups from a common ancestral gene pool. Overall, these results are consistent with the cultural diffusion and do not support the demic model of agriculture diffusion.

Their main trump cards seem to be that they used a denser set of markers, and, they claim they have a more accurate molecular clock. Ergo, in the latter case they produce a better time to the last common ancestor, which is twice as deep as the paper they’re attempting to refute. Someone like Dienekes or Polish Genetics can tackle the controversies in scientific genealogy here (I know Dienekes has a lot of interest in mutational rates which go into the molecular clock for these coalescence times). Rather, I would suggest that usage of Sardinians concerns me for an obvious reason: they’re genetic outliers in Europe. A lot of this has to do with being an island. Islands build up uniqueness because they don’t engage in the normal low level gene flow between adjacent populations because they’re…well, islands. You would know about Sardinia’s position because they’re one of the populations in L. L. Cavalli-Sforza’s HGDP sample and they show up in History & Geography of Human Genes as on the margins of the PCA plots. But here’s a figure from a more recent paper using a much denser market set, constrained to Southern European populations. I labelled some of the main ones so you’d get a sense of why I say Sardinians are outliers:
sardin

Over the two largest independent dimensions of genetic variation you can see a distribution from the southeast Mediterranean all the way to the northwest (in fact, the Basques are an Atlantic group). The Sardinians are out of the primary axis, and that’s why I say they’re an outlier. A few other European groups, like the Icelanders and Sami exhibit this tendency. As I suggested above I think the fact that the Sardinians are on an isolated island relatively far from the European and Africa mainland means that they’ll “random walk” in genetic variation space toward an outlier status naturally, just as the Icelanders have since the year 1000. So though I grant the authors their rationale for using the Sardinians as a reference against the Anatolian source population, the fact that we know that they’re peculiar in their variation in total genome content makes me wary of drawing too many inferences from their relationships to other groups where they are seen as representative of a larger set.

Citation: Morelli L, Contu D, Santoni F, Whalen MB, & Francalacci P (2010). A Comparison of Y-Chromosome Variation in Sardinia and Anatolia Is More Consistent with Cultural Rather than Demic Diffusion of Agriculture PLoS ONE : 10.1371/journal.pone.0010419

CATEGORIZED UNDER: Anthroplogy, Genetics, Science
MORE ABOUT: European Genetics
  • http://haquelebac.wordpress.com/2010/04/06/my-fossil-railroad/ John Emerson

    The actual science in this field is changing so fast that it’s very risky for historians (or prehistorians) to come to any general conclusions. This has been true in archeology for decades — for example, tree ring recalibration of carbon-dating destroyed the main premise of whole chapters of some books.

    On the other hand, prehistorians can’t just leave chapters blank. I suppose that the best anyone could do would be to present the most likely versions of each story, while also for each story indicating what kind of new evidence would confirm or disconfirm it. (You can also give the old stories that have been definitely disconfirmed, and say why).

    A case when old disproven stories are still floating around, even in educated circles, is Stonehenge. We can know for sure that it’s not Celtic or even Indo-European, but a century or more of Druid nostalgia has convinced people that it is. Likewise, it now seems impossible that the Stonehenge civilization diffused from the Egyptian pyramid-builder civilization, since they’re approximately contemporary. But again, there’s a lot of Egyptian lore, Hermes and Thoth, floating around. And “we don’t really know who they were or where they came from” is regarded as an unsatisfactory answer by most audiences.

    If this isn’t your primary area of study, if you’re not actually working in the field, it seems most productive to drop down ever 3 to 5 years and find out what the new consensus is and how it has changed. Which is only to say that this stuff drives me nuts. (What about them Tokharians?)

  • pconroy

    Razib,

    I agree, using Sardinians as a proxy for Western or Southern Europeans or anything else is very problematic!

    I still think the Out of the East Mediterranean is the most likely source for most modern European R1b and downstream Y-DNA. I had previously proposed a fast boat route, across the Mediterranean and then up the Atlantic fringe, all the way to Denmark. With another branch arriving via the Balkans through Central Europe.

    I also think it’s likely that the Southern branch may have moved across North Africa, and then up the Atlantic Fringe…

  • pconroy

    John,

    Newgrange in Ireland is arguably the oldest known pyramidal structure in the world – more here:
    http://en.wikipedia.org/wiki/Newgrange

    It is a solar observatory, and probably related to crop cycles and timing of sowing and harvesting, by an early agricultural people.


    The complex of Newgrange was originally built between c. 3100 and 2900 BC, meaning that it is approximately 5,000 years old. According to Carbon-14 dates, it is more than five hundred years older than the Great Pyramid of Giza in Egypt, and predates Stonehenge by about a thousand years, as well as predating the Mycenaean culture of ancient Greece

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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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