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April 13, 2017

The reality of cultural hitchhiking

Filed under: Anthroplogy,Cultural hitchhiking,Genetics,History — Razib Khan @ 2:55 pm

The figure to the left is from a paper, The mountains of giants: an anthropometric survey of male youths in Bosnia and Herzegovina, which attempts to explain why the people from the uplands of the western Balkans are so tall. Anyone who has watched high level basketball, or perused old physical anthropology textbooks, knows that average heights in the Dinaric Alps are quite high in comparison to the rest of Europe, matched only in the region around Scandinavia. The Dutch of late have been the world champions in height, and explanations such as recent selection and their high consumption of dairy products have been given. In this paper the authors point out that the people who live in the Dinaric uplands are not a population which consumes a inordinately high protein diet, at least in relation to their neighbors.

Rather, they suggest that the height of the people who reside in the Dinarics is due to a genetic factor. There is now good genomic evidence that selection accounts for at least some of the difference in height between Northern and Southern Europeans. That is, seems that there have been divergent pressures in these two locales, their genetic differences due to historical demography aside.

The exception to this north-south gradient is obviously in the Dinarics. Another way in which the Dinarics are exception is that it has the highest frequency of Y chromosomal haplgroup I. The other mode of haplogroup I is in Scandinavia. I1 is common among people who live in Sweden, while I2 among the peoples of the western Balkans. I has an interesting history because the vast majority of Mesolithic hunter-gatherer males in Europe belong to this haplogroup. It is very rare outside of Europe. This is in contrast to the other major European haplogroups, which are found outside of Europe at appreciable frequencies.

It is likely that I is indicative of a lineage which roots in Europe which go back to the late Pleistocene period after Last Glacial Maximum ~20,000 years ago. As the world warmed ~10,000 years ago small populations of hunter-gatherers rapidly expanded from their refuges and either most of the males were I, or in the drift process on the edge of the wave of advance I became very common. It is plausible that in terms of alleles which account for variation in height these hunter-gatherers were enriched for those conferring larger size. Cold weather populations tend to be larger. Additionally, they probably consumed a relatively diversified but high protein diet, allowing for greater median size than among farmers at the Malthusian carrying capacity.

But, there has been a lot of selection over the past 10,000 years, and I am skeptical that this correlation between I and height in Europe is anything but a coincidence. Rather, the phylogeny which I exhibits brings me to another issue which I think is not often highlighted: I1 in particular may have “hitchhiked” with the exogenous lineages such as R1b and R1a in early Indo-European society.

That is, in the patrilineal descent groups expanding across the landscape and monopolizing access to resources and mates, the non-invasive I somehow integrated themselves into the broader cultural complex, and partook in the plenty. Like R1b and R1a it exhibits a rake-like topology which suggests rapid recent expansion.

This would not be exceptional. The modern Russian state’s origins are in the polities created by Keivan Rus, who were famously Scandinavian. Rurik was by origin a Sweden, and his dynasty eventually came to encompass most of the eastern Slavic peoples, and rule over the Russian people and state until the 17th century. Because there were so any descendants of this dynasty it was possible to adduce its Y chromosomal haplogroup, N1c1. The kicker is that this is clearly a Finnic lineage, with the most recent evidence being that it is a remnant of a recent migration out of Siberia to the west. The implication here is that the direct male lineage of Rurik were assimilated into the Scandinavian culture and power structure, and were possibly chieftains of Finnic tribes somewhere along the Baltic littoral.

Another example is the House of Wessex. Alfred the Great is arguably the first true king of England. Here are the names of some of the earlier monarchs of the House of Wessex, Ceawlin, Cynric, and Cynegils. Even someone without a background in historical linguistics may be curious about whether these are Anglo-Saxons, and there is a line of thinking that perhaps the forebears of Alfred were British warlords, who “went Saxon,” in a fashion analogous to Gallo-Roman aristocrats who assimilated to Frankish-Germanic norms and forms in the 6th and 7th centuries in the Merovingian domains.

Overall what you see in the genetic data are many things, but rarely a straightforward story. Just as genes can impact culture (e.g., lactase persistence), so culture impacts the distribution of genes. Just as human polities are coalitions, so genetic lineages themselves in their distribution and evolutionary history exhibit fingerprints of these past socio-political events and ideas.

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