Plows of the gods

How Europeans became Europeans is a big question, in large part because Europeans (i.e., “whites”) are still what an ideology in disrepute would term the herrenvolk of the world. But this reality, the truth of which sows discord in any discourse, does not need to negate the fact that the question itself is of interest, and today is eminently answerable. Europe has a long history of archaeology and its climate is mild-to-frigid in a manner which might aid in preservation of subfossils. For decades archaeologists have debated whether the ancestors of modern Europeans were farmers or hunters. It seems quite likely that the real answer is both, and, it’s complicated.

But the Gordian knot of history’s inscrutable veil is now be shredded by Thor’s hammer of Truth. More literally Pontus Skoglund has another paper out in in Science (how many times will I type that?), Genomic Diversity and Admixture Differs for Stone-Age Scandinavian Foragers and Farmers. If you don’t have academic access, the supplements are quite rich.

ancientDNAThe panel to the left shows the where and when of the samples. The key is that some of these are farmers and some of these are hunter-gatherers (as inferred by their cultural association). They’ve been examined before with more primitive techniques, but this latest paper ups the ante, even granting genomic coverage as relatively modest by current standards. The authors reiterated that there was a massive genetic difference between the first farmers who arrived in Sweden ~5,000 years ago, and a native hunter-gatherer tradition. The Fst was on the order of 0.05. To get a sense of scale the maximum Fst for modern Europeans is between Finns (a highly drifted group) and southern Italians (a highly admixed group with significant Near Eastern ancestry), at ~0.01. The Fst between modern Europeans and modern East Asians is on the order of ~0.10. In other words, two contemporaneous ancient populations in Sweden which were in near proximity for many generations had a genetic distance on the order of half the distance of Eurasia today. In fact this Fst is familiar to me. A few years ago at ASHG an Indian group had a poster which talked about the fact that coexistent South Asian groups (castes, jatis, etc.) within a region might have an Fst as incredibly high as…0.05! Obviously I’m not saying that ancient Sweden was characterized by caste, but I am asserting that genetic distinctiveness in Europe on the cusp of full agriculture within a local region probably mirrored modern India, where occupation and community identity are as informative as geography.

treemixSo why the huge genetic distance? The figure to the left gives a clue as to why. The farmers from Sweden, represented by Gokhem2, have more “hunter-gatherer” admixture than Otzi the Iceman. Ajvide58 has significant “Ancestral North Eurasian,” which is also found in the New World (Anzick1 is a Clovis individual from Montana). What is of note is that both the European farmers have a component with a red shading that has previously been termed “Basal Eurasian,” in that it forms an outgroup in the non-African phylogenetic tree to populations from West Eurasia, East Eurasia, and Australasia. Because it is such an outgroup it no doubt had a large genetic difference from the others, and a high Fst value. Even ~25% contribution, as in the case of Gokhem2, might have been enough to introduce enough diverged drift to generate a great deal of allele frequency difference.

pcMany of the results in this paper were prefigured earlier. For example, it turns out that modern Swedes are closer to the hunter-gatherers than they are to the farmers. The PC plot to the right has northern Europeans at the top and Middle Eastern populations at the bottom. To the right are Finnic groups, with the Sami off the chart (I reedited it). All the ancient hunter-gatherers are outside of the contemporary distribution. One thing to remember is that the ancient individuals were projected upon the variation of modern populations. Therefore I suspect this plot understates how distinctive the ancient groups were. Second, it seems likely that modern Finnic populations are relatively intrusive latecomers to the Nordic scene, as the ancient hunter-gatherers have no particular affinity for them. Rather, if there is one population which resembles the hunter-gatherers from Gotland it is Lithuanians. This is not surprising. I have always held that the last region of Europe to be touched by the farmers from the Near East was the eastern Baltic. It is somewhat ironic that this area, and the Lithuanians precisely, were the last continental Europeans to be Christianized in the 14th century.*

So we’ve established that modern Swedes, and therefore modern Scandinavians, are descended more from the hunter-gatherers than the farmers who brought agriculture to the north. But it is in the functional genome where there’s a twist on the story: the farmers may have looked physically more like modern Swedes than the hunters. That’s because at two SNPs which are fixed (in SLC24A5) or nearly fixed (in SLC45A5) in modern Europeans yield matches to the farmers and not the hunters. These two SNPs are among the strongest quantitative trait loci for pigmentation in Europeans. Without them it seems unlikely that the hunter-gatherers would have been recognized as what we’d term “white.” An immediate objection to this is that the ancient hunter-gatherers had a different genetic architecture for pigmentation, so that their lightening alleles were different. Perhaps, but observe that we’ve already stated that the preponderance of the ancestry of modern Swedes is from these hunter-gatherers, and from what we know the genetic architecture in this population is not particularly surprising. Substituting the ancestral allelic variant at this loci tends to make these individuals darker (that is, through mixed marriage with non-Europeans). One could construct more complex scenarios of gene-gene interactions, but I think at this point we know where the parsimony lay.

With the large genetic distance, as well as the fact that the hunter-gatherers exhibited minimal gene flow from the farmers, and, likely a very salient physical difference, it seems plausible that we have the ingredients for inter-group conflict or at least an uneasy coexistence. Though it seems unlikely that the story of Grendel is an allegory recollecting this far distant time, it might not be far off from the truth in terms of how the farmers and hunter-gatherers interacted. Eventually the two groups congealed, but it took thousands of years.

Finally, let’s get back to the truly exotic fact lodged within these new papers: that there was a group of Basal Eurasians. The Basal Eurasians were further from the hunter-gatherers of Europe than the hunter-gatherers of Europe were from the ancestors of Australians or East Asians. Like the “Ancient North Eurasians” it seems likely that this is a “ghost population,” with no modern exemplars. No doubt as I write this there are papers which are being written or conjectured as to their relationship to populations outside of Europe, as it seems that the Middle East is one area where a deeper probe of possibilities is necessary. But perhaps it is to this group of Basal Eurasians that we owe the innovation of agriculture? Like shadows in our past their cultural impact is strong, but their identity as a distinct people has been eroded away by thousands of years of admixture and the flux and flow of peoples.

Citation: Genomic Diversity and Admixture Differs for Stone-Age Scandinavian Foragers and Farmer, Pontus Skoglund, Helena Malmström, Ayça Omrak, Maanasa Raghavan, Cristina Valdiosera, Torsten Günther, Per Hall, Kristiina Tambets, Jüri Parik, Karl-Göran Sjögren, Jan Apel, Eske Willerslev, Jan Storå, Anders Götherström, and Mattias Jakobsson, Science, DOI:10.1126/science.1253448

* The Sami were Christianized later, but the Sami were not at all part of the European system, as the Lithuanians actually were. The Sami are analogous to various indigenous groups, or Jews. In Europe, but not of it.

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