Eight thousand years of natural selection in Europe
The arrival of farming in Europe around 8,500 years ago necessitated adaptation to new environments, pathogens, diets, and social organizations. While indirect evidence of adaptation can be detected in patterns of genetic variation in present-day people, ancient DNA makes it possible to witness selection directly by analyzing samples from populations before, during and after adaptation events. Here we report the first genome-wide scan for selection using ancient DNA, capitalizing on the largest genome-wide dataset yet assembled: 230 West Eurasians dating to between 6500 and 1000 BCE, including 163 with newly reported data. The new samples include the first genome-wide data from the Anatolian Neolithic culture, who we show were members of the population that was the source of Europe's first farmers, and whose genetic material we extracted by focusing on the DNA-rich petrous bone. We identify genome-wide significant signatures of selection at loci associated with diet, pigmentation and immunity, and two independent episodes of selection on height. [. . .]On the presence of the "East Asian" EDAR variant in Scandinavian hunter-gatherers:
Our sample of 26 Anatolian Neolithic individuals represents the first genome-wide ancient DNA data from the eastern Mediterranean. Our success at analyzing such a large number of samples is likely due to the fact that at the Barcin site–the source of 21 of the working samples–we sampled from the cochlea of the petrous bone 9 , which has been shown to increase the amount of DNA obtained by up to two orders of magnitude relative to teeth (the next-most-promising tissue) 3 . Principal component (PCA) and ADMIXTURE 10 analysis, shows that the Anatolian Neolithic samples do not resemble any present-day Near Eastern populations but are shifted towards Europe, clustering with Neolithic European farmers (EEF) from Germany, Hungary, and Spain 7 (Fig. 1b, Extended Data Fig. 2). Further evidence that the Anatolian Neolithic and EEF were related comes from the high frequency (47%; n=15) of Y-chromosome haplogroup G2a typical of ancient EEF samples 7 (Supplementary Data Table 1), and the low F ST (0.005-0.016) between Neolithic Anatolians and EEF (Supplementary Data Table 2). These results support the hypothesis 7 of a common ancestral population of EEF prior to their dispersal along distinct inland/central European and coastal/Mediterranean routes. The EEF are slightly more shifted to Europe in the PCA than are the Anatolian Neolithic (Fig. 1b) and have significantly more admixture from Western hunter-gatherers (WHG), shown by f 4 -statistics (|Z|>6 standard errors from 0) and negative f 3 -statistics (|Z|>4) 11 (Extended Data Table 3). We estimate that the EEF have 7- 11% more WHG admixture than their Anatolian relatives (Extended Data Fig. 2, Supplementary Information section 2).
We find a surprise in six Scandinavian hunter-gatherers (SHG) from the Motala site in southern Sweden. In three out of six samples, we observe the haplotype carrying the derived allele of rs3827760 in the EDAR gene (Extended Data Fig. 5), which affects tooth morphology and hair thickness and has been the subject of a selective sweep in East Asia 24 , and today is at high frequency in East Asians and Native Americans. The EDAR derived allele is largely absent in present-day Europe except in Scandinavia, plausibly due to Siberian movements into the region millennia after the date of the Motala samples. The SHG have no evidence of East Asian ancestry 4,7 , suggesting that the EDAR derived allele may not have originated not in East Asians as previously suggested 24 . A second surprise is that, unlike closely related western hunter-gatherers, the Motala samples have predominantly derived pigmentation alleles at SLC45A2 and SLC24A5.Polygenic selection on height in Europe:
We also tested for selection on complex traits. The best-documented example of this process in humans is height, for which the differences between Northern and Southern Europe have driven by selection 25 . To test for this signal in our data, we used a statistic that tests whether trait-affecting alleles are both highly correlated and more differentiated, compared to randomly sampled alleles 26 . We predicted genetic heights for each population and applied the test to all populations together, as well as to pairs of populations (Fig. 4). Using 180 height-associated SNPs 27 (restricted to 169 where we successfully targeted at least two chromosomes in each population), we detect a significant signal of directional selection on height (p=0.002). Applying this to pairs of populations allows us to detect two independent signals. First, the Iberian Neolithic and Chalcolithic samples show selection for reduced height relative to both the Anatolian Neolithic (p=0.042) and the Central European Early and Middle Neolithic (p=0.003). Second, we detect a signal for increased height in the steppe populations (p=0.030 relative to the Central European Early and Middle Neolithic). These results suggest that the modern South-North gradient in height across Europe is due to both increased steppe ancestry in northern populations, and selection for decreased height in Early Neolithic migrants to southern Europe. We do not observe any other significant signals of polygenetic selection in five other complex traits we tested: body mass index 28 (p=0.20), waist-to-hip ratio 29 (p=0.51), type 2 diabetes 30 (p=0.37), inflammatory bowel disease 21 (p=0.17) and lipid levels 16 (p=0.50).