The great male migration

The Goldberg et al. preprint that I blogged about late last year has made it into PNAS under a different title and with a few other changes (behind a pay wall here). The authors added a couple of lines about R1a and R1b, which is awesome because I think these markers are crucial to the Indo-European homeland debate, and also made the change from "horse-driven chariots" to "horse-driven wagons", probably as a result of my comment at bioRxiv (scroll down here).

Based on archeological data, as well as ancient and modern Y chromosome data, the later migration from the Pontic-Caspian Steppe has also been hypothesized to be male-biased (5, 24–29). In particular, multiple large-scale studies of modern Y-chromosome data infer a rapid growth of R1a and R1b haplotypes ∼5,000 y ago (27–29). Similarly, Haak et al. (5) provide evidence that R1a and R1b were rare in central Europe before ∼4,500 y ago, but common soon thereafter. They also observe multiple R1b haplotypes in ancient Yamnaya individuals from the steppe. Populations in the Pontic-Caspian Steppe region, such as the Yamnaya or Pit Grave culture, are thought to have strong male-biased hierarchy, as inferred by overrepresentation of male burials, male deities, and kinship terms (26, 30). The region is a putative origin for the domesticated horse in Europe, and the culture is known for its use of horse-driven wagons, a potential male-biased mechanism of dispersal into central Europe (30).

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The signal of a large male bias holds when analyzing late Neolithic Corded Ware individuals and later Bronze Age Unetice individuals separately, with mean X-to-autosomal ancestry ratios in the two groups of 0.716 and 0.474, respectively. Ancestry and sex bias do differ between the groups, with a larger male bias and lower SP ancestry for the later Unetice, although the trend is not statistically significant (SI Appendix, Fig. S1B). Individuals from Bell Beaker archeological sites, a culture that overlapped with Corded Ware and Unetice but occurred over a wider geographic scale, show levels of X and autosomal ancestry suggestive of overall ancestry contributions and levels of sex bias that are similar to Corded Ware and Unetice, with mean X and autosomal ancestry of 0.28 and 0.56, respectively (SI Appendix, Table S7).

Goldberg et al., Ancient X chromosomes reveal contrasting sex bias in Neolithic and Bronze Age Eurasian migrations, PNAS, February 21, 2017, doi: 10.1073/pnas.1616392114

Update 15/03/2017: "Failure to Replicate a Genetic Signal for Sex Bias in the Steppe Migration into Central Europe"