Thursday, October 1, 2015
Near Eastern admixture in Yamnaya: a couple of graphs + some ideas
Update 05/10/2015: Yamnaya's exotic ancestry: The Kartvelian connection
The Afanasievo and Yamnaya samples published to date are remarkably homogeneous. Hopefully the bar graphs below, based on a couple of my recent ADMIXTURE runs, illustrate this well enough.
The Near Eastern-related ancestry proportions among the Yamnaya individuals do appear to rise steadily from early Yamnaya to late Yamnaya/early Catacomb. But the ancestral components remain the same, and if the increase in the Near Eastern-related admixture is real, the process is very subtle.
What this suggests to me is that groups of a southern provenance - in all likelihood Neolithic farmers seeking new land - arrived somewhere on the Pontic-Caspian steppe very early, perhaps even during the Early Neolithic, to eventually blend with local foragers. That's because the basic Yamnaya genotype had to have existed before the Yamnaya or pre-Yamnaya ancestors of the Afanasievo nomads set off on their 2000 km trek to the Minusinsk Basin in South Siberia, probably around 3,300 BC.
No doubt, the mixing didn't stop after the initial farmer/forger admixture event, and this is probably why the Near Eastern-related ancestry proportions rise gradually throughout the Yamnaya period. Indeed, considering the high mobility of Bronze Age steppe pastoralists, it's likely that long distance trade, alliances and marriages resulted in the genetic homogenization of vast stretches of Eastern Europe during their reign.
In this analysis I used samples from the Allentoft et al., Haak et al. and Lazaridis et al. datasets, all of which are publicly available. The latter two are found at the Reich Lab site here.