Way back when, there were only western hunter-gatherers (WHG). These were replaced by farmers from the Levant (EEF: Early European Farmers). Later came a third group, who are most likely the group we know as the Indo-Europeans. They were themselves a mix of two more basic genepools, the WHG and the Ancestral North Eurasians (ANE) -- a group that roamed around Central Asia / Siberia, and contributed genes to the group that would eventually leave Asia and colonize the Americas.
Greg guesses that the Indo-European group could likely have come from the northern or northeastern Caucasus region, as folks there have the highest signal from that ANE genepool. That region has already been considered a likely homeland of the Indo-Europeans based on linguistic evidence.
So perhaps the Chechens and the Irish are more similar than we think, and not by accident?
I left several comments, which I'll copy and paste below in case you don't want to read through a long comment thread. They all pursue the approach of seeing genes, languages, myths, and visual icons as pieces in a larger population bundle. When a group is spreading its genes by moving into a region and displacing the locals, they also set down their language, myths, and icons. To a decent extent, anyway, and there's no way to know how far in any specific case without being curious and looking.
Key point: it's not only by one group adopting another group's language, myths, and icons that those could be spread.
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