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15 Sep, 14 tweets

New genetics paper looking at how landscape has provided refuges within the Caucasus, preserving ancestral lineages and showing how geographic barriers are crucial to migration and community continuity.

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nature.com/articles/s4159…

One major reason the Caucasus are so important to geneticists is the provision of about half of the genetic make-up of the Yamnaya steppe herders, therefore of great importance to any understanding of Indo European history.

Broadly speaking the genetics of today's Caucasian people show deep continuity with the late Upper Palaeolithic and the widest levels of diversity exists across the Y chromosome distribution.

One hypothesis for understanding Caucasian gene flow is the suggestion that ancient refugia from the Upper Palaeolithic and Mesolithic account for the majority of group distinctions. The paper takes this as its working hypothesis.

DNA samples taken from 77 men from a wide array of linguistic and ethnic backgrounds. Only those with a continuity of three generations were considered for the study.

The test for genetic affinity between modern and ancient populations showed some clear results

1) the main ridge of the Greater Caucasus produced a southern Anatolian Laz population and a northern Balkar/Karachay/Chechen population with a distinct northeastern Tush/Khevsur population. The south showed greater internal affinity than the northern groups.

2) A general gradient appears between Levant-Anatolia and Siberian-European, with the modern Caucasian people belonging to the latter.

3) In general, modern populations had the deepest genetic affinity with those ancestral groups closest in space and time.

The authors built geographical models which accorded best with the genetics, taking into account the landscape and impassable or difficult features.

"Our results suggest that the current populations of the Caucasus bear detectable ancestry from Caucasian, Anatolian and Balkan hunter-gatherers. Caucasian hunter-gatherers (CHG) are the major gene contributors to the modern Caucasian populations"

It looks like CHGs survived the Last Glacial Maximum in the mountain refugia before new migrants arrived during the Holocene - Euros/Balkan HGs through the Plains and Anatolians from the south.

The Anatolian incomers also show signals of admixture with the Natufians and Atlas Mountain populations before entering the Caucasus.

The geographical models also confirmed the hypothesis that the Greater and Lesser Caucasus and Pontics were a major barrier to population dispersal, lining up with the gradients identified in the study.

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