The Caucasus is a semipermeable barrier to gene flow
The scientists at the David Reich Lab are a clever bunch. But they're not always on top of things. And this can be a problem.
For instance, they fail to understand that the Caucasus is a semipermeable barrier that has effectively stymied human gene flow between Eastern Europe and West Asia through the ages.
Until they accept and understand this fact, they won't be able to accurately characterize the ancestry of the ancient human populations of the Pontic-Caspian (PC) steppe, including the Yamnaya people.
In turn, they also won't be able to locate the Indo-Anatolian homeland.
Now, the Caucasus isn't a barrier to gene flow because it's difficult to cross, and, indeed, many human populations have managed to cross it since the Upper Palaeolithic. As a result, the peoples of the North Caucasus are today genetically more similar to the populations of the Near East than Europe.
In fact, the clear genetic gap between most West Asian and Eastern European populations through the ages is actually caused by the extreme differentiation between the mountain ecology of the Caucasus and the steppe ecology of the PC steppe.
That is, the Caucasus is ecologically so different from the PC steppe that it has been practically impossible for human populations to make the transition from one to the other.
Indeed, it's important to understand that there's no reliable record of any prehistoric human population successfully making the transition from the mountain ecology to the steppe ecology in this part of the world.
In other words, contrary to claims by people like David Reich and David Anthony, there's no solid evidence of any significant prehistoric human migration from the Caucasus, or from south of the Caucasus, to Eastern Europe by hunter-gatherers, farmers or pastoralists.
But, you might ask, how on earth did the Yamnaya people get their significant Caucasus/Iranian-related admixture if not via a mass migration from the Caucasus and/or the Iranian Plateau, as is often argued by the above mentioned scholars and their many colleagues?
Well, obviously, the diffusion of alleles from one population to another can happen without migration. All that is needed is a contact zone between them.
The ancient DNA and archeological data currently available from the Caucasus and the PC steppe suggest to me that there was at least one such contact zone in this area bringing together the peoples of the mountain and steppe ecoregions. This allowed them to mix, probably gradually and over a long period of time, by and large without leaving their ecoregions.
Once the Caucasus alleles entered the steppe, they were spread around by local hunter-gatherers and pastoralists who were highly mobile and well adapted to the steppe ecology.
Someone should write a paper about this.
Dear David, Nick, Iosif...let's set the record straightUnderstanding the Eneolithic steppeMatters of geography