The Milk Curtain

h/t HBDChick: Yoko Satta and Naoyuki Takahata, the C to T mutation at rs4988235.

The two say this SNP flipped long ago, probably in Ukraine, which date they don't constrain well (21000 - 3000 BC). The new gene underwent Hard Sweeps in the Late Bronze Age, 1600 BCish. They note an earlier G to A at rs182549, which "hitchhiked" along with the milkmaids.

The move to milk strengthened the steppe, keeping other populations from challenging them similarly to Vikings versus the Skraelings. But didn't make them all-powerful: for one thing, proximity to livestock exposed them to diseases, here looking at the smallpox family. Conversely, as the steppe moved more to milk, it didn't need the large towns as seen in Iraq or, for that matter, the Neolithic Balkans; I imagine the cowboys just needed market-camps, which could be seasonal. This meant that those large rat-infested towns died out... and that the steppe populations, themselves, might be more vulnerable to plague on the rare event some visited what towns were left. So the steppe and the farm didn't encroach on each other.

Something changed over the sixteenth century BC, to change the Balkan / northern Mediterranean diet. Thera?