Cochran/Harpending on Proto-Indo-European expansion

Their book (The 10,000 Year Explosion: How Civilization Accelerated Human Evolution) hasn’t yet been released, but much of it is now readable on Google Books. Here is Cochran and Harpending’s take on the spread of Indo-European:

Milk and the Kurgans

Improved variants of the Kurgan hypotheses fit many facts, but what they don’t do is explain why the Proto-Indo-Europeans expanded at the expense of neighboring peoples [. . .]

We suggest that the advantage driving those Indo-European expansions was biological–a high frequency of the European lactose-tolerance mutation (the 13910-T allele). The usual story about lactose tolerance is that it’s the result of a cultural innovation, the domestication of cattle. That innovation led to selection for a new mutation that extended lactase production into adulthood. But there’s more to the story.

Initially, selection favored individual carriers of the lactose-tolerance mutation, but the mutation was rare and had little social effect. Cattle were used for plowing and pulling wagons, for their beef, and as a source of secondary products like leather and tallow. But when the lactase persistence allele became common, so that a majority of the adult population could drink milk, a new kind of pastoralism became possible, one in which people kept cattle primarily for their milk rather than for their flesh. This change is very significant, because dairying is much more efficient than raising cattle for slaughter: It produces about five times as many calories per acre. Dairying pastoralists produce more high-quality food on the same amount of land than nondairy pastoralists, so higher frequencies of lactose tolerance among Indo-Europeans would have caused the carrying capacity of land to increase–for them.

Source:
Cochran/Harpending on Proto-Indo-European expansion
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