Why and when was lactase persistence selected for? Insights from Central Asian herders and ancient DNA

The genetic adaptation of humans to the consumption of animal milk is a textbook example of gene-culture coevolution. Taking advantage of the accumulated ancient DNA data, this Unsolved Mystery article explores where and when lactase persistence emerged. The mutation rapidly spread throughout Eurasia between 4000 and 3000 BP, but if Asian herders managed to culturally adapt to milk consumption, then why have Europeans genetically adapted at all?