yes, the appearance of a defect in the lactose digestion switch which in most animals turns off not long after the animal no longer needs it. for cats that's about 6 months, for humans it's about 8 years. but something like 70% of the human population has this gene and so we can tolerate lactose.

i believe it provide a massive evolutionary advantage to adopting domesticated ruminants, sheep, goats, cows and buffalo, in addition to eating their meat, and the uses of their bones and horns, the milk was also good, especially if fermented, and people who were able to do this had a much more stable food supply than hunters.

there also seems to be some kind of connection between milk and stature because the two average tallest nationalities are dutch and bosnian, and the bosnians are probably the most skilled at making cheese in the balkans, on par with the dutch.