Nature has in interesting article on Neolithic dairying, lactose intolerance, cheese, yogurt, and the spread of genes that allow for lactose digestion. The ability to digest milk in adulthood—called lactase persistence—is less than 40% in Greece and Turky, but higher than 90% in the UK and Scandinavia.
During the most recent ice age, milk was essentially a toxin to adults because — unlike children — they could not produce the lactase enzyme required to break down lactose, the main sugar in milk. But as farming started to replace hunting and gathering in the Middle East around 11,000 years ago, cattle herders learned how to reduce lactose in dairy products to tolerable levels by fermenting milk to make cheese or yogurt. Several thousand years later, a genetic mutation spread through Europe that gave people the ability to produce lactase — and drink milk — throughout their lives. That adaptation opened up a rich new source of nutrition that could have sustained communities when harvests failed.