If you had milk with your coffee this morning, thank evolution:
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.
The remnants of that pattern are still visible today. In southern Europe, lactase persistence is relatively rare – less than 40 percent in Greece and Turkey. In Britain and Scandinavia, by contrast, more than 90 percent of adults can digest milk.