Years and years ago, when I was a vegetarian, I would hear from pro-vegan/vegetarian sources that adult humans weren't meant to drink milk. I've always had a weak spot for cheese and dairy products in general, so this kind of convention wisdom made me feel guilty for diverting some poor calf's sole form of nourishment into cottage cheese, yogurt and brie.
But now I don't have so guilty. The NY Times has an interesting article on how four different human groups independently evolved the ability to digest milk. Swedes and the Dutch are uniformly lactose tolerant, but the new news is the discovery of pastoral groups in Africa who also developed lactose tolerance.
"Genetic evidence shows that the mutations conferred an enormous selective advantage on their owners, enabling them to leave almost 10 times as many descendants as people without them...The survival advantage was so powerful perhaps because those with the mutations not only gained extra energy from lactose but also, in drought conditions, would have benefited from the water in milk."
