Genetic variation, lactose tolerance

| Biology
While nearly all children are able to digest milk, a large fraction of adults lose their ability to process lactose (milk sugar) as they age (lactose intolerance). However, in many cultures (e.g., the Masai, dairy is a major part of the diet, so being able to consume milk is an obviously desirable adaptation, or rather four adaptations.

In this week's Nature Genetics (behind paywall, this post based on the Science summary above). Tishkoff et al. report on a study of African populations finding three novel mutations that allow the digestion of lactose (add this to a previously known mutation found in Finns). As with altitude adaptation, we see that there's been a remarkable amount of separate adaptation to the same problems in different human populations.