NYT genetics reporter Nicholas Wade has a new article with the self-explanatory title "Human Culture, an Evolutionary Force," using good old lactose tolerance as an example. It features a picture of a beautiful Kenyan highland meadow that might make even me want to take up long distance running. (Kenyan herdsmen are sort of "horseless cowboys" who hunt down strays on foot, so distance running ability is a useful trait for them.)

One question is why favorable traits such as lactose tolerance often don't reach fixation.