From a piece in the current issue of Science on recent statistical advances in detecting positive selection in human genes. The puzzle has/had been why we weren’t seeing more dramatic positive mutations that allowed humans to triumph over terrible troubles, whether diseases or otherwise.
Selection is not as sexy as you think. It’s not just about mass famines and the plague. It’s also about women who drank milk, gained a little more weight, and had seven kids to their neighbor’s six. That’s enough to have a huge effect over time.
Gibbons A. Tracing Evolution’s Recent Fingerprints. Science. 2010;329(5993):740. Available at: http://www.sciencemag.org/cgi/content/summary/329/5993/740.