People in Europe are adapted to drink milk as adults

(a) Frequency in Europe of lactase persistence, the expression of the lactase enzyme in adults. (b) Frequency in Europe of the T variant in the lactase gene that appears to control lactase persistence.

[(a) Adapted from Y. Itan et al., BMC Evolutionary Biology 10, 2010, 36. (b) Adapted from A. Beja-Pereira et al. Nature Genetics 35, 2003, 311-313]