The short stature of rain-forest dwellers such as the pygmies of central Africa, for example, appears not to be the product of a single derived allele for shortness carried by virtually everyone in the population. Instead, dozens of gene variants that slightly decrease height have each become slightly more common, and it is their total effect that results in the group's dramatically shorter stature.
"Adaptations to the environment absolutely do occur," said Joseph K. Pickrell, a graduate student at the University of Chicago.
SHOOT: I can vouch for the lack of diversity in East Asia having lived for 4 years in the Far East. Everyone looks like everyone else, and even the Japanese closely resemble the Koreans, and the Koreans the Chinese, the Chinese the Mongols, the Tibetans and Philippinos the Indians (well, sort've), the Indians the Arabs etc.