The difference.

First of a three-part look at modern genetics and what it can tell us about differences between population groups. This programme looks at racial variation, still a taboo subject because of the history of eugenics and racial discrimination. Scientists discuss how pure racial groups stabilised over time do not exist; for example, a black British man with African ancestry and a white British man share a common ancestor from a few thousand years ago. Yet differences do occur, such as a genetic mutation shared by 50% of east Asians that gives tham an extreme intolerance to alcohol. Other factors are involved, such as evolution due to adaptation to various environments. These have led to differences in skin colour and tolerance to heat and coldness.