Implications of genetic variation within and between human populations

Human variation is extensive both within and between populations. This variation affects all traits, including the susceptibility to disease and responses to the environment. For social and political reasons, we tend to think of our species or our own national population as being divided into meaningful groups variously called by such terms as races, or ethnic groups, and there is often an implicit assumption that these groups are relatively homogeneous within and very different between. Examples are given to show that there are major differences in the frequency of genetic susceptibility to various diseases between some such groups, but that the amount of variation among individuals is extensive even within such groups. Population subdivision can be useful for studying disease, but human variation is a general phenomenon tied to groups via their population and geographic history, not value-based categorical differences.