Whenever the members of a group are more likely to mate inside the group than outside, the frequency of particular genetic markers within that group can become higher or lower. But natural selection can also be a factor. Adaptations to climate have to be superficial, because those are the parts of the body that are exposed to the outside world. New Guinea highlanders and sub-Saharan Africans are about as different from each other genetically as any human beings on earth. Yet they have physical similarities because of where they live, including dark skin to protect against the rays of the sun.
Biologists have several options in describing the variation they observe in people.
They can label an individual purely in geographic terms, based, for instance, on the distance he or she lives from the Equator. Or they can sort people entirely in terms of the genetic differences they find. Instead they tend to use the labels generated by our highly fractious culture, even though many of these labels have little to do with the underlying genetics. In this way biologists endow those differences with much more weight than they deserve. All rights reserved.