A clustering of populations that does correspond to classical continental "races" can be acheived by using a special class of non-functional DNA, microsatellites. By selecting among microsatellites, it is possible to find a set that will cluster together African populations, European populations, and Asian populations, etc. These selected microsatellite DNA markers are not typical of genes, however, but have been chosen precisely because they are "maximally informative" about group differences. Thus, they tell us what we already knew about the differences between populations of the classical "races" from skin color, face shape, and hair form. They have the added advantage of allowing us to make good estimates of the amount of intermixture that has occurred between populations as a result of migrations and conquests.
The every-day socially defined geographical races do identify groups of populations that are somewhat more closely similar to each other genetically. Most important from the standpoint of the biological meaning of these racial categories, however, most human genetic variation does not show such "race" clustering. For the vast majority of human genetic variations, classical racial categories as defined by a combination of geography, skin color, nose and hair shape, an occasional blood type or selected microsatellites make no useful prediction of genetic differences. This failure of the clustering of local populations into biologically meaningful "races" based on a few clear genetic differences is not confined to the human species. Zoologists long ago gave up the category of "race" for dividing up groups of animal populations within a species, because so many of these races turned out to be based on only one or two genes so that two animals born in the same litter could belong to different "races."