Many species of living things comprise numbers of populations which may be dispersed geographically and among varying ecological niches. To impart order to the subdivisions within a species, biologists have used several terms such as subspecies, race and population to classify the various groupings of communities that make up a species. Classically, the differences among the races in a species have been identified by their morphology, that is, their observable physical structure. Race is a biological concept. Races are recognized by a combination of geographic, ecological and morphological factors and, since the 1970s, by analyses of the distribution of gene frequencies for numbers of essentially non-morphological, biochemical components. The biological concept of race, as just sketched, has been applied to the living populations of the human species. The race concept can be applied to modern humans, even when one uses the most modern analytical procedures of population geneticists, and such application has been found of heuristic value.