What is a race? Ernst Mayr (1904–2005) distinguishes between species in which biological change
is continuous in space, and species
in which groups of populations with different character combinations are separated by borders. In the latter species, the entities separated by borders are geographic races or subspecies. Many anthropology textbooks describe human races as discrete (or nearly discrete) clusters
of individuals, geographically localized, each of which shares a
set of ancestors, and hence can be distinguished from other races by their common gene pool or by different alleles fixed in each.