In biology, races are distinct populations within the same species with relatively small morphological and genetic differences.
The populations are ecological races if they arise from adaptation to different local habitats or geographic races when they are geographically isolated.
If sufficiently different, two or more races can be identified as subspecies, which is an official biological taxonomy unit below 'species'.
If not, they are called races, which means that a formal rank should not be given to the group, or taxonomists are unsure whether or not a formal rank should be given.
According to Ernst Mayr, "a subspecies is a geographic race that is sufficiently different taxonomically to be worthy of a separate name"