Traditionally, subspecies are seen as geographically isolated and genetically differentiated populations. That is, "the designation 'subspecies' is used to indicate an objective degree of microevolutionary divergence" One objection to this idea is that it does not specify what degree of differentiation is required. Therefore, any population that is somewhat biologically different could be considered a subspecies, even to the level of a local population. As a result, Templeton has argued that it is necessary to impose a threshold on the level of difference that is required for a population to be designated a subspecies.

What are traditionally geographically isolated?