In biology, a deme is a term for a local population of polytypic species that actively interbreed with one another and share a distinct gene pool. When demes are isolated for a very long time they can become distinct subspecies or species. The term deme is mainly used in evolutionary biology and is often used as a synonym for population.
In evolutionary computation a "deme" often refers to any isolated subpopulation subjected to selection as a unit rather than as individuals.
A deme in biological evolution is conceptually related to a meme in cultural evolution.
Examples
Various populations of gorillas can be understood by their geographical separation and have been assessed to determine distinct and disjointed gene pools. The polar bear, Ursus maritimus, is understood to have 19 identifiable demes, even though their circumpolar distribution allows some interchange among the demes.