A form of genetic variation, specifically, a discontinuous variation that occurs within plant and animal species in which distinct forms exist together in the same population, even the rarest of them being too common to be maintained solely by mutation. The human blood groups are examples of polymorphism. In contrast, geographic races are not an example of polymorphism; nor is the diversity of height among humans, because height varies along a continuum and does not fall into distinct tall, medium, and short types.