In genetics, it refers to the co-existence of a number of distinctly different types in a population. An important category of discontinuous variation within species, it consists of two sorts: genetic polymorphism and non-genetic polymorphism, although in practice it is difficult to distinguish between them. An example of the former is human blood groups, and caste systems of social insects such as ants in the case of the latter
See Heterogeneity, Human Genome Project, Population (biology and ecology), Theory of balanced polymorphisms, Theory of natural selection