melanistic

Melanistic is an adjective used to describe organisms with unusually dark pigmentation due to increased production of melanin. Melanistic individuals have darkened skin, fur, feathers, or scales compared with typical members of their species. The trait is usually inherited and can occur across many animal groups; the opposite condition is albinism or leucism, which produce reduced or patchy pigmentation.

Melanism arises from changes in the melanogenesis pathway, often involving higher activity of the pigment-producing cells (melanocytes) and greater deposition of eumelanin. In many species, melanism is controlled by genetic variation at one or a few loci; in others it reflects polygenic regulation. In some taxa, the melanistic allele is dominant to the non-melanistic allele, while in others it is recessive. A well-known example is industrial melanism in the peppered moth, where a melanistic form increased in polluted environments due to camouflage against darkened surfaces.

The occurrence of melanism is documented in a broad range of animals, including mammals (such as black panthers), birds, reptiles, and insects. Melanistic coloration can influence ecological interactions, affecting camouflage, thermoregulation, mate choice, or signaling. Changes in environmental conditions and predation pressures can shift the relative fitness of melanistic individuals, contributing to evolutionary dynamics such as balancing selection or local adaptation.

In humans, melanism is rarely used as a clinical term; pigmentation variation is typically described more broadly as variation in skin, hair, and eye color, with many genes contributing to phenotype.