melanism

Melanism is the development of dark pigmentation in an organism, typically due to increased production or distribution of melanin in the skin, fur, feathers, or scales. It is the opposite of albinism, which involves a deficiency or absence of melanin and results in pale or unpigmented coloration.

Genetically, melanism typically arises from changes that affect melanocytes and the melanin synthesis pathway. In many animals, mutations in genes that regulate pigment production—such as those influencing the production of eumelanin—can convert lighter phenotypes to darker ones. In some species, melanism can be inherited as a dominant trait, while in others it may follow different inheritance patterns depending on the specific gene involved.

Ecologically, melanism can be adaptive in certain environments. Darker individuals may have improved camouflage on dark backgrounds or offer thermoregulatory or antimicrobial advantages in some conditions. A classic example is industrial melanism observed in the peppered moth (Biston betularia) during the industrial revolution, where darker forms became more common in polluted areas and declined when pollution lessened.

Melanism occurs in a variety of animal groups, including some mammals such as black panthers (melanistic leopards and jaguars) and various reptiles, birds, and insects. The trait is studied as an example of natural selection and rapid evolution in response to environmental change, illustrating how pigmentation can influence survival and reproductive success.