dimorphism

Dimorphism is the condition of two distinct forms, morphs, or states within a group. In biology, it most often refers to sexual dimorphism, the systematic differences between males and females of a species in size, coloration, ornamentation, or behavior. Such differences arise from genetic sex and hormonal regulation and can reflect divergent reproductive roles, mating strategies, or ecological pressures. Typical examples include larger body size in males of many mammals, elaborate plumage in male birds, or specialized structures such as antlers or manes. In humans, dimorphism manifests in characteristics such as body mass, fat distribution, voice pitch, and skeletal features.

Dimorphism also occurs beyond primary sexual divergence. Some organisms are dimorphic in life cycle or physiology, alternating between two distinct morphs in response to environmental cues. Dimorphic fungi, for instance, switch between yeast-like and filamentous forms depending on temperature or nutrient conditions; this switch is relevant to pathogenesis in several species, such as Histoplasma capsulatum and other medically important fungi.

In plants, two floral morphs within a species, or heterostyly, are described as floral dimorphism. Such arrangements can influence pollination efficiency and outcrossing.

Dimorphism can be a shorthand for any two-form system in biology or life sciences, distinguishing two discrete phenotypes within a single species or population. It is related to but distinct from polymorphism, which refers to more than two morphs.