What does dimorphism mean?
Dimorphism refers to the existence of two clearly distinct forms of the same organism, substance, or structure. Its most familiar use is biological: sexual dimorphism describes systematic physical differences between males and females of a species beyond the reproductive organs themselves, such as the peacock's ornate tail compared with the peahen's plain plumage, or size differences in many mammals. The concept extends beyond sex-based differences to seasonal color variants, worker-and-queen castes in insects, and other paired forms within one population. In chemistry and mineralogy, dimorphism describes substances capable of crystallizing in two different structural forms, like calcium carbonate appearing as both calcite and aragonite. Derived from Greek roots meaning 'two' and 'form', the term is formal and almost entirely confined to scientific registers. Its adjective is 'dimorphic', and its broader counterpart 'polymorphism' applies when more than two forms occur. Understanding dimorphism offers insight into how evolution shapes variation within a single species.
nounThe occurrence of two distinct forms or morphs within a single species, population, or structure, such as male and female individuals differing in appearance. More generally, the condition of existing in or being divisible into two distinct forms.
- Biology: the existence of two distinct forms of individuals within one species, most commonly differences between males and females (sexual dimorphism), but also including seasonal, geographic, or caste-based variation.
- General/technical: the condition of occurring in or being representable by two distinct forms or phases, used in fields such as chemistry and crystallography.
"Sexual dimorphism is striking in peafowl, where the male's extravagant train contrasts sharply with the female's drab plumage."
"Researchers measured the degree of sexual dimorphism in the fossil skulls to infer social behavior."
"Calcium carbonate shows dimorphism, crystallizing as both calcite and aragonite."
Usually treated as an uncountable mass noun when referring to the general condition; the plural appears mainly when counting instances across different species or compounds.
"The survey catalogued dimorphisms across dozens of bird species."
In some deep-sea anglerfish, sexual dimorphism runs so extreme that the tiny male permanently fuses to the giant female — the word literally means 'two shapes'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dimorphism
Dimorphism comes from the Greek elements 'di-' meaning 'two' and 'morphē' meaning 'form' or 'shape', joined through the combining form '-ismos' denoting a state or condition; it was formed on the model of 'polymorphism', which entered scientific English earlier in the nineteenth century. It shares its root with words such as 'morphology', 'amorphous', and 'metamorphosis', all built on Greek 'morphē'. The term arose in nineteenth-century scientific usage as biologists and mineralogists needed precise language for two-form conditions.
Related word forms
How dimorphism is actually used
Dimorphism is a formal, technical term used chiefly in scientific writing — biology, crystallography, and chemistry — and rarely appears in casual conversation. In biology it most often appears in the fixed phrase 'sexual dimorphism'; outside that collocation it typically requires context indicating which two forms are meant. The adjective form is 'dimorphic' or 'dimorphous'.
Easily confused with dimorphism
Polymorphism refers to many distinct forms within a species or type, whereas dimorphism refers specifically to exactly two forms.