Sexual dimorphism

Sexual dimorphism is a difference in appearance or other traits between males and females of the same species, beyond differences in their reproductive organs.

Sexual selection: Evolutionary change caused by differences in mating success among individuals. Competition for mates and mate choice can favor traits that differ between males and females.
Peacock: A male peafowl, notable for its large, colorful train of tail feathers. The peacock's elaborate train is a classic example of a male-biased ornament.
Charles Darwin: The English naturalist who developed the theory of evolution by natural selection. Darwin used differences between male and female animals to develop sexual selection.
Sexual monomorphism: A condition in which males and females of a species show little or no difference in a particular trait. It describes the opposite pattern: similar rather than distinct traits between the sexes.
Natural selection: Evolutionary change in inherited traits caused by differences in survival and reproduction. Differences between the sexes can evolve when traits affect survival or reproduction differently.
Anglerfish: A group of marine fishes whose species include males that become much smaller than females. Some anglerfish show extreme size differences and male attachment to females.
The Descent of Man, and Selection in Relation to Sex: Charles Darwin's 1871 book on human evolution and sexual selection. Darwin's book gave a systematic evolutionary account of many sex-specific traits.
Sexual polymorphism: The presence of multiple distinct forms within a sex or species, not necessarily divided by sex. Multiple forms can occur within one sex, unlike differences defined between sexes.
Sex hormones: Hormones, including testosterone and estrogen, that influence reproductive development and other bodily traits. Hormonal differences help produce sex-specific traits in many species.
Dioecy: A reproductive system in which individual plants bear either male or female flowers. Separate male and female plants can differ in growth, form, and resource allocation.

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