Humans show a degree of sexual dimorphism — males, on average, are larger than females. This is true for most mammalian species, but the situation is often reversed in other orders — in spiders, for example, the female is usually the larger sex. The origins of sexual dimorphism are not completely understood, but theoretically there is a link between low levels of dimorphism — species where the male and female are similar — and greater input into child rearing by the male. Sexual selection may also play a role. In many species males compete with males for the attention of females, who choose their mates.
Sexual dimorphism - Wikipedia
Any difference, morphological or behavioral, between males and females of the same species. In many animals, the sex of an individual can be determined at a glance. For example, roosters have bright plumage, a comb, and an elaborate tail, all of which are lacking in hens. Sexual dimorphism arises as a result of the different reproductive functions of the two sexes and is a consequence of both natural selection and sexual selection. Primary differences such as the structure of the reproductive organs are driven by natural selection and are key to the individual's function as a mother or father. Other differences such as the peacock's Pavo cristatus enormous tail are driven by sexual selection and increase the individual's success in acquiring mates. See Organic evolution.
Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. The condition occurs in many animals and some plants. Differences may include secondary sex characteristics , size, weight, color, markings, and may also include behavioral and cognitive differences. These differences may be subtle or exaggerated, and may be subjected to sexual selection. The opposite of dimorphism is monomorphism.
Somewhere in the deep, dark depths of the ocean a male anglerfish is hungry. He lacks the artificial, bioluminescent lure that females use to attract prey. This is a rather insignificant problem compared to the fact that he is incapable of digesting food.