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Sexual dimorphism
Sexual dimorphism in biology means that the male and the female of a species look noticeably different. The word comes from the Greek: di (two) and morphe (form).
The features that distinguish the two sexes of a species are called secondary sex characteristics. They are not directly part of the reproductive system.
The difference between sexes can include:
- Size: Males in some species have harems ('ownership' of a group of females). In this case the males are usually larger than the females, e.g. gorillas, lions. In some species the male is smaller.
- Sometimes, one sex has additional features : antlers of deer, breasts of women,...
- Hair quantity (e.g. the Gorilla)
- Teeth: Asian elephants: only the males have tusks. African elephant: both sexes have tusks. pigs and walrusses: the males have very pronounced canines
- Horns or antlers are often carried only by males.
- Colouring: sexual dimorphism in butterflies is common.
Sexual dimorphism may be the result of natural selection or more specifically sexual selection, that is, competition between members of the same species for reproduction: some traits would give an individual an advantage over its rivals in survival and reproduction.[1] More generally, sexual dimorphism is inherited, which means the differences between males and females have survival value.
Some animals show these differences only during mating season.[2] Deer shed their antlers and peacocks shed their tails out of season. This minimises the key disadvantage of sexual dimorphism, which is, it makes the male much easier to be seen by predators.
There is other polymorphisms.
Female (left) and male Argiope appensa spiders: the male is much smaller than the female