Sex - Sexual Dimorphism

Sexual Dimorphism

Many animals and some plants have differences between the male and female sexes in size and appearance, a phenomenon called sexual dimorphism. Sex differences in humans include, generally, a larger size and more body hair in men; women have breasts, wider hips, and a higher body fat percentage. In other species, the differences may be more extreme, such as differences in coloration or bodyweight.

Sexual dimorphisms in animals are often associated with sexual selection – the competition between individuals of one sex to mate with the opposite sex. Antlers in male deer, for example, are used in combat between males to win reproductive access to female deer. In many cases the male of a species is larger than the female. Mammal species with extreme sexual size dimorphism tend to have highly polygynous mating systems—presumably due to selection for success in competition with other males—such as the elephant seals. Other examples demonstrate that it is the preference of females that drive sexual dimorphism, such as in the case of the stalk-eyed fly.

Other animals, including most insects and many fish, have larger females. This may be associated with the cost of producing egg cells, which requires more nutrition than producing sperm—larger females are able to produce more eggs. For example, female southern black widow spiders are typically twice as long as the males. Occasionally this dimorphism is extreme, with males reduced to living as parasites dependent on the female, such as in the anglerfish. Some plant species also exhibit dimorphism in which the females are significantly larger than the males, such as in the moss Dicranum and the liverwort Sphaerocarpos. There is some evidence that, in these genera, the dimorphism may be tied to a sex chromosome, or to chemical signalling from females.

In birds, males often have a more colourful appearance and may have features (like the long tail of male peacocks) that would seem to put the organism at a disadvantage (e.g. bright colors would seem to make a bird more visible to predators). One proposed explanation for this is the handicap principle. This hypothesis says that, by demonstrating he can survive with such handicaps, the male is advertising his genetic fitness to females—traits that will benefit daughters as well, who will not be encumbered with such handicaps.

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Other articles related to "sexual dimorphism, sexual, dimorphism":

Richard J. Smith (anthropologist) - Selected Recent Publications
... Leigh) "Sexual dimorphism in primate neonatal body mass." Journal of Human Evolution 34 173-201 ... (1998) Statistics of sexual size dimorphism ... Cheverud) "Scaling of sexual dimorphism in body mass a phylogenetic analysis of Rensch's Rule in primates" ...
Sexual Selection In Human Evolution - Sexual Dimorphism - Sexual Anatomy
... The theory of sexual selection has been used to explain a number of human anatomical features ... when it is present in other primates, may be due to sexual selection by females looking for an honest advertisement of good health in prospective mates ... However, penis size may have been subject to natural selection, rather than sexual selection, due to a larger penis' efficiency in displacing the sperm of rival males during intercourse ...
Sexual Dimorphism - Fish
... Sexual dimorphism also occurs in hermaphroditic fish ... the size increase is due to a growth spurt at the time of the sexual transition or due to the history of faster growth in sex changing individuals ... case, females which change sex to males are larger and often prove to be a good example of dimorphism ...
Humans - Evolution of Monogamy in Humans - Evolutionary History of Human Monogamy
... are primarily based on the level of sexual dimorphism seen in the fossil record because, in general, the reduced male-male competition seen in monogamous mating results in reduced sexual ... the sexual dimorphism of Australopithecus afarensis, a human ancestor from approximately 3.9–3.0 million years ago, was within the modern human ... that this indicates monogamous mating in early hominids, the authors do say that reduced levels of sexual dimorphism in A ...
Mauritian Tomb Bat - Description - Sexual Dimorphism
... mauritianus does not display an abundance of visual sexual dimorphism concerning their size or coloration ...