Sexual Selection is categorized by individuals that mate and reproduce frequently make a substantial contribution to the gene pool of later generations. This type of selection favours the selection of any trait that influences mating success of the offspring. Sexual dimorphism as well as mating and courtship behaviours result from the differential reproductive success caused by the variation in the ability to obtain mates.
Traits favoured in sexual selection include sexual dimorphism and behavioural difference between the sexes. Sexual dimorphism is defined as the noticeable differences in physical appearances of males and females.
In terms of behavioural differences between the sexes, the most common forms of sexual selection result from female mate choice and male competitions. In most species, females choose males based on physical traits or behavioural traits. In other species, males are equipped with physical features that assist them in gaining control of area and defending that territory against other males. This territory provides an area to attract, and sometime detain females to mate with. Some traits are not produced by selective pressures from environmental conditions. Other traits produced by selective pressures, like sexual dimorphism, would be expected in both sexes. Some species produce traits that are beneficial for mating but detrimental to the survival of the species. This sexual diversity in not limited to animals.
The fiddler crab has an enlarged limb which gives him a physical advantage due to sexual dimorphism.
Penguins do not have noticeable sexual dimorphism. The male and female penguins look similar. A male has to drop a stone at the feet of a would be mate. If the stone is rejected, the penguin is male.
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