As with peacocks, roosters top are brightly colored to attract mates, while chickens middle are dully colored to protect the eggs and young effectively. The same is true of mallard ducks bottom. Though the large, twisted antlers of this buck may get it caught and hinder its survival, this risk is "worth it" evolutionarily, because the buck with the biggest antlers wins a mate, and the big-antler genes are passed on to his offspring.
Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with intersexual selectionand compete with members of the same sex for access to members of the opposite sex intrasexual selection. These two forms of selection mean that some individuals have better reproductive success than others within a populationeither because they are more attractive or prefer more attractive partners to produce offspring. The females then arrive and choose the males with the deepest croaks and best territories.
Sexual Selection I t was Charles Darwin who originally proposed that the so-called secondary sexual characteristics of male animals -- such as the elaborate tails of peacocks, bright plumage or expandable throat sacs in many birds, large racks in mooses, deep voices in men -- evolved because females preferred to mate with individuals that had those features. Sexual selection can be thought of as two special kinds of natural selection, as described below. Natural selection occurs when some individuals out-reproduce others, and those that have more offspring differ genetically from those that have fewer.
Sexual selectiontheory in postulating that the evolution of certain conspicuous physical traits—such as pronounced coloration, increased size, or striking adornments—in animals may grant the possessors of these traits greater success in obtaining mates. Mutual attraction between the sexes is an important factor in reproduction. The males and females of many animal species are similar in size and shape except for the sexual organs and secondary sexual characteristics such as the breasts of female mammals. There are, however, species in which the sexes exhibit striking dimorphism or physical difference.
Introduction Patterns Mechanisms Descent with modification Mechanisms of change Genetic variation Mutations The causes of mutations Gene flow Sex and genetic shuffling Development Genetic drift Natural selection Natural selection at work What about fitness? Sexual selection is a "special case" of natural selection. Sexual selection acts on an organism's ability to obtain often by any means necessary!
So far all of our discussions of selection have been without much regard for the sex of the individual under selection evolution of the sex ratio to can occur through selection for alleles in either males or females that favor the production of the rare sex. But just as with natural selection individuals may differ in their ability to reproduce, in sexual selection there can be differential reproductive success among individuals of the same sex and species. In order to mate, males need to gain access to females and vice versa, and not all individuals will be equally successful at this task.
In evolution, the selection of a mate based on secondary sex characteristics. Sexual selection is thought to lead distinct differences in the appearance of the two sexes within a species. For example, the tail of the male peacock may be the result of sexual selection.
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