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Antagonistic pleiotropy hypothesis


The antagonistic pleiotropy hypothesis was first proposed by George C. Williams in 1957 as an evolutionary explanation for senescence.Pleiotropy is the phenomenon where one gene controls for more than one phenotypic trait in an organism. Antagonistic pleiotropy is when one gene controls for more than one trait where at least one of these traits is beneficial to the organism's fitness and at least one is detrimental to the organism's fitness. The theme of G.C. William's idea about antagonistic pleiotropy was that if a gene caused both increased reproduction in early life and aging in later life, then senescence would be adaptive in evolution. For example, one study suggests that since follicular depletion in human females causes both more regular cycles in early life and loss of fertility later in life through menopause, it can be selected for by having its early benefits outweigh its late costs.

Antagonistic pleiotropy is one of the several reasons evolutionary biologists give for organisms never being able to reach perfection through natural selection. Antagonistically pleiotropic genes are the explanation for fitness trade-offs. This means that genes that are pleiotropic control for some beneficial traits and some detrimental traits; thus, if they happen to persist through natural selection, this will prevent organisms from reaching perfection because if they possess the benefits of the gene, they must also possess the imperfections or faults. An example of this would be female rodents that live in a nest with other females and may end up feeding young that are not theirs due to their intense parental drive. This strong parental drive will be selected for, but the organisms will still make the mistake of feeding young that are not theirs and mis-allocating their resources.

Antagonistic pleiotropy has several negative consequences. It results in delayed adaptation, an altered path of evolution, and reduced adaptation of other traits. In addition, the overall benefit of alleles is cut down significantly (by about half) by pleiotropy. Still, antagonistic pleiotropy has some evolutionary benefits. In fact, the conservation of genes is directly related to the pleiotropic character of an organism. This implies that genes that control for multiple traits, even if the traits have different implications for the organism's fitness, have more staying power in an evolutionary context.


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