Evolution

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Theories of aging.

1. Rate of living : Based on metabolic rates of different animals. But disproved by bats that live longer and also have higher metabolic rates. Another examples is birds.

2. Wear and tear theory : Aging is caused by accumulation of damages to cells due to errors in translation, transcription and replication. Also accumulation of ROS as by product of metabolic reactions in the body. This means that the organisms have minimized the error rate and there is no variation left. But the fruit fly experiment disproved this theory. They were artificially selected for early fertility and late fertility. Those that reproduced later had higher survivorship. Hence, there is scope for variation and longevity has not maximized.

Evolutionary theories

1. Mutation accumulation theory : Deleterious mutations acts late in life as the selection pressure is low in late life. Eg. Late acting deleterious alleles are at higher frequency than early acting deleterious alleles. Inbreeding depression is caused by deleterious recessive alleles. Observed that inbreeding depression increases with age.

2. Antagonistic pleiotropy : Because natural selection is weaker late in life, alleles that enhance early-life reproduction may be favored even if they also hasten death. Eg. Early breeders in birds have smaller clutch size. They have greater life-time reproductive success. O and B fecundity. Early life B>O, late life O>B

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