User:Jay.LovesBio03/sandbox

Selective Shadowing

Selective Shadowing is ideally one of the evolutionary theories of aging which reveals that selection of an individual generally decreases once they essentially pass the sexual mature phase. As a result, this forms a shadow without the account of sexual fitness, which is no longer considered as an individual ages. Essentially this supports the idea that the force of natural selection declines as a function of age, which was first introduced by Peter B. Medewar and J.B.S Haldane. "The key conceptual insight that allowed Medawar, Williams, and others, to develop the evolutionary theory of aging is based on the notion that the force of natural selection, a measure of how effectively selection acts on survival rate or fecundity as a function of age, declines with progressive age."

Medewar developed a model that highlights this, showing the decrease in the survival rate of a population as an individual ages, however the reproduction rate stays constant. The reproduction probability typically peaks during sexual maturity and decreases as an individual ages, while the rest of the population decreases with age as they enter the selection shadow. The model also supports Medewars' theory that due to dangerous and unpredicted conditions in the environment such as diseases, climate changes and predators, many individuals die not too long after sexual maturation. Consequently, the probability of an individual surviving and suffering from age related effects is relatively low. In the same way, many beneficial mutations are selected against if they have a positive effect on an individual later on in life. For instance if a beneficial or deleterious mutation occurs only after an individual's reproductive phase, then it will not affect fitness, which therefore can not be selected against. Subsequently, these later mutations and effects are considered to be in the "shadow region" of selection.