Antagonistic pleiotropy

Antagonistic pleiotropy is the condition in which a single gene produces opposite fitness effects at different life stages or in different environments — typically beneficial early in life but deleterious later. The concept explains why deleterious late-acting genes persist in populations: natural selection is stronger on early survival and reproduction than on post-reproductive health, so genes that boost early fitness are maintained even if they accelerate senescence. This is not a genetic defect but a structural feature of genes as shared developmental resources, where the same molecular machinery cannot be simultaneously optimized for all phases of the life cycle. Antagonistic pleiotropy is one of two major evolutionary theories of aging, competing with the disposable soma theory which emphasizes energetic tradeoffs rather than genetic ones. See also pleiotropy and life history theory.