Looking for Evidence of Antagonistic Pleiotropy in Human Data
The dominant view of the evolution of aging is that it emerges from what is known as antagonistic pleiotropy, a term used to describe a mechanism that is initially helpful but later harmful. Mutations that help early life reproductive fitness will be selected even if they cause later harm, as a greater chance of earlier reproduction tends to win out over a greater chance of sustained reproduction over time. Natural selection thus tends to produce biological systems that invest little in long-term maintenance and sustainability. Aging is the result.
In 1957, evolutionary biologist George Williams proposed that genetic mutations that contribute to aging could be favored by natural selection if they are advantageous early in life in promoting earlier reproduction or the production of more offspring. Researchers have now tested the Williams hypothesis using genetic, reproductive, and death-registry information from 276,406 participants in the UK Biobank database. They found reproduction and lifespan to be genetically strongly negatively correlated, meaning that genetic mutations that promote reproduction tend to shorten lifespan.
In addition, individuals carrying mutations that predispose them to relatively high reproductive rates have lower probabilities of living to age 76 than those carrying mutations that predispose them to relatively low reproductive rates, according to the study. However, the authors caution that reproduction and lifespan are affected by both genes and the environment. And compared with environmental factors - including the impacts of contraception and abortion on reproduction and medical advances on lifespan - the genetic factors discussed in the study play a relatively minor role, according to the authors. "These results provide strong support for the Williams hypothesis that aging arises as a byproduct of natural selection for earlier and more reproduction. Natural selection cares little about how long we live after the completion of reproduction, because our fitness is largely set by the end of reproduction."