Adaptivity and Senescence
An antagonistically pleiotropic gene can be selected for if it has beneficial effects in early life while having its negative effects in later life because genes tend to have larger impacts on fitness in an organism's prime than in their old age. An example of this is testosterone levels in male humans. Higher levels of this hormone lead to increased fitness in early life, while causing decreased fitness in later life due to a higher risk for prostate cancer. This is an example of antagonistic pleiotropy being an explanation for senescence. Senescence is the act of ageing in individuals; it's the failure over time of the individual's life processes by natural causes. Williams's theory has been the motivation for many of the experimental studies on the reasons for aging in the last 25 years. However there is more than one theory out there for aging. The competing model to explain senescence is Medawar's "mutation accumulation" hypothesis, saying that "over evolutionary time, late-acting mutations will accumulate at a much faster rate than early-acting mutation. These late-acting mutations will thus lead to declining viability and/or fertility as an organism ages."
Read more about this topic: Antagonistic Pleiotropy Hypothesis