Why does natural selection favor reproductive success rather than long life?

In the field of Darwinian medicine, natural selection is understood to shape organisms for maximum reproductive success rather than for optimal health or longevity. This occurs because genes that increase an individual's ability to reproduce tend to spread through a population, even if those same genes simultaneously decrease health or shorten the lifespan.1

This prioritization of reproduction over long life is driven by several evolutionary factors:

• Genetic Success: Natural selection favors traits that promote the propagation of an individual's genes. Because early reproduction allows genes to enter the gene pool sooner, there is often a selective advantage to reproducing early in life.23
• Trade-offs: Bodies are subject to engineering constraints and limited resources. An organism must balance the energy it devotes to growth, defense, and reproduction. Investing energy in bodily repair to extend life often comes at the expense of energy available for reproduction, creating a trade-off where reproductive output is prioritized.134
• Diminishing Returns: As an organism ages, its reproductive capacity typically declines. Consequently, natural selection exerts less pressure to maintain bodily integrity in later life, as the potential contribution to future generations is lower than it is during the peak reproductive years.4