Trade-off mediated effects on the genetics of human survival caused by increasingly benign living conditions.

It is sometimes suggested that modern life, with its planned fertility and medically assisted compensation for genetic disadvantage, has greatly reduced the power of natural selection to produce significant further human evolution. However, this overlooks the very recent and dramatic changes that have occurred in the patterns of human mortality, driven by the development of increasingly benign living conditions. Where the genetics of survival are significantly influenced by life history trade-offs, as is now thought to be the case for ageing and longevity, a change in the environment can shift the optimal balance that was established through natural selection under previous conditions. We examine this possibility in the context of the dramatic recent change in the mortality pressure exerted by infectious disease using a model of a hypothetical immunogenetic trade-off that weighs survival against fecundity. Our results predict that such a change might have a significant effect on population genetics over relatively short-timescales, and they may also resolve the paradox of genes that impair fertility in present-day populations by showing how such genes might be a legacy from a powerful trade-off that has acted until very recently.