The cost of living longer

Sexual reproduction and the mixing of alleles that it entails boosts diversity, but also poses a dilemma for individual organisms. given that each organism has ultimately limited resources for reproduction, maintenance and immunity, the choice between fertility and long-term survival is one between two opposite poles of selection that operate across many animal and plant species. the balance between fertility and immunity has direct implications for human health; indeed a growing body of work is investigating the links between disease and reproductive biology. Moreover, epidemiological data shows that humans, especially in developed countries and particularly women, are becoming less fertile, but more immune to infectious and other diseases. this, in addition to factors such as improved healthcare, is further increasing human lifespan in wealthy societies. the hypothesis that investing more energy and resources into maintenance and immunity comes at the expense of fertility was first proposed by thomas Kirkwood (1977), now Director of the institute for ageing and Health at Newcastle university in the uK. His theory was supported by epidemiological and historical data (Westendorp & Kirkwood, 1998), as well as animal experiments and molecular evidence. yet, the exact nature of the link between reproduction and immunity has remained elusive.