⌛ Sterilization and castration increase life expectancy

Why can some animals, like elephants, reach 70 years while having few offspring, while others, like mice, live only a few years but reproduce abundantly? Beyond the size difference between these two species, there is a delicate balance between the ability to reproduce and lifespan.

An international research, involving scientists from the Max Planck Institute for Evolutionary Anthropology, examined this phenomenon on a large scale. By analyzing data from 117 species of captive mammals, researchers found that animals with limited reproduction live on average longer.


The study, which combines observations in zoos and a meta-analysis of scientific publications, reveals that surgical sterilization or hormonal contraception extends life by about 10%. This trend is observed in various groups, from primates to rodents, with striking examples like hamadryas baboons, where females under contraception live 29% older.

Reproduction requires a considerable energy expenditure. Gestation, lactation, sperm production, and parental care mobilize resources that could otherwise be used to maintain the body in good health. Sex hormones, such as testosterone and estrogen, also play a role by influencing behavior and aging, potentially diverting energy to other functions.

In males, the increase in longevity seems linked to the elimination of testosterone through castration, and not to simple vasectomy. For females, avoiding pregnancies and reproductive cycles reduces physiological costs, although ovary removal may have mixed effects on later health, according to studies on laboratory rodents.

Human data, such as that from historical Korean eunuchs, indicate similar patterns, with a longer life for castrated men. However, modern conditions, such as medicine and good nutrition, mitigate these effects.

The role of hormones in aging

Sex hormones, such as testosterone and estrogen, regulate not only reproduction but also other essential body processes. They act as chemical messengers that influence metabolism, the immune system, and tissue repair, playing a key role in maintaining health and the pace of aging. For example, testosterone can stimulate muscle growth but also increase the risks of certain diseases, while estrogen often protects bones and the heart.

These hormones directly affect aging by modulating biological pathways such as inflammation, oxidative stress, and cell regeneration. High levels of testosterone in males are associated with riskier behaviors, such as aggression, which can reduce survival. In females, hormonal fluctuations during reproductive cycles require a lot of energy, potentially at the expense of immune defenses, explaining why limiting reproduction can prolong life.