- Longer lives across species: Limiting reproduction is linked to longer lifespans in many mammals, boosting life expectancy by about ten percent on average and sometimes even more.
- Different biology for males and females: Males live longer only when castration removes testosterone, while females gain longevity from any form of reproductive suppression, likely because avoiding pregnancy and lactation reduces heavy energy demands on the body.
- Shifts in how animals die: Castrated males are less likely to die from aggression or risky behavior, while females with blocked reproduction experience fewer deaths from infections, suggesting stronger immune defenses.
Why Lifespans Differ Across Species
Animals across the natural world age at dramatically different rates. A female elephant can live as long as 80 years, yet she produces only a small number of calves over her lifetime. By contrast, a mouse may survive just a few years but is capable of producing dozens of offspring. Evolutionary biology explains this contrast through a basic principle: energy is limited, and species must divide it between reproduction and maintaining their bodies. A new large-scale study offers fresh evidence that this trade-off plays a major role in shaping how long mammals live, including humans.
An international team of researchers, including scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig, investigated how limiting reproduction influences lifespan in mammals. The study analyzed records from 117 mammal species living in zoos and aquariums worldwide and combined them with a meta-analysis of 71 previously published studies. Together, the data showed that long-term hormonal contraception and permanent surgical sterilization are linked to an average lifespan increase of about ten percent.
The reproduction — survival trade-off
Producing offspring requires enormous biological investment. Pregnancy, nursing, sperm production, courtship behavior, and parental care all consume large amounts of energy. Even outside of active breeding, sex hormones such as testosterone and estrogen continue to affect growth, behavior, and aging, drawing resources away from long-term body maintenance.
“Zoos, where reproduction is carefully managed, provide a unique setting to study these dynamics,” says Johanna Stärk, one of the authors. “Animals may receive contraception or sterilization to prevent breeding, creating natural comparison groups within the same environment.”
The lifespan benefits of reduced reproduction appeared across a wide range of mammals, including primates, marsupials, and rodents. In some cases, the effects were striking. Female hamadryas baboons given hormonal contraception lived 29 percent longer, while castrated males lived 19 percent longer. “This study shows that the energetic costs of reproduction have measurable and sometimes considerable consequences for survival across mammals,” says Fernando Colchero, one of the study’s senior authors. “Reducing reproductive investment may allow more energy to be directed toward longevity.”
Both sexes live longer — but for different reasons
While limiting reproduction extended lifespan in both males and females, the biological pathways involved were not the same. Lead author Mike Garratt of the University of Otago explains that only castration, not vasectomy, increased male lifespan. “This indicates that the effect stems from eliminating testosterone and its influence on core aging pathways, particularly during early-life development. The largest benefits occur when castration happens early in life,” he says.
In females, several forms of sterilization were associated with longer lives, suggesting that the benefit comes from avoiding the intense physical demands of pregnancy, nursing, and reproductive cycling. Removing the ovaries, which stops ovarian hormone production, also extended lifespan. However, a meta-analysis of 47 laboratory rodent studies revealed potential downsides, as later-life health outcomes may worsen. These results could help explain the “survival-health paradox” seen in post-menopausal women, who often live longer than men but experience higher levels of frailty and chronic illness.
Different Causes of Death by Sex
The study also found notable differences in how males and females died. Castrated males were less likely to die from causes linked to aggression or risky behavior. Females whose reproduction was blocked were less likely to die from infections, supporting the idea that the high energy demands of reproduction may weaken immune defenses in mothers.
Direct evidence from humans remains limited. Some historical records, including data from Korean Eunuchs in the pre-19th century Chosun Dynasty, suggest that castrated men lived about 18 percent longer than men who were not castrated. However, researchers caution that these records are debated and should be interpreted carefully.
Among women, surgical sterilization performed for non-cancerous reasons (such as hysterectomy or oophorectomy) is linked to a very small reduction in lifespan, roughly 1 percent compared with similar women who were not sterilized. “Reproduction is inherently costly,” the authors note. “However, human environments — through healthcare, nutrition and social support — can buffer or reshape these costs.”
A Fundamental Evolutionary Trade-Off
Overall, the findings highlight reproduction as a major biological expense for mammals. The balance between producing offspring and preserving the body represents a core evolutionary trade-off that influences aging and survival. These costs arise from a combination of hormonal effects and the physical risks and stresses tied to reproduction.
Many details remain unresolved, and the researchers emphasize the need for further study. “Our findings show that the costs of reproduction are substantial and measurable across a vast range of mammals,” the authors conclude. “Understanding these trade-offs deepens our insight into how aging evolves and how males and females balance survival and reproduction differently.”