Why animals live longer when they stop reproducing

For decades, biologists have suspected a fundamental bargain in nature: energy spent making offspring is energy not spent maintaining the body. 

A sweeping new analysis led by the University of Otago puts fresh, cross-species numbers behind that idea. 

Drawing on records from zoos and aquariums worldwide, the team reports that blocking reproduction is linked to longer life in both males and females across 117 mammal species, with gains typically in the 10–20% range. 

The research also teases apart why the longevity boost arises, and why the reasons differ by sex.

Reproduction and lifespan

Because many animals under human care receive veterinary oversight and live in relatively protected conditions, their life histories form a powerful dataset for questions that are nearly impossible to test at scale in the wild. 

Here, researchers combined two lines of evidence: survival data for living mammals that had undergone contraception or sterilization, and a meta-analysis spanning vertebrate studies more broadly. 

The consistency of the signal is striking: ongoing hormonal contraception and permanent surgical sterilization were associated with increased life expectancy across environments and lineages.

Same result, different routes

The headline finding – longer lifespan when reproduction is blocked – masks different underlying drivers for males and females. 

“In males, only castration extends lifespan – not vasectomy – which indicates that the effect comes from removing sex hormones,” said study lead author Mike Garratt. 

“These hormones may interact with pathways that regulate the biology of aging, particularly during early life development, since early life castration has the strongest effects on lifespan. Health in later life is also increased by castration in laboratory rodents.”

Females tell a different story. Rather than one hormone pathway, multiple routes to suppress or stop reproduction track with longer life. 

“In females, lifespan increases after several different forms of sterilization, suggesting that benefits arise from reducing the substantial energetic and physiological costs of pregnancy, lactation and caring for offspring, rather than from a single hormonal mechanism,” Garratt said. 

In other words, avoiding the repeated, high-cost demands of producing and rearing young appears to free up resources for body upkeep and repair.

How reproduction affects lifespan

“Reproduction is inherently costly, although environments can soften or exaggerate these costs, particularly human environments, which can buffer or modify them thanks to healthcare, nutrition and social safety,” said study co-author Fernando Colchero.

The new analysis shows how those costs express themselves. For males, blocking reproduction also reduced deaths linked to aggression and risk taking – behaviors often stoked by sex hormones. 

For females, the survival advantage correlated with fewer deaths from infection and infectious disease, a pattern consistent with the well-documented dips in immune function that can accompany pregnancy and lactation.

Critically, the effect sizes weren’t fixed. The team reports life expectancy increased by 10 to 20 percent, depending on when in life treatment occurred and the environment the animal experienced. 

That nuance matters for interpreting how broadly the findings apply and how they might translate between managed care and natural settings.

Timing isn’t everything

The study suggests timing and mechanism interact in sex-specific ways. In males, the age at which sex hormones are removed appears pivotal, with early life castration producing the strongest longevity benefit. 

In females, the picture is more forgiving. “Unlike in males, we found no evidence that the effects of contraception on survival are dependent on the timing of sterilization, so not reproducing in later adulthood, even after already producing some offspring, might provide later-life survival benefits in females.” Garratt explained. 

That observation dovetails with a long-running evolutionary puzzle: if reproduction is so central to fitness, why do females of some species – humans most prominently – experience menopause?

Longer life with limited reproduction

According to the researchers, the findings support an evolutionary rationale for menopause.

If stepping back from reproduction in mid- to late life improves survival prospects, then menopause can be understood as part of a life history strategy that shifts energy from reproduction toward maintenance and kin support. 

But there’s a catch: not all routes to suppress reproduction yield the same health outcomes.

“While lifespan was increased by a range of sterilization approaches, in the case of ovary removal, which also removes ovarian hormone production, aspects of health in later life are impaired,” said Garratt.

“These findings on lifespan and healthspan shed light on the health-survival paradox observed in post-menopausal women, who outlive men on average but suffer increased frailty and poorer overall health during aging.” 

Longer life is not always synonymous with healthier years. How reproduction is halted, and which hormones remain in play, can tilt the balance toward durability or decline.

Broader implications of the study

At one level, the message is simple: reproduction pulls hard on an animal’s energy budget, and easing that pull can lengthen life. 

At another, the story is richly textured. Sex hormones sculpt aging biology in males. The sheer energetic drain of reproduction dominates in females.

Context – from veterinary care to social environment – modulates outcomes. And the method of blocking reproduction can either protect or compromise late-life health.

For evolutionary biologists, the study tightens the link between life-history theory and real-world survival patterns across a broad swath of mammals. 

For veterinarians and zoo managers, it offers evidence to weigh when making reproductive and welfare decisions for long-lived species.

And for human health researchers, it highlights the need to distinguish lifespan from healthspan, and to parse how hormones, immune function, and life-course timing interact to shape both.

The research is published published in the journal Nature.

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