Surprising link between not having children and life expectancy

Across 117 different species of mammals, animals that were prevented from having offspring showed increased life expectancy, surviving about 10 percent longer than those that reproduced.

The findings suggest that the physical demands of reproduction, including pregnancy and hormone activity, may shorten lifespan.

Zoo records show life expectancy

Zoo and aquarium records captured births, deaths, and years of contraception decisions, giving teams at the University of Otago a rare comparison.

By sorting those records, Associate Professor Mike Garratt linked blocked reproduction to longer survival.

Across a broad analysis, his team saw longer life expectancy with ongoing birth control and permanent sterilization in many species.

With food, shelter, and veterinary care kept steady, the work singled out reproduction itself as a key drain on longevity.

Male clocks slowed

Male mammals gained years when castration removed the testes, sometimes living for up to 19 percent longer. The same trend was not evident when vasectomy – a sperm-blocking surgery – left hormones unchanged.

Testes produce testosterone, and that hormone pushes growth and risk-taking, so removing it can lower wear on the body.

“This indicates that the effect stems from eliminating testosterone and its influence on core aging pathways, particularly during early-life development,” says Garratt.

Because male benefits depended on hormone removal, the finding points toward biology, not infertility alone, as the lever on life expectancy.

Female bodies saved

Female mammals lived longer when staff prevented pregnancy, whether through hormonal contraception or through surgery that prevented reproduction.

Pregnancy and nursing demand energy and nutrients, and cycling hormones can keep tissues in a constant state of rebuilding.

In hamadryas baboons, females on hormonal contraception outlived untreated peers by 29 percent, one of the biggest jumps observed.

Ovary removal still extended lifespan in animals, but rodent evidence suggests that later-life health could worsen when estrogen disappears.

Death risks changed

Blocking reproduction did not just add years, it also changed what killed animals in late adulthood.

Castrated males were less likely to die from aggression or risky encounters, matching reduced testosterone-driven behavior.

Females with reproduction blocked faced fewer fatal infections, consistent with the idea that pregnancy and lactation leave less energy for immune function.

Necropsy notes in zoos used broad categories, so these differences hint at processes, not a single germ or injury.

Life-expectancy reflects a trade-off

Outside zoo records, the team at the University of Southern Denmark pooled results from 71 earlier studies across vertebrates.

Biodemographer Fernando Colchero framed the pattern as a trade-off between reproduction and survival.

“This study shows that the energetic costs of reproduction have measurable and sometimes considerable consequences for survival across mammals,” said Colchero.

Wild and laboratory reports showed wide variation, meaning environment and species biology can change how large the survival boost becomes.

Timing mattered by gender

For females, the lifespan gain appeared regardless of age at which reproduction is limited. This means that even later contraception reduced the ongoing load of reproduction.

Avoiding additional pregnancies cuts repeated bursts of energy use, and it can leave more resources for immune repair.

Menopause fits this logic, because stopping births may protect older women while allowing care to flow toward grandchildren.

Human societies also change diets, medicine, and support, so the biology seen in other mammals may not map neatly onto people.

Human life-expectancy clues

Evidence on sterilization and lifespan in humans is limited, and most data come from history or medical records.

In Korea before the twentieth century, palace eunuchs – men who had been castrated and served in royal courts – outlived other men by roughly 14 to 19 years.

Among women, permanent surgical sterilization for noncancer reasons showed a slight survival decrease in the pooled evidence.

Healthcare and nutrition can buffer reproductive strain, so the human signal may depend as much on context as biology.

Healthspan told another story

Later-life tests asked about healthspan – years lived with good function – and they did not always mirror life expectancy changes.

In rodents, male castration often improved strength and cognition, while females without ovaries mainly gained protection from mammary tumors.

In contrast, a large United States hysterectomy cohort linked ovary removal to higher overall death risk, even when surgery treated benign disease.

Those mixed outcomes keep the research in perspective, since animal results cannot tell a patient what choice is safest.

Mechanisms still unclear

Many details remain unknown, including which organs actually drive longer survival when reproduction is blocked across so many species.

Zoo care also complicates cause and effect, because contraception may follow illness, aggression problems, or management needs.

Species varied widely, so an intervention that helped a baboon might do little for a lion or a mouse.

Future experiments must isolate hormone effects from surgery stress, then track which tissues improve and which ones pay a cost.

A clearer trade-off

The new evidence ties longer life expectancy in mammals to reduced reproduction, with males and females benefiting through different biological routes.

Better work on those routes could support healthier aging strategies, while leaving human reproductive decisions grounded in values and consent.

The study is published in Nature.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–