New Study Reveals How Reproduction Shortens Mammal Lifespans by Up to 10 Percent

A groundbreaking analysis of 117 mammal species has uncovered a surprising biological trade-off: reproduction significantly shortens lifespan, with animals unable to reproduce living up to 10 percent longer than their breeding counterparts. The findings, published by researchers at the University of Otago and the University of Southern Denmark, suggest that the physical and hormonal demands of reproduction accelerate aging across species, with males experiencing particularly dramatic longevity benefits when testosterone is removed. The study, which analyzed decades of zoo and aquarium records, offers critical insights into how evolutionary biology shapes aging and could inform future human health strategies.

• Reproduction shortens lifespan by up to 10 percent across 117 mammal species
• Male mammals gain up to 19 percent longer lives when castrated, due to testosterone removal
• Female mammals benefit from contraception, with some species living 29 percent longer
• Hormonal changes, not just infertility, drive longevity benefits
• Findings suggest evolutionary trade-offs between reproduction and survival

How Reproduction Affects Mammal Lifespans Across Species

The study, led by Associate Professor Mike Garratt at the University of Otago, examined decades of records from zoos and aquariums, where animals receive consistent care, nutrition, and veterinary treatment. This controlled environment allowed researchers to isolate reproduction as a key factor in lifespan differences. The findings revealed that mammals prevented from reproducing—whether through contraception, sterilization, or natural infertility—lived significantly longer than their breeding counterparts.

Male Mammals Gain Up to 19 Percent Longer Lives

Male mammals experienced the most dramatic longevity benefits when reproduction was blocked, particularly when testosterone was removed. Castrated males lived up to 19 percent longer than intact males, while vasectomized males—who retained their hormones—showed no significant lifespan increase. The study suggests that testosterone, which drives growth and risk-taking behaviors, accelerates aging by increasing metabolic wear and tear.

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

Female Mammals Benefit from Contraception and Sterilization

Female mammals also lived longer when reproduction was prevented, whether through hormonal contraception or surgical sterilization. Pregnancy and nursing place immense energy demands on the body, while cycling hormones keep tissues in a constant state of rebuilding. In hamadryas baboons, females on hormonal contraception outlived untreated peers by 29 percent, one of the largest jumps observed in the study. However, ovary removal had mixed effects, with some species experiencing later-life health declines due to estrogen loss.

Evolutionary Trade-Offs: Reproduction vs. Survival

The study supports the longstanding theory that reproduction and survival are evolutionary trade-offs. "This study shows that the energetic costs of reproduction have measurable and sometimes considerable consequences for survival across mammals," said Fernando Colchero, a biodemographer at the University of Southern Denmark. The findings suggest that menopause in humans may have evolved as a survival strategy, allowing older women to redirect energy toward caregiving rather than additional pregnancies.

Historical Human Evidence Supports Animal Findings

Limited historical data from humans aligns with the study’s findings. In pre-20th-century Korea, palace eunuchs—men who had been castrated—lived 14 to 19 years longer than non-castrated men. However, human data is mixed, with some studies linking hysterectomies to higher mortality risks, highlighting the complexity of applying animal research to human health.

Implications for Human Health and Future Research

While the study provides compelling evidence of the biological link between reproduction and longevity, researchers caution against direct applications to human health decisions. "Animal results cannot tell a patient what choice is safest," the study notes. Future research must explore which organs drive longevity benefits and how environmental factors influence outcomes. The findings could, however, inform strategies for healthier aging, particularly in managing hormonal influences on aging pathways.