Leipzig, Germany, October 4, 2025: A comprehensive new study has found that sexual behavior is a key factor in explaining why female mammals tend to live longer than males. The research, conducted by scientists from institutions in Germany, Denmark, France, Hungary and Belgium, analyzed life expectancy data from more than 1,100 species of mammals and birds, offering one of the most extensive examinations to date of lifespan differences between sexes in the animal kingdom.
Published in the journal Science Advances, the study reviewed data on 528 mammal species and 648 bird species kept in zoological institutions, alongside data from wild populations of 110 species. Results showed that, on average, female mammals lived 12 percent longer than their male counterparts. In contrast, among birds, males outlived females by an average of 5 percent. The longevity gap was more pronounced in wild populations than in zoos, where animals are shielded from environmental stressors such as predators, extreme climate conditions and food scarcity.
Despite the controlled environment, the study found that these sex-based disparities in lifespan persisted, indicating the influence of biological and behavioral factors beyond external conditions. A central focus of the study was the heterogametic sex hypothesis, which posits that the sex with two different sex chromosomes (XY in male mammals, ZW in female birds) is more vulnerable to harmful genetic mutations than the homogametic sex (XX in female mammals, ZZ in male birds). Researchers found evidence consistent with this theory, aligning with observed patterns of longevity across many species.
Genetic sex chromosomes tied to longevity patterns
However, several species deviated from this pattern. In particular, birds of prey such as falcons and hawks displayed longer female lifespans despite females being the heterogametic sex. In these species, females are also larger and often more involved in territorial defense, prompting further investigation into evolutionary influences beyond genetics. To better understand these exceptions, researchers examined the role of sexual selection and reproductive behavior. Species with polygamous mating systems, where males compete more aggressively for mates, showed more significant lifespan differences.
Male mammals in such species typically invested more energy in displays, competition and physical traits that aid reproduction, such as large antlers or increased body size. These traits, while enhancing reproductive success, were associated with reduced longevity. The study also considered the cost of reproduction hypothesis, which suggests that the energetic demands of gestation, childbirth and parenting might shorten female lifespan. However, data from both zoo and wild populations did not support this expectation. In fact, females that provided parental care often lived longer than males, particularly in species where caregiving was the sole responsibility of the female.
Study underscores combined impact of sex and behavior
Researchers noted that in many polygamous species, where males do not contribute to offspring care, females may have evolved to survive longer to ensure the survival of their young. This pattern was observed even in captive populations, indicating that such life-history traits may be deeply embedded in species’ biology. Experts not involved in the study described the findings as a major advancement in understanding the biological and ecological factors driving sex differences in lifespan.
They emphasized that while the heterogametic sex hypothesis remains a strong framework, factors such as mating systems and sexual size differences provide important additional insights. The authors concluded that no single theory fully explains the observed variations. Instead, sex-specific life expectancy appears to be shaped by a combination of genetic mechanisms, mating strategies and reproductive roles that vary across species. The study’s breadth and inclusion of underrepresented taxa underscore its significance in evolutionary biology and comparative life-history research. – By EuroWire News Desk.