Across almost every society and historical era, women tend to live longer than men — a biological pattern that extends beyond humans to much of the animal kingdom. A new international study, published in Science Advances, offers evolutionary insight into this long-observed phenomenon.
According to the research — the largest of its kind — scientists analyzed data from 1,176 species of mammals and birds kept in zoos, as well as field observations of 110 wild species. The findings revealed a clear pattern: female mammals live, on average, 12% longer than males, while in birds the opposite trend appears — males live about 5% longer.
Although medical progress and better living conditions have narrowed the gender longevity gap in some human populations, researchers say it is unlikely to disappear completely. The reasons, they argue, lie deep in evolutionary biology.
1. The Chromosomal Advantage
The first and most well-known explanation involves sex chromosomes. In mammals, females carry two X chromosomes — one from each parent — while males carry one X and one Y. This means that females are better protected against harmful mutations on the X chromosome, since damage to one copy can be compensated by the other.
In birds, however, the chromosomal pattern is reversed: males have two copies of the Z chromosome, while females carry a Z and a W. This likely explains why male birds tend to live longer, mirroring the advantage that female mammals enjoy. Yet, the researchers noted several exceptions, suggesting that chromosomes are only part of a much larger puzzle.
2. The Cost of Sexual Selection
A second explanation is linked to sexual selection. In many species, females are attracted to dominant males displaying impressive traits — such as larger bodies, antlers, or colorful plumage like that of peacocks.
While these characteristics help males succeed in reproduction, they come at a biological cost: they require significant energy, can reduce immune defenses, and ultimately shorten lifespan. This effect is most pronounced in polygamous species where competition between males is intense. In contrast, in monogamous species, where such rivalry is limited, males often live longer.
3. The Role of Parental Care
The third evolutionary theory focuses on parental investment. In many species, females are primarily responsible for raising offspring. Over time, this role may have favored longer female lifespans, allowing mothers to ensure their young survive to maturity.
Environment Plays a Role, But Evolution Runs Deeper
The researchers also found that the longevity gap is smaller among animals in captivity, where environmental stress is reduced. Even so, differences persisted, indicating that genetics and evolution, rather than external factors alone, drive the trend.
The conclusion of the study is clear: while advances in healthcare and lifestyle can improve longevity for both sexes, the female survival advantage is likely to remain — a trait shaped and preserved by millions of years of evolution.
