Females, whether they be human or some other type of mammal, like primates or even whales, tend to outlive men by an average of 5.4 years. A new study suggests that this isn’t just a fluke. This disparity between male and female lifespans is baked into the genetic and social structure of animals.
The research, published in Science Advances and led by primatologist Johanna Stärk, examined lifespan data from more than 1,100 species of mammals and birds, both in the wild and in zoos. They found that in about 72 percent of mammal species, females lived 12 percent longer than males. Weirdly, birds were the animals where the opposite was true: in 68 percent of bird species, males lived about 5 percent longer than females.
The team believes chromosomes are at least partly responsible. In mammals, males are the heterogametic sex, meaning they have one X and one Y chromosome, instead of a matching pair. In birds, it’s the females who are heterogametic, with Z and W chromosomes. Across both groups, the heterogametic sex tends to die sooner.
There are environmental and behavioral factors to consider as well. Researchers found that even in zoos, where animals don’t have to compete for resources and land, the sex-based lifespan persisted. In fact, in the wild, the gap is even wider thanks to competition and parenting.
In species where males fight more, they tend to die younger. In monogamous species, like (and especially) birds, the lifespan gap shrinks, or even reverses. And in species where one sex does more child-rearing (usually females), evolution seems to reward that effort with longer life. Deadbeat dads can kick rocks, according to evolution.
Life expectancy isn’t all about eating right and exercising, though those things can help around the margins. The real determining factor is social structure and evolution itself.
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