In the United States, life expectancy for women outstrips men by about 5.3 years, a huge gap by any measure - but that gap is hardly unique. The worldwide adult life expectancy difference is 5.4 years, and women are favored in virtually every country and region in the world. Some of that is surely behavioral: men smoke more, shoot each other with much greater frequency, and visit the doctor less. But those behaviors don’t fully explain the gap, leaving persistent questions about gender and life expectancy.
There have been a number of competing theories for the life expectancy disparity between men and women, ranging from chromosomal theories to caregiving theories to sexual reproduction competition theories. A new study of animals in both zoos and in the wild lends new support to several of the theories. The study found support for the heterogametic sex hypothesis: it is thought that females, who have two X chromosomes, have an advantage over males, who have one X chromosome and a Y chromosome, because if there are mutations in the X chromosome, males wouldn’t have a copy of that X chromosome to serve as a backup. Thus, mutations may eventually prove harmful and reduce longevity,
The study also found evidence to support the sexual selection theory, that some male animals spend their energy developing traits and behavior to compete for and attract mates, such as changing their physical size or fighting to compete for a female. In doing so, they may be “sacrificing their survival.”
Here’s a twist though: researchers also studied the life expectancy of different bird species, and more than two thirds of them favored males. What does that mean? We have no idea, but until we sprout wings, we’re not going to worry about it.