A growing body of evidence suggests that women’s relative longevity may derive, in part, from having double X chromosomes, a redundancy that protects them against harmful mutations. That theory was further bolstered Wednesday with the publication of the most sweeping analysis to date of the lifespan differences between males and females in more than 1,000 mammal and bird species…
If a baby has a pair of X chromosomes, she’s a girl. If the baby inherits an X chromosome and a Y chromosome, he’s a boy. In birds, however, the situation is reversed. Female birds have a pair of unlike sex chromosomes while males have the like pair… For their study, Colchero, Staerk and their colleagues collected data on the lifespans of 528 mammal species and 648 bird species kept in zoos. The team found that most other mammals are like humans, with the females of nearly three-fourths of mammal species outliving their male counterparts. But in birds, 68 percent of species studied showed a bias toward male longevity, as expected from their chromosomal makeup.
