Lifespan differences in mammals and birds tied to genetics and care

An international team of researchers led by the Max Planck Institute for Evolutionary Anthropology reports that sex differences in lifespan are widespread across mammals and birds and appear rooted in genetics and reproductive strategies, according to a study published in Science Advances. Analyzing records from 1,176 species, the team found that in 72 percent of mammal species females lived longer than males by about 12 percent on average, while in 68 percent of bird species males outlived females by roughly 5 percent.

The researchers tested multiple hypotheses to explain the pattern. Their results support the heterogametic sex hypothesis, which links lifespan differences to sex chromosomes. In most mammals, females have two X chromosomes and males have one X and one Y chromosome. Having two copies of the X can protect against harmful mutations, the authors say, whereas the heterogametic sex may incur a genetic cost. In birds the system is reversed: females are typically ZW and males ZZ, and the observed male advantage in many bird species aligns with that arrangement.

The study also identified reproductive behavior and parental investment as important drivers. Species with...