Chromosomes and biology play a role
Across nearly all human populations, women live longer than men—a pattern echoed in many animal species. Evolutionary biology points to differences in sex chromosomes as one explanation. Because women carry two X chromosomes, harmful mutations on one can often be offset by the other, while men, with only one X, have less genetic protection. This “chromosome buffer” is thought to give females an advantage in longevity.
Hormones, immunity, and reproductive trade-offs
Estrogen is believed to shield cells against damage and strengthen the immune system, slowing age-related decline. In contrast, testosterone may increase risks, such as reduced immunity and higher rates of certain diseases. Evolution also shapes how energy is divided between reproduction and body maintenance. Males of many species invest heavily in competition and mating behaviors, which can shorten life expectancy compared with females.
The role of mitochondria and survival across species
Another factor may be mitochondria, which are inherited only from mothers. Mutations that harm males but not females can accumulate over generations, disproportionately affecting men’s health. Comparative studies in birds and mammals support this idea, showing that the sex with two identical chromosomes often lives longer. Together, these evolutionary forces suggest why women, on average, continue to outlive men across both history and species.
