A recent study led by scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig has explored the evolutionary origins of the lifespan disparity between women and men. This research aims to unravel the longstanding biological mystery regarding the differing aging processes of the sexes.
Historically, women have demonstrated longer lifespans than men across various countries and time periods. Although advancements in medicine and improvements in living standards have narrowed this gap in some regions, the newly published findings indicate that this difference is likely rooted in evolutionary biology and is not expected to disappear. This phenomenon is observed across numerous animal species, suggesting that the factors contributing to longevity extend beyond contemporary lifestyle.
The study analyzed 1,176 species of mammals and birds, revealing that female mammals typically outlive males by approximately 13 percent. Conversely, in bird species, males often outlive females by about five percent. The researchers noted that reproductive strategies significantly influence these patterns, particularly in mammals where male competition for mates is intense, leading to shorter lifespans for males.
Additionally, the study highlights a notable disparity in lifespans between wild and captive animals, with wild populations showcasing a more significant gap between the sexes. This suggests that both genetic factors and environmental conditions play crucial roles in determining longevity.
The researchers propose the “heterogametic sex hypothesis,” which connects lifespan differences to sex chromosomes. Female mammals possess two X chromosomes, while males have one X and one Y chromosome, which may provide females with a genetic advantage by protecting them from harmful mutations. Interestingly, in birds, the situation is reversed, with females being the heterogametic sex.
Data collected from the various species indicated that in most mammals (72 percent), females lived longer, averaging a 12 percent increase in lifespan compared to males. In birds, however, the trend was less consistent, with 68 percent showing males as the longer-lived sex. Some exceptions were noted, particularly among birds of prey, where females are typically larger and live longer than their male counterparts.
The research also examined the role of parental investment and reproductive strategies. In polygamous mammals, where competition is high, males generally die younger. On the other hand, many bird species exhibit monogamous pair bonds, resulting in lower competition and longer lifespans for males. Overall, the lifespan differences were less pronounced in monogamous species, with polygamous and size-disparate species showing a more significant advantage for females.
The findings underscore that the differences in lifespan between males and females are deeply ingrained in evolutionary history, influenced by sexual selection, parental care practices, and genetic factors associated with sex determination. The study concludes that these disparities are not merely coincidental but are intricately linked to our evolutionary background, suggesting they are likely to endure for the foreseeable future.
The research appears in the journal Science Advances under the title “Sexual selection drives sex difference in adult life expectancy across mammals and birds.”
