In humans and many other animals, males age faster and die earlier than females.
New research suggests this might happen because of intense competition over sex.
Scientists compared monogamous species with polygynous species, in which each male mates with many females. Males in monogamous species, such as the barnacle goose or the dwarf mongoose, naturally compete less over females than ones in polygynous species, such as the red-winged blackbird or the savannah baboon.
After investigating about 20 different vertebrate species, researchers Tim Clutton-Brock and Kavita Isvaran at the University of Cambridge in England found the more polygynous a species was, the more likely their males were to age faster and die earlier than females.
The researchers explained that as competition among males for sex grows more intense, each male on average has less time to breed. As such, there is no strong incentive to evolve longevity among males in such species.
Since men age faster and die earlier than women, these findings suggest that "at the time when current human physiology evolved, perhaps around the late Stone Age, polygynous breeding was the norm," Clutton-Brock told LiveScience. "Of course, this doesn't provide any justification for polygyny or promiscuity now for males."
Clutton-Brock and Isvaran detailed their findings online Oct. 17 in the journal Proceedings of the Royal Society B.