It's already a well-known fact that on average, women live longer than men. A European study, however, now indicates that the difference between male and female lifespans is even more pronounced in other types of mammals.
The research was conducted by scientists from the University of Southern Denmark and France's University Lyon 1. They started by compiling demographic data for 101 wild mammal species – for each one, they estimated the average longevity for both sexes, along with the rate of increase in the risk of dying as a function of age.
What the researchers found was that the average female wild mammal lives 18.6 percent longer than a male of the same species. Even greater disparities were present in mammals such as the common brushtail possum, lion, orca, moose, greater kudu and sheep. By contrast, the difference between female and male human lifespans is just 7.8 percent.
It had previously been postulated that the shorter lives of male wild mammals could be due to their engaging in riskier behaviour, such as fighting one another for breeding rights, or hunting prey while their mates tended to the young. According to the new study, though, mammal species in which the males lead rougher lives show no greater difference in lifespans than other more laidback species.
Instead, it is now thought that one of the contributing factors could be the (usually) larger size of males, along with presence of sexual indicators such as bigger horns. That extra body mass requires more energy to maintain, leaving males more vulnerable in harsh environments.
For instance, it was noted that in regions where food is readily available year-round, there is almost no difference in the lifespans of female and male bighorn sheep. In locations with particularly nasty winters, though, females live much longer than males.
It's also possible that male mammals are more susceptible to infections, as they have higher levels of androgens (male hormones) which can impair the immune system when present in large amounts.
The research is described in a paper that was recently published in the journal Proceedings of the National Academy of Sciences of the United States.
Source: University of Southern Denmark
