Research into the lifespan of wild mammals has given more credence to findings that females live substantially longer than their male counterparts.
It’s no new claim that women live longer than men due to an inherent biological and behavioural advantage, with the World Health Organization (WHO) quoting a difference of six to eight years.
However, a group of researchers recently examined age-specific mortality estimates for a widely diverse group of 101 species of mammals at the French National Centre for Scientific Research (CNRS).
In 60 percent of the populations analyzed, it was found that female mammals lived 18.6 percent longer than their male counterparts, a figure quite different from the 7.8 percent gap in humans.
The findings, published in the Proceedings of the National Academy of Sciences, attributed the difference in lifespan to the interaction between sex-specific genes and environmental factors.
“The magnitude of lifespan and ageing across species is an interaction between environmental conditions and sex-specific genetic variations,” said Jean-Francois Lemaître, the lead author.
“Male bighorn sheep use lots of resources towards sexual competition, towards the growth of a large body mass, and they might be more sensitive to environmental conditions.
“Clearly, the magnitude of the difference in lifespan is due to the interaction. Males devote more resources towards specific functions unlike females, and to the local environmental conditions.
“What we show in our paper is that the difference is very variable across species, meaning there are other factors that need to be considered to explain this variability.”
In his part, Tamás Székely, a professor and one of the authors of the study, admitted that women live longer than men, but expressed shocked that the differences in lifespan between the sexes was even more pronounced in wild mammals than in humans.
“We’ve known for a long time that women generally live longer than men, but were surprised to find that the differences in lifespan between the sexes was even more pronounced in wild mammals than in humans,” said Székely, who is from the Milner Centre for Evolution at the University of Bath.
“This could be either because females are naturally able to live longer, or that female mortality drops compared with males.
“For example, lionesses live at least 50% longer in the wild than male lions. We previously thought this was mostly due to sexual selection — because males fight with each other to overtake a pride and thus have access to females, however our data do not support this. Therefore there must be other, more complex factors at play.
“Female lions live together in a pride, where sisters, mothers and daughters hunt together and look after each other, whereas adult male lions often live alone or with their brother and therefore don’t have the same support network.
“Another possible explanation for the sex difference is that female survival increases when males provide some or all of the parental care. This is also true in birds. Giving birth and caring for young becomes a significant health cost for females and so this cost is reduced if both parents work together to bring up their offspring.”
The team found that even though females consistently live longer than males, the risk of mortality does not increase more rapidly in males than in females across species as they get older.
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