The reason men do not live as long as women may be contained in their sperm, a study has suggested.
Men grow bigger than women but at the expense of longevity
Scientists believe a particular male gene may explain why females tend to outlive their male counterparts.
The gene is passed on to offspring by sperm but is only active in men, allowing them to grow bigger bodies at the expense of longevity, according to the theory published in the journal Human Reproduction.
Males are larger to improve their chances of breeding but this makes life expectancy shorter, the scientists said.
In contrast, women live longer because they are careful to conserve energy for childbirth and looking after their offspring, and ensuring they survive to adulthood.
Although the study was conducted on mice, scientists think the findings could apply to all mammals, including humans.
The Japanese researchers looked at mice created with genetic material from two mothers but no father.
Their “bi-maternal” genes were manipulated so that the genes in young mouse eggs behaved like those in sperm, giving them the ability to fertilise.
Scientists tested theory on mice
The altered genetic material was then implanted into eggs of adult female mice to create embryos, with no contribution made by sperm.
BM mice were found, on average, to live a third longer than normal.
Mice created through natural mating lived no longer than 996 days, while the longest-surviving BM mouse lived 1,045 days.
The mice with two mothers were significantly lighter and smaller at birth, and also appeared to have better-functioning immune systems.
Study leader Professor Tomohiro Kono, from the Nodai Research Institute in Tokyo, said: “We believe that the most likely reason for the differences in longevity relates to the repression of a gene called Rasgrf1 in the BM mice.
“The study may give an answer to the fundamental questions… and just maybe, why women are at an advantage over men with regard to lifespan.”
The average lifespan in the UK for men is 75 and for women 79.9.
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