1. ITV Report

Are men to blame for the menopause?

Liverpool John Mores University Credit: PA

The onset of the menopause in humans has been linked to men failing to fly the nest.

Women have the unusual trait of undergoing the menopause - in contrast with the females of most other species who reproduce until the day they die.

Researchers at the University of Liverpool and Liverpool John Moores University discovered the evolution of the menopause in humans was boosted by the tendency for sons and grandsons to remain living close to home.

The two-year study looked at the "grandma hypothesis", that women lived long past the reproductive age in order to help successfully raise their grandchildren.

Co-author and zoologist Dr Hazel Nichols, from Liverpool John Moores, said:

"It is important that the investigation focuses on the males staying, because traditionally in the human race a woman will leave her family when she settles down with a man.

"When she gets married she would go off and join him. She won't have any relatives to help out.

"When she gets older, she will have children and she will have her descendants to help.

"The idea with this investigation is to compare species, and the idea is that when human males stay at home, the older women will enter the menopause because they are required to help out with raising younger members of the family rather than continuing to have their own children."

– Co-author and zoologist Dr Hazel Nichols

Evolutionary biologist Dr Kevin Arbuckle, from the University of Liverpool, said:

"Our results suggest that the menopause arose through a non-adaptive 'mismatch' between lifespan and reproductive span. Subsequently we think that in populations where males remained at home and females dispersed to reproduce, an adaptive benefit drove the extension of this post-reproductive period.

"This adaptive benefit could have come from grandmothers looking after their sons and grandsons at home. As females tend to reproduce more reliably than males, this additional family support could have made it more likely that their grandsons successfully reproduced."

– Evolutionary biologist Dr Kevin Arbuckle

The study, published in the Biology Letters journal, used data from 26 different mammal species, including three different tribal or historical human populations, to test for the effects of lifespan, group size and male and female philopatry - the tendency to remain within a family group - on post-reproductive lifespan.