Five species now known to go through menopause, researchers say

Beluga whales and narwhals are the latest species which scientists have discovered go through the menopause.

The findings of a new study, by researchers from the University of Exeter, University of York and Center for Whale Research, means five species are now known to stop reproducing and continue living after.

Along with humans, killer whales and short-finned pilot whales were the only others previously known to experience the menopause.

Most species in the wild continue reproducing until they die.

The study, published in journal Scientific Reports, used data from the dead whales of 16 species and found dormant ovaries in older beluga and narwhal females.

These species may have social structures which mean females live among more and more close relatives as they age, the researchers said.

They suggest that menopause has evolved independently in three toothed whale species, with beluga whales and narwhals possibly sharing a common ancestor.

Lead author Dr Sam Ellis, from the University of Exeter, said: "For menopause to make sense in evolutionary terms, a species needs both a reason to stop reproducing and a reason to live on afterwards.

"In killer whales, the reason to stop comes because both male and female offspring stay with their mothers for life - so as a female ages, her group contains more and more of her children and grandchildren.

"This increasing relatedness means that, if she keeps having young, they compete with her own direct descendants for resources such as food.

"The reason to continue living is that older females are of great benefit to their offspring and grand-offspring. For example, their knowledge of where to find food helps groups survive."

Research into human ancestors suggests they also lived among more and more relatives as they aged, and may have evolved in a similar way so they could impart their wisdom.

Senior author Professor Darren Croft, from the University of Exeter, said: "It's hard to study human behaviour in the modern world because it's so far removed from the conditions our ancestors lived in.

"Looking at other species like these toothed whales can help us establish how this unusual reproductive strategy has evolved."

There has already been extensive research into the existence of the menopause among killer whales.

Detailed observations of live beluga whales and narwhals have not yet been carried out.