Killer whales and the mystery of human menopause

Jul 01, 2010
A mother and her child watch a captive killer whale. Credit: aconant

The evolutionary mystery of menopause is a step closer to being solved thanks to research on killer whales.

A study by the Universities of Exeter and Cambridge has found a link between killer whales, pilot whales and humans — the only three known species where females stop breeding relatively early in their lifespan.

Despite very different social structures between the three species, the research shows that in each case females become increasingly genetically related to those they live with as they get older. Because of this, there is a motivation for older females to do what is best for the survival of those around them.

This creates a 'grandmother' role, where the success rate of breeding in the group can be helped by older females sharing parenting knowledge and stopping breeding to allow younger females easier access to resources.

The research, published in the , is the first to provide a plausible explanation why these species in particular are the only ones in which females finish reproduction while they still have decades left to live.

Dr Michael Cant, from the University of Exeter's School of Biosciences (Cornwall Campus) and a Royal Society University Research Fellow, said: "It's always been puzzling as to why only humans and toothed whales have evolved menopause, while females in all other long-lived species continue breeding until late in life.

"Although the social behaviours of the three menopausal species are very different, there is a common link: their social systems mean females become more related to those around them as they get older. This predisposes females of our species, and those of killer whales and pilot whales, to the evolution of menopause and late life helping".

Humans are thought to have evolved in groups in which young females left their group to find a mate. This would have meant they started their reproductive lives in families to whom they were genetically unrelated. Later in life, however, as their offspring start to breed, they become more genetically related to those around them and have the option to cease reproduction to help raise their 'grand-offspring'.

However, this argument doesn't seem to explain menopause in or pilot whales, in which both sexes remain in their natal family groups throughout their life, but occasionally come together with other groups to mate. The new research, however, shows this very different social system has the same overall effect on patterns of genetic similarity within groups: females become more closely related to infants in the group as they get older.

By contrast with humans and menopausal whales, in other long lived mammals it is typically males who leave the group to breed, and females who stay with their mother. According to the research, in this case older will be selected to continue breeding rather than give up reproduction to help raise grandchildren.

Dr Rufus Johnstone, from the Department of Zoology at the University of Cambridge, and co-author of the study, said: "For the first time we can see a common link between menopausal species which provides a valid explanation as to why this trait might have evolved. This isn't likely to be the only factor relevant to the evolution of 'grandmothering' and , but it does give us an idea why it is restricted to so few species in the animal kingdom."

Explore further: Rare new species of plant: Stachys caroliniana

Related Stories

New research provides insight into menopause

Mar 31, 2008

Insight into why females of some species undergo menopause while others do not has proven elusive despite an understanding of the biological mechanisms behind the change.

Older killer whales make the best mothers

Feb 03, 2009

Killer whales (Orcinus orca) nearing the menopause may be more successful in rearing their young. New research published in BioMed Central's open access journal Frontiers in Zoology shows that estimated survival rates for cal ...

A helping hand from the grandparents

Dec 21, 2007

A team of scientists led by the University of East Anglia has discovered the existence of ‘grandparent’ helpers in the Seychelles warbler – the first time this behaviour, which rarely occurs except in humans, has been ...

Females avoid incest by causing male relatives to leave home

Aug 15, 2007

Researchers at the University of Sheffield in the UK and Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, have found that female hyenas avoid inbreeding with their male relatives by giving them little ...

Study reveals why starling females cheat

Jun 20, 2007

While women may cheat on men for personal reasons, superb starling females appear to stray from their mates for the sake of their chicks, according to recent Cornell research published in the Proceedings of the Royal Society of ...

Recommended for you

Rare new species of plant: Stachys caroliniana

Nov 21, 2014

The exclusive club of explorers who have discovered a rare new species of life isn't restricted to globetrotters traveling to remote locations like the Amazon rainforests, Madagascar or the woodlands of the ...

Mysterious glowworm found in Peruvian rainforest

Nov 21, 2014

(Phys.org) —Wildlife photographer Jeff Cremer has discovered what appears to be a new type of bioluminescent larvae. He told members of the press recently that he was walking near a camp in the Peruvian ...

The unknown crocodiles

Nov 21, 2014

Just a few years ago, crocodilians – crocodiles, alligators and their less-known relatives – were mostly thought of as slow, lazy, and outright stupid animals. You may have thought something like that ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.