By Sharin Hussain via SWNS
Female whales who undergo the menopause can double their lifespans, living 40 years longer than other whales, a new study reveals.
The discovery sheds light on the reason for menopause as only five species of whale and humans go through the process.
Experts say it allows females to live and care for extended offspring without competing with their daughters.
Lead author Dr. Sam Ellis, from University of Exeter said: “The process of evolution favors traits and behaviors by which an animal passes its genes to future generations.
“The most obvious way for a female to do this is to breed for the entire lifespan – and this is what happens in almost all animal species.
“There are more than 5,000 mammal species, and only six are known to go through menopause.
“So the question is: how and why did menopause evolve? Our study provides some of the answers to this fascinating puzzle.”
The findings, published in the journal Nature, show that certain female whale species that experience menopause live around 40 years longer than other female whales of a similar size.
These females have more years to help their children and grandchildren, without increasing the “overlap” period when they compete with their daughters by breeding and raising calves at the same time.
Professor Dan Franks, University of York, added: “Our study provides evidence that menopause evolved by expanding female lifespan beyond their reproductive years, rather than from reduced reproductive lifespan.
“Previous research on menopause evolution has tended to focus on single species, typically humans or killer whales.
“This study is the first to cross several species, enabled by the recent discovery of menopause in multiple species of toothed whales.
“Our study provides evidence that menopause evolved by expanding female lifespan beyond their reproductive years, rather than from reduced reproductive lifespan.
“This is a question that has long been asked in anthropology, but can only be directly answered with a comparative study.”
Menopause is known to exist in five species of toothed whale: short-finned pilot whales, false killer whales, killer whales, narwhals and beluga whales.
These females are expected to outlive their own male species, like a female killer whale can live twice as long as the males who typically die by 40.
Professor Darren Croft, Executive Director at the Center for Whale Research added the evolution of menopause and a long post-reproductive life can happen by two circumstances.
The first is that female whales spend their lives in close contact with their children and grandchildren or the females improve the survival chances of their family as female toothed whales are smart and can find food when supply is short.
Whales and humans share similar life histories, despite being separated by 90 million years of evolution.
Professor Croft concludes: “It’s fascinating that we share this life history with a taxonomic group we’re so different from.
“Despite these differences, our results show that humans and toothed whales show convergent life history – just like in humans, menopause in toothed whales evolved by selection to increase the total lifespan without also extending their reproductive lifespan.”
