Female killer whales, unlike most animals, survive after menopause because they help their family members find food during hard times, a study has found.
Most animals die around the same time they stop reproducing but killer whales are one of just three species – alongside humans and another type of whale – where females continue to live for many years after giving birth to their last baby.
Female killer whales generally breed between the ages of 12 and 40 but can live into their 90s.
Previous studies have shown that these old females increase their childrens’ and grandchildrens’ chances of survival but how they help their relatives to survive is a mystery.
One idea is that the old females store information about the environment.
The research team, from the Universities of Exeter and York in the UK and the Center for Whale Research in the US, tested this idea by studying leadership in the resident killer whales in the North Pacific ocean off the coasts of the USA and Canada.
The study, published in the journal Current Biology, found that old female killer whales act as “repositories of ecological knowledge” and often lead groups when hunting in salmon grounds.
Lauren Brent of the University of Exeter said: “Our results show for the first time that one way post reproductive females may boost the survival of their kin is through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female killer whales and humans continue to live long after they have stopped reproducing.”
The theory that older women store ecological knowledge is difficult to test in modern human populations, but as non-literate and highly social animals, killer whales can provide insights into how menopause evolved in humans.
“In humans, it has been suggested that menopause is simply an artefact of modern medicine and improved living conditions,” said Professor Darren Croft of the University of Exeter.
“However, mounting evidence suggests that menopause in humans is adaptive. In hunter-gatherers, one way that menopausal women help their relatives, and thus increase the transmission of their own genes, is by sharing food. Menopausal women may have also shared another key commodity – information.”
The researchers also found that females are more likely to lead their sons than daughters.
Killer whale mothers direct more help toward sons than daughters because sons offer greater potential benefits for her to pass on her genes.
Sons have higher reproductive potential and they mate outside the group.
The team used information collected over the last 35 years and made observations on a total of 102 individual killer whales.
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