Darwin’s theory of natural selection states that any genetic trait which reduces our ability to pass on our genes is unlikely to survive the test of time.
So why does the menopause exist?
It’s a question that has baffled evolutionary biologists for years, given that the process shortens the window for reproduction.
But now they might just have found the answer, and it lies in the feeding habits of killer whales – one of just three species known to go through menopause.
For several years, researchers have been observing orcas off the coast of San Juan Island in the North Pacific.
In a new study published in Current Biology, they reveal that older mother orcas share food more than younger mother orcas, helping to feed their entire family, including grown-up offspring, rather than just their newborns. Male orcas, in particular, are highly reliant on their mothers for survival, even when fully grown.
While older mothers’ generosity means the food is shared around, it endangers their young offspring, who don’t always get the attention they need. As a result, orcas born to older mothers are less likely to survive than those born to younger mothers.
The scientists claim that the menopause comes down to a simple cost benefit analysis, namely that stopping having children at a certain age lets older female orcas devote time to ensuring the family survives and its genes are passed on.
Dan Croft, a researcher at the University of Exeter and co-author of the study, told the BBC that humans would have once behaved in a not dissimilar way:
“Before we had Google to ask where the shop was, if there was a drought or a famine, we would go to the elders in the community to find out where to find food and water. That kind of knowledge is accumulated over time - accumulated in individuals.”
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