THE menopause is a puzzle. Why do women, unlike most female mammals, stop reproducing decades before they die? Analysing birth and death records shows that the assistance they give in bringing up grandchildren does have a measurable effect on those grandchildren’s survival. But that does not prove such assistance is more valuable in evolutionary terms than continued fertility would be.
Two other mammals undergo a menopause, however. These are killer whales and short-finned pilot whales. And a long-term analysis of killer-whale populations, by Darren Croft of the University of Exeter, in England, and his colleagues, just published in Current Biology, suggests the missing part of the explanation may be that the menopause not only frees a female to help raise the grandoffspring, but also reduces competition between her and her gravid and nursing daughters.
Dr Croft’s killer whales swim off the coasts of British Columbia, in Canada, and its southern neighbour, the American state of Washington. They have been monitored by marine biologists every year since 1973. They live in…Continue reading
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