British scientists have discovered that menopause in toothed whales, such as killer whales, belugas, and narwhals, may have evolved to increase overall lifespan. The evolution of menopause allows females to assist in the survival of their offspring without competing for mates with their daughters or granddaughters. The findings of this research were recently published in Nature.
Menopause is an extremely rare phenomenon, and its evolutionary process and reasons have long been questioned. Human females are the only known terrestrial mammals to have evolved extended post-reproductive lifespans, but menopause has been observed multiple times in toothed whales. While understanding of the adaptive value of menopause in humans has progressed, it remains unclear whether these findings have broader significance for other species.
Samuel Ellis and colleagues from the University of Exeter assembled and analyzed a new comparative database to test various evolutionary hypotheses about menopause in toothed whales. They propose that menopause in females evolved to extend lifespan without increasing reproductive lifespan. Menopause provides females with opportunities to assist younger offspring in the family, improving their survival chances by sharing food, caring for infants, aiding the group in times of resource scarcity, and protecting their offspring. Menopause allows their lifespan to overlap with that of their offspring and grandchildren, while avoiding reproductive overlap with their daughters to mitigate reproductive competition.
The research findings suggest that menopause evolved when it was advantageous for the species. Although whales exhibit significant differences from humans, the convergent evolution of menopause provides new insights into the overall evolution of menopause.
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