Differences between the breeding success of mothers and daughters may have driven the evolution of menopause, according to a study on killer whales.
Evolutionary biologists have long puzzled over why females of certain species — humans, killer whales and short-finned pilot whales — stop ovulating long before they die. Darren Croft at the University of Exeter, UK, and his colleagues analysed 43 years of data on two populations of killer whales (Orcinus orca; pictured) living off the west coast of North America. They confirmed that females become more closely related to their local group as they age, because they are producing offspring that become part of that group. The team also found that calves born to older mothers are 1.7 times more likely to die if born in groups where younger mothers are also breeding.
The authors say that selection favours younger females that invest more in competition for the limited resources needed for reproduction than do older related females. Menopause seems to be driven both by the high cost of breeding for older mothers and by other benefits they can provide by helping the rest of the group.
Current Biol. http://doi.org/bw6v (2017)
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How menopause emerged in whales. Nature 541, 263 (2017). https://doi.org/10.1038/541263c