Animals explain why grandmothers evolved
IN THE narrowest evolutionary sense, reproduction is the sole measure of success. Menopause, then, poses a bit of a riddle: in a handful of species, including humans, females cease breeding decades before they die. This is puzzling because it limits the number of offspring they can produce. However, two recent studies suggest that, in very different ways, the explanation lies in the extraordinary value of having a grandmother.
Evolutionary success is not just a mad dash to procreate; it also requires as many descendants to survive as possible. So a period of infertility can leave a female free to shepherd a greater number of grandchildren into the next generation. Despite the popularity of this “grandmother hypothesis”, it has been hard to prove decisively, not least because among mammals the menopause seems to have evolved only in humans and some toothed whales. …
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