THE human menopause, which is virtually unparalleled among mammals, has long been one of the great mysteries of biology as it appears to defy evolutionary logic.
Natural selection should have ousted the menopause as women who remained fertile throughout life should have had more offspring and thus passed on their genes to many more descendants. The peculiarities of human anatomy, however, seem to have favoured women who pass through the change of life.
As humans have exceptionally large heads and narrow pelvises, giving birth is much more dangerous for women than it is for other female primates. Therefore although women who went through the menopause had fewer children, they also substantially reduced their risk of dying in childbirth.
According to the “grandmother hypothesis”, first proposed by the anthropologist Kristen Hawkes, there comes a point in a woman’s life at which the evolutionary advantage of having further children is outweighed by the increased danger to her survival.
In middle age, her ability to pass on her genes to further generations is enhanced more by investing in her existing children and grandchildren, who would fare worse were she to die prematurely, than by giving birth again. Over many generations, women who had a menopause would thus have left more descendants than those who did not.
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Strong evidence supporting this theory was advanced in March by a Finnish team, which found that women in pre-industrial societies have two extra surviving children for every decade they live after the age of 50.
Another possible explanation for menopause is the “wise old woman” hypothesis, which holds that societies are less vulnerable to rare catastrophes, such as floods, if they have elderly people who remember the last one.