There's a rare human trait that doesn't often make it into debates about what makes our species unique: menopause. Humans are among just a handful of species where females stop reproducing decades before the end of their lifespan. In evolutionary terms, menopause is intriguing: how could it be advantageous for reproductive ability to end before an individual's life is over? One possible answer: the power of the grandma's guidance and aid to her grandchildren.

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