In evolutionary terms, menopause is something of a mystery since it inhibits further reproduction. The Economist explains the evolutionary advantages of having a grandmother. "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."