An interesting paper: "Women experience more years of vigorous life after ovulation has ceased than do females of other primate species. Is this an epiphenomenon of the greater life expectancy humans have enjoyed in the past century or so, or is long post-menopausal survival the result of an evolutionary selection process? Recent research implies the latter: Long post-menopausal survival came about through natural selection. One prominent line of thought explaining this selection process is the grandmother hypothesis. ... The hypothesis contends that, in past epochs, women who remained vigorous beyond their fertile years may have enhanced their reproductive success by providing care for their grandchildren. This care would have enabled their daughters to resume reproduction sooner, endowing them with greater lifetime fertility. Genes of grandmothers possessing such old-age vigor would be more likely to persist in subsequent generations. Is midlife menopause a uniquely human phenomenon, or does the chimpanzee, our closest primate relative, also display this trait? If so, we might expect a grandmother effect in this species as well. However, female chimpanzees continue to cycle until near the end of their maximum life span of about 60 years. ... Long survival beyond fertility and a long life expectancy are distinctive human adaptations."