Counterintuitive Facts (78): Why Do Only Human Females Have Menopause?

I. In the animal kingdom, females are almost all lifelong fertile. Female gorillas can still give birth until death. Female elephants still have reproductive ability in old age. Almost all mammals are like this. As long as they're alive, they can reproduce.

II. Only two animals are exceptions: human females and killer whales. Human females stop reproducing around age 50. Menopause. Then they can live for decades more. From evolutionary perspective, this is extremely counterintuitive. Evolution's purpose is gene replication. Stopping reproduction means gene transmission ends. Why would nature keep so many old people who "don't work but still eat"?

III. This is the famous Grandmother Hypothesis. Systematically proposed by anthropologist Kristen Hawkes in the 1990s.