In general, women outlive men. This is not a new idea. But what you might not know is that the effect can’t be explained by some simple hand-waving about risk-taking men, or war, or the allure of the Marlboro Man. In fact, the tendency for men to die at a higher frequency than women happens at every age group — even in utero. Fetal males die more often than fetal females. So what makes the men-folk so delicate? NPR’s Robert Krulwich investigates.