Researchers already know that women live longer than men in all parts of the world. Scientists have largely linked the difference in life expectancy between the sexes to biological survival factors. Now, a new study of wild mammals has found great differences in length of life and aging in many species of mammals. The researchers found that, in humans, women live almost 8 percent longer than men. But among wild mammals, females in 60 percent of the studied species live, on average, 18.6 percent longer.