Why Is Sex Fun? - The Evolution of Human Sexuality is a 1997 book by Jared Diamond dealing with the evolutionary development of human sexuality. Diamond addresses some peculiar aspects of human sexuality. These include why women's ovulation is not overtly advertised; why humans have sex in private rather than in public, as Diamond claims is the case in all other mammals; and why the ovaries are u-shaped. The book came five years after Diamond's previous work The Third Chimpanzee and was published in the same year as the well known title Guns, Germs, and Steel. It is dedicated to his wife Marie. It is part of the Science Masters series.