From male killer whales that ride the dorsal fin of another male to female bonobos that rub their genitals together, the animal kingdom tolerates all kinds of lifestyles. A first-ever museum display, "Against Nature?," which opened last month at the University of Oslo's Natural History Museum in Norway, presents 51 species of animals exhibiting homosexuality. "Homosexuality has been observed in more than 1,500 species, and the phenomenon has been well described for 500 of them," said Petter Bockman, project coordinator of the exhibition. The idea, however, is rarely discussed in the scientific community and is often dismissed as unnatural because...