Behavioural observations from both the field and captivity indicate that same-sex sexual interactions are widespread throughout the animal kingdom, and occur quite frequently in certain non-human species. Proximate studies of these phenomena have yielded important insights into genetic, hormonal and neural correlates. In contrast, there has been a relative paucity of research on the evolutionary aspects. Homosexual Behaviour in Animals seeks to redress this imbalance by exploring animal same-sex sexual behaviour from an evolutionary perspective. Contributions focus on animals that routinely...