Animals' Same-Sex Sexual Behaviour Enhances Social Stability in Groups

Bonobo (Pan paniscus), a primate mammal that exhibits same-sex sexual behaviour（圖片來源：natataek，採用 CC BY-SA 3.0 授權）

Same-sex sexual behaviour has long attracted attention from many academic fields, including psychology, sociology, biology, and evolutionary science. Because such behaviour does not directly lead to reproduction, it has often been viewed, in theoretical terms, as disadvantageous from an evolutionary perspective. Yet the behaviour persists in a wide range of animal species. For this reason, some scholars have regarded it as an apparent paradox within evolutionary theory.

At present, more than 1,500 animal species worldwide have been reported to display same-sex sexual behaviour. These species span nearly every major animal group, including insects, spiders, echinoderms, nematodes, fish, amphibians, reptiles, birds, and mammals. Among these groups, mammals show the most frequent occurrence of same-sex sexual behaviour. Consequently, researchers have used mammals as a focal group to investigate what evolutionary advantages this behaviour might provide, allowing it to persist across evolutionary time.

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