List of animals displaying homosexual behavior

For these animals, there is documented evidence of homosexual behavior of one or more of the following kinds: sex, courtship, affection, pair bonding, or parenting, as noted in researcher and author Bruce Bagemihl's 1999 book Biological Exuberance: Animal Homosexuality and Natural Diversity.

Bagemihl writes that the presence of same-sex sexual behavior was not "officially" observed on a large scale until the 1990s due to possible observer bias caused by social attitudes towards LGBT people, making the homosexual theme taboo. Bagemihl devotes three chapters; Two Hundred Years at Looking at Homosexual Wildlife, Explaining (Away) Animal Homosexuality and Not For Breeding Only in his 1999 book Biological Exuberance to the "documentation of systematic prejudices" where he notes "the present ignorance of biology lies precisely in its single-minded attempt to find reproductive (or other) 'explanations' for homosexuality, transgender, and non-procreative and alternative heterosexualities." Petter Bøckman, academic adviser for the Against Nature? exhibit stated "[M]any researchers have described homosexuality as something altogether different from sex. They must realise that animals can have sex with who they will, when they will and without consideration to a researcher's ethical principles." Homosexual behavior is found amongst social birds and mammals, particularly the sea mammals and the primates.

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