bruce 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, which made homosexuality in animals a taboo subject. he 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.