Bagemihl writes that the presence of same-sex sexual behavior was not "officially" observed on a large scale until the 1990s due to observer bias caused by social attitudes towards nonheterosexual 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 realize that animals can have sex with who they will, when they will and without consideration to a researcher's ethicalprinciples." Homosexual behavior is found amongst social birds and mammals, particularly the sea mammals and the primates.
Sexual behavior takes many different forms, even within the same species and the motivations for and implications of their behaviors have yet to be fully understood. Bagemihl's research shows that homosexual behavior, not necessarily sex, has been documented in about five hundred species as of 1999, ranging from primates to gut worms.Homosexuality in animals is seen as controversial by social conservatives because it asserts the naturalness of homosexuality in humans, while others counter that it has no implications and is nonsensical to equate natural animal behaviors to morality. Sexual preference and motivation is always inferred from behavior. Thus homosexual behavior has been given a number of terms over the years. The correct usage of the term homosexual is that an animal exhibits homosexual behavior, however this article conforms to the usage by modern research, applying the term homosexuality to all sexual behavior (copulation, genital stimulation, mating games and sexual display behavior) between animals of the same sex.
The all-female Whiptail lizard species Aspidoscelis neomexicanus (center), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, A. inornatus (left) and A. tigris (right). Research has shown that simulated mating behavior increases fertility for Aspidoscelis neomexicanus. One female lies on top of another, playing the role of the male, the lizard that was on bottom has larger eggs, in most cases. The lizards switch off this role each mating season.
Male homosexuality has been inferred in several species of dragonflies. A survey of damsel and dragonflies reveals characteristic cloacal pincher mating damage in 20–80 percent of the males, indicating a fairly high occurrence of sexual coupling between males.
Male flour beetles engage in same-sex coupling to practice mating and to rid themselves of "old, less effective" sperm.
Harrold, Max (February 16, 1999). "Creature Comforts". The Advocate. No. 779. pp. 61–62. Retrieved March 10, 2018. In his news book, Biological Exuberance: Animal Homosexuality and Natural Diversity ... author Bruce Bagemihl portrays an animal kingdom that embraces a whole spectrum of sexual orientations ... [and] paints a complex mosaic that resembles humanity ... At 751 pages and with photos and documentation of homosexual behaviour in more than 450 species of mammals, birds, repties, and insects, Biological Exuberance brings the dusty facts to light as Bagemihl deconstructs the all-heterosexual Noah's Ark we've been sold.
Liggett, Dave; Columbus Zoo and Aquarium staff. "African Forest: Bonobo". Columbus Zoo and Aquarium. Archived from the original on June 2, 2002. Retrieved November 14, 2011. ...frequent sex (including male-to-male and female-to-female) characterize bonobo society.
Smith, Dinitia (7 February 2004). "Love That Dare Not Squeak Its Name"New York Times. Retrieved on 10 September 2007. Reprinted as "Central Park Zoo's Gay Penguins Ignite Debate", San Francisco Chronicle.
^Sell RL, Wells JA, Wypij D (June 1995). "The prevalence of homosexual behavior and attraction in the United States, the United Kingdom and France: results of national population-based samples". Archives of Sexual Behavior. 24 (3): 235–48. doi:10.1007/BF01541598. PMID7611844. S2CID12929812.
^Wellings, K., Field, J., Johnson, A., & Wadsworth, J. (1994). Sexual behavior in Britain: The national survey of sexual attitudes and lifestyles. London, UK: Penguin Books.[page needed]
^ abBenz G (May 1, 1973). "Role of sex pheromone, and its insignificance for heterosexual and homosexual behaviour of larch bud moth". Experientia. 29 (5): 553–554. doi:10.1007/BF01926659. S2CID39282068.
^Lecomte, C.; Thibout, E.; Pierre, D.; Auger, J. (1998-04-01). "Transfer, Perception, and Activity of Male Pheromone of Acrolepiopsis assectella with Special Reference to Conspecific Male Sexual Inhibition". Journal of Chemical Ecology. 24 (4): 655–671. doi:10.1023/a:1022390102631. ISSN0098-0331. S2CID10001697.
^Palaniswamy P, Seabrook W, Ross R (July 15, 1979). "Precopulatory behavior of males and perception of a potential male pheromone in spruce budworm". Annals of the Entomological Society of America. 72 (4): 544–551. doi:10.1093/AESA/72.4.544. S2CID84678927.
^Sanders C (September 1, 1975). "Factors affecting adult emergence and mating behavior of the eastern spruce budworm, Choristoneura fumiferana (Lepidoptera: Totricidae)". Canadian Entomologist. 107 (9): 967–77. doi:10.4039/ENT107967-9. S2CID86477332.
^Chaudhuri A, Sinha A (July 15, 1997). "A male-male pairing in the tropical tasar silkmoth, Antheraea mylitta (Saturniidae)". News of the Lepidopterists' Society. 39 (3): 39.
^Schmieder-Wenzel C, Schruft G (January 12, 1990). "Courtship behaviour of the European Grape Berry Moth, Eupoecilia ambiguella Hb. (Lep., Tortricidae) in regard to pheromonal and tactile stimuli". Journal of Applied Entomology. 109 (1–5): 341–346. doi:10.1111/j.1439-0418.1990.tb00062.x. S2CID86384073.