Editing Homosexual behavior in animals (section)

=== Other hypotheses ===

One proposal for the adaptive function of homosexual behavior is the formation of alliances and mutual social benefit to the animals. Studies support this in specific species, such as [[black swan]]s, where a quarter of mate pairs consist of two males, who mate with a female and chase her away once she lays the egg, then raise it themselves. These M-M pairs have great success in defending their territory and resources, and keep their young alive until fledgling 80% of the time, compared to 30% for M-F pairs.<ref>{{cite web |last1=Braithwaite |first1=L.Wayne |title=Ecological studies of the black swan |url=http://hdl.handle.net/102.100.100/292286?index=1 |publisher=Australian Wildlife Research |hdl=102.100.100/292286?index=1 |access-date=3 December 2021}}</ref>

Studies done on [[homosexual behavior in birds]] showed a negative correlation between a species' relative parental investment and F-F homosexual behaviors, i.e. in species whose females invested more time and care into their young relative to males, F-F sexual encounters happened less often. Similarly, there was a negative correlation between relative parental investment and M-M homosexual behaviors. This meant that species exhibiting a high degree of [[Animal sexual behaviour#Polygamy|polygamy]] (where females often are the exclusive caretakers of the young) F-F sexual behaviors were very rare, whereas in a socially [[Monogamy in animals|monogamous]] species (in which a M-F pair works together to care for young) they were much more common. The trend was opposite for males, in polygamous species M-M sexual behaviors were quite common and in socially monogamous species they were rare. The study argues that release from parental care, a very energy intensive investment, allows the opportunities for homosexual behaviors to be exhibited, and higher parental care prevents homosexual behaviors from occurring because of the energy cost of the behaviors.<ref>{{cite journal |last1=MacFarlane |first1=Geoff |title=Homosexual behaviour in birds: frequency of expression is related to parental care disparity between the sexes |url=https://www.sciencedirect.com/science/article/pii/S0003347210001855 |journal=Animal Behaviour |year=2010 |volume=80 |issue=3 |pages=375–390 |doi=10.1016/j.anbehav.2010.05.009 |s2cid=53148085 |access-date=3 December 2021|url-access=subscription }}</ref>

A 2019 paper hypothesized that when sex first began to evolve, there was no distinction between homosexuality and [[heterosexuality]], and animals mated with other members of their species indiscriminately. This is a contrast to most perspectives, which try to find explanations for the evolution of homosexual behaviors and separate it completely from the evolution of heterosexual behaviors. The study states that it is unlikely that sexual behaviors evolved simultaneously to the evolution of traits necessary to recognize a compatible sexual mate, such as size, shape, odor, and color. As those secondary sex characteristics evolved, sexuality would have become more discriminatory, leading to less homosexuality, but homosexual behaviors would rarely have had enough cost to be selected against and removed entirely from a population. Additionally, the cost of homosexual behavior would be offset by the cost of mate recognition, which requires psychological adaptations, and excessive discrimination in mate choice can lead to missing out of mating opportunities. With indiscriminate mating, these factors are irrelevant. The paper notes that in some species, especially where survival is very difficult and each energy-related decision could mean the animal's death, homosexual behavior would be strongly selected against, leading to strictly heterosexual species.<ref>{{cite journal |last1=Monk |first1=Julia |title=An alternative hypothesis for the evolution of same-sex sexual behaviour in animals |journal=Nature Ecology & Evolution |year=2019 |volume=3 |issue=12 |pages=1622–1631 |doi=10.1038/s41559-019-1019-7 |pmid=31740842 |s2cid=208144026 |doi-access=free |bibcode=2019NatEE...3.1622M }}</ref>