Editing Homosexual behavior in animals (section)

==Basis==
Sexual behaviors often require a significant energy investment. When sexual behaviors produce offspring, there is an obvious benefit for the animal. However, the benefit from performing homosexual behaviors (which cannot result in the production of offspring) is less obvious, and some scientists have called it a "Darwinian paradox" because it is non-reproductive. A number of non-exclusive different explanations for the emergence of such traits have been put forward.<ref>{{cite encyclopedia|author1-link=Vincent Savolainen |last1=Savolainen |first1=Vincent |title=Encyclopedia of Evolutionary Psychological Science |entry=Evolution of Homosexuality |publisher=[[Springer Publishing]] |year=2016 |pages=1–8|doi=10.1007/978-3-319-16999-6_3403-1 |isbn=978-3-319-16999-6|s2cid=220448278 }}</ref>

===Physiological basis===
A definite [[physiological]] explanation or reason for homosexual activity in animal species has not been agreed upon by researchers in the field. Numerous scholars are of the opinion that varying levels (either higher or lower) of the [[sex hormones]] in the animal,<ref name="Adler 1997 8–9">{{cite journal |last=Adler |first=Tina| name-list-style = vanc |title=Animal's Fancies|journal=Society for Science and the Public|date=4 Jan 1997|volume=151|issue=1|pages=8–9|doi=10.2307/3980720|jstor=3980720}}</ref> in addition to the size of the animal's gonads,<ref name=Bagemihl/>{{rp|164}} play a direct role in the sexual behavior and preference exhibited by that animal. Others firmly argue no evidence to support these claims exists when comparing animals of a specific species exhibiting homosexual behavior exclusively and those that do not. Ultimately, empirical support from comprehensive [[endocrinological]] studies exist for both interpretations.<ref name="Adler 1997 8–9"/><ref name="Somer_2010" /> Researchers found no evidence of differences in the measurements of the gonads, or the levels of the sex hormones of exclusively homosexual [[western gulls]] and [[ring-billed gulls]].<ref name=Bagemihl/>{{rp|164}}

Additional studies pertaining to hormone involvement in homosexual behavior indicate that when administering treatments of testosterone and estradiol to female heterosexual animals, the elevated hormone levels increase the likelihood of homosexual behavior. Additionally, boosting the levels of sex hormones during an animal's pregnancy appears to increase the likelihood of it birthing a homosexual offspring.<ref name="Adler 1997 8–9"/>

===Genetic basis===
Researchers found that disabling the fucose mutarotase<ref>{{cite web | url=http://www.wikigenes.org/e/gene/e/945842.html | archive-url=https://web.archive.org/web/20160610084742/http://www.wikigenes.org/e/gene/e/945842.html | archive-date=10 June 2016 | title=WikiGenes - Collaborative Publishing }}</ref> (FucM) gene in laboratory mice – which influences the levels of [[estrogen]] to which the brain is exposed – caused the female mice to behave as if they were male as they grew up. "The [[Knockout mouse|mutant female mouse]] underwent a slightly altered developmental programme in the brain to resemble the male brain in terms of sexual preference" said professor Chankyu Park of the [[Korea Advanced Institute of Science and Technology]] in Daejon, South Korea, who led the research. His findings were published in the [[BioMed Central|''BMC Genetics'' journal]] on July 7, 2010.<ref>{{cite news|url=https://www.telegraph.co.uk/science/science-news/7877774/Female-mice-can-be-turned-lesbian-by-deleting-gene.html |archive-url=https://web.archive.org/web/20100710155012/http://www.telegraph.co.uk/science/science-news/7877774/Female-mice-can-be-turned-lesbian-by-deleting-gene.html |url-status=dead |archive-date=2010-07-10 |title=Female mice 'can be turned lesbian by deleting gene' |newspaper=The Telegraph |date=2010-07-08 |access-date=2010-11-17 |location=London |first=Matthew |last=Moore| name-list-style = vanc }}</ref><ref>{{cite journal | vauthors = Park D, Choi D, Lee J, Lim DS, Park C | title = Male-like sexual behavior of female mouse lacking fucose mutarotase | journal = BMC Genetics | volume = 11 | pages = 62 | date = July 2010 | pmid = 20609214 | pmc = 2912782 | doi = 10.1186/1471-2156-11-62 | publisher = BioMed Central | doi-access = free }}</ref> Another study found that by manipulating a gene in fruit flies (''[[Drosophila]]''), homosexual behavior appeared to have been induced. However, in addition to homosexual behavior, several abnormal behaviors were also exhibited apparently due to this mutation.<ref>{{cite journal| vauthors = Terry J |title='Unnatural Acts' in Nature: The Scientific Fascination with Queer Animals |journal=GLQ: A Journal of Lesbian and Gay Studies|year= 2000|volume=6|issue=2|pages=151–193|doi=10.1215/10642684-6-2-151|s2cid=145504677 }}</ref>

===Neurobiological basis===
In March 2011, research showed that [[serotonin]] is involved in the mechanism of sexual orientation of mice.<ref>{{cite news|url=https://www.bbc.co.uk/news/health-12825688 |title=Sexual preference chemical found in mice |work=BBC News |date=2011-03-23 |access-date=2011-03-24}}</ref><ref>{{cite journal | vauthors = Liu Y, Jiang Y, Si Y, Kim JY, Chen ZF, Rao Y | title = Molecular regulation of sexual preference revealed by genetic studies of 5-HT in the brains of male mice | journal = Nature | volume = 472 | issue = 7341 | pages = 95–9 | date = April 2011 | pmid = 21441904 | pmc = 4094133 | doi = 10.1038/nature09822 | bibcode = 2011Natur.472...95L }}</ref> A study conducted on fruit flies found that inhibiting the dopamine neurotransmitter inhibited lab-induced homosexual behavior.<ref>{{cite journal|last=Zuk|first=Marlene|name-list-style=vanc|title=Same-sex insects: what do bees-or at least flies-have to tell us about homosexuality?|journal=Natural History|date=22 November 2011|volume=119|issue=10|pages=22 |url=https://experts.umn.edu/en/publications/same-sex-insects-what-do-bees-or-at-least-flies-have-to-tell-us-a}}</ref>
<!-- Homosexual behaviour in insects and arachnids have been difficult to interpret. Most species has a very limited registry of social interactions, making homosexuality as a functional adoptions as seen in social vertebrates less likely. In a review of reports of homosexual behaviour 102 arthropod species, as much as 80% of the observations was suggested as being due to mistaken identity. The authors speculate that the fitness costs to males in same-sex copulation would be less than the cost of ignoring a female, and that the energetic cost of a sensory apparatus with better accuracy outweigh the fitness cost of occasional homosexual behaviour.<ref>{{cite journal| vauthors = Scharf I, Martin OY |title=Same-sex sexual behavior in insects and arachnids: prevalence, causes, and consequences|journal=Behavioral Ecology and Sociobiology|date=2 August 2013|volume=67|issue=11|pages=1719–1730|doi=10.1007/s00265-013-1610-x}}</ref> In some species exhibiting [[traumatic insemination]] (e.g. [[Bed bug|bedbugs]]), male homosexual behaviour will usually cause the death of the inseminated male, which may make such act a form of male combat against competitors.<ref>{{cite web| vauthors = Hansen J |title=A sex life with rape and pepper spray|url=http://dca.au.dk/en/tempside/show/artikel/et-sexliv-med-voldtaegt-og-peberspray/|publisher=DCA - DanishCentre For Food And Agriculture|access-date=8 March 2018}}</ref>> -->

=== 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>