There has been much controversy over the biology or otherwise of homosexuality in the 2012 NZ debate over same-sex marriage. Advocates who say gay is “chosen” (and give true-life examples) have been called “ignorant bigots” and “demented” by well-known bloggers and media ‘because of the science.’ The following post is a summary by me of the main 20th C. sex-science. It is taken from a long academic article by the AllPsych Journal in America which is the largest and most comprehensive psychology website on the Internet. You can check AllPscyh’s veracity and credentials here: http://allpsych.com/journal/homosexuality.
For those who can’t be bothered reading to the end (Gen. Y.) essentially it concludes there is NO SCIENTIFIC EVIDENCE to support homosexuality is biological. A number of small human experiments show differences between some gay and straight people physiologically (actual body differences) but no more than between different individuals or between men and women of different race or individuals of the same race. The scientists themselves are completely divided.
Rider:The Journal did not attempt to discuss the morality of homosexuality. Their examination was not to prove whether or not homosexuality is right or wrong, but rather to establish a thorough understanding of the biological and social theories surrounding the cause of homosexuality.
The Journal concluded:“We have examined many causes for homosexuality…both biological and social. And although an interesting topic of debate, no one theory or experiment leads to a definitive answer.”
“The debate endures because both sides have the ability to create a scientific environment to support their cause.”
HERE IS THE SCIENCE:
1860s, Charles Darwin: “…we do not even in the least know the final cause of sexuality. The whole subject is hidden in darkness.”
Pre-1950s: The American Psychological Association (hereafter APA) defined homosexuality as a mental disorder. Subsequent research into its causes, origins, and development led to that definition being removed by the APA from its list of diagnoses and disorders.
1940s & 50s Kinsey and various 20th C. Biological theorists: found substantial instances of anatomical, genetic, and endocrine evidence to support homosexuality is biological. Experiments yielded that 30% of males had experienced at least orgasm in a homosexual act. The results of this research became the widely popularized Kinsey Scale of Sexuality. This scale rates all individuals on a spectrum of sexuality, ranging from 100% heterosexual to 100% homosexual, and everything in between. While establishing that as many as 10% of adult males reported having sexual relations with a same-sex partner, this research did little more than to put the word homosexual into common language. [It is also the origin of the myth that 10% of populations are gay].
Post-1950s: Although the APA currently states that sexual orientation is not a choice, rather that “…it emerges from most people in early adolescence with no prior sexual experience”, social theorists argue that an individual’s upbringing can directly influence this [sexual orientation].
1957, Evelyn (Karen) Hooker*: executed the first psychological test done to test for biological determinism in 1957, on a grant from the National Institute of Mental Health. These three tests, the Rorschach, Thematic Apperception Test (TAT), and the Make-A-Picture-Story Test (MAPS) yielded no significant differences in answers on any of the three tests. Because both groups’ (stated gay and stated straight) answers scored very similarly, she concluded a zero correlation between social determinism of sexuality.
1970s, 1990s APA: as a result of Hooker’s finding, the APA removed homosexuality from its Diagnostic and Statistical Manual of Psychological Disorders in 1973. In 1975 it released a public statement that homosexuality was not a mental disorder. In 1994, two decades later, the APA finally stated, “…homosexuality is neither a mental illness nor a moral depravity. It is the way a portion of the population expresses human love and sexuality.” This aligned with Aristophanes’ conclusions in the 5th C. BC.
1990s, hypothalamus, D.F. Swaab, Laura Allen: conducted the next noteworthy experiment in 1990. His experiment became the first to document a physiological difference in the anatomical structure of a gay man’s brain. Swaab found in his post-mortem examination of homosexual males’ brains that a portion of the hypothalamus (sexual drive and function) of the brain was structurally different than a heterosexual brain. In the homosexual brains examined, a small portion of the hypothalamus, termed the suprachiasmatic nucleus (SCN), was found to be twice the size of a small survey of heterosexual counterparts.
At the same time, another scientist, Laura S. Allen made a similar discovery in the hypothalamus, finding that the anterior commissure (AC) of the hypothalamus was also significantly larger in some homosexual subjects than of heterosexuals.
Both Swaab’s and Allen’s results became a standing ground for the biological argument on homosexuality.
1990s Simon LeVay: conducted another experiment regarding the hypothalamus of the human brain in 1991. LeVay, like Swaab and Allen also did a post-mortem examination on human brains; however, he did his examinations on patients who had died from AIDS-related illnesses. He discovered that within the hypothalamus, the third interstitial notch of the anterior hypothalamus (INAH3) was two to three times smaller in homosexual men then in heterosexual men. The women examined also exhibited this phenomenon. LeVay concluded the “homosexual and heterosexual men differ in the central neuronal mechanisms that control sexual behavior”, and like Allen and Swaab, agreed that this difference in anatomy was no product of upbringing or environment, but rather prenatal cerebral development and structural differentiation.
20th C. ‘Gay gene’ Neuroendocrine studies & 2000s Hamer (hormone distribution, neuro: “inside” and endocrine: “secrete”): The neuroendocrine viewpoint’s basic hypothesis is that sexual orientation is determined by the early levels (probably prenatal) of androgen on relevant neural structures. If highly exposed to these androgens, the fetus will become masculinized, or attracted to females. Hamer examined the family trees of the same men that on each subject’s mother’s side. There were markedly larger numbers of homosexual men stemming through the maternal lineages. This observation, along with his startling discovery on Xq28, led his findings to be dubbed the “gay gene study”.
While all of this scientific experimentation and conclusion seems evidentiary, socio-behaviorists are not convinced. This opposing point-of-view proposes that homosexuality is the result of environmental factors, not biological ones.
20th C. Social-Behaviourists incl. Halperin and Foucault: Most social theorists see childhood elements as the largest contributing factors to homosexuality. Often they examine childhood play patterns, early peer interactions and relations, differences in parental behavior toward male and female children, and the role of gender constancy in the household. Two predominant social theorists on homosexuality are David Halperin and Jean Foucault. The theorists believe that the homosexual had been an aberration, and had then become a species, justifying itself with a new word.
The central premise of a huge body of 2oth c. social-behavioural science is that just because there are differences in some facets of biology, this does not conclude sexual practices anymore than other differences in humans (which are wide and multifarious) determines other behavioral stereotypes: “Cretans are all lazy” [to quote ancient Cretan poets] ‘one race is more intelligent than another’) etc. Their conclusion is that sexuality is complex, deeply cultural, and related to human psychology.
Conclusions: as stated above, The AllPsych Journal concluded:“We have examined many causes for homosexuality…both biological and social. And although an interesting topic of debate, no one theory or experiment leads to a definitive answer.” “The debate endures because both sides have the ability to create a scientific environment to support their cause.”
Sources worth further exploration: APA Online. “Answers to Your Questions About Sexual Orientation and Homosexuality”. Online. 11 April 2003. Available http://www.apa.org/pubinfo/answers.html.  “Biological Basis for Homosexuality.” Online. 8 April 2003. Available http://www.geocities.com/southbeach/boardwalk/7151/biobasis.html  Bull, James J. and Pease, Craig M. “Biological Correlates of Being Gay” Online. 11 April 2003. Available http://www.utexas.edu/courses/bio301d/Topics/Gay/Text.html.  Fujita, Frank. “The Nature-Nurture Controversy.” Online. 8 April 2003. Available http://www.iusb.edu/~ffujita/Documents/nn.html  Hoback, Wyatt. “Lecture 21. Sociality.” Online. 11 April 2003. Available http://www.unk.edu/acad/biology/hoback/2002bio470/470lecture21.htm.  Moberly, Elizabeth R. Homosexuality: A New Christian Ethic. James Clarke and Co.; Cambridge, MA, 1983.  Pillard, Richard. “NPR Letters on the Biological Basis of Homosexuality.” Online. 8 April 2003. Available http://cas.bellarmine.edu/tietjen/RootWeb/ npr_letters_on_the_biological_ba.htm  Sullivan, Andrew. Virtually Normal: an Argument about Homosexuality. Alfred A. Knopf; New York, NY, 1995.  Thompson and Devine. “Homosexuality: Biologically or Environmentally Constructed?” Online. 8 April 2003. Available http://jrscience.wcp.muohio.edu/Research/ HNatureProposalsArticles/Homosexuality.biologicall.html  Thorp, John. “The Social Construction of Homosexuality.” Online. 8 April 2003. Available http://www.fordham.edu/halsall/med/thorp.html  Taylor, Tim. “Current Theories on the Genesis of Homosexuality.” Online. 11 April 2003. Available http://www.dai.ed.ac.uk/homes/timt/ papers/twin_studies/theories.html. * Evelyn nee Gentry (Caldwell) Hooker seems to be called “Karen” by several scholars. It was perhaps a nickname, or is a confusion with Karen Evelyn Hooker, a child psychologist who is still alive, of NH. Hooker published as “E. Hooker” and the “Evelyn Hooker Center” is named after her.