1.1 Essentialist theories

According to the essentialist theories, four main searchlines are forthcoming.

a) Hormonal arguments

The basic assumption is that our perception, cognition and senses are influences by hormones. Thus it can be assumed, that there might be hormonal differences between gay-or bisexual and heterosexual men, as well as between gay- or bisexual and heterosexual women. Along this theory, during pregnancy the foetus is not provided properly with sex specific hormones. Meyer-Bahlburg (1979) found out that at least one third of tested lesbians showed an elevation of male sex hormone levels (Meyer-Bahlburg, H. (1979) Sex hormones and female homosexuality: A critical examination. Archives of Sexual Behavior 8: 101-108). Other researches got to the conclusion that "women exposed prenatally via their pregnant mothers to diethylstilbestrol (DES, a synthetic nonsteroidal estrogen with masculinizing effects in female mammals) received higher ratings of homosexual behavior (Ehrhardt et al., 1985). Sex hormones do not only have an impact on the brain but on specific genes (hox-genes) as well. The hormonal shortage may lead to an increased “risk” of homosexuality. Hence, representatives of this theory take for granted that homosexual men have less masculine hormones and therefore are “less” masculine. New research in this field shows the more testosterone the brain of a foetus gets the more “masculine” in sense of masculine behaviour the person will show later on.
Since hox genes which are hormonal influenced have an influence on growth of some extremities like fingers, toes and genitals, theories arose showing that lesbian women do have a bigger/smaller index finger than heterosexual women.
Hormonal research nowadays focuses (among other things) on pheromones: These odour molecules might play an important part in the communication between human beings, and therefore also in sexual attraction. Since lesbian women are obviously not attracted to male odour, hormonal dysfunction might be the reason for it.
Blood tests may give indications about hormonal differences. However, such tests yet don't show any significant difference of hormonal level between people of same biological sex but different sexual orientations. Further, none of those researches aiming at hormonal differences of homosexuals show any serious and valid results.

b) Physiological arguments

Representatives of this approach assume that physiological differences – especially in the hypothalamus - between people of same biological sex but different sexual orientations do exist. Simon LeVay (1991) for example examined brain tissues of 41 subjects at routine autopsies of persons who died at seven metropolitan hospitals in New York and California. 19 subjects were homosexual men who died of AIDS, 16 subjects were presumed heterosexual men whereas 6 of them have died of AIDS as well, 6 women of whom 1 died of AIDS as well. The others died of other causes. LeVay hypothesized that two specific small groups of neurons (INAH2 or INAH3) at the hypothalamus are large in individuals sexually oriented toward women (heterosexual men, homosexual women) and small in individuals sexually oriented toward men (heterosexual women, homosexual men). He came to the conclusion that at least the volume of nucleus INAH3 was more than twice as large in the heterosexual men as in the homosexual men. Since all homosexual subjects died of AIDS he compared those with those heterosexual men who had died of AIDS as well. The difference was still significant. AIDS obviously had no effect on the volume of this nucleus. There was a similar difference between heterosexual men and the women but none between homosexual men and women. These data supported his hypothesis that INAH3 is dimorphic not with sex but with sexual orientation.
Nevertheless this research raises some problems: First, AIDS patients represent only an unrepresentative subset of gay men. It is questionable to conclude from one subset to all gay men. Second, the sample showed some exceptions, that is heterosexual men with small INAH3 nuclei and homosexual men with large ones. Maybe the subjects have been misassigned to their subject groups or sexual orientation is not the sole determinant of the size of this nuclei. So far, this kind research shows some methodological deficiencies which cannot be solved technically, since internalised homophobia might be a main factor of misassignment.
Other research focuses on homosexual women. Researches of The University of Texas at Austen, USA found out that there are differences of the auditory system of homo- and bisexual women and heterosexual women (Dennis McFadden and Edward Pasanen 1998). "Normal inner ears make sounds under certain circumstances," said Dr. McFadden, "and these sounds are known as otoacoustic emissions or OAEs." One type of OAE is an echo-like sound that the inner ear makes in response to the presentation of a weak click sound. These click-evoked otoacoustic emissions (CEOAEs) are stronger in women and girls than in men and boys. When McFadden's research team measured the CEOAEs of 61 homosexual and bisexual women, they found them to be significantly weaker than the CEOAEs of the 57 heterosexual women also tested (www.psy.utexas.edu/psy/announcements/dmpub.html). McFadden comes to the conclusion that "It appears that both the inner ears and some (unknown) brain structures responsible for sexual preference have been masculinized in these women."
Both examples of physiological research support the idea of a “feminization” of gay men and “masculinization” of lesbian women. Natural order seems to be heterosexuality, whereas homosexuals are biological deviant. (alleged causes: see hormonal causes)

c) The genetic arguments

According to this genetics, sexual orientation is genetically linked. In 1993, researchers from the Bethesda National Institute against cancer in Maryland, USA, discovered a genetic link to male sexual orientation (Dean H. Hamer, et al. 1993: Science 1993; 261:320-326). They investigated 114 families of homosexual men. Research revealed a correlation between sexual orientation and the inheritance of polymorphic markers (genetic road signs) on the X chromosome in approximately 64% of sibling-pairs tested. The linkage to markers on Xq28 indicates that at least one subtype of male sexual orientation is genetically influenced. Those results have been discussed in Science 1994 but as well as in Nature Genetics in 1994. Here Hamer et.al. published their continued research on that linkage and found out this genetic region contains a locus that influences individual variations in sexual orientation in men but not in women.
Other researches tried to do further study on the grounds of Hamer’s results. George Rice, Carol Anderson, Neil Risch and George Ebers of the Western University of Ontario studied 52 gay male sibling pairs from Canadian families who shared alleles at position Xq28. Four markers at Xq28 were analyzed (DXS1113, BGN, Factor 8, and DXS1108). Allele and haplotype sharing for these markers was not increased over expectation. These results do not support an X-linked gene underlying male homosexuality (George Rice et.al. 1999: Science 23 Vol. 284. no. 5414, pp. 665 – 667). Since then other surveys have been proceeding, yet rather unsuccessfully.

d) The psychological arguments

These psychoanalytical arguments are essentialist in the sense of Freudian theory. To Freud everybody is born bisexual. He established a causal link between circumstances having occurred in earliest childhood and a sexual orientation breaking with the ‘normal’ sexual development (Freud 1935): Auto-erotical fixation, fear for castration, unsettled Oedipus-complex, a weak threatening or missing father and an overprotecting, dominant or castrating mother may cause deviant sexual orientation. Yet none of the presuppositions are sufficient to explain homo-or bi-sexual orientation, since other people with identical defensive mechanisms, similar life-experiences, and like family outlines may perfectly be heterosexual.

Freud himself was speaking differently about homosexuality: to a mother who wanted him to treat her homosexual son, he replied, “Leave him alone, he is not ill.” He thought of psychic bisexuality as being an essential reality.

Even though biological causes cannot be expelled from explaining homosexuality, outlined examples point out that research results are questionable with regard to methods and philosophy. There is no shared biological cause explaining male and female homosexuality – let alone male or female heterosexuality. Some alleged causes aim at a “feminization” of gay men and “masculinization” of lesbian women and finally a deviancy of “normal” heterosexual orientation. This is nothing else than a prolongation of prejudices about homosexuals.

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