In humans, it is suspected that androgen levels are the affecting hormone toward a homosexual disposition among men. Androgen is the male sex hormone which initiates male development physically. In addition to this function, androgen also has effects male brain development. It is assumed that normal-to-high androgen levels of androgen released into the foetus during pregnancy produce heterosexual males. Low androgen levels released into the foetus does not develop the brain in the same way as normal levels and so produced homosexual males. Differences in the make-up of the brain between heterosexual men and homosexual men will be discussed later in the paper. While the theory of androgen and its effects on behaviour are suspected, it can not be proven as testing this on humans at this fragile stage of life would harm the developing child and so therefore can not be conclusive.
Extreme stress levels seems to also have a bearing on male neonates. If a mother carrying a neonate is under extreme duress, she will produce more stress-hormones such as adrenocorticotropic hormones (ACTH), corticosterone, cortisol, and epinephrine (Stechler & Halton, 1982; Ward, 1984, as cited in Ellis & Ames, 1987). All of these hormones retards the effects of testosterone on the infant's development. This effect was tested on pregnant rats in their third trimester. The pregnant rats were placed in an intensely lit cage while she was uncomfortably contained inside a narrow plastic tube. After she gave birth, the male offspring exhibited same-sex behaviour (Ward, 1974, 1977, as cited in Ellis & Ames, 1987). This study has been replicated several times since then (Dahlof, Hard, and Larzzon, 1977; Whitney and Herrenkohl, 1977; Gotz and Dorner, 1980; Rhees and Fleming, 1981, as cited in Ellis & Ames, 1987). Anecdotally, this effect seemed to match historical records from the Second World War (Dorner, Geier, Ahrens, Krell, Munx, Gsieler, Kittner, & Muller, 1980, as cited in Ellis & Ames, 1987). Germany recorded that there were an unusually high number of homosexual men from 1934 through to 1953 who were born from pregnancies carried through the war. The researchers explained that this was an unusually distressing time in German history and perhaps the effect of stress-hormones took hold of a generation of men. Of course it is difficult to prove this relationship because it is too far in the past, however further studies have investigated stress-levels as cause for sexual diversion. A sample of mothers who knew they had homosexual, bisexual, and heterosexual sons were asked if they remembered being particularly stressed during their pregnancy. Answers ranged from divorce, death of a family member, and traumatic financial woes. The study found that two thirds of the mothers of homosexual offspring remembers specifically being extremely stressed at the point of pregnancy. This is in comparison to only one third of the mothers of bisexual children, and less than ten percent of the heterosexual children (Dorner, Schenk, Schmiedel and Ahrens,1983, as cited in Ellis & Ames, 1987). This observed relationship however is difficult to measure as an effect, and the researchers also observed that there would be wide variation between mothers as to how much stress they could deal with before they were overwhelmed and their offspring affected (Dorner, et al., 1983, as cited in Ellis & Ames, 1987).
Lastly in regards to hormones, research has determined that several female contraceptives based on anti-androgen chemical effects. Medroxypogesterone acetate (a.k.a. Depo-Pravera), flutamide, cimetidine and cyproterone acetate are all capable of blocking testosterone's effects or alternatively block the neuro-organisational function of sex hormones (Anand & van Thiel, 1982; Clemens, Gladue, & Coniglio, 1978; Neumann & Steinbeck, 1973, as cited in Ames & Ellis, 1987). These drugs change how androgens synthesize and therefore assist in forming androgen receptors in the male foetus.
Simon LeVay (1991, as cited in Baur & Crooks, 1999) suspected that homosexual attraction could be biological in nature and did a comparative study on the brains of forty-one cadavers. He did post-mortem examinations on nineteen known homosexual men who had died from AIDS, sixteen presumed heterosexual men, two of whom died of AIDS complications, and six presumed heterosexual women. LeVay found that the anterior hypothalamus, which is the area of the brain that influences sexual behaviour, of the homosexual men were half the size of the heterosexual men. By comparison, the anterior hypothalamus of the homosexual men was similar in size to the female counterpart. The results suggest that the size of the anterior hypothalamus is a dimorphic characteristic that separates men and women, and that homosexual men biologically share this characteristic with women. However, LeVay himself said that this was a suggestion that he intended to open to further research and accepted that this study could be criticized by the facts that the homosexual men died of various AIDS complications that could have affected this outcome. This study was replicated with sheep in 2002 at Oregon State University (Gay for Hay?). The research team dissected ten ewes, nine rams that only mated with other rams, and eight rams that mated only with females. They found again that the anterior hypothalamus of the homosexual rams were equal in size to the ewes, and that the anterior hypothalamus of the heterosexual rams were double in size. While across species, this study supports LeVay's findings and possibly negates the effect AIDS had on the findings.
Genetic Theory
Genetics and heritability have long been suspected as contributing to the differences between heterosexual and homosexual men. Irving Kallman's (1952) studied eighty-five sets of male identical twins where one twin was homosexual. Out of those eighty-five, Kallman found that forty pairs which he described as having 'perfect concordance' meaning that when one twin was homosexual, so was the other. He compared this finding with forty-five sets of fraternal twins which he reported as an insignificant level of concordance. Kallman's study does seem to be flawed. It should have been expected that among the fraternal-twin study, while perhaps not as strong as the concordance among identical twins, there would be more an an insignificant level because the fraternal twins still shared half of there genes (Cirese & Wade, 1991). Bailey and Pillard (1991, as cited in Baur & Crooks, 1999) replicated Kallman's study improving the sample by including a test group of adopted brothers. They found similar results among identical twins as Kallman found, with fifty-two percent concordance. The previously criticize fraternal-twin result of Kallman's was reshaped when twenty-two percent concurrence was found in the 1991 study, and among the adopted brothers, there was eleven percent concurrence. Bailey and Pillard noted that in fact their concurrence rates could be higher as all of their twins were raised in the same home, and so environmental factors would have similarly affected the set of brothers. However, the replication of the strong concurrence among identical twins suggest a genetic component. It should be noted though that twin studies can be criticized in how samples for gay identical twins are recruited. The volunteers for these studies are almost exclusively recruited through advertisements in gay-interest magazines and word of mouth throughout gay communities. Therefore, homosexual twin study samples are likely to be affected by volunteer bias as gay identical and fraternal twins are likely to volunteer. The concurrence could be overstated based on the eagerness of volunteers.
However, support for a genetic link is not limited to concurrent homosexual behaviour in twin studies alone. Dean H. Hamer (1993, 1999) discovered similar genes that were shared between homosexual men and other homosexual men they were related to maternally. His study looked at relatives not only among brothers, but inclusive of uncles as well. Out of 182 families that had two or more gay brothers, he found that 13.4% of maternal uncles were gay in contrast to 6.9% of paternal uncles. He hypothesized that a gene found the the X-chromosome, Xq28, was shared between the family members. This would imply that homosexual behaviour is inherited from the mother.
Birth Order Theory
Perhaps the strongest evidence that concerns the sexual orientation of the child is the effect or birth order. Anthony Bogaert (2002) points that national health statistics collected in the United States and The United Kingdom point to the fact that gay men are more likely than heterosexual men to be born middle or last (Laumann, Gagnon, Michael, & Michaels, 1994, as cited by Bogaert, 2002). Biologically, Bogaert theorizes that each male pregnancy that comes to term, essentially 'inoculates' the mother's immune system. When a mother carries a girl, that girl foetus is not attacked by the mother's immune system because her antibodies interpret the foreign object (the baby) as similar in genetic code to the mother. However, in boys, the immune system sees the male foetus as a foreign object that should be attacked. The immune system is easy 'defeated' so to speak when the first male child is brought to term. However, by way of inoculation, when the second male foetus is introduced into the mother, the mother's immune system recognises the 'foreign object' from the first pregnancy and is better prepared to attack it. The mother's body prevents this by releasing antibodies, known as HY antigens, into the womb which deters the immune system. For each male foetus she carries, the immune system gets stronger, and she releases more deterring antibodies. Bogaert theorizes that either these antibodies are having an effect on the androgen levels in the womb on the male foetuses or that the HY antigens are themselves affecting brain masculinisation. Based on LeVay's theory that decreased androgen levels in utero affect the anterior hypothalamus, this would explain why men with two or more older brothers have an increased chance of being homosexual. In fact, for each additional older brother a man has, increases his chances of being homosexual by 33% (Blanchard, 1997).
The Differences of Sexually Dimorphic Traits
Lastly, sexually dimorphic traits that normally differentiate between men and women have been observed occurring in homosexual men, setting them apart from their heterosexual counterparts. Sexual dimorphic traits are the biological traits that that differentiate males from females across species. An example of a dimorphic trait in animals would be antlers on deer. Only a male deer can grow antlers and females can not. Two human examples would be how males have a larger heart than females, and that females have a greater than ninety degree angle in the infrapubic angle of their pelvic bone. Dimorphic traits that normal contrast men and women do occur to contrast heterosexual men and homosexual men. As previously mentioned, the size of the anterior hypothalamus could be interpreted as a dimorphic trait. In addition to this, gay men also share the female pattern of decreased cerebral laterality (Reite, Sheeder, Richardson, & Teale, 1995, as cited in Bailey, Chivers, & Mustanski, 2002). Also, EEG patterns of gay men resemble EEG patterns recorded from heterosexual women during spatial and verbal testing (Alexander & Sufka, 1993, as cited in Bailey et al., 2002).
Conclusion
Biological differences between heterosexual men and homosexual men were largely speculated in the past when scientists were trying to determine a cause of homosexuality when it was considered a mental disorder (Kallman, 1952). Since that time, advances in technology in the fields of microscopy, medicine and genetics, as well as social attitudes surrounding homosexuality as acceptable behaviour and not a disorder have allowed biological characteristics to come to light and be studied by the medical field and social scientists. Biological differences such as hormone levels affecting the neonate, chromosome detection, and birth order seem to be likely factors in determining differences in homosexual and heterosexual men. In addition, new research is finding sexually dimorphic traits normally contrasting heterosexual men and women shared between heterosexual and homosexual men, such as the size of the anterior hypothalamus, brain activities, and performance tasks. Although the origins of this differences are not known and therefore can not imply any conclusions, these findings should inspire new research and studies in the future to detect the reasons these differences exist.
Works Cited
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