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Homosexual orientation

Brief description of some studies of the
cause or causes
of homosexual orientation

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Some studies and indicators:

Studies into the causes of sexual orientation have mainly concentrated on males. All of the studies show that genes play a significant role in determining homosexual orientation. None of the studies show that the environment is solely responsible. We did not pick and choose the studies which are reported here. We have reported all that we have found, regardless of outcome.

bullet Studies on monozygotic twins: These are twins that resulted from the splitting of a single fertilized egg -- the zygote -- into two separate zygotes with identical genetic structure. They are commonly called "identical twins." Studies have been made which involve relatively rare cases in which identical twins were separated at birth and have not been in contact since. Studies consistently show that male homosexual orientation is mainly (perhaps entirely) determined at conception by a person's genes. This is such an important and definitive study that we describe it in more detail in separate multi-part essay.

bullet Suicide implications: The National Institute of Health (a US Federal Government agency) reported that as many as 30% of youth suicides are by gays and lesbians. Since only about 5% of the population identifies as lesbian or gay, this means that LGB youth commit suicide at a rate as high as six times the normal value. These are committed by youth who are certain that they will remain gay or lesbian for the rest of their lives. Many, probably most of these young people who complete a suicide attempt had been taught by their families, religious institutions, schools etc., starting at a very early age, to hate or reject homosexuality. If they had any hope of changing their orientation, they probably would seek counseling instead of killing themselves. Most probably believe that their sexual orientation was genetically caused and is unchangeable.

bullet Introspection: Most sexually active adults are aware that their sexual orientation is not chosen and not changeable. Assuming that you are a heterosexual:

bullet Consider how you would change yourself so that you become sexually attracted to a person of the same gender. You will realize that it is quite impossible to create feelings of sexual attraction if they do not currently exist.

bullet Consider at what age you chose your sexual orientation? You will realize that, as far back as you can remember, you were either asexual or heterosexual.

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Irrationality of choice: In the forward to the book "We Were Baptized Too: Claiming God's Grace for Lesbians and Gays", Anglican Archbishop Desmond Tutu of South Africa wrote:

"Someone has said that if this sexual orientation were indeed a matter of personal choice, the homosexual persons must be the craziest coots around to choose a way of life that exposes them to so much hostility, discrimination, loss, and suffering." 13

bullet Brain Structure: Simon LeVay, a Neuroanatomist at the Salk Institute in California published a study in 1991 which examined the brains of men who had died of AIDS. He found that the INAH 3 (a structure within the hypothalamus) differed in size between heterosexual and homosexual men. This suggested to the researcher that "sexual orientation has a biological substrate". 2 This study has been criticized on a number of grounds. Many of his subjects died of AIDS; perhaps the difference in structure size was caused by the disease, or the medications that they took, rather than the person's sexual orientation. Others have suggested that homosexual or heterosexual activity may have determined the size of the structure, rather than vice-versa. In spite of these weaknesses, the study has wide acceptance among human sexuality researchers.

bullet Hearing: A group of researchers at the University of Texas found structural differences in the inner ears between lesbians and heterosexual women. On average, women have more sensitive cochlea amplifiers than men; they are able to detect softer sounds in a very quiet room. The researchers found that lesbians had inner ear characteristics that were more like those of men. The structure of the inner ear forms before birth and is affected during pregnancy by androgens. 7 These findings indicate that the sexual orientation of females is at least partly decided before birth -- perhaps at conception.
bullet Incidence: Gays and lesbians do not appear to be any less common in societies which condemn and suppress homosexuals; they do not seem to be any more common in accepting societies. They also seem to be equally common in countries where parenting styles are very different. This would argue against sexual orientation being learned from the environment.

bullet Parenting: Almost all children raised in families headed by two gays or two lesbians grow up heterosexual. The sexual orientation of one's parents, and any associated parenting styles appear to have little or no influence over the orientation of their children.

bullet Infection: A new theory has been proposed that homosexuality is caused by a bacteria or virus. It is not a highly regarded theory by researchers. This also would argue against sexual orientation being learned from the environment.

bullet Epigenetics: This is a recent field of research of how gene expression is managed in individuals by temporary switches known as " 'epi-marks.' ... Sex specific epi-marks generally do not transfer between generations and are considered 'erased.' There are some indications that homosexuality can result when these marks are not 'erased' but are passed on from father to daughter or mother to son." 12 The theory suggests that this process may produce daughters with typically male sexual attraction or males with typically female attraction.

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  1. "How PFOX can help," at: 
  2. Simon LeVay, "The Sexual Brain," MIT Press, (1994). Read reviews or order this book safely from online book store
  3. J.M. Bailey, R. C. Pillard, "A Genetic Study of Male Sexual Orientation", Archives of General Psychiatry, 48 (1991): 1089-96.
  4. J. M. Bailey, R. C. Pillard, et al, "Heritable Factors Influence Sexual Orientation in Women" Archives of General Psychiatry, 50 (1993): 217-23.
  5. Chandler Burr, "A Separate Creation: The search for the biological origins of sexual orientation", Hyperon, New York, NY (1996)
  6. J.A.Y. Hall & D. Kimura, "Dermatoglyphic Asymmetry and Sexual Orientation in Men", Behavioral Neuroscience, Vol. 108 #6, 1994-DEC, P. 1203-1206.
  7. "Lesbian Ears", The Globe and Mail, Toronto ON, 1998-MAR-19.
  8. Jeff Donn, "Finger length linked to sexual orientation: Male hormones in womb produce differences: study," Associated Press, 2000-MAR-29
  9. Article, title unknown, Nature, 2000-MAR-30.
  10. Robert T. Lee, "Against Homosexuality," The Society for the Practical Establishment and Perpetuation of the Ten Commandments," 1998-JUN-20, at:
  11. Matt Ridley, "Nature via nurture: Genes, experience, and what makes us human," HarperCollins, (2003). Read reviews or order this book safely from online book store  This book discusses the effects of genes and the environment on human behavior and traits. It touches on homosexuality in a few locations.
  12. "Epigenetics Reveal Biological Information On Homosexuality," redOrbit, 2012-DEC-12, at:
  13. book cover image Marilyn Bennett Alexander & James Preston, "We Were Baptized Too: Claiming God's Grace for Lesbians and Gays," (1996). Read reviews or order this book safely from online book store

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Copyright © 1997 to 2013 by Ontario Consultants on Religious Tolerance
Latest update: 2013-JAN-21
Author: B.A. Robinson

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