The burgeoning field of sexual orientation research is offering revolutionary findings and insight into the origins of sexuality. Here is a snapshot of several key studies:
* In 1993, the National Institute of Health’ Dean Hamer illustrated that homosexuality might be inherited from the mother by her sons through a specific region of the X chromosome (Xq28). Hamer demonstrated this by noting that 33 out of 40 pairs of homosexual brothers whom he studied showed the same variation in the tip of the chromosome.
- Hamer DH, Hu S, Magnuson VL, Hu N. and Pattatucci AML. A linkage between DNA markers on the X chromosome and male sexual orientation. Science 1993; 261:320-326.
Q&A: Molecular Biologist Dean Hamer on ‘ex-gay’ issues
* A June 2006 Canadian study published in the journal, “Proceedings of the National Academy of Sciences,” said that nature, instead of nurture, explains the origins of homosexuality. The study’ author, Prof. Anthony F. Bogaert, at Brock University in Ontario, explored the causes behind what is known as the fraternal birth order. The research showed a correlation between the number of biological older brothers a man has and his sexual orientation. Dividing his sample of more than 900 heterosexual and homosexual men into four groups, Bogaert examined the impact of all types of older brothers, including step and adopted siblings, and the amount of time brothers spent together while growing up.His research found that only the number of biological brothers had an impact on sexuality, regardless of whether the boys were raised together.
- Bogaert, A.F. 2006. Biological versus nonbiological older brothers and men’s sexual orientation. Proceedings of the National Academy of Sciences 103 July 11 2006.
* A study released in May 2006 by Swedish scientists demonstrates that biology plays a key role in determining a person’ sexuality. The research shows that the portion of the brain that helps regulate sexuality — the hypothalamus – reacted the exact same way in straight women and gay men when exposed to male pheromones, which are chemicals designed to provoke a behavior, such as sexual arousal. The same area of the brain only became stimulated in heterosexual men when introduced to female pheromones.
- by Ivanka Savic article in the Proceedings of the National Academy of Sciences, (PNAS) “Brain Response To Putative Pheromones In Homosexual Men,” (Vol. 102 No. 19) May 10, 2005.
* In 2005, Dr. Brian Mustanski of the University of Illinois at Chicago published a study in the esteemed biomedical journal Human Genetics, claiming he identified three chromosomal regions linked to sexual orientation in men: 7q36, 8p12 and 10q26.
- “A Genomewide Scan of Male Sexual Orientation”, Human Genetics, Vol. 116, No. 4, pp. 272-278, 2005.
* In 2003, University of Texas psychoacoustics specialist Dennis McFadden found that when measuring the way the brain reacts to sound, lesbians fell in between heterosexual men and straight women, suggesting they might be exposed to higher than normal levels of male hormone in utero.
- Loehlin, John C.; McFadden, David. “Otoacoustic emissions, auditory evoked potentials, and traits related to sex and sexual orientation”. Archives of Sexual Behavior. 1 April 2003.
* In 2003, University of Liverpool biologist John T. Manning found that the lesbians whom he studied have a hand pattern that resembles a man’ more than a straight female’. Manning concluded from his study that this “strongly tells us that female homosexuals have had higher levels of exposure to testosterone before birth.”
- Neave, N., Laing, S., Fink, B., Manning, J.T (2003) Second to fourth digit ratio, testosterone, and perceived male dominance. Proceedings of the Royal Society B (Lond), 270, 2167-2172.
* A 1991 study by Dr. Simon LeVay found that a specific region of the hypothalamus is twice as large in heterosexual men as it is in women or gay men. This strongly points the role of biology in sexual orientation.
- Levay, Simon “A difference in hypothalamic structure between homosexual and heterosexual men” Science. 1991 Volume 253, Issue 5023, pp. 1034-1037.
* Another 1991 study by scientists Richard Pillard and John M. Baily studied homosexuality among brothers and found that 53 percent of identical twins were both gay. In adoptive brothers, 11 percent were both homosexual. Of non-twin biological siblings, 9 percent were gay. Again, this points to solid evidence that homosexuality is a matter of nature.
- Bailey JM, Pillard RC (1991). A genetic study of male sexual orientation. Archives of General Psychiatry, 48, 1089-1096.
* The JUN/JUL 2006 issue of Seed Magazine points out that at least 450 vertebrate species engage in homosexual behavior.
- Lehrer, Jonah. “The Gay Animal kingdom” Seed Magazine. Jun/Jul 2006.