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Startle responses is known to be an involuntary response rather than learned reaction. It controlled by the limbic system, a region of the brain that also controls sexuality. One of the researchers, Qazi Rahman, said: "The startle response is pre-conscious and cannot be learned...This is very strong evidence that sexual orientation may be 'hard-wired' in this region" of the brain. The researchers claimed that "this study offers the first independent evidence of a non-learned neurological basis for sexual orientation." Dr. Rahman said: "These findings may well affect the way we as a society deal with sexuality and the issues surrounding sexual orientation." 1 to 4
NIH study of multiple genetic origins to male homosexuality:The Hamer study, described above, showed that the Xq28 region of the X chromosome can cause a propensity towards homosexuality. Brian Mustakski of the University of Illinois in Chicago and colleagues at the National Institutes of Health searched for additional genes among other chromosomes which might be also involved in causing male homosexuality. Two articles analyzed his paper in Human Genetics journal and reached opposite conclusions:
Both articles are correct in what they report. However, they interpret the results to confirm their pre-existing beliefs about the cause of homosexuality Mustaksi remarked: "It’s the largest molecular genetic study ever done on sexual orientation." He said: "There is no one 'gay' gene. Sexual orientation is a complex trait, so it's not surprising that we found several DNA regions involved in its expression." They found three such locations. They studied the DNA of persons from 146 families in which there was at least two gay brothers. They included brothers from the 40 families use in the Hamer study of 1993, as well as from 106 new families. Brothers share about 50% of their genes. The study searched for markers --
short strips of DNA that commonly correspond to specific parts of a chromosome.
If all of the brothers in the study shared any specific marker significantly
more than 50% of the time, then the researchers would have found a genetic link to
homosexual orientation. As in previous studies, they were unable to confirm the results of Hamer's discovery of the Xq28 region of the X chromosome as a cause of homosexuality among their 146 test subjects. However, when they retested the 40 pairs that Hamer had used, they found that Xq28 could contain genes linked to sexual orientation. Mustanski refers to this as "locus heterogeneity" –- a situation in which one gene might influence sexual orientation in one family, but not in another family. Recall that Hamer's study selected only gays who had a surplus of gays in their mother's side of the family. Mustanski said: "The fact that we found suggestive evidence of different areas where there might be genes for sexual orientation builds upon the research that’s been done on family studies, twin studies, and previous molecular genetic studies which are consistently showing evidence of genetic influences." The chromosome 7 finding may shed new life on a Dutch study. A gene near 7q36
is known to be responsible for the creation of a brain center called the suprachiasmatic
nucleus. A Dutch research team in 1990 found that men with a homosexual
orientation have a larger suprachiasmatic nucleus than heterosexual men. Mustanski
said: "Perhaps this gene results in
different brain structure and that brain structure causes someone to be
heterosexual or homosexual." Warren Thockmorton and Ray Durwood are professors at the Grove City College -- a conservative Christian college which rejects "relativism and secularism." 7 They reviewed the Mustanki study and said: "The authors describe in the article three non-X chromosomal 'new regions of genetic interest' (7q36, 8p12, and 10q26). In the authors’ view, a noteworthy aspect of the study as follows: 'Our strongest finding was on 7q36 with a combined mlod score of 3.45 and equal distribution from maternal and paternal allele transmission. This score falls just short of Lander and Kruglyak's (1995) criteria for genomewide significance.' They go on to say 'two additional regions (8p12 and 10q26) approached the criteria for suggestive linkage' - again pointing out that neither was statistically significant." 6 If one assumes that the propensity towards homosexual orientation is determined by an interaction of many genes, then no region on any one chromosome can be expected to be conclusively proven. The finding that the chromosome 7 was very close to significant probably shows that it must be significant in some male homosexuals. It is worth noting that most studies into the causes of homosexuality seem to show that about 10% of individuals are set up to be potentially homosexual by some gene or combination of genes. However, only about 55% of them are triggered by an unknown environmental factor during early childhood so that they will develop as homosexuals after puberty. The Mustanski study shows that, if this theory is correct, some combination of multiple genes is involved, rather than a single gene.
LaVay study of brain structure:Simon LeVay, a Neuroanatomist at the Salk Institute in California published a study in 1991 which examined the brains of men, many of whom 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". 8 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, not the sexual orientation. Others have suggested that homosexual or heterosexual activity may have determined the size of the structure, rather than vice-versa. It would seem that the study proves nothing. However, it appears to be frequently cited in books and on the Internet.
Hearing sensitivity: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. 9 These findings indicate that sexual orientation is at least partly decided before birth -- perhaps at conception.
Ear emissions:Everyone's inner ears produce very weak sounds called "spontaneous otoacoustic emissions." These cannot normally be heard by other persons, but can be detected by sensitive instruments. The Washington Post reported that:
Response to pheromones by gay men:Researchers of the Karolinska Institute in Stockholm, Sweden. divided 36 subjects into three groups of 12 each: heterosexual men, heterosexual women and homosexual men. All were healthy, unmedicated, right handed, and HIV negative, of similar age and of comparable educational level. Each subject sniffed a series of odors, while PET scans were taken of their brain activity.
Ivanka Savic, lead author and associate professor of neurology at the Institute said: "The experimental conditions were standardized and identical in all subjects. When adding to the improbability of chance activation by [testosterone] in homosexual men in the brain area very similar to heterosexual women, it seems convincing that we detected an undistorted physiological response." Sandra Witelson, an expert on brain anatomy and sexual orientation at the Michael G. DeGroote School of Medicine at McMaster University in Ontario, Canada, who was not part of the Swedish research team, commented: "It is one more piece of evidence ... that is showing that sexual orientation is not all learned." She said the findings clearly show a biological involvement in sexual orientation. The study was published in the Proceedings of the National Academy of Science on 2005-MAY-10. 11,12
Response to pheromones by lesbians:A research team led by Ivanka Savic at the Karolinska Institute repeated the above study on lesbian subjects. They found that lesbians' brains react differently to sex hormones than those of heterosexual women.
Their study was published in the Proceedings of the National Academy of Sciences on 2006-MAY-09. According to Associated Press: Both this study and the previous one on gay males "...add weight to the idea that homosexuality has a physical basis and is not learned behavior." Sandra Witelson, a specialist on brain anatomy and sexual orientation at McMaster University in Hamilton, ON, Canada, who was not part of the research effort, said "The important thing is to be open to the likely situation that there are biological factors that contribute to sexual orientation." 13
Response to the smell of sweat:Neuroscientist Charles Wysocki led a team at the Monell Chemical Senses Center in Philadelphia, PA. They studied the response of 82 heterosexual men, gay men, heterosexual women and lesbians to the odor of underarm sweat. The samples were collected from 24 donors who varied in sex and sexual orientation. They found that:
This study has two conclusions:
Wysocki said: "Our findings support the contention that gender preference has a biological component that is reflected in both the production of different body odors and in the perception of and response to body odors." The Associated Press reported that: "In particular,....[Wysocki] said, finding differences in body odors between gay and straight individuals indicates a physical difference. It's hard to see how a simple choice to be gay or lesbian would influence the production of body odor, he said." 11
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