Studies 10 to 14 into the causes of homosexual orientation

More detailed coverage of 5 studies on hearing
sensitivity, ear emissions, pheromones & sweat.

This topic is continued from an earlier essay

Study 10: Based on 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. ₁ These findings indicate that sexual orientation is at least partly decided before birth -- perhaps at conception.

Study 11: Based on ear emissions:

Everyone's inner ears produce very weak sounds called "spontaneous otoacoustic emissions." These cannot normally be heard by the individual or by other persons, but can be detected by sensitive instruments. The Washington Post reported that:

"Dennis McFadden and Edward G. Pasanen of the University of Texas in Austin and colleagues compared the emissions of 60 homosexual and bisexual women with those of 57 heterosexual women. As a group, the homosexual and bisexual women's emissions were slightly more like that of men: less frequent and weaker than those of the heterosexual women, the researchers found.

One explanation could be that homosexual and bisexual women were exposed to slightly different levels of hormones when they were developing in the womb, causing subtle changes in their development, the researchers say.

"For us, the most plausible explanation is that the inner ears of the non-heterosexual women were partially masculinized at some time in development, possibly at the same time that whatever brain structures are responsible for sexual orientation were also masculinized," says McFadden, whose study is featured in the April [1999] issue of the Journal of the Acoustical Society of America. ₂

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Study 12: Based on response to pheromones of 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.

When ordinary odors such as lavender and cedar, were used, all subjects experienced similar activity in the part of their brain that handles smells.
When chemicals derived from male and female sex hormones, their reaction was different:
- When gay men and heterosexual woman were exposed to the smell of testosterone, the part of their brain that deals with sexual response was activated. Heterosexual men did not show this reaction.
- When heterosexual men were exposed to testosterone, there was no sexual response in the brain.
- When heterosexual men were exposed to estrogen, there was a sexual response.

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 that 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. _2,4

Study 13: Based on response to pheromones of lesbians:

A research team led by Ivanka Savic at the Karolinska Institute repeated the above study, but on lesbian subjects. They found that lesbians' brains react differently to sex hormones than those of heterosexual women.

Straight women found male and female pheromones about equally pleasant and about equal in intensity; lesbians and straight men found the male hormone more intense than the female one.
Both straight men and lesbian subjects liked the female hormone more and found the male hormone to be more irritating. Heterosexual women were more likely to be irritated by the female hormone.

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." ₅

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Study 14: Based on 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:

Gay men differed from heterosexual men, lesbians and heterosexual women; they preferred odors from other gay men.
Heterosexual men, lesbians and heterosexual women differed from gay men; odors from gay men were least preferred.

This study has two conclusions:

Gay men produce sweat with one or more unique odor components not found in either heterosexual men, heterosexual women and lesbians.
Gay men perceive sweat odors differently from heterosexual men, heterosexual women and lesbians.

Dr. 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." ₃

More studies are described in the next essay

References used:

The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

"Lesbian Ears", The Globe and Mail, Toronto ON, 1998-MAR-19.
"Sexuality and Ear Emissions," Science Notebook, Washington Post, 1999-APR-05, Page A07. Online at: http://equake.geol.vt.edu/
"Gay Men Respond Differently to Pheromones," Associated Press, 2005-MAY-09, at: http://start.earthlink.net/
Oliver Moore, "Response to scent is linked to sexual tendency. Researchers study brains of gay men and straight women," The Globe and Mail, 2005-MAY-10, Page A1. Online at: http://www.theglobeandmail.com/ This is a temporary listing.
Randolphe Schmid, "Sexuality may be in the genes - Study. Lesbians react similarly to men. Researchers test brain differences," Associated Press, 2006-MAY-09.