This is a continuation of another
essay which describes six studies into the causes of homosexuality.
Study of eye blinking inhibition:
In 2003-OCT-2, researchers at University of East London and at
King's College announced the results of a study which differentiates between
homosexuals and heterosexuals. They studied groups of homosexual and
heterosexual men and women and found significant differences in an involuntary
response to being startled with bursts of loud noises. This is formally called "prepulse
inhibition" or (PPI). Subjects were exposed to a low level noise, followed
by a strong noise. Researchers measured the strength of the involuntary
eye-blink responses. These data were then compared to similar strength
measurements taken after exposure to a loud noise without the preceding low
level noise. The lower the response, the stronger the level of inhibition. "The
reaction of the lesbian test subjects was closer to that which would be expected
among straight men. And, gay men reacted closer that of women, although to a
lesser extent."
They found that the average PPI was:
40% for heterosexual men.
32% for gay men.
13% for heterosexual women
33% for lesbians.
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:
One article, published in LifeSite, a conservative Christian web site,
concluded that Mustakski was unable to prove the involvement of other
chromosomes. This supported their belief that
genes are not involved in homosexuality. 5
The other article, published in GayLife, a lesbian, gay, bisexual and
transsexual support group) reached the opposite conclusion: that genes are
involved in homosexuality. 6
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.
They detected three chromosomal regions on the
human genome more than 50 percent of the time; they were on 7, 8, and 10. Of
these, a region 7q36 on chromosome 7 was shared most frequently. Since males "inherited
this region from their fathers just as often as their mothers, a finding that
suggests genes from both parents can contribute to a son's sexual orientation."
5
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."
Richard Pillard, a psychiatrist at Boston University specializing in
sexual orientation suggests that Mustanki's study should be repeated with a
larger number of genetic markers. He said that this study:
"Doesn't come up
with a definitive answer. The first step is to say, 'yes there's a genetic
contribution.' The next step is to say, 'well how are these genes expressed in
the brain, as we presume they must be'?"
Mustanski concluded that:
"There's
a converging line of evidence between the hormonal studies, the genetic studies,
and the neuroanatomical studies. My research has identified candidate genes
within these new chromosomal regions that could link together all of these
different findings."
5
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:
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. 10
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.
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 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.
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 lesbians subjects liked the female hormone more
and found the male hormone to be more irritating. Most 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." 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:
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 by the others.
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.
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
The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.
"Sexual orientation 'hard-wired' before birth - startling new evidence
revealed in the blink of an eye," University of East London, 2003-OCT-2, at:
http://www.uel.ac.uk/
Patrick Letellier, "Study hints sexual, gender identity in genes,"
PlanetOut, 2003-OCT-22, at:
http://www.planetout.com/
"Sexual Orientation Related Differences in Prepulse Inhibition of the
Human Startle Response" Behavioral Neuroscience magazine, 2003-OCT,
published by the American Psychological Association.
Ariel Whitworth, "Studies Suggest
Multiple Genes Contribute to Sexual Orientation,"
Gay Life, 2005-FEB-18, at:
http://www.bgp.org/
"New Genetics Study Undermines Gay Gene
Theory," LifeSite, 2005-FEB-10, at:
http://www.lifesite.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.
