STUDIES ON
THE ORIGINS OF SEXUAL ORIENTATION
Inner Ear Difference In Lesbians
Researchers at the University of Texas, Austin found that the
cochlea (a structure of the inner ear) in lesbians differs from the cochlea of
heterosexual women. The findings were published in the Proceedings of the
National Academy of Sciences (March 1998).
The difference was detected using a test that measures a very
slight sound that the cochlea makes when responding to a soft clicking sound.
Results indicate that lesbians have click responses that are significantly
weaker than those of heterosexual women, and are more similar to those of men.
Generally, the cochlea in women is more sensitive than that of men.
Dennis McFadden, the lead author of the study, believes the
cochlea of lesbians may be affected by hormone exposure before birth. It is
presumed that an unknown site or sites in the brain that influence sexual
orientation may be similarly affected.
While this study has yet to be replicated, it does suggest a
biological component may be involved in the determination of sexual orientation.
Twin Studies
Studies of identical twins who were separated at birth and
raised in different homes have been performed and replicated. It has been found
that in many cases of identical twins, that if one twin is homosexual, the other
twin is also homosexual. This lends credence to the theory that sexuality has a
very strong genetic component, and is not purely determined by life experiences.
Anatomical Brain Differences and Sexual
Orientation
In 1991 Simon LeVay, a neuroanatomist at the Salk Institute,
examined the brain tissue from 41 people as follows:
- 19 homosexual men who had died from complications of AIDS
- 16 heterosexual men (6 had died from complications of AIDS,
and 10 from other causes)
- 6 heterosexual women (none were reported to have AIDS)
- No samples from lesbians were available.
He found the INAH3 (a structure within the hypothalamus)
was twice as large in heterosexual men (even those who had died form AIDS) as in
homosexual men. He also found a similar difference between heterosexual men and
heterosexual women. This study suggests that sexual orientation has a
biological substrate.
Sibling Studies
Psychologist Michael Bailey of Northwestern University and
Psychiatrist Richard Pillard of Boston University studied the sexual orientation
of siblings raised together. They found that if one sibling is homosexual the
chance of another sibling being homosexual is as follows:
- 52% for an Identical Twin
- 22% for a Fraternal Twin (non-identical twins)
- 10%(approx.) for adopted or non-genetic siblings
Again, this study suggests that sexual orientation has a
genetic component.
Atypical Gender Behavior in Children
as an Indicator of Sexual Orientation
Richard Greene of the University of California at Los Angeles
reports that children who manifest aspects of gender-atypical play indicates a
homosexual orientation 75% of the time. Richard Greene's observations suggest
that sexual orientation is in place early in the life cycle.
Finger Print Studies
J.A.Y. Hall and D. Kumura at the University of Western Ontario
at London ON Canada compared the number of ridges(finger prints) on the index
finger and thumb of the left hand with corresponding digits on the right hand.
They found that 30% of homosexuals had excess ridges on the left hand digits,
while only 14% of heterosexuals showed the same characteristic.
Because fingerprints are fully developed in the fetus before
the 17th week and do not change thereafter, this study may suggest a genetic
link to sexual orientation that is determined before birth, perhaps at
conception.
DNA Study
Research led by Dean Hamer at the National Cancer Institute
compared the DNA of 40 pairs of homosexual brothers. They found that almost all
shared a genetic marker in the Xq28 region of the X chromosome (one of the two
sex chromosomes). While this study hasn't precisely isolated a gay gene,
it suggests that sexual orientation may have a genetic component.
*It should be noted that others have not been able to duplicate Hamer's
study.
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