Since the flip in thought shifted from criminal behavior to psychological disorder to congenital behavior, researchers have been trying to figure out what makes a person a homosexual. People within the GLBT community have wanted a genetic explanation to prove that you can’t ‘pray the gay’ away, and that it is okay in God’s eyes, because He made us this way.
Others hope that proof of a genetic element will stop opponents from saying that sexual attraction is simply a choice.
A study done in 1991 found that 52% of identical male twins and 22% of fraternal male twins were concordant for homosexuality – in other words, 52% of the time, both males were homosexual when it came to identical twins, and 22% of the fraternal twins were both gay. Many studies have been performed regarding the concordance of homosexuality in twins. This is because of the shared genetic makeup of identical twins. In the majority of studies done on twins, similar results were found. Identical twins had a higher likelihood of both being gay than fraternal twins, which strongly suggests a genetic aspect.
Criticisms of twin studies has surfaced, stating that a self-selection bias may occur, where homosexuals with gay siblings are more likely to volunteer for studies. Other criticisms include the fact that enough pairs of twins exhibit different sexual orientation, and because of this, statistics do not firmly state that if one twin is gay, the other will be based on genetic makeup alone.
Other studies have been done to determine a biological basis, and there have been some interesting results. In 1997, a study was done that reported that each older brother in a family increases the odds of a man being homosexual by 33%. The hypothesis is that male fetuses provoke a maternal immune reaction that becomes stronger with each successive male fetus. The male fetus releases cells that contain HY antigens. The mother’s immune system makes antibodies against the Y protein. These antibodies are able to cross through the blood/brain barrier (BBB) and alter sexual dimorphism, increasing the likelihood that the affected son would be more attracted to men than women.
Physical differences in the brain have also been documented. Studies have been conducted showing differences in neuron count, size of the hypothalamus, and the presence and level of testosterone.
However, none of these studies have specifically located a ‘gay gene’. Some of the results are interesting, however, like the list of physiological and cognitive differences that have been found:
- Gay men and straight women have, on average, equally proportioned brain hemispheres. Lesbian women and straight men have, on average, slightly larger right brain hemispheres.
- The VIP SCN nucleus of the hypothalamus is larger in men than in women, and larger in gay men than in heterosexual men.
- Gay men report, on an average, slightly longer and thicker penises than non-gay men.
- The average size of the INAH-3 in the brains of gay men is approximately the same size as INAH 3 in women, which is significantly smaller, and the cells more densely packed, than in heterosexual men’s brains.
- The anterior commissure is larger in women than men and was reported to be larger in gay men than in non-gay men, but a subsequent study found no such difference.
- Gay men’s brains respond differently to fluoxetine, a selective serotonin reuptake inhibitor.
- The functioning of the inner ear and the central auditory system in lesbians and bisexual women are more like the functional properties found in men than in non-gay women (the researchers argued this finding was consistent with the prenatal hormonal theory of sexual orientation).
- The suprachiasmatic nucleus was found by Swaab and Hopffman to be larger in gay men than in non-gay men, the suprachiasmatic nucleus is also known to be larger in men than in women.
- The startle response (eyeblink following a loud sound) is similarly masculinized in lesbians and bisexual women.
- Gay and non-gay people’s brains respond differently to two putative sex pheromones (AND, found in male armpit secretions, and EST, found in female urine).
- The amygdala, a region of the brain, is more active in gay men than non-gay men when exposed to sexually arousing material.
- Finger length ratios between the index and ring fingers may be different between non-gay and lesbian women.
- Gay men and lesbians are significantly more likely to be left-handed or ambidextrous than non-gay men and women; Simon LeVay argues that because “[h]and preference is observable before birth… [t]he observation of increased non-right-handness in gay people is therefore consistent with the idea that sexual orientation is influenced by prenatal processes,” perhaps heredity.
- A study of 50 gay men found 23% had counterclockwise hair whorl, as opposed to 8% in the general population. This may correlate with left-handedness.
- Gay men have increased ridge density in the fingerprints on their left thumbs and pinkies.
- Length of limbs and hands of gay men is smaller compared to height than the general population, but only among white men.
- Gay men and lesbians are more verbally fluent than heterosexuals of the same sex (but two studies did not find this result).
- Gay men may receive higher scores than non-gay men on tests of object location memory (no difference was found between lesbians and non-gay women).
New research is showing that it’s quite possible that there is no existence of a ‘gay gene’, but something just as biologically important.
It is believed that something known as ‘epigenetics’ are responsible for homosexuality. It is not the genetic makeup, but rather how the genes are expressed, in certain modifications to how and when DNA is activated, that determine the expression of sexual orientation. The new theory suggests that homosexuality is caused by epigenetic markers, or ‘epi-marks’ related to hormonal sensitivity in the womb. They are compounds that rest on DNA and regulate how active or inactive certain genes are.
The theory comes from researchers at the National Institute for Mathematical and Biological Synthesis (NIMBioS). They believe that gene expression may regulate how a fetus responds to testosterone, and that the epi-marks may buffer levels of testosterone – increasing levels in male fetuses, and decreasing levels in female fetuses. Normally these epi-marks disappear after they are activated, but if they are passed down to the next generation, the same epi-marks may have alternate effects.
For instance, the epi-marks of the father, that allowed for higher levels of testosterone for him, may also allow for higher levels of testosterone in his female offspring, giving her more masculine characteristics. In mothers, the epi-marks that regulated for lower amounts of testosterone may affect the male offspring, giving him more feminine qualities.
While the fight to prove a genetic basis for homosexuality is important, it also lends to some potential downfalls.
For instance, if a ‘gay gene’ is found, what does that mean for the potential of ‘designer babies’? Is it possible that eventually, the ‘gay gene’ could be manipulated out of a fetus’s genetic structure? If the parents don’t want a gay baby, and had enough money, could they genetically alter the child?
Others within the GLBT community don’t want a genetic explanation, stating that they don’t need to prove their own existence.
While I would love to be able to say “I’m born this way” and have genetic evidence to back it up, I understand the other implications to the possibility of a ‘gay gene’. Perhaps one day, a genetic explanation won’t be needed to prove my equality. Perhaps one day, the fact that I’m a human being will be enough to be considered equal.