Sexual orientation has some foundation in biology. In a study conducted by Simon LeVay it was shown that gay men have a larger cluster of cells in their hypothalamus than heterosexual men. LeVay conducted his study blindly so not to bias the results. He examined the brains of patients without knowing which brains belonged to homosexual men, and which belonged to heterosexual men until after he examined all of them and recorded the results. The corpus callosum has been shown to be larger in homosexual men than in heterosexual men. This proves that genetics play some role in determining sexual orientation. It has also been shown that identical twins are more likely to both exhibit homosexual orientations than fraternal twins. This was demonstrated in a study done in 1993 by Bailey and others, and replicated by another study done in Australia by Bailey and others in 1997. The first study found that 52 percent of identical twin brothers of homosexual men were also homosexual, while only 22 percent of fraternal twin brothers were also homosexual. The follow up study concluded that 48 percent of identical twins were both homosexual while only 16 percent of fraternal twins were both homosexual.
Prenatal hormones have also been studied as a cause of sexual orientation. Some studies have shown that homosexual men have fingerprint patterns like those of heterosexual women. Homosexual women also have a more masculine ratio of the length of the index finger to the ring finger. Some scientists believe that when girls are exposed to more testosterone in the womb develop more masculine brains and that when boys are exposed to too little amounts of testosterone they develop more feminine brains.
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