Biology and sexual orientation he topic: SEXUAL ORIENTATION AND SEXUAL IDENTITY...It college Biopsychology. Please focus biopsychology (biology, nature, genetics,) Sexual orientation: Nature or nurture?

'Baby, I was born this way.' The new Lady Gaga song sums up a common theme of the modern gay rights movement: that sexuality is genetic, rather than psychologically determined. Given that homosexuality was once listed as a mental illness in the Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychological Association, it is understandable that gay, lesbian, bisexual and transgendered people would wish to emphasize that sexuality is not a disorder: the only 'disordered' aspect of gay sexuality in society is the prejudice directed against gay people. Current medical research literature seems to largely support this claim.

Scientists operating from a biological paradigm have found certain 'clues' which indicate that sexual orientation is hard-wired within structure of the brain. After studying the brains of right-handed, 18- to 35-year-old homosexual and heterosexual men using structural Magnetic Resonance Imaging (MRI), researchers found that homosexual men have a larger posterior part of the corpus callosum than heterosexual men. "The size of the corpus callosum is largely inherited, suggesting a genetic factor in sexual orientation" (Genetics has a role in determining sexual orientation in men, 2007, ScienceDaily). This organ is "the thick band of nerve fibers connecting the two hemispheres of the brain" and is usually larger in women than in men, allowing for greater hemispheric communication (some have called this structure the source of 'women's...

Men outperformed women overall on spatial relations tasks such as mentally rotating abstract objects and women outperformed males on verbal dexterity tests and remembering the locations of objects. But homosexual males performed considerably better than heterosexual males on verbal dexterity and location recall tests and slightly worse upon the mental rotation tests than their heterosexual counterparts (Sexual orientation affects how we navigate and recall lost objects, 2007, ScienceDaily). A study of 720 volunteers at three street fairs in San Francisco found that lesbians tended to have shorter index fingers than heterosexual women and that gay males tended to have shorter index fingers (relative to their ring fingers) than heterosexual males, also indicating hormonal prenatal influences that might affect sexuality. If an individual has an identical twin, the twin is statistically more likely to be gay, and males with older brothers are also more likely to be gay, for reasons that some researchers hypothesize is due to a hormonally-based immune response on the part of the mother's body (What causes homosexuality, 2008, Religious Tolerance).
There is also experimental evidence derived from research on laboratory animals that indicates that testosterone can affect sexual orientation. "When male [rat] pups are castrated at birth, they no longer seek the company of females after they have gone through puberty. Conversely, when females…