In the past, homosexuality was considered to be either a mental illness or a sexual abnormality related to hormonal imbalance. Multiple studies have shown that homosexuals can be as well adjusted as heterosexuals, and experiments involving hormonal manipulation by injection seemed to affect only the person's sex drive and not his or her sexual preference.
The cause for homosexuality still remains to be discovered; however, new theories are constantly being developed and tested. Considering that biological factors play a strong role in motivating sexual behavior, it is only natural that there has been considerable interest in the possible biological causes of sexual orientation. The results of twin studies suggest that there is a genetic component involved in determining sexual orientation. Among brothers, for example, the closer the genetic similarity the more likely it is that both siblings will be either homosexual or heterosexual. If one brother is homosexual, just over 50 percent of identical siblings will share this samesex orientation, while the number drops to just over 20 percent among fraternal twins. The brain structures of heterosexuals and homosexuals have also been studied, and researchers suggest that differences in a small cluster of neurons in the hypothalamus may be involved in determining sexual orientation. At any rate, homosexuality has become more accepted; samesex marriage in some parts of the world is legal. While the exact cause of homosexuality is unknown, researchers have found that two of the most commonly repeated myths about sexual orientation — that homosexuality is caused by childhood sexual molestation or by an abnormal relationship with a parental figure — are both false.