While there are no concurrent answers as to why some individuals develop a homosexual orientation, many researchers believe that biological factors, among other things, play a significant role in determining a person's sexual orientation. To begin with, twin studies have indicated that there is a possible genetic component to sexual orientation. Studies have shown that in identical twins where one identifies as homosexual, there is around a 52% chance that the other twin will identify as a homosexual as well. In fraternal twins, the chances decrease to about 23%.
In neurological studies, researchers have found that the brain structure is sexually dimorphic, which means that men and women's brains are built differently. Some studies have found size differences in certain structures of homosexual and heterosexual brains, such as the hypothalamus, the suprachiasmatic nucleus and the anterior commissure. Other researchers have suggested that differences in hormone levels, especially during prenatal development, may be associated with a person's sexual orientation. The sex hormones, testosterone and estrogen, impact the fetus's developing brain, and an excess or deficiency in one of these hormones may cause a disruption in this process.
It is difficult to determine which of these theories is most accurate, as scientific research has not produced enough definitive evidence to formulate a conclusive cause.