#3 Being gay is a choice
To test whether genes play a role, researchers have compared identical twins (in which all genes are shared) to fraternal twins (in which about 50 percent of genes are shared). A 2001 review of such twin studies reported that almost all found identical twins were significantly more likely to share a sexual orientation – that is, to be either both gay, or both straight – than fraternal twins, who are less genetically close. Such findings indicate that genes do factor into a person’s orientation.
Other studies have found that biological effects, such as hormone exposure in the womb, can also play a role in shaping sexuality. And findings of physiological differences, such as different inner ear shapes between homosexual and heterosexual women, contribute to this idea.
‘The results support the theory that differences in the central nervous system exist between homosexual and heterosexual individuals and that the differences are possibly related to early factors in brain development,’ said Sandra Witelson of McMaster University in Ontario, an author on the 1998 inner ear finding published in the journal Proceedings of the National Academy of Sciences.”