A new study suggests that homosexuality can be explained by biology, though not by genes specifically. Instead, the researchers propose that there are sex-specific epi-marks on the genes that are triggered during fetal development to maintain a hormone level balance. These switches cause fluctuations in DNA expression that impacts sexual development, including sexual identity and various other gender characteristics. These switches help protect both the fetus and the mother from the natural variation in sex hormone levels present during fetal development, which could help explain why homosexuality has evolved as a common variation of human identity.
Study Finds Biological Causes For Homosexuality