What causes homosexuality

Prenatal biological factors refer to influences on sexual development that occur before birth. Three main hypotheses in this area are: - Hormonal exposures in the womb: Variations in fetal sex hormones (especially androgens) during critical periods of brain development are proposed to shape later sexual attractions. For example, lower fetal androgen action is sometimes linked to greater likelihood of same-sex attraction in males, though findings are complex and not uniform. - Epigenetic markers: Chemical tags on DNA (epigenetic marks) can modulate gene expression without changing the DNA sequence. Some researchers suggest that epigenetic differences established prenatally could influence brain development and later sexual orientation. - Maternal immune responses: The “fraternal birth order” effect — where each older biological brother increases the chance a later-born son is gay — has led to a maternal immune hypothesis: maternal antibodies formed in response to male fetal proteins might affect development of subsequent male fetuses’ sexual differentiation. Overall evidence: Empirical findings support that prenatal biological factors plausibly contribute to sexual orientation, but they are not determinative. Sexual orientation appears to be shaped by multiple interacting biological, developmental, and possibly environmental influences; no single prenatal factor explains all variation (see Bogaert 2018; Bogaert & Skorska 2011). Selected references: - Bogaert, A. F. (2018). Biological versus nonbiological explanations of male sexual orientation. Archives of Sexual Behavior, 47(3), 557–570. - Bogaert, A. F., & Skorska, M. N. (2011). The fraternal birth-order effect: Evidence and mechanisms. In Handbook of the Sociology of Sexualities (pp. 97–112).