What rolesdoheredity and environment play in the development of sexual orientation?

Question

What will be an ideal response?

Answer 1

Heredity makes an important contribution to sexual orientation, but environment also plays a role. The evidence to date indicates that genetic and prenatal biological factors contribute substantially to lesbian and gay sexual orientations. Identical twins of both sexes are more likely than fraternal twins to share a homosexual orientation, as are biological (as opposed to adoptive) relatives. Furthermore, male homosexuality tends to be more common on the maternal than on the paternal side of families, suggesting that it may be X-linked. According to some researchers, certain genes affect the level or impact of prenatal sex hormones, which modify brain structures in ways that induce homosexual feelings and behavior.
Environmental factors can also alter prenatal hormonesand thereby influence sexual orientation. Girls exposed prenatally to very high levels of androgens or estrogens—either because of a genetic defect or from drugs given to the mother to prevent miscarriage—are more likely to develop lesbian or bisexual orientations. Furthermore, gay men tend to be later in birth order and to have a higher-than-average number of older brothers. Perhaps mothers with several male children sometimes produce antibodies to androgens, reducing the prenatal impact of male sex hormones on the brains of later-born boys.