Genetic Clues to Female Homosexuality

Article excerpt

Genes substantially influence the development of homosexuality among women, according to a preliminary study of female twins and adoptive sisters.

"Genes don't account for all individual differences in sexual orientation, but pairs of female identical twins report homosexuality significantly more often than pairs of female fraternal twins or biologically unrelated sisters," says psychiatrist Richard C. Pillard of the Boston University School of Medicine, who conducted the study with psychologist J. Michael Bailey of Northwestern University in Evanston, Ill.

The two researchers presented their findings last week at the annual meeting of the American Psychological Association in Washington, D.C.

Pillard and Bailey recently used the same research strategy to identify a moderate to strong genetic influence on male homosexuality (SN: 1/4/92, p.6).

The researchers recruited homosexual women with an identical, fraternal, or adoptive sister through advertisements in lesbian, gay, and feminist publications throughout the United States. They then interviewed pairs of sisters, usually over the telephone. Additional interviews with relatives of most participants revealed a high degree of agreement within families about each woman's sexual orientation.

A total of 115 twin pairs, about equally divided between identical and fraternal twins, participated in the study, as did 32 pairs of adoptive sisters. Identical twins share all the same genes, whereas fraternal twins share some of the same genes.

Homosexuality or bisexuality occurred among both sisters in nearly half of the identical twin pairs, Bailey asserts. That figure drops to about one-quarter of the fraternal twin pairs and one in six adoptive-sister pairs.

Using estimates of female homosexuality in the general population and the assumption that several genes influence sexual orientation, Pillard and Bailey calculate that genes account for half of the individual differences in women's sexual orientation. …