Etiology of homosexuality.

The range of expression of homosexuality and its association with certain cultural, environmental, and genetic factors are most consistent with the concept of a multifactorial trait. Additionally, genetic heterogeneity in this phenotype (alternative mutants corresponding to a single phenotype) is highly probable. In certain nonhuman and presumably in human species the normal sexual development of the hypothalamus is guided by an appropriate exposure to androgen at a critical early stage, and this in turn presumably contributes to sociopsychologic sex development. Particularly instructive in this regard have been the monogenic experiments of nature in man--XY females with insensitivity to androgens, congenital adrenal hyperplasia, and male pseudohermaphrodites (5-alpha-reductase deficiency). Additionally, in the human, sociopsychologic sex also appears to be molded by sex assigned at birth and sex of rearing. Several of the intersexuality syndromes and psychoses are accompanied by increased homosexuality, but a majority of homosexuals are not in these categories. A limited number of family studies, including twins, tentatively suggests a heritable risk, at least in some families.