A study published on April 16, 2002 in the Proceedings of the National Academy of Sciences has added to a growing body of research which suggests that environmental toxins may cause a defect in hormone function and prenatal sexual development.

The latest study is from Tyrone Hayes, a specialist in the hormone systems of amphibians at UC Berkeley, who found that tadpoles exposed to a common weed killer called atrazine tended to develop into frogs with both male and female sex organs.

Hayes found that atrazine disrupted the endocrine systems of frogs by converting the male hormone testosterone into the female hormone estrogen.

Atrazine has been detected in ground water consumed by humans, although its effect on humans at varying levels of exposure has not yet been demonstrated.

The study on frogs adds to earlier evidence suggesting that environmental pollutants may damage gender development. If these findings are replicated in the small but growing body of studies on humans, then, for example, a boy with a brain that had been feminized in utero by environmental toxins would be at particular risk to establish a weak masculine gender identity and thus to develop homosexually.

This latest study on frogs fits earlier findings in research on humans by LaLumière et al. That earlier study concluded that male homosexuals are about one-third (31%) more likely than heterosexuals to be left-handed (1), while lesbians are almost twice as likely (91%) to be left-handed as heterosexual women.

LaLumière at al. said their findings support the idea that sexual orientation in some men and women probably has an early neuro-developmental basis. They trace this to "disruptive events causing developmental instability" which modify sexual differentiation of the brain "perhaps through hormonal or immunological mechanisms."

Thus in those homosexuals whose condition had a primarily biological rather than psycho-social foundation, homosexuality would be, like left-handedness, a "biological developmental error." Left-handedness has been associated with a wide range of indicators of reduced fitness, from the standpoint of natural selection. Left-handed people, the authors say, have a smaller number of offspring, higher number of spontaneous abortions, lower birth weight, higher number of serious accidents, higher rates of serious disorders, and a shorter life span. Left-handedness has similarly been linked to neural tube defects, autism, stuttering, and schizophrenia.

Two studies reported earlier in Archives of General Psychiatry found significantly higher levels of pathology in the homosexual population than among heterosexuals. One of several possible explanations for the higher level of psychiatric pathology, said researcher J.M. Bailey in a published commentary that echoed the earlier LaLumière study, is that since natural selection leads to heterosexuality, then "homosexuality may represent developmental error" (2).

References

1. Lalumière, M.L.; Blanchard, R.; Zucker, K.L. (2000): "Sexual orientation and handedness in Men and Women: a meta-analysis." Psychological Bulletin 126, 575-592.

2. Bailey, J.M., "Commentary: Homosexuality and Mental Illness," Archives of General Psychiatry, October 1999, vol. 56, no. 10, 876-880.