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from "Born that way" theory
New Evidence for
Biological Influence on Gender
A study just published in the Proceedings of the
National Academy of Sciences (on April 16, 2002)
has added to a growing body of research which
suggests that environmental toxins have a
demasculinizing effect on some developing
organisms.
The latest study (1) was conducted by a specialist
in the hormone systems of amphibians at UC
Berkeley. He found that male tadpoles exposed to
a common weed killer called atrazine tended to
develop into demasculinized adult frogs. Some of
the tadpoles became hermaphrodites, developing
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 is the most commonly used herbicide in
the U.S., and it 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 latest study adds to earlier evidence
suggesting that environmental pollutants may
impair normal gender development. If these
findings are replicated in the small but growing
body of studies on humans, then a boy with a brain
that had been feminized in utero by an
environmental toxin such as atrazine would be at
particular risk to establish a weak masculine
gender identity and thus to develop homosexual
attractions in adulthood.
This latest study on frogs fits earlier findings
in research on humans by LaLumière et al. (2).
That earlier study concluded that male homosexuals
are about one-third (31%) more likely than
heterosexuals to be left-handed, while lesbians
are almost twice as likely (91%) to be left-handed
as heterosexual women. LaLumière believes this
indicates that homosexuality, for a certain
proportion of men and women, probably has an
early, neuro-developmental basis tracing back to
"disruptive events causing developmental
instability" which have modified sexual
differentiation of the brain, "perhaps through
hormonal or immunological mechanisms."
Homosexuality is generally understood to result
from a combination of psychological, biological,
and social factors. In those homosexuals whose
condition had a primarily biological rather than a
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 other 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 LaLumière
study, is that since natural selection leads to
heterosexuality, then "homosexuality may represent
developmental error" (3).
When gender-identity distortion becomes apparent in a young child, whether
due to psychodynamic or biological factors, some therapists say, the at-risk
child's gender distortions can be modified (see "Research Studies of
Interest, the Childhood GID Diagnosis"). Parental interventions that help to
affirm same-sex gender identity, such clinicians observe, will make a
heterosexual adjustment more likely.
-- By Linda Ames Nicolosi
References
1. Hayes, Tyrone; Collins, Atif; Lee, Melissa;
Mendoza, Magdalena; Noriega, Nigel; Stuart, A.A.,
and Vonk, Aaron, "Hermaphroditic, demasculinized
frogs after exposure to the herbicide atrazine at
low ecologically relevant doses," Proc. Natl.
Acad. Sci. USA, vol. 99, Issue 8, 5476-5480, April
16, 2002.
2. 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.
3. Bailey, J.M., "Commentary: Homosexuality and Mental Illness,"
Archives of General Psychiatry, October 1999, vol. 56, no.
10, 876-880.
Updated: 8 February 2008
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