Maternal stress:
In rats, researchers have found a link between maternal stress and demasculinizing effects in the sexual behaviour of male offspring.
The mother’s stress leads to a delayed testosterone surge in male rats. An East German researcher, Dorner, claimed to have found a similar stress effect in humans during the Second World War. If mothers underwent a lot of stress, he found no heterosexuality in their young offspring,25%bisexuality, and 35%homosexuality.
The remainder were too young to know what their preferences
were.
10
These were spectacular results, but the study appears to be
maverick. Other studies on rats could not find the effect, and stress in human mothers delays the testosterone surge much less markedly than in rats. Dorner has also been criticized for not interviewing the mothers.
30
Three other studies on humans did not
find any effect.
30
A later and more sophisticated study, although it
found no correlations with stress for boys, did find an unsurprising relatively strong correlation between homosexual fantasy and childhood gender non-conformity
30
(see Chapter Three). Curiously,
in this study, there was a moderate correlation for girls between maternal stress and lesbianism, which made no sense to the authors. Girls are not exposed to a pre-natal testosterone surge, so a delayed surge makes no sense in this context.
The latest and biggest survey 31 basically concludes that
there is a small weak effect for boys and a more significant effect for girls. A similar survey for the stressful effects of an historic Dutch famine could find no effects.
32
In no case can the effects be described as overwhelming, which is why it has been so hard to establish. It is another minor factor in the development of homosexuality for a few people.
http://www.mygenes.co.nz/PDFs/Ch7.pdf
Summary:
Although there are some pre-natal hormonal effects on sexual
behaviour for lower animals, there is not convincing evidence for such an effect on sexual orientation in humans.
The studies examining the effects of high doses of female hormones to pregnant women are particularly informative because these are very high doses and any hormonal effects on sexual orientation should show up clearly. But the result is a dubious effect on women and no effects on men. Any effects on sexual orientation appear to be better explained in terms of gender non-conformity—a psychological construct.
Sex hormones do increase or lower sex drive, but that
appears to be about all.
The maternal immune hypothesis seems very speculative, and
needs much more evidence before it is taken more seriously.
We leave the last word to several researchers in the field.
James
44
summarises the evidence for effects of prenatal hormone
exposure on subsequent sexual orientation as “weak”.
In summary, the evidence from prenatal endocrine
disorders and from the offspring of hormone-treated
pregnancies suggests that hormones may contribute
to, but do not actually determine, the course of sexual
orientation in individuals with an abnormal sex steroid history during prenatal life.
3
“At this time, the literature does not support a causal link
between hormones and homosexuality.”
12
Also, “In clinical practice numerous patients are encountered with gross abnormalities of their hormonal profiles. As a rule this does not impact on their gender identity or sexual orientation.”
45
So, not only your genes didn’t make you do it, it seems your
hormones didn’t either. In sexual orientation, the strongest stimulation appears to come from the mind and the environment.
http://www.mygenes.co.nz/PDFs/Ch7.pdf