According to an í¼ber-controversial new book called We Are Our Brains by Dutch neurologist Dick Swaab, stress as well as smoking or taking amphetamines while pregnant play a major role in a developing fetus' sexuality. He says there are multiple academic studies to back up the claim, and that the brain in fetuses begins to develop at two weeks, with anything introducing toxins into the body having an impact on the development.
The UK's Sunday Times reports, "Pre-birth exposure to both nicotine and amphetamines increases the chance of lesbian daughters," Swaab, a professor of neurobiology at Amsterdam University, says in his book. "Pregnant women suffering from stress are also more likely to have homosexual children of both genders because their raised level of the stress hormone cortisol affects the production of fetal sex hormones."
Although it's frequently assumed that development after birth also importantly affects our sexual orientation, there's no proof of this whatsoever," he states in his book. "Children brought up by lesbians aren't more likely to be homosexual. Nor is there any evidence at all for the misconception that homosexuality is a "lifestyle choice". (Ok, those two claims I can get behind.)
The Daily Mail reports that when he first explored differences in the brains of homosexual and heterosexual people in the 1980s there was a huge outcry from gay rights campaigners, who said his findings cast homosexuality as a "medical problem". But Professor Swaab says his view that sexuality is decided in the womb slashes the argument, often made by conservative groups, that gay people can be "cured".
While lifestyle factors of the mother are just one influence on the fetus, Swaab did acknowledge that genetics played the most important role.
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Image of pregnant woman courtesy of Shutterstock.