Professor Dick Swaab, a Dutch neurologist at the University of Amsterdam has written a new book claiming that women who smoke during pregnancy could increase the likelihood of their child being gay. The Doctor also said that stress during pregnancy may also cause homosexuality in children. In his book titled, "We are our Brains", Prof. Swaab writes that, "although it’s frequently assumed that development after birth also importantly affects our sexual orientation, there’s no proof of this whatsoever". He believes that a child’s sexuality is determined in the womb and cannot be altered, while others argue that it is affected by upbringing or ‘selected’ as a lifestyle choice. "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. Pre-birth exposure to nicotine or amphetamines also increases the likelihood of lesbian daughters," he writes in the book. And he claims: ‘The more older brothers a boy has, the greater the chance that he will be homosexual". This he said is due to a mother’s immune response to male substances produced by boy babies in the womb, a response that becomes stronger with each pregnancy.