The study suggests sexual orientation may be set in the womb

The Swedish study, published in the Proceedings of the National Academy
of Sciences journal, compared the size of the brain’s halves in 90
adults.

Gay men and heterosexual women had halves of a similar size, while the
right side was bigger in lesbian women and heterosexual men.

A UK scientist said this was evidence sexual orientation was set in the womb.

As far as I’m concerned there is no argument any more – if you are gay, you are born gay Dr Qazi Rahman Queen Mary, University of London

Scientists have noticed for some time that homosexual people of both
sexes have differences in certain cognitive abilities, suggesting there
may be subtle differences in their brain structure.

This is the first time, however, that scientists have used brain scanners to try to look for the source of those differences.

A group of 90 healthy gay and heterosexual adults, men and women, were
scanned by the Karolinska Institute scientists to measure the volume of
both sides, or hemispheres, of their brain.

When these results were collected, it was found that lesbians and
heterosexual men shared a particular “asymmetry” in their hemisphere
size, while heterosexual women and gay men had no difference between the
size of the different halves of their brain.

In other words, structurally, at least, the brains of gay men were more
like heterosexual women, and gay women more like heterosexual men.

A further experiment found that in one particular area of the brain, the amygdala, there were other significant differences.

In heterosexual men and gay women, there were more nerve “connections”
in the right side of the amygdala, compared with the left.

The reverse, with more neural connections in the left amygdala, was the case in homosexual men and heterosexual women.

The Karolinska team said that these differences could not be mainly
explained by “learned” effects, but needed another mechanism to set
them, either before or after birth.

‘Fight, flight or mate’

Dr Qazi Rahman, a lecturer in cognitive biology at Queen Mary,
University of London, said that he believed that these brain differences
were laid down early in foetal development.

“As far as I’m concerned there is no argument any more – if you are gay, you are born gay,” he said.

The amygdala, he said, was important because of its role in
“orientating”, or directing, the rest of the brain in response to an
emotional stimulus – be it during the “fight or flight” response, or the
presence of a potential mate.

“In other words, the brain network which determines what sexual
orientation actually ‘orients’ towards is similar between gay men and
straight women, and between gay women and straight men.

“This makes sense given that gay men have a sexual preference which is
like that of women in general, that is, preferring men, and vice versa
for lesbian women.”

Source:http://news.bbc.co.uk/2/hi/health/7456588.stm