60 Minutes

[Yves]

Some idiot says the greater older brothers a man has, the greater the liklihood he will be gay.
Just another bigot trying to tell the world that being gay is something we can change. And I'm sure some people will take it to heart.
Now I am goign to actally watch 60 minutes and see what he says. Let's hope he isn't a bigot like I said and is just doing some statistics on gays (doubtful).

This is just one of a few current theories on homosexuality expanding on the nature/nuture discussion. The theory in this case is based on statistical observation and probabilities. The researchers are aware of its significant limitations: It doesn´t explain all cases but it might offer an interesting connection to potential in-utero factors.

Here is the original quote from 60 Minutes:
"(....)
While biologists look at hormones for answers about human sexuality, other scientists are looking for patterns in statistics. And hard as this is to believe, they have found something they call "the older brother effect."
"The more older brothers a man has, the greater that man's chance of being gay," says Bailey.
Asked if that's true, Bailey says, "That is absolutely true."
If this comes as a shock to you, you’re not alone. But it turns out, it’s one of the most solid findings in this field, demonstrated in study after study.
And the numbers are significant: for every older brother a man has, his chances of being gay increase by one third. Older sisters make no difference, and there's no corresponding effect for lesbians. A first-born son has about a 2 percent chance of being gay, and the numbers rise from there. The theory is it happens in the womb.
"Somehow, the mother's body is remembering how many boys she's carried before," says Breedlove. "The favorite hypothesis is that the mother may be making antibodies when she sees a boy the first time, and then affect subsequent boys when she carries them in utero."
"You mean, like she's carrying a foreign substance?" Stahl asked.
"And if you think about it, a woman who's carrying a son for the first time, she is carrying a foreign substance," Breedlove replied. "There are some proteins encoded on his Y chromosome that her body has never seen before and that her immune system would be expected to regard as 'invaders,'" he added.
It’s still not a proven theory and it gets even stranger.
"One of the things we've only found out lately is that older brothers affect a boy only if the boy is right-handed," Breedlove said. "If the boy is left-handed, if his brain is organized in a left-handed fashion, it doesn't matter how many older brothers he has, his probability of being gay is just like the rest of the population."
(...)

Source: 60 Minutes - The Science Of Sexual Orientation: Researchers Focus On Twins
http://www.cbsnews.com/stories/2006/03/09/60minutes/main1385230.shtml

The program generated controversy as expected. Attached are links to reactions to the story and the 60 minutes producer response:
http://www.cbsnews.com/blogs/2006/03/14/publiceye/entry1399162.shtml
http://www.cbsnews.com/blogs/2006/03/13/publiceye/entry1397301.shtml