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Nature's curious ways. One of the more interesting stories to appear on 60 Minutes this season was about scientists studying the causes of homosexuality. It's a volatile topic that doesn't get a lot of funding, probably because a definitive answer would open up many cans of worms for people with strong opinions on the subject.

The evidence seems to point to genes and/or hormones as the cause. Yet there are plenty of puzzing examples. Here's the wildest one:

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 ...

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."

posted by Paul Murray at 10:30 PM | permanent link |