Since I'm not an expert on the subject I'll have to defer to other posters to provide that evidence. I've just read a few articles here and there about it.
But having also been around a lot of gays at a former company (airline... they love working for airlines), I just can't see how some of them couldn't be born that way.
It can't all be just "affections". Some of them went out of their way to appear "manly" but everyone could still tell. Based on lots of interaction with them, I just can't see how their could not be a biological difference.
They may choose to BE gay in the sense of active involvement, but I'm not so sure they choose how they are deep down.
This really is a complex subject that is replete with invalid and misrepresented data, very much like the entire global warming scam only more PC.
There is a very small percentage who choose their same-sex attraction and there is a website created for this group (http://queerbychoice.com.
From my own studies I'd say the rest are confused.
If you read everything I've read you'd know there isn't a single credible scientist who believes homosexuals are born with their same sex attraction, and those same credible scientists will tell you environment is a major factor in determining sexuality.
That's just the way it is. Many (even here at FR) will insist homosexuals are born that way but there is still no evidence to support that claim and a growing body of evidence, former homosexuals, that throw a wrench into the mix.