Ask Dr LJ - is being poly like being gay?

I know I've probably just offended someone with that post title. I'd like to hear your opinions on being polyamourous, specifically if you think being poly is something intrinsic to each individual or it is something that can be learned, or turned on and/or off. My (admittedly limited) knowledge of "gay" leads me to believe that it is an intrinsic quality, like having brown eyes, is being poly like this?  Please discuss.