Tahir, I'd say that the title you chose for this thread proves you didn't understand the article.
Being exposed to mercury can be a natural or manmade event, and the chemical imbalances caused by mercury don't offer one set result besides the imbalances themselves. You'd be looking at all sorts variables and outcomes in this, including the possibility of changing an animal's instinct.
As for being "born with it," I don't see why this is so hard to accept. Mice have been found to gravitate towards the same sex when Korean scientists removed a single gene linked to reproductive behavior. If one single gene is the barrier between straight and gay, then we have to start accepting this stuff as a natural occurrence.
But even if it was not "natural", and in fact solely a "choice", I don't see why that would be a problem either. As long as that personal freedom of choice doesn't impinge upon your freedom to live and practice your religion, then this issue is just another huge distraction.