Nice thought, but it doesn't explain how there were transgenders and homos a hundred, two hundred, even a thousand years ago, when the human population wasn't a problem.
I think that just because there are more people, probably makes it seem that there are more of these people than there used to be (also, can't forget that it used to be waaay more frowned upon, so there were a lot of closet homos) - but relatively speaking, there may be the same amount today as there used to be, though I obvsiouly don't have the numbers to back this up.