With all the controversy around the transgendered bathroom issues, one thing that keeps coming up is the idea of whether or not it is "natural." In this matter, there really shouldn't be much argument. Aside from the fact that there are ample humans born intersexed, the idea that transexualism isn't prevelant in nature is wrong.
This TopTenz article discuses ten animals that demonstrate examples of transexualism, whether through animals acting like members of the other sex (like garter snakes) or actually changing gender (like clownfish). The fact is, transgenderism is entirely natural and common in nature.