I'm surprised anyone could think that biology and nature are anything that even comes close to remotely resembling a perfectionist and that it has any "goal" or "drive" to be so. The removal of homosexuality from the DSM also speaks volumes to the fact that abdnormal doesn't necessarily mean disorder or malfunction. God may not play with dice, but nature takes a crap shot every time an organism is born, and another one every time that organism's DNA is replicated. Nature doesn't give one damn about what we humans think about the way things should be. And very typically humans haven't really applied such rigid "either-or"s to their lives for most of our existence.
And just a cursory glance of history and gender will make it apparent that no one has ever applied such standards. But they still had male, female, and commonly something for eunuchs, effeminate men and masculine women. And because the things we have discovered didn't come into existence once we discovered them, it becomes rather obvious we have always depended on standards other than biology and birth-anatomy to determine gender.