To say that animals have natural inclinations is not to say that animals never behave inappropriately, as when one male animal attempts to mount another. Rather it means that the creational design provides a standard for considering the behavior unfitting. In such a case, what nature provides to draw males and females together has misfired. The fact that the creature may become habituated to such behavior leaves this judgment untouched; even things that are bad for us can become “second nature.”
It is easy to see how misfires can happen among subrational animals. During breeding season, the territorial defense response of the male stickleback fish is triggered by the sight of red, because competing male sticklebacks have red bellies. But the male stickleback attacks anything red, not just other fish, because it is incapable of understanding its ends.
Among human beings, the etiology of misfires is much more complex because we have rational souls. Even though we are capable of grasping our ends, we may misunderstand them -- sometimes willfully.
Tomorrow: Paradoxical Dignity