Compared with most animals, we humans engage in a host of behaviors that are destructive to our own kind and to ourselves. We lie, cheat and steal, carve ornamentations into our own bodies, stress out and kill ourselves, and of course kill others. Science has provided much insight into why an intelligent species seems so nasty, spiteful, self-destructive and hurtful. Inside you'll learn what researchers know about some of our most destructive behaviors.