The gravest imperfections in nature, though, are moral ones. Consider how humans and other animals are intermittently tortured by pain throughout their lives, especially near the end. Our pain mechanism may have been designed to serve as a warning signal to protect our bodies from damage, but in the majority of diseases -- cancer, for instance, or coronary thrombosis -- the signal comes too late to do much good, and the horrible suffering that ensues is completely useless.