This is also the most basic function of nervous systems, to provide reward for adaptive behavior and pain for harmful behavior. Pain and reward are the essence of function. For this system to work, however, pain has to “feel” bad and reward circuitry has to “feel” good on some level. As creatures become more sophisticated, their reward and aversion circuitry also become more sophisticated. This evolves into complex emotions. Think, too, about motivation. Fear is a great motivator to get you to focus and marshal all your energy to run really hard away from that predator.
