Chips and circuit boards are useless without a source of energy. So is the brain. It took psychologists a while to realize this, and the realization came not from computer models but from biology. The transformation of psychology based on ideas from biology was one of the major developments of the late twentieth century. Some researchers found that genes had important effects on personality and intelligence. Others began to show that sexual and romantic behavior conformed to predictions from evolutionary theory and resembled aspects of behavior in many animal species. Neuroscientists began to map out brain processes. Others found out how hormones altered behavior. Psychologists were reminded over and over that the human mind exists in a biological body.
~Roy Baumeister & John Tierney, Willpower: Rediscovering the Greatest Human Strength, p. 42-43