Imagine a world in which there was suddenly no emotion--a world in which human beings could feel no love or happiness, no terror or hate. Try to imagine the consequences of such a transformation. People might not be able to stay alive: knowing neither joy nor pleasure, neither anxiety nor fear, they would be as likely to repeat acts that hurt them as acts that were beneficial. They could not learn: They could not benefit from experience because this emotionless world would lack rewards and punishments. Society would soon disappear: People would be as likely to harm one another as to provide help and support. Human relationships would not exist: In a world without friends or enemies, there could be no marriage, affection among companions, or bonds among members or groups. Society's economic underpinnings (基础) would be destroyed: Since there would be no incentives of any kind. For as we will see, incentives imply a capacity to enjoy them. In such a world, the chances that the human species would survive are next to zero, because emotions are the basic instrument of our survival and adaptation. Emotions structure the world for us in important ways. As individuals, we categorize objects on the basis of our emotions. True, we consider the length, shape, size, or texture, but an object's physical aspects are less important than what it has done or can do to us--hurt us, surprise us, anger us or make us joyful. We also use categorizations colored by emotions in our families, communities, and overall society. Out of our emotional experiences with objects and events comes a social feeling of agreement that certain things and actions are 'good' and others are 'bad', and we apply these categories to every aspect of our social life--from what foods we eat and what clothes we wear to how we keep promises and which people our group will accept. In fact, society explains our emotional reactions and attitudes, such as loyalty, morality, pride, shame, guilt, fear and greed, in order to maintain itself. It gives high rewards to individuals who perform. important tasks such as surgery, makes heroes out of individuals for unusual or dangerous achievements such as flying fighter planes in a war, and uses the legal and penal system to make people afraid to engage in antisocial acts. The reason why people might not be able to stay alive in a world without emotion is that ______.