"There are two aspects of our evolved psychology that help explain beliefs about trade. First, humans tend towards zero-sum thinking. That is, we do not intuitively understand the possibilities of economic growth or the benefits of trade in achieving it.
Our ancestors lived in a static world with little intertribal trade and virtually no technological advance. That is the world our minds understand. This doesn't mean that we can't grasp the crucial concept that trade benefits both parties to a transaction—but it does mean that we must learn it.
Positive-sum thinking doesn't come naturally. By analogy, we learn to speak with no teaching, but we must be taught to read. Understanding the mutual benefits of exchange is like reading, not speech.
Second, we evolved in a hostile world. Our ancestors engaged in constant conflict with neighbors, much like present-day chimpanzees. We developed strong in-group and out-group instincts, and for many aspects of behavior we still have such feelings.
These feelings are benign when applied to something like rooting for local sports teams, but are more harmful when applied to international trade. They are most harmful when they generate actual warfare. Yet the metaphor of a "trade war" shows how close to the surface harmful instincts are.
These two sets of beliefs interact to explain our natural (mis)understanding of trade. We believe that the number of jobs is fixed (a result of zero-sum thinking) and that as a result of trade these jobs go to foreigners, whom in a deep sense we view as enemies. Both beliefs are incorrect, but both are natural. And in many cases politicians are only too eager to capitalize on these beliefs to be re-elected.
One of the great triumphs of modern economics is the reduction in tariffs and other barriers to the free international flow of goods. Enough voters have been convinced of the benefits of free trade that it has generally been a winning political position, and those running on protectionist platforms do not do well in contemporary America. It would be a disaster if the current economic malaise reversed this situation."
