Why do people believe in a zero-sum economy?

Zero-sum thinking and aversion to trade pervade our society, yet fly in the face of everyday experience and the consensus of economists. Boyer and Petersen’s evolutionary model invokes coalitional psychology to explain these puzzling intuitions. I raise several empirical challenges to this explanation, proposing two alternative mechanisms—intuitive mercantilism (assigning value to money rather than goods) and errors in perspective-taking.