What is the attraction of socialism? The Cato Institute held a policy forum Wednesday to consider that question, featuring talks from the moral psychologist Jonathan Haidt and the evolutionary psychologists Leda Cosmides and John Tooby. Cosmides pointed out that human beings evolved to handle the social challenges encountered in small bands of 50 to 200 people. Globe-spanning market economies strain our brains. The chief problem, Tooby suggested, is that many people are beguiled by "romantic socialism"—that is, they imagine what their personal lives would be like if everyone shared and treated one another like family. Left-leaning people, observed Haidt, endorse a story he calls "Capitalism is Exploitation"; "Capitalism is Liberation" is the story told by many conservatives and most libertarians. Ultimately, Cosmides argued, those of us who want to preserve liberty and prosperity need to understand how human psychology has evolved and understand why evolved attitudes are so hostile to modern free market societies.