Still, experts argue about these issues. I came across one paper showing that, in fact, altruism could evolve solely through benefits to the altruistic individual, not necessarily to the group, based on simulations of yet another popular game. Known as the ultimatum game, it is widely used today in another realm of game theory research, the “behavioral game theory” explored by scientists like Colin Camerer. Behavioral game theorists believe that getting to the roots of human social behavior—understanding the Code of Nature—ultimately requires knowing what makes individuals tick. In other words, you need to get inside people’s heads. And the popular way of doing that has spawned a hybrid discipline uniting game theory, economics, psychology, and neuroscience in a controversial new discipline called neuroeconomics.