The Darwinian principle of "survival of the fittest" echoes what many people believe about life: To get ahead, you need to look out for No. 1. A cursory read of evolutionary doctrine suggests that the selfish individuals able to outcompete others for the best mates and the most resources are most likely to pass their genes on to the next generation. Then there is classical economic theory, which holds that given the choice, we will often opt for a personal benefit over a personal loss, even if that loss involves a benefit to someone else. The philosopher and economist John Stuart Mill championed the self-centered...