Being programmers, we think of our users like we think of our code. That is: rationally. However, our users are emotional, irrational, and specifically evolved animals. The study of Sociobiology has some really interesting insights for software developers about who your users really are and how you can influence them. For instance, badges seem dumb to me, but why do they work so well for other people? Why do people keep playing Farmville? From AAdvantage to Klout, manipulating people with evolution is all around!