Altruism in business and behaviorial economics is a topic that comes up quite often on kottke.org, even when it's not explicit. (For instance, the central issue in the Atul Gawande article I pointed to yesterday pits the individual financial desires of doctors vs. the health of their patients.) This article from Ode Magazine takes a look at the research done in this area so far and how the idea of altruism in economics is currently on the rise.
The theory is based on the premise that humans evolved in small groups with strong social contracts and plenty of contact with strangers. Cooperation within the tribe was advantageous so long as free riders were punished. It was also the best gambit on encountering strangers. Cooperation, particularly in times of famine, was the only means of survival, so altruism became a favored evolutionary trait.
One of my favorite books on altruism and economics is Robert Wright's Nonzero.