Evolution of coperation is one of my main interests and I think it is a topic that could be very relevant to cancer researchers as I discussed a while ago.

Rand DG, Dreber A, Ellingsen T, Fudenberg D, & Nowak MA (2009). Positive interactions promote public cooperation. Science (New York, N.Y.), 325 (5945), 1272-5 PMID: 19729661

Cooperation in nature occurs mostly between individuals that are closely related from a genetic point of view. In most other instances cooperation happens when all the interacting individuals benefit to some extent from their cooperation. Still, in some situations altruism happens if the benefactor expects to get rewarded at some point in the future, potentially by another individual. This is problematic as it was thought that a mechanism of punishment would be necessary: those that cooperate should be rewarded but those that cheat should be punished. And punishing is not simple: cooperators should stick together to punish the cheaters as punishing itself is rarely cost free. That means that some individuals might be cooperators when it comes to the game but cheaters when it comes to punish. And that would require an extra layer of punishing, one that would deal with those that cheat at the punishing level. This, of course, has no end as one cooperator at one level might be a cheater at the next.

What Rand and colleagues have proven is that punishment might not be necessary for this type of cooperation, at least in the public goods game. Remarkably, in a population that is expected to interact together a number of times. Sometimes just the carrot (when other players reward the best cooperators) can be a better alternative than the stick (punishing the cheaters). Even when both options are available, those groups that leaned on rewarding more than on punishing were more likely to obtain higher payoffs.