Also via GeekPress, an article in the Economist that discusses evolving cooperators and 'punishers' as a solution to the free-rider problem. On the most basic level, the free-rider problem arises in situations where groups of organisms are cooperating for the common good, and a few members of that group cheat the system by taking advantage of the cooperation without giving anything back to the group. The problem is also known as the Tragedy of the Commons, meaning that any resource that is held in common by a group will tend to be abused by individuals rather than used in a coorperative manner, because there is just too much short-term advantage to cheating the system.
Anyway, back to the Economist article. I'm working on my PhD in artificial intelligence, and so I have quite a bit of experience with evolutionary systems such as the one described in the article. I haven't yet read the entire paper in the Proceedings of the National Academy of Sciences, but based on the description in the article, I can't see how their model could achieve cooperative punishment as an emergent phenomena. The author of the paper, Robert Boyd, is a professor at UCLA, so I think I'll email him about it (after I read the paper, of course).
The paper can be found here.
It's pretty interesting. The formulas the author gives are satisfying, but in his discussion section he states that the punishers never do reach a stable equilibrium frequency, which is what I would expect given that they will always be at a disadvantage to the meta-free-riding cooperators. I emailed the Robert Boyd to ask for clarification, in case I am mistaken.