Not entirely spawned by this article, but the whole genre and some other comments on HN by other users: I wonder if part of the "mystery" of cooperation in these simulations is that these people keep investigating the question of cooperation using simulations too simplistic to model any form of trade. A fundamental of economics 101 is that valuations for things differ for different agents. Trade ceases to exist in a world where everybody values everything exactly the same, because the only trade that makes any sense is to two trade two things of equal value, and even then, since the outcome is a wash and neither side obtains any value from it, why bother? I'm not sure the simulation hasn't been simplified to the point that the phenomena we're trying to use the simulation to explain are not capable of manifesting within the simulation.<p>I'm not saying that Trade Is The Answer. I would be somewhat surprised if it doesn't form some of the solution eventually, but that's not the argument I'm making today. The argument I'm making is that if the simulation can't simulate trade at all, that's a sign that it may have been too simplified to be useful. There are probably other things you could say that about; "communication" being another one. The only mechanism for communication being the result of iteration is questionable too, for instance. Obviously in the real world, most cooperation doesn't involve human speech, but a lot of ecology can be seen to involve communication, if for no other reason than you can't have the very popular strategy of "deception" if you don't have "communication" with which to deceive.<p>Which may also explain the in-my-opinion overpopular and excessively studied "Prisoner's Dilemma", since it has the convenient characteristic of explicitly writing communication out of it. I fear its popularity may blind us to the fact that it wasn't ever really meant to be the focus of study of social science, but more a simplified word problem for game theory. Studying a word problem over and over and over may be like trying to understand the real world of train transportation systems by repeatedly studying "A train leaves from Albuquerque headed towards Boston at 1pm on Tuesday and a train leaves from Boston headed towards Albuquerque at 3pm on Wednesday, when do they pass each other?" over and over again.<p>(Or to put it <i>really</i> simply in machine learning terms, what's the point of trying to study cooperation in systems whose bias does not encompass cooperation behaviors in the first place?)