[atrifix]

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Scotch: I hope my clarification helped. Can you now explain why you think the Prisoner in the dilemma is acting altruistically by cooperating?

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I don't. When I said that the prisoner's dilemma requires altruism, I meant that choosing to cooperate from altruism is the theoretical solution to the dilemma, not that the prisoner is being altruistic because he cooperated. If acting altruistically is A and cooperating is B, then I am saying "A therefore B" and (I think) you are hearing "B therefore A".

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I haven't read the other threads on this, but I'll go further than both of you and state that cooperating in the prisoner's dilemma does require either altruism or irrationality.

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I am saying that cooperating increases personal happiness, and the total happiness of those involved -- so it doesn't require altruism.

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If this is true, then the players aren't playing the prisoner's dilemma, they're playing a different game--so you haven't given a solution to the prisoner's dilemma.

There are some other assumptions that have to be made in the finitely repeated prisoner's dilemma (most importantly, common knowledge of rationality), but including all the assumptions leads to a unique equilibrium where players defect on all rounds. So either one of the assumptions has to go or we have to conclude that players are altruistic.