C O O P E R A T I O N   1

The Prisoner's Dilemma

Axelrod began by considering the "Prisoner's Dilemma" experiment. This is a kind of thought game which examines the rewards and punishments for either cooperating or not. The story usually given runs like this:

Suppose you and an accomplice (whom you barely know) in some crime are arrested. The chief detective visits you. He says, "We know you and your pal did it. And you're both going to jail for it. But we always like to make sure, so you've got a choice. You can tell us what your pal did, or you can keep quiet. (And by the way, we're giving him this same choice you're getting.)"

"If you give us evidence against him, and he keeps quiet about you, then you get one year, and he spends six behind bars. If you keep quiet and he gives us the goods on you, you stay for six and he's out in one. If you both keep quiet, you both get three years; if you both turn each other in, you both get five years. So what'll it be?"

You must select one of two options--you can either cooperate with your fellow prisoner (by keeping quiet) or defect (by providing evidence). You have no way of passing information between you, and you don't know him well enough to predict what he'll choose based on his personality. So which will you choose?

The table below describes what is called the "payoff matrix" of this classic formulation of the Prisoner's Dilemma:

Note: In this table the results are the payoffs to you. They are categorized as follows:

T: Temptation for defecting when the other party cooperates

S: "Sucker's payoff" for cooperating when the other party defects

R: Reward to both players for both cooperating

P: Punishment to both players for both defecting

Looking at the table in a purely rational way, it would seem that your best choice is to defect. The two possible results of your defection mean a chance for jail time of either 1 year (if your compatriot cooperates by keeping quiet about you) or 5 years (if he talks), for an average risk of 3 years. On the other hand, if you cooperate with your accomplice, you get 3 years if he cooperates too and 6 years if he defects, for an average risk of 4.5 years.

What's more, you have to assume that your accomplice is capable of thinking about this just like you did. Since he--just like you--is likely to conclude that defection is less risky, he'll probably defect... in which case you have even less incentive to cooperate.

And so you defect. And so does your accomplice. And so you both come away worse off than if you had cooperated with each other.

It appears that as long as the temptation to defect is greater than the reward for cooperating, there's no reason to cooperate. Yet it's clear that in the real world we do cooperate. So could there be some other factor at work, the addition of which to the Prisoner's Dilemma might make its outcomes more realistic?

Next:

The Iterated Prisoner's Dilemma

The Prisoner's Dilemma

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