HONOR AMONG THIEVES

Of the practical dilemmas in Flood’s paper, by far the most important was the third, dubbed “A Non-cooperative Pair.” The first scientific discussion of a prisoner’s dilemma, this part of the paper describes an experiment done in January 1950 in collaboration with RAND colleague Melvin Dresher.

The original experiment is probably not the best way to introduce the prisoner’s dilemma. Instead, let’s jump to a modern version of the prisoner’s dilemma, in the form of a story.

Suppose you have stolen the Hope Diamond and are trying to sell it. You learn of a potential buyer, an underworld figure called Mr. Big – the most ruthless man on earth. Though extremely intelligent, Mr. Big is notoriously greedy and equally notorious for double-crossing. You have agreed to exchange the diamond for an attaché case full of $100 bills. Mr. Big suggests that you meet out in a deserted wheat field somewhere to make the exchange. That way there are no witnesses.

You happen to know that Mr. Big has negotiated with many other sellers of contraband in the past. Each time he has suggested a remote locale for the exchange. Every time, Mr. Big showed up and opened the attaché case to show his good will. Then Mr. Big pulled out a tommy gun, shot the other person dead, and left with both the money and the goods.

You say you don’t think the wheat-field plan is such a good idea.

You suggest the two-wheat-field plan. Mr. Big hides his attaché case of money in a wheat field in North Dakota, while you hide the diamond in a wheat field in South Dakota. Then both parties go to the nearest public phone and exchange directions on how to find the hidden goods.

This plan has built-in safeguards (tactfully, you don’t mention that). You need have nothing of value on you when you go to recover Mr. Big’s attaché case. Mr. Big (who is no homicidal maniac, just a shrewd businessman) will have no reason to wait in the North Dakota field to ambush you. Mr. Big agrees to the two-wheat-field plan.

You find a wheat field in South Dakota. As you are about to hide the attaché case with the diamond, an idea pops into your head. Why not just keep the diamond? Mr. Big will have no way of knowing that you betrayed him until he gets to South Dakota (you would wait for his phone call and give him directions as if nothing were wrong). By that time, you would be in North Dakota to pick up the money. Then you would hop on a plane to Rio. You would never see Mr. Big again.

A worse thought pops into your head. Mr. Big must be thinking the exact same thing! He’s just as smart as you are, and probably ten times greedier. He has equal incentive to betray you, and you wouldn’t be able to retaliate any more than he will. The dilemma looks like this: