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By Root 693 0

powerful scavengers are high, and the outcome would be fatal. One could watch for predators while the other eats, but chances are the watcher gets nothing while the scavenger feasts. If they each scavenged for a few minutes and then stopped and listened for a few minutes, they’d get some food and avoid a fatal encounter with a predator. But the moment one of them stops to watch, the other will have a clear field to gorge himself at the look-out’s expense. What to do? The dominant strategy is to scavenge like mad and don’t bother looking out for threats. If the other guy splits his time between eating and watching, you’re better off, and if the other guy doesn’t, your watching for predators lets him take the best cuts. One thing they can’t do is agree with one another to alternate eating and watching. Even if they are smart enough to figure this out and have enough language to bargain to an agreement, there is no way they can enforce the agreement on one another. That would take time from eating from the carcass and watching for predators. What is more important, neither will be prepared to enforce on the other the promise each makes to alternate eating and watching. That would just take time from eating or watching. Their mutual promises will be cheap talk, empty words. A classic PD.

Of course, watching and eating are not the only strategies available to each scavenger. Another option is to just kill the other guy the moment he turns his back and starts to scavenge. That will leave everything to the killer, at least till a stronger predator arrives. Of course, if they both left the other alone and began to eat, they’d each do better than dying. Neither can afford to risk that. All they can do is warily stalk each other, getting hungrier all the time, while the vultures take all the meat on the carcass.

The PD problem kicks in even before there is a chance to feed. Suppose two scavengers come upon a carcass being eaten by one lone hyena. If they both expose themselves, making noise and throwing rocks, there is a good chance they’ll drive the hyena away and have a decent meal. But there is a chance one or both might be injured by the surprised hyena. If one hides while the other tries to scare the hyena away, he’ll do better no matter what happens—less risk, more eating time. Each hangs back in the undergrowth, waiting for the other to charge the hyena—that’s the dominant strategy. As a result, neither of them gets anything. But they can’t enforce on each other the mutually beneficial strategy of both of them scaring the hyena. Another PD.

In everyday life today, we still find ourselves in PD situations—for example, every time we go shopping. Consider the last time you purchased a soft drink at a convenience store just off the highway in a region of the country you’ll never visit again. You have a dollar bill in your hand and want a drink; the salesperson behind the counter has the drink and wants the bill in your hand. He proffers the bottle, with the other hand held out for the money. His best strategy is to take your bill and hang on to the drink. If you complain, he’ll simply deny you paid him. You won’t call the police. You simply don’t have time and it’s not worth the trouble, in spite of your moral indignation; you’re better off just going to the next convenience store on the road. Your best strategy is to grab the bottle, pocket your bill, and drive off. Will the salesperson call the police? If he did, would they give chase just for a bottle of Coke? The answer to each of these questions is no. It’s not worth their trouble.

Knowing all this, neither of you does the rational thing. Thoughtlessly, irrationally, you both cooperate, exchanging the dollar bill for the drink. There are infinte examples like this. Consider the last time you left a tip, flushed a public toilet, or added some change to a street musician’s take. People find themselves in PDs constantly and almost never choose the dominant egoistical strategy. The economists need an explanation for why we are nice when it doesn’t look like the rational strategy.