Primates in the driver's seat
It looked like they should all be dead. Multicar accidents, bloody incidents of road rage. Cars should have been ramming one another in huge demolition derbies, a global auto-da-fe.

But they were primates, they were social creatures. The brain had ballooned to its current size precisely to enable it to make the calculations necessary to get along in groups. These were the parts of the brain engaged when people drove in crowded traffic. Thus along with all the jockeying and frustration came the almost subliminal satisfactions of winning a competition, or the grudging solidarities of cooperating to mutual advantage. Let that poor idiot merge before his on-ramp lane disappeared; it would pay off in the overall speed of traffic. Thus the little primate buzz.

When things went well. But so often what one saw were people playing badly. It was like a giant game of prisoners' dilemma, the classic game in which two prisoners are separated and asked to tell tales on the other one, with release offered to them if they do. The standard computer model scoring system had it that if the prisoners cooperate with each other by staying silent, they each get three points; if both defect against the other, they each get one point; and if one defects and the other doesn't, the defector gets five points and the sap gets zero points. Using this scoring system to play the game time after time, there is a first iteration which says, it is best always to defect. That's the strategy that will gain the most points over the long haul, the computer simulations said if you are only playing strangers once, and never seeing them again. And of course traffic looked as if it were that situation.

But the shadow of the future made all the difference. Day in and day out you drove into the same traffic jam, with the same basic population of players. If you therefore played the game as if playing with the same opponent every time, which in a sense you were, with you learning them and them learning you, then more elaborate strategies would gain more points than always defect. The first version of the more successful strategy was called tit for tat, in which you did to your opponent what they last did to you. This out-competed always defect, which in a way was a rather encouraging finding. But tit for tat was not the perfect strategy, because it could spiral in either direction, good or bad, and the bad was an endless feud. Thus further trials had found successful variously revised versions of tit for tat, like generous tit for tat, in which you gave opponents one defection before turning on them, or always generous, which in certain limited conditions worked well. Or, the most powerful strategy Frank knew of, an irregularly generous tit for tat, where you forgave defecting opponents once before turning on them, but only about a third of the time, and unpredictably, so you were not regularly taken advantage of by one of the less cooperative strategies, but could still pull out of a death spiral of tit-for-tat feuding if one should arise. Various versions of these firm but fair irregular strategies appeared to be best if you were dealing with the same opponent over and over.

In traffic, at work, in relationships of every kind social life was nothing but a series of prisoners' dilemmas. Compete or cooperate? Be selfish or generous? It would be best if you could always trust other players to cooperate, and safely practice always generous; but in real life people did not turn out to earn that trust. That was one of the great shocks of adolescence, perhaps, that realization; which alas came to many at an even younger age. And after that you had to work things out case by case, your strategy a matter of your history, or your personality, who could say.

- Forty Signs of Rain (Kim Stanley Robinson)