This is the 20th anniversary of Robert Axelrod’s The Evolution of Cooperation, which showed how cooperation could emerge from egoistic maximizers through a prisioner’s dilemma tournament. The tournament’s winning strategy “Tit-for-tat”, submitted by Anatol Rapaport, illuminated phenomenon as diverse as salmon mating habits and spontaneous cease-fires in World War I. The tournament, held in 1980, long preceded the book, and the findings, along with their implications for biology, had been publish in Science in 1981. (Robert Axelrod and William D. Hamilton, “The evolution of cooperation.” Science 211:1390-6, 1981)
Ever since the tournament, new strategies for maximizing payoffs in an iterated prisioners’ dilemma are developed all the time, but “tit-for-tat” has consistently outperformed all challengers . . . until now.
“[T]he Southampton [University in England] team submitted 60 programs. These, Jennings explained, were all slight variations on a theme and were designed to execute a known series of five to 10 moves by which they could recognize each other. Once two Southampton players recognized each other, they were designed to immediately assume ‘master and slave’ roles — one would sacrifice itself so the other could win repeatedly.
If the program recognized that another player was not a Southampton entry, it would immediately defect to act as a spoiler for the non-Southampton player. The result is that Southampton had the top three performers — but also a load of utter failures at the bottom of the table who sacrificed themselves for the good of the team.”
UPDATE: Cosma Shalizi at Three-Toed Sloth is skeptical and makes somes good points.
The clever thing the Southampton group did was to engineer a situation that TFT couldn’t cope with, namely collusion among the competing players. If, indeed, one agent is willing to be stomped on, forever, to the greater glory of another, without getting anything out of it, then its master will indeed get all the benefits that the dilemma is capable of providing. (At this point, you can add your own allusions to Hegel, or “safe, sane and consensual” jokes, as you prefer.) This does not seem to me at all an evolutionarily stable situation, however, since the slave agents have, by construction, exactly no incentive to participate in the arrangement. In fact, a mutant which used the coding scheme to recognize supposed masters and always defected against them, but played TFT with everyone else, should do better than a slave, and without slaves the master-type agents are not going to do well. (I will leave it to others [Bill? Gary? Tim?] to draw the obvious morals.) So I strongly doubt that in the wild, e.g., in actual social dilemmas, we will ever see Southampton-type strategies, which means that TFT should still be robust, and strong reciprocity is saved for another day.
(For the really hard core people. I can’t begin to imagine Southampton strategies appearing in biological evolution. Case 1: slaves are not related to masters. Then slaves obviously go extinct, after which masters are not long for this world. If memory serves, Darwin, in the Origin, gives basically this case as an example of an observation which would refute evolution by natural selection. Case 2: slaves are related to masters. Then we’ve got the usual kin selection case of, e.g., sterile castes in eusocial insects. Since the pay-off function has to be inclusive fitness, we don’t really have the Prisoners’ Dilemma at all!)
I guess we’ll watch this unfold.