Several years ago, our family took a trip to Bali, Indonesia. Bali is an amazing place to visit, but I wouldn't recommend going there if you are afraid of monkeys (apparently this is even more true since the COVID-19 pandemic)! I've posted about our scary trip through the Ubud Monkey Forest in a post last year ("Dart-throwing Monkeys").
We visited a lot of Hindu temples during our trip. A lot of monkeys seemed to congregate around these temples, perhaps because the tourists were also congregating there! The monkeys would often confront an unsuspecting tourist (usually one taking a picture and not paying attention to the monkeys) and use the opportunity to steal a hat, sunglasses, cameras, or anything else that they could get their hands on. They would then run off and sit just out of reach of the tourist. They would only give the item back in exchange for food. You can't say that these monkeys were unintelligent!
I am sure the monkey didn't realize it was using what is called, at least in game theory, a "tit for tat" strategy. Several years ago, Robert Axelrod, a political scientist from the University of Michigan, held a tournament to determine the optimal strategy for the Prisoner's Dilemma, one of the classic problems in game theory (first described by Merrill Flood and Melvin Dresher at the RAND Corporation in 1950). More on Axelrod's experiment below, but first let me explain the Prisoner's Dilemma game.
While there are a number different variations to this game, the basic set-up is the same. Two criminals have been arrested and are now being held prisoner in separate jail cells. The police don't have enough evidence to convict them on the principal charge, but they do have enough evidence to convict them on a lesser charge. The police offer each prisoner a bargain - betray the other (testify against the other prisoner - this has also been called "defect" in the literature) and go free or remain silent (this has also been called "cooperate" in the literature) and serve the 1 year prison sentence on the lesser charge. As outlined above, the possible outcomes to the game are as follows:
- A and B each betray the other - each of them serve two years in prison
- A betrays B, but B remains silent - A is set free and B serves three years in prison
- A remains silent, B betrays A - A serves three years in prison and B is set free
- A and B both remain silent - each of them serve only one year in prison
As you can see, the best option for both prisoners is to remain silent (i.e. "cooperate" with each other) and spend only 1 year in prison. Remember though that the prisoners are acting independently. How can they trust each other not to betray each other? If only one betrays the other, he or she goes free (and the other goes to prison for three years). However, if both of them betray each other, they go to prison for two years. Since two years of prison is better than three years, they end up betraying each other rather than taking the risk of staying silent (which would have been the better option, hence, the dilemma).
Axelrod set up his tournament so that games would be repeated multiple times. Over 20 individuals (all experts in game theory) submitted a strategy for an online Prisoner's Dilemma tournament. Each of the strategies was paired off with the others to see which strategy was the most effective. Surprisingly, a very simple strategy known as "tit for tat" was the most effective strategy in the tournament. The "tit for tat" strategy is one of simple reciprocity in which the player cooperates on the first move and then does whatever the other player did in the previous move in all subsequent moves. An example of a sequence of player using the "tit for tat" strategy is shown below (note that Player One is using the "tit for tat" strategy):
Player One Player Two
Cooperate Defect
Defect Cooperate
Cooperate Defect
Defect Cooperate
Cooperate Cooperate
Cooperate Cooperate
Axelrod conducted a second tournament with more subjects, including individuals who weren't experts in game theory. Again, the "tit for tat" strategy was the most effective strategy played. Axelrod subsequently published the results of his findings in the journal Science in a paper entitled "The Evolution of Cooperation". He later expanded upon this paper in a book with the same title, which describes how cooperation can emerge in a variety of contexts (his theory has subsequently become a very important theory in evolutionary biology, as well as game theory).
As it turns out, cooperation is a widespread phenomenon in nature. For example, one member of a meerkat colony usually performs sentry duty. When the sentry sees a predator (a jackal, for example), the sentry makes a very loud and distinctive cry, which acts as a warning signal to the rest of the meerkat colony that danger is close. Think about it for a second. By crying out loudly, the sentry is drawing attention to itself, which increases the risk of being attacked by the predator and eaten. However, this selfless act alerts (and likely saves) the rest of the colony. The sentry is using a version of the "tit for tat" strategy - the sentry understands that it may be with the colony the next time that another member of the colony is performing sentry duties (reciprocity and mutual cooperation).
Cooperation is the preferred (some would say dominant) strategy in nature. We can learn a lot from the animal kingdom! I hope to return to this discussion in future posts, as the topic on the evolution of cooperation is absolutely fascinating and quite instructive.
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