Game theory.

Step 1 of 4

The prisoner’s dilemma

Game theory studies decisions among several players, where what is best for one depends on what the others do. In the prisoner’s dilemma each player chooses in secret: cooperate or betray. Mutual cooperation gives each $3$⁠ points, and mutual betrayal $1$⁠. When one betrays and the other cooperates, the betrayer gets $5$⁠ and the betrayed $0$⁠.

Step 2 of 4

Average against the table

In the scene three strategies share a table: unconditional cooperators in green, unconditional defectors in red, and tit for tat in blue: it cooperates in the first round, and from then on does what the other did in the round before. Every player plays everyone else, and each strategy’s coin stack is its average points a round.

Defectors at the start are $30\%$⁠, and of the rest half play tit for tat. All the settings are fixed now.

Step 3 of 4

Generation after generation

Now the tournament is ecological: after each generation, each strategy’s share of the table grows in proportion to the points it collected. No one decides anything; strategies that do well simply become more common. The Generations slider runs $30$⁠ generations.

Step 4 of 4

A repeated game

When the same players meet again and again, a move today has a price tomorrow: whoever betrays now may be betrayed in the next round. Rounds per match sets how many rounds each match between two players lasts.

Try it: after checking, slide it back down to 1 and find how many rounds tit for tat needs to win.

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