The previous part in this series looked at what happens when a prisoners’ dilemma game is played multiple times. It turns out that the best strategy is ‘tit for tat’, where you start off co-operating and then copy the other players previous action.

This is a situation that can be observed in nature with stickleback fish.

When a stickleback is approached by a predator they swim towards them to check out the predator before darting back to safety. Getting close to the predator gives the stickleback more information but carries a greater risk of being attacked. If two sticklebacks co-operate then they can get closer to the predator than a single fish could. They do this each taking turns to move a little bit closer. This confuses the predator who doesn’t know which one to go for.

For this to work one of the fish needs to go first and then be followed by the other. If the other doesn’t co-operate then the first fish is left vulnerable to attack.

When this is tested it turns out that the fish follow a tit-for-tat strategy. The fish have evolved to find the strategy which will give them the best chance of surviving.

**Today’s takeaway: Game theory occurs naturally, it isn’t just a theoretical concept.**

The earlier parts of this post are here:

Part one – introduction to the Prisoners’ Dilemma