MEI Conference 2009
Interactive workshops
The prisoner’s dilemma
World War 1
The situation
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There are two parties; they may well be rivals
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They can nonetheless co-operate
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At any time one or both may stop cooperating and defect
Other examples
A model
Side 2 cooperates
Side 2
defects
Side 1 cooperates
CC
CD
Side 2
defects
DC
DD
Scoring system
CC
DD
DC
CD
3
1
5
0
3
1
0
5
Scoring system
CC
DD
DC
CD
1
-1
3
-2
1
-1
-2
3
Questions
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What is a good strategy for the game ?
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What can the game tell us about human
behaviour ?
Axelrod’s experiments
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Axelrod ran two competitions for the best strategy
Entrants were from around the world. They
submitted computer programs. There were 14 first
time and 62 next time
Each played the other 5 times over 200 rounds
In both experiments Tit-for-tat was the winner
Successful strategies
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•
•
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They are nice; they never defect first
They always retaliate when the other side
defects
They are forgiving returning quickly to cooperation
They are non-envious seeking their own
benefit rather than harming the other party
Evolution of behaviour
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The different Rules in Axelrod’s experiment could be
taken to be types of human behaviour.
Initially all Rules are equally represented.
The whole experiment is run for 1000 rounds
Each round of the experiment is a generation and the
numbers for each Rule at each generation are in
proportion to the previous score.
Some Rules die out and others become dominant and
influence our system of values.
Evolution of behaviour