Selfish traits not favoured by evolution, study shows

A study involving simulations of the Prisoner's Dilemma suggests that cooperative strategies can be individually beneficial over numerous interactions if previous communication are taken into account.  The study is consistent with human experiments involving repeated play cycles without a known end.  The paper introduces the concept of an 'evolutionarily stable strategy' that not only needs to win over other strategies but also "play well against itself".

A classic 'game theory' situation, the Prisoner's Dilemma is 'stacked' to discourage co-operation.

Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of speaking to or exchanging messages with the other. The police admit they don't have enough evidence to convict the pair on the principal charge. They plan to sentence both to a year in prison on a lesser charge. Simultaneously, the police offer each prisoner a Faustian bargain. If he testifies against his partner, he will go free while the partner will get three years in prison on the main charge. Oh, yes, there is a catch ... If both prisoners testify against each other, both will be sentenced to two years in jail.

Regardless of what prisoner A decides to do, prisoner B is better off betraying prisoner A.  The reverse also applies.  As a result, the rational solution results in both prisoners getting 2 years, although by co-operating they could get half the sentence.

  Prisoner B Silent Prisoner B Betrays
Prisoner A Silent A gets 1 year, B gets 1 year A gets 3 years, B goes free
Prisoner A Betrays A goes free, B gets 3 years A gets 2 years, B gets 2 years

The study implies that co-operation can appear even without the influence of altruism or other moral factors.  It would be intriguing to look for evidence that the strategies identified by this study actually are found in natural systems.


Adami, Christoph, and Arend Hintze. “Evolutionary Instability of Zero-determinant Strategies Demonstrates That Winning Is Not Everything.” Nature Communications 4 (August 1, 2013). doi:10.1038/ncomms3193.

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