Playing At Evolution

Following on from the group dynamics post of yesterday, I tripped over another report on the computer modeling of the evolution of group behaviors. In this case dominance issues weren’t the point of the study, but the altruistic responses, or not, of the group individuals.

This report is from Zhang and Hui from the rather quaintly named Centre of Invasion Biology of Stellenbosch U (1). This simulation leans heavily on game theory and uses the “Prisoner Dilemma” game at its core.

For those of you who aren’t inveterate watchers of the TV series “Law & Order”, the idea of the game is two friends are arrested and grilled separately. If they both say nothing, they end up with a one-month jail term. If they both rat on each other, they get three months each. If one rats and the other doesn’t, the one ratted out gets a long term and the other goes free.

In the non-thriller version played here, the concept is that there is a cost in cooperation, which also gives a benefit back to the cooperator. The non-cooperator (also termed defector) can take something for nothing giving an even greater loss to the cooperator.

As the simulation is looking at the evolution of the population behavior and sustainability, the birth and death of “players” is added into the mix. The big difference between this study looking at group evolution and past attempts is that the previous ones were based on interaction frequency, whereas this one is based on population density distributions in a harsh environment. The latter is made harsher by beefing up the death rates.

By now we are all on the edge of our seats awaiting the results so here are brief highlights. Low density populations mean that you interact with people you know, or are related to even, so that cooperation is more likely.  Density increase reduces that tendency and so invasion by defectors will occur and the cooperative population won’t run at a stable state.

In brief, to have a good cooperative society, knowing your neighbors is essential, and that tough environments mean that you’re more likely to know and cooperate with your neighbors. Those of us who have lived in both big cities and in the boonies, know exactly what the authors mean.


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