Certain similarities between the evolution of cooperation and phase transitions in physics

The theory of evolution of cooperation presents a number of striking similarities to the theory of phase transitions in physics. A system that is in a higher energy phase P + will make a transition to a lower energy phase P − , given enough time, as long as the intervening energy barrier is not too high. The phase transition is realized through the nucleation of a sufficiently large bubble of the energetically preferred phase P − within the higher energy phase P + . Similarly, if we think of the strategies of Defection and of Tit for Tat as the phases P + and P − respectively, a population using the ‘energetically unfavourable’ Defection strategy will switch over to the ‘energetically favourable’ Tit for Tat strategy, provided the players interact continuously and substantially. The presence of a large enough Tit for Tat concentration is necessary for the onset of this change. Copyright © 2001 John Wiley & Sons, Ltd.