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

The theory of evolution of cooperation presents a number of striking simila rities 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 hig h. The phase transition is realized through the nucleation of a sufficientl y large bubble of the energetically preferred phase P- within the higher en ergy 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 'ene rgetically 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 (C) 2001 John Wiley & Sons, Ltd.