A simple illustration of the influence of on the evolution of cooperation in PDG.

<p>Here, pink nodes denote cooperators and blue nodes denote defectors. All the two top nodes’ friends overlap, therefore the tie strength between them equals one. All other relations have a tie strength equals . We set the two mutual best friends as cooperators initially. (a) When , the game is a classical PDG. The two cooperators get a payoff of and all the defectors get . Therefore, cooperators will imitate the strategy of defectors and defection becomes prevalent; (b) When , the two cooperators will invest all their investments to each other. Both cooperators get and all defectors get 0. Therefore, in the next round, all defectors will adopt C and cooperation becomes prevalent.