In [i]The Selfish Gene[/i], 2nd edition, 1989, chapter 12 (not in the 1st edition), is about Robert Axelrod's work on "reciprocal altruism", which tested different computer programs against one another that simulated competitive strategies. The winner was the "Tit for Tat" scheme which cooperates initially but retaliates if the other participant reneges. - Richard Dawkins explains "The birds ... who removed ticks from each other's feathers were playing an iterated prisoner's Dilemma game." The outcomes depend on the relative advantages of the various strategies, e.g. in terms of energy use. - Axelrod and biologist W.D.Hamilton combined to publish a paper on "The Evolution of Cooperation" (1981): - http://www.sciencemag.org/cgi/content/abstract/211/4489/1390 - http://en.wikipedia.org/wiki/The_Evolution_of_Cooperation - In biological terms the concept becomes one of "evolutionary stable strategies". This provides a mathematically justified basis for the evolution of all these symbiotic relationships that DT finds beyond his imagination.