"No instinct has been produced for the exclusive good of other animals, but each animal takes advantage of the instincts of others" 
Charles Darwin

The question why in the spite of all the 'selfish genes' animals seem to altruistically help each other and cooperate has intrigued researchers ever since Darwin. Research in this field has revealed a major dichotomy: The evolution of cooperation in (a) related and (b) in unrelated individuals. While W.D. Hamilton provided a persuasive theory for the evolution of cooperation in related individuals, the evolution of cooperation in communities of unrelated individuals is the playground of game theory and the iterated Prisoner's Dilemma (IPD). The journal Science has published two excellent reviews on the evolution of cooperation:

Both reviews feature in-depth, up-to-date treatment of both Hamilton's rule and the IPD, along with very helpful references. For my own work in both fields see:

(a) Please have a look at my article on Hamilton's theory (PDF) for Academic Press's Encyclopedia of Genetics.

(b) The non-zero-sum game 'Prisoner's Dilemma' is used as the standard metaphor to conceptualise the conflict between mutual support and selfish exploitation among interacting non-relatives in biological communities. During a half-year stay at the University of Umeå, Sweden, I wrote a review-article which was published in OIKOS: Brembs, B. (1996): Chaos cheating and cooperation: potential solutions to the Prisoner's Dilemma. OIKOS 76: 14-24.  (HTML/PDF)
For a short description of the Prisoner's Dilemma see the Principia Cybernetica article on the matter. Or go to to the PRISON project page for more detailed information.

There is also software available for simulating the iterated Prisoner's Dilemma: WinPRI (ZIP-file, 305kb). It runs flawlessly on Windows 9x/NT but I don't know, if it runs on win16. I can enthusiastically recommend it! The program was written by Philippe Mathieu and Frédéric Grignion from the University of Lille in France.