From the NY Times

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NY Times, July 31, 2007

http://www.nytimes.com/2007/07/31/science/31prof.html?ex=1343620800&en=b63e24b50a3a687f&ei=5124&partner=permalink&exprod=permalink\\

Title: In Games, an Insight Into the Rules of Evolution

... When biologists speak of cooperation, they speak more broadly than the rest of us. Cooperation is what happens when someone or something gets a benefit because someone or something else pays a cost. The benefit can take many forms, like money or reproductive success. A friend takes off work to pick you up from the hospital. A sterile worker bee tends to eggs in a hive. Even the cells in the human body cooperate. Rather than reproducing as fast as it can, each cell respects the needs of the body, helping to form the heart, the lungs or other vital organs. Even the genes in a genome cooperate, to bring an organism to life.

In recent papers, Dr. Nowak has argued that cooperation is one of the three basic principles of evolution. The other two are mutation and selection. On their own, mutation and selection can transform a species, giving rise to new traits like limbs and eyes. But cooperation is essential for life to evolve to a new level of organization. Single-celled protozoa had to cooperate to give rise to the first multicellular animals. Humans had to cooperate for complex societies to emerge.

“We see this principle everywhere in evolution where interesting things are happening,” Dr. Nowak said ...

... As Dr. Nowak developed this neighborhood model, he realized it would help him study human cooperation. “The reality is that I’m much more likely to interact with my friends, and they’re much more likely to interact with their friends,” Dr. Nowak said. “So it’s more like a network.”

Dr. Nowak and his colleagues found that when they put players into a network, the Prisoner’s Dilemma played out differently. Tight clusters of cooperators emerge, and defectors elsewhere in the network are not able to undermine their altruism. “Even if outside our network there are cheaters, we still help each other a lot,” Dr. Nowak said. That is not to say that cooperation always emerges. Dr. Nowak identified the conditions when it can arise with a simple equation: B/C>K. That is, cooperation will emerge if the benefit-to-cost (B/C) ratio of cooperation is greater than the average number of neighbors (K).

“It’s the simplest possible thing you could have expected, and it’s completely amazing,” he said.