(I wrote a fun little essay about Press & Dyson and Adami & Hintze for my scientific writing class last summer. The assignment was to write an essay of no more than 1000 words, intended for a non-scientific audience. Not sure if pasting it here is too much for HN etiquette, but it's not published anywhere else, so here goes. I hadn't read the article linked above when I wrote this, but it covers very similar ground in much simpler terms. Disclaimer: I didn't actually interview any of the researchers for the purpose of this short class assignment, so I was speculating a bit about their subjective states!)

Christoph Adami and Arend Hintze didn't believe what they were reading. The two evolutionary biologists suspected that something didn't quite add up in a 2012 article by two of the most influential physicists of our time, William Press and Freeman Dyson.[1] Press and Dyson claimed that they had discovered a mathematical trick that flew in the face of results from three decades earlier, which had so far stood the test of time.

The subject of their argument was a paradoxical "game" called the Prisoner's Dilemma. This game was invented half a century ago to challenge the tenets of game theory, a branch of mathematics beloved by economists and political scientists. In the Prisoner's Dilemma, two players face an awkward situation in which they cannot communicate but their choices affect each other. Each player must make a simple choice: Will you "cooperate" or will you "defect"?

The game is set up so that it presents a common dilemma faced in real life. The players will be better off if they both cooperate than if they both defect. But either player can gain an advantage by defecting when the other player cooperates. With every move, you are tempted to take advantage of the other player and afraid that they will take advantage of you, even though you both know that overall it's better to cooperate.

The Prisoner's Dilemma is reminiscent of any situation in which two individuals will share equally in the benefits of a shared activity. Cooperating then means giving it your all and defecting means slacking off. If you both cooperate then you both benefit from your hard work. If you both defect then there are no benefits to be had. Whenever the other player cooperates, however, you are better off defecting in order to benefit from their effort without exerting any yourself. Likewise, whenever the other player defects, then once again you are better off defecting yourself because it's not worth your effort to support them.

The paradox of the Prisoner's Dilemma is this: If it always seems better to defect, no matter what the other player does, how do we ever end up cooperating? This question, and therefore the Prisoner's Dilemma itself, is of prime interest to economists, political scientists, biologists, and many others. The standard answer from game theory was that a "rational" player would always defect, but some researchers suspected that cooperation might actually be favored by evolution in the long run.

In a crucial paper in 1981, political scientist Robert Axelrod and evolutionary biologist William Hamilton reported on a Prisoner's Dilemma tournament that Axelrod had conducted.[2] Axelrod invited dozens of researchers to submit computer programs that would play the game thousands of times. Hoping that the tournament would provide insights into how cooperation might evolve, he contacted one of its participants, biologist Richard Dawkins, who introduced him to Hamilton,[3] a biologist at Axelrod's own university who had published a research paper of his own about the Prisoner's Dilemma.

In the preceding decades, discussion of the Prisoner's Dilemma was largely philosophical. It was an interesting ethical puzzle, intriguingly simple and yet maddeningly difficult to reason about. With his computerized tournament, Axelrod advanced Prisoner's Dilemma resear...