According to a report over at the BBC:
Crucially, in an evolutionary environment, knowing your opponent’s decision would not be advantageous for long because your opponent would evolve the same recognition mechanism to also know you, Dr Adami explained.
This is exactly what his team found, that any advantage from defecting was short-lived. They used a powerful computer model to run hundreds of thousands of games, simulating a simple exchange of actions that took previous communication into account.
“What we modelled in the computer were very general things, namely decisions between two different behaviours. We call them co-operation and defection. But in the animal world there are all kinds of behaviours that are binary, for example to flee or to fight,” Dr Adami told BBC News.
“It’s almost like what we had in the cold war, an arms race – but these arms races occur all the time in evolutionary biology.”
“Darwin himself was puzzled about the co-operation you observe in nature. He was particularly struck by social insects,” he explained.
So we really shouldn’t be wondering where morality comes from. Reading comments on various news websites, you invariably get someone — usually religious — who rhetorically asks why don’t we murder or steal if god doesn’t exist; or what basis do we have for morality if no god exists and our morals are entirely secular. This BBC article gives some further evidence that being selfish isn’t a logical or winning strategy. Also, Less Wrong had a Prisoner’s Dilemma game run between programs that people wrote and submitted. The winning strategy there, as in the strategy hard coded by the programmers, was to lean towards cooperation. Note that this is a game between computer programs; the person just presses play and waits for the outcome.
It seems like it’s a rule of the universe that defection is good for a single instance of the PD, but cooperation is more rational over the long run. So if you ever find yourself in an iterated PD with someone, let them know that the winning strategy is cooperation… no god required.