bunch of selfish prisoners having sex and mutating. WHOA.
very basic evolutionary algorithm, a last night's play.

a problem:

Will the two prisoners cooperate to minimize total loss of liberty, or will one of them,
trusting the other to cooperate, betray him so as to go free?

In the iterated prisoner's dilemma the game is played repeatedly.
Thus each player has an opportunity to "punish" the other player for previous non-cooperative play. 
Cooperation may then arise as an equilibrium outcome.

solutions:

I didn't get tit for tat which I originaly expected,
nor did I manage to get a cooperative equilibrium. cooperation does evolve, but it doesn't last,
strange, I expected that cooperative species will raise and stay dominant as I enlarge the number of
interactions before a step in the evolution. (its rational to be nice if you need to stick around)

need to think about this some more.

I'll post more info and code later or never.
screenshot and someone with a different approach and a spacial dimension.