1) play tournament

2) eliminate bottom 5

3) reproduce top 5

Let's say there are three kinds of players:
Always Cooperate, Always Cheat & Tit For Tat

"What happens when you let a mixed population play against each other, and evolve over time?

Always Cheat dominates at first, but when it runs out of suckers to exploit, its empire collapses – and the fairer Tit For Tat takes over.

We are not punished for our sins, but by them.
- Elbert Hubbard