All TFT did was cooperate on the first Prisoner’s Dilemma round, then in every subsequent round, it did whatever the opponent did previously—that is, if on the previous round the opponent cooperated, it cooperated on the next round; if the opponent betrayed, it betrayed on the next round. This simple program decimated the competition. So Axelrod ran the tournament again. He reached out to even more experts and this time had sixty-two entries. Some algorithms were more complex and some were variants on TFT. Who won? Simple ol’ tit for tat. Again.
