[Ninjalicious]

I didn't read the article but the headline makes me postulate that this is because the optimal individual strategy in Prisoner's Dilemma is tit-for-tat.

Respond in kind to every action taken against you. If someone offends, attack, if they offer peace, be peaceful.

Nice people will more often offer the olive branch (sub-optimally), so anyone else playing the optimal strategy will offer it back. Over time this probably results in a lower violence rate. Even mean people (also sub-optimal) will get dragged into niceness over time since nice/mean probably changes dynamically.

[andybak]

A strategy that could beat tit-for-tat consistently was discovered* but tit-for-tat is still fascinating because it is incredibly simple and is almost the optimal strategy.

( * I think it's this: https://sciencehouse.wordpress.com/2012/09/04/a-new-strategy... )

[Ninjalicious]

People get mad when you don't read the article.

[saycheese]

(People get mad when you say you didn't read the article, especially in the first sentence; that is they read that, downvote, and don't read the comment.)

[quadrangle]

I only skimmed the article, but I'm pretty sure that tit-for-tat as a strategy is not the relevant point. The point is that there are people whose strategy is always-cooperate, and enough of those players in a group results in a situation that will stabilize to having a decent amount of real cooperation. Tit-for-tat might have some similar results but probably would need a greater number of tit-for-tat players for stability versus the critical mass of always-cooperate players needed for stability (my speculation).