You are thinking of tit for tat, right? I remember reading about generous T4T where in ~10% of the cases they were generous [CITATION NEEDED] it performed better that pure retaliation. Now there is a new paper in Nature[1] that I just stumbled onto in trying to answer your question. It seems like extortion is at least competitive with a generous strategy, though I need to give it a closer read.<p>[1] <a href="http:&#x2F;&#x2F;www.nature.com&#x2F;ncomms&#x2F;2016&#x2F;160412&#x2F;ncomms11125&#x2F;full&#x2F;ncomms11125.html" rel="nofollow">http:&#x2F;&#x2F;www.nature.com&#x2F;ncomms&#x2F;2016&#x2F;160412&#x2F;ncomms11125&#x2F;full&#x2F;nc...</a>