One way I might do that is, occasionally throw in a 'cooperate' independent of whatever other strategy I've got. Doing that will tend to convert tit-for-tatter

One way I might do that is, occasionally throw in a 'cooperate' independent of whatever other strategy I've got. Doing that will tend to convert tit-for-tatters and might flip other strategies into cooperating. If you grade by the total number of cooperate moves in the group, the group wins by 'kindness' flipping a variety of strategies into cooperate mode. It'll tend to expand pockets of cooperation. No immediate personal benefit, but tends to make the environment better which may seem like a benefit. I don't think 'survival of the fittest' has to mean 'kneecap all your opponents and rent-seek', but that's the popular interpretation in Western capitalism :)