Define strategy S[n] as TfT until turn n and defect ever since. In the limit of infinite population having non-zero initial number of S[n] for each n, S[0], i.e. DefectBot, eventually dominates. Starting with equal subpopulations, initially most successful is S[99] which preys on S[100] and finally drives it to extinction. But then, S[98] gains advantage over S[99] and so on.
With not so big population however, the more defectorish strategies die out sooner than the environment becomes suitable for them. (I have done it with population of 2000 strategies and the lowest surviving after several hundred generations was S[80] or so).
Try another strategy. I[n] - TfT until turn n, defect on turn n, on later turns check if result on turn n was (defect,defect) and play TfT, otherwise defect. Idea is selfcooperation.
Define strategy S[n] as TfT until turn n and defect ever since. In the limit of infinite population having non-zero initial number of S[n] for each n, S[0], i.e. DefectBot, eventually dominates. Starting with equal subpopulations, initially most successful is S[99] which preys on S[100] and finally drives it to extinction. But then, S[98] gains advantage over S[99] and so on.
With not so big population however, the more defectorish strategies die out sooner than the environment becomes suitable for them. (I have done it with population of 2000 strategies and the lowest surviving after several hundred generations was S[80] or so).
Try another strategy. I[n] - TfT until turn n, defect on turn n, on later turns check if result on turn n was (defect,defect) and play TfT, otherwise defect. Idea is selfcooperation.
Except that in the initial state S[0] will get driven to extinction long before s[100] will.
With reasonably sized population, yes. In the limit of infinite population, or with sufficiently large population, no.