Escaping the IPD

In order to avoid exploitation by travelling defectors, one can imagine several countermoves: while xenophobia or initiation rites may increase travel costs tau, a cooperating individual may also try the other way round: decrease each investment in cooperation and compensate by increasing the number of interactions, until the net gain of defection will drop below tau. As a result, average coalition time THETA would be prolonged and the system may come to lie above the line, depicted in Fig. 2.
In Axelrod's original definition, this would correspond to R>T, which means that selfishness and altruism become equivalent. Such a strategy would have put itself outside the IPD, manipulating the payoff matrix. If that rule also altered S>P, defection would never pay and ALLC would be the sole ESS (Mesterton-Gibbons 1991). The resulting cooperative system would certainly be classified as by-product mutualism, according to the definition by Dugatkin et al. (1992).