. Partnership. J. Theoret. Biol. 208.457-474. Eshel. I.. Weinshall. D.. 1988. Cooperation in a repeated game with random payment function. J. Appl. Probab. 25.478-491. Ewer's. W.J.. 2004. Mathematical Population Genetics. Volume I: Theoretical Foun- dations. Springer-Verlag. Berlin. Fisher. RA. 1930.