kenbach, B., & Milinski, M. (2006). The efficient interaction of indirect reciprocity and costly punishment. Nature, 444(7120), 718-723; Sigmund, K., Hauert, C., & Nowak, M. (2001). Reward and punishment. Proceedings of the National Academy of Sciences, 989), 10757- 10762; Trivers, R.L. (1971). The evolut