1. Aarne, A., & Thompson, S. (1961). The types of the folktale: A classification and bibliography. Helsinki: The Finnish Academy of Science and Letters.
2. Boesch, C., Bolé, C., Eckhardt, N., & Boesch, H. (2010). Altruism in forest chimpanzees: The case of adoption. PLOS ONE, 5(1), e8901.
3. Choi, J. K., & Bowles, S. (2007). The coevolution of parochial altruism and war. Science, 318, 636–640.
4. Dundes, A. (1997). The motif-index and the tale type index: A critique. Journal of Folklore Research, 34(3), 195–202.
5. Mauss, M. (1966). The gift: Forms and functions of exchange in archaic societies. London: Cohen and West.