1. Arrow, Kenneth J. 1975. ‘Gifts and Exchanges’. In Altruism, Morality, and Economic Theory, ed. Edmund S. Phelps, 13–28. New York: Russell Sage Foundation.
2. Axelrod, Robert. 1981. ‘The Emergence of Cooperation among Egoists’. American Political Science Review 75 (2): 306–18.
3. Backhouse, Roger. 2004. The Penguin History of Economics. London: Penguin Books.
4. Becker, Gary S. 1974. ‘A Theory of Socal Interactions’. Journal of Political Economy 82 (6): 1063–93.
5. Bolnick, Bruce R. 1975. ‘Toward a Behavioral Theory of Philanthropic Activity’. In Altruism, Morality, and Economic Theory, ed. Edmund S. Phelps, 197–223. New York: Russell Sage Foundation.