1. Charles Darwin, The Descent of Man, second edition (New York: Penguin, [1871] 2004), 120.
2. For general analyses of such rules, see Cristina Bicchieri, The Grammar of Society: The Nature and Dynamics of Norms (Cambridge: Cambridge University Press, 2006);
3. Gerald Gaus, The Order of Public Reason (Cambridge: Cambridge University Press, 2011), Ch. 3 and 4.
4. Anthony O’Hear, Beyond Evolution: Human Nature and the Limits of Evolutionary Explanation (Oxford: Oxford University Press, 1997), 101.
5. Ken Binmore, Natural Justice (Oxford: Oxford University Press, 2005), 1.