1. Jeffrey Weeks, Against nature: Essays on history, sexuality and identity (London: 1991), pp. 68–69.
2. Steven Pinker, How the mind works (London and New York: 1997), pp. 307–8.
3. Pierre L. van den Berghe, Human family systems: An evolutionary view (Westport CT: 1979), p. 68
4. see also Christopher Badcock, Evolution and individual behviour (Oxford: 1991), pp. 125–28
5. R.A. Hinde, “A biologist looks at anthropology,” Man, N.S. vol. 26 (1991): 583–608