1. Willians, G.G. (1975). Sex and evolution. Princeton: Princeton University Press.
2. Trivers, R.L. (1972). Parental investment and sexual selection. In B.G. Campbell (Ed.), Sexual selection and the descent of man (pp. 136– 179). Chicago: Aldine.
3. Darwin, C. (1871). The descent of man and selection in relation to sex. London: Murray.
4. Fisher, R.A. (1930). The genetical theory of natural selection. Oxford: Clarendon Press.
5. Lorenz, K. (1965). Evolution and modification of behavior. Chicago: University of Chicago Press.