1. Darwin, C. The Descent of Man, and Selection in Relation to Sex (John Murray, London, 1871).
2. Bateman, A. J. Heredity 2, 349–368 (1948).
3. Trivers, R. L. in Sexual Selection and the Descent of Man (ed. Campbell, B.) 136–177 (Aldine, Chicago, 1972).
4. Hrdy, S. B. The Woman that Never Evolved (Harvard Univ. Press, Cambridge, Massachusetts, 1981).
5. Symons, D. Q. Rev. Biol. 57, 297–298 (1982).