1. Darwin, C. The Descent of Man, and Selection in Relation to Sex (Murray, London, 1871).
2. Halliday, T. R. in Behavioural Ecology. An Evolutionary Approach (eds Krebs, J. R. & Davies, N. B.) 180–213 (Blackwell, Oxford, 1978).
3. Halliday, T. R. in Mate Choice (ed. Bateson, P.) 3–32 (Cambridge University Press, 1983).
4. Partridge, L. in Mate Choice (ed. Bateson, P.) 227–255 (Cambridge University Press, 1983).
5. Zahavi, A. J. theor. Biol 53, 205–214 (1975).