INTRODUCTION

William James, one of the founders of scientific psychology (see James, 1890), tells a personal story in which he awoke from a dream one night with a flash of insight. Wanting not to forget it, he scribbled down, in his half-wakened state, the insight and went back to bed. In the morning he recalled having this revelation but not its content, and excitedly went to read his recording. Disappointed, he found these words: Higamus, hogamus, women are monogamous; Hogamus, higamus, men are polygamous (Kitcher, 1987).

Almost certainly, James would not have been able to anticipate that, 100 years later, the whole question of female monogamy or its absence, polyandry, would become one of the most fascinating topics in behavioural biology.

A recent paper published in Animal Behaviour (Zeh & Zeh, 2001, p. 1051) claimed that behavioural ecology is in the process of undergoing a paradigm shift, with ‘the traditional concept of the choosy, monogamous female increasingly giving way to the realisation that polyandry is pervasive in natural populations’ even when males invest substantially in offspring. One form of polyandry that has received much attention is extra-pair copulation (EPC) – sex that a female with a social mate has with a male who is not the social mate. The data showing a mean extra-pair paternity rate of 10–15 per cent in socially monogamous birds (with some rates as high as 70 per cent) are highly familiar (Birkhead & Møller, 1995; Petrie & Kempenaers, 1998).