Résumé
In numerous species, such as the peacock and the red deer, males differ morphologically and behaviourally from females. They are often bigger, more brightly coloured, and have more complex songs. Charles Darwin was the first to address the paradox of sexual dimorphism: why do males acquire traits that render them more detectable and appear to reduce their survival? These observations seemed to contradict his theory of evolution by natural selection (Darwin 1859). To address this contradiction he invented the concept of sexual selection, defined as ‘the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction’ (Darwin 1871, ch. VIII). Briefly, the extravagant traits of males would increase their reproductive success, thus compensating for their reduced survival. Research in this field has increased considerably in recent decades.