How stupid not to have thought of that: post-copulatory sexual selection


  • Editor: Steven Le Comber

Tim R. Birkhead, Department of Animal & Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.


Science progresses through ideas or hypotheses; novel ways of viewing the world. If those ideas survive testing, then they are considered ‘the truth’, or more crucially, truth-for-now, for the essence of science is that if a new idea provides a better explanation of the way the world is, the truth changes. Darwin's idea of evolution by natural selection, published as the Origin in 1859, replaced the earlier truth of physico- or natural-theology introduced by John Ray in 1691. Despite resistance by the church, Darwin's truth gained widespread acceptance, in part due to the efforts of T. H. Huxley, who on reading the Origin said ‘How extremely stupid not to have thought of that!’ Despite natural selection's enormous explanatory power, there were certain phenomena it apparently could not explain, including female promiscuity. It was only in the 1960s when natural selection was viewed as operating explicitly on individuals (rather than populations or groups), that this changed. Rather than being a cooperative venture between the sexes, sexual reproduction was now viewed in terms of conflicts of interests, and in so doing provided an explanation for female promiscuity (albeit in a male-biased sort of way). Until this point, sexual selection had been concerned exclusively with mate acquisition. With an evolutionary perspective focussing on individuals, it was recognized that sexual selection might continue after insemination, and that rather than competing for partners, males compete for fertilizations. Later it was acknowledged that females, through cryptic processes can also influence the outcome of sperm competition. Today, post-copulatory sexual selection provides explanations for many previously bewildering reproductive traits, including the extraordinary diversity in male and female genitalia, the design of spermatozoa and ova, of seminal fluid and of copulation behaviour itself