From Darwin’s statement (above) about the superiority of natural selection over the argument from design, we might imagine that Ray’s questions about reproduction would have been answered soon after the publication the Origin in 1859. Not so. Natural selection was, and still is, a better conceptual framework for

thinking about the natural world, and provided a compelling and straightforward explanation for the existence of parasites and parasitoids. Sex, however, continued to be a mystery, and because Darwin largely avoided questions about the Crenolanib supplier number of sperm and copulation behaviour, it was almost a century before anyone tackled these questions and offered a convincing answer. Retrospectively, biologists such

as Smith (1984, 1998) attributed Darwin’s lack of interest in promiscuity to a statement in Descent: ‘It is shown by various facts, given hereafter, and by the results fairly attributable to sexual selection, that the female, though comparatively passive, generally exerts some choice and accepts one male in preference to the others’ (Darwin, 1871). The emphasis here being on one male, a clear indication that Darwin assumed females at least to be sexually monogamous. I have suggested that Darwin made this assumption as a way of avoiding embarrassment, both with the public and within his learn more family, especially his wife Emma and daughter Etty (Henrietta), the latter who helped him correct the proofs of Descent (Birkhead, 1997). Darwin’s desire to avoid offending his family, undoubtedly Chloroambucil reinforced by Victorian prudery, inhibited his writing on sexual matters. When he felt it necessary to discuss the sexual swellings of female primates, for example in Descent he wrote the passage in Latin knowing that Etty would be unable to read it. Darwin was well aware of female promiscuity, from the literature, from his correspondents and from personal observation (Barrett et al., 1987; Smellie, 1790). With reference to the pigeons he kept and bred, Darwin (1868) wrote: ‘even when a male does break his marriage-vow, he does not permanently desert his

mate’. Notice here that the emphasis is the male rather than the female breaking the marriage vow. Most pigeon breeders, however, including Girton (1765), whose book Darwin owned, recognized the existence of extra-pair copulations, pointing to the fact that selective breeding could easily be disrupted by a ‘false tread’ (an extra-pair copulation). Even more significantly, Darwin was aware of the extensive literature on so-called ‘thief pigeons’ in which particularly attractive males could cause paired females to abandon their partner in favour of themselves – even during the incubation period (Darwin, 1871; Birkhead, 2008). Darwin also knew that whatever it was that made these males irresistible to females was inherited, for pigeon breeders could select for it.