Defining sexual selection as sex-dependent selection

Animal Behaviour 77 (2009) 749–751

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Commentaries

Defining sexual selection as sex-dependent selection
Juan Carranza*
Biology & Ethology Research Group, University of Extremadura

a r t i c l e i n f o
Article history: Received 8 August 2008 Initial acceptance 29 September 2008 Final acceptance 2 November 2008 Published online 3 December 2008 MS. number: 08-00516 Keyword: sexual selection

After almost 150 years of research, the very definition of sexual selection remains unclear. The term sexual selection was coined in 1859 by Darwin (1859), who described it in more detail in his later book (Darwin 1871), as an explanation for the evolution of those characters of males of some species that did not seem to contribute to survival in the struggle for existence, those features previously referred to by Hunter (1837) as ‘secondary sexual characters’. From that date, sexual selection has become a sexy topic that has attracted huge interest among behavioural ecologists and evolutionary biologists. However, as Clutton-Brock (2004, page 26) stated, ‘one of the problems in writing about sexual selection today is that the term is used in so many different ways’, and recent debate on the basic structure of sexual selection theory (Roughgarden et al. 2006; Kavanagh 2007; Clutton-Brock 2007) indicates that its definition has probably never been clear enough. Darwin himself was ambiguous in the definition of the term, and was imprecise about what type of elements in the behaviour and life history of individuals should or should not be included in the sexual selection process, and how to differentiate between natural and sexual selection. Darwin initially defined sexual selection on the basis of intrasexual advantages in relation to reproduction. However, in describing the process he always referred to the advantages in relation to access to mating