Joan Roughgarden lists a number of phenomena that she feels sexual selection theory is ill-suited to explain (Features, June 4). There is not space to deal with all of her list, so I shall focus on homosexuality as an example.

Roughgarden says sexual selection theory cannot explain homosexuality without stating what aspect of homosexuality she would like explained by the theory. This is tantamount to claiming that it cannot explain the cycles of the moon or football's offside rule.

It might be that she wishes to know why a sexual orientation that does not lead to reproduction exists. Some social scientists have sought to use the existence of homosexuality to support the idea that sexualities are socially constructed and that social behaviours can trump genetic endowments. Others look for a role for natural selection, not sexual selection.

Evolutionary theorists are beginning to understand certain forms of homosexuality (and sexuality more generally) as a polygenic trait. It is entirely possible for heterosexual males, for example, to carry "gay genes". It is only when an individual possesses so many gay genes, and passes a threshold, that he will express homosexuality.

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Those gay genes may well confer advantages for straight men who have them.

They might, for example, make males better at forming long-term relationships. Sexual selection theory might not have much to say about homosexuality because it might be that the behaviours seen in mate choice, the predilection for more partners and so on, are a consequence of an evolved psychology that straight and gay men share. What might need explaining is the choice of targets.

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All of this theorising could be wrong, it is after all work in progress, but it posits an intriguing set of excellent challenges for science, and none of it undermines Darwinism.

Tom Dickins
University of East London