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Sexual selection: Horny ladies

If females must compete, evolution will furnish them with weapons to do soWHEN a species evolves traits that seem to have little to do with individual survival—bright colours, say, or oversize horns, it is typically the male alone who sports these excesses. Observing this, Charles Darwin proposed the idea of “selection in relation to sex” as a follow-up to his theory of natural selection. He defined it as the struggle between members of one sex, “generally male”, to possess the other. The plumage of peacocks attracts peahens. The stag’s antlers are there to fight off other stags. And so on.But females, it turns out, have some tricks of their own. Nicola Watson and Leigh Simmons of the University of Western Australia have published a paper this week in the Proceedings of the Royal Society about Onthophagus sagittarius, a species of dung beetle in which not only do both sexes sport horns, but those of the females are larger than those of the males. They set out to discover wh

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