Not spineless

THE battle of the sexes is, presumably, as old as sex itself. But evidence for its past engagements is sparse, as behaviour does not fossilise. But the battle that takes place within a sex for access to mates often results in physical evidence—deer antlers, for example, or peacocks' tails. In a paper just published in Biology Letters, Robert Knell of Queen Mary College, London, and Richard Fortey, of that city's Natural History Museum, suggest that this is the explanation for one of palaeontology's more extravagant features, trilobite spines.