Exaggerated ornaments such as beetle horns, deer antlers, and extreme tail lengths in birds are typically assumed to be subject to sexual selection because they signal the quality of an individual's breeding status—but how? Emlen et al. present a general mechanistic model for the evolution of exaggerated traits, proposing that sensitivity to the insulin response pathway can explain variation among individuals. The exaggerated size of such ornaments and their increased variability between individuals are a result of sexual selection for traits that are honest signals of the fitness of the individual.
D. J. Emlen, I. A. Warren, A. Johns, I. Dworkin, L. Corley Lavine, A mechanism of extreme growth and reliable signaling in sexually selected ornaments and weapons. Science 337, 860–864 (2012). [Abstract] [Full Text]