  Species spanning the animal kingdom have evolved extravagant and costly
ornaments to attract mating partners. Zahavi's handicap principle offers an
elegant explanation for this: ornaments signal individual quality, and must be
costly to ensure honest signalling, making mate selection more efficient. Here
we incorporate the assumptions of the handicap principle into a mathematical
model and show that they are sufficient to explain the heretofore puzzling
observation of bimodally distributed ornament sizes in a variety of species.
