Extravagant and costly ornaments (e.g., deer antlers or peacock feathers) are found throughout the animal kingdom. Charles Darwin was the first to suggest that female courtship preferences drive ornament development through sexual selection. I this talk I will describe a minimal mathematical model for ornament evolution which incorporates two key components: an intrinsic cost of ornamentation to an individual, and a social benefit of relatively large ornaments within a population. Using bifurcation analysis and perturbation theory, I will show that an animal population should split into two niches, one with large ornaments and one with small — a phenomenon observed in many species.