The beauty of the peacock troubled Darwin for a long time. It didn't quite fit into his theory of evolution and the idea of "survival of the fittest." Darwin came to the conviction that animals must also possess a sense of beauty. Especially the females, who select the "beautiful" males. Modern-day ornithologist Richard O. Prum is convinced that "the complexity of aesthetic and sexual pleasure" in the animal kingdom is far more developed than we give it credit for.