A peacock's plumage is rather arbitrary and weird, as well. But for whatever reason, vibrant plumage worked to attract the attention of peahens, so it was selec

A peacock's plumage is rather arbitrary and weird, as well. But for whatever reason, vibrant plumage worked to attract the attention of peahens, so it was selected for. I've heard it argued that the existence of decorative traits indicates fitness because it shows that an organism has a enough extra energy to devote to decoration. But that's speculative. Sexual selection isn't really a logical proces. It's just an accumulating response to stimuli, over time.