The Evolution of the Human Spirit (excerpt) The remarkable aspect of evolution by sexual selection, which Darwin so courageously proposed, is that it is driven merely by the desire for a trait, in this case the desire for justice. I had realized that sexual selection is not only driven by the peahen's desire for the peacock's tail, but also by the peacock's desire to be desired for his tail (i.e., vanity). So what gave sexual selection the creative power to launch and then sustain our hominin tr...