Humans used to be unique in lots of ways. We were the only species who made tools, murdered each other, passed on culture. And each of those supposed defining features has now been demonstrated in other species. We’re not so special after all. But there are still ways that humans appear to stand alone. One of those is hugely important: the human capacity to think symbolically. Metaphors, similes, parables, figures of speech—they exert enormous power over us. We kill for symbols, die for them. Yet symbols generate one of the most magnificent human inventions: art.