Elon Musk has turned a long-running joke about being an extraterrestrial into a central part of his public persona, even as he argues that humanity may be the only intelligent life in the universe.

Are we alone? No. Should we be? Yes, until we smarten up and act like intelligent beings and stop setting our planet on fire.

Humans have created countless inventions that shape our lives in amazing ways. Some are practical, some are revolutionary, and some are simply fascinating. But if aliens suddenly appeared, which ...