Human evolution is a story writ slow. It’s been about 3.8 billion years since life on Earth emerged and steadily began to spread its reach from the tidal pools to the oceans to the shorelines to the grasslands to the forests—and, ultimately to New York and Tokyo and Shanghai and more. Having exhausted our terrestrial destination, humanity is now reaching for extraterrestrial ones. Our dream of going back to the moon and onto Mars and more distant worlds—not least to ensure our species’ survival