For most of our evolutionary history as a species, we lived with the constant threat of sudden death. A sudden rustling from a nearby bush. A new, brightly-colored fruit—these could betoken a tasty meal, it’s true, but a ferocious tiger or toxic snack are forever. We’re inclined, therefore, all these millennia later, to overreact to novelty as a potential threat. Even if you’re the adventurous type, the excitement of new experiences is likely mixed with adrenaline-pumping fear. And the truly...