Science fiction has imagined everything from little green men to tentacled monsters—but real biology may offer clearer clues.

Claims that aliens are already here are everywhere, but proving them is another matter. The strongest cases become more ...

, Steven Spielberg’s new film about aliens, a question as old as science fiction itself resurfaces: if aliens were to arrive on Earth, would they come to conquer us, to study us… or perhaps to eat? We ...