The alien brains living on Earth.
(US Army/Flickr/CC BY 2.0) To look for aliens, most people peer towards the sky. But if you look down, you'll discover they already live among us. It has only been within the last three decades that technology has let people see octopuses' natural behaviour. These aliens have brains, like we do, but they're mostly inside their arms, and each arm acts as if it has a mind of its own. I'm speaking, of course, of the octopus. This tentacled beast – along with its cephalopod relatives, the squid and cuttlefish – are some of the strangest, most alien creatures on our planet. Scientists have a hard enough time getting into the minds of our nearest relatives, the apes and monkeys, let alone more distantly related mammals like dolphins or elephants. Octopuses? Forget about it. Our last common ancestor with the octopus was probably around 800 million years ago.