An Octopus Has Nine Brains

An octopus has nine brains.

One central brain in its head handles vision and learning, plus eight mini-brains, one in each arm, each with 40 million neurons. Two-thirds of its 500 million neurons are in its arms, not its head.

Those arm brains can taste, touch, and act independently. An arm severed from the body will still reach for food and recoil from pain. In life, the central brain gives a loose command like 'explore', and each arm figures out how to do it.

Each arm has 200-300 suckers packed with chemoreceptors that taste what they touch. An octopus literally tastes the world as it crawls. It evolved completely separately from vertebrates - the last common ancestor with humans was a flatworm 600 million years ago. Intelligence, invented twice.