A young sea squirt swims. It looks a little like a tadpole, with a tail, a simple eye and a brain of a couple of hundred neurons, and it has a short time to find a good rock. Once it glues itself down it absorbs the tail and takes most of that brain apart. The neuroscientist Rodolfo Llinás used it to argue that brains are for moving: an animal with nowhere left to go has no more decisions to make, so it stops paying for the equipment. Academics have long told this as a joke about tenure. Asked about it in an interview, Llinás allowed only, “To some professors.” I like that he left the door open for the others.