Spark: The Revolutionary New Science of Exercise and the Brain

by John J. Ratey MD

a tiny jellyfish-like animal called a sea squirt: Born with a simple spinal cord and a three hundred–neuron “brain,” the larva motors around in the shallows until it finds a nice patch of coral on which to put down its roots. It has about twelve hours to do so, or it will die. Once safely attached, however, the sea squirt simply eats its brain. For most of its life, it looks much more like a plant than an animal, and since it’s not moving, it has no use for its brain. Llinás’s interpretation: “That which we call thinking is the evolutionary internalization of movement.”

The truth is, her situation hasn’t changed all that much—just her response to it and thus her attitude.

if you’re not busy living, your body will be busy dying.