This sea squirt is probably the least remarkable creature that you will never meet. It hangs around rocky shores, reefs and piers. It is altogether uninteresting except for one amazing fact.
After being born with a brain, shortly thereafter it eats it. It eats it because it is hungry and thereby forgoes its free swimming phase, and attaches itself to a rock where it scoops up the unsuspecting meal of plankton. The sea squirt therefore serves as a perfect example of the importance of the brain to movement, When it no longer moves, it has no need for its brain.
This relationship has long been of interest to me. Thirty years ago when I was working with Richard Leakey in Nairobi I wrote a paper in the Journal of Human Evolution, entitled "Physical Exercise as an Evolutionary Force." (1) In it, I proposed that the reason the human brain has grown from its original size of 500 milliliters, like a chimpanzee, to our current size of 1,200 milliliters is that through the millennia we were very physically active. Importantly the Neanderthals actually had bigger brains than did our forefathers reflecting their vigorous lifestyles. Wild animals also have bigger brains than their domestic cousins.
I suggested that our Paleolithic forebears adopted the feeding strategy of persistence hunting which compelled them to exercise mightily in the midday sun. They simply ran down their prey by keeping them moving. They lost their hair and started to sweat, and grew their brains. My suggestion was subsequently updated by Dan Lieberman at Harvard in Nature a couple of years ago. (2)
The exercise/ brain size connection was extended by the discovery that a chemical called brain derived nerve factor, BDNF, was stimulated by exercise (Carl Cotman at UC Irvine (3)). The brain acts like a rheostat where it is the major dispatch center that integrates the elevated energetic requirements displayed with exercise.
Our knowledge of this brain/ exercise relationship expands rapidly, and is now having real clinical application. The two neuro-degenerative diseases of today, Alzheimer's Disease and Parkinson's Disease, both are retarded by an exercise protocol.
No current drug can equal their benefit, cheaper and safer and universally available. Drug companies eat your brains out.
References:
1) Bortz, W. Physical Exercise as an Evolutionary Force. J. Human Evolution 1985: 14:145-155.
2) Bramble D, Lieberman D, Endurance Running and the Evolution of Homo 2004; 431:345-352.
3) Neeper,S, Gomez-Pinilla F, Choi J, Cotman, C. Exercise and Brain Neurotrophins Nature 1995; 313:109.