Thinking about Tails
Lots of animals have tails and tails have been used for quite a wide range of functions.
Fish and whales and beavers use their tails for propulsion.
Moneys use tails as a fifth hand and for balance.
Dogs and cats use tails to express emotions.
Lizards and sheep use tails to store fat and decoy predators.
Kangaroos use tails to store energy for the next jump.
Of course the great apes have no tails.
Richard Dawkins in the Ancestors Tale speculates that when monkeys become bipedal because they live on the ground their tails become an nuisance. While for monkeys leaping through trees the tree is a positive benefit as a sensory organ. And so without a selection pressure keeping it the tail in the great apes just faded away.
Dawkins makes the very interesting observation that arboreal monkeys that leap horizontally from branch to branch have tails while those like gibbons and Tarzan that swing through the trees with their bodies vertical have no no tails.
This has happened many times; for instance, Dawkins cites the example of lorises that creep around trees having short tails. So one thing to think about tails is the amazing variety of uses to which they are put by natural selection.
Some of the biggest dinosaurs - the ones with really long necks and tiny heads long tails and legs the size of trees apparently needed two brains. The problem was that the brain in the head could no more drive the hind legs in real-time than we can drive a race car by remote control on Mars The signal speed of nerves is too slow for long distance coordination. So they evolved a second brain, presumably subsurvient to the head, but with a certain amount of autonomy. The hind legs would obey marching orders, but they knew now to march on their own.
Dinosaurs were pretty big and they had a lot of cells to coordinate and it was worth the developmental energy to actually grow a second brain.
But consider most of our own actions - when I want to walk my body knows how to walk. So in a way we are like dinosaurs. Our legs know how to walk on their own. It's just that we don't have enough cells involved so far from the center we don't need the extra layer of a brain to maintain coordination.
But with the tail of a monkey we have a sensory organ. It's not only for grasping - its for FEELING it's balance and orientation in space. By moving it's tail it generates data that has predictable results and if the prediction isn't fulfilled then an automatic feed-back loop can bring the data back into line.
This dynamic system is working in parallel with the balance system in the inner ear. And it seems that this calculation is done IN THE TAIL - the brain just tells the tail it's job and the tail knows how to do it.
We have all felt a similar thing ourselves - but not with out tails; with our arms and hands instead.
Imagine jumping down 5 feet into a pile of sand - there is no danger - it's fun. But what do you do? You extend your arms and wave them around as you fall. Your arms are acting as semi-autonomous sensory organs, and also semi-autonomous control mechanisms. With your arms you feel how your body responds to their movements. With your hands you feel the air pressing your two palms. Your arms are telling your brain what's going on but the brain isn't in control.
We can see this with dogs and cats. They have lively tails much used for expressing emotion. We have all been amused at well fed cats so excited by stalking a bird that it can't control it's tail - startling the bird. And we're all in trouble if it's the dog that makes the tail wag instead of the tail wagging itself. (Hint: we don't need devious dogs. Cats are special:-)
Last week we have seen how the neocortex seems to be a vast network of pattern matchers. The functional structure of them all is much the same - the structure of neurons is much the same for low level modules at high level ones. The amazing capability of the system isn't found in any of the modules. It's found in the amazing weighted neural network structure that all those modules are a part of.
So consider a tail - there it is, far removed from the head, with it's own specialized functions. The head can't be bothered with all the minute details of making a cat's tail twitch. All it has to do is tell the tail that it's in a certain sort of mood, and the tail takes over. Heck - sometimes cat tails do their own thing even without the mood,
How about humans - here we are with hands as wannabe tails. Our hands help us with communication and balance - those might be more of their function for us than being able to grasp and manipulate things.
But our hands are so much a part of how we speak that many people cannot control their hands - they gesture like they have a mind of their own. I know mine do. I bet you couldn't walk across a log over a stream withot extending your arms automatically - without thinking about it. Many of us touch type and we know the feeling of our hands knowing what to do as we write. I don't think at all of the details of how to press a key. My mind is full of words and sentences, not minute muscle moves.
I notice this particularly at work where I run a speciallized keyboard on a cash register. We do a couple of transactions a minute. After a few years my hands now tell me when I've made a mistake. I'll be reading 'Large Pop' and my fingers will say "we're in 'Small Pop' guy".
And so we approach the phenomenologist's idea - the brain isn't a central controller. And we move further - there is no central controller. Instead we have a whole set of modules from tails and hands to eyes and ears to face recognizers and line detectors. These are all informing each other about their own state and what they have discovered. Other modules are based on the narrative generators that we find in the neo-cortex. We go from raw data to stories about what's happening and what we are doing.
What do you think?