Brain power

The human brain: a miracle of evolution

Once the human body has stopped preparing for surviving the perils of living, it settles down to the everyday business of acquiring knowledge.

"The brain is the miracle of evolution. It is the most complex thing in the universe," says Professor Robert Winston, presenter of 'Brain power', the fifth programme in the BBC's flagship series, The Human Body.

From our ape-like beginnings and a Fiat 500-sized brain, humans have become sophisticated beings with brains on a par with a sports car engine.

The human brain is now three times as big as it was two and a half million years ago - very rapid progress in evolutionary terms. With each generation, the brain has added 150,000 nerve cells.

Growth spurt

The reason for this growth spurt dates back to when humans decided to stand up and walk. This freed up their hands, which developed from being rough instruments used to grasp implements and walk to being finely tuned tools which could perform a wide variety of tasks.

Electric impulses pass from neuron to neuron

One fifth of the body's energy is used by the brain - an unattractive organ which, according to Robert Winston, is "wrinkled like a walnut with the consistency of a mushroom".

Aristotle, the first person to think about the functioning of the brain, believed that it regulated body temperature while the heart controlled the emotions.

Neurons

Now, with sophisticated machinery, we can actually see inside the brain and observe how it functions, how different parts of the brain deal with memory, consciousness and the senses and how the electrical impulses are passed from one neuron to another at a speed of 400 kilometres an hour.

The brain contains 100 billion neurons, enough to illuminate a light bulb if all their power were harnessed together. Between each neuron is a tiny gap which is bridged by chemical go-betweens which transmit our thoughts.

Humans can alter the balance of their brains by submitting them to chemical changes, for example, by drinking a few pints. Alcohol slows the chemical reactions in our brains.

Termites

Robert Winston compares the brain to a mound of termites. None of them has an overall knowledge of what they are doing, but together, almost by chemical signals, they work to create complex structures.

People can learn new skills easily

The success of the brain depends on all its many units working in harmony. The brain has to adapt to new tasks. Like a child, an astronaut has to learn to move and function in an alien gravity-less world.

But once learnt, the body automatically remembers these skills. The cerebellum is the part of the brain that controls these learned movements. In most animals the cerebellum is the largest part of the brain. But in humans, it is at the base of the brain, dwarfed by the part that controls conscious thought.

Consciousness

One quarter of the brain is devoted to vision and the optic nerve penetrates from the eye to the back of the brain. It works in coordination with other parts of the brain which control our other senses, balance, movement and understanding.

Vision takes up one quarter of the brain

The average person stores one million items in their brain. No-one really understands how this is done, but there are theories that neurons containing repeated movements, feelings and thoughts link up in the brain.

Some people seem to have better memories than others and can remember huge lists of numbers and facts. But scientists believe they are not particularly special. They have just trained their brains to work in this way.

The conscious part of the brain also controls our ability to socialise and gives us our own individual personalities. It allows us to appreciate the arts, science, ideas and is what makes us human.

It makes us question the nature of all things - both physical and spiritual - and realise that there are some things that are still beyond the scope of the human brain, despite its complexity.

The Human Body series is accompanied by a £19.99 book and a CD Rom, priced £29.99.