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It's difficult to get across how rapidly the human brain enlarged. From our ape-like ancestors to the bigger-brained humans was two and a half million years. That may seem a long time, but in evolutionary terms, it's remarkably quick. The human brain was increasing by the equivalent of 150,000 nerve cells at each generation. But in nature, there's no such thing as a free lunch. Everything has its cost, and a bigger brain, like a bigger engine, is more expensive to run. The human brain power uses up more energy to run than any other organ in the body, burning a whopping one fifth of the food that we consume. This makes the head hotter than the rest of the body, shown here by a heat-sensitive camera. We invest so much in the brain because of its importance. It's what makes each one of us who we are. It's amazing to consider that I'm holding in my hands the place where someone once felt, thought and loved. From just looking at it, there's nothing to suggest very much ability at all. It appears rather gruesome - wrinkled like a walnut and with the consistency of mushroom. For centuries, scientists have been battling to understand what this unappealing object is all about. The philosopher Aristotle, of ancient Greece, believed that the brain helped regulate the body's temperature. A runny nose was the cooling fluid leaking out of the brain. He reasoned that since the heart beat faster when you were excited, it must be responsible for our feelings and thoughts. It's easy to laugh at him now, but Aristotle was the first person to think seriously about how the human body worked. We've come a long way since the fourth century BC. Now we can actually see inside a living brain. Medical scanners prove the brain is indeed where we think and feel. When a particular area of my brain is working hard, extra blood flows there, through my arteries, to provide energy for the active nerve cells. The scanner can detect these changes in blood flow, giving us a completely new window into the fascinating world of the mind. Using this technique, we can actually watch the brain at work. Here I'm listening to music. Not one, but several areas light up. This part of the brain is where we process all sounds, and this is where we appreciate music. Amazingly, there are even separate bits for melody... for rhythm... and for pitch. But what's actually happening deep inside the brain? It's a fascinating story, but it's complicated. It all starts with this tree-like structure: a single brain cell or neuron. Here is an actual neuron, magnified 10,000 times. Neurons are the tiny building blocks of the brain. They do something remarkable, which prompts all our thoughts. They fire an electrical impulse. Amazingly, we can now see one firing. This is the first time it's been shown on television. The electricity is bursting along the neuron at 400 kilometres an hour. Here we're seeing it in slow motion. Within a tiny fraction of a second, it's ready to fire again. Your brain has a staggering 100 billion of these neurons. Together they could generate enough electricity to illuminate a light bulb. To make things more complicated still, the branches of each neuron are connected to thousands of other neurons. It's hard to grasp the sheer scale of all these connections. Go deeper into this tangle, travel along a single neuron and take a close look at the junction with its neighbor. Oddly, the neurons are not physically joined together at all. There's a tiny gap. To bridge this gap, the neurons release minute quantities of chemicals every time they fire, chemical go-betweens that influence our thoughts. This cocktail of chemicals swirling about the brain is finely balanced. It needs to be to control the activity of the brain. Because it's so much on a knife-edge, it's very easy to disrupt. People do it every day. I like to do it, just occasionally, with some Cabernet Sauvignon. People have been drinking alcohol for thousands of years. But surprisingly, it's only in the last couple of years that scientists have discovered precisely how it works. So, in the interests of science, I've put myself forward as a guinea pig. Before I start, I need to test my reaction time. Some people compare the brain to a computer, but I think it's much more like a termite mound. It's all to do with the whole thing being greater than the sum of its parts. The intricate behavior of the termite colony emerges from the collective effort of all the termites. Here, a group of worker termites are constructing a new wall. Not a single one of them carries a blueprint for the wall, but working together, it gets built. Termites send out chemical signals, and between them they pile up their tiny mouthfuls of mud. Clearly the human brain is totally different from the termite mound. Both, though, are composed of numerous building blocks; either neurons or termites. Each, when acting in harmony, is capable of extraordinary feats. It makes no sense to search for the root of knowledge in single neurons in the brain, or, for that matter, in one termite in a colony. The success of both depends on many millions of simple units working together. So it's teams of neurons acting in unison that give us all our skills. Each team, based in a particular region of the brain, takes on a different responsibility, from our most advanced human abilities, such as language and memory, to the more basic ones, like movement. Because we walk, run and reach without thinking, we forget how such incredible precision is possible. To see how much brain effort is required, look what happens when we're plunged into a totally new environment. OK, there we go. Astronauts have to learn to move from scratch when they enter a world without gravity. The reason why we're able to learn new tasks and carry them out automatically lies here. It's a part of the brain called the cerebellum, or little brain, because it sticks out right at the base of the brain proper. Here are stored the practiced movements we all learn, be it riding a bike, playing the piano, or even fixing a satellite. The astronauts are in the cargo bay of the shuttle, but they're not out in space. This is the closest they can get to space back on Earth, an enormous swimming pool - a pool so large that four space shuttles can fit inside it. Here astronauts can practice their tasks over and over again, until they can move automatically without thinking. I had to jig it a little to lock. Yeah, it is finicky about being directly perpendicular to the rail, so try to wriggle it back and forth, from starboard to port, and from forward to aft. OK. We're assuming the latches didn't work. So they're manually. A thought starts it off, and then the cerebellum does the work, sending out instructions to the rest of the body. This happens without us even being aware of it. In fact, the unconscious part of the brain is often more skilful than the conscious part. On the space shuttle is a robot arm. The astronauts have to train hard to operate it, using a joystick. But the secret with moving a robot arm smoothly is not to think too much about it. Let the cerebellum take over. For me it was difficult to think about moving each joint as I moved it. And I just did it, and it got there. The more experienced you get, the more rotations you can make at the same time. That's probably true of learning to use your hand. When you reach for something, you make complex motions with your arm, and that's probably as learned a response as it is learning to control the robot arm. The astronauts use the same mental equipment to control the robot arm as we first use as babies to control or flesh and blood arms. People have a fantastic ability to make almost any tool an extension of their bodies. As an infertility doctor, I make full use of my cerebellum to perform keyhole surgery. Here, I'm investigating why a woman is unable to conceive. Surgical tools allow me to examine inside her, without resorting to major surgery. After enough training, it is relatively simple for me to co-ordinate what I do with my hands with what I see on the screen. Truth is that this surgical manipulation, like all surgical manipulation, looks incredibly skilled and very intricate. But actually, most of the time you're doing it totally on autopilot and you can do quite involved procedures without really thinking about it. It's only when there's something untoward, or the surgeon hits an emergency, that you suddenly need to concentrate much harder and the conscious brain takes over. Most mammals have a cerebellum just as developed as ours. A rat's primitive brain is largely cerebellum. They don't need much more for their relatively simple lives. And in humans, the basic design of this rudimentary part of the brain has changed little as we've evolved. It is the rest of our brain that has enlarged so massively. Why did it get so big? Well, surprisingly, a whole quarter of our oversized brain is devoted to vision, much more than for any of our other senses. What you see when you peer into the back of the eye is the only part of the brain which is visible from the outside world. The optic nerve at the back of the eye is a direct extension of the brain. Travelling along the optic nerve, we pass right through the brain. Here, at the back of the head, is where the visual information arrives. Our eyes are just a window. We actually see with our brain. It's difficult to grasp how complicated vision is, until you try to programme a computer to see. It's staggeringly difficult. What the scientists hadn't realized was that the eye is merely the first step. The brain does most of the real work. These robots have excellent cameras on board, but they lack the clout of the brain to make sense of what they see. This can be a handicap. Our brains are so powerful that we very much take our visual skills for granted. To fly this 1940s biplane, Marsha Ivens relies more on the view from the cockpit than the instrument panel. In an airplane like this, vision is your primary means of knowing where you are, relative to the world, in the airplane. My brand of flying doesn't really require? Whole lot of dials. I can tell what my rate of descent is. You learn with experience. I make periodic checks of the altimeter and the airspeed and the vertical speed indicator for that information, but mostly I do that by looking outside. Whenever we look around us, we see the world instantly. The shape of a plane, its movement, its colour. But what's surprising is that all these aspects of the image have to be processed by the brain separately. We know these various elements of vision are distinct, because certain people with brain damage are missing one of them. As the brain power of our ancestors increased, they not only observed the world but also invented ways of shaping it. We can see this in action by looking at the tools that chimps make. The chimps from this group use an impressive 19 types of tool. Most of them are to get at food. Thin sticks help them catch ants and termites. Chimps even use stone anvils and wooden hammers to crush the shells of nuts. It's jolly difficult making a stone tool. So, here's one that was prepared earlier. About two million years earlier. The creature that made it chipped away slivers of stone to give it a sharp edge, and it was probably used as a kind of axe. Archaeologists here in the Great Rift Valley of Africa are really excited about this and the other tools they've found, because it wasn't apes that made them, it was people. Louise, what's so interesting about this area? This entire site is special because there're such vast concentrations of stone tools here, and this is because it was a lake basin. The early humans were coming down to catch their animals, kill them and use the stone tools on the carcasses. I found it quite difficult making a stone tool. What's the trick? You need a big brain, and to be quite well practiced to manipulate your hands to strike a flake off a piece of rock and come up with a result like this. I'll forgive the slur on my brain, but how do you know that these were used to butcher meat? That seems a bit far-fetched. We've found stone tools with a carcass, say of an early elephant, where you've got stone tools and bones which show cut marks, so you're pretty sure those stone tools were used to butcher that animal. A chimp cannot make a stone hand axe. It's not just the lack of brains. A chimp's thumb is very short compared to its other fingers, making it awkward to use all but the simplest tools. But over hundreds of thousands of years, our human thumb lengthened. This gave us an enormous advantage. We could make a precise finger pinch between thumb and forefinger. It's called ''the opposable thumb,'' and it allowed us to manipulate objects with great dexterity. Marsha harnesses this precision control of her fingers to do safety checks on her plane. I pluck the wires on the tail and should hear them ring the same tone. And the pilot. As I walk around the airplane, sometimes your hand will feel something your eye doesn't see. If I run my fingers along the propeller, I can feel a nick that I wouldn't necessarily see. I don't want nicks, as that disrupts the airflow. The sensitivity of our fingers comes from the ridges and grooves of our fingerprints. These ridges also give us better grip, especially in wet conditions, just like the tread of a car tyre, cornering in the rain. But what have fingers got to do with the brain? Well, throughout our evolution, developments of the brain and the body were constantly bouncing off one another. As one advanced, it drove the other forward. This feedback relied on a key turning point, one that other animals failed to make. Chimp hands aren't very dexterous, because they do two contradictory jobs with them. They hold things, but they also walk on their hands. So their hands are a compromise. Not bad for knuckle walking, but not so good for creating tools. Human hands excelled at creating tools and manipulating objects because they were largely dedicated to just one activity. Unlike chimps, we did this. We stood up on our hind limbs. This crucial advance happened over 3.5 million years ago. Standing up gave our hands enormous freedom and boosted our brain power dramatically. We never looked back. Standing tall on two legs happened very early on in the development of the human body, before we had opposable thumbs, before we had stone tools, before we had language. Indeed, standing helped these developments.
Brain Power annotations
Early humans literally had time on their hands - time to challenge their tiny Fiat 500 brain, jump-starting it into further evolution. As our brain got bigger, so it perfected one rather special trick. It learned to make order out of chaos, putting things into categories. Coffee with caffeine and coffee without? Kenyan or Colombian? It's no accident that this is how we organize our daily life. I'll take a couple of those. Thank you. We came to classify things this way so that we could cope with the complexity of nature. To survive, we had to learn which plants were poisonous and which we could eat; to know which animals would make a good meal and which were likely to make a meal of us.
Brain Power remarks
Animals do this to some extent, but the human brain excelled at it. We still use this skill in city life, but in the natural world, you can witness it the way it was originally deployed. Philip Alderson is a park ranger in north Australia. Forest fires sweep the park in the dry season, and Philip lights small control fires to burn up dry tinder and stop the spread of a bigger fire that's approaching. It's called ''back burning,'' and has been used by Aboriginal people for thousands of years. You can see the big cloud of smoke over there, and it's roaring through. When the main fire front comes along, it gets really windy, with little whirly winds everywhere. The back burning stops it from coming any further with the wind. It would carry it across the other side of the road, all that debris and sparks.
Brain Power quotes
The ability to understand and control the natural world was crucial to survival throughout our past. This river is teeming with crocodiles. The same skills that Philip's ancestors used to kill them, Philip now uses to count them. He tracks them down by knowing their habits. They live underneath the bank where there are tree roots. They dig a hole underneath the tree root. If you see this hole, you know it's a breathing hole. They pick out an area for their hunting. If another crocodile goes in there, they soon have a go at him, because they get very territorial. To outwit nature, we needed our brains above all.
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