"This athlete is a champion of one of the world's most spectacular sports - bull jumping." "CHEERING AND APPLAUSE" "This boxer survives being hit by a fist..." "..travelling with the force of a third of a tonne." "And this man is hoping that surgeons will replace his damaged limbs with another man's hands." "Can we Twitter that the surgery has started?" "Their stories are part of your story... ..the story of what makes you human." "Hidden deep beneath your skin is an extraordinary universe... ..where billions of tiny powerhouses generate energy." "Where vast forests digest food... ..and where the tiniest movements set off violent chain reactions." "This is a fantastic voyage through the most complex organism on Earth..." "..you." "BICYCLE BELL RINGS" "This is Ealing in West London." "It's a nice quiet place, but a few years ago, when I was cycling along here on my way to work, I almost got killed." "I was just meandering along, not thinking about anything in particular, when, suddenly, there was a van coming straight towards me." "It went smack right into me." "HORN SOUNDS" "I was knocked unconscious and I was so badly concussed that when I came to in the hospital, I didn't know where I was or who I was." "A doctor asked me, "Does the name Michael Mosley" ""mean anything to you?" And I said, "No, never heard of him."" "It was a truly shocking experience to have been that close to death." "But the fact is we live in a hostile world, a place full of unexpected threats." "In this programme, I want to show you just how hard your body has to work to keep you safe." "Because, as well as protecting you from the more obvious physical dangers... it must shield you from potentially lethal solar radiation." "It must keep in check the 10 trillion bacteria that cover your skin." "It must deal ruthlessly with any invaders..." "..and, if things go wrong, immediately heal the damage." "Your body does all of this without your having to think about it." "And it works so effectively that most of us can expect to reach our 70th birthday." "Some will live a lot longer." "Esther Tuttle is in her 100th year." "I've got 21 great-grandchildren now." "I even have one great-great-grandchild." "Despite the years, she's in great shape." "In the morning, when I first get up, I do my yoga to exercise every muscle in my body that I can think of." "And then I go up on the roof where I take a walk for a half an hour without stopping." "So then I have a glass of orange juice, oatmeal and black coffee - no sugar, no cream, no toast." "Over the last century, she's fought countless wars against largely unseen enemies." "Well, as a child, I had all the usual diseases." "I had tonsillectomy and measles and chicken pox." "As I grew older, I had to have a hysterectomy at one point and I had an appendectomy at another point." "And then about 15 years ago, I had breast cancer..." "And I think that's about all the diseases I've had." "Esther leads a healthy life and has access to excellent medical care." "But perhaps the real reason she has lived so long is because, like you, she has her own private army working for her around the clock." "Right now, as you watch this programme, your immune system is fighting to keep you safe, every single breath you take." "This tiny speck of dust is alive." "It's a fungal spore." "The air you breathe is filled with them." "Each spore is looking for a warm, moist home." "And it's just found one... in your lungs." "Every minute, you breathe in a couple of spores just like this one." "Once it reaches a quiet corner of your lungs, the spore implants and begins to grow." "Left unchecked, it would fill this entire chamber, stopping oxygen passing from the air into your blood." "Within weeks, you'd be dead." "Fortunately, your body is armed and ready." "It unleashes macrophages - prowling, remorseless, marauding killers." "They follow a chemical signal given off by the fungus." "The spore is doomed." "Unnoticed and unappreciated, the macrophage saves your life." "And it does this breath after breath, day in and day out." "But your body is not just protecting you from tiny, invisible things." "It's also designed to help you cope with more obvious threats..." "..like a fast-moving stick... ..a huge hockey player..." "..or a hard object coming at you at nearly 100 miles an hour." "To survive in a fast-moving world, you have to be able to react in an instant." "Ice hockey players have particularly fast reaction times." "I'm going to see how mine compare." "A little bit nervous." "That thing travels fast, and it's very hard, but let's see." "To help you cope with high-speed threats, your brain has to anticipate." "OK..." "'Your eyes are taking in every movement, 'your ears picking up every sound.'" "And your brain has to process all this information, which is pouring in at a truly astonishing rate, because the world can change in an instant." "That puck was in the back of the net before I even saw it." "Professional goalkeeper Steve Lyle should do rather better." "He can react in less than a fifth of a second." "That's just the blink of an eye." "So how does he do it?" "Even before his opponent hits the puck, the goalie is already beginning to work out where the puck might go." "He's making a guess, based on his opponent's body position and previous knowledge." "Your brain has to come up with an action plan before it actually does anything." "How fast is the puck going?" "What's its likely trajectory?" "Another part of the brain is recovering memories of previous occasions when he's saved goals." "Then his brain tells his body what to do." "Everything up to now has been done entirely subconsciously." "It's only at this point that the goalie becomes consciously aware that the puck has been hit." "What he's doing is something that you do instinctively any time that you are confronted by unexpected danger." "But reaction times are only part of the story." "You also rely on muscles." "# Pump it up" "# When you don't really need it" "# Pump it up" "# Until you can feel it... #" "You have 640 muscles that together make up 40% of your body weight." "COCK CROWS" "Cristian Seraa relies on his muscles rather more than most of us do." "He's a champion of a truly terrifying sport." "He jumps over bulls for a living." "Cristian has no illusions about the dangers." "HE SPEAKS SPANISH" "His fragile body regularly goes head-to-head with half a tonne of charging muscle." "So, every day, on his farm in eastern Spain, he hones his muscles." "In this form of bullfighting, known as recortes, it's the men who risk their lives - the bulls are unharmed." "But no less bad-tempered." "First in the ring are some of Cristian's competitors." "They're not allowed to use weapons or armour." "Instead, they rely on speed and agility to dodge a gruesome goring." "It's now Cristian's turn to enter the ring." "As a champion recortador, he takes some of the greatest risks." "Risks that, even with all his experience, he finds scary." "Escaping uninjured will depend on how his muscles respond in the next few moments." "We all have two different kinds of skeletal muscle fibres." "Just like a chicken, we have dark and white meat." "You use your dark, slow-twitch muscles for things like walking." "They work tirelessly for long periods of time, so they need a constant supply of oxygen-rich blood." "But you also have white, fast-twitch muscles, which allow you to react quickly." "And these are the muscles Cristian is about to use to try and leap over the bull." "APPLAUSE" "Hey!" "Hey!" "Hey!" "Hey!" "When you're dodging a bull, you don't have time to burn oxygen for power, so these fast-twitch muscles do something ingenious." "They reply on a rapid chemical reaction that allows them to constrict four times faster than slow-twitch muscles..." "..which gives Cristian just enough time to escape." "ANNOUNCER:" "Arriba!" "APPLAUSE" "BELL RINGS" "In some sports, muscles and reaction times aren't enough to keep you out of danger." "Getting damaged is an occupational hazard for a boxer." "This is the first live boxing match I've ever been to, and it is certainly faster, more vicious, more brutal than watching it on television." "These guys can really punch." "I mean, the sort of force that they're hitting with is at least ten times what I could possibly do." "Inevitably, if you're punching with this sort of speed, this sort of force, you're going to get injured." "Fortunately, your body is incredibly good at healing injuries." "And that's something that boxer Johnny Greaves relies on..." "..because he gets hit a lot." "Get in close with this kid, cos he's tall, mate, you know what I mean?" "Tonight, Johnny is fighting a man who's three inches taller and five years younger." "I'm a professional opponent." "I fight week in, week out." "I get all the tough jobs against all the up-and-coming boys, the good ticket sellers." "I basically get paid to fight and I do a good job." "For Johnny, boxing isn't just a sport, it's his livelihood." "I'm here primarily to pay my bills and to keep my kids OK, so, obviously, that's the first thought in my mind, is bringing home the bacon." "CROWD SHOUTS" "Johnny has fought in 53 professional fights." "But he's only won two of them." "He knows that tonight he's likely to get hurt." "BELL RINGS" "Johnny works hard to avoid serious injury." "He ducks and dives, dodging punches." "He works at a frantic rate to keep himself a moving target." "But as Johnny tires, his defences begin to fail." "And then he gets injured." "The delicate blood vessels that wind through the fat cells under his eye are destroyed by a punch." "As the vessels burst, blood cells rush out." "On the outside, the full extent of Johnny's injury is not yet obvious, but a black eye is about to form." "What his body does next is normal and yet also utterly remarkable." "It begins to heal." "A repair crew is already on the way." "Travelling in the blood are some very special cell fragments." "Called platelets, they are there to stop the bleeding." "They extend arms that stick to each other and form a net to catch the leaking blood cells." "This clot plugs the hole, and the bleeding stops." "But this is just the start." "Soon after the fight, Johnny's eye turns red and begins to swell." "It's caused by fluid seeping into the tissue around his eye." "The fluid is coming from tiny pores in the blood vessel." "This is not a sign of damage." "It's actually a rather clever form of defence." "The force of the flow would stop any infection in the wound from travelling into the bloodstream..." "..trapping it in the tissue instead." "Johnny's eye isn't just puffed up." "His bruise has now turned a lurid shade of purple." "The colour is the result of decaying blood cells trapped outside the circulatory system." "Here they can't survive." "Now Johnny's body starts to clear up the mess." "Scavenging macrophages sweep through the tissue and gobble up the dying cells." "Inside the macrophages, the chemical that gives blood cells their red colour, haemoglobin, begins to break down." "It's this that gives the bruise its familiar cocktail of colours." "As the haemoglobin breaks apart, it transforms into different-coloured chemicals." "Over time, the colour shifts from green to yellow and finally to brown." "As the macrophages leave, they draw the coloured chemicals away from the skin." "Healing is now complete." "Two weeks later, and Johnny is fighting fit once again... ..so he can step back into the ring to earn his living." "Your body works really hard to keep you out of harm's way." "And when that fails, it will try to repair the damage." "But prevention is always better than cure." "And when it comes to prevention, it's not all about honed muscles and fast reaction times." "You also have the largest organ in your body to fall back on." "That organ is, of course, your skin." "If you were to skin me alive and then spread it all out, then my skin would cover an area about the size and thickness of this beach towel." "And it's covered with receptors that are constantly monitoring the world... ..and feeding back information." "Whoo!" "HE GASPS" "'This water is a very chilly ten degrees.'" "Ah!" "(PANTING) God, that is cold!" "Now, my skin is packed with sensors which warn me about danger." "And some of the sensors are telling me at the moment, the pain sensors, of which there are a few million, are screaming, "This is really cold, this is really unpleasant."" "Not damagingly unpleasant, so my brain is going, "Don't panic, it's all right," but unpleasant." "Phew!" "At the same time, my temperature receptors, which are also in the skin, are shouting, "This is cold, go faster," ""try and warm up."" "So your skin is a very effective early warning system." "But it does something else that is essential for your survival." "Your skin is wonderfully waterproof, which is invaluable when it's cold and wet, but even more so when it's hot and dry." "That's something that Jamie Donaldson is counting on." "OK, first step - identify the value of the last..." "Decimal..." "Place." "She's a maths teacher, but she leads a double life." "Could this be simplified any more?" "Yes or no?" "CHILDREN:" "No!" "Jamie is about to run the equivalent of five marathons in the hottest and driest place in North America" " Death Valley." "It's neat to see what the body is really capable of doing and to prove that you can do a lot more than you think you can." "Here, temperatures can reach 56 degrees Celsius." "Water evaporates faster than almost anywhere else on Earth." "CROWD:" "Three, two, one, zero!" "THEY CHEER" "Jamie has entered the Badwater Ultramarathon." "She'll be running across this inhospitable environment for over 24 hours non-stop." "And Jamie will be relying on her skin to protect her from the brutal heat." "In the desert, you never really do know what is going to happen to your body." "It's extremely hot." "Jamie's greatest threat is dehydration." "Every step, the parched air is trying to suck the moisture out of her body." "What stops her shrivelling up like a prune is a substance made by the skin that most of us casually wash away every morning." "At the base of every hair on your body is a tiny sebaceous gland." "It squeezes an oily substance called sebum onto the surface of your skin." "It makes your hair greasy... ..and gives you spots." "But this oil also makes your skin waterproof." "Waterproofing is essential in hot, dry climates..." "..because sebum doesn't just keep water out." "It also stops bodily fluids from evaporating into the desert air." "By next morning, Jamie is still running." "She has covered 135 miles in record time." "CROWD CHEERS" "26 hours 16 minutes, new women's record..." "CHEERING AND APPLAUSE" "..and the champion, Jamie Donaldson." "Here's your medal." "As well as protecting you from drying out, your skin also protects you from the sun's radiation." "The darker your skin, the more protection you have." "But we're all vulnerable if we stay in the sun too long." "Ultraviolet radiation breaks down the DNA in skin cells." "Your skin responds by flooding the area with blood to repair the damage." "This heats up the skin and produces the familiar redness of sunburn." "But there can also be long-term damage." "I used to get horribly sunburnt when I was a child and since then, I've also had years of heavy sun exposure." "You can see it in the fine lines and the wrinkles on my face." "But if you really want to see the damage that's been done, it's best to compare it with my daughter, who is many decades younger." "Kate!" "'Kate is 11 and has had much less exposure to sunlight.'" "What do you think the most obvious difference between our skin is?" "Well, yours is..." "I don't want to be mean, but yours is more wrinkly." "So, my skin is obviously wrinklier, but also try doing this, try pinching your skin and let it go." "Yours springs straight back, doesn't it?" "It's really weird!" "My skin's lost the elasticity it once had, which is a little bit sad." "'This sagginess is caused by a loss of collagen beneath the skin 'and it's made worse by too much sunlight.'" "But I want to show you something else." "Put on these glasses and prepare to be surprised, because we're going to look at our faces under ultraviolet light." "Oh, it's so weird!" "By using the same ultraviolet light that does the damage, you can see the hidden effects of exposure to the sun." "Basically, your face is just sort of pale, which suggests that your skin isn't damaged in any way." "There's hardly any splodges at all, whereas mine is a great patchwork of strange, different colours." "The dark areas suggest skin damage, and you can only really see it under this special light." "If you look at my nose, this is all damage that has accumulated over the years." "A bit spooky-looking." "Ooh, it's a bit horrible." "Whereas your skin, I have to say, is in very good nick." "We can choose whether or not to expose ourselves to the sun's rays." "But there's another threat out there that never goes away." "Each square centimetre of skin has ten million bacteria camped out on it." "The tissues inside your body would provide a nice, juicy environment if only they could get in." "What keeps them at bay is the way your skin cells lock together, just like armour plating." "But your skin is also pushing outwards." "As new layers grow, the old surface layers peel away... ..carrying a cargo of microbes with them." "But this also means you lose 30,000 skin cells every minute." "By this time next month, you'll have replaced all the skin on your body." "'Platform nine for the South West Trains service to Hampton Court.'" "Your skin is an absolutely fabulous barrier against infections, but, unfortunately, it has great big holes in it." "I'm talking through one at the moment." "You've got the ears." "And, of course, there are a few other orifices that I don't even want to think about." "But oddly enough, it's holes that you probably don't even regard as holes that are particularly vulnerable." "They are your eyes." "Your eyes are one of the weak points that microbes use to get into your body." "So, imagine somebody has sneezed and a few droplets have landed here on this table top." "I'm just sort of drumming my fingers." "The viruses have got on my fingertips." "I now play around with my face a bit." "And then, because I'm feeling, ooh, a bit tired, I decide to rub my eyeballs." "And that's when the viruses get in." "Viruses have found a way to use our own defence mechanism - sneezing - against us." "A sneeze is all it takes for microbes to jump from one person to another." "The main reason you sneeze is to clear your nose of dust and other fine particles." "But as you blast out air at up to 100 miles an hour, you also spray a fine mist of droplets containing millions of microbes..." "..anything up to 12 feet away... ..giving the microbes the perfect opportunity to find a new host." "If they do get inside you, your body quickly responds by mobilising an army of white blood cells." "Now, if you want to see some of these ferocious little fighters in action, all you have to do is prick your finger." "Ooh..." "In a tiny drop of blood like this one here, there are around 400,000 white cells." "These are my white blood cells up here on the screen." "They're called phagocytes, because they eat things." "And these little green blobs are fake bacteria." "It may look like a cheap computer game, but what you're seeing in action is one of the most sophisticated defence systems on the planet." "And there's one here that's just begun to attack." "What's it going to do?" "It's sort of sniffing around." "It's obviously grabbed this bacteria." "Having a bit of a wrestling match." "And there it goes, it's swallowed it." "One up there... ..seems to have managed to..." "He's a greedy little one." "He seems to have got rid of three or four of them." "This is just a tiny fraction of the forces your body can call on to fight infection." "It is absolutely astonishing that this is all going on inside me at this very moment." "I don't have to think about it, it just does it." "Right or left?" "Do you know that letter?" "Yes." "Rowan O'Brien is three years old." "He should be at school, but he's feeling unwell." "What letter's that one?" "Muh!" "That's it." "That's it." "He's got the flu." "No, that's not right." "No. 1, 2, 3, 4, 5..." "Inside him, his body is about to engage in all-out war with one of the most infectious viruses on the planet." "Flu viruses start by attacking the tissue at the back of your throat." "But strangely enough, it's not only the virus that will make you feel ill, it's also your own immune system." "Your body's first response to infection is fever." "The flu virus thrives at your normal body temperature of 37 degrees Celsius..." "..so you raise your temperature by a few degrees." "It's just enough to slow the infection down." "Meanwhile, an army of phagocytes flood the infection site." "They have come to feast on their enemies." "But instead of destroying the viruses, the fighters are themselves infected and are forced to self-destruct." "HE SNEEZES" "As their bodies pile up, they form the basis of your snot." "Rowan's symptoms are getting worse." "You're a little bit hot." "It's a sign the battle inside him is hotting up." "His body has launched a second wave of attack - the killer Ts." "They home in on the throat cells that have been infected by the virus." "They administer the kiss of death, destroying the viruses inside." "But this approach has its cost." "The killer Ts are causing heavy collateral damage." "HE COUGHS" "Rowan is feeling the effects." "HE COUGHS He's got a really sore throat." "Despite everything, the virus remains undefeated." "Now your immune system tries a completely different approach." "Instead of trying to destroy the virus head-on, it releases a cloud of Y-shaped antibodies." "These are specifically produced to destroy this strain of virus." "They coat the viruses, making them stick together." "Now they are easily swept up." "Rowan finally starts to feel better." "And with his energy restored, he can go back to doing what three-year-old boys do best." "HE GIGGLES" "He's experienced an everyday miracle." "He's fought off an infection." "Whee!" "Your body's life-support system is remarkably versatile and able to cope with most of what life has to throw at it, but sometimes it gets overwhelmed, in which case you end up here - in casualty." "You know those pull-out windows?" "Yeah." "I literally just got up and just smashed me head, dropped, and then my mate was coming up, running over, and he said," ""Get up cos your head's bleeding." I realised blood was coming out." "And you weren't knocked out at all?" "No." "'When I went into medicine, I realised pretty quickly' it's not really about healing, it's more about giving the body an opportunity to heal itself." "We're going to place a special adhesive glue..." "We bring the edges of the skin together and we drip it across, and then your body basically does the rest, and it will bind the wound back together." "Then, really, it's just a matter of time, letting the body get on with doing all the repair." "It may sting a touch." "Your body is brilliantly versatile when it comes to dealing with injury." "It can mend damaged nerves, plug leaking blood vessels, regenerate broken bones, heal your skin and repair ripped muscles." "It works hard to protect you from getting infected." "And if that doesn't work, it will vigorously fight off intruders." "Your body is so adaptable, it can even be encouraged to accept and repair part of someone else's body." "Buns." "Let's see..." "Put the buns right here." "Richard Edwards is a chiropractor." "He has a loving wife and family, and considers himself a lucky man." "He doesn't even know what food is!" "But five years ago, Richard was caught in a freak accident." "It really is hot, guys." "He found himself trapped in a burning vehicle." "Everything was on fire behind me." "My electrical system had burnt up, and I couldn't unlock my door." "I couldn't even manually lift up the lock." "I was having trouble breathing and I quickly looked over to the passenger side to see if it was unlocked, so maybe I could get out that way, and as soon as I looked over to the passenger door," "I remember seeing the window on the passenger side, it just exploded into several thousands of pieces of glass, and I'd already started..." "burning alive." "Every time I open one of these things, the heat, that blast from the heat..." "Yeah, I know." "..is a memory of... the moments in the truck, but..." "The heat from the fire left 30% of his body severely burnt." "With medical help, most of his injuries have now healed, but his hands were too badly damaged." "OK, guys?" "He can't button buttons." "He can't do his zipper very easily." "I have to look around the rest room and find a guy that I think is, maybe the most, or the least...masculine..." "SHE LAUGHS" "..and ask, "Would you mind unzipping my pants for me?"" "This fire has really put a stop to my life." "I want to be able to go back to work and grab an X-ray and separate one sheet of X-ray from another and talk to patients about how I can help THEM again instead of... checking out of life like I have done for the last couple of years." "Richard has decided to undergo a radical operation." "It will push his body's ability to heal to the absolute limit." "SIREN WAILS, MACHINE BEEPS" "A very unusual package is being delivered to a hospital in Louisville, Kentucky." "With just a few hours' notice, Richard is rushed to the hospital." "He's about to have a double hand transplant." "His hands will be cut off and replaced with someone else's." "97 over 54 is his blood pressure." "It's the first time something as radical as this has ever been attempted." "OK, so have you guys decided who's going on what team to start?" "The operation will be masterminded by Dr Warren Breidenbach." "There'll be four teams working simultaneously at one point." "There'll be two teams on each of the arms that we're preparing, that is the patient himself, and there'll be two teams working on the arms that have come from the donor." "The new hands have come from someone who died in the last 15 hours." "It's a race against time to connect them to Richard's blood supply before they begin to deteriorate." "Okey-dokey." "That arm is ready to shake, rattle and roll..." "To give Richard's body the best chance of accepting the new hands, both the donor's blood type and bone structure were matched to his." "Did we Twitter that the surgery has started?" "It's going to be a long night, everybody." "The first thing they do is prepare Richard's damaged hands for amputation." "His nerves and blood vessels need to be carefully preserved." "Let me have the knife." "The same is done to the vessels in the donor arm." "Don't throw any of those veins away, OK?" "Save the veins as though they're going to work." "Once his hands are off, there is no going back." "The donor arm came off at 5.30." "So we're five-and-a-half hours now, so we want to try to get some blood into it." "Very carefully, the new hands are attached, vessel by vessel, nerve by nerve." "Nerve, I need nerve." "OK, nerve." "Next, 54 bones and 56 muscles have to be connected so that Richard will be able to control his new limbs." "Find the motor branch." "Yes." "Dissect it back in here, connect it to that." "After 18 hours of painstaking surgery, the new hands are attached." "Hand looks pretty pink." "Everything looks good." "Pretty cool, huh?" "Just ten hours after surgery, Richard sees his new hands for the first time." "It will take months for his body to complete this remarkable repair job." "Thanks, Doctor." "You're welcome!" "You can go ahead and let this go down." "But astonishingly, Richard is already able to take control of someone else's hands." "Let's go ahead and get him moving." "Pull that down." "That's good and strong." "Pull that down." "That's pretty strong." "Remember the one we tightened up?" "It's good and strong." "Pull it down - little finger." "That's strong." "It's amazing." "I'm very thankful to have a new pair of hands." "I've waited a long time for this." "Now and for the rest of his life, Richard will have to take drugs to suppress his immune system and prevent his body rejecting the new, alien hands." "Yep, I think it looks excellent." "But if the drugs work... ..his bones will fuse together with the bones of the new hands." "They will join as one." "Blood will flow from his body into the donor tissue." "And the nerves of his body will grow, connect and control what were once a stranger's hands." "Three months later, Richard is trying out his new accessories." "Back to the tough stuff!" "He's gained some sensation in his new fingers, and these hands are already changing his life." "It hits us, I think, every single day about how amazing, how miraculous it is to have a brand-new set of hands on me." "Mm-hm." "When we thought I was... er, never going to be able to have another set of hands," "I had to live with what I had." "His body is beginning to take full control of them." "They really look like they belong and fit to him." "Oh, yeah, they feel like my hands... ..in...in every way." "She loves them." "These are his hands to me and, er..." "At least I can see that in her eyes!" "SHE LAUGHS" "Look at the wrist." "The wrist..." "Richard's recovery is impressive." "Ooh, nice catch!" ""Bet she won't get that."" "A real tribute to his own resilience and to the skill of his medical and surgical team." "I can hold her hand again." "Now I can do it." "All right." "THEY LAUGH" "We are, each and every one of us, biological marvels, able to adapt to a challenging world." "Although we have our differences, we are fundamentally all the same." "Whoa!" "CHILDREN LAUGH" "We smile using the same facial muscles." "We all stare out and see the world using the same eyes." "We have the same hearts... ..which work around the clock to keep us alive, tirelessly pumping blood, picking up oxygen from our lungs and transporting it to every cell in our body." "We have such remarkable life-support systems that, at one level, all we really need is a bit of water and a small bite of food." "And that nourishment feeds the most complex brains that have ever existed." "Each of our brains has 100 billion cells that are constantly processing a mass of information, rushing in through our senses." "We all began the same way, when a precious egg and a single sperm came together, creating a new individual - you." "HEART BEATS" "As our hearts began to beat, we grew from a tiny embryo... ..into the 100 trillion cells that make up every one of us." "CHILDREN CHEER" "What our bodies can do is truly astonishing, but we are also so much more than the sum of our parts." "We are impressive in our own right, but it's when we all get together that we're capable of truly remarkable things." "Is that right?" "ALL:" "Yes!" "CHILDREN CHEER" "Subtitles by Red Bee Media Ltd" "E-mail subtitling@bbc.co.uk"