1 00:00:38,800 --> 00:00:43,191 What you are about to see is one of the miracles of nature, 2 00:00:45,040 --> 00:00:50,398 the extraordinary transformation that will turn this caterpillar into a butterfly. 3 00:00:58,840 --> 00:01:04,472 But we human beings go through a transformation that is just as dramatic. 4 00:01:05,440 --> 00:01:10,719 0ver four agonising years, our bodies and minds are transformed. 5 00:01:12,680 --> 00:01:17,629 At the end of it, like the butterfly, we'll be sexually mature. 6 00:01:19,320 --> 00:01:22,596 This incredible change is called puberty. 7 00:01:38,000 --> 00:01:41,879 Best thing about puberty? That would be my voice getting deeper. 8 00:01:42,040 --> 00:01:44,235 Girls start liking you and you start liking girls. 9 00:01:44,360 --> 00:01:46,316 It's very interesting. I like it a lot. 10 00:01:46,480 --> 00:01:48,311 Worse thing? God! 11 00:01:48,440 --> 00:01:51,910 The worst thing for me is the ups and downs of life: 12 00:01:52,120 --> 00:01:55,078 having to deal with acne and hair and stuff like that. 13 00:01:55,280 --> 00:01:58,875 I don't have any facial hair, so people start to compare me with those who do. 14 00:01:59,040 --> 00:02:00,359 It's like a rollercoaster. 15 00:02:00,480 --> 00:02:03,278 You don't know where it's going to turn. You could go a good way, a bad way. 16 00:02:03,480 --> 00:02:05,630 Just dealing with it is a drag. 17 00:02:05,840 --> 00:02:08,274 # Let's talk about sex, baby, 18 00:02:08,400 --> 00:02:10,675 # Let's talk about you and me, 19 00:02:10,800 --> 00:02:12,870 # Let's talk about all the good things... # 20 00:02:13,000 --> 00:02:17,357 Unlike caterpillars, these teenage boys have no cocoon to hide in 21 00:02:17,480 --> 00:02:20,233 while they travel from childhood to adulthood. 22 00:02:20,360 --> 00:02:23,432 We all make the journey, and it can be a bumpy ride. 23 00:02:25,120 --> 00:02:29,398 We often have the illusion that we're in control of our bodies. 24 00:02:30,240 --> 00:02:34,518 The reality is that it's usually our biology which controls us. 25 00:02:34,920 --> 00:02:40,233 That's particularly obvious during the great rollercoaster ride of puberty. 26 00:02:40,360 --> 00:02:43,591 We don't precisely know when it's going to start, 27 00:02:43,720 --> 00:02:46,712 we don't even know how long it's going to take, 28 00:02:46,840 --> 00:02:50,071 and although we think we know what's going to happen, 29 00:02:50,200 --> 00:02:53,078 nothing can quite prepare us 30 00:02:53,200 --> 00:02:56,033 for exactly how we're going to feel. 31 00:03:08,480 --> 00:03:13,759 It feels exciting and dangerous and you don't know where the next shock's coming from. 32 00:03:16,440 --> 00:03:20,831 And the worst thing is that just as you think you've mastered it, 33 00:03:20,960 --> 00:03:23,315 suddenly something else happens 34 00:03:24,400 --> 00:03:27,312 and your body changes again. 35 00:03:37,760 --> 00:03:40,877 If living through puberty feels like a horror story, 36 00:03:41,000 --> 00:03:43,514 the villains of the piece are hormones. 37 00:03:44,640 --> 00:03:48,315 These tiny chemical messengers are beyond our control. 38 00:03:48,440 --> 00:03:53,833 Suddenly hordes of them start racing through our bloodstream, ordering our bodies to change. 39 00:03:56,280 --> 00:04:01,434 They tell us to switch on to sex, getting us ready to make babies. 40 00:04:01,960 --> 00:04:05,919 They tell our muscles and bones to get bigger and stronger. 41 00:04:06,880 --> 00:04:09,633 They make hair sprout in unusual places. 42 00:04:10,680 --> 00:04:13,433 Sometimes they really let us down. 43 00:04:16,360 --> 00:04:21,309 Amazing though it seems, hormones will affect our brains, too. 44 00:04:23,880 --> 00:04:26,440 They'll make us think about new things. 45 00:04:27,160 --> 00:04:29,720 We'll think about them in a new way. 46 00:04:37,920 --> 00:04:43,119 The result in the emerging adult is confusion and defiance. 47 00:04:44,640 --> 00:04:50,192 But eventually as physical, emotional and sexual maturity. 48 00:04:50,720 --> 00:04:52,312 Go on! 49 00:04:52,440 --> 00:04:57,036 This programme tells the story of the human body's enormous changes during puberty. 50 00:04:57,160 --> 00:05:00,516 It's also about what it feels like to experience puberty. 51 00:05:00,680 --> 00:05:02,796 - All right now. - Is that with Doris Day? 52 00:05:02,920 --> 00:05:06,276 We followed a group of teenage boys in California, 53 00:05:06,400 --> 00:05:09,039 and we've done something unique. 54 00:05:16,880 --> 00:05:19,394 For a crucial eighteen months of her life, 55 00:05:19,520 --> 00:05:24,719 we've watched and listened as a British girl goes through the ups and downs of adolescence. 56 00:05:27,880 --> 00:05:30,440 Now, she's on the threshold of adulthood. 57 00:05:30,560 --> 00:05:34,314 But when we first met she looked and felt very different. 58 00:05:35,240 --> 00:05:39,677 My name's Beatrice. I'm twelve years old. My birthday's in November. 59 00:05:41,520 --> 00:05:45,479 My parents are divorced and I live with my mother and stepfather. 60 00:05:45,600 --> 00:05:50,355 My mum's a councillor and my stepfather is a solicitor. 61 00:05:50,480 --> 00:05:52,232 Sean, shut up. 62 00:05:53,600 --> 00:05:57,149 At twelve years old, Beatrice is a success. 63 00:05:58,360 --> 00:06:01,113 It's not just that she's bright and likeable. 64 00:06:01,240 --> 00:06:05,199 In terms of biology, she's done everything a child should do. 65 00:06:07,600 --> 00:06:10,558 She's survived her most dangerous moment, her birth. 66 00:06:10,880 --> 00:06:14,634 From being a helpless baby, she's gained control. 67 00:06:15,400 --> 00:06:17,550 She's learnt to walk and talk 68 00:06:17,680 --> 00:06:20,433 and to cope with the complex social world around her. 69 00:06:21,800 --> 00:06:23,552 Thanks a lot. 70 00:06:25,680 --> 00:06:29,639 But she's all too aware of what her future holds in store. 71 00:06:31,000 --> 00:06:34,959 When you're a teenager, apparently you go bolshie. 72 00:06:35,120 --> 00:06:39,079 You get periods, you get pubic hair, you get taller. 73 00:06:39,200 --> 00:06:44,149 You get sort of...you get wider at the hips, I think it is, I can't remember. 74 00:06:44,280 --> 00:06:47,113 And you get breasts and all this. 75 00:06:47,240 --> 00:06:49,595 And I don't know, I just... 76 00:06:51,400 --> 00:06:54,358 I just don't want it to happen, really. 77 00:06:54,920 --> 00:06:57,878 (TEACHER) Remembering back to your achievements last year, 78 00:06:58,000 --> 00:07:00,560 when you won the, was it cross country? 79 00:07:00,680 --> 00:07:03,433 (BEATRICE) I'm quite happy with myself the way I am. 80 00:07:04,440 --> 00:07:09,798 And I don't know, I mean, I'm quite happy being a kid. 81 00:07:10,920 --> 00:07:14,674 But however unattractive the prospect of leaving childhood is, 82 00:07:14,800 --> 00:07:18,759 in one way, Beatrice is very lucky to have had one at all. 83 00:07:20,440 --> 00:07:25,594 Human beings are unique in the way they linger as children for an extraordinary long time. 84 00:07:25,920 --> 00:07:28,673 If Beatrice was any other animal, 85 00:07:28,800 --> 00:07:31,758 she'd have stopped being a kid a long time ago. 86 00:07:32,520 --> 00:07:36,479 It's a bit of a puzzle, because other animals mature very differently. 87 00:07:38,160 --> 00:07:43,109 This is Nica. She's a Bengal tiger and she's just 13 weeks old. 88 00:07:44,120 --> 00:07:48,079 For her, like most animals, the journey from babyhood to full-grown 89 00:07:48,200 --> 00:07:50,156 happens as one continuous process. 90 00:07:50,600 --> 00:07:54,957 In about three years time, she'll be able to have cubs of her own. 91 00:07:55,520 --> 00:07:57,476 If I'd grown in the same way, 92 00:07:57,600 --> 00:08:00,160 I could have fathered a child at the age of four, 93 00:08:00,280 --> 00:08:03,238 and would be completely grown at the age of six. 94 00:08:04,040 --> 00:08:09,194 The reason I didn't do that is because the human body does something very unusual. 95 00:08:09,840 --> 00:08:15,597 It breaks the journey from baby to sexual maturity when we're tiny, just six months old. 96 00:08:16,560 --> 00:08:22,317 And though we keep growing, we wait more than a decade to gear up to have children. 97 00:08:25,440 --> 00:08:27,590 For Nica's ancient ancestors, 98 00:08:27,720 --> 00:08:32,475 spending ten tiger years without getting ready to have sex and make cubs 99 00:08:32,600 --> 00:08:34,955 would simply be a dangerous waste of time. 100 00:08:35,920 --> 00:08:39,674 But for our ancestors, things must have been quite different. 101 00:08:39,800 --> 00:08:44,749 They needed time for something so vital to their survival that even sex could wait. 102 00:08:44,880 --> 00:08:48,839 That something is quite surprising. It's learning. 103 00:08:49,040 --> 00:08:51,190 Nought times six is nought. 104 00:08:51,320 --> 00:08:53,675 One times six is six. 105 00:08:53,800 --> 00:08:55,950 Two times six is twelve. 106 00:08:57,640 --> 00:09:02,395 Wherever you look in the world, all children have to learn the skills they need for survival. 107 00:09:03,480 --> 00:09:06,438 Not just the obvious ones, like making yourself understood, 108 00:09:06,560 --> 00:09:09,518 but the things we don't even think of as learning at all, 109 00:09:09,640 --> 00:09:11,790 like walking and controlling our bodies. 110 00:09:13,040 --> 00:09:17,989 As children, we can learn faster than we'll ever be able to again. 111 00:09:20,680 --> 00:09:25,629 Magnified ten thousand times, this is a single human brain cell. 112 00:09:26,480 --> 00:09:29,233 Your brain has a hundred billion of them. 113 00:09:35,600 --> 00:09:40,549 Every one is connected to thousands of others through their tiny branches. 114 00:09:41,240 --> 00:09:46,598 Each join adds a little bit more to the intricate picture of who we are. 115 00:09:49,440 --> 00:09:52,398 As children, the connections are still being made. 116 00:09:54,120 --> 00:09:56,475 Like a plant exploring its surroundings, 117 00:09:56,600 --> 00:09:59,558 brain cells like these are growing their branches, 118 00:09:59,680 --> 00:10:02,240 constantly reaching out to each other. 119 00:10:04,680 --> 00:10:08,639 Learn to ride a bike and you wire up a tiny part of the brain. 120 00:10:10,120 --> 00:10:15,069 Learn a new word or how to catch a ball, and you forge new links. 121 00:10:17,840 --> 00:10:20,593 And with difficult tasks, like writing, 122 00:10:20,720 --> 00:10:24,269 it's only by doing the same thing over and over again 123 00:10:24,400 --> 00:10:26,550 that the connections are made strong. 124 00:10:28,880 --> 00:10:33,032 In the end, they take root and stay with us for the rest of our lives. 125 00:10:41,040 --> 00:10:43,998 But though learning is so vitally important, 126 00:10:44,120 --> 00:10:46,873 there comes a time when our bodies have to move on, 127 00:10:47,240 --> 00:10:50,596 and the rollercoaster of puberty lurches into action. 128 00:10:53,280 --> 00:10:56,238 We don't know what exactly decides when that should be, 129 00:10:56,360 --> 00:11:00,717 but we do know that when it starts it's the brain that's in control. 130 00:11:03,760 --> 00:11:08,117 Peering deep inside the head, you can see where it all happens. 131 00:11:08,840 --> 00:11:11,798 Shaded white, it's the body's autopilot, 132 00:11:11,960 --> 00:11:18,911 a tiny gland that constantly adjusts things like temperature, blood pressure, thirst and hunger. 133 00:11:20,040 --> 00:11:24,989 It's called the hypothalamus and it's the driving force behind puberty. 134 00:11:25,800 --> 00:11:27,950 From its position in the centre of the head, 135 00:11:28,080 --> 00:11:33,632 it can control parts of the body far away and it does so with a remarkable trick - 136 00:11:33,880 --> 00:11:37,236 by dispatching highly efficient chemicals into the blood. 137 00:11:39,920 --> 00:11:44,869 These chemicals are called hormones, and each carries a different message. 138 00:11:45,840 --> 00:11:49,992 For example, adrenalin makes you run faster just for a moment, 139 00:11:50,120 --> 00:11:53,874 but the hormones of puberty change your life forever. 140 00:11:56,720 --> 00:12:02,272 This system is so sensitive that even minute amounts of hormones make massive changes. 141 00:12:02,800 --> 00:12:05,553 If my taste buds were as sensitive, 142 00:12:07,680 --> 00:12:11,639 I'd be able to detect a pinch of salt in a swimming pool. 143 00:12:14,080 --> 00:12:16,833 You can't see hormones in the blood, 144 00:12:16,960 --> 00:12:20,316 but take them out of the body and they're suddenly revealed. 145 00:12:21,280 --> 00:12:26,115 Each one is a uniquely-shaped molecule which, like a key in a lock, 146 00:12:26,240 --> 00:12:28,993 can fit into specific receptors all over the body. 147 00:12:31,440 --> 00:12:33,795 They're subtle and they're in control... 148 00:12:35,720 --> 00:12:39,872 and at the start of puberty they come out at night. 149 00:12:46,960 --> 00:12:49,520 In the restless nights of early puberty, 150 00:12:49,640 --> 00:12:54,589 Beatrice's brain dispatches its chemical messages every ninety minutes... 151 00:12:59,200 --> 00:13:02,954 and her body listens to the signals carried in her blood. 152 00:13:04,440 --> 00:13:08,718 Not just to the amount of hormones, but to the patterns of their release. 153 00:13:10,400 --> 00:13:14,359 In a boy, it will be the testes that pick up the signals. 154 00:13:14,480 --> 00:13:16,835 In Beatrice, it's her ovaries. 155 00:13:23,920 --> 00:13:28,471 The ovaries and testes spike the blood with two potent ingredients, 156 00:13:28,600 --> 00:13:31,160 oestrogen and testosterone. 157 00:13:33,480 --> 00:13:36,233 Circulating everywhere, from head to toe, 158 00:13:37,040 --> 00:13:39,793 these are the real heavyweights of puberty. 159 00:13:41,760 --> 00:13:46,311 They make the rollercoaster an unpredictable and emotional ride. 160 00:13:48,840 --> 00:13:50,796 Some days you feel like you're the bomb, 161 00:13:50,920 --> 00:13:53,275 like everything in your life is going great, 162 00:13:53,400 --> 00:13:55,755 you can't expect anything more. 163 00:13:55,880 --> 00:13:59,634 And then it feels like you're nothing, like you've made mistakes, 164 00:13:59,760 --> 00:14:02,513 that it's over and stuff, that you might as well give up, 165 00:14:02,640 --> 00:14:04,596 and then it goes back up and then it goes back down. 166 00:14:04,720 --> 00:14:07,075 It's always up and down, up and down. 167 00:14:07,200 --> 00:14:11,796 It's never a straight line or inclining up, it's always bumpy. 168 00:14:20,000 --> 00:14:22,878 Beatrice, too, can't control the journey she's on. 169 00:14:23,000 --> 00:14:27,949 Biology has taken over, and the hormones inside her have reached critical levels. 170 00:14:28,080 --> 00:14:31,231 Her body is now being rebuilt around her. 171 00:14:34,160 --> 00:14:36,720 I don't like the physical side of it. 172 00:14:37,080 --> 00:14:41,835 I just wish it appeared one morning, but then that would be a bit awkward. 173 00:14:43,080 --> 00:14:45,640 Your upper body begins to... 174 00:14:46,080 --> 00:14:50,198 You get pubic hairs and that's a right bummer. 175 00:14:52,560 --> 00:14:58,510 And then you, I don't know, you get larger in different places and smaller and whatever. 176 00:14:59,200 --> 00:15:01,156 (D0CT0R) Big breaths in and out. 177 00:15:02,800 --> 00:15:04,950 There you go. 178 00:15:05,080 --> 00:15:07,640 Lovely, right. Let me swivel round and I'll sit in front. 179 00:15:07,760 --> 00:15:09,716 - How old are you now, Beatrice? - Thirteen. 180 00:15:09,840 --> 00:15:11,796 Thirteen? Right. Can I listen here? 181 00:15:12,640 --> 00:15:15,791 I haven't got hips yet, but I'm supposed to get hips. 182 00:15:16,760 --> 00:15:19,513 I don't know whether I want hips or not. 183 00:15:19,640 --> 00:15:21,596 That's lovely, well done. 184 00:15:21,720 --> 00:15:23,870 And just pop it round here. 185 00:15:24,000 --> 00:15:26,355 Have you put much weight on recently? 186 00:15:26,480 --> 00:15:28,232 - No. - No? 187 00:15:28,360 --> 00:15:30,316 I don't know, I don't think so. 188 00:15:33,440 --> 00:15:36,398 0ne of the remarkable things about puberty 189 00:15:36,520 --> 00:15:39,876 is how different the changes are in boys from girls. 190 00:15:40,360 --> 00:15:42,715 Take this perfectly ordinary family. 191 00:15:43,000 --> 00:15:47,949 There's a vast and pretty obvious difference between Mum's and Dad's bodies. 192 00:15:48,800 --> 00:15:51,553 Yet the two children are surprisingly similar. 193 00:15:53,640 --> 00:15:57,599 Christopher and his sister Kerry are seven and nine. 194 00:15:57,720 --> 00:16:01,918 Until they reach puberty, their chests are biologically identical. 195 00:16:05,280 --> 00:16:08,431 So what makes them change in such different ways? 196 00:16:08,560 --> 00:16:12,519 It's those hormones again, which arrive in very different combinations. 197 00:16:12,640 --> 00:16:17,191 Girls' bodies are flooded with oestrogen and their chests respond. 198 00:16:20,920 --> 00:16:24,276 Across the world, there's a huge variety of size and shape, 199 00:16:24,400 --> 00:16:28,359 but every woman's breasts go through the same stages of development. 200 00:16:28,480 --> 00:16:34,157 First, the cells which will eventually make milk ducts start dividing. 201 00:16:34,280 --> 00:16:37,238 The dark area around the nipple begins to grow. 202 00:16:38,400 --> 00:16:41,233 Within months, the breasts start expanding. 203 00:16:41,360 --> 00:16:44,477 Fat is laid down as the adult shape forms. 204 00:16:46,160 --> 00:16:50,119 It'll be around four years before the skin around the nipples lies flat, 205 00:16:50,240 --> 00:16:53,073 forming the smooth contour of the adult breast. 206 00:16:56,280 --> 00:16:59,192 It's painful to run, let me tell you that. 207 00:16:59,320 --> 00:17:02,630 Because what happens up above, you have to start wearing a bra. 208 00:17:02,760 --> 00:17:04,796 Sorry, had to mention it. 209 00:17:04,920 --> 00:17:07,070 It gets really painful to run. 210 00:17:08,760 --> 00:17:12,309 Bras are really, really uncomfortable. 211 00:17:13,080 --> 00:17:17,949 It's just like having a strap put across your chest, permanently. 212 00:17:18,600 --> 00:17:22,036 But just getting breasts is not the end of the story. 213 00:17:22,160 --> 00:17:24,594 They will grow again during pregnancy 214 00:17:24,720 --> 00:17:28,076 and only after a woman gives birth will they be fully mature, 215 00:17:28,200 --> 00:17:30,760 when in most cases they start producing milk. 216 00:17:36,960 --> 00:17:39,713 While a girl's body begins to change shape, 217 00:17:39,840 --> 00:17:45,198 a less obvious, but more important transition is taking place deep inside her, 218 00:17:47,280 --> 00:17:49,236 in her ovaries. 219 00:17:49,560 --> 00:17:55,510 The size and shape of a walnut, these two off-white organs rest either side of the pelvis. 220 00:17:56,520 --> 00:17:59,910 Not only do they produce the hormones that drive puberty, 221 00:18:00,040 --> 00:18:04,192 but they contain the raw material of new life - a woman's eggs. 222 00:18:04,920 --> 00:18:07,673 More than a hundred thousand in each one. 223 00:18:07,800 --> 00:18:11,759 From puberty, once a month, one of these eggs will be set free. 224 00:18:13,560 --> 00:18:15,949 Carried inside the Fallopian tube, 225 00:18:16,080 --> 00:18:21,837 it takes the egg three days to make the 15 cm journey from ovary to womb. 226 00:18:23,240 --> 00:18:26,630 Meanwhile, the womb prepares for a possible pregnancy. 227 00:18:27,360 --> 00:18:31,114 Its lining thickens, ready to be home for a fertilised egg. 228 00:18:34,320 --> 00:18:38,154 This is it, ten thousand times larger than real life. 229 00:18:39,360 --> 00:18:41,920 A strange and dramatic landscape. 230 00:18:47,480 --> 00:18:50,233 A food-rich bed, up to a centimetre thick. 231 00:18:50,800 --> 00:18:53,997 Its only purpose is to nurture new life. 232 00:18:55,440 --> 00:18:58,796 But if the egg is not fertilised, the bed is not needed. 233 00:19:01,160 --> 00:19:05,631 These remarkable pictures reveal the cervix, the opening of the womb. 234 00:19:06,360 --> 00:19:09,796 They show the lining, unused, beginning to flow away. 235 00:19:09,920 --> 00:19:12,275 In her period which follows, 236 00:19:12,400 --> 00:19:15,756 the average woman will lose an eggcup-full of blood. 237 00:19:16,760 --> 00:19:18,796 I don't want to get periods. 238 00:19:18,920 --> 00:19:22,356 I'll tell you why, because people tend to get moody. 239 00:19:22,480 --> 00:19:26,871 One of my friends has got her periods and she gets really, really moody. 240 00:19:37,280 --> 00:19:42,229 And some people get pains and I don't know if I will. I hope not. 241 00:19:43,800 --> 00:19:47,759 I don't like the idea of getting my periods or whatever. 242 00:19:51,000 --> 00:19:55,357 Like it or not, once the rollercoaster starts, there's no stopping it. 243 00:19:57,640 --> 00:20:03,397 With hormones pulsing through her every day, Beatrice's body races ahead out of control. 244 00:20:08,680 --> 00:20:11,433 Yet it can all seem painfully slow. 245 00:20:14,160 --> 00:20:19,109 You know, I wish, I just really wish that it just appeared one morning, 246 00:20:19,240 --> 00:20:24,075 that you went into a little cocoon and woke up and it was all there. 247 00:20:24,200 --> 00:20:26,156 And you were used to it. 248 00:20:26,280 --> 00:20:29,238 Not it happening over three years. 249 00:20:29,360 --> 00:20:31,999 Or four or five or whatever it is. 250 00:20:36,200 --> 00:20:39,158 One of the things I like, everyone used to be taller than me. 251 00:20:39,280 --> 00:20:44,308 Now, lots of my friends are still taller than me, but mostly adults are really short. 252 00:20:44,440 --> 00:20:49,798 I like the fact I'm taller than a lot of people, and being bulky and big, too. 253 00:20:51,240 --> 00:20:55,756 Boys' bodies too, are growing faster than at any time since they were toddlers. 254 00:20:56,240 --> 00:20:59,550 It's easier to develop your body, too, when you're in puberty. 255 00:20:59,680 --> 00:21:02,717 When you're little and you work out, it doesn't show up so much. 256 00:21:02,840 --> 00:21:04,398 - It takes less. - Yeah, yeah. 257 00:21:04,520 --> 00:21:06,750 You start eating a lot, you eat a lot. 258 00:21:06,880 --> 00:21:12,557 Then you start getting bigger and you feel other things getting bigger, so you feel manly. 259 00:21:13,480 --> 00:21:18,759 All the changes they experience are driven by their own sex hormone, testosterone. 260 00:21:18,880 --> 00:21:20,916 And it's made in the testes. 261 00:21:21,640 --> 00:21:24,473 As puberty starts, the testes begin to grow. 262 00:21:25,000 --> 00:21:28,709 It's the first outward sign that anything is happening. 263 00:21:29,200 --> 00:21:33,478 The skin of the scrotum gets rougher and there's a wispy growth of pubic hair. 264 00:21:35,400 --> 00:21:38,870 Inside, the testes are a tangle of tiny tubes, 265 00:21:39,600 --> 00:21:42,956 miniature factories that will soon start to churn out sperm. 266 00:21:45,600 --> 00:21:48,160 And they'll do it on a massive scale. 267 00:21:49,320 --> 00:21:51,356 A thousand every second. 268 00:21:53,600 --> 00:21:58,355 Shortly after the testes start growing, the penis itself starts catching up. 269 00:21:58,960 --> 00:22:00,996 The skin gets darker, 270 00:22:01,120 --> 00:22:05,079 and in four years the machinery of reproduction is complete. 271 00:22:06,760 --> 00:22:12,312 With a special camera that shows heat as colour, we can see why the testicles are where they are. 272 00:22:12,440 --> 00:22:17,798 The red and yellow of the tummy show that it's hotter than the bits coloured green and blue. 273 00:22:18,520 --> 00:22:23,196 Sperm factories work best when slightly cooler than the bulk of a man's body. 274 00:22:23,320 --> 00:22:25,675 Hanging low keeps them cool. 275 00:22:29,280 --> 00:22:34,638 And it's now, of course, that the penis starts getting up to some new tricks. 276 00:22:39,800 --> 00:22:42,519 I had one first erection when I didn't know what it was. 277 00:22:42,640 --> 00:22:44,870 Then I had a first erection where I knew what it was. 278 00:22:45,000 --> 00:22:49,437 - One that I didn't know what it was... - That's the first one. 279 00:22:49,560 --> 00:22:51,994 -The first one, you didn't know what it was? - Right, right. 280 00:22:52,120 --> 00:22:54,429 - The second one, you knew what it was. - Exactly. 281 00:22:54,560 --> 00:22:56,790 - The first one... (LAUGHTER) 282 00:22:56,920 --> 00:23:00,833 It was, like, pulsating. Bedong! Bedong! Bedong! 283 00:23:00,960 --> 00:23:03,713 I'm sitting and I have to use the bathroom. 284 00:23:03,840 --> 00:23:06,798 I really had to piss, 'cause I didn't know what it was. 285 00:23:08,760 --> 00:23:14,596 Inside, the penis is made of a spongy tissue filled with thousands of tiny blood vessels. 286 00:23:14,720 --> 00:23:18,076 Normally, blood flows in and out at a constant rate. 287 00:23:19,480 --> 00:23:23,314 During an erection, blood flow increases dramatically. 288 00:23:23,440 --> 00:23:26,671 Blood vessels at the base of the penis are squeezed. 289 00:23:26,960 --> 00:23:29,713 Blood still flows in, but it can't get out. 290 00:23:30,600 --> 00:23:32,352 Pressure builds up. 291 00:23:34,000 --> 00:23:38,516 The thermal camera shows the heat produced by all that extra blood. 292 00:23:40,080 --> 00:23:44,358 And, to the horror of its owner, the penis seems to have a mind of its own. 293 00:23:44,480 --> 00:23:47,392 I don't like it when you get an erection in class. 294 00:23:47,520 --> 00:23:49,636 You're sitting like... 295 00:23:49,760 --> 00:23:53,036 - So you try and hide it. - I try and tuck it under my belt. 296 00:23:53,160 --> 00:23:56,994 - Yeah? - I fix it up and try to hold it down. 297 00:23:57,120 --> 00:24:02,592 These involuntary stirrings happen as the body learns to control its functions. 298 00:24:02,720 --> 00:24:05,473 But there's still one more surprise in store. 299 00:24:06,120 --> 00:24:11,114 It was in sixth grade, I was watching TV one night and I saw this foreign girl, 300 00:24:11,240 --> 00:24:15,791 and it was some movie where there was this really nice-looking girl, 301 00:24:15,920 --> 00:24:17,956 and I thought she looked good. 302 00:24:18,080 --> 00:24:20,640 I dreamed about her and I woke up in the middle of the night, 303 00:24:20,760 --> 00:24:23,194 and something was wet on my pants, on my boxers. 304 00:24:26,640 --> 00:24:31,634 I had Sex Ed a little before that so I knew then I was OK. 305 00:24:31,760 --> 00:24:35,196 - I'm ready to be a man! - Now I gotta clean it up. 306 00:24:35,320 --> 00:24:38,153 - And change my boxers. - That shit's sticky! 307 00:24:38,280 --> 00:24:40,794 - Not on my bed, just my boxers. - That's horrible! 308 00:24:41,600 --> 00:24:44,194 This is a view inside the sperm ducts. 309 00:24:45,320 --> 00:24:50,030 It's unlikely that the boys' first wet dreams contained any sperm at all. 310 00:24:50,160 --> 00:24:54,119 It takes time for the machinery of production to crank up. 311 00:24:54,640 --> 00:24:57,552 And the first few times, it's firing blanks. 312 00:25:07,520 --> 00:25:12,071 Even when the system kicks in, most of the fluid isn't sperm at all. 313 00:25:12,200 --> 00:25:16,557 It's a liquid which both protects sperm from the acid of a woman's vagina 314 00:25:16,680 --> 00:25:20,434 and gives them energy for their long swim ahead. 315 00:25:22,840 --> 00:25:26,913 But once the sperm factory is up and running, there's no going back. 316 00:25:27,040 --> 00:25:30,032 A man will go on producing sperm for the rest of his life. 317 00:25:42,400 --> 00:25:45,278 Quite apart from the physical transformation they bring, 318 00:25:45,400 --> 00:25:48,153 hormones trigger a much wider change. 319 00:25:48,280 --> 00:25:51,158 They influence teenagers' whole outlook on life. 320 00:25:51,280 --> 00:25:53,919 (BEATRICE) My mum says that I wear too much black. 321 00:25:54,040 --> 00:25:56,076 (GIRL) How can you wear too much black? 322 00:25:56,200 --> 00:25:58,953 I think the tie-dyed, try on the smallest one. 323 00:25:59,080 --> 00:26:02,197 For Beatrice and her friends, this means experimenting, 324 00:26:02,400 --> 00:26:04,550 learning to take charge of their lives, 325 00:26:04,680 --> 00:26:07,831 trying out attitudes and opinions to see if they fit. 326 00:26:07,960 --> 00:26:11,350 You might as well wear a couple of wires joined up. 327 00:26:11,480 --> 00:26:14,836 - Might as well wear a bikini. - It's basically see-through. 328 00:26:14,960 --> 00:26:17,190 (GIRL) I don't know why they have so much decoration. 329 00:26:17,320 --> 00:26:19,709 (BEATRICE) Who'll see them? Your husband? Your...? 330 00:26:19,840 --> 00:26:22,593 - What d'you think? - Yeah, I like the top. 331 00:26:22,880 --> 00:26:26,589 - Wonderful, yeah. - Ooh, nice, Kerry. 332 00:26:27,080 --> 00:26:31,198 I quite like that, I'm sorry. This might seem extremely sad, but I like that. 333 00:26:32,240 --> 00:26:34,993 Just as the body is test-driving its systems, 334 00:26:35,120 --> 00:26:37,873 the brain is beginning to explore its new world. 335 00:26:38,320 --> 00:26:42,950 She's become, since the summer, significantly more independent, 336 00:26:43,080 --> 00:26:45,514 but still likes to have us around, I think, 337 00:26:45,640 --> 00:26:48,996 in the background so we're there, but she's doing her own thing, 338 00:26:49,120 --> 00:26:51,270 so she's got some safety, I suppose. 339 00:26:51,480 --> 00:26:53,789 OK! What d'you think? 340 00:26:53,920 --> 00:26:56,912 The top, not the skirt, the top, not the skirt? 341 00:26:57,040 --> 00:27:01,397 She was very proud of me because I caught the train by myself to Southampton. 342 00:27:03,040 --> 00:27:05,395 And it was a big achievement. 343 00:27:06,680 --> 00:27:12,232 She's quite testing in the sort of questions she asks and her opinions. 344 00:27:12,360 --> 00:27:15,113 She's got lots and lots of opinions about things 345 00:27:15,240 --> 00:27:20,234 that all come from outside or come from school, and that's all quite different. 346 00:27:21,120 --> 00:27:25,113 Teenagers, notoriously, want to break free from their parents. 347 00:27:25,240 --> 00:27:27,993 Their rebellion can cause pain all around. 348 00:27:28,120 --> 00:27:31,510 - Uhh! - OK? 349 00:27:32,480 --> 00:27:34,710 Oh, my ear! I can't hear! 350 00:27:36,640 --> 00:27:39,518 - OK? - OK. 351 00:27:41,720 --> 00:27:43,631 Not too bad, was it? 352 00:27:43,760 --> 00:27:48,356 But children are only doing what's needed to maintain the next generation: 353 00:27:48,480 --> 00:27:50,914 learning to become effective parents. 354 00:27:51,040 --> 00:27:53,395 They're beginning to look after themselves 355 00:27:53,520 --> 00:27:56,318 and recognise the responsibilities of adulthood. 356 00:27:57,280 --> 00:28:02,308 Emotionally, you get down on yourself more as a teenager when you're sixteen, 357 00:28:02,440 --> 00:28:04,351 than when I was eleven. 358 00:28:04,480 --> 00:28:08,632 Usually, I didn't have anything to worry about when I was eleven. 359 00:28:08,760 --> 00:28:12,150 But now I have a lot of stuff to worry about in life and stuff - 360 00:28:12,280 --> 00:28:16,671 girls, parents, teachers, school. So that's a lot of difference. 361 00:28:16,800 --> 00:28:22,636 When I was eleven, I had more people watching me and making choices for me or with me. 362 00:28:22,760 --> 00:28:25,672 Now it's more by myself, with a little help. 363 00:28:25,800 --> 00:28:28,109 In future it'll be by myself. 364 00:28:35,960 --> 00:28:39,555 Many of the changes in puberty are quite subtle. 365 00:28:39,680 --> 00:28:42,148 But one is blindingly obvious. 366 00:28:42,280 --> 00:28:44,350 We just grow much bigger. 367 00:28:45,000 --> 00:28:48,470 And how that happens is really rather surprising. 368 00:28:48,600 --> 00:28:54,152 To reveal the secret of how we grow, we need to look at my own bones. 369 00:28:56,240 --> 00:29:01,189 This scanner produces a magnetic field ten thousand times greater than the Earth's. 370 00:29:01,320 --> 00:29:03,356 Enough to see right through me. 371 00:29:04,840 --> 00:29:09,118 My hand and wrist are an intricate mesh of tightly-packed bones. 372 00:29:09,240 --> 00:29:14,394 If you could have seen them when I was a child, they would have been very different. 373 00:29:15,840 --> 00:29:18,229 This X-ray study is unique. 374 00:29:18,360 --> 00:29:22,672 And going backwards over twenty years reveals a remarkable thing. 375 00:29:23,760 --> 00:29:26,320 The hands of children are not all bone. 376 00:29:31,240 --> 00:29:33,708 There, for instance, no knuckles. 377 00:29:34,360 --> 00:29:36,920 And there, look at the gaps in the wrist. 378 00:29:37,640 --> 00:29:42,191 Instead of bone, there's cartilage, something the machine can't see. 379 00:29:42,640 --> 00:29:46,076 0nly when cartilage turns into bone can the the hand grow. 380 00:29:47,120 --> 00:29:49,475 And how does this happen? 381 00:29:49,920 --> 00:29:51,990 It's hormones again. 382 00:29:52,640 --> 00:29:56,633 Puberty pumps them out and joints get bigger and limbs get longer. 383 00:29:56,760 --> 00:30:01,959 By the end of our teens, there is no more cartilage and there can be no more growth. 384 00:30:18,840 --> 00:30:21,877 Boys and girls have two distinct periods of growth. 385 00:30:22,000 --> 00:30:26,118 When we are children, our bodies grow in a more or less constant way. 386 00:30:26,240 --> 00:30:29,994 Boys are generally no taller or stronger than girls. 387 00:30:31,080 --> 00:30:33,548 But at puberty all that changes. 388 00:30:34,880 --> 00:30:37,440 James and Annie are brother and sister, 389 00:30:37,560 --> 00:30:42,873 but James, a year and a half older than Annie, is a good ten centimetres shorter. 390 00:30:43,240 --> 00:30:48,075 A lot of my friends are shorter than me, but a lot are the same height. 391 00:30:51,040 --> 00:30:54,589 So, I'm not exceptionally tall, and he's not tall. 392 00:30:58,720 --> 00:31:00,472 He just don't grow. 393 00:31:00,600 --> 00:31:03,114 - Shut up! - You don't, you look freaky. 394 00:31:03,240 --> 00:31:05,959 You've been that height for about a year. 395 00:31:06,080 --> 00:31:08,275 What makes Annie taller at the moment 396 00:31:08,400 --> 00:31:11,836 is that girls get their growth spurt at the start of puberty, 397 00:31:11,960 --> 00:31:14,872 while boys get theirs at the end, 398 00:31:15,000 --> 00:31:17,639 which could be as much as three years later. 399 00:31:17,760 --> 00:31:19,910 But James needn't worry. 400 00:31:20,320 --> 00:31:23,232 Starting late means starting from a taller base. 401 00:31:23,720 --> 00:31:27,190 So, like most boys, he'll end up bigger than most girls, 402 00:31:27,320 --> 00:31:29,470 and that probably includes Annie. 403 00:31:33,520 --> 00:31:39,152 From having very similar body shapes, boys and girls now follow very different paths. 404 00:31:40,600 --> 00:31:43,956 A girl's shape changes to get ready for bearing children. 405 00:31:45,800 --> 00:31:49,110 The hip bones spread outwards and become flatter. 406 00:31:50,920 --> 00:31:54,799 But more important is what happens to the space in the middle. 407 00:31:55,960 --> 00:32:00,192 It opens, ending four centimetres wider than in men, 408 00:32:00,400 --> 00:32:03,437 just enough for a baby's head to squeeze through. 409 00:32:17,200 --> 00:32:22,672 The changes in a boy's body stem from his need, in times gone by, to be strong. 410 00:32:24,440 --> 00:32:27,637 The testosterone in his system has dramatic effects. 411 00:32:27,760 --> 00:32:30,354 His heart and lungs get bigger. 412 00:32:32,600 --> 00:32:35,558 With each breath, more air travels down his windpipe. 413 00:32:37,600 --> 00:32:40,512 Through a mass of tubes, it ends here, 414 00:32:40,640 --> 00:32:44,553 in the three hundred million air sacs that make up his lungs. 415 00:32:44,680 --> 00:32:48,275 0xygen passes through the membranes and into his blood. 416 00:32:48,840 --> 00:32:52,276 The more that gets to his muscles, the faster he can run. 417 00:32:55,360 --> 00:32:59,558 At the same time, the mechanical parts of his body are adding to his power. 418 00:33:04,120 --> 00:33:09,592 Here we can see the complex array of muscles and tendons that hold the knee together. 419 00:33:13,880 --> 00:33:17,839 Watching how they move reveals how impressive the human body is. 420 00:33:19,120 --> 00:33:21,236 The two bones don't actually touch. 421 00:33:21,360 --> 00:33:25,592 The soft tissue between them allows them to move in a smooth and precise way. 422 00:33:26,360 --> 00:33:31,992 This whole physical system gets better as muscles and tendons grow larger and stronger. 423 00:33:34,840 --> 00:33:39,038 There's another change at puberty that you can hear easier than you can see. 424 00:33:39,160 --> 00:33:42,038 But I'm going to try and show you with this. 425 00:33:46,840 --> 00:33:51,391 Looking across the tongue and down the throat, these are vocal chords. 426 00:33:51,520 --> 00:33:56,958 The whiter bits in the middle make sound, vibrating furiously when air flows past. 427 00:33:59,840 --> 00:34:04,311 I can alter pitch just by changing the tension of the chords. 428 00:34:05,800 --> 00:34:08,109 Tight for high notes. 429 00:34:08,240 --> 00:34:10,196 0oohhh. 430 00:34:10,320 --> 00:34:11,912 Slack for low. 431 00:34:12,040 --> 00:34:13,837 Aaaawww. 432 00:34:13,960 --> 00:34:16,315 In boys, the whole set-up grows. 433 00:34:16,800 --> 00:34:18,916 You can see it from outside. 434 00:34:19,040 --> 00:34:22,350 Vocal chords get longer, voice chamber bigger, 435 00:34:22,480 --> 00:34:25,995 sending a man's voice an octave lower than a woman's. 436 00:34:28,360 --> 00:34:31,193 Most of the time, this change happens gradually. 437 00:34:31,640 --> 00:34:33,676 But the transition is huge. 438 00:34:34,120 --> 00:34:39,831 The brain is having to re-learn all the intricate muscle controls it uses to make our voices work. 439 00:34:40,680 --> 00:34:43,831 It's like having to learn a new musical instrument, 440 00:34:43,960 --> 00:34:47,589 but sometimes even the brain can hit a bum note. 441 00:34:48,080 --> 00:34:50,275 I hate it when your voice starts getting lower, 442 00:34:50,400 --> 00:34:53,870 - and you start cracking all the time. - Yeah, yeah, yeah. 443 00:34:57,160 --> 00:34:59,390 I say something to my mom or something, 444 00:34:59,520 --> 00:35:03,752 I'll say it all squeaky and then it turns back deep. 445 00:35:03,880 --> 00:35:07,509 - And...um... - It echoes. 446 00:35:07,640 --> 00:35:11,315 Sometimes I can't control it. It just happens. 447 00:35:16,480 --> 00:35:19,517 With all those hormones wreaking havoc inside us, 448 00:35:19,640 --> 00:35:24,111 the body chooses now to confront us with one of life's trickiest challenges. 449 00:35:24,400 --> 00:35:26,231 Sex! 450 00:35:28,200 --> 00:35:32,557 I want you to tell me the first thing you think of when you hear that word, sex. 451 00:35:32,680 --> 00:35:34,796 - Just shout it out. Steve? - Boys and girls. 452 00:35:34,920 --> 00:35:37,275 Boys and girls. Nice and loud, shout 'em out. 453 00:35:37,400 --> 00:35:39,356 - Orgasm! - Pregnancy! 454 00:35:39,480 --> 00:35:41,516 - Pregnancy. - Positions! 455 00:35:41,640 --> 00:35:44,712 - Diseases! - STDs! 456 00:35:44,840 --> 00:35:50,551 It's no accident that teenagers seem to wake up one morning thinking of nothing but sex. 457 00:35:50,680 --> 00:35:52,955 What else do you think of when you hear the word sex? 458 00:35:53,080 --> 00:35:54,433 - Lust! - Lust. 459 00:35:54,560 --> 00:35:57,677 - Trust! - Erection! 460 00:35:57,800 --> 00:36:02,191 When we're children, sex, for the most part, passes us by. 461 00:36:02,320 --> 00:36:05,676 But in puberty the amount of oestrogen and testosterone 462 00:36:05,800 --> 00:36:08,519 pumping through the blood rise month by month. 463 00:36:12,880 --> 00:36:17,829 When they reach a critical level, they seem to affect the central part of our brain. 464 00:36:17,960 --> 00:36:21,714 This is the part responsible for our feelings and desires. 465 00:36:25,200 --> 00:36:29,512 Sex on the brain, one-track minds, that'll be our hormones. 466 00:36:31,880 --> 00:36:34,110 You know a word that I don't see up here? 467 00:36:34,240 --> 00:36:35,878 - What? - What? 468 00:36:36,000 --> 00:36:39,231 (WH0LE CLASS) Love! 469 00:36:40,000 --> 00:36:44,630 Why is that the last thing some people think of, instead of the first thing? 470 00:36:44,760 --> 00:36:46,239 Good question. 471 00:36:46,360 --> 00:36:52,037 The answer seems to be that teenagers' physical development runs ahead of emotional maturity. 472 00:36:52,160 --> 00:36:56,438 The body has sexual urges that the mind can't deal with. 473 00:36:56,560 --> 00:37:00,519 And while it's catching up, there's plenty of scope for turmoil. 474 00:37:01,120 --> 00:37:04,237 Guys shouldn't be as nervous as some are towards girls, 475 00:37:04,360 --> 00:37:07,238 because girls in the long run want the same thing. 476 00:37:07,360 --> 00:37:10,796 And so they should be more outspoken, 477 00:37:13,440 --> 00:37:18,673 and should just come forward and say what they feel and say what they mean. 478 00:37:18,800 --> 00:37:22,759 I think first of all, it's physical. 479 00:37:22,880 --> 00:37:26,077 I think that's what you notice first. You don't look inside a girl and say, 480 00:37:28,280 --> 00:37:30,510 You'll look at her because you like what you see. 481 00:37:30,640 --> 00:37:34,394 I think after you go out with them for a couple of times, 482 00:37:34,520 --> 00:37:39,548 and you get to see what they're really thinking, that's when you decide that's the girl you want. 483 00:37:39,920 --> 00:37:42,673 (UPBEAT S0UL MUSIC) 484 00:37:47,320 --> 00:37:50,118 Perhaps it's one of nature's little jokes. 485 00:37:50,720 --> 00:37:56,078 Just as we're really growing up, and how we look is as important as life itself, 486 00:37:56,200 --> 00:37:58,555 our body starts playing tricks on us. 487 00:37:58,680 --> 00:38:00,636 (B0Y MAKES D0G N0ISES) 488 00:38:03,000 --> 00:38:05,275 Are you guys gonna dance at the party? 489 00:38:05,400 --> 00:38:08,392 No sooner have we begun to take an interest in the opposite sex 490 00:38:08,520 --> 00:38:13,469 than we're hit with strange growths that do nothing at all to help romance. 491 00:38:13,640 --> 00:38:16,677 Zits, two of 'em...three of 'em. 492 00:38:16,800 --> 00:38:20,873 They're a teenager's worst nightmare, and they serve no useful purpose. 493 00:38:22,480 --> 00:38:25,119 The upper body is covered in oil glands. 494 00:38:25,240 --> 00:38:30,439 They're a leftover from our hairy past when they kept our hair sleek and waterproof. 495 00:38:31,040 --> 00:38:34,715 I hate my spots, I really wish I didn't have them. 496 00:38:35,400 --> 00:38:39,678 During the onslaught of puberty, these glands go crazy. 497 00:38:41,320 --> 00:38:45,359 They produce a sudden rush of oil with which our skin can't cope. 498 00:38:45,960 --> 00:38:48,838 The oil blocks the ducts, trapping bacteria 499 00:38:48,960 --> 00:38:52,555 and provoking those nasty but irresistible spots. 500 00:38:55,480 --> 00:38:58,313 And at puberty something else grows. 501 00:39:05,400 --> 00:39:09,951 The sudden appearance of hair is one of the more visible signs of maturity. 502 00:39:10,440 --> 00:39:13,750 Quite why it sprouts, in just a few small patches, 503 00:39:13,880 --> 00:39:16,314 is something of a mystery. 504 00:39:20,200 --> 00:39:22,953 Bizarrely, the answer is probably sweat. 505 00:39:23,720 --> 00:39:26,473 0n most of our body sweat is water-based. 506 00:39:26,600 --> 00:39:29,353 It helps cool us down when we overheat. 507 00:39:33,960 --> 00:39:36,713 But where we have our hair, sweat is different. 508 00:39:38,520 --> 00:39:40,476 It's thicker and milky. 509 00:39:40,600 --> 00:39:43,558 It contains fat and gives off its own smell, 510 00:39:43,680 --> 00:39:47,434 which some people believe makes us attractive to each other. 511 00:39:48,360 --> 00:39:50,874 You smell more. Like musk. 512 00:39:51,000 --> 00:39:52,479 - Body odour. - Yeah. 513 00:39:52,600 --> 00:39:54,192 Y'all funktify. 514 00:39:54,600 --> 00:39:56,795 Body odour is one stage further. 515 00:39:58,120 --> 00:40:00,111 Bacteria love fatty sweat. 516 00:40:00,240 --> 00:40:05,553 If it stays around for long, they'll happily rot it away with alarming results. 517 00:40:07,440 --> 00:40:10,671 I reckon we should tell her about her BO problem. 518 00:40:13,960 --> 00:40:17,919 0ddly, while the rest of our hair varies from person to person, 519 00:40:18,040 --> 00:40:20,793 pubic hair is nearly always the same, 520 00:40:20,920 --> 00:40:22,876 thick-stranded, short and curly. 521 00:40:23,200 --> 00:40:25,589 It's like a forest, like a wilderness. 522 00:40:26,840 --> 00:40:30,469 This hair, magnified 400 times, shows you why. 523 00:40:35,200 --> 00:40:38,317 The hairs aren't round, but flattened. 524 00:40:38,440 --> 00:40:41,193 They've been squeezed by the hair follicle 525 00:40:43,600 --> 00:40:45,830 so as they grow, they spiral. 526 00:40:47,360 --> 00:40:49,920 But why aren't pubic hairs much longer? 527 00:40:52,560 --> 00:40:54,630 They grow for just six months. 528 00:40:54,760 --> 00:40:57,832 So when they die and drop out, they're still quite short. 529 00:40:57,960 --> 00:41:01,509 If they were like head hairs, they'd grow for seven years 530 00:41:01,640 --> 00:41:03,358 and we'd all be in trouble. 531 00:41:03,680 --> 00:41:05,910 It's a bit irritating sometimes. 532 00:41:06,920 --> 00:41:09,480 Especially when you have to do that first bikini line. 533 00:41:12,240 --> 00:41:15,471 It's now almost a year since we first filmed Beatrice. 534 00:41:17,720 --> 00:41:22,510 In that time, the hormonal cycles driving her body towards maturity 535 00:41:22,640 --> 00:41:24,596 have been getting stronger. 536 00:41:31,720 --> 00:41:35,872 Now, the one change Beatrice has been dreading has arrived. 537 00:41:37,040 --> 00:41:40,794 Yeah, I started my period, and it caught me completely off-guard. 538 00:41:40,920 --> 00:41:42,512 But I was all right. 539 00:41:42,840 --> 00:41:47,391 She was very matter-of-fact about it, more so than I was. 540 00:41:47,520 --> 00:41:53,436 She let me know by ringing me at work, and she said, 541 00:41:56,720 --> 00:41:59,837 The good news was that she was going to be in a top stream. 542 00:42:06,200 --> 00:42:08,589 And then she decided to go out and celebrate, 543 00:42:08,720 --> 00:42:13,316 but we didn't go out. She baked a cake and bought me some chocolate eclairs, 544 00:42:13,440 --> 00:42:15,396 which was very nice of her. 545 00:42:15,520 --> 00:42:20,150 Quite a lot of people I know celebrated when they got their period. 546 00:42:20,280 --> 00:42:22,316 It seems strange, but, hey! 547 00:42:25,320 --> 00:42:27,675 (BEATRICE'S M0THER) She's sort of ambivalent about it. 548 00:42:27,800 --> 00:42:30,872 I think she's rather proud to have her periods. 549 00:42:31,000 --> 00:42:34,629 At the time, I felt quite tearful, quite sad about it. 550 00:42:34,760 --> 00:42:41,393 I didn't talk to her about that because I felt it was really the end of my little girl, 551 00:42:41,520 --> 00:42:43,954 even though she's not little any more. 552 00:42:44,080 --> 00:42:47,959 But it was an absolute, this is it now. 553 00:42:48,200 --> 00:42:51,670 The good part of it is I know I'm perfectly normal. 554 00:42:51,800 --> 00:42:54,917 I know I'm a girl, I'm a female. 555 00:42:55,040 --> 00:43:01,957 Then, it's the fact that I get a period and, until I get the menopause, it'll still be that. 556 00:43:06,920 --> 00:43:09,832 Physically, Beatrice has nearly finished her journey. 557 00:43:09,960 --> 00:43:14,078 But there is more to being an adult than having an adult body. 558 00:43:14,200 --> 00:43:19,718 The boys will soon be men, but that means accepting adult responsibility, 559 00:43:19,840 --> 00:43:22,638 something 0lof is finding hard to do. 560 00:43:22,760 --> 00:43:25,115 He's in trouble with his dad. 561 00:43:25,240 --> 00:43:29,518 He's desperate to go to a party, but he's failed to finish his chores 562 00:43:29,640 --> 00:43:31,596 and he's been grounded. 563 00:43:31,720 --> 00:43:34,917 I've just been told I can't attend the party, 564 00:43:35,040 --> 00:43:38,316 under my dad's decision. 565 00:43:38,440 --> 00:43:40,795 He said I can't go. 566 00:43:41,040 --> 00:43:44,589 We had asked him to do a certain thing and he had not done it. 567 00:43:44,720 --> 00:43:49,999 More so than not doing the task, it was not accepting responsibility 568 00:43:50,120 --> 00:43:51,951 for not doing it. 569 00:43:52,640 --> 00:43:56,519 It's just a party and I... 570 00:43:57,280 --> 00:44:01,398 This is just a small example of a much bigger part of development, 571 00:44:01,520 --> 00:44:05,308 learning to use our reasoning to cope with complex situations. 572 00:44:05,440 --> 00:44:07,715 (TEACHER) These are four digits, you know. 573 00:44:07,840 --> 00:44:11,037 Young children tend to see life in black and white. 574 00:44:11,160 --> 00:44:14,596 Pose them a problem that has no clear right or wrong answer, 575 00:44:14,720 --> 00:44:17,188 and they'll have a very simplistic view. 576 00:44:17,320 --> 00:44:19,390 Take this story, for example. 577 00:44:19,520 --> 00:44:22,910 0nce upon a time, there was a man called George. 578 00:44:23,040 --> 00:44:24,996 His wife was dying. 579 00:44:25,120 --> 00:44:30,240 The chemist had a medicine that could save her life, but the medicine cost £1,000. 580 00:44:30,360 --> 00:44:36,310 George didn't have £1,000 and, however hard he tried, he couldn't find the money. 581 00:44:36,440 --> 00:44:38,635 So he stole the medicine. 582 00:44:38,760 --> 00:44:41,228 (TEACHER) Do you think George should have done that? 583 00:44:41,360 --> 00:44:45,512 No, 'cause he could have gone to the police. They could have arrested him. 584 00:44:45,640 --> 00:44:47,437 And that's illegal. 585 00:44:47,560 --> 00:44:49,596 (TEACHER) Illegal? What's illegal? 586 00:44:49,720 --> 00:44:51,278 To steal. 587 00:44:51,480 --> 00:44:54,756 He has got a right, but he has got a wrong to it. 588 00:44:54,880 --> 00:44:56,359 What's right? 589 00:44:56,480 --> 00:44:58,198 The right is that... 590 00:44:58,640 --> 00:45:04,397 Well, he did ask nicely to get the medicine and the wrong is he stole it. 591 00:45:04,520 --> 00:45:06,556 He shouldn't have done that. 592 00:45:06,760 --> 00:45:09,957 - It's bad to steal. - Why is it bad to steal? 593 00:45:10,120 --> 00:45:14,159 He can get into big trouble. You wouldn't like it if somebody stole from you. 594 00:45:14,280 --> 00:45:19,798 Three years on, the certainty has all but gone and the response is dramatically different. 595 00:45:19,920 --> 00:45:22,229 Was there no other way that he'd find the money? 596 00:45:22,360 --> 00:45:26,035 - He tried everything. - He tried everything. 597 00:45:26,160 --> 00:45:31,678 In that case, he should break into the lab and get the medicine for his wife. 598 00:45:31,800 --> 00:45:34,872 Why do you think he should have done that? 599 00:45:35,000 --> 00:45:40,791 Because a life is more important than stealing something. 600 00:45:41,320 --> 00:45:45,279 It's a difficult thing. It's a moral subject. 601 00:45:45,400 --> 00:45:46,958 Why is it difficult? 602 00:45:47,080 --> 00:45:51,471 Because you're doing wrong and we've always been told not to steal things. 603 00:45:51,600 --> 00:45:53,636 - But he's stealing. - Yes? 604 00:45:53,760 --> 00:45:58,231 - So, it's a problem? - Yeah. 605 00:45:58,360 --> 00:46:01,511 This ability to make complex moral judgements, 606 00:46:01,640 --> 00:46:05,553 to see grey where before there was only black and white, 607 00:46:05,680 --> 00:46:08,148 may well come from changes in the brain. 608 00:46:10,200 --> 00:46:13,476 In childhood, the brain is constantly evolving, 609 00:46:13,600 --> 00:46:18,116 as slowly an insulating coat grows around the nerves in the brain. 610 00:46:18,240 --> 00:46:21,198 This helps information travel faster. 611 00:46:21,320 --> 00:46:26,269 0ne theory is that at puberty the front part of the brain, 612 00:46:26,400 --> 00:46:28,755 the area responsible for complex reasoning, 613 00:46:28,880 --> 00:46:30,791 gets its coating. 614 00:46:30,920 --> 00:46:34,708 It may be this that opens the door to mature judgement. 615 00:46:41,240 --> 00:46:44,391 The rollercoaster ride is almost over. 616 00:46:46,560 --> 00:46:48,630 0ur hormones have done their worst. 617 00:46:48,760 --> 00:46:52,389 Girl has become woman, boy has become man. 618 00:46:55,200 --> 00:47:00,558 And if the human body were to make a sound as it neared the end of this turbulent transition, 619 00:47:00,680 --> 00:47:03,558 it would probably be a sigh of relief. 620 00:47:08,320 --> 00:47:10,880 For us, there is also relief. 621 00:47:11,000 --> 00:47:15,471 Having spent the last few years on the great ride of puberty, 622 00:47:15,600 --> 00:47:18,990 we now regain at least the illusion of being in control. 623 00:47:19,120 --> 00:47:21,554 0f course, there will be fine tuning, 624 00:47:21,680 --> 00:47:24,831 and emotional turmoil will no doubt visit us throughout life. 625 00:47:25,320 --> 00:47:29,029 Biologically, we are, at last, the finished article. 626 00:47:29,160 --> 00:47:33,836 We are equipped for adulthood and, ready or not, we face the future. 627 00:47:34,480 --> 00:47:37,950 I don't mind the physical changes at all. 628 00:47:38,080 --> 00:47:40,992 They were meant to happen anyway. 629 00:47:41,120 --> 00:47:45,238 I don't think I'd like to go round looking twelve for the rest of my life. 630 00:47:45,360 --> 00:47:47,715 I don't think I'd be too happy about that. 631 00:47:47,840 --> 00:47:49,717 I'm glad it's happened. 632 00:47:51,640 --> 00:47:56,316 My biggest fear is taking responsibility for myself. 633 00:47:56,440 --> 00:48:02,037 I can't rely on anybody else, once I've got full responsibility over myself. 634 00:48:02,160 --> 00:48:07,439 It's my problem and I can't always rely on everybody else to take care of me. 635 00:48:09,680 --> 00:48:15,596 I stick by my statement that I wish you woke up one morning and you were an adult. 636 00:48:15,720 --> 00:48:19,554 I don't mind the growing, the growing in height, 637 00:48:19,680 --> 00:48:24,993 but any other way is just a curse, the curse of puberty.