1 00:00:17,720 --> 00:00:19,280 They're not the prettiest... 2 00:00:23,120 --> 00:00:24,640 ..or the brightest... 3 00:00:25,840 --> 00:00:27,240 ..and it's fair to say... 4 00:00:29,800 --> 00:00:31,480 ..they're a bit odd. 5 00:00:34,200 --> 00:00:38,560 But ostriches produce something truly astonishing... 6 00:00:40,400 --> 00:00:43,440 ..the biggest eggs on the planet. 7 00:00:55,600 --> 00:00:57,680 Can I ask you to stop for a moment 8 00:00:57,680 --> 00:01:01,200 and think about something truly remarkable? 9 00:01:01,200 --> 00:01:04,360 Something so commonplace, so everyday, that we 10 00:01:04,360 --> 00:01:06,160 take it for granted. 11 00:01:06,160 --> 00:01:10,600 Life creates new life, 12 00:01:10,600 --> 00:01:13,240 and it's happening right here in front of me. 13 00:01:14,320 --> 00:01:15,440 If I bend down... 14 00:01:17,840 --> 00:01:21,680 RATTLING Oh, yes! I can hear it! 15 00:01:21,680 --> 00:01:23,200 I can hear it tapping. 16 00:01:25,080 --> 00:01:28,080 It's as if it's yearning to get out of the egg. 17 00:01:30,200 --> 00:01:31,640 Oh! 18 00:01:31,640 --> 00:01:35,920 And you know, around 40 days ago, the chick that's just about to break 19 00:01:35,920 --> 00:01:41,320 out of here into the big wide world was just a tiny collection of cells. 20 00:01:47,560 --> 00:01:51,640 And look at this, it's started! 21 00:01:51,640 --> 00:01:54,880 I can see inside, I can see its little eyes, its beak. 22 00:01:54,880 --> 00:01:56,880 It's blinking at me. 23 00:01:56,880 --> 00:01:58,400 CHIRPING Oh! 24 00:02:00,360 --> 00:02:03,080 It's quite emotional, if I'm honest with you! 25 00:02:03,080 --> 00:02:05,320 CHIRPING CONTINUES 26 00:02:07,120 --> 00:02:10,560 So, how did this marvel of nature come to be? 27 00:02:14,120 --> 00:02:17,800 Well, to answer that question we have to travel back... 28 00:02:20,240 --> 00:02:21,560 ..way back... 29 00:02:24,680 --> 00:02:26,080 ..before birds... 30 00:02:28,800 --> 00:02:30,760 ..before dinosaurs... 31 00:02:32,880 --> 00:02:35,760 ..before there were even eggs... 32 00:02:38,040 --> 00:02:42,360 ..following an unbroken chain of life that stretches back 33 00:02:42,360 --> 00:02:45,280 over four billion years. 34 00:02:50,680 --> 00:02:55,800 This is the extraordinary story of how evolution gave 35 00:02:55,800 --> 00:02:59,800 rise to the ostrich, and its enormous egg. 36 00:03:18,000 --> 00:03:20,200 THUNDERCLAP 37 00:03:44,200 --> 00:03:48,720 These are some of the world's first living things. 38 00:03:52,440 --> 00:03:55,200 They can't see, they can't hear... 39 00:03:58,000 --> 00:04:00,560 ..but right from the very beginning, 40 00:04:00,560 --> 00:04:04,160 life on Earth was really good at one thing... 41 00:04:07,040 --> 00:04:08,360 ..reproducing. 42 00:04:13,120 --> 00:04:18,200 But back then, they did it in a way that seems quite alien to us. 43 00:04:21,080 --> 00:04:26,960 They split themselves in half to create an identical copy. 44 00:04:29,560 --> 00:04:30,680 A clone. 45 00:04:36,960 --> 00:04:40,360 As soon as life appeared on Earth, it began reproducing 46 00:04:40,360 --> 00:04:43,480 and once it started, it did so at a remarkable rate, 47 00:04:43,480 --> 00:04:48,240 churning out copy after copy after copy for billions of years. 48 00:04:49,560 --> 00:04:53,360 The problem is, though, that when you're just copying yourself, 49 00:04:53,360 --> 00:04:57,200 it means that life's scope is quite limited. 50 00:04:57,200 --> 00:05:01,520 You see, for billions of years we had nothing with eyes, 51 00:05:01,520 --> 00:05:05,680 nothing with legs, nothing with a brain, just single-celled 52 00:05:05,680 --> 00:05:10,080 microbes, and it looked like life was just going to stay like that. 53 00:05:12,760 --> 00:05:18,160 Imagine a world filled with nothing but microbes. 54 00:05:19,720 --> 00:05:24,200 No plants, no insects, no birds of any kind. 55 00:05:26,680 --> 00:05:29,000 And definitely no people. 56 00:05:37,320 --> 00:05:41,440 You see, it's not that I've got anything against microbes, 57 00:05:41,440 --> 00:05:45,640 but let's face it, life would be dull. 58 00:05:50,640 --> 00:05:54,520 But for almost two billion years, 59 00:05:54,520 --> 00:05:57,920 that's exactly how life was. 60 00:06:00,880 --> 00:06:03,440 There was some mixing of DNA 61 00:06:03,440 --> 00:06:06,640 and different species of microbe evolved. 62 00:06:08,400 --> 00:06:13,880 But the chances of life getting any bigger than a pinhead looked slim. 63 00:06:15,600 --> 00:06:16,800 Until... 64 00:06:18,160 --> 00:06:22,160 ..somewhere in this sea of simple cells... 65 00:06:27,920 --> 00:06:30,520 ..a revolutionary emerges. 66 00:06:33,800 --> 00:06:39,320 Now, it may seem similar to all the microbes that came before it, 67 00:06:39,320 --> 00:06:44,360 but it is in fact on a new branch of the tree of life. 68 00:06:45,800 --> 00:06:52,160 You, me and the ostrich - we are all here today 69 00:06:52,160 --> 00:06:56,640 because this microbe does something scandalous. 70 00:07:02,440 --> 00:07:05,680 It takes a shine to another microbe. 71 00:07:10,120 --> 00:07:13,160 Their cell membranes fuse, 72 00:07:13,160 --> 00:07:16,920 allowing all their DNA to mix. 73 00:07:20,360 --> 00:07:23,800 This is the first sex... 74 00:07:25,160 --> 00:07:30,000 ..and it would change the course of life on Earth forever. 75 00:07:40,800 --> 00:07:44,600 It certainly wasn't romantic and it wasn't earth shattering, 76 00:07:44,600 --> 00:07:48,200 but the first sex was a very big deal. 77 00:07:48,200 --> 00:07:51,680 And to understand why, we need to understand what sex is, 78 00:07:51,680 --> 00:07:55,400 and I know what you're thinking, don't worry. No naff diagrams. 79 00:07:55,400 --> 00:07:56,800 Fundamentally, 80 00:07:56,800 --> 00:08:01,720 sexual reproduction is about two living things coming together 81 00:08:01,720 --> 00:08:07,640 to share their genes, to create new life, a new life which is unique. 82 00:08:07,640 --> 00:08:12,480 And that's why the first sex was so pivotal, because after 83 00:08:12,480 --> 00:08:18,040 billions of years of just copying, here was a chance for mixing. 84 00:08:18,040 --> 00:08:22,480 The first sex set life on a new path. 85 00:08:28,200 --> 00:08:32,600 The offspring of this pair won't be clones of their parents. 86 00:08:34,000 --> 00:08:38,480 Instead, they'll inherit a random mix of genes from both. 87 00:08:39,520 --> 00:08:43,520 Sex creates variety 88 00:08:43,520 --> 00:08:48,080 and it sends evolution into overdrive. 89 00:08:54,960 --> 00:08:59,280 Let's fast forward through the next one and a half billion years... 90 00:09:00,960 --> 00:09:05,280 ..during which time there is a sexual revolution. 91 00:09:07,200 --> 00:09:08,560 Some cells join forces... 92 00:09:11,080 --> 00:09:14,360 ..leading to big, complex bodies... 93 00:09:16,920 --> 00:09:19,000 ..the first animals. 94 00:09:31,440 --> 00:09:33,520 By the Cambrian period, 95 00:09:33,520 --> 00:09:37,640 the oceans are filled with a huge diversity of animal life... 96 00:09:39,360 --> 00:09:43,840 ..from simple sponges to species 97 00:09:43,840 --> 00:09:46,600 with eyes, legs and shells. 98 00:09:51,040 --> 00:09:54,160 But all share one thing in common... 99 00:09:59,440 --> 00:10:01,240 ..they're a randy bunch. 100 00:10:07,400 --> 00:10:11,520 We have a good understanding of how rich and varied life was in the 101 00:10:11,520 --> 00:10:15,320 Cambrian seas, down to the enormous abundance of fossils that we've 102 00:10:15,320 --> 00:10:18,920 recovered from that period, and you know how much I love a fossil. 103 00:10:18,920 --> 00:10:22,840 Look at this Trilobite. What a beauty! 104 00:10:22,840 --> 00:10:25,480 You can see it's got its segmented body here, 105 00:10:25,480 --> 00:10:29,200 its rounded, smooth head, compound eyes. 106 00:10:29,200 --> 00:10:32,560 And I can tell you that we've identified no less 107 00:10:32,560 --> 00:10:37,440 than around 20,000 different species of Trilobite. 108 00:10:38,840 --> 00:10:41,560 I've got another fossil here. Look at this. 109 00:10:41,560 --> 00:10:44,680 This is an Eocrinoid, 110 00:10:44,680 --> 00:10:48,080 an animal that's related to the sea urchins, and we think that the 111 00:10:48,080 --> 00:10:52,920 bottom part of it here was rooted into the seabed and these tendrils 112 00:10:52,920 --> 00:10:57,680 here would have been wafting in the water flow, getting its food. 113 00:10:57,680 --> 00:11:01,040 So, there was a great diversity of life in those Cambrian seas, 114 00:11:01,040 --> 00:11:04,560 but also a diversity of shape and size, 115 00:11:04,560 --> 00:11:08,600 and that made sex altogether more challenging 116 00:11:08,600 --> 00:11:13,200 because organisms like this couldn't reproduce in the same way that their 117 00:11:13,200 --> 00:11:17,960 ancient single-celled ancestors did, by simply fusing together. 118 00:11:17,960 --> 00:11:21,240 I mean, imagine a couple of trilobites like this trying 119 00:11:21,240 --> 00:11:23,440 to get it on. It's not going to work, is it, 120 00:11:23,440 --> 00:11:28,040 with the hard exoskeleton, all of their legs, their internal organs? 121 00:11:28,040 --> 00:11:31,400 Nature needed to come up with a different way. 122 00:11:34,280 --> 00:11:38,240 And nature's solution is an extremely effective one. 123 00:11:42,600 --> 00:11:46,000 Back in the Cambrian, many animals have adopted it. 124 00:11:52,600 --> 00:11:56,400 These tiny specks are eggs... 125 00:12:02,040 --> 00:12:05,960 ..and these even tinier ones are sperm. 126 00:12:08,000 --> 00:12:13,320 And they do exactly what those ancient microbes did. 127 00:12:13,320 --> 00:12:17,520 They fuse together and combine their DNA 128 00:12:17,520 --> 00:12:20,800 to create a new, unique life. 129 00:12:32,400 --> 00:12:36,960 The Cambrian seas are quite literally fertile oceans... 130 00:12:38,960 --> 00:12:41,040 ..but for many creatures here, 131 00:12:41,040 --> 00:12:46,080 there's something unfamiliar about the way they go about reproducing. 132 00:12:54,040 --> 00:12:57,680 A lot of people don't like snails. I'm not one of them. 133 00:12:57,680 --> 00:13:02,080 There's something therapeutic about having them slime 134 00:13:02,080 --> 00:13:04,200 up and down your fingers. 135 00:13:04,200 --> 00:13:07,520 These are a highly successful group of animals. 136 00:13:07,520 --> 00:13:11,120 There are more than 40,000 species in the world, 137 00:13:11,120 --> 00:13:15,320 and one of the keys to their success is their reproductive capacity. 138 00:13:15,320 --> 00:13:19,960 Like many snails, it produces sperm and eggs. 139 00:13:19,960 --> 00:13:22,120 It's a hermaphrodite. 140 00:13:24,360 --> 00:13:27,840 Let's think about the repercussions of that. 141 00:13:27,840 --> 00:13:32,760 When this snail goes looking for a potential partner, any other that it 142 00:13:32,760 --> 00:13:38,240 finds of the same species and about the same size, is a potential mate. 143 00:13:40,800 --> 00:13:45,320 And once they've copulated, they can both produce a batch of eggs, 144 00:13:45,320 --> 00:13:50,800 doubling the capacity to produce a lot more snails. 145 00:13:50,800 --> 00:13:56,040 Now, this is such an efficient and successful strategy that many 146 00:13:56,040 --> 00:14:00,600 scientists believe that the earliest animals were all hermaphrodite. 147 00:14:00,600 --> 00:14:05,320 As soon as they could produce sperm and eggs, they produced both, 148 00:14:05,320 --> 00:14:11,200 which begs the question, why aren't we all hermaphrodites today? 149 00:14:13,680 --> 00:14:18,400 It's hard to know for certain, but there's a theory 150 00:14:18,400 --> 00:14:22,880 that during the Cambrian, something upset the status quo... 151 00:14:26,920 --> 00:14:30,800 ..and it may have happened in a creature like this. 152 00:14:37,960 --> 00:14:42,560 It's so bizarre, it's hard to believe it really existed. 153 00:14:45,920 --> 00:14:51,520 But fossil evidence shows that it really did look like this. 154 00:14:59,600 --> 00:15:01,560 It's a Vetulicolian. 155 00:15:03,800 --> 00:15:07,360 It's not a fish, it's not a crustacean. 156 00:15:07,360 --> 00:15:10,880 In fact, it's unlike anything that lives today... 157 00:15:12,480 --> 00:15:17,200 ..and it's radically different from its single-celled ancestors. 158 00:15:19,880 --> 00:15:25,480 But it has inherited a key trait - a one-track mind. 159 00:15:30,840 --> 00:15:35,480 Now, if we assume Vetulicolians are hermaphrodites, 160 00:15:35,480 --> 00:15:40,480 that means that any member of the same species is a potential mate. 161 00:15:47,160 --> 00:15:50,880 But when this pair come together to release their eggs and sperm... 162 00:15:52,000 --> 00:15:53,520 ..there's a problem. 163 00:15:57,200 --> 00:16:01,160 You see, one of them was born partially sterile. 164 00:16:02,200 --> 00:16:04,040 It can't produce sperm. 165 00:16:07,520 --> 00:16:11,440 For many animals, this would be the end of their family line... 166 00:16:13,840 --> 00:16:17,080 ..but not for a hermaphrodite. 167 00:16:21,080 --> 00:16:24,200 Because if it can still produce eggs... 168 00:16:25,760 --> 00:16:28,400 ..it can still reproduce. 169 00:16:31,000 --> 00:16:34,680 Its genes get passed down to the next generation... 170 00:16:36,720 --> 00:16:40,520 ..and some of them are born partially sterile too. 171 00:16:44,440 --> 00:16:45,720 So, think about it. 172 00:16:45,720 --> 00:16:50,080 In biological terms, that snail, if it could only produce eggs, 173 00:16:50,080 --> 00:16:51,840 we'd call it a female. 174 00:16:51,840 --> 00:16:55,680 If it could only produce sperm, we would call it a male. 175 00:16:55,680 --> 00:16:59,440 So, there is the possibility that the division of the sexes, 176 00:16:59,440 --> 00:17:05,600 the origin of males and females, came down to a chance mutation, 177 00:17:05,600 --> 00:17:08,240 that we were mistakes. 178 00:17:14,400 --> 00:17:19,880 Today, only 5% of animal species are hermaphrodites. 179 00:17:21,720 --> 00:17:26,600 The rest have separate sexes, 180 00:17:26,600 --> 00:17:28,640 and it's thought that males 181 00:17:28,640 --> 00:17:33,520 and females evolved multiple times, in many different species, 182 00:17:33,520 --> 00:17:37,880 allowing females to specialise in producing fewer, 183 00:17:37,880 --> 00:17:40,840 higher quality eggs, 184 00:17:40,840 --> 00:17:45,120 whilst males make faster, more numerous sperm. 185 00:17:48,800 --> 00:17:50,920 Nature is of course flexible. 186 00:17:52,400 --> 00:17:55,200 Clownfish males can turn into females... 187 00:17:56,240 --> 00:17:58,840 ..seahorse dads get pregnant. 188 00:18:04,080 --> 00:18:07,520 It really doesn't matter who does what. 189 00:18:07,520 --> 00:18:11,520 it's being a specialist that counts. 190 00:18:20,000 --> 00:18:24,480 For animal life, this specialisation is a turning point. 191 00:18:30,760 --> 00:18:35,400 As we jump forward 150 million years, 192 00:18:35,400 --> 00:18:38,040 it adds fuel to evolution's fire. 193 00:18:39,920 --> 00:18:44,280 Fishes emerge and fill every marine habitat. 194 00:18:55,960 --> 00:19:00,960 And eventually, some even brave a new frontier... 195 00:19:11,400 --> 00:19:13,680 ..the freshwater streams. 196 00:19:17,480 --> 00:19:21,800 This ancestor of the ostrich is looking for a safe place 197 00:19:21,800 --> 00:19:23,080 to lay her eggs. 198 00:19:30,120 --> 00:19:33,680 With streamlined bodies and powerful tails... 199 00:19:35,360 --> 00:19:38,520 ..her shoal swim upstream with ease. 200 00:19:39,960 --> 00:19:41,000 But... 201 00:19:42,280 --> 00:19:44,040 ..they're being followed. 202 00:19:55,880 --> 00:19:58,760 If I were to time travel back to the Devonian, 203 00:19:58,760 --> 00:20:02,400 you would not find me wading in a river like this. 204 00:20:02,400 --> 00:20:05,560 No matter how sweaty the swamps were, I wouldn't be tempted 205 00:20:05,560 --> 00:20:10,920 to take to the waters because I might lose my toes, or even my legs. 206 00:20:10,920 --> 00:20:14,640 The rivers were filled full of predatory fish, 207 00:20:14,640 --> 00:20:18,240 armed with sharp teeth for tearing through flesh. 208 00:20:18,240 --> 00:20:23,400 Some of them the size of minnows, others the size of crocodiles. 209 00:20:23,400 --> 00:20:25,600 If you were a fish living in here, 210 00:20:25,600 --> 00:20:29,640 you'd have enough trouble protecting yourself, let alone your eggs. 211 00:20:36,360 --> 00:20:38,960 Left unguarded in these ancient waters, 212 00:20:38,960 --> 00:20:42,080 nutritious eggs don't stand a chance. 213 00:20:51,440 --> 00:20:56,040 These fish need to find a safer breeding ground... 214 00:20:57,280 --> 00:21:00,240 ..or there'll be no next generation. 215 00:21:02,720 --> 00:21:06,800 But they have something on their side that other fish don't. 216 00:21:13,000 --> 00:21:17,320 This is a 3D scan of a fossil of one of those fishes. 217 00:21:17,320 --> 00:21:18,960 And when you first look at it, 218 00:21:18,960 --> 00:21:23,720 it looks pretty much like a modern, conventional fish - it's long, 219 00:21:23,720 --> 00:21:26,160 fairly streamlined, it's got a bit of a blunt head there, 220 00:21:26,160 --> 00:21:28,720 would have had a tail at the back for propelling it through 221 00:21:28,720 --> 00:21:33,560 the water, and all of the fins are pretty much in the right places. 222 00:21:33,560 --> 00:21:37,520 Looks a little bit like a salmon, but on closer inspection, 223 00:21:37,520 --> 00:21:39,640 in fact it's very different. 224 00:21:39,640 --> 00:21:43,920 Let's zoom in on this fin here. 225 00:21:43,920 --> 00:21:47,880 You can see that it's much longer and the bones that 226 00:21:47,880 --> 00:21:53,160 lead from it back to the core of the skeleton are much more robust. 227 00:21:53,160 --> 00:21:57,080 It could be that it was using these fins to propel 228 00:21:57,080 --> 00:22:00,040 itself along the bottom of the river. 229 00:22:00,040 --> 00:22:04,520 They're much stronger than those delicate ray fins that we 230 00:22:04,520 --> 00:22:08,880 see on modern fishes. These are fins that you could stand on. 231 00:22:18,120 --> 00:22:23,800 The strong fins that help these fish move along the riverbed also 232 00:22:23,800 --> 00:22:27,520 allow them to do something revolutionary... 233 00:22:39,600 --> 00:22:41,040 ..leave the river... 234 00:22:43,640 --> 00:22:45,360 ..and walk on land. 235 00:22:54,880 --> 00:22:58,680 And beyond the main river lies a network of streams 236 00:22:58,680 --> 00:23:00,760 the predators can't reach. 237 00:23:02,760 --> 00:23:07,720 We can't be certain why those lobe-finned fish climbed 238 00:23:07,720 --> 00:23:09,880 out of the water. I mean, they could have been 239 00:23:09,880 --> 00:23:13,200 looking for food, they could have been avoiding being food themselves, 240 00:23:13,200 --> 00:23:15,760 but there is the possibility 241 00:23:15,760 --> 00:23:20,640 that they were looking for somewhere safe to lay their eggs, to spawn. 242 00:23:20,640 --> 00:23:24,400 But one thing's for sure, once they waddled out of the water 243 00:23:24,400 --> 00:23:28,000 and climbed onto land, there was no going back. 244 00:23:35,920 --> 00:23:39,160 Fish with the strongest fins are more likely to reach 245 00:23:39,160 --> 00:23:41,000 the predator-free waters. 246 00:23:46,280 --> 00:23:51,320 They have more offspring, which inherit their strong fins. 247 00:23:54,760 --> 00:24:01,440 Over countless generations, the bones get longer, stronger... 248 00:24:02,840 --> 00:24:05,280 ..and better for walking on land... 249 00:24:11,160 --> 00:24:16,120 ..until eventually, after millions of years, 250 00:24:16,120 --> 00:24:21,480 a fish's fin has become a limb. 251 00:24:28,440 --> 00:24:33,960 There's absolutely no doubt that this was a pivotal moment. 252 00:24:33,960 --> 00:24:35,400 I mean, think about it. 253 00:24:35,400 --> 00:24:39,240 Life on Earth had evolved in water, and up until this point, 254 00:24:39,240 --> 00:24:43,520 almost all life was still living in water. 255 00:24:43,520 --> 00:24:46,000 OK, around 100 million years earlier, 256 00:24:46,000 --> 00:24:49,480 plants have made the difficult transition onto land, 257 00:24:49,480 --> 00:24:54,840 insects had managed it, too, but now here was a new group - 258 00:24:54,840 --> 00:25:01,480 animals walking on land on four legs and four feet for the first time. 259 00:25:01,480 --> 00:25:04,120 The amphibians. 260 00:25:04,120 --> 00:25:08,440 Now, I'm about to show you something which is remarkable, 261 00:25:08,440 --> 00:25:11,720 astonishing even, and I think very beautiful. 262 00:25:11,720 --> 00:25:12,800 Take a look at this. 263 00:25:15,000 --> 00:25:18,160 This is a drawing of the bones in the foot 264 00:25:18,160 --> 00:25:21,360 of one of those ancient amphibians. 265 00:25:21,360 --> 00:25:25,800 It lived over 300 million years ago. 266 00:25:25,800 --> 00:25:27,200 But look at it. 267 00:25:27,200 --> 00:25:31,440 Does it look familiar? It should do. 268 00:25:31,440 --> 00:25:38,320 That's because these ancient amphibians were our ancestors, 269 00:25:38,320 --> 00:25:43,360 and not only our ancestors, but the ancestors of all the animals 270 00:25:43,360 --> 00:25:49,360 with backbones that have ever lived or are living on land today. 271 00:25:59,760 --> 00:26:06,080 If those ancient microbes hadn't discovered sex, bigger, 272 00:26:06,080 --> 00:26:09,800 more complex animals may never have evolved. 273 00:26:13,560 --> 00:26:16,720 We wouldn't have males and females... 274 00:26:18,480 --> 00:26:20,040 ..with precious eggs, 275 00:26:20,040 --> 00:26:21,720 that need protecting. 276 00:26:26,280 --> 00:26:31,120 And the ancestors of every land animal with a backbone, 277 00:26:31,120 --> 00:26:34,400 including the ostrich, and us... 278 00:26:37,560 --> 00:26:40,040 ..may never have left the water... 279 00:26:41,040 --> 00:26:43,640 ..and evolved to live on land. 280 00:26:50,200 --> 00:26:54,000 Now, we jump forward tens of millions of years... 281 00:27:02,280 --> 00:27:07,000 ..and the amphibians are the planet's dominant land animals. 282 00:27:16,360 --> 00:27:19,200 But no reign lasts forever. 283 00:27:23,600 --> 00:27:26,240 This is Casineria. 284 00:27:26,240 --> 00:27:29,000 She can live happily in water and on land... 285 00:27:33,400 --> 00:27:38,160 ..but like many animals here, Casineria is in trouble. 286 00:27:43,040 --> 00:27:45,240 Drought has set in. 287 00:27:51,520 --> 00:27:57,120 Swamps that once stretched as far as the eye can see are now 288 00:27:57,120 --> 00:27:59,640 little more than muddy puddles. 289 00:28:06,400 --> 00:28:08,760 To understand why this was a problem... 290 00:28:11,080 --> 00:28:13,720 ..we only have to look at amphibians today. 291 00:28:17,640 --> 00:28:20,640 Clearly out of practice, but I did manage to catch one. 292 00:28:20,640 --> 00:28:23,200 This frog is rather attractive, I have to say. 293 00:28:23,200 --> 00:28:26,560 Look at those eyes, like little golden jewels. 294 00:28:26,560 --> 00:28:29,280 It looks slimy, but it's not. 295 00:28:29,280 --> 00:28:32,960 It's shiny, and it's shiny because it's wet, 296 00:28:32,960 --> 00:28:38,080 and when it's wet, frogs like this can breathe through their skin. 297 00:28:38,080 --> 00:28:39,720 But it does need to be wet. 298 00:28:39,720 --> 00:28:41,880 So, there's an inherent vulnerability there. 299 00:28:41,880 --> 00:28:45,840 They do need to return to water. They can't dry out. 300 00:28:46,920 --> 00:28:49,080 And it's not just the adults. 301 00:28:49,080 --> 00:28:51,800 Their eggs need water too. 302 00:28:51,800 --> 00:28:56,080 Amphibians can't reproduce without water. 303 00:29:00,680 --> 00:29:06,080 In periods of drought, amphibians suffer. 304 00:29:10,760 --> 00:29:14,120 But Casineria has managed to cling on. 305 00:29:18,080 --> 00:29:23,920 Her survival is partly down to luck, but also, 306 00:29:23,920 --> 00:29:27,320 the unique mix of genes she inherited. 307 00:29:33,240 --> 00:29:35,400 Now, had I been a bit sharper 308 00:29:35,400 --> 00:29:38,120 and been able to catch another one of these frogs, 309 00:29:38,120 --> 00:29:43,000 then probably, to you and I, they would look identical, like clones. 310 00:29:43,000 --> 00:29:47,600 But of course they're not, because frogs reproduce sexually. 311 00:29:47,600 --> 00:29:52,640 They mix their genetic material to produce unique individuals 312 00:29:52,640 --> 00:29:55,520 and this doesn't only make life more interesting. 313 00:29:55,520 --> 00:29:58,760 Critically, it makes life more resilient. 314 00:29:58,760 --> 00:30:00,240 Think about it. 315 00:30:00,240 --> 00:30:01,680 At this point in time, 316 00:30:01,680 --> 00:30:05,640 this lovely stream is probably the perfect place for this frog to be. 317 00:30:05,640 --> 00:30:07,720 But what about if conditions change? 318 00:30:07,720 --> 00:30:12,560 What about if it got drier or wetter or the vegetation changed, 319 00:30:12,560 --> 00:30:16,000 or something much more subtle like the mineral content of the water? 320 00:30:17,600 --> 00:30:20,080 Well, because every frog is different, 321 00:30:20,080 --> 00:30:23,520 some will fare better than others. 322 00:30:23,520 --> 00:30:28,400 They'll live longer and have more offspring, and those 323 00:30:28,400 --> 00:30:33,160 offspring will inherit the genes that helped their parents survive. 324 00:30:34,840 --> 00:30:39,800 Essentially, that's what we call survival of the fittest. 325 00:30:46,880 --> 00:30:52,800 Casineria's unique mix of genes determines everything from her 326 00:30:52,800 --> 00:30:55,840 size to her skin colour. 327 00:30:55,840 --> 00:30:59,360 And it also determines her eggs. 328 00:31:06,000 --> 00:31:07,520 As luck would have it, 329 00:31:07,520 --> 00:31:12,040 they're better at retaining moisture than most amphibian eggs... 330 00:31:15,480 --> 00:31:21,600 ..and in these dry conditions, that difference means everything. 331 00:31:29,040 --> 00:31:33,760 The slightest variation in the surface structure or composition 332 00:31:33,760 --> 00:31:39,000 of the egg is all it takes for one egg to survive 333 00:31:39,000 --> 00:31:40,800 when others don't. 334 00:31:43,480 --> 00:31:47,600 And as generations pass, the egg begins to change. 335 00:31:59,040 --> 00:32:02,640 The surface gets tougher and thicker. 336 00:32:02,640 --> 00:32:06,360 Special membranes form to prevent moisture loss. 337 00:32:08,080 --> 00:32:14,640 The egg gets larger, stronger, and takes on an iconic shape... 338 00:32:17,320 --> 00:32:21,000 ..until eventually, after millions of years, 339 00:32:21,000 --> 00:32:24,520 something extraordinary has emerged... 340 00:32:29,760 --> 00:32:34,000 ..an egg that can survive on dry land. 341 00:32:41,520 --> 00:32:47,520 From dying swamps, entirely new groups of animals emerge. 342 00:32:47,520 --> 00:32:51,280 Among them, the reptiles. 343 00:32:53,720 --> 00:32:58,520 Look at this rock monitor, what a beauty! 344 00:32:58,520 --> 00:33:00,960 Sadly, you don't have time to watch me 345 00:33:00,960 --> 00:33:04,880 falling in love with a lizard, so let's look at the similarities 346 00:33:04,880 --> 00:33:08,240 between this animal and those ancient amphibians. 347 00:33:08,240 --> 00:33:11,800 Well, firstly, it's got the same streamlined nose 348 00:33:11,800 --> 00:33:15,080 and long tail there. 349 00:33:15,080 --> 00:33:19,320 Then look at her limbs, all four of those legs and feet, 350 00:33:19,320 --> 00:33:22,320 strong with those sturdy bones that have been 351 00:33:22,320 --> 00:33:26,360 passed down generations from the lobed-fin fishes. 352 00:33:26,360 --> 00:33:28,280 But there are differences too. 353 00:33:28,280 --> 00:33:29,920 The skin is a striking one. 354 00:33:29,920 --> 00:33:34,480 I mean, that is not shiny, moist and breathable. 355 00:33:34,480 --> 00:33:39,000 It's scaly and hard. It's about keeping moisture in. 356 00:33:39,000 --> 00:33:41,200 And then critically, 357 00:33:41,200 --> 00:33:46,200 this reptile doesn't need to return to water to breed. 358 00:33:46,200 --> 00:33:50,080 You see, the amphibians might have been first to walk the Earth, 359 00:33:50,080 --> 00:33:54,200 but they were always limited by that need for water. 360 00:33:54,200 --> 00:33:58,640 It was the reptiles which really conquered the land. 361 00:34:05,800 --> 00:34:09,920 Reptile eggs are far more sophisticated than the jelly 362 00:34:09,920 --> 00:34:11,960 blobs of the amphibians. 363 00:34:13,840 --> 00:34:19,240 Known as amniotic eggs, they have a tough outer shell, 364 00:34:19,240 --> 00:34:25,480 a nutrient rich yolk, and perhaps most extraordinary of all, 365 00:34:25,480 --> 00:34:30,120 a special sac of fluid in which the embryo 366 00:34:30,120 --> 00:34:34,000 floats in its own private pool. 367 00:34:35,720 --> 00:34:40,240 The amniotic egg is like a pond on dry land. 368 00:34:45,920 --> 00:34:47,760 But when it came to sex, 369 00:34:47,760 --> 00:34:52,120 these new high-tech reptile eggs presented some challenges. 370 00:34:52,120 --> 00:34:54,040 You see, an egg like this, 371 00:34:54,040 --> 00:34:57,080 and this is a crocodile's egg, is no good on its own. 372 00:34:57,080 --> 00:34:58,760 It's got to be fertilised. 373 00:34:58,760 --> 00:35:03,040 But there is absolutely no chance 374 00:35:03,040 --> 00:35:07,160 of a sperm breaking through this shell, so what's the solution? 375 00:35:07,160 --> 00:35:10,240 Well, the solution is to get the sperm to the 376 00:35:10,240 --> 00:35:15,320 egg before the shell goes on, before the egg is laid. 377 00:35:15,320 --> 00:35:18,840 You see, the reptiles didn't only have to reinvent the egg, 378 00:35:18,840 --> 00:35:21,200 they had to reinvent sex. 379 00:35:27,040 --> 00:35:32,600 {\an8}The solution is found on almost every male reptile today. 380 00:35:34,880 --> 00:35:38,120 It begins to grow around the tenth day of life. 381 00:35:39,960 --> 00:35:43,120 A tiny bud, like an extra limb. 382 00:35:46,320 --> 00:35:49,520 It's a penis. 383 00:35:54,680 --> 00:35:59,240 Reptiles were amongst the first animals to get penises... 384 00:36:00,240 --> 00:36:02,760 ..but they certainly weren't the last. 385 00:36:07,720 --> 00:36:13,800 The blue whale has the largest, averaging 2.5 metres. 386 00:36:15,680 --> 00:36:20,160 The gorilla has one of the smallest, compared to its body size. 387 00:36:22,440 --> 00:36:25,520 Duck penises are shaped like corkscrews... 388 00:36:26,840 --> 00:36:30,520 ..and cats' are covered in barbs. 389 00:36:33,280 --> 00:36:37,040 Penises are as diverse as their owners. 390 00:36:40,400 --> 00:36:45,800 Now, despite what some people say, penises are limited in size, 391 00:36:45,800 --> 00:36:47,480 even for blue whales. 392 00:36:47,480 --> 00:36:50,280 So, therefore for the males to deliver the sperm where 393 00:36:50,280 --> 00:36:53,680 they need to, they need to get close to the females. 394 00:36:53,680 --> 00:36:55,640 They need to mate... 395 00:36:55,640 --> 00:36:58,960 Bonking, shagging, making love... 396 00:36:58,960 --> 00:37:02,000 The terminology that we use in scientific parlance is 397 00:37:02,000 --> 00:37:06,640 copulation and the reptiles weren't the first to get at it. 398 00:37:06,640 --> 00:37:09,720 Some ancient fish had been doing it for years, 399 00:37:09,720 --> 00:37:15,600 but when it came to life on land, sex as we know it had been invented. 400 00:37:21,680 --> 00:37:24,360 With their sophisticated eggs... 401 00:37:26,120 --> 00:37:28,680 ..and a new way to fertilise them... 402 00:37:30,200 --> 00:37:33,880 ..the reptiles went forth and multiplied. 403 00:37:44,520 --> 00:37:49,640 Their fossilised remains have been found in abundance. 404 00:37:58,200 --> 00:38:01,280 But world domination wasn't the only 405 00:38:01,280 --> 00:38:04,120 consequence of their reproductive success. 406 00:38:09,000 --> 00:38:11,960 The egg, the penis, copulation... 407 00:38:11,960 --> 00:38:16,040 All of these adaptations helped with the mechanics of sex, 408 00:38:16,040 --> 00:38:19,400 but what was to happen next was altogether different. 409 00:38:19,400 --> 00:38:23,760 You see, copulation didn't only change the way that animals looked. 410 00:38:23,760 --> 00:38:26,520 It changed the way they behaved, 411 00:38:26,520 --> 00:38:29,800 and the consequences of that were extraordinary. 412 00:38:38,120 --> 00:38:42,400 Around 100 million years after the first reptiles emerged... 413 00:38:48,160 --> 00:38:53,080 ..some of them have evolved into the most legendary creatures to 414 00:38:53,080 --> 00:38:54,880 have ever walked the Earth. 415 00:38:59,040 --> 00:39:01,760 This is Coelophysis, 416 00:39:01,760 --> 00:39:04,040 one of the first dinosaurs. 417 00:39:05,920 --> 00:39:11,200 Just like his ancient ancestors, he has strong legs for walking on land. 418 00:39:14,880 --> 00:39:19,920 But like all early dinosaurs, he walks on two instead of four. 419 00:39:21,960 --> 00:39:28,520 Bigger strides allow him to cover more distance, which is handy, 420 00:39:28,520 --> 00:39:31,720 because this young male is looking for a mate. 421 00:39:35,440 --> 00:39:38,680 There are plenty of females around. 422 00:39:38,680 --> 00:39:42,080 The tricky part is getting their attention. 423 00:39:48,280 --> 00:39:51,280 So how do you impress a female? 424 00:39:51,280 --> 00:39:53,480 I'm probably not the best person to answer that, 425 00:39:53,480 --> 00:39:55,600 I've been struggling all of my life, 426 00:39:55,600 --> 00:39:58,360 but I reckon this guy's in with a chance. 427 00:39:58,360 --> 00:40:04,040 What a magnificent animal, so handsome, honestly! 428 00:40:04,040 --> 00:40:08,440 This is a Nyala, a Southern African antelope, 429 00:40:08,440 --> 00:40:12,920 and this is a mature male, and he's very, very impressive, 430 00:40:12,920 --> 00:40:15,800 certainly from that female's point of view. 431 00:40:18,800 --> 00:40:20,680 OK, he doesn't have a sports car. 432 00:40:20,680 --> 00:40:22,880 Doesn't need it, he's got these beautiful curled, 433 00:40:22,880 --> 00:40:24,560 yellow-tipped horns. 434 00:40:26,120 --> 00:40:27,840 Doesn't live in a mansion. 435 00:40:27,840 --> 00:40:29,320 Doesn't need that either. 436 00:40:29,320 --> 00:40:31,720 He's got those broad, powerful flanks. 437 00:40:33,520 --> 00:40:36,960 And what's more, it's not just those characteristics. 438 00:40:36,960 --> 00:40:41,880 It's the fact that he's lived long enough to be able to grow them. 439 00:40:41,880 --> 00:40:45,200 I mean, imagine if this guy had been born short-sighted or with a limp. 440 00:40:45,200 --> 00:40:46,920 He would never have survived. 441 00:40:49,560 --> 00:40:55,440 His good looks are visible signs that he's fit and healthy, 442 00:40:55,440 --> 00:40:59,440 and ultimately, that's what the females are looking for. 443 00:41:01,040 --> 00:41:05,480 Getting pregnant, developing your youngster, giving birth, 444 00:41:05,480 --> 00:41:06,960 then looking after it... 445 00:41:06,960 --> 00:41:12,040 Those females can't afford to bank on a weedy male. 446 00:41:12,040 --> 00:41:16,400 They want the genes from the real deal, like this guy. 447 00:41:23,800 --> 00:41:27,240 When it comes to reproduction, it tends to be the biggest, 448 00:41:27,240 --> 00:41:29,720 hairiest males that succeed. 449 00:41:32,680 --> 00:41:37,640 Their genes get passed down, making future generations even bigger 450 00:41:37,640 --> 00:41:39,680 and hairier than the last... 451 00:41:41,680 --> 00:41:45,440 ..which is how you end up with exaggerated physical 452 00:41:45,440 --> 00:41:47,000 traits like this. 453 00:41:48,080 --> 00:41:52,040 But let's be very clear here, these physical 454 00:41:52,040 --> 00:41:57,520 characteristics are not necessarily directly related to survival. 455 00:41:57,520 --> 00:42:02,040 What they're about is finding a mate, attracting that mate 456 00:42:02,040 --> 00:42:04,440 and then successfully reproducing. 457 00:42:04,440 --> 00:42:09,640 Evolution is not always about survival of the fittest. 458 00:42:09,640 --> 00:42:14,840 It's critically about getting your genes into the next generation, 459 00:42:14,840 --> 00:42:19,040 and that was as profoundly important to the dinosaurs 460 00:42:19,040 --> 00:42:21,240 as it is to these Nyala. 461 00:42:26,560 --> 00:42:29,520 For Coelophysis, just like the Nyala, 462 00:42:29,520 --> 00:42:33,240 good looks are a sign that the male is in good condition. 463 00:42:36,120 --> 00:42:39,240 And just look at that attractive fuzz. 464 00:42:43,320 --> 00:42:48,040 But what's a male to do if no-one seems to notice him? 465 00:42:51,280 --> 00:42:55,880 Scientists suspect that some dinosaurs did what many 466 00:42:55,880 --> 00:42:57,600 animals still do today. 467 00:43:03,480 --> 00:43:05,840 They show off. 468 00:43:05,840 --> 00:43:07,800 It starts with head bobbing... 469 00:43:10,160 --> 00:43:11,720 ..followed by twirls... 470 00:43:14,200 --> 00:43:18,760 ..but to really impress her, he has one final trick. 471 00:43:27,920 --> 00:43:29,880 It's irresistible. 472 00:43:36,480 --> 00:43:40,880 His offspring will inherit his attractive fuzz, 473 00:43:40,880 --> 00:43:43,920 and go on to have fuzzy offspring of their own... 474 00:43:46,560 --> 00:43:50,600 ..becoming part of an extraordinary evolutionary transformation. 475 00:43:52,520 --> 00:43:59,280 Over time, fuzzy strands get longer, and wider, and split into 476 00:43:59,280 --> 00:44:05,880 multiple filaments, making an even bigger surface area for display. 477 00:44:11,280 --> 00:44:15,960 Until eventually, after tens of millions of years 478 00:44:15,960 --> 00:44:17,880 and countless generations... 479 00:44:19,080 --> 00:44:23,640 ..those fuzzy strands are so exaggerated... 480 00:44:25,000 --> 00:44:27,680 ..they've become something new... 481 00:44:36,400 --> 00:44:37,480 ..feathers. 482 00:44:41,400 --> 00:44:45,600 When the first fossilised feather was found, scientists were 483 00:44:45,600 --> 00:44:49,120 struck by its similarity to the feathers of modern birds. 484 00:44:50,240 --> 00:44:55,800 But this feather is 150 million years old, 485 00:44:55,800 --> 00:45:00,600 placing it firmly in the era of the dinosaurs. 486 00:45:04,400 --> 00:45:07,760 We don't know for certain what drove their evolution. 487 00:45:09,680 --> 00:45:14,000 Insulation and camouflage may have played a role. 488 00:45:14,000 --> 00:45:17,560 But we are now in little doubt 489 00:45:17,560 --> 00:45:21,920 that some dinosaurs had feathers. 490 00:45:25,640 --> 00:45:31,160 And many scientists believe it was the need to attract a mate 491 00:45:31,160 --> 00:45:37,600 that transformed dinosaurs from scaly reptiles into flamboyant, 492 00:45:37,600 --> 00:45:39,440 feathered creatures. 493 00:45:52,560 --> 00:45:58,120 This is the tail feather of a ring-necked pheasant. 494 00:45:58,120 --> 00:45:59,520 It's beautiful, isn't it? 495 00:45:59,520 --> 00:46:03,120 And whilst it still serves as a tail, as you can see, 496 00:46:03,120 --> 00:46:05,840 it's been given over to display. 497 00:46:05,840 --> 00:46:07,400 It's elongated. 498 00:46:07,400 --> 00:46:11,200 It's got this beautiful bronze colouring with all of these 499 00:46:11,200 --> 00:46:14,080 spots and when it comes to display feathers, of course, 500 00:46:14,080 --> 00:46:17,520 nothing beats the male peacock. 501 00:46:17,520 --> 00:46:20,400 Look at that with that very distinctive eye. 502 00:46:20,400 --> 00:46:22,720 But this is a typical feather. Look at it. 503 00:46:22,720 --> 00:46:26,400 It's light, it's flexible, it's durable. 504 00:46:26,400 --> 00:46:28,480 It's essentially repairable. 505 00:46:28,480 --> 00:46:31,840 If those barbs are pulled apart, it can be fixed here. 506 00:46:31,840 --> 00:46:35,800 But it's also symmetrical, very much 507 00:46:35,800 --> 00:46:40,720 like the feathers that we first saw when they appeared on the dinosaurs. 508 00:46:40,720 --> 00:46:42,840 But tens of millions of years later, 509 00:46:42,840 --> 00:46:46,240 something different cropped up in the fossil record. 510 00:46:46,240 --> 00:46:48,720 Something like this, 511 00:46:48,720 --> 00:46:52,760 and you can see this is different because it's asymmetrical. 512 00:46:52,760 --> 00:46:55,720 The quill or the rachis, if you like, here, 513 00:46:55,720 --> 00:46:58,560 is much closer to this side. 514 00:46:58,560 --> 00:47:01,560 Now, there is a theory which says that this was 515 00:47:01,560 --> 00:47:07,000 the result of a chance mutation, that this was a mistake. 516 00:47:07,000 --> 00:47:10,480 But if it was a mistake, it was a very fortunate one, 517 00:47:10,480 --> 00:47:15,280 because by shifting the rachis closer to one side, 518 00:47:15,280 --> 00:47:18,640 it means that when this feather is pushed through the air, 519 00:47:18,640 --> 00:47:22,640 it generates lift like an aircraft wing. 520 00:47:23,800 --> 00:47:28,960 The dinosaurs that were equipped with these could fly. 521 00:47:35,560 --> 00:47:40,600 Around 25 million years after the first feathers evolved, 522 00:47:40,600 --> 00:47:44,240 flying dinosaurs filled the skies. 523 00:47:47,440 --> 00:47:50,080 Today, we have another name for them... 524 00:47:52,480 --> 00:47:53,720 ..birds. 525 00:47:57,960 --> 00:48:00,680 For almost 100 million years, 526 00:48:00,680 --> 00:48:03,560 they thrived alongside their giant cousins... 527 00:48:07,040 --> 00:48:12,840 ..and they were there to witness one of our planet's darkest days. 528 00:48:12,840 --> 00:48:16,520 EXPLOSION 529 00:48:29,560 --> 00:48:33,280 When we say that all of the dinosaurs became extinct, 530 00:48:33,280 --> 00:48:35,040 it's not technically true, is it? 531 00:48:35,040 --> 00:48:39,520 Because those that had evolved into birds survived, 532 00:48:39,520 --> 00:48:41,760 and the ones that did best were the small ones, 533 00:48:41,760 --> 00:48:45,400 they could hide away, and also those with a very broad diet. 534 00:48:45,400 --> 00:48:50,640 But as the Earth began to recover, they had one other key asset, 535 00:48:50,640 --> 00:48:53,240 the amniotic egg. 536 00:48:53,240 --> 00:48:57,880 You see, with that embryo protected on the inside from the hostile world 537 00:48:57,880 --> 00:49:01,880 on the outside, they could continue to reproduce, generation after 538 00:49:01,880 --> 00:49:08,320 generation, to the extent that they didn't just survive, they thrived. 539 00:49:12,440 --> 00:49:16,160 The surviving birds were largely ground dwellers. 540 00:49:18,640 --> 00:49:21,360 Amongst them, the paleognaths, 541 00:49:21,360 --> 00:49:23,200 some of whom would never 542 00:49:23,200 --> 00:49:24,800 return to the skies. 543 00:49:26,640 --> 00:49:30,320 Instead, they became big and heavy, 544 00:49:30,320 --> 00:49:33,680 and better adapted for life on the ground. 545 00:49:33,680 --> 00:49:38,160 And to allow their chicks to hatch fully formed and ready to run... 546 00:49:39,560 --> 00:49:43,240 {\an8}..their eggs evolved truly gigantic sizes. 547 00:49:45,920 --> 00:49:47,440 {\an8}And one of this group... 548 00:49:51,280 --> 00:49:54,320 ..produces the largest eggs of all. 549 00:50:10,600 --> 00:50:14,520 Ostriches, our largest birds. 550 00:50:14,520 --> 00:50:18,240 And look at them standing there on those strong legs, 551 00:50:18,240 --> 00:50:23,560 with those sturdy bones that they inherited from lobed-fin fishes. 552 00:50:23,560 --> 00:50:26,840 And I can see those legs are covered in scales, 553 00:50:26,840 --> 00:50:31,440 so are their toes, signs of their reptilian ancestry. 554 00:50:33,080 --> 00:50:35,840 And their feathers are no longer used for flying, 555 00:50:35,840 --> 00:50:38,920 they're for display and brooding their young. 556 00:50:38,920 --> 00:50:43,120 And of course, they don't need to return to water to lay their eggs. 557 00:50:43,120 --> 00:50:48,480 These birds lay the largest amniotic egg on the planet. 558 00:50:52,960 --> 00:50:55,880 They lay them on the dry ground, 559 00:50:55,880 --> 00:50:58,920 just as their reptilian ancestors did. 560 00:51:01,960 --> 00:51:05,680 And safely cocooned inside each one, 561 00:51:05,680 --> 00:51:10,440 a new life begins floating in water, 562 00:51:10,440 --> 00:51:13,280 just as it's always done. 563 00:51:24,960 --> 00:51:29,440 These chicks are the next chapter of an extraordinary evolutionary 564 00:51:29,440 --> 00:51:34,280 story, four billion years long... 565 00:51:35,880 --> 00:51:38,280 ..that reveals how the ostrich 566 00:51:38,280 --> 00:51:41,400 and its enormous egg came to be. 567 00:51:45,360 --> 00:51:49,160 And although those ancestors are long gone, 568 00:51:49,160 --> 00:51:54,280 their legacy lives on, not just in the ostrich... 569 00:51:55,720 --> 00:51:57,160 ..but in all of us. 570 00:52:00,680 --> 00:52:05,160 Just like this chick, all of us started our lives in water, 571 00:52:05,160 --> 00:52:10,560 floating in that amniotic fluid in the womb, our very own private pool. 572 00:52:10,560 --> 00:52:15,200 And that's because we share an evolutionary history with this bird. 573 00:52:15,200 --> 00:52:19,120 We share ancient ancestors in a wonderful, 574 00:52:19,120 --> 00:52:24,360 unbroken chain of reproduction, stretching back billions of years. 575 00:52:24,360 --> 00:52:27,320 And of course, we're not just connected to ostriches. 576 00:52:27,320 --> 00:52:31,880 We're connected to all life on Earth. 577 00:52:31,880 --> 00:52:36,880 Everything that walks, flies, slithers, slimes and crawls, 578 00:52:36,880 --> 00:52:39,360 we're connected to it. 579 00:52:39,360 --> 00:52:42,160 And that's all down to reproduction. 580 00:52:42,160 --> 00:52:44,760 Over time, sexual reproduction has shaped us 581 00:52:44,760 --> 00:52:46,160 into different species... 582 00:52:48,000 --> 00:52:50,280 ..and sexual reproduction has one other 583 00:52:50,280 --> 00:52:54,080 absolutely extraordinary impact. 584 00:52:54,080 --> 00:52:57,400 It makes us all unique. 585 00:52:57,400 --> 00:53:01,360 Nothing exactly the same as me, you, 586 00:53:01,360 --> 00:53:05,080 or her has ever lived, 587 00:53:05,080 --> 00:53:11,640 or will ever live ever, in the entire history 588 00:53:11,640 --> 00:53:15,280 of this wonderful little blue planet we call home. 589 00:53:32,200 --> 00:53:33,400 Next time... 590 00:53:34,520 --> 00:53:36,600 {\an8}..how the bat evolved one of the most 591 00:53:36,600 --> 00:53:39,000 {\an8}insatiable appetites on the planet. 592 00:53:39,000 --> 00:53:40,800 Look at this! 593 00:53:40,800 --> 00:53:42,320 Truly spectacular! 594 00:53:44,760 --> 00:53:49,720 From a prehistoric anus that caused a mass extinction, 595 00:53:49,720 --> 00:53:54,240 to gaping mouths...that became jaws. 596 00:53:56,600 --> 00:54:00,840 And a surprising new way of finding food. 597 00:54:02,360 --> 00:54:07,320 This is the incredible story of one of nature's... Oh! 598 00:54:07,320 --> 00:54:09,840 ..most formidable feeders. 599 00:54:09,840 --> 00:54:11,040 Look at that! 600 00:54:15,720 --> 00:54:17,320 But first... 601 00:54:17,320 --> 00:54:21,080 ..how do we know birds are living dinosaurs? 602 00:54:23,200 --> 00:54:27,200 When most people look at a bird, they don't see a dinosaur. 603 00:54:29,680 --> 00:54:33,440 The first clue of the extraordinary evolutionary relationship 604 00:54:33,440 --> 00:54:37,760 between birds and dinosaurs came in the mid-19th century. 605 00:54:38,800 --> 00:54:45,120 The Jurassic species, Archaeopteryx, is an icon of evolution. 606 00:54:45,120 --> 00:54:49,080 Archaeopteryx certainly looked a little like a bird. 607 00:54:50,360 --> 00:54:51,880 It had feathered wings, 608 00:54:51,880 --> 00:54:55,320 and yet upon those wings were fully functional three-fingered 609 00:54:55,320 --> 00:55:00,160 hands with claws, which is reptile-like, and a long tail. 610 00:55:00,160 --> 00:55:03,720 It had a head like that of a bird, 611 00:55:03,720 --> 00:55:09,920 and yet, inside its mouth were rows of sharp teeth. 612 00:55:09,920 --> 00:55:13,680 So, Archaeopteryx wasn't just a bird. 613 00:55:14,840 --> 00:55:17,320 It was also a dinosaur. 614 00:55:19,800 --> 00:55:24,280 Other discoveries followed that left no room for doubt. 615 00:55:25,680 --> 00:55:30,120 Birds are a type of theropod dinosaur. 616 00:55:30,120 --> 00:55:33,960 We can see the evolutionary origins of many bird 617 00:55:33,960 --> 00:55:38,080 traits among their ancestors, the dinosaurs. 618 00:55:38,080 --> 00:55:43,040 Things like a beak, warm bloodedness, feathers, a wishbone. 619 00:55:43,040 --> 00:55:46,080 Tyrannosaurus rex itself has a wishbone. 620 00:55:46,080 --> 00:55:49,960 But one key question remains. 621 00:55:49,960 --> 00:55:53,560 What helped birds survive when all of their dinosaurian 622 00:55:53,560 --> 00:55:56,560 relatives went extinct, for me is one of the most fascinating 623 00:55:56,560 --> 00:55:59,320 questions in all of evolutionary biology. 624 00:56:02,520 --> 00:56:06,000 A question that could have remained unanswered 625 00:56:06,000 --> 00:56:08,600 if it wasn't for a chance find. 626 00:56:09,680 --> 00:56:14,240 The first time I saw this fossil, I was not very enthusiastic. 627 00:56:14,240 --> 00:56:17,680 It's basically just a block of limestone with a couple 628 00:56:17,680 --> 00:56:20,120 broken bones poking out from it. 629 00:56:20,120 --> 00:56:23,560 But we decided to take a closer look at it anyway. 630 00:56:23,560 --> 00:56:28,040 A CT scanner revealed what was hidden inside. 631 00:56:29,600 --> 00:56:34,520 When I first saw that skull on the computer screen, it took 632 00:56:34,520 --> 00:56:39,560 a second of silence, and then I realised immediately that this 633 00:56:39,560 --> 00:56:45,200 was one of the most important fossil bird specimens ever discovered. 634 00:56:45,200 --> 00:56:48,680 Daniel had stumbled across the oldest fossil of what 635 00:56:48,680 --> 00:56:51,520 we would now recognise as a modern bird. 636 00:56:51,520 --> 00:56:57,720 And it lived alongside dinosaurs just before the asteroid impact. 637 00:56:57,720 --> 00:57:00,680 It is toothless like modern birds. 638 00:57:00,680 --> 00:57:04,720 Its beak looks quite a bit like a small chicken bill, 639 00:57:04,720 --> 00:57:05,960 and that's interesting. 640 00:57:05,960 --> 00:57:10,400 It suggests to us that this animal was probably a generalist feeder. 641 00:57:10,400 --> 00:57:12,440 That is to say it wouldn't have been very picky, 642 00:57:12,440 --> 00:57:14,320 just like living chickens. 643 00:57:16,760 --> 00:57:20,840 Being flexible was critical to surviving the asteroid impact. 644 00:57:20,840 --> 00:57:24,040 One of the best ways to survive was to simply have the 645 00:57:24,040 --> 00:57:25,640 ability to eat anything. 646 00:57:26,720 --> 00:57:30,000 And that might have been one of the important features that 647 00:57:30,000 --> 00:57:33,640 helped birds like this one survive the mass extinction event. 648 00:57:35,160 --> 00:57:39,760 These small chicken-like ancestors and a few other bird species 649 00:57:39,760 --> 00:57:44,000 would make sure that not all the dinosaurs were lost. 650 00:57:45,200 --> 00:57:47,000 When I see an ostrich, 651 00:57:47,000 --> 00:57:51,400 I see that the... The story of dinosaur evolution is not over. 652 00:57:52,600 --> 00:57:56,000 Today there are over 10,000 species of birds. 653 00:57:56,000 --> 00:58:00,440 In some ways, we are still living in the age of dinosaurs. 654 00:58:05,440 --> 00:58:08,840 Do you want to know how an elephant is related to a clownfish? 655 00:58:08,840 --> 00:58:13,400 Discover more in a poster from the Open University on the tree of life. 656 00:58:13,400 --> 00:58:17,560 To get your free copy, scan the QR code on screen, or ring... 657 00:58:20,960 --> 00:58:22,760 Or visit...