1 00:00:12,500 --> 00:00:14,420 Look at this! 2 00:00:16,020 --> 00:00:19,060 What an extraordinary place. 3 00:00:22,680 --> 00:00:26,900 These caves are home to a creature that is undeniably 4 00:00:26,900 --> 00:00:29,540 one of evolution's weirdest. 5 00:00:35,520 --> 00:00:38,740 Oh, my goodness, look at that. 6 00:00:38,740 --> 00:00:40,820 That is spectacular! 7 00:00:44,140 --> 00:00:47,740 The cave is caked in bats. 8 00:00:52,260 --> 00:00:57,980 Using ultrasonic clicks, they can navigate in darkness. 9 00:00:57,980 --> 00:01:02,140 And with elongated finger bones covered in a membrane of skin... 10 00:01:03,900 --> 00:01:07,300 ..bats are the only mammals that can fly. 11 00:01:14,540 --> 00:01:17,940 But there's something even weirder about them. 12 00:01:21,060 --> 00:01:23,980 Each evening, they begin swarming... 13 00:01:23,980 --> 00:01:26,980 Oh, my goodness me, look at that! 14 00:01:26,980 --> 00:01:30,580 ..driven by an impulse they just can't deny... 15 00:01:33,460 --> 00:01:38,140 ..an almost unrivalled need to feed. 16 00:02:03,180 --> 00:02:07,820 Flight is an enormously energetically expensive exercise, 17 00:02:07,820 --> 00:02:12,700 and as a consequence, these bats have a gargantuan appetite. 18 00:02:15,020 --> 00:02:17,500 Each one of them's going to need to find thousands 19 00:02:17,500 --> 00:02:21,300 of tiny insects tonight, eat half of its own body weight. 20 00:02:22,940 --> 00:02:27,380 A bit like me eating 70 pizzas in just a few hours! 21 00:02:27,380 --> 00:02:33,900 Their whole existence is governed by a drive to find food, 22 00:02:33,900 --> 00:02:34,940 and a lot of it. 23 00:02:44,340 --> 00:02:49,620 So, how did the bat become one of the hungriest animals on the planet? 24 00:02:51,540 --> 00:02:56,820 To answer that question, we must go back in time... 25 00:02:58,180 --> 00:03:01,700 ..way back in time, 26 00:03:01,700 --> 00:03:05,220 ..to meet a handful of ancient relatives of the bat... 27 00:03:09,980 --> 00:03:14,100 ..who, between them, hold the evolutionary secrets... 28 00:03:18,340 --> 00:03:21,140 ..to how the bat's giant appetite... 29 00:03:25,380 --> 00:03:26,820 ..came to be. 30 00:03:53,340 --> 00:03:58,540 Our story begins in the shallows of an ancient ocean... 31 00:04:04,020 --> 00:04:08,740 ..where today, a new life is emerging. 32 00:04:15,020 --> 00:04:18,780 This is a distant ancestor of the bat 33 00:04:18,780 --> 00:04:20,780 and all of us. 34 00:04:22,540 --> 00:04:25,620 Its home is an alien-looking ecosystem, 35 00:04:25,620 --> 00:04:28,300 known as the Ediacaran Garden... 36 00:04:30,260 --> 00:04:33,500 ..and its neighbours are some of the strangest animals 37 00:04:33,500 --> 00:04:35,180 to ever live on our planet. 38 00:04:41,460 --> 00:04:45,020 Now, I know it might not look like much, 39 00:04:45,020 --> 00:04:49,700 but this little creature is about to play a pivotal role 40 00:04:49,700 --> 00:04:51,660 in the story of life on Earth... 41 00:04:54,580 --> 00:04:59,460 ..one that would change eating forever. 42 00:05:05,580 --> 00:05:10,580 Now, the Ediacaran is one of the most enigmatic periods 43 00:05:10,580 --> 00:05:12,300 in our Earth's history, 44 00:05:12,300 --> 00:05:16,260 not least because it's the first time that we find fossils 45 00:05:16,260 --> 00:05:20,180 of large, complex animals in the geological record, 46 00:05:20,180 --> 00:05:23,700 and I've got some casts of some of those in here. 47 00:05:24,740 --> 00:05:27,180 Just look at this. 48 00:05:27,180 --> 00:05:29,180 That's pretty good, isn't it? 49 00:05:29,180 --> 00:05:30,900 This is Charnia. 50 00:05:33,660 --> 00:05:37,140 I know it looks a little bit like a plant, perhaps like a fern, 51 00:05:37,140 --> 00:05:40,740 but scientists can tell that at least some of these specimens 52 00:05:40,740 --> 00:05:44,140 were living in depths of water where plants couldn't prosper, 53 00:05:44,140 --> 00:05:46,460 so we think that it was an animal. 54 00:05:46,460 --> 00:05:51,380 Now, take a look at Dickinsonia. 55 00:05:51,380 --> 00:05:53,900 Now, that is special. 56 00:05:53,900 --> 00:05:57,100 That is a beautiful fossil. 57 00:06:05,220 --> 00:06:08,540 550 million years ago, 58 00:06:08,540 --> 00:06:12,820 these bizarre animals are thriving, 59 00:06:12,820 --> 00:06:15,420 because they have plenty to eat. 60 00:06:18,540 --> 00:06:20,220 Why was that? 61 00:06:20,220 --> 00:06:23,900 Well, I can show you with a third fossil. 62 00:06:25,020 --> 00:06:26,500 And I know what you're thinking - 63 00:06:26,500 --> 00:06:28,820 "Well, that's not very special at all. 64 00:06:28,820 --> 00:06:31,340 "That just looks like some ripples on the beach." 65 00:06:31,340 --> 00:06:33,180 But you've got to look more closely. 66 00:06:34,580 --> 00:06:36,740 These are traces of millions, 67 00:06:36,740 --> 00:06:40,740 billions, trillions of tiny microbes. 68 00:06:46,980 --> 00:06:51,100 These microscopic organisms are the secret ingredient 69 00:06:51,100 --> 00:06:53,020 of the Ediacaran Garden. 70 00:06:55,220 --> 00:06:59,500 So numerous, they form a nutritious green mat, 71 00:06:59,500 --> 00:07:01,380 several centimetres deep, 72 00:07:01,380 --> 00:07:04,460 that carpets the seabed in every direction. 73 00:07:08,900 --> 00:07:11,060 For the animals that live here, 74 00:07:11,060 --> 00:07:14,260 the floor is literally made of food. 75 00:07:17,820 --> 00:07:24,660 A 24-hour, all-you-can-eat buffet means no-one goes hungry here, 76 00:07:24,660 --> 00:07:26,460 including, of course... 77 00:07:27,860 --> 00:07:29,820 ..the bat's ancestor. 78 00:07:35,860 --> 00:07:40,380 Officially, its name is the Urbilaterian. 79 00:07:45,340 --> 00:07:48,940 It spends its days leisurely grazing, 80 00:07:48,940 --> 00:07:52,220 hoovering up microbial mat into its mouth... 81 00:07:53,460 --> 00:07:59,060 ..digesting and then, a while later, regurgitating the leftovers. 82 00:08:01,180 --> 00:08:03,260 Not terribly pleasant! 83 00:08:04,420 --> 00:08:10,820 And the evidence we have for all of this comes not from a fossil, 84 00:08:10,820 --> 00:08:13,300 but from a creature alive today. 85 00:08:21,940 --> 00:08:26,820 This blobby animal is called an acoel. 86 00:08:26,820 --> 00:08:28,180 It's a marine organism. 87 00:08:28,180 --> 00:08:30,660 They normally measure only a few millimetres in length, 88 00:08:30,660 --> 00:08:32,780 and you can find them all over the world. 89 00:08:32,780 --> 00:08:36,780 This particular species is called Hofstenia miamia, 90 00:08:36,780 --> 00:08:40,860 and it's a favourite of scientists that study early life. 91 00:08:40,860 --> 00:08:45,100 You see, acoels are what we call basal animals. 92 00:08:45,100 --> 00:08:46,300 A long time ago, 93 00:08:46,300 --> 00:08:49,540 they went down a certain evolutionary road different than 94 00:08:49,540 --> 00:08:53,060 other animals, and they've retained some ancient characteristics. 95 00:08:55,180 --> 00:09:00,420 Acoels have a mouth, opening into a very basic gut, 96 00:09:00,420 --> 00:09:02,420 shaped a bit like a sack. 97 00:09:07,620 --> 00:09:12,660 And we think that this kind of gut was common in the Ediacaran. 98 00:09:17,780 --> 00:09:21,220 So, for the Urbilaterian, 99 00:09:21,220 --> 00:09:23,900 the simplest route for waste to come out 100 00:09:23,900 --> 00:09:26,780 is the same way the food came in. 101 00:09:28,900 --> 00:09:33,060 But this way of feeding was about to get an upgrade. 102 00:09:35,900 --> 00:09:38,100 Compared to the rest of its kind, 103 00:09:38,100 --> 00:09:42,780 this individual has a genetic difference, 104 00:09:42,780 --> 00:09:44,100 a mutation... 105 00:09:46,100 --> 00:09:52,140 ..that almost imperceptibly lengthens its body. 106 00:09:52,140 --> 00:09:56,100 A difference so trivial, it doesn't cause it any harm... 107 00:09:58,420 --> 00:10:01,740 ..but, when passed on, will change the destiny 108 00:10:01,740 --> 00:10:04,180 of a tiny reproductive pore. 109 00:10:12,020 --> 00:10:19,140 Over many generations, subsequent mutations lengthen the body further, 110 00:10:19,140 --> 00:10:25,220 driving the pore and the gut closer and closer together, until... 111 00:10:27,860 --> 00:10:29,700 ..they connect... 112 00:10:35,060 --> 00:10:38,060 ..forming a continuous tube through its body... 113 00:10:42,180 --> 00:10:46,260 ..a tube that changes everything. 114 00:10:48,100 --> 00:10:53,220 This new animal was, to all intents and purposes, a worm. 115 00:10:53,220 --> 00:10:56,580 You see, unlike the simple creature that came before it, 116 00:10:56,580 --> 00:10:59,020 it had a new body part. 117 00:10:59,020 --> 00:11:02,900 Aside from a mouth to take food in - 118 00:11:02,900 --> 00:11:05,660 just like you, just like me, 119 00:11:05,660 --> 00:11:08,780 just like everything that walks, flies and slithers - 120 00:11:08,780 --> 00:11:12,260 it had another hole to excrete the waste. 121 00:11:12,260 --> 00:11:14,260 It had a bottom. 122 00:11:14,260 --> 00:11:15,500 It had a bum! 123 00:11:15,500 --> 00:11:19,780 Technically speaking, it had an anus. 124 00:11:19,780 --> 00:11:21,180 Now, I know what you're thinking. 125 00:11:21,180 --> 00:11:24,700 If you're running through a list of evolution's greatest innovations, 126 00:11:24,700 --> 00:11:27,980 the anus is probably not scoring near the top of it. 127 00:11:27,980 --> 00:11:31,420 But then think about the alternative, 128 00:11:31,420 --> 00:11:35,780 and the advantages become immediately clear. 129 00:11:35,780 --> 00:11:41,260 I mean, imagine that you have a lovely lunch and that you digest it, 130 00:11:41,260 --> 00:11:44,980 but before you can have your dinner, you've got to throw it up. 131 00:11:44,980 --> 00:11:46,660 See what I mean? 132 00:11:46,660 --> 00:11:48,980 The anus was a breakthrough. 133 00:11:54,940 --> 00:12:01,220 With a mouth leading to a gut that goes all the way through its body, 134 00:12:01,220 --> 00:12:07,020 this new worm can do something that no animal has ever done before. 135 00:12:14,260 --> 00:12:16,100 It can poo! 136 00:12:18,500 --> 00:12:21,020 And this is a superpower! 137 00:12:22,540 --> 00:12:26,340 You see, it means the worm can feed continually... 138 00:12:28,380 --> 00:12:31,660 ..eating more than any animal that came before. 139 00:12:36,060 --> 00:12:38,060 In their quest for food, 140 00:12:38,060 --> 00:12:41,820 the ravenous worms burrow into the microbial mat, 141 00:12:41,820 --> 00:12:44,180 devouring it and churning it up... 142 00:12:46,740 --> 00:12:50,700 ..disrupting an ecosystem that had dominated the Earth 143 00:12:50,700 --> 00:12:52,860 since life's inception. 144 00:13:01,780 --> 00:13:04,340 And as the microbial mat declines... 145 00:13:05,740 --> 00:13:11,140 ..almost all of the strange animals that rely on it for food die out. 146 00:13:14,540 --> 00:13:18,740 The evolution of the anus may well have led 147 00:13:18,740 --> 00:13:23,900 to the first mass extinction of animal life on Earth. 148 00:13:30,260 --> 00:13:34,020 But the legacy of the anus would prove to be more than just 149 00:13:34,020 --> 00:13:35,380 an extinction event. 150 00:13:37,100 --> 00:13:41,820 It helped animal life take on a bold new form. 151 00:13:46,540 --> 00:13:50,780 The sea anemone and the nudibranch, the sea slug, 152 00:13:50,780 --> 00:13:52,820 are two soft-bodied marine organisms. 153 00:13:52,820 --> 00:13:54,900 They look pretty similar. 154 00:13:54,900 --> 00:13:59,980 But the extraordinary thing is that I am more closely related 155 00:13:59,980 --> 00:14:04,340 to that nudibranch than it is to that anemone. 156 00:14:05,460 --> 00:14:07,420 So, why is that? 157 00:14:07,420 --> 00:14:11,340 Well, it's because the anemone doesn't have an anus. 158 00:14:12,940 --> 00:14:15,980 It's descended from a group of animals that found its own 159 00:14:15,980 --> 00:14:21,900 evolutionary path before the development of that through-gut. 160 00:14:21,900 --> 00:14:28,260 But the nudibranch, like myself, has a mouth, a through-gut and an anus. 161 00:14:30,740 --> 00:14:32,380 It can poo, 162 00:14:32,380 --> 00:14:37,220 and the ability to poo has a profound effect on our body plans. 163 00:14:40,100 --> 00:14:43,220 The anemone has a circular body plan... 164 00:14:45,380 --> 00:14:48,340 ..but the nudibranch is symmetrical down the middle. 165 00:14:51,340 --> 00:14:53,860 It has what we call bilateral symmetry... 166 00:14:56,260 --> 00:15:00,700 ..just like our shared ancestor, that ancient worm. 167 00:15:03,900 --> 00:15:07,500 And the through-gut unleashed the full potential 168 00:15:07,500 --> 00:15:09,940 of this bilateral body plan. 169 00:15:15,780 --> 00:15:19,860 Then you've got an animal with a mouth, the gut and an anus. 170 00:15:19,860 --> 00:15:22,020 Essentially, you've got a front and a back, 171 00:15:22,020 --> 00:15:26,940 and the front, where the mouth is, is the bit that wants to find food. 172 00:15:26,940 --> 00:15:28,460 So, think about it. 173 00:15:28,460 --> 00:15:31,620 That's the best place to put any sensory organs, 174 00:15:31,620 --> 00:15:34,260 like eyes to look for that food. 175 00:15:34,260 --> 00:15:37,620 And then if you've got the sensory organs there, that would be 176 00:15:37,620 --> 00:15:40,540 the best place to have the brain, so they could react quickly 177 00:15:40,540 --> 00:15:42,420 when they find that food. 178 00:15:42,420 --> 00:15:46,900 So then you've got a mouth, eyes and a brain in the same place. 179 00:15:46,900 --> 00:15:49,660 What you've got is a head. 180 00:15:49,660 --> 00:15:51,140 A head! 181 00:15:51,140 --> 00:15:56,820 And I absolutely love the fact that for life to evolve a head, 182 00:15:56,820 --> 00:16:00,540 it had to evolve an arse first! 183 00:16:00,540 --> 00:16:01,580 I love that! 184 00:16:05,900 --> 00:16:09,460 A head end and a tail end, 185 00:16:09,460 --> 00:16:11,700 joined by a through-gut, 186 00:16:11,700 --> 00:16:14,140 proved to be a winning formula... 187 00:16:32,180 --> 00:16:37,500 ..one that means, today, we see bilateral symmetry everywhere. 188 00:16:50,900 --> 00:16:56,940 99% of known animal species on the planet have this body plan... 189 00:17:06,740 --> 00:17:14,300 ..all of us descendants of that world-changing little worm. 190 00:17:21,740 --> 00:17:25,180 It is hard to understate what a revolutionary moment 191 00:17:25,180 --> 00:17:28,780 the evolution of the anus was. 192 00:17:28,780 --> 00:17:32,540 Microbial mats, which for three billion years had been 193 00:17:32,540 --> 00:17:36,740 the dominant ecosystem on Earth, all but disappeared. 194 00:17:36,740 --> 00:17:41,460 Today, we find them in environments which are inhospitable to animals - 195 00:17:41,460 --> 00:17:45,900 beneath the ice in Antarctica or in steaming-hot volcanic springs. 196 00:17:45,900 --> 00:17:47,220 And for animals, 197 00:17:47,220 --> 00:17:51,860 the development of the through-gut had far-reaching consequences. 198 00:17:51,860 --> 00:17:54,740 Its increased efficiency meant they could grow bigger, 199 00:17:54,740 --> 00:17:56,980 move more purposefully. 200 00:17:56,980 --> 00:18:01,140 And it cemented the bilaterally symmetrical body plan 201 00:18:01,140 --> 00:18:03,660 over other options. 202 00:18:03,660 --> 00:18:10,220 The drive to find food had changed the course of life on Earth, 203 00:18:10,220 --> 00:18:12,180 and it wouldn't be the last time. 204 00:18:13,660 --> 00:18:17,820 The worms unleash a new era of eating. 205 00:18:21,700 --> 00:18:24,820 Fuelled by the extra energy they're gathering... 206 00:18:26,340 --> 00:18:29,740 ..their descendants develop more complex bodies... 207 00:18:31,740 --> 00:18:34,860 ..and keener senses for finding food. 208 00:18:41,100 --> 00:18:44,660 Just 35 million years later, 209 00:18:44,660 --> 00:18:47,780 one of those descendants is a worm no more. 210 00:18:50,540 --> 00:18:53,620 We might even call it a fish. 211 00:19:01,540 --> 00:19:05,420 A small fish, living in a very big pond. 212 00:19:10,460 --> 00:19:16,660 The oceans of the Cambrian Period are dominated by giant arthropods - 213 00:19:16,660 --> 00:19:18,740 early cousins of insects. 214 00:19:23,540 --> 00:19:27,180 Among them, Earth's first top predators. 215 00:19:31,540 --> 00:19:36,100 And the secret to survival for this little fish 216 00:19:36,100 --> 00:19:39,340 comes down to its strange mouth. 217 00:19:42,740 --> 00:19:47,660 Now, take a look at this. It's the fossil of that primitive fish, 218 00:19:47,660 --> 00:19:50,860 about five centimetres long. It's called Metaspriggina. 219 00:19:50,860 --> 00:19:54,580 Just look at the detail that you can see here, 220 00:19:54,580 --> 00:19:57,180 particularly at the front of its head. 221 00:19:57,180 --> 00:20:00,220 These two black dots, those are its eyes. 222 00:20:00,220 --> 00:20:02,340 And under scrutiny, scientists have discovered 223 00:20:02,340 --> 00:20:06,620 that they are pointing upwards, so it could be that this little fish 224 00:20:06,620 --> 00:20:10,580 was swimming along on the bottom, using those eyes to look up into 225 00:20:10,580 --> 00:20:12,940 the water column for any potential predators - 226 00:20:12,940 --> 00:20:14,820 perhaps those giant arthropods - 227 00:20:14,820 --> 00:20:19,340 that might have made a tasty snack out of a tiny fish like this. 228 00:20:20,740 --> 00:20:23,060 There's another photograph here. 229 00:20:23,060 --> 00:20:25,860 This time, we're looking down on it, 230 00:20:25,860 --> 00:20:32,380 and what appear to be ribs here, we think are not ribs but gill arches - 231 00:20:32,380 --> 00:20:34,940 structures which support gills. 232 00:20:36,700 --> 00:20:38,100 As it swims, 233 00:20:38,100 --> 00:20:42,860 a constant stream of water flows into the fish's open mouth. 234 00:20:50,340 --> 00:20:53,220 This is how Metaspriggina breathes - 235 00:20:53,220 --> 00:20:56,620 passing water over its gills, 236 00:20:56,620 --> 00:20:59,460 supported by those gill arches. 237 00:21:00,780 --> 00:21:04,140 But this mouth is multipurpose. 238 00:21:04,140 --> 00:21:07,380 Something else is extracted at the same time. 239 00:21:08,660 --> 00:21:11,820 Metaspriggina is a filter feeder. 240 00:21:13,660 --> 00:21:19,820 And getting both oxygen and food into their bodies fast 241 00:21:19,820 --> 00:21:24,380 is critical if they want to survive these perilous waters. 242 00:21:36,540 --> 00:21:41,460 This is survival of the fittest in action, 243 00:21:41,460 --> 00:21:43,060 and it means this fish, 244 00:21:43,060 --> 00:21:47,860 its strange mouth and those gill arches hidden deep within 245 00:21:47,860 --> 00:21:52,660 are already on a path that will shake up the world of eating 246 00:21:52,660 --> 00:21:54,820 all over again. 247 00:21:57,460 --> 00:22:01,420 Scientists have found that Metaspriggina's front gill arches 248 00:22:01,420 --> 00:22:03,780 are actually thicker 249 00:22:03,780 --> 00:22:09,060 and appear to lack oxygen-absorbing gill filaments, 250 00:22:09,060 --> 00:22:14,140 a tantalising hint that they may have jettisoned their old role 251 00:22:14,140 --> 00:22:20,340 for a new one - keeping the fish's gaping mouth wide open. 252 00:22:24,580 --> 00:22:29,300 Because thick gill arches lead to a wider mouth, 253 00:22:29,300 --> 00:22:33,060 more food and oxygen and more energy to escape... 254 00:22:36,740 --> 00:22:39,700 ..it's an advantage that's passed on. 255 00:22:49,820 --> 00:22:53,260 Across countless generations, 256 00:22:53,260 --> 00:22:57,100 the gill arches continue to thicken and strengthen. 257 00:23:03,900 --> 00:23:05,740 New structures erupt... 258 00:23:09,660 --> 00:23:12,820 ..and after tens of millions of years... 259 00:23:13,980 --> 00:23:16,100 ..what was once a gill arch... 260 00:23:19,060 --> 00:23:22,820 ..becomes a revolutionary new body part... 261 00:23:24,300 --> 00:23:26,180 ..which means this fish... 262 00:23:28,500 --> 00:23:30,180 ..can bite! 263 00:23:51,860 --> 00:23:55,300 Many body parts have been lost to the passage of time. 264 00:23:55,300 --> 00:23:57,860 Whales and dolphins have lost limbs, 265 00:23:57,860 --> 00:24:01,260 and fish that have been marooned in pitch-dark cave systems 266 00:24:01,260 --> 00:24:02,540 have lost their eyes. 267 00:24:02,540 --> 00:24:08,660 Even the not-so-humble anus has disappeared on multiple occasions. 268 00:24:08,660 --> 00:24:11,100 But jaws, never. 269 00:24:11,100 --> 00:24:13,180 Jaws are simply too useful. 270 00:24:15,740 --> 00:24:20,180 Look, jaws didn't just change how animals ate, 271 00:24:20,180 --> 00:24:22,180 but where they ate. 272 00:24:24,740 --> 00:24:28,140 This little creature is a mud skipper, 273 00:24:28,140 --> 00:24:30,420 one of around 25 species of fish 274 00:24:30,420 --> 00:24:31,700 that you can find all over the world, 275 00:24:31,700 --> 00:24:36,340 typically in intertidal mangrove swamps like this. 276 00:24:36,340 --> 00:24:38,500 Now, what's extraordinary about them 277 00:24:38,500 --> 00:24:42,180 is the amount of time that they can spend out of the water... 278 00:24:43,980 --> 00:24:47,540 ..some of them 90% of their lives, and they're able to do that 279 00:24:47,540 --> 00:24:50,180 because they've got some remarkable adaptations. 280 00:24:52,540 --> 00:24:57,860 Firstly, this little fish is breathing through its skin. 281 00:24:57,860 --> 00:25:01,020 It also has jointed pectoral fins, 282 00:25:01,020 --> 00:25:04,660 which means that it can skip across the surface of the mud, 283 00:25:04,660 --> 00:25:07,340 almost as if it were walking. 284 00:25:09,500 --> 00:25:13,260 So there are some behavioural comparisons there that we can make 285 00:25:13,260 --> 00:25:17,380 with those fish that struggled out of water, onto land, 286 00:25:17,380 --> 00:25:20,460 375 million years ago, 287 00:25:20,460 --> 00:25:23,300 to begin an amphibious lifestyle. 288 00:25:26,060 --> 00:25:27,580 But here's one thing. 289 00:25:27,580 --> 00:25:29,380 They couldn't have done it without jaws. 290 00:25:29,380 --> 00:25:30,860 Just think about it. 291 00:25:30,860 --> 00:25:35,540 If these and those fish were dependent upon filter feeding, 292 00:25:35,540 --> 00:25:40,380 dependent upon that water carrying morsels of food into their mouth, 293 00:25:40,380 --> 00:25:44,540 that would mean that no matter how much time they could spend on land, 294 00:25:44,540 --> 00:25:48,060 they would have to return to water to feed. 295 00:25:48,060 --> 00:25:51,780 The difference is they've got jaws - they can bite. 296 00:25:51,780 --> 00:25:56,260 And you can bite just as well out of water as you can in the water. 297 00:26:09,340 --> 00:26:12,300 Thanks in part to the evolution of the jaw, 298 00:26:12,300 --> 00:26:16,020 fish were no longer reliant on feeding in water... 299 00:26:17,940 --> 00:26:21,700 ..opening up a new world of possibilities. 300 00:26:25,020 --> 00:26:27,100 Now, I know it's going to sound absurd... 301 00:26:30,780 --> 00:26:33,860 ..but from an evolutionary perspective at least, 302 00:26:33,860 --> 00:26:38,340 these elephants are - wait for it - jawed fish. 303 00:26:38,340 --> 00:26:42,300 Of course, they're highly modified jawed fish, but fish nevertheless. 304 00:26:42,300 --> 00:26:44,820 But then so am I, so are you, 305 00:26:44,820 --> 00:26:49,460 so is every other terrestrial animal that's got a backbone and a jaw. 306 00:26:52,220 --> 00:26:53,820 So, here in Borneo, 307 00:26:53,820 --> 00:26:58,500 that means 300 species of reptile, 150 amphibians, 650 birds 308 00:26:58,500 --> 00:27:01,300 and 250 species of mammal, 309 00:27:01,300 --> 00:27:04,740 all of whom are descended from those fish 310 00:27:04,740 --> 00:27:07,140 that made that leap out of the water. 311 00:27:09,500 --> 00:27:11,060 ELEPHANT GRUNTS 312 00:27:17,900 --> 00:27:22,580 Globally, there are at least 30,000 species of vertebrates 313 00:27:22,580 --> 00:27:27,060 living on land, with a dizzying array of jaws, 314 00:27:27,060 --> 00:27:29,380 adapted to many different ways of feeding. 315 00:27:30,500 --> 00:27:35,460 Some are lined with teeth, others have become beaks. 316 00:27:37,220 --> 00:27:39,900 And some open so far, 317 00:27:39,900 --> 00:27:44,980 their owners can swallow meals wider than their bodies. 318 00:27:50,660 --> 00:27:54,020 What began as a tiny Ediacaran creature... 319 00:27:56,340 --> 00:27:59,740 ..gave rise to a through-gut 320 00:27:59,740 --> 00:28:03,100 and a worm with an appetite that upended the world... 321 00:28:05,780 --> 00:28:08,500 ..and led to a fish 322 00:28:08,500 --> 00:28:11,620 with a jaw that could finally take a bite. 323 00:28:17,220 --> 00:28:19,860 From their aquatic origins, 324 00:28:19,860 --> 00:28:22,980 jawed animals spread to all corners of the globe... 325 00:28:27,580 --> 00:28:33,340 ..and diversify to exploit new sources of food. 326 00:28:40,980 --> 00:28:44,380 Until, 200 million years later, 327 00:28:44,380 --> 00:28:47,420 we find one of them on the move. 328 00:28:58,780 --> 00:29:01,060 This is Agilodocodon. 329 00:29:06,820 --> 00:29:09,140 It's a female, and she's tiny... 330 00:29:13,580 --> 00:29:15,540 ..the size of a shrew. 331 00:29:19,820 --> 00:29:24,620 With warm blood and fur, she's a primitive mammal 332 00:29:24,620 --> 00:29:28,540 who spends most of her time hunting insects in trees. 333 00:29:36,060 --> 00:29:40,540 But right now, it's not her own hunger she's concerned with... 334 00:29:52,460 --> 00:29:53,980 ..it's theirs. 335 00:30:03,340 --> 00:30:08,020 Mammals have a quirky advantage over many other types of animal. 336 00:30:08,020 --> 00:30:11,340 You see, we don't have to find food for our babies. 337 00:30:11,340 --> 00:30:14,340 We don't abandon them to find their own. 338 00:30:14,340 --> 00:30:21,180 We make it, and milk is the perfect food for a growing infant. 339 00:30:21,180 --> 00:30:24,900 And it's perfect, unlike so many other types of food, 340 00:30:24,900 --> 00:30:27,940 because evolution has driven it to be so. 341 00:30:34,500 --> 00:30:38,580 Of course, milk, made by mammary glands, 342 00:30:38,580 --> 00:30:41,060 has given us mammals our name. 343 00:30:43,540 --> 00:30:47,980 But the evolution of milk impacted more than just babies. 344 00:30:49,420 --> 00:30:53,140 It's changed how mammals feed at every age. 345 00:30:58,580 --> 00:31:01,220 I've got a couple of lovely skulls here. 346 00:31:01,220 --> 00:31:05,780 This is from a crocodile, and this one from an orangutan. 347 00:31:05,780 --> 00:31:09,260 Now, they're clearly very different in terms of their size and shape, 348 00:31:09,260 --> 00:31:11,540 but also their teeth. 349 00:31:11,540 --> 00:31:13,820 Let's take a look at the crocodile first. 350 00:31:13,820 --> 00:31:19,380 Its teeth are very simple, and they're pretty much all the same - 351 00:31:19,380 --> 00:31:24,460 cylindrical at the base, peg-like and sharp, ideal for grabbing 352 00:31:24,460 --> 00:31:26,660 and then gripping their prey. 353 00:31:26,660 --> 00:31:32,780 But, look, you can see that they don't fit together terribly well. 354 00:31:32,780 --> 00:31:36,180 There are large gaps in between them. 355 00:31:36,180 --> 00:31:40,820 Contrast that with the skull of the orangutan. 356 00:31:43,260 --> 00:31:45,180 Its teeth are not so simple. 357 00:31:45,180 --> 00:31:46,900 They come in a range of forms. 358 00:31:46,900 --> 00:31:49,100 You've got these at the front here. 359 00:31:49,100 --> 00:31:53,540 These are the incisors that are used for slicing and nibbling. 360 00:31:53,540 --> 00:31:56,820 And then you've got these very powerful canines 361 00:31:56,820 --> 00:31:59,220 for piercing and gripping. 362 00:31:59,220 --> 00:32:04,860 And lastly, when I fit the jaw on as it would sit in life, 363 00:32:04,860 --> 00:32:06,780 look at these teeth at the back here. 364 00:32:06,780 --> 00:32:10,780 They fit together almost perfectly. 365 00:32:10,780 --> 00:32:13,260 These are the molars, 366 00:32:13,260 --> 00:32:17,220 and one of the major reasons that molars have been able to evolve 367 00:32:17,220 --> 00:32:18,700 comes down to milk. 368 00:32:21,380 --> 00:32:23,500 The ancestors of mammals 369 00:32:23,500 --> 00:32:26,420 had simple, reptilian-like teeth 370 00:32:26,420 --> 00:32:27,820 that were replaced continually 371 00:32:27,820 --> 00:32:30,620 as the animals grew. 372 00:32:30,620 --> 00:32:33,460 But when they started to evolve milk, 373 00:32:33,460 --> 00:32:36,500 babies were no longer reliant on teeth to feed. 374 00:32:37,620 --> 00:32:41,300 Fewer sets were needed throughout life, 375 00:32:41,300 --> 00:32:45,620 so this allowed more complex teeth to evolve. 376 00:32:47,820 --> 00:32:49,580 In the mid Jurassic, 377 00:32:49,580 --> 00:32:53,340 it's thought that the young of species like Agilodocodon, 378 00:32:53,340 --> 00:32:56,180 now sustained entirely on milk, 379 00:32:56,180 --> 00:32:58,580 are born toothless. 380 00:33:06,180 --> 00:33:09,260 It's only because their adult molars don't emerge 381 00:33:09,260 --> 00:33:13,140 until their jaws are almost fully grown 382 00:33:13,140 --> 00:33:17,420 that they are some of the first to interlock perfectly. 383 00:33:30,980 --> 00:33:34,700 And this helps today's mammals do something 384 00:33:34,700 --> 00:33:37,620 that's surprisingly rare in the animal kingdom. 385 00:33:51,300 --> 00:33:55,860 Take a look at this beautiful orangutan here. 386 00:33:57,780 --> 00:34:01,020 A female with a nursing youngster. 387 00:34:02,500 --> 00:34:06,580 But put her beauty to one side and concentrate on what she's doing. 388 00:34:06,580 --> 00:34:08,580 She is chewing. 389 00:34:08,580 --> 00:34:10,260 We can chew. 390 00:34:12,140 --> 00:34:17,260 Those gentle movements of the lower jaw, 391 00:34:17,260 --> 00:34:20,420 those molars grinding up that fruit. 392 00:34:22,260 --> 00:34:25,140 Imagine you had to take that fruit into your kitchen 393 00:34:25,140 --> 00:34:28,300 and cut it up into chunks that you could swallow. 394 00:34:28,300 --> 00:34:30,500 You'd have to slice it, you'd have to dice it, 395 00:34:30,500 --> 00:34:32,700 and then you'd have to mash it. 396 00:34:32,700 --> 00:34:36,380 But she's doing all of that with consummate ease. 397 00:34:39,540 --> 00:34:45,220 Her teeth are highly efficient food-processing machines, 398 00:34:45,220 --> 00:34:48,100 and what they're trying to do is grind that food up 399 00:34:48,100 --> 00:34:50,100 to increase its surface area, 400 00:34:50,100 --> 00:34:52,460 so that when it reaches the stomach and the gut, 401 00:34:52,460 --> 00:34:56,660 the digestive juices can act upon it far more quickly. 402 00:34:56,660 --> 00:35:00,900 It massively speeds up the rate of digestion. 403 00:35:00,900 --> 00:35:03,180 I mean, contrast it with those crocodiles. 404 00:35:03,180 --> 00:35:05,380 They swallow their food whole, or in massive chunks, 405 00:35:05,380 --> 00:35:07,740 and it takes weeks to digest it. 406 00:35:09,220 --> 00:35:12,860 But me, you and the orangutan, 407 00:35:12,860 --> 00:35:17,180 we can have a meal and digest it in just a matter of hours. 408 00:35:41,540 --> 00:35:44,620 For primitive mammals like Agilodocodon... 409 00:35:49,260 --> 00:35:54,260 ..this ability to chew helps drive a surprising evolutionary change. 410 00:36:03,420 --> 00:36:05,580 Over generations, 411 00:36:05,580 --> 00:36:10,060 a lower jaw, made of several bones, is gradually reconfigured. 412 00:36:15,900 --> 00:36:17,540 One bone gets larger... 413 00:36:19,060 --> 00:36:21,220 ..whilst the others shrink... 414 00:36:24,060 --> 00:36:28,940 ..until a single, powerful lower jaw evolves. 415 00:36:33,900 --> 00:36:37,180 The old jawbones wither away, 416 00:36:37,180 --> 00:36:39,940 but not all are lost. 417 00:36:45,620 --> 00:36:49,220 These are the remnants of those jawbones. 418 00:36:49,220 --> 00:36:52,220 They're called the malleus and the incus, 419 00:36:52,220 --> 00:36:56,420 although you might know them as the hammer and the anvil. 420 00:36:57,740 --> 00:37:00,660 They're two of the smallest bones in our body, 421 00:37:00,660 --> 00:37:03,940 and they're disconnected from the rest of our skeleton. 422 00:37:03,940 --> 00:37:06,780 But the key thing is, when we were in the womb, 423 00:37:06,780 --> 00:37:12,580 they started off as part of our jaw and then migrated up to our ear, 424 00:37:12,580 --> 00:37:15,940 where they are joined by this bone, 425 00:37:15,940 --> 00:37:19,700 and this one is called the stapes, or the stirrup. 426 00:37:19,700 --> 00:37:24,940 And together, they connect our eardrum to our inner ear, 427 00:37:24,940 --> 00:37:27,940 greatly enhancing our capacity to hear, 428 00:37:27,940 --> 00:37:31,420 particularly a wider range of frequencies. 429 00:37:35,180 --> 00:37:39,660 The evolution of the middle ear bones, known as the ossicles, 430 00:37:39,660 --> 00:37:45,340 transformed hearing for modern mammals, meaning that today, 431 00:37:45,340 --> 00:37:50,020 mammals have some of the most sensitive hearing of all animals. 432 00:38:08,980 --> 00:38:14,940 It's remarkable to think that over 400 million years ago, 433 00:38:14,940 --> 00:38:20,620 these tiny bones were part of an ancient fish's gill arches. 434 00:38:20,620 --> 00:38:25,460 This is the power of evolution, right here in the palm of my hand. 435 00:38:25,460 --> 00:38:30,420 No designer was involved in making these bones, which are currently 436 00:38:30,420 --> 00:38:35,300 floating in your head, allowing you to hear what I'm saying. 437 00:38:35,300 --> 00:38:41,660 All that was needed was life's relentless drive to find food. 438 00:38:41,660 --> 00:38:44,340 That and quite a bit of time! 439 00:38:48,220 --> 00:38:51,980 And time, of course, keeps ticking... 440 00:38:57,540 --> 00:39:02,540 ..and mammals, now with acute hearing, keep evolving... 441 00:39:04,780 --> 00:39:07,300 ..for tens of millions of years... 442 00:39:13,140 --> 00:39:14,860 ..until, one morning... 443 00:39:16,340 --> 00:39:22,060 ..a little mammal picks up a sound it's never heard before... 444 00:39:24,540 --> 00:39:29,500 ..a sound that, once again, would change everything. 445 00:39:34,500 --> 00:39:36,940 By the time we get to the Cretaceous Period, 446 00:39:36,940 --> 00:39:40,620 when T-Rex was on the prowl, most of those traits that we consider 447 00:39:40,620 --> 00:39:44,140 to be typically mammalian are already there - 448 00:39:44,140 --> 00:39:50,220 warm-bloodedness, fur, complex teeth in powerful jaws and acute hearing. 449 00:39:50,220 --> 00:39:53,820 And that acute hearing meant that mammals had already conquered 450 00:39:53,820 --> 00:39:57,140 the night, and it was going to prove to be significant. 451 00:39:57,140 --> 00:40:01,180 You see, that classic myth that mammals at this time were living 452 00:40:01,180 --> 00:40:05,220 in the shadow of the dinosaurs, it may not have been like that. 453 00:40:05,220 --> 00:40:08,860 That hearing contributed to the fact that they could find more food. 454 00:40:08,860 --> 00:40:11,260 Those jaws could catch it and process it. 455 00:40:11,260 --> 00:40:12,660 They were getting more energy. 456 00:40:12,660 --> 00:40:15,580 They were able to build bigger bodies. 457 00:40:15,580 --> 00:40:18,820 In fact, some scientists think that those early mammals 458 00:40:18,820 --> 00:40:22,700 could have been well on the way to standing shoulder to shoulder 459 00:40:22,700 --> 00:40:25,300 with those giant reptiles. 460 00:40:25,300 --> 00:40:29,980 But, of course, as we know, that story was going to be cut short. 461 00:40:39,660 --> 00:40:41,620 The sound the mammal heard 462 00:40:41,620 --> 00:40:45,740 had its origins thousands of kilometres away... 463 00:40:47,540 --> 00:40:50,580 ..where, an hour or so earlier, 464 00:40:50,580 --> 00:40:53,660 a rock, 12km wide, 465 00:40:53,660 --> 00:40:56,380 had plunged into the Gulf of Mexico. 466 00:40:58,980 --> 00:41:03,500 In a moment, the world is changed irrevocably. 467 00:41:08,620 --> 00:41:12,300 The day that asteroid plummeted into the Gulf of Mexico 468 00:41:12,300 --> 00:41:16,380 was probably the worst single day for life since it arose 469 00:41:16,380 --> 00:41:21,660 around four billion years ago, because in that one chance moment, 470 00:41:21,660 --> 00:41:25,580 life's progress was stopped dead - quite literally - 471 00:41:25,580 --> 00:41:29,020 and millions of years of evolutionary tinkering 472 00:41:29,020 --> 00:41:31,420 were wiped out in an instant. 473 00:41:31,420 --> 00:41:34,180 And it was such a twist of fate. 474 00:41:34,180 --> 00:41:38,260 Had that asteroid impacted just 30 seconds later, 475 00:41:38,260 --> 00:41:40,700 the Earth would have spun on its axis. 476 00:41:40,700 --> 00:41:42,900 It would have smashed into much deeper water 477 00:41:42,900 --> 00:41:45,820 and caused far less devastation. 478 00:41:45,820 --> 00:41:49,260 You never know - those giant reptiles might not have died out. 479 00:41:49,260 --> 00:41:53,300 We might have had mammals, but not the mammal fauna that we've got now. 480 00:41:53,300 --> 00:41:57,420 There might have been no humans on Earth. 481 00:41:58,620 --> 00:42:02,780 Standing here in this oil palm plantation... 482 00:42:04,180 --> 00:42:06,780 ..I'll leave you to make of that what you will. 483 00:42:19,940 --> 00:42:23,980 And whatever happens, life will find a way. 484 00:42:39,500 --> 00:42:43,500 Although in the 15-year winter that follows the impact... 485 00:42:45,780 --> 00:42:50,540 ..three quarters of species are erased from the face of the Earth. 486 00:42:54,660 --> 00:42:58,340 A tiny fraction of mammal species endure. 487 00:43:07,220 --> 00:43:10,660 We know this, of course, because I'm here, because you're here, 488 00:43:10,660 --> 00:43:14,940 because all the mammals we currently share our planet with are here. 489 00:43:14,940 --> 00:43:19,300 But what do we know about our shared ancient ancestors, 490 00:43:19,300 --> 00:43:22,100 those creatures that survived the storm of all storms, 491 00:43:22,100 --> 00:43:24,460 the almost endless night? 492 00:43:24,460 --> 00:43:27,700 Well, we think they were small, rodent-like animals - 493 00:43:27,700 --> 00:43:29,940 not a single species, but a group of them. 494 00:43:29,940 --> 00:43:32,660 And they carried those traits like complex teeth, 495 00:43:32,660 --> 00:43:35,540 which would have enabled them to eat a broad diet - 496 00:43:35,540 --> 00:43:39,060 everything from rotting vegetation to insects, 497 00:43:39,060 --> 00:43:43,180 which would have bounced back quite quickly after that near catastrophe. 498 00:43:43,180 --> 00:43:46,340 They might have also been burrowing animals, 499 00:43:46,340 --> 00:43:50,980 so they could get beneath the ground to avoid all of that climate chaos 500 00:43:50,980 --> 00:43:53,940 which was causing so many other species to become extinct. 501 00:44:05,060 --> 00:44:10,900 Just a few hundred thousand years after that apocalyptic day, 502 00:44:10,900 --> 00:44:14,540 we start to see the descendants of those surviving mammals 503 00:44:14,540 --> 00:44:15,940 in the fossil record. 504 00:44:22,700 --> 00:44:25,700 In a world vacated by dinosaurs, 505 00:44:25,700 --> 00:44:28,140 mammals rapidly diversified. 506 00:44:36,220 --> 00:44:39,260 Among them, a remarkable new group... 507 00:44:40,740 --> 00:44:44,700 ..that would use their acute mammalian hearing 508 00:44:44,700 --> 00:44:47,100 in a truly innovative way. 509 00:44:48,740 --> 00:44:53,300 This is a replica fossil of an approximately 510 00:44:53,300 --> 00:44:57,740 52-million-year-old creature called Icaronycteris. 511 00:44:57,740 --> 00:45:02,260 And you might be able to guess what type of animal it is. 512 00:45:02,260 --> 00:45:07,300 Firstly, look at its fingers here - very long and narrow, extended. 513 00:45:07,300 --> 00:45:10,380 I'll give you another clue by turning it up this way. 514 00:45:10,380 --> 00:45:14,860 Yes, those fingers have transformed into wings. 515 00:45:14,860 --> 00:45:17,380 This animal could fly. 516 00:45:17,380 --> 00:45:22,300 This is the fossil of a bat. 517 00:45:22,300 --> 00:45:26,860 Now, there's a lot more we need to learn about the evolution of bats. 518 00:45:26,860 --> 00:45:30,580 There's a big gap between that period when the asteroid hit 519 00:45:30,580 --> 00:45:34,020 and this, 14 million years later. 520 00:45:34,020 --> 00:45:37,700 And the reason for that is that these delicate, light, little bones 521 00:45:37,700 --> 00:45:41,620 don't fossilise terribly well. We don't find many fossil bats. 522 00:45:42,860 --> 00:45:45,580 But scientists have X-rayed this skull 523 00:45:45,580 --> 00:45:52,100 and they found that inside its inner ear, it has an enlarged cochlea. 524 00:45:52,100 --> 00:45:54,940 And that, alongside the fact it had ossicles, 525 00:45:54,940 --> 00:46:00,860 might suggest that this creature could echolocate. 526 00:46:00,860 --> 00:46:02,980 What about that?! 527 00:46:02,980 --> 00:46:07,260 Quite when creatures like this started to echolocate, 528 00:46:07,260 --> 00:46:08,340 we're not sure. 529 00:46:08,340 --> 00:46:12,860 Perhaps just after they could fly, perhaps at the same time. 530 00:46:12,860 --> 00:46:17,300 But it's a beautiful specimen. I covet this. 531 00:46:17,300 --> 00:46:19,700 I might actually steal it! 532 00:46:24,940 --> 00:46:27,540 Because bat fossils are so rare... 533 00:46:29,420 --> 00:46:33,740 ..we don't know exactly why bats first evolved powered flight. 534 00:46:37,020 --> 00:46:42,420 But combined with echolocation, it's an adaptation that pays off. 535 00:46:44,060 --> 00:46:47,580 Despite being so energetically demanding, 536 00:46:47,580 --> 00:46:52,580 flight allowed access to a great, untapped source of food 537 00:46:52,580 --> 00:46:53,980 in the night sky. 538 00:47:07,580 --> 00:47:10,140 Today, they're one of the most successful 539 00:47:10,140 --> 00:47:12,260 mammalian lineages on Earth... 540 00:47:17,420 --> 00:47:21,060 ..with over 1,000 species of echolocating bat... 541 00:47:24,140 --> 00:47:28,260 ..inhabiting every continent except Antarctica. 542 00:47:46,020 --> 00:47:50,860 Here in Borneo, there are more bats than any other type of mammal. 543 00:47:54,180 --> 00:47:59,140 Among them, those wrinkle-lipped bats 544 00:47:59,140 --> 00:48:03,500 that roost in Gomantong Caves in their hundreds of thousands. 545 00:48:06,460 --> 00:48:09,420 But bats don't just live in caves. 546 00:48:13,820 --> 00:48:17,540 You can find them in the most unexpected of places. 547 00:48:32,820 --> 00:48:36,380 Oh, yes, yes, yes! Look at that! 548 00:48:36,380 --> 00:48:40,100 It's a little cluster of bamboo bats. 549 00:48:46,060 --> 00:48:48,100 And this is where they like to roost - 550 00:48:48,100 --> 00:48:50,620 in these hollow stems of bamboo. 551 00:48:57,540 --> 00:49:00,740 One of the smallest bat species in the world, 552 00:49:00,740 --> 00:49:06,220 one of the smallest mammals in the world, they can weigh up to 5g. 553 00:49:06,220 --> 00:49:09,620 That's about the same size as a large bumblebee. 554 00:49:09,620 --> 00:49:11,540 Look at them all in there. 555 00:49:11,540 --> 00:49:16,780 Oh! I honestly didn't think we were going to find any. 556 00:49:22,660 --> 00:49:25,780 Any minute now, when these bats emerge to hunt, 557 00:49:25,780 --> 00:49:29,860 they will be able to fly at speeds of several metres per second, 558 00:49:29,860 --> 00:49:33,540 and they're able to do that because they can digest their insect prey in 559 00:49:33,540 --> 00:49:38,220 about 30 minutes - quick enough to power their fiery metabolism, 560 00:49:38,220 --> 00:49:42,140 the metabolism that allows them to fly. 561 00:49:42,140 --> 00:49:45,740 And then, of course, they've got that extremely acute hearing. 562 00:49:45,740 --> 00:49:49,660 They can hear frequencies five times higher than I can. 563 00:49:49,660 --> 00:49:52,660 That means they can detect their echolocation calls, 564 00:49:52,660 --> 00:49:57,980 find those tiny insects metres away, out there in the darkness. 565 00:50:01,500 --> 00:50:06,340 In so many ways, they are extraordinary organisms... 566 00:50:09,460 --> 00:50:14,660 ..but then, in some ways, they're really quite ordinary. 567 00:50:14,660 --> 00:50:19,860 Just like their Ediacaran ancestor that lived half a billion years ago, 568 00:50:19,860 --> 00:50:21,740 they're bilaterally symmetrical. 569 00:50:21,740 --> 00:50:24,460 They've got a head end, a back end, and a through-gut 570 00:50:24,460 --> 00:50:31,860 running in between, like 99% of all of the animals that live on Earth. 571 00:50:31,860 --> 00:50:35,900 And just like all of the vertebrates living on this island, 572 00:50:35,900 --> 00:50:39,420 they've inherited a jaw from that ancient fish 573 00:50:39,420 --> 00:50:41,700 that struggled onto land. 574 00:50:43,260 --> 00:50:47,580 Their ears have those ossicles, just like ours. 575 00:50:49,820 --> 00:50:56,860 We're both born helpless, completely dependent upon our mothers, 576 00:50:56,860 --> 00:51:00,140 and the hormones that make them hungry 577 00:51:00,140 --> 00:51:03,420 are the hormones that make me hungry, too. 578 00:51:11,260 --> 00:51:13,220 From the humblest beginnings... 579 00:51:14,860 --> 00:51:17,900 ..millennia by millennia, 580 00:51:17,900 --> 00:51:19,900 mouthful by mouthful... 581 00:51:23,660 --> 00:51:29,180 ..the need to feed transformed life on Earth. 582 00:51:34,700 --> 00:51:38,580 Evolution is at times brutal, 583 00:51:38,580 --> 00:51:41,620 but also exquisitely beautiful... 584 00:51:41,620 --> 00:51:42,940 Wow! 585 00:51:43,980 --> 00:51:47,300 ..as echoes of these ancestors live on... 586 00:51:47,300 --> 00:51:49,180 Oh! So good. 587 00:51:56,340 --> 00:51:58,900 ..and not just in the bat. 588 00:52:09,660 --> 00:52:15,900 Now, I share about 92% of my genes with these little bats, 589 00:52:15,900 --> 00:52:18,500 so you could say that their evolutionary story 590 00:52:18,500 --> 00:52:23,180 is my evolutionary story, is your evolutionary story. 591 00:52:23,180 --> 00:52:26,860 And so many of the things that make them extraordinary 592 00:52:26,860 --> 00:52:29,780 are the things that make you extraordinary, too. 593 00:52:29,780 --> 00:52:31,780 And it's not a story that's come to an end. 594 00:52:31,780 --> 00:52:36,100 Life goes on. Evolution goes on. 595 00:52:36,100 --> 00:52:38,940 So I want to ponder at this point - 596 00:52:38,940 --> 00:52:44,940 what if our species can finally get a grip on all the terrible damage 597 00:52:44,940 --> 00:52:49,380 that it's doing to this, our one beautiful home? 598 00:52:49,380 --> 00:52:53,900 Just where might evolution take us all next? 599 00:52:59,780 --> 00:53:00,860 Next time... 600 00:53:02,180 --> 00:53:05,620 ..how did the dolphin get so smart? 601 00:53:05,620 --> 00:53:08,260 Absolutely amazing! 602 00:53:10,340 --> 00:53:13,340 From the first animals to set eyes on our world... 603 00:53:14,940 --> 00:53:20,780 ..to the land-based ancestors who stepped back into the oceans, 604 00:53:20,780 --> 00:53:23,620 reshaping their minds, 605 00:53:23,620 --> 00:53:28,460 giving rise to the dolphin and its brilliant brain. 606 00:53:29,460 --> 00:53:31,460 Oh! My goodness me! 607 00:53:31,460 --> 00:53:33,460 I've just been to dolphin heaven! 608 00:53:38,940 --> 00:53:40,100 But first... 609 00:53:41,580 --> 00:53:44,660 ..how do we bring ancient creatures to life? 610 00:53:50,540 --> 00:53:52,460 - Oh! It's so cute! 611 00:53:52,460 --> 00:53:54,380 - HE CHUCKLES 612 00:53:54,380 --> 00:53:55,420 - I love the mouth. 613 00:53:56,940 --> 00:53:59,020 - Such a weird creature as well, isn't it? 614 00:54:01,020 --> 00:54:02,860 - Throughout Earth's history, 615 00:54:02,860 --> 00:54:06,940 animals have evolved into all manner of weird and wonderful forms... 616 00:54:09,100 --> 00:54:11,980 ..but how do we know what they looked like 617 00:54:11,980 --> 00:54:15,540 when they lived millions of years ago? 618 00:54:15,540 --> 00:54:20,420 In this episode, we met the delightful oddity Metaspriggina. 619 00:54:22,420 --> 00:54:24,420 - Looks like he's screaming for his life. 620 00:54:25,780 --> 00:54:28,180 - To paint a picture of this ancient animal, 621 00:54:28,180 --> 00:54:30,940 scientists have to start with the evidence. 622 00:54:33,380 --> 00:54:35,900 And in the case of Metaspriggina, 623 00:54:35,900 --> 00:54:41,100 that evidence came in the form of a fossil site unlike any other. 624 00:54:43,660 --> 00:54:47,300 - The Burgess Shale is an exceptional preservation site, 625 00:54:47,300 --> 00:54:51,540 and that's because there was a big underwater mudslide 626 00:54:51,540 --> 00:54:54,900 that swept all the animals away into anoxic waters. 627 00:54:56,100 --> 00:54:58,260 And without oxygen in the water, 628 00:54:58,260 --> 00:55:00,460 the microbes couldn't decay their bodies. 629 00:55:01,900 --> 00:55:05,220 - Meaning they were perfectly preserved, 630 00:55:05,220 --> 00:55:11,940 trapped under layers of silt, until 500 million years later, 631 00:55:11,940 --> 00:55:15,620 their faces saw the light of day once again. 632 00:55:15,620 --> 00:55:18,500 - It's almost like they have been caught by surprise. 633 00:55:19,660 --> 00:55:24,660 - Entire shoals of Metaspriggina, preserved perfectly. 634 00:55:26,220 --> 00:55:28,620 - Most of the fossils we know and are familiar with 635 00:55:28,620 --> 00:55:32,260 are things with hard parts, things like bones and shells. 636 00:55:32,260 --> 00:55:34,860 But the Burgess Shale was exceptionally different 637 00:55:34,860 --> 00:55:38,340 in that you get soft body preservation. 638 00:55:38,340 --> 00:55:44,180 - Everything from muscles to cartilage, even internal organs. 639 00:55:45,260 --> 00:55:47,140 - Metaspriggina...is tiny. 640 00:55:47,140 --> 00:55:49,780 The fact that we were able to get so much detail off of them, 641 00:55:49,780 --> 00:55:53,260 after so many hundreds of millions of years, is mind-boggling. 642 00:55:59,700 --> 00:56:01,460 - With this knowledge, 643 00:56:01,460 --> 00:56:05,820 we can begin to reconstruct exactly what Metaspriggina looked like. 644 00:56:14,460 --> 00:56:17,260 - This was an animal with visible gills, eyes, 645 00:56:17,260 --> 00:56:19,140 even something you might call a face. 646 00:56:20,940 --> 00:56:24,340 - But understanding the appearance of an extinct animal 647 00:56:24,340 --> 00:56:27,220 isn't the only challenge. 648 00:56:27,220 --> 00:56:30,820 - Fossils don't tend to move, and so bringing these animals, 649 00:56:30,820 --> 00:56:34,140 these organisms, back to life is actually... 650 00:56:34,140 --> 00:56:36,060 It's a massive endeavour. 651 00:56:39,740 --> 00:56:41,980 - The preservation is really, really exceptional. 652 00:56:41,980 --> 00:56:44,300 We can see so much of the details of the muscles. 653 00:56:44,300 --> 00:56:47,380 We can actually reconstruct how they moved and how they swam. 654 00:56:49,380 --> 00:56:54,940 - Looking closer, scientists noticed distinct W-shaped muscle lines 655 00:56:54,940 --> 00:57:00,460 in the fossils, identical to those found in some modern-day fish... 656 00:57:02,540 --> 00:57:07,740 ..meaning Metaspriggina must have swum in a similar way, 657 00:57:07,740 --> 00:57:10,540 swishing its body from side to side. 658 00:57:11,780 --> 00:57:14,740 - I think the VFX reconstruction is outstanding 659 00:57:14,740 --> 00:57:18,620 and is true to how this animal would have moved in the water. 660 00:57:18,620 --> 00:57:24,620 - Thanks to these discoveries, we can bring Metaspriggina back to life. 661 00:57:24,620 --> 00:57:29,420 - Metasprigginas really did change our understanding of the story 662 00:57:29,420 --> 00:57:31,540 of the evolution of life. 663 00:57:31,540 --> 00:57:35,580 - It's incredible to think these simple, tiny little forms 664 00:57:35,580 --> 00:57:39,140 are the ancestors of such diversity of life today. 665 00:57:43,700 --> 00:57:47,180 - Do you want to know how an elephant is related to a clownfish? 666 00:57:47,180 --> 00:57:51,380 Discover more in a poster from the Open University on the tree of life. 667 00:57:51,380 --> 00:57:52,860 To get your free copy, 668 00:57:52,860 --> 00:57:54,820 scan the QR code on screen, 669 00:57:54,820 --> 00:57:55,860 or ring... 670 00:57:58,940 --> 00:57:59,980 ..or visit...