1 00:00:00,099 --> 00:00:03,180 Viewers like you make this program possible. 2 00:00:03,440 --> 00:00:05,260 Support your local PBS station. 3 00:00:15,860 --> 00:00:18,179 It's the most enigmatic structure 4 00:00:18,180 --> 00:00:19,840 in all of biology. 5 00:00:23,850 --> 00:00:26,710 The brain is everything that we are. 6 00:00:28,270 --> 00:00:31,130 It's headquarters, it's, it's mission control. 7 00:00:33,600 --> 00:00:36,079 Though we still don't fully understand 8 00:00:36,080 --> 00:00:37,400 how brains work. 9 00:00:38,860 --> 00:00:40,799 The number of connections 10 00:00:40,800 --> 00:00:42,400 is incredibly daunting. 11 00:00:42,780 --> 00:00:44,900 They're still, in many ways, black boxes to us. 12 00:00:45,640 --> 00:00:47,879 Scientists are beginning to understand 13 00:00:47,880 --> 00:00:49,659 how they evolved. 14 00:00:49,660 --> 00:00:51,979 I think intelligence is 15 00:00:51,980 --> 00:00:54,840 perhaps unavoidable, in terms of evolution. 16 00:00:55,600 --> 00:00:57,536 The role played by the senses... 17 00:00:57,537 --> 00:01:00,950 Visual systems would definitely drive 18 00:01:00,951 --> 00:01:02,999 the evolution of a brain. 19 00:01:03,000 --> 00:01:06,560 The chance events that rewired ancient brains. 20 00:01:07,019 --> 00:01:08,419 The virus led 21 00:01:08,420 --> 00:01:09,699 to a quantum change 22 00:01:09,700 --> 00:01:11,140 in the sophistication of the brain. 23 00:01:11,520 --> 00:01:12,619 And the evolutionary 24 00:01:12,620 --> 00:01:15,747 forces that boosted problem-solving powers. 25 00:01:15,748 --> 00:01:17,198 BHART-ANJAN BHULLAR: Relentlessly, 26 00:01:17,199 --> 00:01:20,639 brains are driven to expand and become more 27 00:01:20,640 --> 00:01:22,840 and more and more elaborated. 28 00:01:23,719 --> 00:01:26,640 How did brains, as we know them, come to be? 29 00:01:30,160 --> 00:01:31,160 "Evolution: Brain Power." 30 00:01:31,800 --> 00:01:33,552 Right now, on "NOVA." 31 00:02:02,660 --> 00:02:05,460 One of the most successful families of mammals 32 00:02:06,359 --> 00:02:07,700 isn't found on land. 33 00:02:16,599 --> 00:02:19,099 They live in Earth's oceans. 34 00:02:36,949 --> 00:02:39,288 Dolphins have taken the ancestral mammalian 35 00:02:39,289 --> 00:02:42,109 body form, which is a land-adapted body, 36 00:02:42,429 --> 00:02:43,749 and made it into something 37 00:02:43,750 --> 00:02:46,549 that's exquisitely designed for moving around in the water. 38 00:02:48,469 --> 00:02:51,649 Dolphins can slow their heart rate when they're diving, 39 00:02:51,889 --> 00:02:53,069 so they use less oxygen. 40 00:02:54,689 --> 00:02:57,757 They have a sensory system called echolocation. 41 00:03:00,050 --> 00:03:03,149 They send out pulses of sound and they listen 42 00:03:03,150 --> 00:03:05,650 to the echoes and they perceive their environment. 43 00:03:05,810 --> 00:03:07,195 They can see with sound. 44 00:03:10,859 --> 00:03:13,719 Dolphins are actually a type of toothed whale. 45 00:03:15,959 --> 00:03:17,898 And though their physical adaptations 46 00:03:17,899 --> 00:03:20,420 to life under the waves are impressive... 47 00:03:22,079 --> 00:03:25,360 ...there is something even more extraordinary about them. 48 00:03:27,440 --> 00:03:30,339 Dolphin behavior, if you observe it for any length of time, 49 00:03:30,739 --> 00:03:32,920 just screams intelligence. 50 00:03:35,039 --> 00:03:36,259 They're very social, 51 00:03:36,639 --> 00:03:39,419 they learn from each other, they teach each other. 52 00:03:39,779 --> 00:03:41,439 They have a system 53 00:03:41,440 --> 00:03:43,759 of communication which appears very much 54 00:03:43,760 --> 00:03:44,849 as if it's language. 55 00:03:48,450 --> 00:03:51,310 They plan, strategize, 56 00:03:51,810 --> 00:03:52,810 collaborate, 57 00:03:52,970 --> 00:03:55,088 coordinate with other 58 00:03:55,089 --> 00:03:56,429 members of their group 59 00:03:57,209 --> 00:03:59,429 and that takes enormous 60 00:04:00,290 --> 00:04:01,589 cognitive ability. 61 00:04:02,389 --> 00:04:03,449 They are thinking. 62 00:04:03,890 --> 00:04:06,949 They're playful as well, which is something which we 63 00:04:06,950 --> 00:04:08,806 strongly associate with human intelligence. 64 00:04:12,550 --> 00:04:13,749 They almost seem like 65 00:04:13,750 --> 00:04:15,469 they're enjoying themselves in the water 66 00:04:15,470 --> 00:04:16,670 rather than just making a living. 67 00:04:19,400 --> 00:04:22,269 Intelligence is a very elusive 68 00:04:22,270 --> 00:04:26,590 concept-- it's very difficult to measure, even among humans, 69 00:04:26,710 --> 00:04:29,190 much less between humans and animals. 70 00:04:30,150 --> 00:04:32,650 Though intelligence might be hard to define, 71 00:04:33,150 --> 00:04:36,450 scientists agree humans aren't the only ones that have it. 72 00:04:36,730 --> 00:04:37,730 There is 73 00:04:38,030 --> 00:04:40,349 absolutely no question in my mind 74 00:04:40,350 --> 00:04:43,589 that dolphins are among the most intelligent animals 75 00:04:43,590 --> 00:04:44,850 ever to have lived. 76 00:04:47,920 --> 00:04:49,299 Underpinning dolphin intelligence 77 00:04:49,300 --> 00:04:51,700 is an extremely complex brain. 78 00:04:53,000 --> 00:04:56,139 One of the largest in comparison with their body size 79 00:04:56,140 --> 00:04:57,960 of any mammal on Earth. 80 00:05:00,080 --> 00:05:03,020 So, how did dolphins come to be so smart? 81 00:05:06,800 --> 00:05:08,400 To answer that question, 82 00:05:08,800 --> 00:05:10,500 we need to turn back the clock... 83 00:05:14,300 --> 00:05:17,500 ...and meet the ancient relatives of the dolphin 84 00:05:18,120 --> 00:05:22,280 whose minds were reshaped by their struggle for survival. 85 00:05:24,000 --> 00:05:27,319 Uncover the forces that led to the earliest brains, 86 00:05:28,160 --> 00:05:30,499 and discover how the first senses 87 00:05:30,500 --> 00:05:33,180 put life on the long road to intelligence. 88 00:05:35,560 --> 00:05:38,559 This is the amazing story of how the dolphin 89 00:05:38,560 --> 00:05:41,492 and its giant brain came to be. 90 00:06:00,949 --> 00:06:05,589 The story of intelligence begins long, long ago. 91 00:06:07,889 --> 00:06:10,289 Long before the first spark of thought. 92 00:06:12,170 --> 00:06:14,930 Before there were even animals on the planet. 93 00:06:20,550 --> 00:06:23,889 Mostly simple single cells live in these oceans, 94 00:06:25,760 --> 00:06:27,210 and they quite literally 95 00:06:27,790 --> 00:06:30,510 do not have a single brain cell between them. 96 00:06:34,580 --> 00:06:35,580 Yet... 97 00:06:36,180 --> 00:06:38,419 ...there is a process underway here 98 00:06:38,420 --> 00:06:40,379 that in time will come 99 00:06:40,380 --> 00:06:44,840 to be intimately tied with the evolution of the earliest minds. 100 00:06:48,080 --> 00:06:50,020 Something that may seem simple, 101 00:06:50,640 --> 00:06:54,380 but around three billion years ago, is revolutionary. 102 00:07:03,100 --> 00:07:07,519 These cells can sense the light of the sun. 103 00:07:11,830 --> 00:07:14,038 If an organism can't sense light, then essentially 104 00:07:14,039 --> 00:07:16,310 it doesn't have any sense of the rhythm of the Earth, right? 105 00:07:16,590 --> 00:07:17,630 Sunrise, sunset, 106 00:07:17,830 --> 00:07:19,129 and that's gonna have a lot of effects 107 00:07:19,130 --> 00:07:20,650 on, you know, temperature conditions, 108 00:07:20,890 --> 00:07:23,170 the immediate environment that that cell finds itself. 109 00:07:23,370 --> 00:07:24,829 So just being able to sense light, 110 00:07:24,970 --> 00:07:28,029 that would be a huge, huge step 111 00:07:28,030 --> 00:07:29,030 in evolution. 112 00:07:34,194 --> 00:07:36,278 If they're photosynthetic cells, 113 00:07:36,279 --> 00:07:38,848 they could move towards a source of light, 114 00:07:38,849 --> 00:07:40,908 and that light's going to provide them 115 00:07:40,909 --> 00:07:42,030 with energy. 116 00:07:43,789 --> 00:07:46,049 But moving away from the light might be 117 00:07:46,050 --> 00:07:47,190 an advantage as well. 118 00:07:50,470 --> 00:07:53,330 Sunlight, we may perceive it as very nice and pleasant, 119 00:07:53,650 --> 00:07:54,629 actually contains 120 00:07:54,630 --> 00:07:57,130 harmful radiation, the UV radiation. 121 00:07:57,890 --> 00:07:59,350 With the ability to sense light, 122 00:07:59,510 --> 00:08:02,429 these single cells could detect if that light was present 123 00:08:02,430 --> 00:08:05,230 and could move away from that light. 124 00:08:07,310 --> 00:08:10,396 Key to these ancient cells being able to sense light 125 00:08:10,397 --> 00:08:13,628 is a molecule called retinal, 126 00:08:13,629 --> 00:08:16,450 which changes shape as it absorbs a photon of light. 127 00:08:19,000 --> 00:08:21,620 This acts as an on or off signal, 128 00:08:22,380 --> 00:08:24,420 which tells the cell to move. 129 00:08:25,520 --> 00:08:27,059 Sensing light and being able 130 00:08:27,060 --> 00:08:29,860 to move away from it, um, that is a behavior. 131 00:08:30,640 --> 00:08:32,780 I don't think there's any real computation involved. 132 00:08:32,980 --> 00:08:35,100 It's, it's kind of fundamentally chemistry. 133 00:08:36,360 --> 00:08:37,558 It may be simple, 134 00:08:37,559 --> 00:08:39,640 and it certainly isn't thinking, 135 00:08:40,520 --> 00:08:43,279 but three billion years ago, this ability 136 00:08:43,280 --> 00:08:47,059 to sense light with retinal, will change everything. 137 00:08:47,900 --> 00:08:49,340 Once retinal is in play, 138 00:08:49,500 --> 00:08:52,199 we have a molecule which allows 139 00:08:52,200 --> 00:08:55,058 early cells to detect light that they 140 00:08:55,059 --> 00:08:56,298 can then respond to, 141 00:08:56,299 --> 00:08:59,340 and that eventually leads to more complex behavior 142 00:09:00,060 --> 00:09:03,259 and possibly the development of the brain itself. 143 00:09:07,079 --> 00:09:11,139 Sensing light had set life on a new path. 144 00:09:18,350 --> 00:09:21,909 Over the next two-and-a-half billion years... 145 00:09:24,410 --> 00:09:25,889 ...life diversifies. 146 00:09:28,600 --> 00:09:32,139 From single-celled to multicellular forms. 147 00:09:34,950 --> 00:09:37,629 And along with some of the earliest animals... 148 00:09:40,049 --> 00:09:42,122 ...the first nervous systems arise. 149 00:09:55,570 --> 00:09:58,750 This tiny, soft bodied creature is, 150 00:09:59,150 --> 00:10:02,290 unbelievably, a distant ancestor of the dolphin. 151 00:10:03,709 --> 00:10:06,490 And it's searching for a place to hide. 152 00:10:07,890 --> 00:10:09,150 Not from any predator, 153 00:10:10,370 --> 00:10:14,550 but from the punishing UV radiation of the rising sun. 154 00:10:19,049 --> 00:10:23,069 Thanks to retinal, it can still sense the light intensifying. 155 00:10:27,270 --> 00:10:31,370 Retinal found in two simple spots at the front of its body, 156 00:10:32,530 --> 00:10:34,130 known as eye spots. 157 00:10:36,250 --> 00:10:38,169 An eye spot is just like a collection 158 00:10:38,170 --> 00:10:41,190 of light sensing cells that are kind of clustered together 159 00:10:41,449 --> 00:10:42,449 in one place. 160 00:10:42,650 --> 00:10:44,550 These eye spots would have been connected 161 00:10:44,910 --> 00:10:47,930 to excitable cells, primitive neurons, 162 00:10:48,503 --> 00:10:50,421 nerve cells, which would have allowed 163 00:10:50,422 --> 00:10:52,609 information about light in the environment 164 00:10:52,610 --> 00:10:56,249 to be transmitted from the eye spot to the rest of the animal. 165 00:10:56,250 --> 00:10:58,830 That light signal is essentially like a stoplight, 166 00:10:59,030 --> 00:11:01,410 you know, green, go, you know, red, stop, 167 00:11:01,510 --> 00:11:02,789 in terms of the movement 168 00:11:02,790 --> 00:11:03,850 of the animal. 169 00:11:04,250 --> 00:11:05,790 And so this is a simple behavior, 170 00:11:06,230 --> 00:11:07,829 but important behavior, because 171 00:11:07,830 --> 00:11:09,789 it can determine the orientation of the creature 172 00:11:09,790 --> 00:11:12,050 and where it is in the water column and things like this. 173 00:11:12,850 --> 00:11:15,150 This process doesn't require 174 00:11:16,010 --> 00:11:19,010 any huge evaluation of the signals, 175 00:11:19,190 --> 00:11:19,909 but it's getting 176 00:11:19,910 --> 00:11:22,230 close to the beginnings of thought. 177 00:11:25,850 --> 00:11:29,470 Yet among this population of shade-seeking animals, 178 00:11:30,310 --> 00:11:32,930 the dolphin's ancestor has a slight edge. 179 00:11:35,300 --> 00:11:36,659 It has inherited 180 00:11:36,660 --> 00:11:38,300 a series of mutations. 181 00:11:41,220 --> 00:11:44,540 Genetic changes which mean that instead of being flat... 182 00:11:45,900 --> 00:11:49,380 ...its eye spots cave ever so slightly inwards... 183 00:11:53,790 --> 00:11:55,230 ...becoming little dimples. 184 00:11:59,250 --> 00:12:01,730 This difference might seem insignificant. 185 00:12:03,149 --> 00:12:05,690 But it is in fact a superpower. 186 00:12:10,750 --> 00:12:13,389 So if we look at a flat plate like this, 187 00:12:13,390 --> 00:12:14,710 and I shine a light on it, 188 00:12:15,029 --> 00:12:17,389 when the light's on the plate, it's fully illuminated. 189 00:12:17,810 --> 00:12:19,190 But when I rotate it, 190 00:12:19,710 --> 00:12:21,830 the light switches off completely. 191 00:12:22,409 --> 00:12:26,509 And then I rotate back again, and it's fully illuminated. 192 00:12:28,190 --> 00:12:30,990 So, by contrast, this is a curved surface. 193 00:12:31,610 --> 00:12:34,068 As the curved surface starts to move, 194 00:12:34,069 --> 00:12:35,069 you see shadows 195 00:12:35,190 --> 00:12:36,569 appearing and you can kind of 196 00:12:36,570 --> 00:12:38,989 sense the direction of the light, 197 00:12:38,990 --> 00:12:41,049 'cause the light is not going to be 198 00:12:41,050 --> 00:12:44,330 bathing the entire surface at all times. 199 00:12:46,030 --> 00:12:48,349 The significance of having an eye spot 200 00:12:48,350 --> 00:12:49,869 with a slightly curved surface 201 00:12:49,870 --> 00:12:50,870 is huge. 202 00:12:51,190 --> 00:12:54,869 This is the first step of allowing these animals to have 203 00:12:54,870 --> 00:12:58,190 a sense of where more precise light is coming from. 204 00:12:58,409 --> 00:13:01,070 In a way that is a big step towards real vision. 205 00:13:04,330 --> 00:13:07,589 Little dimples like these ones may well 206 00:13:07,590 --> 00:13:09,910 have been the first simple eyes. 207 00:13:15,150 --> 00:13:17,050 It's an intriguing theory. 208 00:13:17,829 --> 00:13:20,790 But one for which there is no fossil evidence. 209 00:13:27,782 --> 00:13:29,500 The early stages of eye evolution 210 00:13:29,501 --> 00:13:32,599 were happening in soft, small creatures 211 00:13:32,600 --> 00:13:34,420 that don't fossilize very well. 212 00:13:34,520 --> 00:13:36,400 So, we're not going to have, you know, 213 00:13:36,600 --> 00:13:38,240 a perfect historical record. 214 00:13:41,340 --> 00:13:45,198 However, fossils aren't the only clues available to scientists 215 00:13:45,199 --> 00:13:46,219 studying evolution. 216 00:13:48,450 --> 00:13:49,490 Oh, wow. 217 00:13:50,710 --> 00:13:52,330 This species of butterfly, 218 00:13:52,790 --> 00:13:54,270 we call them morpho. 219 00:13:55,170 --> 00:13:57,850 If you see their eyes, like most insects, 220 00:13:58,390 --> 00:14:00,330 they're made of many different lenses. 221 00:14:00,730 --> 00:14:03,070 This is what we call compound eyes. 222 00:14:05,050 --> 00:14:08,350 For tropical biologist, Stephanie Valle Cubero, 223 00:14:09,210 --> 00:14:12,550 Costa Rica's jungles are a paradise for studying eyes. 224 00:14:15,850 --> 00:14:17,970 This is a poisonous frog. 225 00:14:18,370 --> 00:14:21,889 Their eyes are just like our eyes-- they have just 226 00:14:21,890 --> 00:14:25,410 one lens and this is what we call camera eyes. 227 00:14:29,100 --> 00:14:31,999 But one animal here can offer insight 228 00:14:32,000 --> 00:14:35,460 into what vision was like over half-a-billion years ago. 229 00:14:38,449 --> 00:14:39,869 Velvet worms are 230 00:14:39,870 --> 00:14:41,310 very, very bizarre. 231 00:14:41,829 --> 00:14:44,169 That name, velvet worm, comes from the fact 232 00:14:44,170 --> 00:14:46,829 that they have this soft, velvety skin. 233 00:14:47,569 --> 00:14:49,409 However, the problem that 234 00:14:49,410 --> 00:14:51,930 they have is that because they breathe through their skin, 235 00:14:52,370 --> 00:14:55,949 they can lose humidity as they're breathing. 236 00:14:58,500 --> 00:15:02,359 To keep their skin moist, velvet worms seek shady 237 00:15:02,360 --> 00:15:03,360 places to hide. 238 00:15:04,440 --> 00:15:06,379 Something they do using their 239 00:15:06,380 --> 00:15:07,640 unusual eyes. 240 00:15:10,149 --> 00:15:13,489 So, if you look at a velvet worm, the eyes 241 00:15:13,490 --> 00:15:16,549 are just beneath these antennae 242 00:15:16,550 --> 00:15:17,429 on the base. 243 00:15:17,430 --> 00:15:19,690 It's these tiny, tiny pinpricks. 244 00:15:20,510 --> 00:15:22,389 Tiny black spots that you see 245 00:15:22,390 --> 00:15:23,829 right on the base of the antenna. 246 00:15:25,250 --> 00:15:28,389 The velvet worm doesn't have complex camera eyes. 247 00:15:29,090 --> 00:15:31,530 Instead, it has simple eyes, 248 00:15:32,110 --> 00:15:34,429 similar in function to those thought to exist 249 00:15:34,430 --> 00:15:36,690 over half-a-billion years ago. 250 00:15:37,529 --> 00:15:40,889 And these eyes give the velvet worm basic vision. 251 00:15:42,069 --> 00:15:45,509 Here I have a video where 252 00:15:45,510 --> 00:15:48,249 we can compare the way we see the world 253 00:15:48,250 --> 00:15:49,189 on the left, 254 00:15:49,190 --> 00:15:53,089 and the way a velvet worm would perceive the world on the right. 255 00:15:53,250 --> 00:15:54,809 Instead of seeing all the details 256 00:15:54,810 --> 00:15:56,250 of the objects around it, 257 00:15:56,610 --> 00:15:59,110 the velvet worm sees a very blurry image. 258 00:15:59,469 --> 00:16:00,269 However, 259 00:16:00,270 --> 00:16:02,249 this image does allow 260 00:16:02,250 --> 00:16:04,869 for the velvet worm to perceive where there is 261 00:16:04,870 --> 00:16:08,369 more and less light, to find spots where there 262 00:16:08,370 --> 00:16:12,889 isn't as much light and where it can avoid dehydration, 263 00:16:12,890 --> 00:16:15,149 which is actually what the velvet worm needs 264 00:16:15,150 --> 00:16:16,005 to be able to survive. 265 00:16:20,050 --> 00:16:21,068 Eyes like those 266 00:16:21,069 --> 00:16:23,028 of the velvet worm suggest 267 00:16:23,029 --> 00:16:26,730 that the dolphin's ancestor can also see blurry images. 268 00:16:32,250 --> 00:16:34,949 And the theory goes that compared 269 00:16:34,950 --> 00:16:36,510 to the others of its species, 270 00:16:37,750 --> 00:16:39,409 this vision allows it 271 00:16:39,410 --> 00:16:41,910 to more rapidly find a place to shelter. 272 00:16:44,129 --> 00:16:46,450 An advantage that is passed on. 273 00:16:47,990 --> 00:16:50,070 So, over the years, 274 00:16:50,350 --> 00:16:53,790 further mutations drive the dimples to become deeper. 275 00:16:57,030 --> 00:17:01,370 Protective cells grow over the opening, forming a lens, 276 00:17:02,010 --> 00:17:06,269 which focuses light onto a layer of light sensitive cells 277 00:17:06,270 --> 00:17:11,230 we now call a retina, producing a sharper image. 278 00:17:13,110 --> 00:17:14,710 Over countless generations, 279 00:17:15,310 --> 00:17:17,430 simple eye spots transform 280 00:17:17,970 --> 00:17:21,749 into one of the most complex biological instruments 281 00:17:21,750 --> 00:17:23,890 evolution has ever produced. 282 00:17:27,098 --> 00:17:29,680 Eyes, as we know them, have arrived. 283 00:17:35,599 --> 00:17:37,560 Over millions of years... 284 00:17:39,499 --> 00:17:43,079 ...eyes begin to appear across the animal kingdom. 285 00:17:54,200 --> 00:17:56,300 And by the Cambrian Period... 286 00:17:57,800 --> 00:17:59,860 ...complex eyes are everywhere. 287 00:18:05,619 --> 00:18:07,200 Coming in many forms... 288 00:18:11,849 --> 00:18:13,209 ...and many numbers. 289 00:18:16,989 --> 00:18:20,109 Eyes change the dynamics of life entirely. 290 00:18:23,059 --> 00:18:26,720 Because if animals can see the world more clearly... 291 00:18:28,700 --> 00:18:32,180 ...they can see one another. 292 00:18:34,100 --> 00:18:38,260 Meaning life is no longer just focused on seeking shade. 293 00:18:40,950 --> 00:18:43,990 It is now about strategy. 294 00:19:00,280 --> 00:19:01,799 Paleontologist Karma Nanglu 295 00:19:01,800 --> 00:19:04,159 studies fossils from the Cambrian Period. 296 00:19:05,740 --> 00:19:07,499 During the Cambrian, we see a huge 297 00:19:07,500 --> 00:19:08,940 diversity of eyes start to develop. 298 00:19:09,280 --> 00:19:11,119 And a big part of this is the relationship 299 00:19:11,120 --> 00:19:12,360 between predator and prey. 300 00:19:12,800 --> 00:19:14,979 So as one group starts to develop larger 301 00:19:14,980 --> 00:19:16,760 and more complicated eyes to see the other, 302 00:19:17,200 --> 00:19:19,918 the other groups like the prey might develop 303 00:19:19,919 --> 00:19:22,059 larger eyes to sense their predators and escape them. 304 00:19:25,700 --> 00:19:28,199 One of the first groups of animals to evolve eyes 305 00:19:28,200 --> 00:19:29,200 are the trilobites. 306 00:19:29,340 --> 00:19:31,019 So this is a trilobite from Utah. 307 00:19:31,500 --> 00:19:34,000 It's about 506, 507 million years old, 308 00:19:34,340 --> 00:19:35,620 called "Elrathia kingii." 309 00:19:36,140 --> 00:19:37,979 And we can see all sorts of beautiful features 310 00:19:37,980 --> 00:19:39,120 on the surface of this fossil. 311 00:19:39,559 --> 00:19:42,360 But one of the most notable ones are two very prominent eyes. 312 00:19:44,961 --> 00:19:46,582 Here is a fossil from China 313 00:19:46,583 --> 00:19:47,929 called "Lyrarapax." 314 00:19:47,930 --> 00:19:51,390 And really most notable in this fossil... 315 00:19:52,310 --> 00:19:54,809 ...is the front, where you can see two very 316 00:19:54,810 --> 00:19:56,990 prominent eyes that are preserved very darkly here. 317 00:19:58,190 --> 00:20:00,649 But Cambrian fossils don't just give us 318 00:20:00,650 --> 00:20:03,090 the first tangible evidence of complex eyes. 319 00:20:03,590 --> 00:20:05,549 These dark bands running towards the center 320 00:20:05,550 --> 00:20:07,290 are what we think are actually neural tissue. 321 00:20:07,910 --> 00:20:09,689 And in the center then we have a large, 322 00:20:09,690 --> 00:20:12,130 sort of, blob-like area, kind of like a dark blue color. 323 00:20:12,690 --> 00:20:14,910 That's the central nervous system or brain. 324 00:20:17,350 --> 00:20:19,809 The idea that you can have such exceptional 325 00:20:19,810 --> 00:20:21,668 preservation of any of these animals 326 00:20:21,669 --> 00:20:23,889 from so long ago that we can actually get 327 00:20:24,777 --> 00:20:26,418 a direct look at their brains is really astounding. 328 00:20:26,419 --> 00:20:27,280 And honestly, 329 00:20:27,281 --> 00:20:28,588 it's pretty much a minor miracle 330 00:20:28,589 --> 00:20:30,949 every time one of these fossils is uncovered and described. 331 00:20:33,880 --> 00:20:36,759 It's no coincidence that on the rare occasions 332 00:20:36,760 --> 00:20:38,700 fossilized brains are found, 333 00:20:39,280 --> 00:20:41,240 eyes are often found, too. 334 00:20:42,360 --> 00:20:45,020 Vision is a lot of information, right? 335 00:20:45,160 --> 00:20:47,740 So vision involves color, it involves light, 336 00:20:48,079 --> 00:20:50,019 it involves direction, it involves movement. 337 00:20:52,350 --> 00:20:54,509 And that information starts to need to be 338 00:20:54,510 --> 00:20:57,051 processed by something like the brain. 339 00:20:58,510 --> 00:21:00,609 There must be a very strong relationship 340 00:21:00,610 --> 00:21:03,409 between the evolution of complex eyes and complex brains. 341 00:21:03,709 --> 00:21:06,049 If you had the best optics and the best camera 342 00:21:06,050 --> 00:21:07,688 in the world, if you wouldn't know what to do 343 00:21:07,689 --> 00:21:09,709 with the information, it would be useless. 344 00:21:11,429 --> 00:21:14,549 Though other senses such as touch and smell 345 00:21:14,550 --> 00:21:15,829 also helped drive 346 00:21:15,830 --> 00:21:19,609 the evolution of early brains, scientists believe 347 00:21:19,610 --> 00:21:21,770 vision played a major role. 348 00:21:33,434 --> 00:21:34,289 Today, 349 00:21:34,290 --> 00:21:36,410 the world is full of different 350 00:21:36,710 --> 00:21:38,249 kinds of complex eyes 351 00:21:38,250 --> 00:21:39,250 and brains. 352 00:21:41,070 --> 00:21:42,809 Attuned to perceive the world 353 00:21:42,810 --> 00:21:45,610 in whatever way is most useful to them. 354 00:21:49,439 --> 00:21:51,679 Compound eyes give a wide field of view 355 00:21:51,680 --> 00:21:52,940 to smaller brains. 356 00:21:55,810 --> 00:21:58,129 Giant camera eyes gather information 357 00:21:58,130 --> 00:21:59,610 in the darkest depths. 358 00:22:01,090 --> 00:22:04,949 And forward-facing eyes help some of the largest brains 359 00:22:04,950 --> 00:22:07,389 judge depth as they navigate 360 00:22:07,390 --> 00:22:08,630 their jungle homes. 361 00:22:16,500 --> 00:22:18,700 But half-a-billion years ago, 362 00:22:19,820 --> 00:22:22,240 animals and their newly evolved brains, 363 00:22:22,659 --> 00:22:25,760 are just waking up to the world around them. 364 00:22:30,689 --> 00:22:33,390 Leaping forward 75 million years, 365 00:22:34,830 --> 00:22:36,590 as the ancestors of insects 366 00:22:37,129 --> 00:22:38,829 begin colonizing the land... 367 00:22:41,760 --> 00:22:42,800 ...under the waves... 368 00:22:44,520 --> 00:22:47,360 ...brains are getting more complex. 369 00:22:55,659 --> 00:22:57,259 Welcome to the Silurian. 370 00:22:59,519 --> 00:23:01,979 Where some fish have now 371 00:23:01,980 --> 00:23:03,800 evolved into hunters. 372 00:23:07,150 --> 00:23:11,570 This fierce looking creature is a primitive form of a placoderm. 373 00:23:15,900 --> 00:23:20,139 A group of fish for whom the predator-prey arms race 374 00:23:20,140 --> 00:23:24,319 is so acute... that it has changed 375 00:23:24,320 --> 00:23:26,920 the way their entire bodies are built. 376 00:23:35,100 --> 00:23:36,259 This is a fossil 377 00:23:36,260 --> 00:23:38,860 of a placoderm called "Coccosteus cuspidatus," 378 00:23:39,439 --> 00:23:40,799 and it's a really beautiful fossil. 379 00:23:40,939 --> 00:23:42,898 It was discovered in Scotland, and what you can see is 380 00:23:42,899 --> 00:23:45,019 basically the entirety of its body is preserved. 381 00:23:45,659 --> 00:23:47,179 You can see a very long looking tail. 382 00:23:47,379 --> 00:23:50,099 You can see actually little bits of what looks like a dorsal fin. 383 00:23:50,480 --> 00:23:51,480 And so, from that perspective, 384 00:23:51,600 --> 00:23:52,760 very much like a modern fish. 385 00:23:54,240 --> 00:23:56,519 But there is one feature above all 386 00:23:56,520 --> 00:23:58,540 that makes placoderms special. 387 00:23:59,199 --> 00:24:02,239 The whole head region is covered in these bony plates 388 00:24:02,240 --> 00:24:05,240 that would have served as armor to protect some of the softer, 389 00:24:05,399 --> 00:24:08,179 more sensitive parts of the animal's body like its eye, 390 00:24:08,419 --> 00:24:09,178 but ultimately, 391 00:24:09,179 --> 00:24:11,639 that most important part of the animal, which is its brain. 392 00:24:15,320 --> 00:24:17,299 Placoderm fossils have been found 393 00:24:17,300 --> 00:24:19,780 on every continent on Earth. 394 00:24:20,920 --> 00:24:22,980 Coming in many shapes and sizes. 395 00:24:24,440 --> 00:24:26,879 All with heads covered in thick armor 396 00:24:26,880 --> 00:24:29,080 to protect their precious brains. 397 00:24:33,380 --> 00:24:34,119 Placoderms are 398 00:24:34,120 --> 00:24:36,520 the sister lineage to living, jawed vertebrates. 399 00:24:37,480 --> 00:24:39,939 And they can tell us a lot about brain evolution 400 00:24:39,940 --> 00:24:41,197 because inside their thick armor, 401 00:24:41,198 --> 00:24:44,106 they have a proto skull that surrounds the brain. 402 00:24:46,180 --> 00:24:49,559 Though the brains of placoderms are seldom preserved directly, 403 00:24:50,299 --> 00:24:53,220 the cavities left inside their proto skulls are. 404 00:24:54,850 --> 00:24:56,299 And they can be studied, 405 00:24:56,300 --> 00:24:59,180 thanks to an innovative, modern technique. 406 00:25:01,040 --> 00:25:02,380 There is no 407 00:25:03,679 --> 00:25:06,159 modern study of the brains 408 00:25:06,160 --> 00:25:08,273 of fossil animals without CT scanning. 409 00:25:12,450 --> 00:25:15,810 You would have to utterly destroy a fossil, 410 00:25:15,990 --> 00:25:16,990 a fossil skull, 411 00:25:17,350 --> 00:25:18,610 to get at the brain cavity. 412 00:25:18,810 --> 00:25:20,769 Even then, whatever you did 413 00:25:20,770 --> 00:25:24,129 would be a very incomplete reconstruction, but, 414 00:25:24,130 --> 00:25:26,870 with CT scanning, effortlessly, 415 00:25:27,370 --> 00:25:29,150 with no damage to the fossil, 416 00:25:29,549 --> 00:25:32,289 we can see inside all of these spaces. 417 00:25:33,590 --> 00:25:34,729 After we CT scanned 418 00:25:34,730 --> 00:25:36,989 the placoderm, we can use that 3D data 419 00:25:36,990 --> 00:25:40,490 to build up a 3D model of the internal structure. 420 00:25:42,530 --> 00:25:44,149 Here is a 3D print 421 00:25:44,150 --> 00:25:45,270 of a placoderm brain. 422 00:25:46,950 --> 00:25:49,930 So these two bulges here, these are the cerebellum, 423 00:25:50,030 --> 00:25:51,629 so this is the part of the brain that's involved 424 00:25:51,630 --> 00:25:53,030 in cognition, in thinking, 425 00:25:53,450 --> 00:25:54,450 and in movement. 426 00:25:54,750 --> 00:25:56,969 These are really large, so placoderms are the first 427 00:25:56,970 --> 00:25:59,570 group of animals to have this really developed cerebellum. 428 00:26:01,549 --> 00:26:03,528 These are the semicircular canals, 429 00:26:03,529 --> 00:26:05,190 which are used for balance and orientation. 430 00:26:07,009 --> 00:26:08,309 These are cranial nerves. 431 00:26:08,450 --> 00:26:10,130 So, they link the brain to the different organs. 432 00:26:10,509 --> 00:26:12,309 So, this one here is called the optic nerve, 433 00:26:12,450 --> 00:26:14,009 and it links the brain to the eye. 434 00:26:15,870 --> 00:26:17,050 So, taken together, 435 00:26:17,170 --> 00:26:18,308 this tells us that placoderms 436 00:26:18,309 --> 00:26:19,929 had really sophisticated brains, 437 00:26:19,930 --> 00:26:21,970 even though they lived 400 million years ago. 438 00:26:22,450 --> 00:26:24,569 They were much more developed than brains 439 00:26:24,570 --> 00:26:27,129 from animals that diverged from the evolutionary tree 440 00:26:27,130 --> 00:26:28,550 just a few million years earlier. 441 00:26:29,970 --> 00:26:32,649 There is a theory that part of the reason 442 00:26:32,650 --> 00:26:34,769 for this leap in brain complexity... 443 00:26:36,130 --> 00:26:38,449 ...was a bizarre fluke of biology 444 00:26:38,450 --> 00:26:40,430 that happened in the ancient seas. 445 00:26:47,650 --> 00:26:48,770 Despite its armor, 446 00:26:49,550 --> 00:26:54,130 this primitive placoderm has been attacked by a tiny invader. 447 00:26:55,270 --> 00:26:56,270 A virus. 448 00:26:56,670 --> 00:26:59,509 One whose impacts would ripple through time. 449 00:27:00,590 --> 00:27:03,450 Viruses are really curious entities. 450 00:27:07,499 --> 00:27:10,318 They contain many of the components 451 00:27:10,319 --> 00:27:12,219 that you would find in a living cell, 452 00:27:12,459 --> 00:27:14,699 and yet they are not themselves living. 453 00:27:15,699 --> 00:27:16,938 And the reason being is that 454 00:27:16,939 --> 00:27:19,080 by themselves, they can't make copies of themselves, 455 00:27:19,320 --> 00:27:21,438 and being able to replicate is one of the definitions 456 00:27:21,439 --> 00:27:22,459 of being alive. 457 00:27:23,639 --> 00:27:24,639 So, viruses, 458 00:27:25,080 --> 00:27:26,340 in order to replicate themselves, 459 00:27:26,939 --> 00:27:28,939 they go into the living cell 460 00:27:29,079 --> 00:27:31,758 and they're kind of hijacking the living cell's machinery 461 00:27:31,759 --> 00:27:33,059 to make copies. 462 00:27:33,659 --> 00:27:35,739 Eventually, they've made enough copies 463 00:27:35,740 --> 00:27:38,919 that now they want to go and infect the next living cell, 464 00:27:39,100 --> 00:27:40,138 and in order to do that, 465 00:27:40,139 --> 00:27:42,020 they burst out of the cell 466 00:27:42,159 --> 00:27:43,719 and that actually can kill the cell. 467 00:27:43,860 --> 00:27:45,760 That triggers an immune response, 468 00:27:46,120 --> 00:27:47,438 and that's why we end up with 469 00:27:47,439 --> 00:27:49,318 kind of a runny nose and sneezing 470 00:27:49,319 --> 00:27:51,740 and all of the things you might expect from the common cold. 471 00:27:52,839 --> 00:27:56,419 But other viruses use a more sophisticated approach. 472 00:27:57,639 --> 00:27:59,519 Retroviruses are a very cunning type of virus. 473 00:27:59,980 --> 00:28:01,779 What they do is they enter the cell 474 00:28:01,780 --> 00:28:05,018 and then put their genes into the DNA of the host cell, 475 00:28:05,019 --> 00:28:08,240 and then use that as a mechanism for making copies of themselves. 476 00:28:12,150 --> 00:28:14,529 But it's on the rare occasions 477 00:28:14,530 --> 00:28:16,969 that retroviruses infect the cells 478 00:28:16,970 --> 00:28:19,090 that give rise to eggs and sperm 479 00:28:19,570 --> 00:28:22,410 that they have the longest lasting impact. 480 00:28:24,370 --> 00:28:27,249 That means that bit of retroviral DNA 481 00:28:27,250 --> 00:28:29,189 will get propagated or transmitted 482 00:28:29,190 --> 00:28:30,750 from one generation to the next. 483 00:28:34,520 --> 00:28:36,400 Luckily for this ancient fish, 484 00:28:36,820 --> 00:28:38,879 her immune system kicks into gear, 485 00:28:38,880 --> 00:28:41,539 and she recovers from the immediate effects 486 00:28:41,540 --> 00:28:42,540 of the infection. 487 00:28:43,220 --> 00:28:45,740 But because the virus is a retrovirus, 488 00:28:46,140 --> 00:28:49,220 she never quite clears it from all of her cells. 489 00:28:49,480 --> 00:28:53,380 And by chance, it makes its way into her eggs 490 00:28:53,800 --> 00:28:57,860 and is integrated into her offspring's entire genomes. 491 00:28:58,980 --> 00:29:02,699 Over generations, the hidden viral DNA 492 00:29:02,700 --> 00:29:04,890 does something extraordinary. 493 00:29:10,750 --> 00:29:16,070 It triggers one of the fish's genes to go into overdrive. 494 00:29:19,650 --> 00:29:21,590 Altering the way neurons develop. 495 00:29:25,539 --> 00:29:28,798 Causing areas of the brain to fade from grey, 496 00:29:28,799 --> 00:29:30,500 to eerily pale. 497 00:29:31,579 --> 00:29:34,539 But these new pale areas aren't damaged-- 498 00:29:35,279 --> 00:29:39,480 instead, they change how the brain functions forever. 499 00:29:41,650 --> 00:29:43,270 When we look at brain scans, 500 00:29:43,410 --> 00:29:45,190 there are two obvious regions. 501 00:29:45,830 --> 00:29:47,930 There's an outer layer of grey matter, 502 00:29:48,269 --> 00:29:50,509 which is where the neuron cell bodies sit 503 00:29:50,510 --> 00:29:52,189 and where they make connections 504 00:29:52,190 --> 00:29:53,550 with other brain cells. 505 00:29:54,050 --> 00:29:56,530 And then on the inside, there's white matter. 506 00:29:57,570 --> 00:29:59,869 The reason the white matter is called white matter 507 00:29:59,870 --> 00:30:01,989 is because the nerve fibers are covered 508 00:30:01,990 --> 00:30:03,889 in a fatty insulating material 509 00:30:03,890 --> 00:30:04,910 that we call myelin. 510 00:30:08,250 --> 00:30:12,070 Myelin coats the long fibers of neurons, called axons, 511 00:30:12,470 --> 00:30:14,269 in the body, as well as the brain 512 00:30:14,270 --> 00:30:17,570 in structures known as myelin sheaths. 513 00:30:18,610 --> 00:30:19,669 Myelin sheaths 514 00:30:19,670 --> 00:30:21,249 are lined up along a nerve fiber, 515 00:30:21,250 --> 00:30:22,330 like a string of sausages, 516 00:30:23,390 --> 00:30:24,832 and the impulses are actually generated 517 00:30:24,833 --> 00:30:25,880 between the myelin sheaths, 518 00:30:25,881 --> 00:30:27,744 so the gaps between the sausages on the string. 519 00:30:30,830 --> 00:30:32,310 Without a myelin sheath, 520 00:30:32,750 --> 00:30:35,350 an impulse will move along a nerve fiber very slowly-- 521 00:30:35,615 --> 00:30:38,049 badoom, badoom, badoom, badoom, badoom, badoom. 522 00:30:38,050 --> 00:30:40,050 With a myelin sheath, 523 00:30:40,290 --> 00:30:41,643 it whizzes along the axon-- 524 00:30:41,644 --> 00:30:42,689 b'dum, b'dum, b'dum, b'dum, b'dum, b'dum. 525 00:30:42,690 --> 00:30:45,869 And the increase in speed of impulse conduction 526 00:30:45,870 --> 00:30:47,605 is about 200-fold. 527 00:30:49,690 --> 00:30:51,949 It's thought the retrovirus infection 528 00:30:51,950 --> 00:30:55,610 that led to the evolution of myelin happened many times, 529 00:30:56,030 --> 00:30:58,210 across several vertebrate lineages. 530 00:30:59,310 --> 00:31:00,590 And it was a gamechanger, 531 00:31:01,590 --> 00:31:05,426 as faster conduction times meant bodies could grow bigger. 532 00:31:10,300 --> 00:31:12,259 But the evolution of myelin 533 00:31:12,260 --> 00:31:15,672 had another profound effect on vertebrate life. 534 00:31:18,050 --> 00:31:19,530 So, throughout evolution, 535 00:31:19,790 --> 00:31:22,329 there has been a very great pressure for impulses 536 00:31:22,330 --> 00:31:24,750 to be transmitted along nerve fibers more rapidly. 537 00:31:26,129 --> 00:31:27,989 The invertebrates have come up with a solution 538 00:31:27,990 --> 00:31:30,148 of making impulse conduction more rapid, 539 00:31:30,149 --> 00:31:32,310 by making the nerve fibers bigger. 540 00:31:32,870 --> 00:31:35,209 And that reaches its zenith 541 00:31:35,210 --> 00:31:37,030 in giant squids, 542 00:31:38,070 --> 00:31:40,349 where the largest nerve fibers are about 543 00:31:40,350 --> 00:31:42,249 a millimeter in diameter. 544 00:31:42,250 --> 00:31:45,790 In contrast, 545 00:31:46,290 --> 00:31:49,189 the widest nerve fibers found in jawed vertebrates 546 00:31:49,190 --> 00:31:51,530 are up to one-tenth of a millimeter. 547 00:31:53,409 --> 00:31:55,709 Myelin means they are far less reliant 548 00:31:55,710 --> 00:31:56,849 on thick neurons 549 00:31:56,850 --> 00:31:58,490 to achieve fast conduction. 550 00:32:02,350 --> 00:32:05,049 So, there is a huge advantage 551 00:32:05,050 --> 00:32:07,649 in terms of saving space. 552 00:32:08,330 --> 00:32:09,750 So, when myelin appeared, 553 00:32:09,990 --> 00:32:11,729 it led to a quantum change 554 00:32:11,730 --> 00:32:13,209 in the sophistication of the brain, 555 00:32:13,469 --> 00:32:16,370 like the invention of microprocessors in computing. 556 00:32:17,449 --> 00:32:18,449 It's possible 557 00:32:18,610 --> 00:32:20,629 that we would not be able to have 558 00:32:20,630 --> 00:32:22,888 any form of conscious decision-making 559 00:32:22,889 --> 00:32:23,889 without myelin. 560 00:32:24,490 --> 00:32:28,250 Myelin enables rapid thought to transfer across the brain, 561 00:32:28,689 --> 00:32:30,628 and that's what consciousness relies on. 562 00:32:30,629 --> 00:32:32,909 The best you could do would be an octopus brain... 563 00:32:34,569 --> 00:32:35,969 which is quite sophisticated, 564 00:32:36,289 --> 00:32:38,048 but it hasn't written Shakespeare's sonnets 565 00:32:38,049 --> 00:32:40,541 or, you know, got us to the moon and back. 566 00:32:51,850 --> 00:32:54,490 Armed with turbocharged nervous systems, 567 00:32:55,169 --> 00:32:56,929 jawed vertebrates get bigger. 568 00:32:58,469 --> 00:33:01,810 And survival strategies grow more complex, 569 00:33:03,949 --> 00:33:07,189 leading some to leave the oceans entirely. 570 00:33:10,249 --> 00:33:13,609 On land, they are faced with an unfamiliar world. 571 00:33:16,350 --> 00:33:17,990 And as they adapt, 572 00:33:18,809 --> 00:33:22,649 their brains are forced to reshape once more. 573 00:33:30,800 --> 00:33:31,800 Compared to today, 574 00:33:31,900 --> 00:33:34,500 the Triassic was a vastly different environment. 575 00:33:35,100 --> 00:33:37,159 The continents were smashed together 576 00:33:37,160 --> 00:33:39,180 in a great continent called Pangaea. 577 00:33:41,840 --> 00:33:44,399 Pangaea was especially warm 578 00:33:44,400 --> 00:33:45,840 and dry, or arid. 579 00:33:46,240 --> 00:33:47,500 And in those conditions, 580 00:33:48,580 --> 00:33:49,939 there is a... 581 00:33:49,940 --> 00:33:52,079 a heightened struggle for existence, 582 00:33:52,080 --> 00:33:55,340 because of the scarcity of all kinds of food. 583 00:34:01,709 --> 00:34:03,990 During the Triassic, on land, 584 00:34:04,310 --> 00:34:05,928 two notable vertebrate groups 585 00:34:05,929 --> 00:34:07,490 included the archosaurs, 586 00:34:08,350 --> 00:34:10,330 meaning "ruling reptiles" in Greek, 587 00:34:10,889 --> 00:34:12,449 and the cynodonts. 588 00:34:14,089 --> 00:34:16,329 During the Triassic, the archosaurs 589 00:34:16,330 --> 00:34:18,670 truly became ruling reptiles, 590 00:34:19,089 --> 00:34:20,968 in that they rapidly became 591 00:34:20,969 --> 00:34:24,830 much larger, and they started to diversify, 592 00:34:25,170 --> 00:34:29,549 and one part would be the dinosaur line. 593 00:34:32,250 --> 00:34:35,489 Some of the cynodonts responded very differently. 594 00:34:35,969 --> 00:34:38,530 They evolved smaller and smaller body sizes, 595 00:34:38,790 --> 00:34:40,689 which helped them be more efficient 596 00:34:40,690 --> 00:34:42,810 in a world with limited resources. 597 00:34:43,190 --> 00:34:45,949 So what I have here is a skull of one of these animals. 598 00:34:46,130 --> 00:34:48,329 This is a kind a cynodont called a Thrinaxodon, 599 00:34:48,789 --> 00:34:50,369 and as you can see, it's really small. 600 00:34:50,610 --> 00:34:52,530 This would have probably been about the size of a rabbit. 601 00:34:53,550 --> 00:34:55,229 And so imagine what it was like 602 00:34:55,230 --> 00:34:57,190 being a cynodont in the Triassic. 603 00:34:57,489 --> 00:34:59,428 You're this tiny little thing 604 00:34:59,429 --> 00:35:02,120 in this world of big, scary reptiles. 605 00:35:06,179 --> 00:35:09,400 This little creature is one of those cynodonts, 606 00:35:09,780 --> 00:35:11,872 and an ancestor of the dolphin. 607 00:35:13,920 --> 00:35:14,920 She's hungry, 608 00:35:15,180 --> 00:35:18,300 but she knows the archosaurs patrolling outside 609 00:35:18,800 --> 00:35:20,000 are hungry, too. 610 00:35:22,449 --> 00:35:23,989 But as night falls, 611 00:35:25,289 --> 00:35:27,549 the threat seems to lessen. 612 00:35:31,130 --> 00:35:33,044 She's spotted an opportunity. 613 00:35:37,899 --> 00:35:40,658 Cynodonts seem to have dealt with the existence 614 00:35:40,659 --> 00:35:44,139 of huge imposing reptiles 615 00:35:44,659 --> 00:35:46,219 by separating themselves, 616 00:35:47,500 --> 00:35:50,459 and part of the separation was their development 617 00:35:50,460 --> 00:35:51,500 of the ability to burrow... 618 00:35:52,119 --> 00:35:55,099 but it may well be that during this time too, 619 00:35:56,180 --> 00:35:57,700 Cynodonts became increasingly 620 00:35:58,459 --> 00:35:59,879 nocturnal, or active in the night. 621 00:36:04,050 --> 00:36:06,829 So, cynodonts would forage for food 622 00:36:06,830 --> 00:36:08,590 at night, when it was safe. 623 00:36:10,289 --> 00:36:12,989 But of course, the sense that had helped drive 624 00:36:12,990 --> 00:36:15,630 much of the evolution of the brain-- vision-- 625 00:36:15,970 --> 00:36:18,110 was now much less useful. 626 00:36:19,290 --> 00:36:22,210 In becoming nocturnal, cynodonts' senses 627 00:36:22,710 --> 00:36:24,610 had to do very different things. 628 00:36:25,710 --> 00:36:26,949 So, you can imagine 629 00:36:26,950 --> 00:36:30,270 a big population of little snuffling cynodonts. 630 00:36:31,710 --> 00:36:34,130 And some of them might have had, 631 00:36:34,610 --> 00:36:36,569 genetically, a somewhat greater ability 632 00:36:36,570 --> 00:36:38,929 to find their way around using touch, 633 00:36:38,930 --> 00:36:40,710 or slightly better senses of smell. 634 00:36:42,570 --> 00:36:46,669 And if those things conferred 635 00:36:46,670 --> 00:36:47,929 some kind of advantage 636 00:36:47,930 --> 00:36:50,569 that would ultimately allow those individuals 637 00:36:50,570 --> 00:36:53,010 to be more successful in reproducing, 638 00:36:54,030 --> 00:36:55,389 then eventually those characteristics 639 00:36:55,390 --> 00:36:57,110 would come to be present in 640 00:36:57,910 --> 00:36:59,390 most or all of the population. 641 00:37:01,599 --> 00:37:04,959 And so, with these changing and improving senses, 642 00:37:04,960 --> 00:37:07,279 there was so much more information, 643 00:37:07,839 --> 00:37:10,798 and thus more evolutionary pressure on the brain 644 00:37:10,799 --> 00:37:12,120 to develop in tandem. 645 00:37:16,300 --> 00:37:18,980 It was this flood of new information, 646 00:37:19,420 --> 00:37:21,740 gathered by senses sharpening to the night 647 00:37:22,340 --> 00:37:25,799 that scientists think helped drive a monumental change 648 00:37:25,800 --> 00:37:27,922 in the brains of those cynodonts. 649 00:37:34,380 --> 00:37:36,600 Over tens of millions of years, 650 00:37:37,060 --> 00:37:38,620 the brain changes shape. 651 00:37:40,300 --> 00:37:43,720 Areas involved in smell and touch expand. 652 00:37:45,740 --> 00:37:48,179 And the brain increases in size 653 00:37:48,180 --> 00:37:50,400 by over 40%. 654 00:37:51,739 --> 00:37:54,119 And to process all the extra information, 655 00:37:54,980 --> 00:37:57,380 a game-changing region of the brain develops. 656 00:38:01,850 --> 00:38:03,270 And alongside it, 657 00:38:04,529 --> 00:38:06,610 a new type of animal emerges. 658 00:38:07,990 --> 00:38:09,588 So in this little bottle here 659 00:38:09,589 --> 00:38:12,089 is the preserved brain of a rabbit, 660 00:38:12,250 --> 00:38:13,810 which is, of course, a modern mammal. 661 00:38:14,510 --> 00:38:16,949 This large bulbous part that we see here 662 00:38:16,950 --> 00:38:18,170 is called the neocortex. 663 00:38:24,150 --> 00:38:27,230 This is a uniquely mammalian part of the brain. 664 00:38:29,010 --> 00:38:30,709 The neocortex contains 665 00:38:30,710 --> 00:38:32,830 a bewildering number of neural circuits. 666 00:38:33,450 --> 00:38:35,649 It's the area of the brain that allows them to process 667 00:38:35,650 --> 00:38:38,390 all that additional really complex sensory information. 668 00:38:39,970 --> 00:38:41,909 Here is the brain of a boar, 669 00:38:41,910 --> 00:38:43,350 which is a member of the pig family, 670 00:38:43,750 --> 00:38:44,909 and what you can see 671 00:38:44,910 --> 00:38:46,268 is that the neocortex 672 00:38:46,269 --> 00:38:47,650 is highly folded. 673 00:38:48,769 --> 00:38:51,429 And this means that the surface area is much larger, 674 00:38:51,430 --> 00:38:54,029 which means that you can contain many more neural circuits 675 00:38:54,030 --> 00:38:56,129 and therefore a much greater level 676 00:38:56,130 --> 00:38:58,390 of sophistication in neural processing. 677 00:39:00,130 --> 00:39:03,469 Though it was driven to expand in part by improving 678 00:39:03,470 --> 00:39:05,450 senses of smell and touch, 679 00:39:06,390 --> 00:39:09,209 today, the neocortex does much more 680 00:39:09,210 --> 00:39:11,050 than aid in sensory processing. 681 00:39:12,690 --> 00:39:16,010 Mammals... the group of animals with a neocortex, 682 00:39:16,449 --> 00:39:20,990 have an enormous range of complex behaviors 683 00:39:21,570 --> 00:39:25,730 that are really unmatched almost anywhere else among vertebrates. 684 00:39:27,350 --> 00:39:29,789 The neocortex is generally 685 00:39:29,790 --> 00:39:32,410 involved in very high-level processing. 686 00:39:34,430 --> 00:39:35,229 Self-awareness, 687 00:39:35,230 --> 00:39:36,290 social cognition, 688 00:39:36,970 --> 00:39:39,590 some forms of memory, problem solving. 689 00:39:40,790 --> 00:39:42,969 So, the evolution of the neocortex 690 00:39:42,970 --> 00:39:45,669 was absolutely essential for what we think of 691 00:39:45,670 --> 00:39:48,510 now as the high intelligence of mammals. 692 00:39:51,000 --> 00:39:52,400 Of course, today, 693 00:39:52,700 --> 00:39:54,159 mammals aren't the only ones 694 00:39:54,160 --> 00:39:56,300 to display higher levels of intelligence. 695 00:39:59,280 --> 00:40:03,160 Other groups have taken their own evolutionary routes 696 00:40:03,660 --> 00:40:05,420 to problem-solving brains. 697 00:40:10,050 --> 00:40:11,530 But for mammals, 698 00:40:12,090 --> 00:40:15,666 the neocortex has been truly transformational. 699 00:40:20,710 --> 00:40:21,710 It's interesting, 700 00:40:21,850 --> 00:40:24,850 because the neocortex in particular 701 00:40:25,209 --> 00:40:28,510 is incredibly expensive energetically, 702 00:40:29,089 --> 00:40:30,850 both to develop and to maintain. 703 00:40:31,310 --> 00:40:32,489 But I think that the power 704 00:40:34,310 --> 00:40:37,470 of being able to think your way through problems 705 00:40:37,930 --> 00:40:40,210 is just so immense, 706 00:40:41,169 --> 00:40:44,770 that the advantages conferred by that power 707 00:40:45,830 --> 00:40:49,129 override nearly any cost that you can imagine. 708 00:40:55,550 --> 00:40:59,168 Fast forward through the next 150 million years. 709 00:41:06,220 --> 00:41:08,339 Fueled by warm blood and milk, 710 00:41:09,620 --> 00:41:11,779 mammalian brains keep developing, 711 00:41:13,560 --> 00:41:14,560 until... 712 00:41:17,369 --> 00:41:20,210 it's the mammals' turn to take center stage. 713 00:41:23,750 --> 00:41:26,530 Then, 50 million years ago, 714 00:41:26,790 --> 00:41:28,670 we find one lineage... 715 00:41:30,929 --> 00:41:34,130 on the verge of an extraordinary metamorphosis. 716 00:41:46,660 --> 00:41:49,920 This little mammal is called Indohyus. 717 00:41:55,300 --> 00:41:57,560 The size of a domestic cat, 718 00:41:58,300 --> 00:41:59,980 with spindly, deerlike legs 719 00:42:00,480 --> 00:42:02,160 and the snout of a dog. 720 00:42:03,120 --> 00:42:05,539 Quite frankly, she's a bit of an oddball. 721 00:42:09,540 --> 00:42:11,140 Tiptoeing on her little hooves, 722 00:42:11,360 --> 00:42:13,334 she's on the lookout for lunch. 723 00:42:20,050 --> 00:42:22,350 But she's not the only one. 724 00:42:23,250 --> 00:42:25,150 As a small herbivore, 725 00:42:25,390 --> 00:42:27,009 she would be easy pickings 726 00:42:27,010 --> 00:42:30,289 for the giant predatory birds that circle above... 727 00:42:32,390 --> 00:42:34,729 if it weren't for one advantage 728 00:42:34,730 --> 00:42:37,790 scientists think Indohyus has on her side. 729 00:42:41,750 --> 00:42:43,930 This is a thigh bone of Indohyus, 730 00:42:44,130 --> 00:42:45,229 and from the size, 731 00:42:45,230 --> 00:42:46,129 you can tell that this 732 00:42:46,130 --> 00:42:47,829 was a small animal, this is actually 733 00:42:47,830 --> 00:42:50,370 similar in size to the thigh bone of a cat. 734 00:42:50,730 --> 00:42:53,730 In addition to these complete thigh bones, 735 00:42:53,830 --> 00:42:55,408 we also found some broken ones, 736 00:42:55,409 --> 00:42:57,530 so here's the same bone, but now the broken part. 737 00:42:57,950 --> 00:43:00,470 And yet this is very important for us, 738 00:43:00,570 --> 00:43:03,190 because on the cut section of this bone, 739 00:43:03,670 --> 00:43:07,143 you can tell that the outside of the bone is very thick. 740 00:43:09,270 --> 00:43:11,230 Compared with related species, 741 00:43:11,590 --> 00:43:13,189 the leg bones of Indohyus 742 00:43:13,190 --> 00:43:14,610 are unusually thick, 743 00:43:15,430 --> 00:43:16,690 making the bones heavy. 744 00:43:17,870 --> 00:43:18,909 As far as the purpose 745 00:43:18,910 --> 00:43:21,230 of the heavy leg bones of Indohyus, 746 00:43:21,370 --> 00:43:23,249 we have clues in the animal kingdom 747 00:43:23,250 --> 00:43:24,609 when we look at the bones 748 00:43:24,610 --> 00:43:25,686 of hippos. 749 00:43:29,460 --> 00:43:32,040 Hippopotamus have heavy leg bones, 750 00:43:32,940 --> 00:43:34,300 and it helps them 751 00:43:34,700 --> 00:43:36,219 to move along 752 00:43:36,220 --> 00:43:38,880 by walking on the bottom of a lake, 753 00:43:39,339 --> 00:43:40,939 and I think it's possible 754 00:43:40,940 --> 00:43:42,900 that Indohyus did the same thing. 755 00:43:46,380 --> 00:43:48,400 Scientists think that for Indohyus, 756 00:43:49,100 --> 00:43:50,559 water is a refuge. 757 00:43:52,700 --> 00:43:56,580 And for the individuals most adapted to an aquatic lifestyle, 758 00:43:57,299 --> 00:44:01,832 this new world also offers up plenty of new food sources. 759 00:44:08,700 --> 00:44:10,839 So, over generations, 760 00:44:11,640 --> 00:44:14,399 Indohyus's relatives become more streamlined. 761 00:44:15,899 --> 00:44:17,779 Limbs gradually transform 762 00:44:18,359 --> 00:44:19,359 into flippers. 763 00:44:21,839 --> 00:44:25,699 Nostrils migrate farther away from their long snouts. 764 00:44:28,075 --> 00:44:32,728 Tails get flatter and more powerful, 765 00:44:32,729 --> 00:44:35,670 in one of the most remarkable transformations 766 00:44:36,090 --> 00:44:39,010 in the history of life on Earth. 767 00:44:48,449 --> 00:44:53,129 So, in just 10 to 15 million years after Indohyus, 768 00:44:53,290 --> 00:44:55,068 the little deer-like creature 769 00:44:55,069 --> 00:44:56,790 at the edge of the water, 770 00:44:57,089 --> 00:45:00,169 we have this massive aquatic predator. 771 00:45:03,169 --> 00:45:04,969 Biologist Kel Melillo Sweeting 772 00:45:04,970 --> 00:45:08,529 studies the behavior and communication of marine mammals. 773 00:45:09,230 --> 00:45:12,730 Here is a model skull of Dorudon. 774 00:45:13,649 --> 00:45:16,349 It's no longer breathing out of the tip of its snout. 775 00:45:17,010 --> 00:45:20,410 Its nostrils have shifted farther up, 776 00:45:20,609 --> 00:45:22,870 closer to the eyes, to be more efficient. 777 00:45:23,310 --> 00:45:27,430 So that it can stay submerged while it takes a breath. 778 00:45:28,089 --> 00:45:30,909 It's living its entire life in the water. 779 00:45:32,390 --> 00:45:34,528 The transformation from Indohyus 780 00:45:34,529 --> 00:45:36,410 to Dorudon was incredible, 781 00:45:36,910 --> 00:45:39,470 but in only a few more million years... 782 00:45:41,330 --> 00:45:42,330 Simocetus. 783 00:45:44,850 --> 00:45:46,369 Simocetus belonged to a group 784 00:45:46,370 --> 00:45:47,930 of pioneering marine mammals. 785 00:45:49,269 --> 00:45:51,049 The first toothed whales. 786 00:45:51,890 --> 00:45:53,409 A group who developed 787 00:45:53,410 --> 00:45:55,569 an extraordinary new sensory capacity. 788 00:45:57,800 --> 00:46:02,280 It has this concave area at the front of its skull. 789 00:46:03,100 --> 00:46:05,499 This is suggestive that it had space 790 00:46:05,500 --> 00:46:07,080 for an organ called the melon. 791 00:46:07,540 --> 00:46:09,119 The melon is a fatty tissue, 792 00:46:09,120 --> 00:46:11,653 and is indicative of echolocation. 793 00:46:14,750 --> 00:46:16,889 The melon allowed Simocetus 794 00:46:16,890 --> 00:46:18,029 to focus the soundwaves 795 00:46:18,430 --> 00:46:20,008 of its echolocation calls. 796 00:46:27,550 --> 00:46:30,436 A vital body part that has been passed down... 797 00:46:31,789 --> 00:46:35,625 ...allowing Simocetus's modern relatives to echolocate today. 798 00:46:44,466 --> 00:46:47,637 We've got dolphins at 3:00. 799 00:46:47,638 --> 00:46:49,053 Some dorsal fins 800 00:46:49,054 --> 00:46:50,714 and they're coming to the boat. They're coming, 801 00:46:50,899 --> 00:46:52,600 and they're riding the bow. 802 00:46:53,359 --> 00:46:56,160 Oh man, they are so graceful. 803 00:46:59,680 --> 00:47:02,500 It's just amazing to see them this close. 804 00:47:08,300 --> 00:47:09,819 Dolphin communication 805 00:47:09,820 --> 00:47:14,640 is very complex, just as our communication is very complex. 806 00:47:15,200 --> 00:47:17,879 You have friendships between individuals 807 00:47:17,880 --> 00:47:19,840 that extend over 808 00:47:20,100 --> 00:47:23,740 not just days or weeks, but over years, 809 00:47:24,100 --> 00:47:26,919 allowing information to be passed on 810 00:47:26,920 --> 00:47:30,399 between individuals and also passed down 811 00:47:30,400 --> 00:47:31,400 through the generations. 812 00:47:33,040 --> 00:47:34,920 Tens of millions of years ago, 813 00:47:35,440 --> 00:47:37,499 as the ancestors of these dolphins 814 00:47:37,500 --> 00:47:41,800 took to hunting together, their brains began to change. 815 00:47:43,400 --> 00:47:45,519 Regions likely involved in bonding, 816 00:47:45,520 --> 00:47:47,920 emotions, and communication 817 00:47:48,539 --> 00:47:50,160 underwent rapid expansion. 818 00:47:53,740 --> 00:47:54,920 Meaning that today, 819 00:47:55,480 --> 00:47:58,320 the dolphins' most remarkable adaptation of all 820 00:47:59,180 --> 00:48:01,980 is the one hidden inside their skulls. 821 00:48:07,199 --> 00:48:09,959 So, this is the, the brain of a common dolphin. 822 00:48:09,960 --> 00:48:10,938 It's really large. 823 00:48:10,939 --> 00:48:12,200 It's probably bigger than my brain. 824 00:48:12,799 --> 00:48:14,159 So, the complex structures 825 00:48:14,160 --> 00:48:16,259 and crinkliness of this brain 826 00:48:16,260 --> 00:48:17,438 tells me that this animal 827 00:48:17,439 --> 00:48:20,439 would have had a huge surface area in its neocortex. 828 00:48:20,659 --> 00:48:22,979 It would've been able to process really complex thoughts 829 00:48:22,980 --> 00:48:24,339 and really complex information. 830 00:48:25,260 --> 00:48:26,259 It's really quite astonishing 831 00:48:26,260 --> 00:48:29,118 to think that everything that makes an animal what it is 832 00:48:29,119 --> 00:48:31,579 and how it behaves is held in a structure like this. 833 00:48:33,599 --> 00:48:35,460 When you're looking at a dolphin brain, 834 00:48:36,399 --> 00:48:37,839 you're looking at someone. 835 00:48:39,560 --> 00:48:42,100 You're looking at someone's mind. 836 00:48:48,590 --> 00:48:50,410 Just like for human beings, 837 00:48:51,810 --> 00:48:53,209 intelligence is a trait 838 00:48:53,210 --> 00:48:55,630 that has paid enormous dividends for dolphins. 839 00:49:01,150 --> 00:49:03,029 Today, 38 species 840 00:49:03,030 --> 00:49:05,710 of oceanic dolphin are found across the planet. 841 00:49:07,670 --> 00:49:09,520 Ranging from smaller species... 842 00:49:11,750 --> 00:49:13,690 up to the mighty orca. 843 00:49:14,950 --> 00:49:16,129 Different dolphin groups 844 00:49:16,130 --> 00:49:19,188 have regional quirks and specificities, 845 00:49:19,189 --> 00:49:22,670 the triumphs and traumas that other groups don't have. 846 00:49:25,690 --> 00:49:27,950 And, in whatever way... 847 00:49:29,110 --> 00:49:31,330 those elements are transmitted 848 00:49:31,970 --> 00:49:33,869 down the generations and persist, 849 00:49:33,870 --> 00:49:34,654 that's culture. 850 00:49:38,950 --> 00:49:40,528 It's always exciting 851 00:49:40,529 --> 00:49:42,549 to see them riding the bow of the boat, 852 00:49:42,770 --> 00:49:43,809 getting a free ride, 853 00:49:43,810 --> 00:49:44,822 having some fun. 854 00:49:48,182 --> 00:49:48,839 Scientists, 855 00:49:48,840 --> 00:49:50,739 we're often told we need to be 856 00:49:50,740 --> 00:49:51,740 very objective 857 00:49:51,960 --> 00:49:54,300 and very serious and all of that, 858 00:49:54,520 --> 00:49:56,200 but if you love your work, 859 00:49:57,160 --> 00:49:59,660 how could you not look at dolphins 860 00:50:00,740 --> 00:50:03,300 and see ourselves in them, right? 861 00:50:03,520 --> 00:50:05,019 Someone once said they're, 862 00:50:05,020 --> 00:50:08,379 they're what human beings might have been 863 00:50:08,380 --> 00:50:10,020 had we returned to the sea... 864 00:50:10,500 --> 00:50:12,400 and I think that that's true. 865 00:50:16,080 --> 00:50:18,499 Dolphins have a level of 866 00:50:18,500 --> 00:50:24,019 social cohesion that is really, I think, in many ways, 867 00:50:24,020 --> 00:50:26,240 beyond what we have as humans. 868 00:50:26,780 --> 00:50:30,220 Um, they not only care for each other, 869 00:50:30,359 --> 00:50:31,839 but they stay together. 870 00:50:32,060 --> 00:50:34,540 So, if a mother has a calf, 871 00:50:35,399 --> 00:50:37,559 there are other female dolphins 872 00:50:37,560 --> 00:50:40,960 around who attend to her like midwives. 873 00:50:42,080 --> 00:50:43,898 We've even observed orcas, 874 00:50:43,899 --> 00:50:46,720 feeding disabled individuals of their pods. 875 00:50:48,100 --> 00:50:49,379 I think it's pretty clear 876 00:50:49,999 --> 00:50:53,080 that dolphins are an empathetic species. 877 00:50:54,399 --> 00:50:56,739 Something that I find very inspiring is that, 878 00:50:56,740 --> 00:50:58,260 that empathetic characteristic 879 00:50:58,760 --> 00:51:00,700 seems to be more and more developed, 880 00:51:00,839 --> 00:51:04,104 the more intelligent a mammalian lineage becomes. 881 00:51:07,550 --> 00:51:09,650 An evolutionary journey, 882 00:51:09,950 --> 00:51:12,889 which began with the first tentative steps 883 00:51:12,890 --> 00:51:15,910 towards sensing a world bathed in light, 884 00:51:16,990 --> 00:51:18,670 produced the first neurons... 885 00:51:20,310 --> 00:51:21,870 and primitive brains, 886 00:51:23,910 --> 00:51:25,050 supercharged by myelin, 887 00:51:26,370 --> 00:51:29,330 to finally form the mammalian neocortex. 888 00:51:30,630 --> 00:51:33,790 And in a few select lineages... 889 00:51:35,470 --> 00:51:38,190 this gave rise to problem-solving, 890 00:51:38,610 --> 00:51:41,690 cooperative, and deeply emotional brains. 891 00:51:43,990 --> 00:51:45,630 I, personally-- 892 00:51:46,250 --> 00:51:47,379 and perhaps this is because 893 00:51:47,380 --> 00:51:48,589 I'm a vertebrate biologist 894 00:51:48,590 --> 00:51:50,830 and an animal biologist in general-- 895 00:51:51,170 --> 00:51:54,589 have absolutely no problem asserting that the brain 896 00:51:54,590 --> 00:51:57,110 is more or less the pinnacle 897 00:51:57,480 --> 00:51:59,989 of what evolution can do 898 00:51:59,990 --> 00:52:02,830 with life's natural biotechnology. 899 00:52:03,110 --> 00:52:05,650 Brains are complex. They just are. 900 00:52:06,810 --> 00:52:08,290 And then what you have in the dolphin 901 00:52:08,670 --> 00:52:10,510 is just a brain that 902 00:52:11,410 --> 00:52:14,610 is one of the most complex on earth.