1 00:00:01,024 --> 00:00:03,540 What is so special about the human brain? 2 00:00:03,540 --> 00:00:05,660 Why is it that we study other animals 3 00:00:05,660 --> 00:00:07,660 instead of them studying us? 4 00:00:07,660 --> 00:00:09,580 What does a human brain have or do 5 00:00:09,580 --> 00:00:11,420 that no other brain does? 6 00:00:11,420 --> 00:00:14,220 When I became interested in these questions about 10 years ago, 7 00:00:14,220 --> 00:00:15,700 scientists thought they knew 8 00:00:15,700 --> 00:00:17,380 what different brains were made of. 9 00:00:17,380 --> 00:00:19,140 Though it was based on very little evidence, 10 00:00:19,140 --> 00:00:21,020 many scientists thought that all mammalian brains, 11 00:00:21,020 --> 00:00:22,820 including the human brain, 12 00:00:22,820 --> 00:00:24,260 were made in the same way, 13 00:00:24,260 --> 00:00:25,700 with a number of neurons that was always 14 00:00:25,700 --> 00:00:27,700 proportional to the size of the brain. 15 00:00:27,700 --> 00:00:29,700 This means that two brains of the same size, 16 00:00:29,700 --> 00:00:33,140 like these two, with a respectable 400 grams, 17 00:00:33,140 --> 00:00:35,860 should have similar numbers of neurons. 18 00:00:35,860 --> 00:00:37,780 Now, if neurons are the functional 19 00:00:37,780 --> 00:00:40,620 information processing units of the brain, 20 00:00:40,620 --> 00:00:42,260 then the owners of these two brains 21 00:00:42,260 --> 00:00:44,820 should have similar cognitive abilities. 22 00:00:44,820 --> 00:00:47,260 And yet, one is a chimp, 23 00:00:47,260 --> 00:00:50,020 and the other is a cow. 24 00:00:50,020 --> 00:00:52,260 Now maybe cows have a really rich 25 00:00:52,260 --> 00:00:54,620 internal mental life and are so smart 26 00:00:54,620 --> 00:00:58,380 that they choose not to let us realize it, 27 00:00:58,380 --> 00:01:00,300 but we eat them. 28 00:01:00,300 --> 00:01:01,660 I think most people will agree 29 00:01:01,660 --> 00:01:03,660 that chimps are capable of much more complex, 30 00:01:03,660 --> 00:01:06,500 elaborate, and flexible behaviors than cows are. 31 00:01:06,500 --> 00:01:08,540 So this is a first indication that the 32 00:01:08,540 --> 00:01:10,420 "all brains are made the same way" scenario 33 00:01:10,420 --> 00:01:11,860 is not quite right. 34 00:01:11,860 --> 00:01:13,700 But let's play along. 35 00:01:13,700 --> 00:01:15,460 If all brains were made the same way 36 00:01:15,460 --> 00:01:17,820 and you were to compare animals with brains of different sizes, 37 00:01:17,820 --> 00:01:20,340 larger brains should always have more neurons 38 00:01:20,340 --> 00:01:21,940 than smaller brains, 39 00:01:21,940 --> 00:01:23,340 and the larger the brain, 40 00:01:23,340 --> 00:01:25,500 the more cognitively able its owner should be. 41 00:01:25,500 --> 00:01:27,620 So the largest brain around should also be 42 00:01:27,620 --> 00:01:30,140 the most cognitively able. 43 00:01:30,140 --> 00:01:31,860 And here comes the bad news: 44 00:01:31,860 --> 00:01:34,340 our brain, not the largest one around. 45 00:01:34,340 --> 00:01:36,140 It seems quite vexing. 46 00:01:36,140 --> 00:01:38,860 Our brain weighs between 1.2 and 1.5 kilos, 47 00:01:38,860 --> 00:01:42,100 but elephant brains weigh between four and five kilos, 48 00:01:42,100 --> 00:01:44,500 and whale brains can weigh up to nine kilos, 49 00:01:44,500 --> 00:01:49,180 which is why scientists used to resort to saying 50 00:01:49,180 --> 00:01:51,380 that our brain must be special 51 00:01:51,380 --> 00:01:54,380 to explain our cognitive abilities. 52 00:01:54,380 --> 00:01:57,220 It must be really extraordinary, 53 00:01:57,220 --> 00:01:59,380 an exception to the rule. 54 00:01:59,380 --> 00:02:03,100 Theirs may be bigger, but ours is better, 55 00:02:03,100 --> 00:02:04,900 and it could be better for example 56 00:02:04,900 --> 00:02:06,700 in that it seems larger than it should be, 57 00:02:06,700 --> 00:02:09,260 with a much larger cerebral cortex than it should have, 58 00:02:09,260 --> 00:02:10,860 for the size of our bodies. 59 00:02:10,860 --> 00:02:12,620 So that would give us extra cortex 60 00:02:12,620 --> 00:02:15,580 to do more interesting things than just operating the body. 61 00:02:15,580 --> 00:02:17,260 That's because the size of the brain 62 00:02:17,260 --> 00:02:19,300 usually follows the size of the body. 63 00:02:19,300 --> 00:02:21,540 So the main reason for saying that 64 00:02:21,540 --> 00:02:23,780 our brain is larger than it should be 65 00:02:23,780 --> 00:02:25,660 actually comes from comparing ourselves 66 00:02:25,660 --> 00:02:27,300 to great apes. 67 00:02:27,300 --> 00:02:29,940 Gorillas can be two to three times larger than we are, 68 00:02:29,940 --> 00:02:32,300 so their brains should also be larger than ours, 69 00:02:32,300 --> 00:02:34,260 but instead it's the other way around. 70 00:02:34,260 --> 00:02:37,980 Our brain is three times larger than a gorilla brain. 71 00:02:37,980 --> 00:02:39,700 The human brain also seems special 72 00:02:39,700 --> 00:02:41,500 in the amount of energy that it uses. 73 00:02:41,500 --> 00:02:44,220 Although it weighs only two percent of the body, 74 00:02:44,220 --> 00:02:46,940 it alone uses 25 percent of all the energy 75 00:02:46,940 --> 00:02:49,940 that your body requires to run per day. 76 00:02:49,940 --> 00:02:52,940 That's 500 calories out of a total of 2,000 calories, 77 00:02:52,940 --> 00:02:55,900 just to keep your brain working. 78 00:02:55,900 --> 00:02:58,780 So the human brain is larger than it should be, 79 00:02:58,780 --> 00:03:00,900 it uses much more energy than it should, 80 00:03:00,900 --> 00:03:02,820 so it's special. 81 00:03:02,820 --> 00:03:05,020 And this is where the story started to bother me. 82 00:03:05,020 --> 00:03:06,660 In biology, we look for rules 83 00:03:06,660 --> 00:03:09,460 that apply to all animals and to life in general, 84 00:03:09,460 --> 00:03:11,340 so why should the rules of evolution 85 00:03:11,340 --> 00:03:14,860 apply to everybody else but not to us? 86 00:03:14,860 --> 00:03:16,980 Maybe the problem was with the basic assumption 87 00:03:16,980 --> 00:03:19,220 that all brains are made in the same way. 88 00:03:19,220 --> 00:03:21,020 Maybe two brains of a similar size 89 00:03:21,020 --> 00:03:23,180 can actually be made of very different numbers of neurons. 90 00:03:23,180 --> 00:03:24,940 Maybe a very large brain 91 00:03:24,940 --> 00:03:26,780 does not necessarily have more neurons 92 00:03:26,780 --> 00:03:29,140 than a more modest-sized brain. 93 00:03:29,140 --> 00:03:31,780 Maybe the human brain actually has the most neurons 94 00:03:31,780 --> 00:03:34,260 of any brain, regardless of its size, 95 00:03:34,260 --> 00:03:36,740 especially in the cerebral cortex. 96 00:03:36,740 --> 00:03:38,860 So this to me became the important question 97 00:03:38,860 --> 00:03:40,420 to answer: 98 00:03:40,420 --> 00:03:42,220 how many neurons does the human brain have, 99 00:03:42,220 --> 00:03:44,620 and how does that compare to other animals? 100 00:03:44,620 --> 00:03:46,980 Now, you may have heard or read somewhere 101 00:03:46,980 --> 00:03:49,060 than we have a hundred billion neurons, 102 00:03:49,060 --> 00:03:51,300 so 10 years ago, I asked my colleagues 103 00:03:51,300 --> 00:03:53,540 if they knew where this number came from. 104 00:03:53,540 --> 00:03:55,060 But nobody did. 105 00:03:55,060 --> 00:03:56,420 I've been digging through the literature 106 00:03:56,420 --> 00:03:58,140 for the original reference for that number, 107 00:03:58,140 --> 00:04:00,060 and I could never find it. 108 00:04:00,060 --> 00:04:02,660 It seems that nobody had actually ever counted 109 00:04:02,660 --> 00:04:04,380 the number of neurons in the human brain, 110 00:04:04,380 --> 00:04:06,820 or in any other brain for that matter. 111 00:04:06,820 --> 00:04:10,260 So I came up with my own way to count cells in the brain, 112 00:04:10,260 --> 00:04:12,260 and it essentially consists of 113 00:04:12,260 --> 00:04:14,660 dissolving that brain into soup. 114 00:04:14,660 --> 00:04:17,465 It works like this: 115 00:04:17,465 --> 00:04:20,500 you take a brain, or parts of that brain, 116 00:04:20,500 --> 00:04:22,460 and you dissolve it in detergent, 117 00:04:22,460 --> 00:04:24,260 which destroys the cell membranes 118 00:04:24,260 --> 00:04:26,312 but keeps the cell nuclei intact, 119 00:04:26,312 --> 00:04:29,100 so you end up with a suspension of free nuclei 120 00:04:29,100 --> 00:04:31,340 that looks like this, 121 00:04:31,340 --> 00:04:33,060 like a clear soup. 122 00:04:33,060 --> 00:04:34,860 This soup contains all the nuclei 123 00:04:34,860 --> 00:04:36,620 that once were a mouse brain. 124 00:04:36,620 --> 00:04:39,420 Now, the beauty of a soup is that because it is soup, 125 00:04:39,420 --> 00:04:42,580 you can agitate it and make those nuclei 126 00:04:42,580 --> 00:04:44,580 be distributed homogeneously in the liquid, 127 00:04:44,580 --> 00:04:46,500 so that now by looking under the microscope 128 00:04:46,500 --> 00:04:50,260 at just four or five samples of this homogeneous solution, 129 00:04:50,260 --> 00:04:53,180 you can count nuclei, and therefore tell 130 00:04:53,180 --> 00:04:55,060 how many cells that brain had. 131 00:04:55,060 --> 00:04:56,700 It's simple, it's straightforward, 132 00:04:56,700 --> 00:04:58,180 and it's really fast. 133 00:04:58,180 --> 00:05:00,100 So we've used that method to count neurons 134 00:05:00,100 --> 00:05:02,180 in dozens of different species so far, 135 00:05:02,180 --> 00:05:03,900 and it turns out that all brains 136 00:05:03,900 --> 00:05:06,220 are not made the same way. 137 00:05:06,220 --> 00:05:08,500 Take rodents and primates, for instance: 138 00:05:08,500 --> 00:05:10,860 in larger rodent brains, the average size 139 00:05:10,860 --> 00:05:12,700 of the neuron increases, 140 00:05:12,700 --> 00:05:14,900 so the brain inflates very rapidly 141 00:05:14,900 --> 00:05:18,220 and gains size much faster than it gains neurons. 142 00:05:18,220 --> 00:05:20,260 But primate brains gain neurons 143 00:05:20,260 --> 00:05:22,580 without the average neuron becoming any larger, 144 00:05:22,580 --> 00:05:24,460 which is a very economical way 145 00:05:24,460 --> 00:05:26,220 to add neurons to your brain. 146 00:05:26,220 --> 00:05:27,940 The result is that a primate brain 147 00:05:27,940 --> 00:05:30,860 will always have more neurons than a rodent brain of the same size, 148 00:05:30,860 --> 00:05:32,420 and the larger the brain, 149 00:05:32,420 --> 00:05:34,540 the larger this difference will be. 150 00:05:34,540 --> 00:05:36,460 Well, what about our brain then? 151 00:05:36,460 --> 00:05:38,220 We found that we have, on average, 152 00:05:38,220 --> 00:05:40,020 86 billion neurons, 153 00:05:40,020 --> 00:05:42,620 16 billion of which are in the cerebral cortex, 154 00:05:42,620 --> 00:05:44,700 and if you consider that the cerebral cortex 155 00:05:44,700 --> 00:05:47,380 is the seat of functions like 156 00:05:47,380 --> 00:05:51,100 awareness and logical and abstract reasoning, 157 00:05:51,100 --> 00:05:53,900 and that 16 billion is the most neurons 158 00:05:53,900 --> 00:05:56,660 that any cortex has, 159 00:05:56,660 --> 00:05:58,500 I think this is the simplest explanation 160 00:05:58,500 --> 00:06:01,660 for our remarkable cognitive abilities. 161 00:06:01,660 --> 00:06:04,940 But just as important is what the 86 billion neurons mean. 162 00:06:04,940 --> 00:06:06,500 Because we found that the relationship 163 00:06:06,500 --> 00:06:08,607 between the size of the brain and its number of neurons 164 00:06:08,607 --> 00:06:10,740 could be described mathematically, 165 00:06:10,740 --> 00:06:12,820 we could calculate what a human brain 166 00:06:12,820 --> 00:06:15,340 would look like if it was made like a rodent brain. 167 00:06:15,340 --> 00:06:18,500 So, a rodent brain with 86 billion neurons 168 00:06:18,500 --> 00:06:23,020 would weigh 36 kilos. 169 00:06:23,020 --> 00:06:24,300 That's not possible. 170 00:06:24,300 --> 00:06:25,820 A brain that huge would be crushed 171 00:06:25,820 --> 00:06:27,020 by its own weight, 172 00:06:27,020 --> 00:06:28,500 and this impossible brain would go 173 00:06:28,500 --> 00:06:31,180 in the body of 89 tons. 174 00:06:31,180 --> 00:06:34,220 I don't think it looks like us. 175 00:06:34,220 --> 00:06:36,620 So this brings us to a very important conclusion already, 176 00:06:36,620 --> 00:06:39,420 which is that we are not rodents. 177 00:06:39,420 --> 00:06:42,580 The human brain is not a large rat brain. 178 00:06:42,580 --> 00:06:45,300 Compared to a rat, we might seem special, yes, 179 00:06:45,300 --> 00:06:47,260 but that's not a fair comparison to make, 180 00:06:47,260 --> 00:06:49,780 given that we know that we are not rodents. 181 00:06:49,780 --> 00:06:51,540 We are primates, 182 00:06:51,540 --> 00:06:54,020 so the correct comparison is to other primates. 183 00:06:54,020 --> 00:06:55,540 And there, if you do the math, 184 00:06:55,540 --> 00:06:57,540 you find that a generic primate 185 00:06:57,540 --> 00:06:59,500 with 86 billion neurons 186 00:06:59,500 --> 00:07:02,580 would have a brain of about 1.2 kilos, 187 00:07:02,580 --> 00:07:04,500 which seems just right, 188 00:07:04,500 --> 00:07:06,580 in a body of some 66 kilos, 189 00:07:06,580 --> 00:07:08,980 which in my case is exactly right, 190 00:07:08,980 --> 00:07:11,660 which brings us to a very unsurprising 191 00:07:11,660 --> 00:07:14,860 but still incredibly important conclusion: 192 00:07:14,860 --> 00:07:16,540 I am a primate. 193 00:07:16,540 --> 00:07:19,100 And all of you are primates. 194 00:07:19,100 --> 00:07:21,140 And so was Darwin. 195 00:07:21,140 --> 00:07:23,140 I love to think that Darwin would have really appreciated this. 196 00:07:23,140 --> 00:07:25,660 His brain, like ours, 197 00:07:25,660 --> 00:07:29,140 was made in the image of other primate brains. 198 00:07:29,140 --> 00:07:31,180 So the human brain may be remarkable, yes, 199 00:07:31,180 --> 00:07:34,254 but it is not special in its number of neurons. 200 00:07:34,254 --> 00:07:36,140 It is just a large primate brain. 201 00:07:36,140 --> 00:07:37,940 I think that's a very humbling 202 00:07:37,940 --> 00:07:39,580 and sobering thought 203 00:07:39,580 --> 00:07:42,340 that should remind us of our place in nature. 204 00:07:42,340 --> 00:07:44,460 Why does it cost so much energy, then? 205 00:07:44,460 --> 00:07:46,260 Well, other people have figured out 206 00:07:46,260 --> 00:07:47,980 how much energy the human brain 207 00:07:47,980 --> 00:07:49,540 and that of other species cost, 208 00:07:49,540 --> 00:07:50,900 and now that we knew how many neurons 209 00:07:50,900 --> 00:07:53,180 each brain was made of, we could do the math. 210 00:07:53,180 --> 00:07:54,940 And it turns out that both human 211 00:07:54,940 --> 00:07:57,900 and other brains cost about the same, 212 00:07:57,900 --> 00:08:01,260 an average of six calories per billion neurons per day. 213 00:08:01,260 --> 00:08:03,460 So the total energetic cost of a brain 214 00:08:03,460 --> 00:08:05,540 is a simple, linear function 215 00:08:05,540 --> 00:08:07,249 of its number of neurons, 216 00:08:07,249 --> 00:08:09,140 and it turns out that the human brain 217 00:08:09,140 --> 00:08:13,180 costs just as much energy as you would expect. 218 00:08:13,180 --> 00:08:15,180 So the reason why the human brain 219 00:08:15,180 --> 00:08:17,020 costs so much energy is simply because 220 00:08:17,020 --> 00:08:19,020 it has a huge number of neurons, 221 00:08:19,020 --> 00:08:20,860 and because we are primates 222 00:08:20,860 --> 00:08:22,820 with many more neurons for a given body size 223 00:08:22,820 --> 00:08:24,540 than any other animal, 224 00:08:24,540 --> 00:08:28,020 the relative cost of our brain is large, 225 00:08:28,020 --> 00:08:31,020 but just because we're primates, not because we're special. 226 00:08:31,020 --> 00:08:32,580 Last question, then: 227 00:08:32,580 --> 00:08:35,540 how did we come by this remarkable number of neurons, 228 00:08:35,540 --> 00:08:37,580 and in particular, if great apes 229 00:08:37,580 --> 00:08:39,060 are larger than we are, 230 00:08:39,060 --> 00:08:41,379 why don't they have a larger brain than we do 231 00:08:41,379 --> 00:08:42,900 with more neurons? 232 00:08:42,900 --> 00:08:44,620 When we realized how much expensive it is 233 00:08:44,620 --> 00:08:46,460 to have a lot of neurons in the brain, I figured, 234 00:08:46,460 --> 00:08:48,940 maybe there's a simple reason. 235 00:08:48,940 --> 00:08:50,700 They just can't afford the energy 236 00:08:50,700 --> 00:08:53,620 for both a larger body and a large number of neurons. 237 00:08:53,620 --> 00:08:55,140 So we did the math. 238 00:08:55,140 --> 00:08:56,540 We calculated on the one hand 239 00:08:56,540 --> 00:08:58,620 how much energy a primate gets per day 240 00:08:58,620 --> 00:09:00,340 from eating raw foods, 241 00:09:00,340 --> 00:09:01,900 and on the other hand, how much energy 242 00:09:01,900 --> 00:09:03,940 a body of a certain size costs 243 00:09:03,940 --> 00:09:06,900 and how much energy a brain of a certain number of neurons costs, 244 00:09:06,900 --> 00:09:08,540 and we looked for the combinations 245 00:09:08,540 --> 00:09:10,460 of body size and number of brain neurons 246 00:09:10,460 --> 00:09:12,020 that a primate could afford 247 00:09:12,020 --> 00:09:15,060 if it ate a certain number of hours per day. 248 00:09:15,060 --> 00:09:17,140 And what we found is that 249 00:09:17,140 --> 00:09:18,620 because neurons are so expensive, 250 00:09:18,620 --> 00:09:21,820 there is a tradeoff between body size and number of neurons. 251 00:09:21,820 --> 00:09:24,340 So a primate that eats eight hours per day 252 00:09:24,340 --> 00:09:27,580 can afford at most 53 billion neurons, 253 00:09:27,580 --> 00:09:29,460 but then its body cannot be any bigger 254 00:09:29,460 --> 00:09:31,340 than 25 kilos. 255 00:09:31,340 --> 00:09:33,100 To weigh any more than that, 256 00:09:33,100 --> 00:09:34,900 it has to give up neurons. 257 00:09:34,900 --> 00:09:37,460 So it's either a large body 258 00:09:37,460 --> 00:09:39,140 or a large number of neurons. 259 00:09:39,140 --> 00:09:40,660 When you eat like a primate, 260 00:09:40,660 --> 00:09:42,620 you can't afford both. 261 00:09:42,620 --> 00:09:44,660 One way out of this metabolic limitation 262 00:09:44,660 --> 00:09:47,340 would be to spend even more hours per day eating, 263 00:09:47,340 --> 00:09:49,300 but that gets dangerous, 264 00:09:49,300 --> 00:09:51,220 and past a certain point, it's just not possible. 265 00:09:51,220 --> 00:09:53,540 Gorillas and orangutans, for instance, 266 00:09:53,540 --> 00:09:55,540 afford about 30 billion neurons 267 00:09:55,540 --> 00:09:58,460 by spending eight and a half hours a day eating, 268 00:09:58,460 --> 00:10:01,500 and that seems to be about as much as they can do. 269 00:10:01,500 --> 00:10:03,260 Nine hours of feeding per day 270 00:10:03,260 --> 00:10:07,100 seems to be the practical limit for a primate. 271 00:10:07,100 --> 00:10:08,460 What about us? 272 00:10:08,460 --> 00:10:10,460 With our 86 billion neurons 273 00:10:10,460 --> 00:10:12,420 and 60 to 70 kilos of body mass, 274 00:10:12,420 --> 00:10:16,380 we should have to spend over nine hours 275 00:10:16,380 --> 00:10:20,140 per day every single day feeding, 276 00:10:20,140 --> 00:10:21,980 which is just not feasible. 277 00:10:21,980 --> 00:10:23,860 If we ate like a primate, 278 00:10:23,860 --> 00:10:26,820 we should not be here. 279 00:10:26,820 --> 00:10:28,500 How did we get here, then? 280 00:10:28,500 --> 00:10:31,020 Well, if our brain costs just as much energy 281 00:10:31,020 --> 00:10:32,820 as it should, and if we can't spend 282 00:10:32,820 --> 00:10:36,540 every waking hour of the day feeding, 283 00:10:36,540 --> 00:10:38,420 then the only alternative, really, 284 00:10:38,420 --> 00:10:40,300 is to somehow get more energy 285 00:10:40,300 --> 00:10:42,100 out of the same foods. 286 00:10:42,100 --> 00:10:45,900 And remarkably, that matches exactly 287 00:10:45,900 --> 00:10:49,060 what our ancestors are believed to have invented 288 00:10:49,060 --> 00:10:51,100 one and a half million years ago, 289 00:10:51,100 --> 00:10:53,620 when they invented cooking. 290 00:10:53,620 --> 00:10:55,820 To cook is to use fire 291 00:10:55,820 --> 00:10:59,020 to re-digest foods outside of your body. 292 00:10:59,020 --> 00:11:01,780 Cooked foods are softer, so they're easier to chew 293 00:11:01,780 --> 00:11:04,820 and to turn completely into mush in your mouth, 294 00:11:04,820 --> 00:11:06,820 so that allows them to be completely digested 295 00:11:06,820 --> 00:11:08,500 and absorbed in your gut, 296 00:11:08,500 --> 00:11:12,140 which makes them yield much more energy in much less time. 297 00:11:12,140 --> 00:11:14,460 So cooking frees time for us to do 298 00:11:14,460 --> 00:11:16,660 much more interesting things with our day 299 00:11:16,660 --> 00:11:18,340 and with our neurons 300 00:11:18,340 --> 00:11:20,060 than just thinking about food, 301 00:11:20,060 --> 00:11:21,780 looking for food, and gobbling down food 302 00:11:21,780 --> 00:11:23,220 all day long. 303 00:11:23,220 --> 00:11:25,380 So because of cooking, what once was 304 00:11:25,380 --> 00:11:27,380 a major liability, this large, 305 00:11:27,380 --> 00:11:30,260 dangerously expensive brain with a lot of neurons, 306 00:11:30,260 --> 00:11:32,620 could now become a major asset, 307 00:11:32,620 --> 00:11:34,900 now that we could both afford the energy 308 00:11:34,900 --> 00:11:36,380 for a lot of neurons 309 00:11:36,380 --> 00:11:38,621 and the time to do interesting things with them. 310 00:11:38,621 --> 00:11:40,580 So I think this explains why the human brain 311 00:11:40,580 --> 00:11:43,620 grew to become so large so fast in evolution, 312 00:11:43,620 --> 00:11:47,180 all of the while remaining just a primate brain. 313 00:11:47,180 --> 00:11:50,060 With this large brain now affordable by cooking, 314 00:11:50,060 --> 00:11:53,220 we went rapidly from raw foods to culture, 315 00:11:53,220 --> 00:11:55,580 agriculture, civilization, grocery stores, 316 00:11:55,580 --> 00:11:57,620 electricity, refrigerators, 317 00:11:57,620 --> 00:11:59,380 all of those things that nowadays 318 00:11:59,380 --> 00:12:01,300 allow us to get all the energy we need 319 00:12:01,300 --> 00:12:04,020 for the whole day in a single sitting 320 00:12:04,020 --> 00:12:07,020 at your favorite fast food joint. 321 00:12:07,020 --> 00:12:09,180 So what once was a solution 322 00:12:09,180 --> 00:12:11,140 now became the problem, 323 00:12:11,140 --> 00:12:16,460 and ironically, we look for the solution in raw food. 324 00:12:16,460 --> 00:12:19,860 So what is the human advantage? 325 00:12:19,860 --> 00:12:21,180 What is it that we have 326 00:12:21,180 --> 00:12:23,220 that no other animal has? 327 00:12:23,220 --> 00:12:25,540 My answer is that we have the largest number 328 00:12:25,540 --> 00:12:27,180 of neurons in the cerebral cortex, 329 00:12:27,180 --> 00:12:28,900 and I think that's the simplest explanation 330 00:12:28,900 --> 00:12:31,098 for our remarkable cognitive abilities. 331 00:12:31,098 --> 00:12:33,940 And what is it that we do that no other animal does, 332 00:12:33,940 --> 00:12:36,140 and which I believe was fundamental 333 00:12:36,140 --> 00:12:38,900 to allow us to reach that large, 334 00:12:38,900 --> 00:12:41,460 largest number of neurons in the cortex? 335 00:12:41,460 --> 00:12:43,460 In two words, we cook. 336 00:12:43,460 --> 00:12:47,180 No other animal cooks its food. Only humans do. 337 00:12:47,180 --> 00:12:50,020 And I think that's how we got to become human. 338 00:12:50,020 --> 00:12:51,787 Studying the human brain changed the way 339 00:12:51,787 --> 00:12:53,100 I think about food. 340 00:12:53,100 --> 00:12:54,540 I now look in my kitchen, 341 00:12:54,540 --> 00:12:56,180 and I bow to it, 342 00:12:56,180 --> 00:12:57,700 and I thank my ancestors for coming up 343 00:12:57,700 --> 00:12:59,460 with the invention that probably made us humans. 344 00:12:59,460 --> 00:13:01,500 Thank you very much. 345 00:13:01,500 --> 00:13:07,714 (Applause)