1 00:00:05,080 --> 00:00:09,560 Speaker 1: Today's episode is about color. What is the very specific 2 00:00:09,680 --> 00:00:14,400 Speaker 1: reason that hunters wear orange? Why do birds and bees 3 00:00:14,480 --> 00:00:18,079 Speaker 1: go to different flowers? Why do most mammals look like 4 00:00:18,280 --> 00:00:21,640 Speaker 1: they've evolved at least in part for moving around at night? 5 00:00:22,079 --> 00:00:25,200 Speaker 1: And what does that have to do with hairless humans 6 00:00:25,480 --> 00:00:28,000 Speaker 1: getting angry? And what does any of this have to 7 00:00:28,040 --> 00:00:32,960 Speaker 1: do with road signs or camouflage or mantis shrimp or 8 00:00:33,040 --> 00:00:36,479 Speaker 1: the sun or the dress that broke the Internet or 9 00:00:36,640 --> 00:00:43,880 Speaker 1: women who can see more colors than you can. Welcome 10 00:00:43,880 --> 00:00:46,839 Speaker 1: to Inner Cosmos with me David Eagleman. I'm a neuroscientist 11 00:00:46,920 --> 00:00:50,120 Speaker 1: and an author at Stanford, and in these episodes we 12 00:00:50,240 --> 00:00:52,760 Speaker 1: look at the world inside us and around us to 13 00:00:52,880 --> 00:00:56,640 Speaker 1: understand why and how our lives look the way they do. 14 00:01:12,959 --> 00:01:16,440 Speaker 1: Today's episode and next week's as well, is about the 15 00:01:16,680 --> 00:01:22,800 Speaker 1: absolutely amazing and often underappreciated topic of color. And if 16 00:01:22,840 --> 00:01:25,199 Speaker 1: I do my job right, this is going to allow 17 00:01:25,280 --> 00:01:27,360 Speaker 1: you to see the world around you with. 18 00:01:27,440 --> 00:01:28,880 Speaker 2: Totally fresh eyes. 19 00:01:29,240 --> 00:01:32,840 Speaker 1: As a neuroscientist, I've always been obsessed with color, what 20 00:01:33,240 --> 00:01:37,440 Speaker 1: purposes it serves, how different people see it differently, why 21 00:01:37,520 --> 00:01:41,360 Speaker 1: some people or some animals see more or fewer colors, 22 00:01:41,440 --> 00:01:45,080 Speaker 1: or why kings and queens always love to wear purple, 23 00:01:45,560 --> 00:01:49,200 Speaker 1: Or why some birds evolve to be red, or why 24 00:01:49,680 --> 00:01:53,720 Speaker 1: blue animals are so rare, or what having to scavenge 25 00:01:53,760 --> 00:01:56,240 Speaker 1: at night two hundred and fifty million years ago means 26 00:01:56,320 --> 00:01:59,600 Speaker 1: for my dog's color vision. Today, in my laboratory, I've 27 00:01:59,640 --> 00:02:03,040 Speaker 1: studied color illusions, and next week I'll show you how 28 00:02:03,080 --> 00:02:06,040 Speaker 1: to see impossible colors that you've never seen before. 29 00:02:06,560 --> 00:02:07,960 Speaker 2: So let's get started. 30 00:02:08,600 --> 00:02:12,120 Speaker 1: Of all the qualities of our experience, color is one 31 00:02:12,120 --> 00:02:15,200 Speaker 1: of the most intimate and vivid. It's tied to our 32 00:02:15,240 --> 00:02:19,840 Speaker 1: emotions and our memories and our reactions. We remember the 33 00:02:19,919 --> 00:02:24,000 Speaker 1: red of a childhood wagon, the green of summer leaves, 34 00:02:24,040 --> 00:02:29,040 Speaker 1: the yellow of a favorite sweater. Color feels fundamental, like 35 00:02:29,120 --> 00:02:31,760 Speaker 1: something that exists out there in the world, waiting for 36 00:02:31,880 --> 00:02:35,119 Speaker 1: us to notice it. But of course it doesn't exist 37 00:02:35,400 --> 00:02:38,280 Speaker 1: in the outside world. The weird thing is that color 38 00:02:38,880 --> 00:02:43,400 Speaker 1: is not a property of light itself. Photons the particles 39 00:02:43,400 --> 00:02:47,640 Speaker 1: of light. They don't carry color. They carry energy defined 40 00:02:47,680 --> 00:02:53,040 Speaker 1: by their wavelength. The sensation of orange or cobalt blue 41 00:02:53,639 --> 00:02:58,640 Speaker 1: or chartruse that only happens inside your head. Color is 42 00:02:58,720 --> 00:03:03,720 Speaker 1: a construct that your brain invents based on electrical signals 43 00:03:03,760 --> 00:03:08,000 Speaker 1: from your eyes. The world reflects and emits different wavelengths 44 00:03:08,040 --> 00:03:12,000 Speaker 1: of light, but it's your brain that assigns those wavelengths 45 00:03:12,320 --> 00:03:17,080 Speaker 1: different experiences, and we give these different names and feelings 46 00:03:17,120 --> 00:03:22,000 Speaker 1: and meanings. So we live in a colorless world until 47 00:03:22,080 --> 00:03:26,440 Speaker 1: a brain comes along to paint it. This episode and 48 00:03:26,480 --> 00:03:29,400 Speaker 1: the next is a journey into that strange truth. We're 49 00:03:29,440 --> 00:03:33,880 Speaker 1: going to explore what color really is and the strange 50 00:03:34,040 --> 00:03:37,800 Speaker 1: and idiosyncratic ways that we and other animals perceive it. 51 00:03:38,120 --> 00:03:40,480 Speaker 1: But we're not going to stop just with the biology. 52 00:03:40,680 --> 00:03:44,120 Speaker 1: Color also shows up in language and culture, so next 53 00:03:44,160 --> 00:03:48,120 Speaker 1: week tackles several surprising aspects about that, and along the 54 00:03:48,160 --> 00:03:53,000 Speaker 1: way we'll meet animals with very different visual worlds. Color 55 00:03:53,080 --> 00:03:57,680 Speaker 1: turns out to be a relationship between physics and perception, 56 00:03:57,840 --> 00:04:01,280 Speaker 1: between the wavelengths of light and the circuits of the brain. 57 00:04:01,400 --> 00:04:06,360 Speaker 1: It's part physics, part neuro So today let's look at 58 00:04:06,520 --> 00:04:09,360 Speaker 1: what we see, what we don't see, and how our 59 00:04:09,360 --> 00:04:16,599 Speaker 1: brains fill in the gaps with stories painted in light. Okay, 60 00:04:16,680 --> 00:04:21,560 Speaker 1: so starting at the beginning, light is electromagnetic radiation, which 61 00:04:21,600 --> 00:04:25,480 Speaker 1: is a traveling wave of electric and magnetic fields. Now 62 00:04:25,520 --> 00:04:28,760 Speaker 1: here's the thing. These waves can span a huge range 63 00:04:28,880 --> 00:04:30,160 Speaker 1: of wavelengths. 64 00:04:30,480 --> 00:04:32,320 Speaker 2: You've got radio waves that. 65 00:04:32,279 --> 00:04:36,960 Speaker 1: Are kilometers long, to gamma rays that are subatomic, and 66 00:04:37,080 --> 00:04:40,960 Speaker 1: things even outside of that. But of the entire spectrum, 67 00:04:41,320 --> 00:04:44,679 Speaker 1: our eyes are sensitive to just a very narrow band, 68 00:04:44,839 --> 00:04:47,440 Speaker 1: really narrow, less than a ten. 69 00:04:47,400 --> 00:04:49,080 Speaker 2: Trillionth of the spectrum. 70 00:04:49,520 --> 00:04:52,520 Speaker 1: The human eye is able to pick up on wavelengths 71 00:04:52,640 --> 00:04:55,960 Speaker 1: roughly four hundred to seven hundred nanometers, and this narrow 72 00:04:56,080 --> 00:05:00,480 Speaker 1: little band is what we label visible light. This little 73 00:05:00,520 --> 00:05:03,520 Speaker 1: band includes all the colors of the rainbow, and it's 74 00:05:03,560 --> 00:05:07,480 Speaker 1: the only part of the spectrum that we can directly see. Now, 75 00:05:07,520 --> 00:05:09,960 Speaker 1: what that means is that all the rest of the spectrum, 76 00:05:10,000 --> 00:05:14,159 Speaker 1: microwaves and radio programs and X rays and cosmic rays 77 00:05:14,160 --> 00:05:17,640 Speaker 1: and infrared and ultraviolet, that's all passing right. 78 00:05:17,520 --> 00:05:18,480 Speaker 2: Through your body. 79 00:05:19,000 --> 00:05:21,520 Speaker 1: And this is totally invisible to you because you don't 80 00:05:21,560 --> 00:05:25,120 Speaker 1: have the receptors to pick up on these It's all 81 00:05:25,200 --> 00:05:29,200 Speaker 1: electromagnetic radiation, it's all light. But you can't see these 82 00:05:29,240 --> 00:05:31,599 Speaker 1: other things. So we're just going to concentrate on that 83 00:05:31,760 --> 00:05:35,440 Speaker 1: little bit that you can see, which we call visible light, 84 00:05:35,560 --> 00:05:39,880 Speaker 1: which spans ROYGBIV red, orange, yellow, green, blue, indigo, violet. 85 00:05:39,960 --> 00:05:43,440 Speaker 1: Now here's the important thing which I mentioned before. Electromagnetic 86 00:05:43,520 --> 00:05:48,960 Speaker 1: radiation has no intrinsic color. A photon doesn't know that 87 00:05:49,080 --> 00:05:53,240 Speaker 1: it's red or blue. It just has a certain wavelength. 88 00:05:53,720 --> 00:05:56,799 Speaker 1: When that photon hits the back of your eye, your retina, 89 00:05:57,360 --> 00:06:02,120 Speaker 1: it interacts with particular cells depending on its wavelength, and 90 00:06:02,160 --> 00:06:06,799 Speaker 1: then your brain starts the journey of constructing the experience 91 00:06:07,240 --> 00:06:14,000 Speaker 1: of color, that perceptual quality, that private experience synthesized by 92 00:06:14,040 --> 00:06:18,840 Speaker 1: your neural networks. It's your internal model's response to the 93 00:06:18,920 --> 00:06:22,680 Speaker 1: frequency of the incoming light. So when we look at 94 00:06:22,720 --> 00:06:26,720 Speaker 1: a red apple, what's happening. The surface of the apple 95 00:06:26,920 --> 00:06:31,960 Speaker 1: absorbs most wavelengths of light, but it reflects those around 96 00:06:31,960 --> 00:06:35,960 Speaker 1: seven hundred nanometers, the long waves that we associate. 97 00:06:35,480 --> 00:06:36,840 Speaker 2: With the color red. 98 00:06:37,600 --> 00:06:41,960 Speaker 1: Those photons hit your eye and they activate this cascade 99 00:06:42,040 --> 00:06:46,080 Speaker 1: of cells, and your brain interprets that signal as red. 100 00:06:46,160 --> 00:06:48,559 Speaker 1: But it's not the apple that's red, it's your brain 101 00:06:49,000 --> 00:06:52,320 Speaker 1: painting that surface with meaning. So to get everything set 102 00:06:52,360 --> 00:06:55,719 Speaker 1: up for this episode, let's start at the beginning. The retina, 103 00:06:55,800 --> 00:06:58,120 Speaker 1: which is the lawn of cells at the back of 104 00:06:58,160 --> 00:07:01,279 Speaker 1: your eye. This has two types of cells that are 105 00:07:01,839 --> 00:07:06,560 Speaker 1: sensitive to light. These are called photoreceptors. These two types 106 00:07:06,600 --> 00:07:09,400 Speaker 1: of cells are rods and cones. Now you have tons 107 00:07:09,400 --> 00:07:11,280 Speaker 1: of rods, like one hundred and twenty million of them, 108 00:07:11,560 --> 00:07:13,960 Speaker 1: and they're extremely sensitive to light, but they don't give 109 00:07:13,960 --> 00:07:17,760 Speaker 1: you any color information. They're what allows us to see 110 00:07:17,800 --> 00:07:20,600 Speaker 1: in dim light, but all the air information is just 111 00:07:20,640 --> 00:07:22,600 Speaker 1: black and white. It's just telling you how much light 112 00:07:22,680 --> 00:07:25,600 Speaker 1: is there at that spot, whatever the wavelength. But the 113 00:07:25,800 --> 00:07:31,640 Speaker 1: other type of light sensitive cell is a cone, and cones. 114 00:07:31,320 --> 00:07:33,000 Speaker 2: Are at the center of our story today. 115 00:07:32,800 --> 00:07:36,800 Speaker 1: Because these are the microscopic cells that lead to our 116 00:07:36,840 --> 00:07:41,160 Speaker 1: experience of color. Now, first, there are many fewer cones 117 00:07:41,200 --> 00:07:43,400 Speaker 1: than rods. There's only about six million of them, and 118 00:07:43,440 --> 00:07:46,080 Speaker 1: they're all concentrated at the center of your vision, not 119 00:07:46,200 --> 00:07:47,040 Speaker 1: in the periphery. 120 00:07:47,160 --> 00:07:49,720 Speaker 2: And cones come in three flavors. 121 00:07:49,720 --> 00:07:52,680 Speaker 1: You've got those that are most responsive to red, which 122 00:07:52,720 --> 00:07:53,760 Speaker 1: is a long wavelength. 123 00:07:53,960 --> 00:07:55,280 Speaker 2: Then you've got those that are most. 124 00:07:55,160 --> 00:07:58,720 Speaker 1: Responsive to green, which is a medium wavelength, and those 125 00:07:58,760 --> 00:08:01,040 Speaker 1: that are most responsive to the light that we perceive 126 00:08:01,200 --> 00:08:04,120 Speaker 1: as blue. These are short wavelength, so what you are 127 00:08:04,160 --> 00:08:07,040 Speaker 1: picking up on is essentially red, green, blue, And your 128 00:08:07,080 --> 00:08:10,920 Speaker 1: perception of color doesn't come from any one cone, but 129 00:08:11,000 --> 00:08:13,600 Speaker 1: from the pattern of activity. 130 00:08:13,240 --> 00:08:14,920 Speaker 2: Across all three types. 131 00:08:15,320 --> 00:08:18,840 Speaker 1: For example, if both your red and green cones are activated, 132 00:08:19,320 --> 00:08:22,520 Speaker 1: you will perceive yellow. Now what I just described with 133 00:08:22,600 --> 00:08:26,400 Speaker 1: the cones, that's only the very first layer straight away. 134 00:08:26,560 --> 00:08:29,640 Speaker 1: Even before the signals get to your visual cortex, other 135 00:08:29,760 --> 00:08:33,000 Speaker 1: cells begin to compare and contrast the signals. 136 00:08:33,280 --> 00:08:36,960 Speaker 2: So colors get analyzed in opposing pairs. 137 00:08:37,400 --> 00:08:41,480 Speaker 1: Red versus green, blue versus yellow, black versus white. And 138 00:08:41,520 --> 00:08:46,480 Speaker 1: this is why you can't see reddish green or bluish yellow. 139 00:08:46,840 --> 00:08:50,679 Speaker 1: Those combinations cancel out in our visual system. Okay, Then 140 00:08:50,720 --> 00:08:54,160 Speaker 1: the signals get to the visual cortex and an enormous 141 00:08:54,200 --> 00:08:57,640 Speaker 1: amount of further processing takes place. I'm going to skip 142 00:08:57,640 --> 00:09:00,440 Speaker 1: all the details here. I'll post a chap from my 143 00:09:00,520 --> 00:09:03,160 Speaker 1: textbook on the show notes. But the point I want 144 00:09:03,200 --> 00:09:05,600 Speaker 1: to make is that you might wonder, wait, why is 145 00:09:05,640 --> 00:09:09,280 Speaker 1: there so much computation involved here? Why don't you just 146 00:09:09,320 --> 00:09:12,120 Speaker 1: look at the wavelength hitting the retina and have your 147 00:09:12,200 --> 00:09:16,000 Speaker 1: perception that way. Well, it turns out that wouldn't be 148 00:09:16,120 --> 00:09:21,720 Speaker 1: nearly enough because the lighting conditions totally change what's bouncing 149 00:09:21,760 --> 00:09:24,000 Speaker 1: off an object and hitting your eye. But if you're 150 00:09:24,000 --> 00:09:27,480 Speaker 1: going to assign colors to things and that's going to 151 00:09:27,559 --> 00:09:31,360 Speaker 1: carry some sort of information, you need to somehow account 152 00:09:31,720 --> 00:09:34,439 Speaker 1: for the lighting changes. In other words, one of the 153 00:09:34,520 --> 00:09:39,360 Speaker 1: most important tricks that the brain pulls off is color constancy. 154 00:09:39,840 --> 00:09:43,559 Speaker 1: This is your brain's ability to perceive and objects color 155 00:09:43,640 --> 00:09:46,760 Speaker 1: as stable even when the lighting changes. 156 00:09:47,000 --> 00:09:48,480 Speaker 2: So let's say I'm wearing a white T. 157 00:09:48,520 --> 00:09:51,880 Speaker 1: Shirt that looks white to you out in the sunlight, 158 00:09:51,960 --> 00:09:55,199 Speaker 1: and it also looks white when I'm in the yellowish 159 00:09:55,280 --> 00:09:58,240 Speaker 1: light of an indoor lamp, or when I'm standing at 160 00:09:58,240 --> 00:10:00,280 Speaker 1: a campfire, or when I'm in the. 161 00:10:00,080 --> 00:10:01,560 Speaker 2: Bright lights of a store. 162 00:10:02,040 --> 00:10:06,640 Speaker 1: But technically the wavelengths bouncing off my white T shirt 163 00:10:06,920 --> 00:10:10,839 Speaker 1: are very different in those conditions. Your brain accounts for 164 00:10:11,160 --> 00:10:14,280 Speaker 1: the context by looking at all the other colors in 165 00:10:14,320 --> 00:10:19,600 Speaker 1: the scene and subtracting that to keep your perception stable. 166 00:10:21,559 --> 00:10:23,680 Speaker 1: This is, by the way, in the laboratory why we 167 00:10:23,720 --> 00:10:27,760 Speaker 1: can make so many color illusions. If you manipulate the 168 00:10:27,880 --> 00:10:32,439 Speaker 1: surrounding light and shade, you can make two identical patches 169 00:10:32,600 --> 00:10:36,560 Speaker 1: appear wildly different in color. If you're interested more on this, 170 00:10:36,600 --> 00:10:39,720 Speaker 1: I'm linking a paper I wrote in Nature Reviews Neuroscience 171 00:10:39,840 --> 00:10:41,400 Speaker 1: on visual illusions. 172 00:10:41,760 --> 00:10:42,480 Speaker 2: But here's the. 173 00:10:42,400 --> 00:10:44,800 Speaker 1: Point I want to get to how weird it is 174 00:10:45,160 --> 00:10:48,040 Speaker 1: that we can study all the pieces and parts of 175 00:10:48,040 --> 00:10:50,559 Speaker 1: the brain and the physiology, but that doesn't really tell 176 00:10:50,600 --> 00:10:54,720 Speaker 1: us anything about why you experience the color a particular way. 177 00:10:54,960 --> 00:10:58,640 Speaker 1: Why don't our brains just register something about wavelength like, oh, 178 00:10:58,679 --> 00:11:02,920 Speaker 1: that's four hundred and fifty animeters, instead of experiencing purpleness 179 00:11:03,000 --> 00:11:07,200 Speaker 1: or a yellowness or a greenness. So consider this thought 180 00:11:07,320 --> 00:11:11,280 Speaker 1: experiment called Mary's Room, which was proposed by the philosopher 181 00:11:11,360 --> 00:11:15,040 Speaker 1: Frank Jackson in nineteen eighty two. He was essentially asking 182 00:11:15,480 --> 00:11:20,040 Speaker 1: how our private, subjective experiences like color can be reduced 183 00:11:20,120 --> 00:11:25,200 Speaker 1: to physical information. Here's the setup he proposed. Mary is 184 00:11:25,240 --> 00:11:28,240 Speaker 1: a brilliant scientist who knows everything there is to know 185 00:11:28,400 --> 00:11:30,280 Speaker 1: about this science of color. 186 00:11:30,640 --> 00:11:33,880 Speaker 2: She understands the wavelengths. 187 00:11:33,160 --> 00:11:36,520 Speaker 1: The neural processes, in other words, the physics and the biology. 188 00:11:36,800 --> 00:11:41,080 Speaker 1: But Mary has lived her entire life in a black 189 00:11:41,120 --> 00:11:45,040 Speaker 1: and white room, and she has never actually seen color. 190 00:11:45,400 --> 00:11:48,560 Speaker 1: She reads about red in the sense that it's a 191 00:11:48,679 --> 00:11:53,400 Speaker 1: seven hundred nanimeter wavelength. She understands how it stimulates particular 192 00:11:53,480 --> 00:11:56,640 Speaker 1: cones in the retina, how it's processed in the visual cortex, 193 00:11:56,920 --> 00:12:02,480 Speaker 1: but she's never experienced red. Then one day she steps 194 00:12:02,520 --> 00:12:08,319 Speaker 1: outside and sees a ripe tomato for the first time. Now, 195 00:12:08,400 --> 00:12:12,640 Speaker 1: Jackson's question is does Mary learn something new when she 196 00:12:13,040 --> 00:12:16,320 Speaker 1: sees red for the first time. If she does, then 197 00:12:16,320 --> 00:12:22,000 Speaker 1: there's something about the experience of color, some qualitative first 198 00:12:22,120 --> 00:12:27,559 Speaker 1: person knowledge that isn't captured just by the objective physical facts. 199 00:12:28,000 --> 00:12:33,559 Speaker 1: And that thought experiment illustrates the difficulty in explaining subjective 200 00:12:33,640 --> 00:12:38,040 Speaker 1: experience just in terms of physical mechanisms. And the weirdest 201 00:12:38,080 --> 00:12:42,120 Speaker 1: part is that the way the brain constructs this subjective 202 00:12:42,160 --> 00:12:45,520 Speaker 1: experience is not necessarily the same for you and me. 203 00:12:46,240 --> 00:12:49,880 Speaker 1: This is why the dress broke the Internet. You remember 204 00:12:49,920 --> 00:12:53,600 Speaker 1: that viral photo that you might have seen as black 205 00:12:53,640 --> 00:12:56,640 Speaker 1: and blue, or you might have seen as white and gold. 206 00:12:57,080 --> 00:13:01,000 Speaker 1: It comes down to the assumptions that eat brain makes 207 00:13:01,200 --> 00:13:05,000 Speaker 1: about the lighting in the photo. Your brain sees this 208 00:13:05,160 --> 00:13:08,040 Speaker 1: little picture of the dress in a shop, and it 209 00:13:08,080 --> 00:13:13,840 Speaker 1: makes dozens of assumptions totally unconsciously. What is the light 210 00:13:13,920 --> 00:13:17,160 Speaker 1: source in the photograph? Is the dress being lit mostly 211 00:13:17,200 --> 00:13:21,360 Speaker 1: by fluorescent lights or by sunlight? Is the dress facing 212 00:13:21,440 --> 00:13:24,920 Speaker 1: a window or is the window behind it? What time 213 00:13:24,960 --> 00:13:28,480 Speaker 1: of day is it, what season is it? The wild 214 00:13:28,559 --> 00:13:31,720 Speaker 1: part is that you just open your eyes and there 215 00:13:31,720 --> 00:13:34,360 Speaker 1: it is. There's the color of the dress. But under 216 00:13:34,440 --> 00:13:39,320 Speaker 1: the hood, your brain is doing an enormous amount of computation, 217 00:13:40,000 --> 00:13:45,000 Speaker 1: asking questions and making assumptions you never have any awareness of. 218 00:13:45,559 --> 00:13:50,120 Speaker 1: And you believe the colors that your brain tells you. 219 00:13:50,640 --> 00:13:54,160 Speaker 1: But illusions like the dress tell us that your head 220 00:13:54,640 --> 00:13:57,880 Speaker 1: may be making those assumptions differently than the head sitting 221 00:13:57,920 --> 00:14:01,679 Speaker 1: next to you, and therefore the color you're seeing isn't 222 00:14:01,720 --> 00:14:07,040 Speaker 1: something true, it's just your brain's result of the computations. 223 00:14:07,559 --> 00:14:11,040 Speaker 1: For more on the dress, listen to episode thirty one. Okay, 224 00:14:11,600 --> 00:14:14,040 Speaker 1: there's a lot more to say about color perception and 225 00:14:14,080 --> 00:14:16,520 Speaker 1: how different people see things differently, and we're going to 226 00:14:16,559 --> 00:14:19,640 Speaker 1: return to that next week, but for now, I want 227 00:14:19,680 --> 00:14:22,560 Speaker 1: to see how this gets even weirder when we compare 228 00:14:22,560 --> 00:14:27,240 Speaker 1: against other species. Because while you think you're just seeing 229 00:14:27,320 --> 00:14:32,560 Speaker 1: what's out there, what you're actually experiencing is one evolutionary 230 00:14:32,640 --> 00:14:37,640 Speaker 1: solution among many. For example, we humans have three types 231 00:14:37,680 --> 00:14:41,680 Speaker 1: of color photoreceptors, these cones, but most other mammals have 232 00:14:41,720 --> 00:14:45,360 Speaker 1: only two types. Now, why do mammals tend to be 233 00:14:45,480 --> 00:14:48,760 Speaker 1: limited in this way? One idea about this is what's 234 00:14:48,760 --> 00:14:52,280 Speaker 1: called the nocturnal bottleneck hypothesis. 235 00:14:52,400 --> 00:14:54,080 Speaker 2: The idea is that the. 236 00:14:53,960 --> 00:14:58,160 Speaker 1: Common ancestor of mammals and reptiles and birds had more 237 00:14:58,200 --> 00:15:01,360 Speaker 1: photoreceptor types, but we he lost them. 238 00:15:01,600 --> 00:15:01,920 Speaker 2: Why. 239 00:15:02,360 --> 00:15:05,360 Speaker 1: It's because two hundred and fifty million years ago, during 240 00:15:05,360 --> 00:15:09,480 Speaker 1: the Mesozoic era, the ancestors of mammals had to become 241 00:15:09,560 --> 00:15:14,680 Speaker 1: mostly nocturnal to avoid getting stomped and eaten by dinosaurs. 242 00:15:14,760 --> 00:15:19,440 Speaker 1: The large predatory dinosaurs dominated the daytime, and so early 243 00:15:19,520 --> 00:15:23,880 Speaker 1: mammals adapted to nocturnal living to avoid them. So these 244 00:15:23,920 --> 00:15:27,680 Speaker 1: many tens of millions of years of nocturnal activity led 245 00:15:27,720 --> 00:15:32,800 Speaker 1: to several adaptations that reflect nighttime living. So, for example, 246 00:15:33,000 --> 00:15:37,200 Speaker 1: mammals developed excellent senses of hearing and smell, which you 247 00:15:37,280 --> 00:15:40,000 Speaker 1: need for navigating and foraging in the dark, and they 248 00:15:40,040 --> 00:15:44,920 Speaker 1: evolved eyes optimized for low light conditions, like large pupils 249 00:15:45,200 --> 00:15:48,280 Speaker 1: and lots of really good rod cells which allow them 250 00:15:48,320 --> 00:15:51,160 Speaker 1: to see better in dim environments. So, in other words, 251 00:15:51,200 --> 00:15:53,960 Speaker 1: when we look at mammalian eyes today, they seem to 252 00:15:54,000 --> 00:15:58,560 Speaker 1: have been shaped during this prolonged period of nighttime activity. 253 00:15:58,720 --> 00:16:02,120 Speaker 1: And here's the key for today day since detailed color 254 00:16:02,200 --> 00:16:06,880 Speaker 1: vision is less useful at night, mammals lost their capacity 255 00:16:07,240 --> 00:16:12,320 Speaker 1: for trichromatic vision, in other words, seeing three primary colors. Instead, 256 00:16:12,640 --> 00:16:16,920 Speaker 1: they got a deeper reliance on senses better suited for 257 00:16:17,000 --> 00:16:19,800 Speaker 1: nocturnal activity, like better hearing and smell. So this is 258 00:16:19,840 --> 00:16:24,760 Speaker 1: presumably why modern mammals retain nocturnal traits even after the 259 00:16:24,800 --> 00:16:29,480 Speaker 1: extinction of dinosaurs, which allowed them to diversify into daytime niches. 260 00:16:29,840 --> 00:16:32,440 Speaker 2: In other words, evolutionary pressures. 261 00:16:31,960 --> 00:16:35,960 Speaker 1: Can shape an entire class of animals, leaving a long 262 00:16:36,080 --> 00:16:40,280 Speaker 1: lasting imprint on their physiology and behavior even after the 263 00:16:40,360 --> 00:16:42,040 Speaker 1: environmental conditions change. 264 00:16:42,160 --> 00:16:43,000 Speaker 2: So just as an. 265 00:16:42,880 --> 00:16:47,040 Speaker 1: Example, my dog and your dog, they are di chromatic. 266 00:16:47,120 --> 00:16:49,680 Speaker 1: They only have two types of cones, and their vision 267 00:16:49,720 --> 00:16:53,360 Speaker 1: resembles red green color blindness in humans. They see a 268 00:16:53,440 --> 00:16:58,440 Speaker 1: world of muted blues and yellows, and they can't distinguish 269 00:16:58,840 --> 00:17:02,400 Speaker 1: reds from greens. This is the same with cats, with horses, 270 00:17:02,440 --> 00:17:06,679 Speaker 1: with rodents, and over ninety percent of mammals. Okay, so 271 00:17:06,720 --> 00:17:10,400 Speaker 1: the nocturnal bottleneck hypothesis suggests why a lot of mammals 272 00:17:10,800 --> 00:17:15,840 Speaker 1: have not so great color vision, but some mammals, like humans, 273 00:17:16,320 --> 00:17:20,959 Speaker 1: have evolved better color vision. We have become trichromatic again. 274 00:17:21,600 --> 00:17:24,560 Speaker 1: Now why would it make sense to regain the ability 275 00:17:24,680 --> 00:17:28,879 Speaker 1: to distinguish red and green. Well, one common argument is 276 00:17:28,920 --> 00:17:32,520 Speaker 1: that if you can distinguish red and green, then you 277 00:17:32,600 --> 00:17:36,760 Speaker 1: can see a ripe fruit against a tree canopy at 278 00:17:36,800 --> 00:17:39,000 Speaker 1: a distance, and that's really useful. 279 00:17:39,200 --> 00:17:42,000 Speaker 2: But maybe it's something even deeper than that. 280 00:17:42,440 --> 00:17:44,879 Speaker 1: So let me tell you one of my favorite hypotheses 281 00:17:44,880 --> 00:17:49,359 Speaker 1: about why we humans re evolved red green color vision. 282 00:17:49,440 --> 00:17:53,080 Speaker 1: This comes from my colleague Mark Changizi, and it flips 283 00:17:53,119 --> 00:17:54,159 Speaker 1: the usual story. 284 00:17:53,920 --> 00:17:54,440 Speaker 2: On its head. 285 00:17:54,480 --> 00:18:00,000 Speaker 1: It suggests something deeply social. He argues that we didn't 286 00:18:00,080 --> 00:18:02,240 Speaker 1: evolve red green vision to forage better. 287 00:18:02,600 --> 00:18:07,000 Speaker 2: We evolved to read each other better. So here's the idea. 288 00:18:07,200 --> 00:18:11,040 Speaker 1: Human skin is packed with tiny blood vessels just beneath 289 00:18:11,040 --> 00:18:15,360 Speaker 1: the surface, and when your emotions shift, when you're embarrassed 290 00:18:15,760 --> 00:18:20,439 Speaker 1: or you're angry, or you're afraid or you're aroused, blood 291 00:18:20,480 --> 00:18:25,399 Speaker 1: flow changes. Your skin flushes red or it pails. It 292 00:18:25,440 --> 00:18:28,320 Speaker 1: happens in fractions of a second, and we pick up 293 00:18:28,359 --> 00:18:47,879 Speaker 1: on this in other faces without even realizing it. So 294 00:18:48,000 --> 00:18:52,800 Speaker 1: Tchannghisi suggests that our color vision system is tuned to 295 00:18:53,000 --> 00:18:57,720 Speaker 1: detect these subtle changes in oxygenation of the hemoglobe and 296 00:18:57,800 --> 00:19:00,879 Speaker 1: under the skin. The spacing of our red and green 297 00:19:01,000 --> 00:19:06,200 Speaker 1: cone sensitivities is almost perfect for distinguishing these tiny shifts 298 00:19:06,280 --> 00:19:09,159 Speaker 1: in skin tone. In other words, we're not just seeing 299 00:19:09,520 --> 00:19:11,920 Speaker 1: red and green on apples and trees. We're seeing it 300 00:19:12,280 --> 00:19:18,000 Speaker 1: in faces, in ears, in emotional states, and those social 301 00:19:18,040 --> 00:19:22,520 Speaker 1: signals is why CHANGESI suggests we evolved the ability in 302 00:19:22,560 --> 00:19:26,680 Speaker 1: the first place to track the emotion of the other. Now, 303 00:19:26,680 --> 00:19:30,040 Speaker 1: this potentially helps explain something I mentioned that most mammals 304 00:19:30,359 --> 00:19:34,840 Speaker 1: don't have trichromatic vision, but about two thirds of primates do, 305 00:19:35,280 --> 00:19:39,600 Speaker 1: and these animals, including us, tend to have less fur 306 00:19:39,800 --> 00:19:44,840 Speaker 1: on their faces. Less fur means more exposed skin. More 307 00:19:44,880 --> 00:19:48,639 Speaker 1: skin means more visible blood flow, and more reason to 308 00:19:48,840 --> 00:19:52,200 Speaker 1: evolve a visual system that can pick up on the 309 00:19:52,320 --> 00:19:56,600 Speaker 1: language of color as it plays out in living flesh. 310 00:19:56,920 --> 00:19:59,840 Speaker 1: So maybe red green vision isn't about navigating the jungle, 311 00:20:00,119 --> 00:20:03,080 Speaker 1: about navigating each other. By the way, you might wonder 312 00:20:03,160 --> 00:20:06,280 Speaker 1: does this apply to people with more pigment in their skin, 313 00:20:06,600 --> 00:20:10,480 Speaker 1: Because in people with darker skin, melanin absorbs more light 314 00:20:10,520 --> 00:20:13,520 Speaker 1: and that can make those blood float changes harder to see. 315 00:20:13,680 --> 00:20:16,600 Speaker 1: But the signals are still there, They're just more subtle. 316 00:20:16,800 --> 00:20:20,359 Speaker 1: Even with darker skin. Changes in coloration can be seen 317 00:20:20,920 --> 00:20:23,320 Speaker 1: in eras where the skin is thinner, like the lips 318 00:20:23,320 --> 00:20:23,560 Speaker 1: and the. 319 00:20:23,520 --> 00:20:25,400 Speaker 2: Eyelids and the palms and the cheeks. 320 00:20:25,840 --> 00:20:29,000 Speaker 1: So we see the world differently than most of our 321 00:20:29,040 --> 00:20:32,919 Speaker 1: mammalian cousins, and understanding this sort of thing can clarify 322 00:20:33,160 --> 00:20:36,399 Speaker 1: a lot of the world around you. For example, why 323 00:20:36,440 --> 00:20:40,439 Speaker 1: do hunters wear bright orange vests? You might correctly assume 324 00:20:40,480 --> 00:20:43,200 Speaker 1: it so they can spot one another, right, But why 325 00:20:43,200 --> 00:20:47,200 Speaker 1: don't they wear chartreuse or bright yellow or any other 326 00:20:47,400 --> 00:20:51,280 Speaker 1: equally detectable color. Well, as we just saw, the ability 327 00:20:51,320 --> 00:20:56,600 Speaker 1: to detect reddish colors was lost during the Mesozoic, and 328 00:20:56,640 --> 00:20:59,320 Speaker 1: the great apes, including humans, regained it. 329 00:21:00,160 --> 00:21:03,160 Speaker 2: Deer did not, so deer. 330 00:21:03,000 --> 00:21:06,720 Speaker 1: Can only see two ranges of color, blue and yellow green. 331 00:21:07,240 --> 00:21:10,000 Speaker 1: Deer have great smell and hearing, and they've got great 332 00:21:10,119 --> 00:21:14,320 Speaker 1: night vision, but they're not sensitive to red or orange light. 333 00:21:14,680 --> 00:21:18,760 Speaker 1: And that's why hunters wear blaze orange, which is easily 334 00:21:18,800 --> 00:21:22,160 Speaker 1: spotted by the other humans but not by the deer. 335 00:21:22,600 --> 00:21:25,320 Speaker 1: This color that helps hunters spot each other at a 336 00:21:25,359 --> 00:21:29,960 Speaker 1: distance makes them nearly invisible to their prey. In this case, 337 00:21:30,040 --> 00:21:35,760 Speaker 1: our evolutionary divergence from other species our trichromatic vision, and 338 00:21:35,760 --> 00:21:40,960 Speaker 1: their dichromatic becomes a tactical advantage. We can design ourselves 339 00:21:41,280 --> 00:21:44,400 Speaker 1: to be invisible to them. And by the way, this 340 00:21:44,440 --> 00:21:48,399 Speaker 1: is why you see nature red birds. It's the same idea. 341 00:21:48,840 --> 00:21:52,280 Speaker 1: The red birds can be there against the green leaves 342 00:21:52,640 --> 00:21:55,600 Speaker 1: and they don't have to worry about getting spotted because 343 00:21:55,680 --> 00:21:59,520 Speaker 1: their predators are red green colorblind. And it turns out 344 00:21:59,560 --> 00:22:03,919 Speaker 1: its getically easier to express red than green, So expressing 345 00:22:04,000 --> 00:22:07,159 Speaker 1: red feathers is a perfectly good way to go. Now, 346 00:22:07,200 --> 00:22:10,360 Speaker 1: let's come back to the deer hunters. Note that they 347 00:22:10,440 --> 00:22:15,000 Speaker 1: never wear blue jeans. Why not because deer are much 348 00:22:15,080 --> 00:22:18,000 Speaker 1: more sensitive to blue even than we are to them. 349 00:22:18,280 --> 00:22:22,080 Speaker 1: Blue jeans shine like a warning beacon, so the hunters 350 00:22:22,119 --> 00:22:26,719 Speaker 1: wear camouflage or earthstone pants to blend in. Okay, So 351 00:22:26,840 --> 00:22:30,600 Speaker 1: back to humans with their three types of photoreceptors. It 352 00:22:30,640 --> 00:22:34,600 Speaker 1: turns out that's most humans. A small fraction of humans 353 00:22:34,840 --> 00:22:38,520 Speaker 1: have some forms of color blindness where they're missing one 354 00:22:38,600 --> 00:22:42,240 Speaker 1: type of color photoreceptor, or two types, or all three, 355 00:22:42,600 --> 00:22:45,320 Speaker 1: and you can guess what their experience is. They can 356 00:22:45,359 --> 00:22:49,040 Speaker 1: distinguish fewer and fewer colors. What you might not know 357 00:22:49,440 --> 00:22:53,560 Speaker 1: is that a small fraction of the human female population. 358 00:22:54,080 --> 00:22:56,600 Speaker 1: They have a fourth type of cone. They are called 359 00:22:56,920 --> 00:23:00,960 Speaker 1: tetrachromatic instead of the typical chromatic vision. 360 00:23:01,000 --> 00:23:03,439 Speaker 2: With three types, these women can. 361 00:23:03,320 --> 00:23:07,840 Speaker 1: Distinguish something like one hundred million shades of color, so 362 00:23:07,880 --> 00:23:11,840 Speaker 1: for them, a sunset contains hues that the rest of 363 00:23:11,920 --> 00:23:15,320 Speaker 1: us have no capacity to see and no words for. 364 00:23:15,880 --> 00:23:18,359 Speaker 1: By the way, it's only women because the mutation in 365 00:23:18,400 --> 00:23:21,399 Speaker 1: the photoreceptor is on one of the X chromosomes and 366 00:23:21,440 --> 00:23:23,560 Speaker 1: not on the other. And it's not just the rare 367 00:23:23,640 --> 00:23:27,560 Speaker 1: human female who's tetrachromatic. A whole lot of birds and 368 00:23:27,600 --> 00:23:32,080 Speaker 1: reptiles and insects are tetrachromats, and in animals, the fourth 369 00:23:32,119 --> 00:23:36,520 Speaker 1: cone type often extends into the ultraviolet, so bees, for example, 370 00:23:36,600 --> 00:23:41,280 Speaker 1: can see ultraviolet patterns on flowers that are completely invisible 371 00:23:41,280 --> 00:23:44,920 Speaker 1: to us. These patterns help them locate the nectar. They're 372 00:23:44,960 --> 00:23:48,600 Speaker 1: like little runways on the flower pedal that don't look 373 00:23:48,680 --> 00:23:52,760 Speaker 1: like anything to us. And then there's the mantis shrimp. 374 00:23:52,840 --> 00:23:59,200 Speaker 1: This little crustacean has sixteen types of photoreceptors. These photoreceptors 375 00:23:59,200 --> 00:24:04,720 Speaker 1: can detect ultraviolet and polarized light, and presumably colors we 376 00:24:04,880 --> 00:24:08,720 Speaker 1: can't imagine, but are useful in their niche. Of course, 377 00:24:08,760 --> 00:24:11,720 Speaker 1: it's impossible for us to know exactly what the experience 378 00:24:11,880 --> 00:24:15,200 Speaker 1: of the shrimp is because it depends what its brain 379 00:24:15,320 --> 00:24:18,040 Speaker 1: is doing with that data. But what all these examples 380 00:24:18,080 --> 00:24:22,879 Speaker 1: show is that color vision is about usefulness. Millions of 381 00:24:22,960 --> 00:24:27,080 Speaker 1: years of evolution tends to equip species with the ability 382 00:24:27,160 --> 00:24:32,600 Speaker 1: to perceive what enhances survival and reproduction. Our color vision 383 00:24:32,760 --> 00:24:36,159 Speaker 1: is not what a mantis shrimps is, but it was 384 00:24:36,200 --> 00:24:40,400 Speaker 1: good enough to spot ripe fruit, and detect emotional signals 385 00:24:40,400 --> 00:24:45,600 Speaker 1: and flushed skin and navigate a multicolored environment. Okay, now 386 00:24:45,640 --> 00:24:47,920 Speaker 1: I want to talk about the birds and the bees. 387 00:24:47,640 --> 00:24:48,119 Speaker 2: For a moment. 388 00:24:48,480 --> 00:24:51,800 Speaker 1: Here's the thing. We usually think of a flower as 389 00:24:51,840 --> 00:24:55,720 Speaker 1: just a flowersome color and nice scent, But every petal, 390 00:24:55,800 --> 00:24:59,239 Speaker 1: every hue of the flower, every tiny detail is a 391 00:24:59,320 --> 00:25:03,840 Speaker 1: carefully c afted advertisement. It's a billboard designed to say hey, 392 00:25:03,840 --> 00:25:09,000 Speaker 1: I'm open for business to a very specific clientele. And 393 00:25:09,119 --> 00:25:13,320 Speaker 1: the best part about this botanical dating game is how 394 00:25:13,400 --> 00:25:17,480 Speaker 1: birds and bees have entirely different preferences when it comes 395 00:25:17,520 --> 00:25:21,600 Speaker 1: to the colors that they find attractive. So imagine you 396 00:25:21,640 --> 00:25:25,120 Speaker 1: walk into a store and some of the products are 397 00:25:25,160 --> 00:25:26,399 Speaker 1: completely invisible to you. 398 00:25:26,960 --> 00:25:29,439 Speaker 2: That's what happens in the floral world. 399 00:25:29,680 --> 00:25:32,680 Speaker 1: So let's start with the bees. When a bee flies 400 00:25:32,720 --> 00:25:37,760 Speaker 1: into your garden, it's not seeing the same spectrum of colors. 401 00:25:37,320 --> 00:25:37,920 Speaker 2: That you are. 402 00:25:38,520 --> 00:25:42,440 Speaker 1: For the bee, red flowers are a complete no go. 403 00:25:42,600 --> 00:25:46,399 Speaker 1: It's like a black screen. Bees see in shades of 404 00:25:46,960 --> 00:25:49,760 Speaker 1: blue and purple and violet and yellow, So those are 405 00:25:49,800 --> 00:25:52,480 Speaker 1: the flowers they go for. And as I mentioned, many 406 00:25:52,520 --> 00:25:56,920 Speaker 1: flowers that look plain to us have hidden ultraviolet patterns 407 00:25:56,920 --> 00:26:01,800 Speaker 1: that act like glowing landing strip for the bee, guiding 408 00:26:01,840 --> 00:26:04,440 Speaker 1: it straight to the nectar. It's like a secret map 409 00:26:04,480 --> 00:26:06,160 Speaker 1: that only they can read. 410 00:26:06,560 --> 00:26:07,760 Speaker 2: So if you're a. 411 00:26:07,680 --> 00:26:12,760 Speaker 1: Bee, that vibrant red rose might just be invisible. Now 412 00:26:13,240 --> 00:26:17,680 Speaker 1: turn to our feathered friends like hummingbirds, which are big pollinators, 413 00:26:17,960 --> 00:26:21,080 Speaker 1: and guess what their favorite color is. It's red and 414 00:26:21,240 --> 00:26:24,399 Speaker 1: orange is a close second. So think about this. Hummingbird 415 00:26:24,440 --> 00:26:29,119 Speaker 1: feeders are always red, right, that's no accident because birds, 416 00:26:29,400 --> 00:26:33,479 Speaker 1: unlike bees, can see red perfectly and they're drawn to 417 00:26:33,520 --> 00:26:36,560 Speaker 1: it like a magnet. And you'll notice that these bird 418 00:26:36,640 --> 00:26:42,080 Speaker 1: pollinated red flowers often have long tubular shapes, perfect for 419 00:26:42,400 --> 00:26:46,520 Speaker 1: a hummingbird's beak to dip in so why this color divide. 420 00:26:46,520 --> 00:26:51,399 Speaker 1: Over millions of years, flowers have evolved to attract the 421 00:26:51,440 --> 00:26:55,600 Speaker 1: most effective pollinators for whatever their needs are. If a 422 00:26:55,760 --> 00:26:59,280 Speaker 1: flower wants a bee to carry its pollen, it's going 423 00:26:59,320 --> 00:27:01,720 Speaker 1: to evolve to be blue or yellow, and it'll have 424 00:27:01,760 --> 00:27:05,840 Speaker 1: those secret ultraviolet patterns. If it wants a bird, then 425 00:27:05,920 --> 00:27:09,000 Speaker 1: it flaunts reds and oranges, knowing that the bees won't 426 00:27:09,000 --> 00:27:09,840 Speaker 1: even notice. 427 00:27:09,960 --> 00:27:10,640 Speaker 2: This kind of. 428 00:27:10,600 --> 00:27:14,800 Speaker 1: Color specialization ensures that the pollen gets where it needs 429 00:27:14,840 --> 00:27:20,520 Speaker 1: to go. It's the botanical equivalent of targeted advertising. So 430 00:27:20,560 --> 00:27:23,240 Speaker 1: the next time you're outside, take a closer look at 431 00:27:23,240 --> 00:27:26,600 Speaker 1: the flowers around you, and you can guess their intended 432 00:27:26,680 --> 00:27:28,760 Speaker 1: audience by their color. 433 00:27:29,119 --> 00:27:29,919 Speaker 2: If you didn't. 434 00:27:29,640 --> 00:27:31,720 Speaker 1: Already know this, it gives you a new way to 435 00:27:31,840 --> 00:27:53,640 Speaker 1: appreciate the intricate dance of life happening all around us. Okay, now, 436 00:27:53,720 --> 00:27:56,879 Speaker 1: even though the human eye is limited to a narrow 437 00:27:57,040 --> 00:28:00,359 Speaker 1: sliver of visible light, we've spent the recent century trees 438 00:28:00,680 --> 00:28:04,439 Speaker 1: building tools that let us see beyond that. So we 439 00:28:04,520 --> 00:28:09,520 Speaker 1: have infrared cameras that reveal heat signatures of animals at night, 440 00:28:09,640 --> 00:28:12,720 Speaker 1: or we have X rays that show us our bones, 441 00:28:13,080 --> 00:28:16,359 Speaker 1: where we construct telescopes to pick up on microwave or 442 00:28:16,440 --> 00:28:20,440 Speaker 1: ultraviolet frequencies, and that shows us a very different universe 443 00:28:20,480 --> 00:28:22,520 Speaker 1: than the one we can see with our eyes. But 444 00:28:22,600 --> 00:28:25,680 Speaker 1: now that we know that that huge spectrum of wavelengths 445 00:28:25,680 --> 00:28:28,399 Speaker 1: is out there, why don't we see all the rest 446 00:28:28,480 --> 00:28:32,399 Speaker 1: with our eyes. The answer to that question lies one 447 00:28:32,480 --> 00:28:37,800 Speaker 1: hundred and fifty million kilometers away. It's the Sun. Our 448 00:28:37,880 --> 00:28:42,240 Speaker 1: star emits light, electromagnetic radiation across the whole spectrum. 449 00:28:42,480 --> 00:28:45,200 Speaker 2: But when this sunlight passes through. 450 00:28:45,000 --> 00:28:49,000 Speaker 1: Earth's atmosphere, shorter and longer wavelengths, light, gamma rays, and 451 00:28:49,040 --> 00:28:52,640 Speaker 1: most ultraviolet that's all filtered out, and much of the 452 00:28:52,640 --> 00:28:56,080 Speaker 1: infrared is absorbed as heat. So what punches through all 453 00:28:56,080 --> 00:28:58,680 Speaker 1: the way to the surface where we're hanging out is 454 00:28:58,720 --> 00:29:02,680 Speaker 1: a pretty narrow window of light wavelengths between about four 455 00:29:02,760 --> 00:29:06,240 Speaker 1: hundred and seven hundred nanimeters. Of all the energy that 456 00:29:06,280 --> 00:29:10,800 Speaker 1: gets released from the Sun, only this tiny sliver reaches 457 00:29:10,920 --> 00:29:12,640 Speaker 1: us in abundance, And. 458 00:29:12,640 --> 00:29:14,680 Speaker 2: So that's what evolution seesed on. 459 00:29:15,400 --> 00:29:20,280 Speaker 1: Our ancestors' eyes evolved to pick up on what was available. 460 00:29:20,640 --> 00:29:24,720 Speaker 1: This little band of light provided enough data to distinguish 461 00:29:25,000 --> 00:29:29,640 Speaker 1: edges and shapes and motion and color plants reflect the 462 00:29:29,840 --> 00:29:34,000 Speaker 1: particular wavelengths we see as green, right, fruit often reflects 463 00:29:34,040 --> 00:29:36,880 Speaker 1: another set of wavelengths we see red or yellow. Blood 464 00:29:36,880 --> 00:29:41,040 Speaker 1: looks red, fire looks orange, and presumably our ancestors who 465 00:29:41,080 --> 00:29:44,640 Speaker 1: could detect these sorts of distinctions had a better shot 466 00:29:44,880 --> 00:29:49,320 Speaker 1: at survival. Color perception had nothing to do with esthetic pleasures, 467 00:29:49,360 --> 00:29:51,880 Speaker 1: which we'll get into in the next episode, at least 468 00:29:52,000 --> 00:29:55,600 Speaker 1: not originally it was about spotting. What mattered is that 469 00:29:55,640 --> 00:29:59,320 Speaker 1: fruit ripe, is that animal bleeding, is that flash of 470 00:29:59,360 --> 00:30:03,440 Speaker 1: color over there, a flower or a threat. Over tens 471 00:30:03,480 --> 00:30:09,240 Speaker 1: of millions of years, animal brains became color detectives. It's 472 00:30:09,280 --> 00:30:12,760 Speaker 1: not that we wanted to marvel at rainbows. It's that 473 00:30:12,920 --> 00:30:17,000 Speaker 1: it was extraordinarily useful to decode a layer of information 474 00:30:17,480 --> 00:30:22,400 Speaker 1: bouncing off objects in the world. We extract meaning from 475 00:30:22,440 --> 00:30:26,760 Speaker 1: the quality of the reflected light. I suspect that berry 476 00:30:27,000 --> 00:30:30,280 Speaker 1: is full of sugar and calories because it's reflecting a 477 00:30:30,360 --> 00:30:34,240 Speaker 1: wavelength that I see as red. That yellowing leaf tells 478 00:30:34,280 --> 00:30:39,120 Speaker 1: me about decay. The flush in that guy's cheek reveals anger. 479 00:30:39,600 --> 00:30:40,880 Speaker 2: In this way, we. 480 00:30:41,080 --> 00:30:44,840 Speaker 1: And other animals learned to read the mood and state 481 00:30:45,280 --> 00:30:49,480 Speaker 1: of the world. Now I want to circle back to 482 00:30:49,720 --> 00:30:53,120 Speaker 1: the deer hunter or the red bird to double click 483 00:30:53,160 --> 00:30:57,560 Speaker 1: on this issue of camouflage and also the opposite of camouflage, 484 00:30:57,680 --> 00:31:01,080 Speaker 1: because color can serve a couple of functions in nature 485 00:31:01,360 --> 00:31:04,560 Speaker 1: in the sense that it can allow animals to blend 486 00:31:04,640 --> 00:31:08,920 Speaker 1: in like camouflage, or to stand out like warning coloration. 487 00:31:09,520 --> 00:31:14,360 Speaker 1: Both blending in and standing out rely on exploiting the 488 00:31:14,440 --> 00:31:17,960 Speaker 1: visual systems of other species. So take a tiger in 489 00:31:18,000 --> 00:31:21,160 Speaker 1: the jungle. He's got these really bold orange and black 490 00:31:21,200 --> 00:31:25,400 Speaker 1: stripes that might seem like a terrible disguise, But most 491 00:31:25,400 --> 00:31:28,920 Speaker 1: of the tigers prey don't see red well, so the 492 00:31:29,000 --> 00:31:33,480 Speaker 1: orange appears as a muted gray. The stripes help the 493 00:31:33,560 --> 00:31:39,280 Speaker 1: tiger's body dissolve into the dappled shadows and reeds. Now 494 00:31:39,320 --> 00:31:43,720 Speaker 1: flip to the opposite strategy, what's called warning coloration. So 495 00:31:43,880 --> 00:31:47,440 Speaker 1: picture the bright yellow and black stripes on a wasp 496 00:31:47,640 --> 00:31:51,200 Speaker 1: or the super bright red of a poisoned dart frog. 497 00:31:51,280 --> 00:31:53,880 Speaker 1: I'm putting some pictures in the show notes on Eagleman 498 00:31:53,920 --> 00:31:57,840 Speaker 1: dot com slash podcast. The point is that these colors 499 00:31:57,920 --> 00:32:02,160 Speaker 1: serve as honest ad advertisements. It says don't eat me, 500 00:32:02,360 --> 00:32:05,880 Speaker 1: I'm dangerous, and other animals learn very quickly not to 501 00:32:05,960 --> 00:32:07,240 Speaker 1: mess with those patterns. 502 00:32:07,680 --> 00:32:09,200 Speaker 2: So a young. 503 00:32:09,040 --> 00:32:13,040 Speaker 1: Bird who eats a monarch butterfly and becomes violently ill 504 00:32:13,520 --> 00:32:15,720 Speaker 1: learns to avoid anything. 505 00:32:15,400 --> 00:32:16,360 Speaker 2: That looks like that. 506 00:32:16,480 --> 00:32:20,080 Speaker 1: In the future, we humans, of course, have co opted 507 00:32:20,080 --> 00:32:23,640 Speaker 1: the same idea and our own signaling systems. We have 508 00:32:24,120 --> 00:32:28,680 Speaker 1: road signs and hazard labels and life jackets and construction gear. 509 00:32:29,000 --> 00:32:33,160 Speaker 1: We build these all with high contrast, high saturated colors, 510 00:32:33,480 --> 00:32:36,920 Speaker 1: and this taps into our built in alert system designed 511 00:32:37,000 --> 00:32:39,520 Speaker 1: to grab our attention and to hold it. Now, just 512 00:32:39,640 --> 00:32:44,040 Speaker 1: note that not all warning colors are truthful. Nature has 513 00:32:44,160 --> 00:32:48,840 Speaker 1: its con artists. Some animals mimic the colors of toxic 514 00:32:48,920 --> 00:32:54,840 Speaker 1: species without being toxic themselves. So think of the viceroy butterfly, 515 00:32:55,200 --> 00:32:59,880 Speaker 1: which looks like the monarch butterfly. Predators who have tasted 516 00:33:00,080 --> 00:33:02,520 Speaker 1: a monarch and regretted it are. 517 00:33:02,480 --> 00:33:03,640 Speaker 2: Likely to avoid both. 518 00:33:03,680 --> 00:33:08,040 Speaker 1: And this is deception through color, using color as a 519 00:33:08,120 --> 00:33:11,440 Speaker 1: kind of costume. And then let's not forget about the 520 00:33:11,440 --> 00:33:14,320 Speaker 1: theatricality of sexual selection. 521 00:33:15,160 --> 00:33:16,000 Speaker 2: Charles Darwin. 522 00:33:16,120 --> 00:33:18,840 Speaker 1: At first he found the peacock's tail to be a 523 00:33:18,880 --> 00:33:22,240 Speaker 1: headache for his theory of natural selection, because it seems 524 00:33:22,280 --> 00:33:26,480 Speaker 1: to hinder survival. But then Darwin realized that traits like 525 00:33:26,520 --> 00:33:31,160 Speaker 1: the peacock's tail could provide an advantage in the competition 526 00:33:31,360 --> 00:33:34,960 Speaker 1: for mates. In other words, it's for sex appeal. Now, 527 00:33:34,960 --> 00:33:38,400 Speaker 1: this apparently scandalized many scientists when he first proposed it, 528 00:33:38,640 --> 00:33:42,600 Speaker 1: but the evidence holds. In many species, the brightest, most 529 00:33:42,760 --> 00:33:48,920 Speaker 1: colorful individuals are auditioning. They're working to signal health or 530 00:33:49,000 --> 00:33:53,520 Speaker 1: genetic quality or dominance. Just think about a male mandrill's 531 00:33:53,560 --> 00:33:57,280 Speaker 1: brilliantly colored face and rump. Those are just for decoration. 532 00:33:57,520 --> 00:34:02,520 Speaker 1: They're billboards of status. I'll also mention that in some species, 533 00:34:02,840 --> 00:34:06,840 Speaker 1: color shifts with mood or with context. So you may 534 00:34:06,840 --> 00:34:10,760 Speaker 1: have seen a cuttlefish who can change their skin pattern 535 00:34:10,800 --> 00:34:15,399 Speaker 1: in seconds, and some fish develop intense coloration only during 536 00:34:15,440 --> 00:34:20,839 Speaker 1: mating season. These color changes serve as social cues. They 537 00:34:20,840 --> 00:34:26,080 Speaker 1: are visually broadcasting their intentions. So what we see is 538 00:34:26,080 --> 00:34:31,000 Speaker 1: that color is one of evolution's most versatile tools. That 539 00:34:31,160 --> 00:34:35,920 Speaker 1: can hide, it can warn, it can deceive, it can seduce, 540 00:34:36,320 --> 00:34:38,799 Speaker 1: and it can do all of this differently depending on 541 00:34:39,040 --> 00:34:45,000 Speaker 1: who is watching and what their color capabilities are. So 542 00:34:45,280 --> 00:34:47,360 Speaker 1: I want to zoom the camera out to see what 543 00:34:47,400 --> 00:34:51,360 Speaker 1: we've covered today. Color isn't something out there in the world. 544 00:34:51,360 --> 00:34:55,839 Speaker 1: It's something our brains create. Photons have no color. It's 545 00:34:55,880 --> 00:35:00,400 Speaker 1: our brain that absorbs the raw wavelengths and transfer forms 546 00:35:00,400 --> 00:35:05,880 Speaker 1: them into experience. This transformation starts with light sensitive cells 547 00:35:05,880 --> 00:35:07,680 Speaker 1: in your retinam goes all the way to your brain, 548 00:35:07,960 --> 00:35:12,520 Speaker 1: and the color you perceive ends up being shaped by context, 549 00:35:12,880 --> 00:35:16,640 Speaker 1: and your brain's best guess becomes your visual reality. 550 00:35:16,840 --> 00:35:17,920 Speaker 2: And we saw how. 551 00:35:17,800 --> 00:35:21,680 Speaker 1: Our color vision is a patchwork of evolutionary trade offs, 552 00:35:22,000 --> 00:35:25,799 Speaker 1: shaped by ancient nocturnal life, and by the need to 553 00:35:26,160 --> 00:35:28,799 Speaker 1: spot fruit, and perhaps by the need to read each 554 00:35:28,800 --> 00:35:32,239 Speaker 1: other's emotions. We looked at how different animals live in 555 00:35:32,680 --> 00:35:37,080 Speaker 1: very different color worlds, and how our narrow window of 556 00:35:37,160 --> 00:35:41,279 Speaker 1: vision was sculpted by sunlight and survival. And we saw 557 00:35:41,360 --> 00:35:46,600 Speaker 1: how evolutionary pressures shaped the palette of our world. Flowers 558 00:35:46,640 --> 00:35:50,920 Speaker 1: evolved colors not for us, but for the eyes of pollinators. 559 00:35:51,440 --> 00:35:55,880 Speaker 1: The natural world is performing for eyes. Now that we 560 00:35:55,960 --> 00:35:58,239 Speaker 1: have the basics down, next week we're going to move 561 00:35:58,440 --> 00:36:02,840 Speaker 1: to deeper levels, include beyond biology into culture and language 562 00:36:02,840 --> 00:36:06,879 Speaker 1: and art. Because once we understand how color is made 563 00:36:06,960 --> 00:36:10,000 Speaker 1: in the brain, it opens up all sorts of new questions. 564 00:36:10,440 --> 00:36:13,160 Speaker 2: Why was purple the color of royalty. 565 00:36:13,360 --> 00:36:16,560 Speaker 1: How do we see colors that are recent ancestors never 566 00:36:16,640 --> 00:36:20,520 Speaker 1: saw in their lives. Why are you unable to imagine 567 00:36:20,719 --> 00:36:23,640 Speaker 1: a new color? Are there, in fact new colors that 568 00:36:23,719 --> 00:36:26,640 Speaker 1: you could see? Could you lose. 569 00:36:26,360 --> 00:36:28,680 Speaker 2: Your color vision? And many other questions. 570 00:36:29,320 --> 00:36:32,279 Speaker 1: So to wrap today, the main lesson we see is 571 00:36:32,280 --> 00:36:36,480 Speaker 1: that color is a construction. It's a useful fiction of 572 00:36:36,560 --> 00:36:39,600 Speaker 1: the brain, a mental model painted on. 573 00:36:39,600 --> 00:36:40,640 Speaker 2: Top of physics. 574 00:36:40,880 --> 00:36:44,120 Speaker 1: But it's also one of the richest and most emotionally 575 00:36:44,280 --> 00:36:48,120 Speaker 1: resonant parts of being alive. So just take a moment 576 00:36:48,200 --> 00:36:51,640 Speaker 1: and look around at the light. What you're seeing is 577 00:36:51,719 --> 00:36:54,640 Speaker 1: what your brain makes of that light. The colors aren't 578 00:36:54,640 --> 00:36:59,120 Speaker 1: out there, they're in here. Your brain isn't just perceiving 579 00:36:59,160 --> 00:37:08,719 Speaker 1: the world, it's actively constructing it. Go to eagleman dot 580 00:37:08,760 --> 00:37:12,600 Speaker 1: com slash podcast for more information and to find further reading. 581 00:37:13,320 --> 00:37:16,680 Speaker 1: Join the weekly discussions on my substack and check out 582 00:37:16,680 --> 00:37:19,719 Speaker 1: on Subscribe to Inner Cosmos on YouTube for videos of 583 00:37:19,719 --> 00:37:23,279 Speaker 1: each episode and to leave comments until next time. I'm 584 00:37:23,360 --> 00:37:26,000 Speaker 1: David Eagleman, and this is Inner Cosmos.