WEBVTT 00:13.100 --> 00:16.930 Professor Paul Bloom: We began the course by talking 00:16.927 --> 00:20.817 about one of the foundational ideas of modern psychology. 00:20.820 --> 00:24.210 This is what Francis Crick described as "The Astonishing 00:24.208 --> 00:26.978 Hypothesis," the idea that our mental life, 00:26.980 --> 00:28.980 our consciousness, our morality, 00:28.984 --> 00:32.934 our capacity to make decisions and judgments is the product of 00:32.929 --> 00:34.869 a material physical brain. 00:34.870 --> 00:37.060 What I want to talk about today and introduce it, 00:37.060 --> 00:39.620 and it's going to be a theme that we're going to continue 00:39.615 --> 00:41.345 throughout the rest of the course, 00:41.350 --> 00:44.830 is a second idea which I think is equally shocking, 00:44.829 --> 00:46.499 perhaps more shocking. 00:46.500 --> 00:50.270 And this has to do with where mental life comes from, 00:50.271 --> 00:54.551 not necessary its material nature, but rather its origin. 00:54.550 --> 00:57.340 And the notion, this other "astonishing 00:57.341 --> 01:01.311 hypothesis," is what the philosopher Daniel Dennett has 01:01.308 --> 01:04.318 described as Darwin's dangerous idea. 01:04.319 --> 01:09.279 And this is the modern biological account of the origin 01:09.279 --> 01:13.499 of biological phenomena including psychological 01:13.504 --> 01:16.884 phenomena. Now, people have long been 01:16.883 --> 01:20.993 interested in the evolution of complicated things. 01:20.989 --> 01:25.059 And there is an argument that's been repeated throughout history 01:25.060 --> 01:28.100 and many people have found it deeply compelling, 01:28.096 --> 01:29.966 including Darwin himself. 01:29.970 --> 01:33.660 Darwin, as he wrote The Origin of Species, was 01:33.662 --> 01:37.922 deeply persuaded and moved by this argument from--in the form 01:37.923 --> 01:41.193 presented by the theologian William Paley. 01:41.190 --> 01:43.100 So, Paley has an example here. 01:43.099 --> 01:46.429 Paley tells--gives the example of you're walking down the beach 01:46.434 --> 01:47.944 and your foot hits a rock. 01:47.940 --> 01:49.920 And then you wonder, "Where did that rock come 01:49.918 --> 01:51.728 from?" And you don't really expect an 01:51.734 --> 01:53.544 interesting answer to that question. 01:53.540 --> 01:54.570 Maybe it was always there. 01:54.570 --> 01:56.280 Maybe it fell from the sky. 01:56.280 --> 01:59.060 Who cares? But suppose you found a watch 01:59.063 --> 02:03.313 on the ground and then you asked where the watch had come from. 02:03.310 --> 02:07.950 Paley points out that it would not be satisfying to simply say 02:07.952 --> 02:12.292 it's always been there or it came there as an accident. 02:12.289 --> 02:16.289 And he uses this comparison to make a point, 02:16.293 --> 02:21.233 which is a watch is a very complicated and interesting 02:21.228 --> 02:24.628 thing. Paley is--was a medical doctor 02:24.633 --> 02:29.833 and Paley goes on to describe a watch and compare a watch to the 02:29.827 --> 02:34.687 eye and noticing that a watch and the eye contain multitudes 02:34.691 --> 02:38.571 of parts that interact in complicated ways to do 02:38.566 --> 02:40.706 interesting things. 02:40.710 --> 02:44.830 In fact, to change and to update the analogy a little bit, 02:44.827 --> 02:48.797 an eye is very much like a machine known as a camera. 02:48.800 --> 02:52.120 And they're similar at a deep way. 02:52.120 --> 02:55.390 They both have lenses that bend light and project an image onto 02:55.385 --> 02:56.855 a light-sensitive surface. 02:56.860 --> 02:59.610 For the eye the light-sensitive surface is the retina. 02:59.610 --> 03:02.000 For the camera it's the film. 03:02.000 --> 03:04.610 They both have a focusing mechanism. 03:04.610 --> 03:08.280 For the eye it's muscles that change the shape of the lens. 03:08.280 --> 03:12.530 For a camera it's a diaphragm that governs the amount of 03:12.534 --> 03:16.354 incoming light. Even they're both encased in 03:16.354 --> 03:18.984 black. The light-sensitive part of the 03:18.978 --> 03:22.458 eye and part of the camera are both encased in black. 03:22.460 --> 03:27.200 The difference is--So in fact, the eye and a camera look a lot 03:27.197 --> 03:30.767 alike and we know the camera is an artifact. 03:30.770 --> 03:34.300 The camera has been constructed by an intelligent--by 03:34.299 --> 03:37.149 intelligent beings to fulfill a purpose. 03:37.150 --> 03:39.950 In fact, if there's any difference between things like 03:39.950 --> 03:41.800 the eye and things like a camera, 03:41.800 --> 03:45.370 the difference is that things like the eye are far more 03:45.366 --> 03:48.136 complicated than things like the camera. 03:48.139 --> 03:51.809 When I was a kid I had this incredible TV show called "The 03:51.807 --> 03:53.477 Six Million Dollar Man." 03:53.479 --> 03:55.819 Anybody here ever seen it or heard of it? 03:55.820 --> 04:00.020 Oh. Anyway, the idea is there's a 04:00.018 --> 04:04.698 test pilot, Steve Austin, and his rocket jet crashes and 04:04.701 --> 04:08.381 he loses his--both legs, his arm and his eye, 04:08.378 --> 04:12.238 which sounds really bad but they replace them with bionic 04:12.239 --> 04:13.879 stuff, with artificial leg, 04:13.884 --> 04:16.504 artificial arm and an artificial eye that are really 04:16.498 --> 04:19.638 super-powered. And then he fights crime. 04:19.639 --> 04:20.959 [laughter] It was [laughs] 04:20.958 --> 04:22.328 really the best show on. 04:22.329 --> 04:24.509 It was really good, [laughter] 04:24.507 --> 04:27.207 but the thing is this was in 1974. 04:27.209 --> 04:32.059 It's now over thirty years later and it's true then and 04:32.063 --> 04:35.033 it's true now, this is fantasy. 04:35.029 --> 04:37.069 It doesn't make it to the level of science fiction. 04:37.070 --> 04:40.490 It's fantasy. We are impossibly far away from 04:40.486 --> 04:43.666 developing machines that could do this. 04:43.670 --> 04:47.730 We are impossibly far away from building a machine that can do 04:47.729 --> 04:49.459 what the human eye does. 04:49.459 --> 04:52.759 And so somebody like Paley points out, "Look. 04:52.759 --> 04:56.589 The complexity of the biological world suggests that 04:56.588 --> 05:01.018 these things are complicated artifacts created by a designer 05:01.017 --> 05:04.017 far smarter than any human engineer. 05:04.019 --> 05:07.419 And the designer, of course, would be God." 05:07.420 --> 05:09.620 I went to Goggle Images. 05:09.620 --> 05:12.250 That--I don't mean that to be sacrilegious [laughter] 05:12.251 --> 05:14.331 in any sense. You could try this. 05:14.329 --> 05:19.709 I went to "Google Images" and typed in "God" and this is what 05:19.707 --> 05:23.737 showed up right in the middle so--And this, 05:23.740 --> 05:26.190 Paley argued, and it was--has been convincing 05:26.191 --> 05:28.921 throughout most of history, is a perfectly logical 05:28.921 --> 05:32.321 explanation for where these complicated things come from. 05:32.319 --> 05:35.759 It also has the advantage of being compatible with scripture 05:35.756 --> 05:39.016 and compatible with religious beliefs, but Paley made the 05:39.017 --> 05:40.937 point this stands on its own. 05:40.940 --> 05:45.100 If you find complicated things that--complicated artifacts, 05:45.102 --> 05:48.262 you don't assume they emerged by accident. 05:48.259 --> 05:52.609 You assume that they were created by an intelligent being. 05:52.610 --> 05:56.610 Now, this view has always had problems. 05:56.610 --> 06:00.070 This view, you could call it "creationism," which is that 06:00.068 --> 06:03.648 biological structures were created by an intelligent being, 06:03.650 --> 06:05.380 has always had problems. 06:05.379 --> 06:08.889 One problem is it pushes back the question. 06:08.889 --> 06:11.489 So you ask, "Where did that intelligent being come from?" 06:11.490 --> 06:14.190 And this is a particularly serious problem from the 06:14.193 --> 06:17.333 standpoint of the evolution of psychological structures. 06:17.329 --> 06:20.939 So, we want to know, "how is it that creatures came 06:20.944 --> 06:25.434 across--upon this earth with the ability to reason and plan and 06:25.425 --> 06:28.095 do things?" And then the answer is "well, 06:28.099 --> 06:30.729 another creature with that ability created us." 06:30.730 --> 06:34.230 That doesn't necessarily mean it's wrong, but it means it's 06:34.233 --> 06:36.463 unsatisfying. You immediately want to get an 06:36.461 --> 06:38.841 explanation for where that other creature comes from. 06:38.839 --> 06:41.989 More to the point, there's always been evidence 06:41.993 --> 06:44.843 for evolution. And what I mean by evolution 06:44.841 --> 06:47.531 here isn't necessarily a specific mechanism, 06:47.530 --> 06:51.350 but merely the fact that body parts like the eye didn't emerge 06:51.346 --> 06:55.246 all of a sudden, but rather have parallels both 06:55.250 --> 07:00.430 within other existing animals and across human and biological 07:00.430 --> 07:03.690 history. This evidence comes in 07:03.687 --> 07:07.037 different forms. There is fossil evidence for 07:07.044 --> 07:10.594 different body parts suggesting that they have evolved from more 07:10.585 --> 07:11.705 rudimentary form. 07:11.709 --> 07:14.649 There is vestigial characteristics. 07:14.649 --> 07:18.769 And what this means is there are characteristics that human 07:18.766 --> 07:21.956 bodies have that are somewhat inexplicable, 07:21.959 --> 07:26.109 like the human tailbone or goose-bumps, unless you view 07:26.108 --> 07:30.408 them--the human body in its current form as modifications 07:30.409 --> 07:32.329 from a previous form. 07:32.329 --> 07:35.359 There are parallels with other animals. 07:35.360 --> 07:36.900 And this is clear in psychology. 07:36.899 --> 07:39.519 So, a human brain is different from the rat, 07:39.518 --> 07:42.808 cat, and monkey brain but at the same time you see them 07:42.807 --> 07:46.337 following a sort of common plan and common structures. 07:46.339 --> 07:50.169 And one rational inference from this is that they're linked 07:50.171 --> 07:52.221 through evolutionary descent. 07:52.220 --> 07:55.890 Finally, there is occasional poor design. 07:55.889 --> 08:00.799 So, Paley rhapsodized about the remarkable powers of the human 08:00.795 --> 08:03.685 body and the different body parts, 08:03.689 --> 08:06.219 but even Paley admitted that there are some things which just 08:06.220 --> 08:07.190 don't work very well. 08:07.189 --> 08:10.799 Your eye contains a blind spot because of how the nerves are 08:10.797 --> 08:13.997 wired up. In the male urinary system the 08:14.000 --> 08:18.720 urethra goes through the prostate gland instead of around 08:18.723 --> 08:20.723 it, which leads to many physical 08:20.715 --> 08:22.515 problems in men later on in life. 08:22.519 --> 08:27.409 And so you're forced to either argue that these are really good 08:27.411 --> 08:31.831 things or that God is either malicious or incompetent. 08:31.829 --> 08:34.169 And those are difficult arguments to make. 08:34.169 --> 08:37.509 So, these are problems with the creationist view. 08:37.509 --> 08:41.149 But still, for the longest time in human intellectual history 08:41.151 --> 08:42.791 there was no alternative. 08:42.789 --> 08:44.849 And in fact, Richard Dawkins, 08:44.847 --> 08:48.297 the most prominent evolutionary--one of the most 08:48.300 --> 08:52.190 prominent evolutionary biologists alive and one of the 08:52.193 --> 08:55.503 most staunchest critics of creationism, 08:55.500 --> 08:58.980 has written in The Blind Watchmaker saying, 08:58.977 --> 09:03.377 look, anybody 100 years ago or 150 years ago who didn't believe 09:03.378 --> 09:07.068 that God created humans and other animals was a moron 09:07.068 --> 09:11.538 because the argument from design is a damn good argument. 09:11.539 --> 09:14.779 And in the absence of some other argument you should 09:14.779 --> 09:16.049 go--defer to that. 09:16.049 --> 09:19.029 You should say, "Well, there are all of these 09:19.028 --> 09:22.748 problems but humans and other biological forms must have 09:22.750 --> 09:26.880 divine creation because of their incredible rich and intricate 09:26.879 --> 09:30.809 structure." What changed all that of course 09:30.812 --> 09:34.442 was Darwin. And Darwin--Darwin's profound 09:34.438 --> 09:39.268 accomplishment was showing how you get these complicated 09:39.272 --> 09:42.812 biological structures, like the eye, 09:42.805 --> 09:47.015 emerging through a purely non-intentional, 09:47.017 --> 09:51.607 non-created process, a purely physical process. 09:51.610 --> 09:56.560 And this could be seen as equal in importance to the claim that 09:56.561 --> 10:00.951 the Earth revolves around the Sun and that we're not the 10:00.953 --> 10:03.113 center of the universe. 10:03.110 --> 10:05.480 And in fact, some scholars have made a 10:05.479 --> 10:08.619 suggestion which seems plausible, that the idea of 10:08.617 --> 10:12.777 natural selection is the most important idea in the sciences, 10:12.780 --> 10:15.060 period. So, this is not a course in 10:15.061 --> 10:17.631 evolution and I expect people to have some background. 10:17.629 --> 10:20.789 If you don't have a background in it, you could get your 10:20.786 --> 10:23.996 background from external readings but also from--the Gray 10:24.001 --> 10:27.671 textbook and the Norton readings will both--will each provide you 10:27.674 --> 10:30.434 with enough background to get up to speed. 10:30.429 --> 10:33.449 But the general idea is that there are three components to 10:33.450 --> 10:34.510 natural selection. 10:34.510 --> 10:36.100 There is variation. 10:36.100 --> 10:39.970 And this variation gives rise to different degrees of survival 10:39.971 --> 10:44.031 and reproduction and gets passed on from generation to generation 10:44.032 --> 10:48.712 and gives rise to adaptations, what Darwin described as "that 10:48.707 --> 10:53.907 perfection of structure that justly excites our imagination." 10:53.909 --> 10:57.759 And the biological world has all sorts of examples. 10:57.760 --> 10:59.380 You look at camouflage. 10:59.379 --> 11:03.039 Prior to Darwin one might imagine that some intelligent 11:03.035 --> 11:06.415 creator crafted animals to hide from their prey. 11:06.419 --> 11:09.769 But now we have a different alternative, which is that 11:09.771 --> 11:12.871 animals that were better hidden survive better, 11:12.870 --> 11:15.330 reproduce more, and over the course of 11:15.333 --> 11:17.933 thousands, perhaps millions of years, 11:17.929 --> 11:20.699 they've developed elaborate camouflage. 11:20.700 --> 11:24.800 There's been a lot of work on Paley's favorite example – the 11:24.797 --> 11:27.027 eye. So Darwin himself noted that 11:27.029 --> 11:30.819 the human eye did not seem to emerge all at once but rather 11:30.819 --> 11:34.609 you could look at other animals and find parallels in other 11:34.609 --> 11:38.459 animals that seem to suggest that more rudimentary forms are 11:38.464 --> 11:41.604 possible. And more recently computer 11:41.598 --> 11:46.738 simulations have developed--have been developed that have crafted 11:46.740 --> 11:51.720 eyes under plausible assumptions of selective pressure and what 11:51.720 --> 11:53.890 the starting point is. 11:53.889 --> 11:57.859 So, this is the theory of natural selection. 11:57.860 --> 12:00.800 The good question to ask is, "why am I talking about 12:00.797 --> 12:03.617 evolution in Introduction to Psychology class?" 12:03.620 --> 12:08.330 And the answer is that there are two ideas which come 12:08.333 --> 12:10.023 together. And in fact, 12:10.020 --> 12:12.150 they're both of the dangerous ideas. 12:12.149 --> 12:17.149 One idea is that Darwin's idea--that biological forms 12:17.153 --> 12:21.583 evolve through this purely physical process. 12:21.580 --> 12:24.960 The second idea, the rejection of Descartes, 12:24.961 --> 12:29.291 is that our minds are the product of physical things and 12:29.287 --> 12:33.507 physical events. You bring these together and it 12:33.507 --> 12:38.377 forces you to the perspective that what we are--our mental 12:38.376 --> 12:42.626 life is no less than the eye, no less than camouflage, 12:42.627 --> 12:45.977 the product of this purely physical process of natural 12:45.978 --> 12:48.408 selection. More to the point, 12:48.409 --> 12:53.329 our cognitive mechanisms were evolved not to please God, 12:53.326 --> 12:57.536 not as random accidents, but rather for the purpose of 12:57.536 --> 12:59.206 survival and reproduction. 12:59.210 --> 13:02.340 More contentiously, you could argue they've been 13:02.344 --> 13:06.084 shaped by natural selection to solve certain problems. 13:06.080 --> 13:08.280 And so, from an evolutionary point of view, 13:08.277 --> 13:11.307 when you look at what the brain is and what the brain does, 13:11.312 --> 13:13.722 you look at it in terms of these problems. 13:13.720 --> 13:22.790 And this is what psychology is for. 13:22.789 --> 13:24.589 This is what our thinking is for. 13:24.590 --> 13:28.360 We have evolved mental capacities to solve different 13:28.358 --> 13:31.908 problems: perception of the world, communication, 13:31.906 --> 13:35.006 getting nutrition and rest, and so on. 13:35.009 --> 13:42.449 Now, we're going to talk about how to apply evolutionary theory 13:42.450 --> 13:46.350 to psychology. But as we're doing so we have 13:46.346 --> 13:48.796 to keep in mind two misconceptions. 13:48.799 --> 13:51.269 There are two ways you can go seriously wrong here. 13:51.269 --> 13:54.699 The first is to think that, well, if we're taking an 13:54.701 --> 13:58.331 evolutionary approach then natural selection will cause 13:58.334 --> 14:01.164 animals to want to spread their genes. 14:01.159 --> 14:04.649 So, if we're being biological about it, that means everybody 14:04.653 --> 14:07.913 must run around thinking "I want to spread my genes." 14:07.909 --> 14:12.369 I want to--and this is just really --Oops. 14:12.370 --> 14:13.330 I shouldn't do that. 14:13.330 --> 14:15.010 This is really wrong. 14:15.010 --> 14:19.190 It's even in red. 14:19.190 --> 14:22.440 And what this fails to do is make a distinction between 14:22.440 --> 14:25.150 ultimate causation and proximate causation. 14:25.149 --> 14:29.009 And those are technical terms referring to--Ultimate causation 14:29.009 --> 14:32.679 is the reason why something is there in the first place, 14:32.679 --> 14:35.469 over millions of years of history. 14:35.470 --> 14:38.110 Proximate causation is why you're doing it now. 14:38.110 --> 14:40.430 And these are different. 14:40.429 --> 14:43.619 Obviously, for instance, animals do all sorts of things 14:43.615 --> 14:47.035 to help survive and reproduce but a cockroach doesn't think 14:47.038 --> 14:48.818 "oh, I'm doing this to help survive 14:48.819 --> 14:50.389 and reproduce and spread my genes." 14:50.389 --> 14:52.909 A cockroach doesn't know anything about genes. 14:52.909 --> 14:57.229 Rather, the mechanisms that make it do what it does are 14:57.234 --> 15:01.884 different from its own mental states, if it has any--why it 15:01.878 --> 15:04.848 does them. This is a point nicely made by 15:04.853 --> 15:07.103 William James. So, William James is asked, 15:07.099 --> 15:09.069 "Why do we eat?" And he writes, 15:09.070 --> 15:12.090 Not one man in a billion when taking his dinner ever 15:12.090 --> 15:13.150 thinks of utility. 15:13.149 --> 15:16.139 He eats because the food tastes good and makes him want more. 15:16.139 --> 15:18.639 If you asked him why you should want to eat more of what tastes 15:18.641 --> 15:20.821 like that, instead of revering you as a philosopher, 15:20.820 --> 15:23.470 he will probably laugh at you for a fool. 15:23.470 --> 15:25.200 And it's really the common sense answer. 15:25.200 --> 15:26.640 "Why are you eating?" 15:26.639 --> 15:29.699 Nobody's going to answer, "Because I must sustain my body 15:29.697 --> 15:31.987 so as to spread my genes in the future." 15:31.990 --> 15:34.910 Rather, you eat because you're hungry. 15:34.909 --> 15:37.709 Those two theories, you eat because you're hungry 15:37.706 --> 15:41.316 and you eat to sustain your body so you could spread your genes 15:41.318 --> 15:43.588 in the future, are not alternative. 15:43.590 --> 15:46.460 Rather, they're different levels of explanation. 15:46.460 --> 15:49.930 And you can't confuse them. 15:49.929 --> 15:54.449 The ultimate level which does appeal to survival and 15:54.452 --> 15:58.442 reproduction does not--is independent from the 15:58.442 --> 16:00.572 psychological level. 16:00.570 --> 16:03.720 To give another example, people protect their children 16:03.724 --> 16:06.824 so you ask, "Why do people protect their children? 16:06.820 --> 16:10.370 Why would somebody devote so much effort to protecting and 16:10.365 --> 16:12.725 helping and feeding their children?" 16:12.730 --> 16:15.780 Well, the evolutionary explanation is animals that 16:15.780 --> 16:19.330 don't protect their offspring don't last over evolutionary 16:19.329 --> 16:21.629 time. We protect our offspring 16:21.630 --> 16:25.040 because they contain fifty percent of our genes, 16:25.038 --> 16:28.518 but that's not the psychological explanation. 16:28.519 --> 16:31.269 Nobody but a deranged psychologist would ever answer, 16:31.272 --> 16:34.612 "Oh, I love my children because they contain fifty percent of my 16:34.607 --> 16:36.847 genes." Rather, the psychological 16:36.847 --> 16:40.557 explanation is a deeper--is different and has a different 16:40.560 --> 16:43.100 texture. And this will be a lot clearer 16:43.098 --> 16:46.718 when we talk about the emotions, where you could really see a 16:46.716 --> 16:50.576 distinction between the question of why we feel something from an 16:50.575 --> 16:54.305 evolutionary point of view and why we feel it from a day-to-day 16:54.313 --> 16:57.443 point of view. The second misconception is 16:57.443 --> 17:01.453 that natural selection entails that everything is adaptive, 17:01.446 --> 17:04.476 that everything we do, everything we think is 17:04.483 --> 17:10.073 adaptive. This is wrong. 17:10.069 --> 17:13.299 Natural selection and evolution, more generally, 17:13.300 --> 17:17.630 distinguish between adaptations and byproducts and accidents. 17:17.630 --> 17:22.150 Many of you are currently, or will as you get older, 17:22.154 --> 17:23.844 suffer back pain. 17:23.839 --> 17:26.559 If I was to ask you, "So, why do you suffer back 17:26.564 --> 17:29.104 pain? How does back pain help you 17:29.103 --> 17:31.003 survive and reproduce?" 17:31.000 --> 17:33.590 Well, the answer is it's not an adaptation. 17:33.589 --> 17:36.899 Back pain is an accidental byproduct of how our backs are 17:36.898 --> 17:39.618 shaped. Don't go looking for an 17:39.616 --> 17:45.406 adaptive reason for hiccups or self-pity or bloating after you 17:45.414 --> 17:48.264 eat. There's all sorts of things a 17:48.264 --> 17:51.284 body will do that have no adaptive value, 17:51.277 --> 17:53.157 rather just accidents. 17:53.160 --> 17:55.370 We have a body that does all sorts of things. 17:55.369 --> 17:59.179 Some things it will do by accident and this is certainly 17:59.177 --> 18:00.697 true for psychology. 18:00.700 --> 18:04.080 18:04.079 --> 18:06.739 So, a lot of the things, for instance, 18:06.740 --> 18:11.130 that occupy our interest or our fascination in day-to-day life 18:11.127 --> 18:14.577 are almost certainly evolutionary accidents. 18:14.579 --> 18:18.939 The number--The three--Three of the main preoccupations of 18:18.938 --> 18:23.628 humans are pornography, television, and chocolate but 18:23.628 --> 18:27.458 if I asked you, "Why do you like porn?" 18:27.460 --> 18:30.940 and you'd say, "Because my ancestors who liked 18:30.936 --> 18:35.106 porn reproduced more than those who didn't," [laughter] 18:35.109 --> 18:39.219 it's not true. Rather, you like porn, 18:39.223 --> 18:42.443 assuming you do, [laughter] 18:42.441 --> 18:46.751 as an accident. You have evolved--For instance, 18:46.748 --> 18:50.498 should you be a heterosexual male, you have evolved to be 18:50.504 --> 18:51.984 attracted to women. 18:51.980 --> 18:55.480 That is most likely to be an evolutionary adaptation because 18:55.475 --> 18:58.905 being attracted to women and wanting to have sex with women 18:58.912 --> 19:01.462 is one step to the road to having kids, 19:01.460 --> 19:03.750 which is very good from an evolutionary perspective. 19:03.750 --> 19:07.420 It so happens, though, in our modern 19:07.423 --> 19:13.933 environment that people have created images that substitute. 19:13.930 --> 19:17.370 So, instead of actually going out and seeking out women you 19:17.372 --> 19:20.812 could just surf the web for hours and hours and watch dirty 19:20.814 --> 19:24.854 movies and read dirty books – evolutionary adaptive dead ends. 19:24.850 --> 19:25.760 They're accidents. 19:25.759 --> 19:28.509 Why do you like chocolate bars, assuming that you do? 19:28.509 --> 19:31.519 It is not because your ancestors in the African savanna 19:31.522 --> 19:34.652 who enjoyed chocolate bars reproduced more than those who 19:34.646 --> 19:37.286 didn't. Rather, it is because we've 19:37.287 --> 19:39.837 evolved a taste for sweet things. 19:39.839 --> 19:42.029 And we've evolved a taste for sweet things, 19:42.028 --> 19:44.478 in part, because the sweet things in our natural 19:44.477 --> 19:46.767 environment like fruit were good for us. 19:46.769 --> 19:50.659 In the modern world we have created things like chocolate, 19:50.663 --> 19:54.013 which are not so good for us but we eat anyway. 19:54.009 --> 19:58.369 A lot of the debates--There's a lot of controversy in psychology 19:58.367 --> 20:01.547 over the scope of evolutionary explanations. 20:01.549 --> 20:07.659 And a lot of the debate tends to be over what's an adaptation 20:07.659 --> 20:11.079 and what isn't. There are some clear cases. 20:11.080 --> 20:12.570 We have color vision. 20:12.570 --> 20:13.840 Why do we have color vision? 20:13.839 --> 20:18.199 Well, I think everybody would agree we have color vision as an 20:18.197 --> 20:21.837 adaptation because of the advantages it gives us for 20:21.839 --> 20:24.839 seeing and making visual distinctions. 20:24.840 --> 20:28.040 We are afraid of snakes. 20:28.039 --> 20:31.089 We're going to talk about that in more detail but there's a 20:31.087 --> 20:33.397 straightforward adaptive story about that. 20:33.400 --> 20:35.520 We are afraid of snakes because, really, 20:35.517 --> 20:38.117 our ancestors who weren't afraid of snakes didn't 20:38.123 --> 20:40.353 reproduce as much as those that were. 20:40.349 --> 20:46.059 We like chocolate bars and we enjoy NASCAR. 20:46.059 --> 20:49.179 Those cannot be adaptations because chocolate bars and 20:49.181 --> 20:52.361 NASCAR are recent developments that could not have been 20:52.361 --> 20:54.071 anticipated by evolution. 20:54.070 --> 20:55.520 Those are easy questions. 20:55.520 --> 20:56.650 Here are some hard questions. 20:56.650 --> 21:00.920 Music. Everywhere in the world people 21:00.921 --> 21:05.431 like music. Is this an adaptation for some 21:05.428 --> 21:09.708 selective advantage or is it an accident? 21:09.710 --> 21:11.600 Steven Pinker, who wrote The Language 21:11.598 --> 21:14.358 Instinct that you read before, caused a huge amount of 21:14.358 --> 21:17.258 controversy when he argued that music is just an evolutionary 21:17.263 --> 21:19.673 accident. He described it as auditory 21:19.673 --> 21:23.413 cheesecake, something we like to gorge ourselves on that have 21:23.413 --> 21:25.473 no--has no adaptive advantage. 21:25.470 --> 21:28.590 Other people argue music does have an adaptive advantage. 21:28.589 --> 21:33.319 Sometimes males use violence to coerce sex. 21:33.319 --> 21:37.019 Is male sexual violence a biological adaptation or is it 21:37.018 --> 21:40.278 an accident? There's more than one language. 21:40.279 --> 21:43.499 Is that just an accidental byproduct of the way language 21:43.504 --> 21:47.084 works or is there some sort of group or selectionist advantage 21:47.079 --> 21:50.479 sketched out in some way of having multiple languages? 21:50.480 --> 21:51.720 What about visual art? 21:51.720 --> 21:52.930 What about fiction? 21:52.930 --> 21:54.590 What about our love for stories? 21:54.589 --> 21:57.499 Those are all matters of heated debate. 21:57.500 --> 22:01.990 And so, we have to keep in mind some things plainly are 22:01.991 --> 22:04.201 accidents. Some things almost certainly 22:04.201 --> 22:04.981 aren't accidents. 22:04.980 --> 22:08.480 Where the action is in the study of psychology and the 22:08.475 --> 22:12.625 study of evolution of cognition is trying to figure out which is 22:12.630 --> 22:14.510 which. So, those are the 22:14.510 --> 22:16.880 misconceptions we have to avoid. 22:16.880 --> 22:19.060 But still, who cares? 22:19.059 --> 22:22.329 Again this is an Introduction to Psych course. 22:22.329 --> 22:23.769 Why are we talking about evolution? 22:23.769 --> 22:28.399 Why should it matter to a psychologist how the mind has 22:28.402 --> 22:30.592 evolved? I'm going to talk about 22:30.587 --> 22:33.587 evolution now but for the rest of the course I'm just 22:33.588 --> 22:36.068 interested in how our minds are, period. 22:36.070 --> 22:38.350 S,o why would evolution matter? 22:38.349 --> 22:41.569 Well, many people think it doesn't. 22:41.569 --> 22:46.619 For instance – and they think it doesn't for different reasons 22:46.616 --> 22:49.656 – one claim is a metaphysical one. 22:49.660 --> 22:51.090 You might be a dualist. 22:51.089 --> 22:54.149 You might reject the idea your mental life is the product of 22:54.154 --> 22:57.124 your brain and hence evolution is irrelevant to psychology 22:57.115 --> 22:59.915 because the brain and the mind--because the brain, 22:59.920 --> 23:02.600 which may have evolved, has nothing interesting to do 23:02.604 --> 23:05.894 with the mind. Lisa Simpson got it wrong when 23:05.888 --> 23:10.558 she said the Pope--She got it half right when she said the 23:10.559 --> 23:12.689 Pope favored evolution. 23:12.690 --> 23:15.430 It is true. John Paul II, 23:15.426 --> 23:20.536 many years ago, made a statement saying that 23:20.541 --> 23:25.301 Darwinian theory is not incompatible. 23:25.299 --> 23:29.759 Darwinian theory is a view about the evolution of species 23:29.762 --> 23:32.792 that is not motivated by any animus, 23:32.789 --> 23:36.549 is a genuine scientific theory, and should it turn out to be 23:36.551 --> 23:40.571 true, it is not incompatible to truth about man as taught by the 23:40.568 --> 23:43.118 Church. And scientists were thrilled by 23:43.119 --> 23:46.459 this and they were--they said he's endorsing evolution. 23:46.460 --> 23:50.130 But what a fewer people talk about is the fact that after he 23:50.127 --> 23:51.927 said this he drew the line. 23:51.930 --> 23:56.150 He allowed for evolution of the body but he would not allow for 23:56.154 --> 23:57.794 evolution of the mind. 23:57.790 --> 24:00.860 So it was--he wrote: If the human body takes 24:00.860 --> 24:03.170 its origin from preexisting living matter, 24:03.166 --> 24:06.086 the spiritual soul is immediately created by God. 24:06.089 --> 24:08.049 Consequently, theories of evolution which 24:08.050 --> 24:11.040 consider the mind as emerging from the forces of living matter 24:11.040 --> 24:13.980 or as a mere epiphenomenon of this matter are incompatible to 24:13.981 --> 24:17.091 the truth about man. So, you might not want 24:17.089 --> 24:21.289 evolution to be true about the mind because you might believe 24:21.289 --> 24:25.489 that the mind is not subject to the same physical laws as the 24:25.490 --> 24:27.730 rest of the physical world. 24:27.730 --> 24:31.210 That's one way you could reject evolutionary psychology. 24:31.210 --> 24:34.100 Another way to reject evolutionary psychology is to 24:34.100 --> 24:37.220 accept that the mind is a physical thing but then argue 24:37.222 --> 24:40.862 that all of these instincts and these hard-wired facets of human 24:40.864 --> 24:44.334 nature might exist for other animals but they don't exist for 24:44.332 --> 24:47.102 people. So, the anthropologist Ashley 24:47.097 --> 24:49.647 Montagu in '73, close to when The Six 24:49.650 --> 24:52.530 Million Dollar Man was shown, by the way, 24:52.530 --> 24:54.510 said: With the exception of the 24:54.512 --> 24:56.912 reactions of infants to sudden withdrawals of support and to 24:56.914 --> 24:59.554 sudden loud noises, the human being is entirely 24:59.548 --> 25:01.788 instinctless. Man is man because he has no 25:01.792 --> 25:04.862 instincts, because everything he is and has become he has learned 25:04.861 --> 25:07.141 from his culture, from the man-made part of the 25:07.138 --> 25:09.138 environment, from other human beings. 25:09.140 --> 25:12.460 You might say, "Look. 25:12.460 --> 25:14.850 He could believe that in '74 but, of course, 25:14.852 --> 25:17.862 all of the infant studies that have come out since then 25:17.855 --> 25:20.855 suggested that's not true and nobody would believe that 25:20.859 --> 25:22.419 nowadays." But in fact, 25:22.420 --> 25:24.990 the view is often hold--held--Louis Menand in a 25:24.990 --> 25:27.840 New Yorker article a few years ago wrote, 25:27.839 --> 25:31.319 "Every aspect of life has a biological foundation in exactly 25:31.317 --> 25:33.567 the same sense, which is that unless it was 25:33.574 --> 25:35.484 biologically possible it wouldn't exist. 25:35.480 --> 25:37.500 After that it's up for grabs." 25:37.500 --> 25:40.990 And this is in the context of an argument that evolution can't 25:40.991 --> 25:44.541 tell us anything about what's most interesting about people. 25:44.539 --> 25:49.269 Menand is not--is an educated, intelligent scholar. 25:49.269 --> 25:52.659 He is presumably well aware of the findings of Spelke and 25:52.659 --> 25:56.289 Baillargeon about how people are hard-wired to understand the 25:56.290 --> 25:58.530 objects in social life and so on. 25:58.529 --> 26:02.009 But his point is just that when it comes to the more interesting 26:02.012 --> 26:04.992 aspects of human nature, the stuff we're naturally, 26:04.985 --> 26:07.875 intuitively interested in, that's more cultural. 26:07.880 --> 26:10.810 And the evolutionary theory and Darwinian theory just doesn't 26:10.811 --> 26:12.621 have anything much to say about it, 26:12.619 --> 26:16.499 not because the mind is separate from the brain but just 26:16.501 --> 26:20.031 because humans are much more cultural organisms, 26:20.029 --> 26:23.439 and so biology has little to say about it. 26:23.440 --> 26:27.210 There's a third objection, which is you might think, 26:27.205 --> 26:31.335 "Okay, the human mind actually does contain instincts. 26:31.339 --> 26:35.749 There is a human nature but we should just study it by studying 26:35.749 --> 26:37.729 people. How could evolution, 26:37.725 --> 26:41.265 the study of evolution, the consideration of evolution 26:41.265 --> 26:43.465 tell us anything interesting?" 26:43.470 --> 26:47.330 I actually, in my own work, think evolution can tell us 26:47.330 --> 26:49.190 some interesting things. 26:49.190 --> 26:53.930 And I want to try to make a case for ways in which evolution 26:53.925 --> 26:58.255 can inform and enlighten us about the mind as it is. 26:58.259 --> 27:02.769 First, I want to make a point, which is although this course 27:02.765 --> 27:06.655 is Intro Psych and it is about the mind as it is, 27:06.660 --> 27:10.160 still I think by any account the evolution of consciousness, 27:10.163 --> 27:13.663 morality and so on, just is intuitively interesting. 27:13.660 --> 27:17.050 It's the sort of thing that people are just fascinated by 27:17.052 --> 27:20.442 and I think it's a question of interest in and of its own 27:20.444 --> 27:23.384 right. But here's how it could tell us 27:23.384 --> 27:24.744 about psychology. 27:24.740 --> 27:28.430 For one thing, it can tell us what can be 27:28.432 --> 27:30.742 innate and what cannot. 27:30.740 --> 27:33.830 So, some problems, some evolutionary problems, 27:33.830 --> 27:37.750 have been around for a long time and could lead to special 27:37.745 --> 27:39.595 biological adaptations. 27:39.599 --> 27:43.069 If I told you there is a biological adaptation for 27:43.069 --> 27:45.689 talking, mate selection, childcare; 27:45.690 --> 27:48.310 maybe it's true, maybe it isn't, 27:48.307 --> 27:50.077 but it's not crazy. 27:50.079 --> 27:53.689 From an evolutionary point of view, it's a reasonable 27:53.692 --> 27:55.432 possibility that it is. 27:55.430 --> 27:59.420 Other problems are recent and our brains could not be 27:59.415 --> 28:03.625 specialized to deal with them: written communication, 28:03.630 --> 28:06.210 interacting with strangers, driving a car, 28:06.205 --> 28:08.825 playing chess. If you were to argue that 28:08.825 --> 28:12.175 there's a part of the brain devoted to playing chess, 28:12.184 --> 28:14.514 I would say you're utterly wrong. 28:14.509 --> 28:17.219 You cannot be right because, from an evolutionary point of 28:17.223 --> 28:19.753 view, there could be no such part of the brain evolved 28:19.747 --> 28:22.077 because playing chess is a recent innovation. 28:22.079 --> 28:24.869 As a result, a focus on evolution could help 28:24.868 --> 28:28.688 discipline us to make coherent claims about what is built-in 28:28.694 --> 28:30.514 and what isn't built-in. 28:30.509 --> 28:35.539 Third, we're going to talk about human differences in this 28:35.536 --> 28:37.916 course. We're going to devote a class 28:37.915 --> 28:41.405 to human differences of the sort of what makes you different from 28:41.413 --> 28:42.893 her, different from her. 28:42.890 --> 28:45.570 Why do we have different intelligences in this class? 28:45.569 --> 28:48.289 Why are some of us arrogant and some of us humble? 28:48.289 --> 28:52.709 Some of us like--attracted to men, others attracted to women, 28:52.706 --> 28:55.216 and so on. But there's also questions of 28:55.215 --> 28:56.275 group differences. 28:56.279 --> 28:59.589 And evolutionary theory can help us say intelligent things 28:59.587 --> 29:02.657 about what sort of group differences you should expect 29:02.662 --> 29:05.972 because evolutionary theory predicts that some populations 29:05.969 --> 29:08.869 should evolve in different ways than others. 29:08.869 --> 29:14.499 The most obvious example is that children should be 29:14.498 --> 29:17.198 different from adults. 29:17.200 --> 29:20.950 The evolutionary problems faced by a child are very different 29:20.951 --> 29:24.141 from the evolutionary problems faced by an adult. 29:24.140 --> 29:27.350 And you can make specific and rather interesting predictions 29:27.354 --> 29:30.404 about how children's brains should different--differ from 29:30.404 --> 29:32.994 adults' brains. Evolutionary theory 29:32.993 --> 29:37.163 predicts--does not make any predictions about racial 29:37.164 --> 29:40.194 differences or ethnic differences. 29:40.190 --> 29:42.790 Some might exist, but there's no adaptive reason 29:42.790 --> 29:46.000 why humans who have evolved in different parts of the world 29:45.999 --> 29:49.539 should have profound differences in their mental capacities. 29:49.539 --> 29:52.719 What does evolutionary theory say about sex differences? 29:52.720 --> 29:56.570 Well, it says some interesting things, and we're going to 29:56.566 --> 29:59.036 devote a class to discussing them, 29:59.039 --> 30:03.949 but what I think is going to be true--proved to be important is 30:03.947 --> 30:08.137 that we'll be able to use evolutionary biology to talk 30:08.143 --> 30:13.133 sensibly about what sort of distinctions between the sexes, 30:13.130 --> 30:16.670 between males and females, one would expect to find and 30:16.674 --> 30:19.304 what sort one wouldn't expect to find. 30:19.299 --> 30:21.269 We can make educated predictions. 30:21.269 --> 30:25.069 I'm going to have--I want to put here a clip of a man. 30:25.069 --> 30:28.319 This is a scene from a movie, the movie "Roger Dodger," that 30:28.315 --> 30:31.335 begins with a man making quasi-evolutionary claims about 30:31.339 --> 30:33.649 the differences between men and women. 30:33.650 --> 30:37.210 And I want to put this as an example of what you could call 30:37.210 --> 30:39.420 "barroom evolutionary psychology." 30:39.420 --> 30:44.280 And I want us to hold this in our minds because we're going to 30:44.283 --> 30:48.433 return to these claims and discuss their validity. 30:48.430 --> 30:50.070 I like this for a few reasons. 30:50.069 --> 30:53.219 First, I like the backward reference to William James and 30:53.217 --> 30:55.657 utility. Second, it is a gorgeous 30:55.656 --> 31:00.576 combination of some things that are actually reasonably rational 31:00.581 --> 31:02.381 and total bull crap. 31:02.380 --> 31:06.240 And--but what evolutionary biology will give us is the 31:06.239 --> 31:09.079 tools to distinguish between the two. 31:09.079 --> 31:12.369 On the face of it immediately, the ability to read maps, 31:12.373 --> 31:15.733 the claim that that has a biological--that differences in 31:15.726 --> 31:18.656 that ability have a biological root is crazy. 31:18.660 --> 31:21.850 On the other hand, the claim that one--that males 31:21.851 --> 31:26.041 may develop a trait not because it's advantageous but to attract 31:26.041 --> 31:27.771 females is less crazy. 31:27.769 --> 31:31.079 The telepathic stuff is really crazy but--;So, 31:31.081 --> 31:35.201 I'm not at this point--We're going to devote a lecture to 31:35.201 --> 31:36.691 sex. I do not, at this point, 31:36.693 --> 31:38.353 want to make any claims one way or another. 31:38.349 --> 31:41.629 But what I want to suggest is that from a biological point of 31:41.626 --> 31:44.846 view we could say sensible and intelligent things about what 31:44.848 --> 31:47.468 differences should exist and what shouldn't. 31:47.470 --> 31:51.130 Finally, and most of all, looking at something from the 31:51.132 --> 31:54.292 perspective of design, the perspective of what's it 31:54.290 --> 31:57.190 for, can often give you interesting insights as to its 31:57.186 --> 31:59.816 current nature. And I'll give you two quick 31:59.816 --> 32:03.166 examples, one that's not from psychology, one that is. 32:03.170 --> 32:07.670 Women suffer--Often women who are pregnant early in their 32:07.671 --> 32:11.371 pregnancy suffer from morning sickness, nausea, 32:11.369 --> 32:13.459 throwing up and so on. 32:13.460 --> 32:16.820 This has traditionally been viewed as just a breakdown in 32:16.819 --> 32:19.939 the system--too much hormones, everything's askew; 32:19.940 --> 32:21.590 women get nauseous. 32:21.589 --> 32:25.239 Margie Profet suggested an alternative and this won her the 32:25.237 --> 32:28.817 MacArthur Genius Award. And this was the claim that 32:28.821 --> 32:31.841 maybe pregnancy sickness is not an accident; 32:31.839 --> 32:35.369 rather, it's designed, it has a biological purpose. 32:35.369 --> 32:39.379 In particular, as the baby develops in the 32:39.376 --> 32:44.646 uterus, it is vulnerable to various sorts of poisons or 32:44.654 --> 32:48.854 teratogens. Profet suggested that pregnancy 32:48.853 --> 32:54.143 sickness is a hypersensitive period where women are extremely 32:54.143 --> 32:57.573 sensitive, get extremely nauseous towards 32:57.572 --> 33:01.302 the sorts of foods that could damage their baby. 33:01.299 --> 33:05.339 Now, if she just ended there it's a story. 33:05.340 --> 33:06.800 How do we know it's true? 33:06.799 --> 33:09.939 But then she went on to examine it the same way that any 33:09.942 --> 33:13.202 scientist examines any claim – by making predictions and 33:13.198 --> 33:15.498 testing them. And this makes some interesting 33:15.501 --> 33:18.041 predictions. It suggests the timing of onset 33:18.038 --> 33:21.548 and offset of pregnancy sickness, of morning sickness, 33:21.549 --> 33:25.909 should correspond to the period of maximal vulnerability on the 33:25.914 --> 33:28.804 part of the developing embryo or fetus. 33:28.799 --> 33:32.679 Suggested the types of foods avoided should correspond to 33:32.675 --> 33:36.755 those sorts of foods that were most deadly for the fetus and 33:36.759 --> 33:40.979 that were deadly for the fetus during the periods where humans 33:40.981 --> 33:43.481 evolved. This last qualification is an 33:43.479 --> 33:46.119 important one. Women do not develop an 33:46.117 --> 33:50.777 aversion to alcohol during pregnancy even though alcohol is 33:50.775 --> 33:54.545 extremely dangerous to the developing child. 33:54.550 --> 33:56.360 The answer is an easy one. 33:56.359 --> 33:59.929 Alcohol wasn't around during our evolutionary history and we 33:59.929 --> 34:03.739 could not have evolved a system to protect ourselves from it. 34:03.740 --> 34:06.380 And finally, there should be a relationship 34:06.384 --> 34:09.664 between miscarriage and birth defects in a surprising 34:09.658 --> 34:12.158 direction. For Profet, and she has 34:12.159 --> 34:15.819 evidence to back this up, pregnancy sickness is not a 34:15.820 --> 34:17.510 glitch in the system. 34:17.510 --> 34:20.990 Rather, it's the sign of a healthy act of protective 34:20.987 --> 34:22.417 mechanism going on. 34:22.420 --> 34:24.610 And in fact, the more morning sickness the 34:24.608 --> 34:26.528 more the baby should be protected. 34:26.530 --> 34:28.270 Something which, by and large, 34:28.269 --> 34:29.529 appears to be true. 34:29.530 --> 34:32.300 That's an example of how the question--when dealing with this 34:32.296 --> 34:34.876 they say, "Hey. Women throw up when they get 34:34.878 --> 34:36.868 pregnant" and then say, "Look. 34:36.870 --> 34:38.390 Maybe that's not just a glitch. 34:38.390 --> 34:41.960 What's it for?" You could then learn some 34:41.963 --> 34:43.273 interesting things. 34:43.269 --> 34:47.239 Here's a different example based on the last lecture, 34:47.243 --> 34:52.063 this wonderful lecture by Peter Salovey on sex and love where he 34:52.058 --> 34:54.578 talked about the "big three." 34:54.579 --> 34:58.229 These are the "big three" to remind you of what attracts us 34:58.225 --> 34:59.415 to somebody else. 34:59.420 --> 35:03.640 You are very attracted to the person next to you or a person 35:03.638 --> 35:07.498 that--because of proximity, similarity, familiarity. 35:07.500 --> 35:11.670 And there is abundant evidence supporting the truth of this. 35:11.670 --> 35:16.260 It's almost always true but the evolutionary psychologist looks 35:16.263 --> 35:20.563 at this and says there's something seriously wrong here. 35:20.559 --> 35:24.579 There are some cases where that has to be totally, 35:24.583 --> 35:26.393 absolutely mistaken. 35:26.389 --> 35:30.949 To realize what this is, think for a moment. 35:30.949 --> 35:37.509 What humans are you most close to, most similar to and most 35:37.510 --> 35:41.710 familiar with? What humans did you spend over 35:41.713 --> 35:45.703 ten years of your life with who are genetically and 35:45.702 --> 35:50.412 environmentally as close to you as if they were related, 35:50.409 --> 35:53.499 who you are intimately familiar with? 35:53.500 --> 35:58.240 Are those the humans that you find the hottest? 35:58.240 --> 36:05.160 [laughter] No. They're your siblings and they 36:05.156 --> 36:08.326 are not hot. [laughter] 36:08.328 --> 36:10.468 I was on Google Images this morning. 36:10.469 --> 36:16.619 I put up some hot siblings and--but--although we may find 36:16.623 --> 36:22.013 them hot, they do not typically, with some rare and bizarre 36:22.007 --> 36:24.857 exceptions, find [laughter] one another hot. 36:24.860 --> 36:30.220 Why not? Well, this is not a huge puzzle 36:30.222 --> 36:34.032 from the standpoint of evolutionary biology. 36:34.030 --> 36:37.580 Evolutionary biology posits that humans, as well as other 36:37.576 --> 36:40.106 animals, should have incest avoidance. 36:40.110 --> 36:43.950 We should love--we should be attracted to those familiar to 36:43.946 --> 36:45.926 us, similar to us, close to us, 36:45.931 --> 36:48.921 but not kin. Kin are off limits. 36:48.920 --> 36:50.530 There is a good reason why. 36:50.530 --> 36:56.300 Because if you inter-mate with your kin you have bad offspring 36:56.304 --> 37:00.094 [laughter] and so animals should be wired 37:00.091 --> 37:03.311 up not to mate with their kin. 37:03.309 --> 37:06.349 And in fact, this is what happens. 37:06.349 --> 37:11.989 There are--Parents of teenagers have all sorts of concerns. 37:11.989 --> 37:15.039 And a lot of the concerns are, in fact, sexual. 37:15.039 --> 37:18.069 How do you keep your son and/or your daughter from going out and 37:18.066 --> 37:20.566 having sex with too many people, or the wrong people, 37:20.565 --> 37:21.665 or unprotected sex? 37:21.670 --> 37:24.980 But there are no parenting guides in the world that say 37:24.981 --> 37:28.291 "How do you keep your children from having sex with one 37:28.292 --> 37:29.672 another?" [laughter] 37:29.665 --> 37:33.115 You typically do not need to because they do not want to have 37:33.118 --> 37:34.498 sex with one another. 37:34.500 --> 37:38.480 Now, this is--actually also illustrates the difference 37:38.480 --> 37:41.710 between proximate and ultimate causation. 37:41.710 --> 37:44.310 So, you think for yourself, "Eew. 37:44.309 --> 37:45.999 Do I want to have sex with my sister?" 37:46.000 --> 37:48.550 You don't think to yourself, "I would prefer not to, 37:48.553 --> 37:51.463 for the offspring that we will create will be nonviable and 37:51.456 --> 37:53.906 it'll be a waste of my reproductive efforts." 37:53.909 --> 37:57.899 Rather, you think, "Eew," because at a gut level 37:57.901 --> 38:01.311 you respond. And this sort of instinctive 38:01.311 --> 38:06.311 response is what you get from an evolutionary analysis of sex. 38:06.309 --> 38:10.869 But this story is deeply incomplete because the question 38:10.872 --> 38:14.192 that gets raised is "how do you tell?" 38:14.190 --> 38:18.290 You don't want to have sex with your kin but how do you tell 38:18.286 --> 38:21.236 your kin? People don't carry their DNA 38:21.239 --> 38:24.209 markers on strips that you could see. 38:24.210 --> 38:26.490 How do you tell who your kin are? 38:26.489 --> 38:29.509 And this actually turns out to be a really interesting 38:29.512 --> 38:32.482 question. It used--And some research 38:32.480 --> 38:35.720 suggests that the answer is simple. 38:35.719 --> 38:38.969 You avoid sex with people you grew up with. 38:38.969 --> 38:42.189 And these studies actually come from kibbutz studies, 38:42.190 --> 38:45.600 studies where people are raised communally on an Israeli 38:45.596 --> 38:48.526 kibbutz. They know they're not related, 38:48.534 --> 38:52.704 but still, the fact that they were raised together as kids 38:52.704 --> 38:57.394 suggests that there's a cue at a gut level not to be attracted to 38:57.386 --> 39:00.126 one another. It turns out there's some 39:00.130 --> 39:03.010 reason now to believe this story is incomplete. 39:03.010 --> 39:06.420 A paper that came out in Nature five days ago 39:06.423 --> 39:09.973 reported a series of extremely interesting studies. 39:09.969 --> 39:15.029 And they found that the cue of being raised together as a child 39:15.027 --> 39:18.647 with somebody--yes, that does diminish sexual 39:18.652 --> 39:22.862 desire, but an even bigger cue was "did you observe your 39:22.858 --> 39:24.678 parents, and in particular, 39:24.684 --> 39:26.984 your mother, taking care of that person?" 39:26.980 --> 39:30.990 If you did, that seriously diminishes sexual desire and 39:30.987 --> 39:34.027 brings it down to the level of disgust. 39:34.030 --> 39:38.460 And again, these are the sort of questions and issues you 39:38.457 --> 39:42.957 begin to ask when you approach things from an evolutionary 39:42.964 --> 39:45.144 perspective. Okay. 39:45.140 --> 39:48.990 39:48.989 --> 39:52.449 For this lecture--the rest of this lecture and then the next 39:52.448 --> 39:55.288 couple of lectures, I'll be discussing some basic 39:55.294 --> 39:58.694 aspects of human nature that are, to some extent or another, 39:58.690 --> 40:01.210 informed by evolutionary theory. 40:01.210 --> 40:06.550 And what I want to start for the remainder of this lecture is 40:06.550 --> 40:09.220 a discussion of rationality. 40:09.219 --> 40:13.879 Now, some of you maybe not want to go into--not want to go into 40:13.877 --> 40:18.307 psychology because there's no Nobel Prize for psychology. 40:18.309 --> 40:20.609 You might all think, "Hey, if I'm going to go into 40:20.610 --> 40:22.300 the sciences I want a Nobel Prize. 40:22.300 --> 40:26.060 Think how proud Bubby and Zadie would be if I won a Nobel Prize. 40:26.060 --> 40:27.610 Wouldn't that be the best?" 40:27.610 --> 40:34.320 You can get one. Psychologists have won the 40:34.316 --> 40:36.046 Nobel Prize. Most recently, 40:36.048 --> 40:38.278 Danny Kahneman won a Nobel Prize. 40:38.280 --> 40:41.090 You win it in economics, sometimes medicine; 40:41.090 --> 40:45.020 not a big deal. He won it for his work done 40:45.016 --> 40:50.226 over the course of many decades on human rationality. 40:50.230 --> 40:54.260 And this work was done in collaboration with Amos Tversky, 40:54.256 --> 40:56.796 who passed away several years ago. 40:56.800 --> 41:02.260 And this work entirely transformed the way we think 41:02.258 --> 41:07.278 about human decision-making and rationality. 41:07.280 --> 41:10.150 Kahneman and Tversky caused a revolution in economics, 41:10.150 --> 41:13.020 psychology, and the social sciences more generally, 41:13.019 --> 41:16.859 by causing us to shift from the idea that we're logical 41:16.864 --> 41:20.924 thinkers, who think in accord with the axioms of logic and 41:20.921 --> 41:25.291 mathematics and rationality, more towards the idea that we 41:25.285 --> 41:28.875 actually have sort of rough and ready heuristics. 41:28.880 --> 41:32.710 These heuristics served us well during the time--during our 41:32.708 --> 41:36.068 evolutionary history, but sometimes they can lead us 41:36.074 --> 41:38.384 astray. And I want to give some 41:38.383 --> 41:40.453 examples of these heuristics. 41:40.449 --> 41:45.629 And I'll give four examples of heuristics that are argued to 41:45.626 --> 41:47.816 permeate our reasoning. 41:47.820 --> 41:49.630 The first is "framing effects." 41:49.630 --> 41:54.490 This was a classic study by Kahneman and Tversky involving 41:54.492 --> 41:56.542 this sort of question. 41:56.539 --> 41:58.089 The U.S. is preparing for the outbreak 41:58.088 --> 42:00.388 of a disease that's going to kill six hundred people. 42:00.390 --> 42:02.120 There are two programs. 42:02.119 --> 42:05.969 Program A: If you follow it two hundred people will be saved. 42:05.969 --> 42:10.189 Program B: There's a one-third chance everybody will be saved 42:10.186 --> 42:13.416 and a two-third chance nobody will be saved. 42:13.420 --> 42:14.900 Who would choose program B? 42:14.900 --> 42:18.330 42:18.330 --> 42:21.330 Who would choose program A? 42:21.330 --> 42:24.160 Okay. And that fits the responses. 42:24.160 --> 42:26.170 Most people choose program A. 42:26.170 --> 42:28.340 That's--It could go either way. 42:28.340 --> 42:32.670 What's interesting is if you frame the question differently, 42:32.666 --> 42:36.036 like this, you get very different responses. 42:36.039 --> 42:38.769 And instead of focusing on the people who will be saved, 42:38.767 --> 42:40.897 you focus on the people who will die and, 42:40.900 --> 42:43.100 instead of focusing on the chance that nobody will die and 42:43.095 --> 42:44.515 the chance that everybody will die, 42:44.519 --> 42:48.359 you'd flip it around, you get a corresponding flip. 42:48.360 --> 42:51.290 And this is known as a "framing effect." 42:51.289 --> 42:55.739 The idea of a framing effect is that you could respond 42:55.738 --> 43:00.608 differently to a situation depending on how the options are 43:00.606 --> 43:02.876 framed. And, in particular, 43:02.884 --> 43:05.454 this combines with "loss aversion." 43:05.450 --> 43:08.610 People hate a certain loss. 43:08.610 --> 43:12.830 "Four thousand of these people will die" is extremely aversive 43:12.830 --> 43:16.290 and so the framing can influence your decisions. 43:16.289 --> 43:20.099 And clever advertisers and clever decision makers will 43:20.103 --> 43:24.063 frame things in different ways to give you--give rise to 43:24.061 --> 43:25.861 different intuitions. 43:25.860 --> 43:27.850 Sometimes this could be fairly simple. 43:27.849 --> 43:32.179 So, you have this ad of a hamburger that's eighty percent 43:32.181 --> 43:36.591 fat free versus twenty percent fat--You don't have to be a 43:36.591 --> 43:41.311 brilliant ad executive to figure out which one to go for. 43:41.309 --> 43:46.829 It turns out that this sort of fundamental act – the 43:46.826 --> 43:52.656 fundamental role of framing effects – is not limited to 43:52.655 --> 43:55.795 humans. So, I want to take a second and 43:55.798 --> 43:59.278 tell you some work done by my colleague, Laurie Santos, 43:59.278 --> 44:00.888 with capuchin monkeys. 44:00.889 --> 44:05.229 And what she does is she takes these capuchin monkeys and she 44:05.233 --> 44:07.263 teaches them to use money. 44:07.260 --> 44:12.040 She teaches them to use little discs to buy themselves either 44:12.035 --> 44:15.055 pieces of banana or pieces of apple. 44:15.060 --> 44:16.410 And they like to eat this. 44:16.409 --> 44:19.899 And they very quickly learn you can hand over a disc to get some 44:19.896 --> 44:21.166 banana or some apple. 44:21.170 --> 44:40.800 44:40.800 --> 44:41.800 [laughter] Now, Dr. 44:41.795 --> 44:44.995 Santos and her colleagues have done many studies using this 44:45.002 --> 44:48.102 method, but the study I'm interested in illustrating here 44:48.098 --> 44:51.138 shows framing effects in these nonhuman primates. 44:51.139 --> 44:54.699 So, what she does is--There's two options. 44:54.699 --> 44:58.209 In one option, the experimenter shows one 44:58.212 --> 45:03.132 object to the capuchin and low--and then either gives one 45:03.129 --> 45:08.329 or two--half the time gives one, half the time gives two, 45:08.325 --> 45:11.205 for an average of one and a half. 45:11.210 --> 45:15.470 The other experimenter does exactly the same thing; 45:15.469 --> 45:17.929 gives one or two for an average of one and a half, 45:17.926 --> 45:19.526 but starts off displaying two. 45:19.530 --> 45:22.930 Now, if you weren't a human, how would you feel about these 45:22.928 --> 45:24.098 two experimenters? 45:24.099 --> 45:26.049 They both give you the same amount. 45:26.050 --> 45:29.560 And capuchins are extremely sensitive to how much they get, 45:29.560 --> 45:32.770 but it turns out as predicted they don't like the pink 45:32.768 --> 45:36.278 experimenter because the pink experimenter is--he gives you 45:36.278 --> 45:39.908 two--shows you two and half the time he gives you one. 45:39.909 --> 45:43.629 This guy shows you one, and half the time gives you 45:43.633 --> 45:46.463 two. And over time they develop a 45:46.455 --> 45:51.795 preference for the experimenter that shows them one initially, 45:51.800 --> 45:55.420 suggesting that they are being subject to framing effects or 45:55.423 --> 45:57.883 choices relative to a reference point. 45:57.880 --> 46:01.660 A different sort of demonstration is the "endowment 46:01.655 --> 46:03.805 effect." This is a robust and very 46:03.809 --> 46:04.929 interesting effect. 46:04.930 --> 46:09.810 Here's the idea. I show you something like a cup 46:09.806 --> 46:13.966 or a chocolate bar and I say, "How much will you give me for 46:13.968 --> 46:15.518 this chocolate bar? 46:15.519 --> 46:16.619 It looks like you're pretty hungry. 46:16.619 --> 46:18.189 How much will you give me for this chocolate bar?" 46:18.190 --> 46:20.500 And you say, "I'll give you two dollars for 46:20.500 --> 46:21.710 this chocolate bar." 46:21.710 --> 46:24.390 Most people on average give two--the chocolate bar--gives 46:24.391 --> 46:26.021 two dollars for a chocolate bar. 46:26.019 --> 46:29.279 The other condition's exactly the same except I hand you a 46:29.284 --> 46:32.204 chocolate bar and say, "How much money will you sell 46:32.204 --> 46:33.984 me that chocolate bar for?" 46:33.980 --> 46:38.680 There, people say, "Two fifty," and in fact, 46:38.681 --> 46:45.351 what happens is once you own something its value shoots up. 46:45.349 --> 46:48.329 And this has mystified economists and psychologists. 46:48.330 --> 46:49.520 It makes no sense. 46:49.519 --> 46:51.639 The chocolate bar doesn't even have to move. 46:51.639 --> 46:54.359 I just leave it on the table and say either "How much will 46:54.363 --> 46:56.803 you spend," "How much will you give me for this?" 46:56.800 --> 46:58.330 or "Okay. It's yours. 46:58.329 --> 47:00.749 How much do you want for me to take it back?" 47:00.750 --> 47:03.130 The answer is, it's framing. 47:03.130 --> 47:07.270 If you're asking how much you want for it, it's a game. 47:07.269 --> 47:09.909 It's just how much will you pay to get something. 47:09.909 --> 47:14.519 But if you're being asked how much do you want for me to take 47:14.520 --> 47:17.440 it from you, you treat it as a loss. 47:17.440 --> 47:20.370 And as a loss it becomes more valuable. 47:20.370 --> 47:23.260 Those are framing effects. 47:23.260 --> 47:25.700 The second example is base rates. 47:25.699 --> 47:28.769 There are seventy lawyers--sorry, 47:28.771 --> 47:34.241 seventy engineers and thirty lawyers and John is chosen at 47:34.244 --> 47:36.964 random. Let me tell you about John: 47:36.956 --> 47:39.406 forty-years old, married, three children, 47:39.410 --> 47:41.680 conservative, cautious, no interest in 47:41.680 --> 47:43.950 politics, awkward around people. 47:43.949 --> 47:46.929 His hobbies include carpentry, sailing, and solving 47:46.928 --> 47:49.488 mathematical puzzles, like online dating. 47:49.490 --> 47:53.190 47:53.190 --> 47:54.850 [laughter] What do you think John is? 47:54.850 --> 47:56.530 A lawyer or an engineer? 47:56.530 --> 47:57.860 Who thinks he's a lawyer? 47:57.860 --> 48:02.220 Good. Who thinks he's an engineer? 48:02.220 --> 48:04.260 Okay. Most people think he's an 48:04.258 --> 48:05.458 engineer, but here's the thing. 48:05.460 --> 48:07.730 You switch it. Right? 48:07.730 --> 48:09.180 Thirty engineers, seventy lawyers? 48:09.180 --> 48:11.280 It doesn't change. 48:11.280 --> 48:14.500 People--No matter what this number is--these numbers--it 48:14.496 --> 48:18.116 doesn't seem to change who you think he is or how confident you 48:18.122 --> 48:20.372 are. People look at John as an 48:20.368 --> 48:24.568 individual and they ignore the background status of where he 48:24.565 --> 48:27.285 came from. They ignore base rates. 48:27.289 --> 48:31.749 Base rates are very difficult to think about and I want to 48:31.745 --> 48:34.085 give you an example of this. 48:34.090 --> 48:38.220 And the example will be on the slides for when you print them 48:38.216 --> 48:42.206 out--print it out because you might want to work through it 48:42.205 --> 48:44.165 yourself. But I'll give this to you 48:44.166 --> 48:46.436 quickly. There's a disease that hits one 48:46.437 --> 48:49.297 in a thousand people, a pretty common disease. 48:49.300 --> 48:52.050 There's a test for the disease and if you have it, 48:52.046 --> 48:54.116 it's going to tell you you have it. 48:54.119 --> 48:57.309 It tests for a certain thing in your blood and "boom," if the 48:57.312 --> 48:59.922 thing is in your blood the test will go "boom." 48:59.920 --> 49:02.170 If you have it, it will tell you you have it. 49:02.170 --> 49:05.090 It doesn't miss. On the other hand, 49:05.085 --> 49:06.165 it's not perfect. 49:06.170 --> 49:08.300 It has a false positive rate of five percent. 49:08.300 --> 49:11.080 So, if you don't have the disease, five percent of the 49:11.079 --> 49:13.019 time the test will say you have it. 49:13.019 --> 49:18.209 So, if the test says you don't have it, you're fine. 49:18.210 --> 49:21.880 But if the test says you have it, maybe you have it but maybe 49:21.881 --> 49:23.351 it's a false positive. 49:23.350 --> 49:25.200 You take the test. 49:25.200 --> 49:27.360 It says you have the disease. 49:27.360 --> 49:30.780 Without pen and paper, how likely do you think the 49:30.783 --> 49:33.023 odds are you have the disease? 49:33.020 --> 49:36.960 49:36.960 --> 49:39.700 Who says over fifty percent? 49:39.700 --> 49:42.850 Okay. Before people sinisterly 49:42.852 --> 49:45.942 shouted the right answer, people will tend--medical 49:45.940 --> 49:49.420 students were given this, medical students less savvy 49:49.415 --> 49:52.835 than you, and the average is between fifty percent and 49:52.842 --> 49:54.332 ninety-five percent. 49:54.329 --> 49:57.139 The answer is, as some people quickly noted, 49:57.143 --> 50:02.293 two percent. And here's how it works. 50:02.289 --> 50:04.359 One percent of a thousand will have the disease. 50:04.360 --> 50:05.630 That person will test positive. 50:05.630 --> 50:07.220 The test never misses. 50:07.219 --> 50:09.199 That leaves nine hundred ninety-nine people who don't 50:09.199 --> 50:10.799 have the disease, and we'll say about fifty 50:10.799 --> 50:12.169 percent of these people have it. 50:12.170 --> 50:15.240 So, for every fifty-one people who test positive, 50:15.240 --> 50:19.140 only one will have the disease, giving an average of about two 50:19.142 --> 50:21.622 percent. This sort of thing is very 50:21.617 --> 50:24.437 difficult. Our minds are not evolved to do 50:24.441 --> 50:26.001 base rate computation. 50:26.000 --> 50:29.050 And so, any problems involving base rate computation, 50:29.045 --> 50:33.155 including real world problems, like what to do when you come 50:33.164 --> 50:36.264 back with a positive test, we screw up. 50:36.260 --> 50:39.370 And often we screw up in the direction of panic. 50:39.369 --> 50:42.269 The third bias is the "availability bias." 50:42.269 --> 50:45.979 And this is simply that if you want to know how frequent 50:45.981 --> 50:48.881 something is, how available it is to come to 50:48.883 --> 50:50.843 mind is an excellent cue. 50:50.840 --> 50:53.880 But this could lead to mistakes. 50:53.880 --> 50:57.470 A classic example by Kahneman and Tversky is you ask 50:57.466 --> 51:01.896 people--one group of people how many English words end with "ng" 51:01.897 --> 51:04.707 or what proportion of English words, 51:04.710 --> 51:09.730 another group of people what proportion end with "ing." 51:09.730 --> 51:13.770 It turns out you get much bigger numbers for "ing" than 51:13.774 --> 51:17.374 "ng" though, of course "ng" has to--"ing"--sorry, 51:17.369 --> 51:20.739 "ng" would include everything with "ing." 51:20.739 --> 51:25.959 It's just a lot easier to think about these things. 51:25.960 --> 51:28.310 This can show up in the real world. 51:28.309 --> 51:30.839 What are your risk of getting killed--What's your risk of 51:30.843 --> 51:32.113 getting killed by a shark? 51:32.110 --> 51:37.090 Well, if you ask people what their risk of getting killed by 51:37.085 --> 51:41.045 a shark is, they characteristically overestimate 51:41.049 --> 51:43.219 it. I will give you the news of 51:43.220 --> 51:46.030 what the risk is for getting killed by a shark. 51:46.030 --> 51:50.450 Injured in any given year: one in six million. 51:50.449 --> 51:53.269 Killed: one in five hundred million. 51:53.269 --> 51:56.279 If you live in Florida, which apparently is Shark 51:56.280 --> 52:00.110 Central, your chance of getting injured is about one in a half 52:00.107 --> 52:03.137 million. People will overestimate the 52:03.137 --> 52:06.877 risks because shark attacks are very salient. 52:06.880 --> 52:08.930 They are always reported in the news and they're very 52:08.928 --> 52:11.938 interesting. What is the chance of getting 52:11.942 --> 52:13.982 killed by potato salad? 52:13.980 --> 52:15.890 [laughter] Well, food poisoning, 52:15.893 --> 52:19.173 death by food poisoning, injury by food poisoning runs 52:19.166 --> 52:24.216 to about one in fifty-five, one in 800 for some sort of 52:24.221 --> 52:28.061 injury and one in 55,000 killed. 52:28.059 --> 52:35.789 Potato salad is 1,000 more times more dangerous than shark 52:35.793 --> 52:38.853 attacks. But you get it wrong because 52:38.845 --> 52:40.535 you don't think, "Oh, my God, 52:40.540 --> 52:44.390 big news story. Somebody dies by potato salad." 52:44.389 --> 52:47.989 [laughter] And so, we tend to overestimate 52:47.993 --> 52:52.303 the chance of being killed by dramatic effects. 52:52.300 --> 52:55.050 How many Jews in the United States, what proportion? 52:55.050 --> 53:00.000 Who thinks it's over three quarters of the United States is 53:00.001 --> 53:01.021 Jewish? [laughter] 53:01.022 --> 53:01.732 I'm kind of anchoring here. 53:01.730 --> 53:02.700 Okay. Okay. 53:02.700 --> 53:05.960 Who thinks over half? 53:05.960 --> 53:09.650 Who thinks over forty percent? 53:09.650 --> 53:11.570 Who thinks over twenty percent? 53:11.570 --> 53:15.240 Okay. Who thinks over fifteen percent? 53:15.240 --> 53:17.540 Who thinks over ten percent? 53:17.539 --> 53:21.649 Who thinks over seven and one-half percent? 53:21.650 --> 53:23.660 Who thinks over five percent? 53:23.660 --> 53:25.810 Okay. Who thinks overall there's more 53:25.809 --> 53:28.229 than five percent of the United States that's Jewish? 53:28.230 --> 53:31.820 53:31.820 --> 53:35.250 Who thinks over three percent? 53:35.250 --> 53:39.840 The answer is somewhere between 1.9 and 2.1%. 53:39.840 --> 53:44.790 Most people think--The average American thinks it's twenty 53:44.791 --> 53:47.111 percent. There is-- [laughter] 53:47.114 --> 53:49.614 If you're curious about demographics, 53:49.607 --> 53:53.347 and this map isn't to be entirely trusted because I got 53:53.347 --> 53:55.517 it from Wikipedia, [laughter] 53:55.519 --> 53:58.359 this is the distribution of the Jewish population, 53:58.360 --> 54:01.660 self-identified as Jewish in different parts of the United 54:01.664 --> 54:03.084 States. [laughter] 54:03.082 --> 54:06.122 New York City is, of course, the most dense 54:06.117 --> 54:08.427 population with nine percent. 54:08.430 --> 54:14.560 New Haven has 3.5%. 54:14.560 --> 54:19.470 54:19.470 --> 54:23.030 Now, why do people get it wrong? 54:23.030 --> 54:25.460 Well, there's all sorts of reasons and this is going to 54:25.463 --> 54:27.993 come out in the context of social psychology when we talk 54:27.987 --> 54:30.057 about how people think about human groups. 54:30.059 --> 54:35.709 But one quick answer is people who are plainly Jewish are 54:35.712 --> 54:40.762 prominent in positions where people notice them, 54:40.760 --> 54:44.460 like entertainment or, in the case of you guys, 54:44.456 --> 54:46.636 academia. And this could lead to--this 54:46.642 --> 54:48.412 availability-- "Can I think of a Jew? 54:48.410 --> 54:52.850 Yeah." [laughter] 54:52.854 --> 54:57.564 This availability causes us to overestimate the proportion to 54:57.563 --> 55:01.333 which Jews are represented in the population. 55:01.330 --> 55:05.290 Final example. Confirmation bias. 55:05.289 --> 55:08.779 This is a very nice study and it's very simple. 55:08.780 --> 55:12.830 It's--You're in a jury of a custody case. 55:12.829 --> 55:16.519 You have to give a child custody – either a mother or 55:16.524 --> 55:18.034 father sole custody. 55:18.030 --> 55:20.470 One parent has average income, average health, 55:20.468 --> 55:23.118 average working hours, reasonable rapport with the 55:23.123 --> 55:25.673 child, and a relatively stable social life. 55:25.670 --> 55:28.160 The second parent has an above-average income, 55:28.158 --> 55:31.088 minor health problems, lots of work-related travel, 55:31.090 --> 55:33.640 a very close relationship with the travel--with the child, 55:33.639 --> 55:35.339 and an extremely active social life. 55:35.340 --> 55:36.530 Think for a moment. 55:36.530 --> 55:37.960 Who would you award custody with? 55:37.960 --> 55:40.180 There's no--Obviously, there's no right answer here. 55:40.180 --> 55:42.730 Just think for a moment. 55:42.730 --> 55:45.790 Who would award custody to parent A? 55:45.789 --> 55:49.339 Who would award custody to parent B? 55:49.340 --> 55:52.720 Okay. As I think there is in this 55:52.722 --> 55:58.062 room, when this study is done there's a slight advantage to 55:58.056 --> 56:01.516 parent B. Here's what's interesting. 56:01.519 --> 56:04.909 You give another group of people this question. 56:04.909 --> 56:07.899 "Which parent would you deny custody to?" 56:07.900 --> 56:11.210 You get a slight advantage for parent B. 56:11.210 --> 56:14.550 Now, this is to some extent an illustration of framing problem 56:14.546 --> 56:17.826 but it's also a more general illustration of the confirmation 56:17.827 --> 56:19.937 bias. So, when you're asked to award 56:19.943 --> 56:22.923 custody to, you then ask, "Well, what is a good--what is 56:22.920 --> 56:25.140 a sign that somebody's a good parent?" 56:25.139 --> 56:28.559 And the good parent aspects of B jump out. 56:28.559 --> 56:30.529 When asking about denying custody you ask, 56:30.531 --> 56:32.841 "Where is a cue that somebody's a bad parent?" 56:32.840 --> 56:37.410 And the bad parent aspects of B jump out. 56:37.409 --> 56:40.259 In general, when we have a hypothesis we look for 56:40.260 --> 56:42.780 confirmations. This makes some things, 56:42.783 --> 56:46.343 which are logically easy extremely difficult problems 56:46.341 --> 56:49.011 when we face them in the real world. 56:49.010 --> 56:52.750 And I'll end with my final example, that of the Wason 56:52.747 --> 56:55.227 selection task. Here's the game. 56:55.230 --> 56:59.500 And people--I don't want people to shout it out just yet. 56:59.500 --> 57:01.350 There is four cards. 57:01.349 --> 57:06.529 Each card has a letter on one side and a number on the other 57:06.534 --> 57:10.174 side. You have to judge whether this 57:10.172 --> 57:12.592 claim is true or false. 57:12.590 --> 57:17.380 "If a card has a 'D' on one side, it has a '3' on the other 57:17.379 --> 57:20.659 side." How many cards do you have to 57:20.657 --> 57:24.807 turn over to test whether that rule is right? 57:24.810 --> 57:27.310 Okay. Somebody shout out what one 57:27.311 --> 57:29.621 card is you have to turn over. 57:29.620 --> 57:32.710 "D." Everybody gets that right. 57:32.710 --> 57:34.730 What else? Do you need to do any other 57:34.726 --> 57:34.916 cards? 57:34.920 --> 57:39.320 57:39.320 --> 57:42.060 How many people think it's "D" and "3"? 57:42.060 --> 57:45.580 I'm raising my hand to fool you. 57:45.579 --> 57:49.669 [laughter] People answer either "D" or "D" 57:49.668 --> 57:52.558 and "3" but think about it. 57:52.560 --> 57:54.570 What would make this rule wrong? 57:54.570 --> 57:57.930 It's wrong if it has "D" on one side and not "3" on the other. 57:57.930 --> 57:59.730 Right? That's what it would be to be 57:59.733 --> 58:01.483 wrong. You then would have to check 58:01.479 --> 58:03.929 "D" to see if there is a "3" on the other side. 58:03.930 --> 58:05.320 You were all right about that. 58:05.320 --> 58:08.880 That means you'd check "8" to see if there's a "D" on the 58:08.882 --> 58:11.212 other side. "Three's" not going to tell you 58:11.214 --> 58:14.844 anything. That's hard. 58:14.840 --> 58:16.570 People find this very hard. 58:16.570 --> 58:17.950 Okay. Big deal. 58:17.949 --> 58:22.119 But what's interesting is you can modify it in certain ways to 58:22.118 --> 58:23.688 make it a lot easier. 58:23.690 --> 58:26.630 And this is the work of Leda Cosmides and her colleague, 58:26.631 --> 58:29.791 an evolutionary psychologist at Santa Barbara who has argued 58:29.786 --> 58:32.456 that if you frame these questions in ways that make 58:32.460 --> 58:35.200 ecological sense, people are much better at them. 58:35.199 --> 58:38.549 And basically, she does studies where she has 58:38.546 --> 58:41.736 people who are evaluating a social rule. 58:41.740 --> 58:43.750 Imagine these cards. 58:43.750 --> 58:47.630 On one side of the card is an alcohol--is a drink. 58:47.630 --> 58:52.590 On the other side is a person's age. 58:52.590 --> 58:55.480 You are a bartender and you want to make sure nobody under 58:55.481 --> 58:56.751 twenty-one drinks beer. 58:56.750 --> 59:00.460 Which cards do you turn over? 59:00.460 --> 59:04.290 Well, now it's easier but the logic is the same. 59:04.289 --> 59:06.859 It's a violation that there's "under twenty-one" on one side, 59:06.855 --> 59:10.195 "beer" on the other side, so you need to check the "under 59:10.197 --> 59:14.147 twenty-one" here and you need to check the "beer" here. 59:14.150 --> 59:19.730 And when you make these logical problems more ecologically valid 59:19.729 --> 59:22.739 they turn out to be much easier. 59:22.740 --> 59:23.670 Okay. 59:23.670 --> 59:29.460 59:29.460 --> 59:33.830 There's a little bit more but I'll hold it off until next 59:33.826 --> 59:36.896 class. And I'll end with the reading 59:36.901 --> 59:41.891 response, which is to do your own bit of reverse engineering 59:41.889 --> 59:44.509 and evolutionary psychology. 59:44.510 --> 59:49.000 And I'll see you all on Wednesday.