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  • Professor Paul Bloom: We began the course by talking

  • about one of the foundational ideas of modern psychology.

  • This is what Francis Crick described as "The Astonishing

  • Hypothesis," the idea that our mental life,

  • our consciousness, our morality,

  • our capacity to make decisions and judgments is the product of

  • a material physical brain. What I want to talk about today

  • and introduce it, and it's going to be a theme

  • that we're going to continue throughout the rest of the

  • course, is a second idea which I think

  • is equally shocking, perhaps more shocking.

  • And this has to do with where mental life comes from,

  • not necessary its material nature, but rather its origin.

  • And the notion, this other "astonishing

  • hypothesis," is what the philosopher Daniel Dennett has

  • described as Darwin's dangerous idea.

  • And this is the modern biological account of the origin

  • of biological phenomena including psychological

  • phenomena. Now, people have long been

  • interested in the evolution of complicated things.

  • And there is an argument that's been repeated throughout history

  • and many people have found it deeply compelling,

  • including Darwin himself. Darwin, as he wrote The

  • Origin of Species, was deeply persuaded and moved by

  • this argument from--in the form presented by the theologian

  • William Paley. So, Paley has an example here.

  • Paley tells--gives the example of you're walking down the beach

  • and your foot hits a rock. And then you wonder,

  • "Where did that rock come from?"

  • And you don't really expect an interesting answer to that

  • question. Maybe it was always there.

  • Maybe it fell from the sky. Who cares?

  • But suppose you found a watch on the ground and then you asked

  • where the watch had come from. Paley points out that it would

  • not be satisfying to simply say it's always been there or it

  • came there as an accident. And he uses this comparison to

  • make a point, which is a watch is a very

  • complicated and interesting thing.

  • Paley is--was a medical doctor and Paley goes on to describe a

  • watch and compare a watch to the eye and noticing that a watch

  • and the eye contain multitudes of parts that interact in

  • complicated ways to do interesting things.

  • In fact, to change and to update the analogy a little bit,

  • an eye is very much like a machine known as a camera.

  • And they're similar at a deep way.

  • They both have lenses that bend light and project an image onto

  • a light-sensitive surface. For the eye the light-sensitive

  • surface is the retina. For the camera it's the film.

  • They both have a focusing mechanism.

  • For the eye it's muscles that change the shape of the lens.

  • For a camera it's a diaphragm that governs the amount of

  • incoming light. Even they're both encased in

  • black. The light-sensitive part of the

  • eye and part of the camera are both encased in black.

  • The difference is--So in fact, the eye and a camera look a lot

  • alike and we know the camera is an artifact.

  • The camera has been constructed by an intelligent--by

  • intelligent beings to fulfill a purpose.

  • In fact, if there's any difference between things like

  • the eye and things like a camera,

  • the difference is that things like the eye are far more

  • complicated than things like the camera.

  • When I was a kid I had this incredible TV show called "The

  • Six Million Dollar Man." Anybody here ever seen it or

  • heard of it? Oh.

  • Anyway, the idea is there's a test pilot, Steve Austin,

  • and his rocket jet crashes and he loses his--both legs,

  • his arm and his eye, which sounds really bad but

  • they replace them with bionic stuff,

  • with artificial leg, artificial arm and an

  • artificial eye that are really super-powered.

  • And then he fights crime. [laughter]

  • It was [laughs] really the best show on.

  • It was really good, [laughter]

  • but the thing is this was in 1974.

  • It's now over thirty years later and it's true then and

  • it's true now, this is fantasy.

  • It doesn't make it to the level of science fiction.

  • It's fantasy. We are impossibly far away from

  • developing machines that could do this.

  • We are impossibly far away from building a machine that can do

  • what the human eye does. And so somebody like Paley

  • points out, "Look. The complexity of the

  • biological world suggests that these things are complicated

  • artifacts created by a designer far smarter than any human

  • engineer. And the designer,

  • of course, would be God." I went to Goggle Images.

  • That--I don't mean that to be sacrilegious [laughter]

  • in any sense. You could try this.

  • I went to "Google Images" and typed in "God" and this is what

  • showed up right in the middle so--And this,

  • Paley argued, and it was--has been convincing

  • throughout most of history, is a perfectly logical

  • explanation for where these complicated things come from.

  • It also has the advantage of being compatible with scripture

  • and compatible with religious beliefs, but Paley made the

  • point this stands on its own. If you find complicated things

  • that--complicated artifacts, you don't assume they emerged

  • by accident. You assume that they were

  • created by an intelligent being. Now, this view has always had

  • problems. This view, you could call it

  • "creationism," which is that biological structures were

  • created by an intelligent being, has always had problems.

  • One problem is it pushes back the question.

  • So you ask, "Where did that intelligent being come from?"

  • And this is a particularly serious problem from the

  • standpoint of the evolution of psychological structures.

  • So, we want to know, "how is it that creatures came

  • across--upon this earth with the ability to reason and plan and

  • do things?" And then the answer is "well,

  • another creature with that ability created us."

  • That doesn't necessarily mean it's wrong, but it means it's

  • unsatisfying. You immediately want to get an

  • explanation for where that other creature comes from.

  • More to the point, there's always been evidence

  • for evolution. And what I mean by evolution

  • here isn't necessarily a specific mechanism,

  • but merely the fact that body parts like the eye didn't emerge

  • all of a sudden, but rather have parallels both

  • within other existing animals and across human and biological

  • history. This evidence comes in

  • different forms. There is fossil evidence for

  • different body parts suggesting that they have evolved from more

  • rudimentary form. There is vestigial

  • characteristics. And what this means is there

  • are characteristics that human bodies have that are somewhat

  • inexplicable, like the human tailbone or

  • goose-bumps, unless you view them--the human body in its

  • current form as modifications from a previous form.

  • There are parallels with other animals.

  • And this is clear in psychology. So, a human brain is different

  • from the rat, cat, and monkey brain but at

  • the same time you see them following a sort of common plan

  • and common structures. And one rational inference from

  • this is that they're linked through evolutionary descent.

  • Finally, there is occasional poor design.

  • So, Paley rhapsodized about the remarkable powers of the human

  • body and the different body parts,

  • but even Paley admitted that there are some things which just

  • don't work very well. Your eye contains a blind spot

  • because of how the nerves are wired up.

  • In the male urinary system the urethra goes through the

  • prostate gland instead of around it,

  • which leads to many physical problems in men later on in

  • life. And so you're forced to either

  • argue that these are really good things or that God is either

  • malicious or incompetent. And those are difficult

  • arguments to make. So, these are problems with the

  • creationist view. But still, for the longest time

  • in human intellectual history there was no alternative.

  • And in fact, Richard Dawkins,

  • the most prominent evolutionary--one of the most

  • prominent evolutionary biologists alive and one of the

  • most staunchest critics of creationism,

  • has written in The Blind Watchmaker saying,

  • look, anybody 100 years ago or 150 years ago who didn't believe

  • that God created humans and other animals was a moron

  • because the argument from design is a damn good argument.

  • And in the absence of some other argument you should

  • go--defer to that. You should say,

  • "Well, there are all of these problems but humans and other

  • biological forms must have divine creation because of their

  • incredible rich and intricate structure."

  • What changed all that of course was Darwin.

  • And Darwin--Darwin's profound accomplishment was showing how

  • you get these complicated biological structures,

  • like the eye, emerging through a purely

  • non-intentional, non-created process,

  • a purely physical process. And this could be seen as equal

  • in importance to the claim that the Earth revolves around the

  • Sun and that we're not the center of the universe.

  • And in fact, some scholars have made a

  • suggestion which seems plausible, that the idea of

  • natural selection is the most important idea in the sciences,

  • period. So, this is not a course in

  • evolution and I expect people to have some background.

  • If you don't have a background in it, you could get your

  • background from external readings but also from--the Gray

  • textbook and the Norton readings will both--will each provide you

  • with enough background to get up to speed.

  • But the general idea is that there are three components to

  • natural selection. There is variation.

  • And this variation gives rise to different degrees of survival

  • and reproduction and gets passed on from generation to generation

  • and gives rise to adaptations, what Darwin described as "that

  • perfection of structure that justly excites our imagination."

  • And the biological world has all sorts of examples.

  • You look at camouflage. Prior to Darwin one might

  • imagine that some intelligent creator crafted animals to hide

  • from their prey. But now we have a different

  • alternative, which is that animals that were better hidden

  • survive better, reproduce more,

  • and over the course of thousands, perhaps millions of

  • years, they've developed elaborate

  • camouflage. There's been a lot of work on

  • Paley's favorite examplethe eye.

  • So Darwin himself noted that the human eye did not seem to

  • emerge all at once but rather you could look at other animals

  • and find parallels in other animals that seem to suggest

  • that more rudimentary forms are possible.

  • And more recently computer simulations have developed--have

  • been developed that have crafted eyes under plausible assumptions

  • of selective pressure and what the starting point is.

  • So, this is the theory of natural selection.

  • The good question to ask is, "why am I talking about

  • evolution in Introduction to Psychology class?"

  • And the answer is that there are two ideas which come

  • together. And in fact,

  • they're both of the dangerous ideas.

  • One idea is that Darwin's idea--that biological forms

  • evolve through this purely physical process.

  • The second idea, the rejection of Descartes,

  • is that our minds are the product of physical things and

  • physical events. You bring these together and it

  • forces you to the perspective that what we are--our mental

  • life is no less than the eye, no less than camouflage,

  • the product of this purely physical process of natural

  • selection. More to the point,

  • our cognitive mechanisms were evolved not to please God,

  • not as random accidents, but rather for the purpose of

  • survival and reproduction. More contentiously,

  • you could argue they've been shaped by natural selection to

  • solve certain problems. And so, from an evolutionary

  • point of view, when you look at what the brain

  • is and what the brain does, you look at it in terms of

  • these problems. And this is what psychology is

  • for. This is what our thinking is

  • for. We have evolved mental

  • capacities to solve different problems: perception of the

  • world, communication, getting nutrition and rest,

  • and so on. Now, we're going to talk about

  • how to apply evolutionary theory to psychology.

  • But as we're doing so we have to keep in mind two

  • misconceptions. There are two ways you can go

  • seriously wrong here. The first is to think that,

  • well, if we're taking an evolutionary approach then

  • natural selection will cause animals to want to spread their

  • genes. So, if we're being biological

  • about it, that means everybody must run around thinking "I want

  • to spread my genes." I want to--and this is just

  • really --Oops. I shouldn't do that.

  • This is really wrong. It's even in red.

  • And what this fails to do is make a distinction between

  • ultimate causation and proximate causation.

  • And those are technical terms referring to--Ultimate causation

  • is the reason why something is there in the first place,

  • over millions of years of history.

  • Proximate causation is why you're doing it now.

  • And these are different. Obviously, for instance,

  • animals do all sorts of things to help survive and reproduce

  • but a cockroach doesn't think "oh,

  • I'm doing this to help survive and reproduce and spread my

  • genes." A cockroach doesn't know

  • anything about genes. Rather, the mechanisms that

  • make it do what it does are different from its own mental

  • states, if it has any--why it does them.

  • This is a point nicely made by William James.

  • So, William James is asked, "Why do we eat?"

  • And he writes, Not one man in a billion

  • when taking his dinner ever thinks of utility.

  • He eats because the food tastes good and makes him want more.

  • If you asked him why you should want to eat more of what tastes

  • like that, instead of revering you as a philosopher,

  • he will probably laugh at you for a fool.

  • And it's really the common sense answer.

  • "Why are you eating?" Nobody's going to answer,

  • "Because I must sustain my body so as to spread my genes in the

  • future." Rather, you eat because you're

  • hungry. Those two theories,

  • you eat because you're hungry and you eat to sustain your body

  • so you could spread your genes in the future,

  • are not alternative. Rather, they're different

  • levels of explanation. And you can't confuse them.

  • The ultimate level which does appeal to survival and

  • reproduction does not--is independent from the

  • psychological level. To give another example,

  • people protect their children so you ask, "Why do people

  • protect their children? Why would somebody devote so

  • much effort to protecting and helping and feeding their

  • children?" Well, the evolutionary

  • explanation is animals that don't protect their offspring

  • don't last over evolutionary time.

  • We protect our offspring because they contain fifty

  • percent of our genes, but that's not the

  • psychological explanation. Nobody but a deranged

  • psychologist would ever answer, "Oh, I love my children because

  • they contain fifty percent of my genes."

  • Rather, the psychological explanation is a deeper--is

  • different and has a different texture.

  • And this will be a lot clearer when we talk about the emotions,

  • where you could really see a distinction between the question

  • of why we feel something from an evolutionary point of view and

  • why we feel it from a day-to-day point of view.

  • The second misconception is that natural selection entails

  • that everything is adaptive, that everything we do,

  • everything we think is adaptive.

  • This is wrong. Natural selection and

  • evolution, more generally, distinguish between adaptations

  • and byproducts and accidents. Many of you are currently,

  • or will as you get older, suffer back pain.

  • If I was to ask you, "So, why do you suffer back

  • pain? How does back pain help you

  • survive and reproduce?" Well, the answer is it's not an

  • adaptation. Back pain is an accidental

  • byproduct of how our backs are shaped.

  • Don't go looking for an adaptive reason for hiccups or

  • self-pity or bloating after you eat.

  • There's all sorts of things a body will do that have no

  • adaptive value, rather just accidents.

  • We have a body that does all sorts of things.

  • Some things it will do by accident and this is certainly

  • true for psychology.

  • So, a lot of the things, for instance,

  • that occupy our interest or our fascination in day-to-day life

  • are almost certainly evolutionary accidents.

  • The number--The three--Three of the main preoccupations of

  • humans are pornography, television, and chocolate but

  • if I asked you, "Why do you like porn?"

  • and you'd say, "Because my ancestors who liked

  • porn reproduced more than those who didn't," [laughter]

  • it's not true. Rather, you like porn,

  • assuming you do, [laughter]

  • as an accident. You have evolved--For instance,

  • should you be a heterosexual male, you have evolved to be

  • attracted to women. That is most likely to be an

  • evolutionary adaptation because being attracted to women and

  • wanting to have sex with women is one step to the road to

  • having kids, which is very good from an

  • evolutionary perspective. It so happens,

  • though, in our modern environment that people have

  • created images that substitute. So, instead of actually going

  • out and seeking out women you could just surf the web for

  • hours and hours and watch dirty movies and read dirty books

  • evolutionary adaptive dead ends. They're accidents.

  • Why do you like chocolate bars, assuming that you do?

  • It is not because your ancestors in the African savanna

  • who enjoyed chocolate bars reproduced more than those who

  • didn't. Rather, it is because we've

  • evolved a taste for sweet things.

  • And we've evolved a taste for sweet things,

  • in part, because the sweet things in our natural

  • environment like fruit were good for us.

  • In the modern world we have created things like chocolate,

  • which are not so good for us but we eat anyway.

  • A lot of the debates--There's a lot of controversy in psychology

  • over the scope of evolutionary explanations.

  • And a lot of the debate tends to be over what's an adaptation

  • and what isn't. There are some clear cases.

  • We have color vision. Why do we have color vision?

  • Well, I think everybody would agree we have color vision as an

  • adaptation because of the advantages it gives us for

  • seeing and making visual distinctions.

  • We are afraid of snakes. We're going to talk about that

  • in more detail but there's a straightforward adaptive story

  • about that. We are afraid of snakes

  • because, really, our ancestors who weren't

  • afraid of snakes didn't reproduce as much as those that

  • were. We like chocolate bars and we

  • enjoy NASCAR. Those cannot be adaptations

  • because chocolate bars and NASCAR are recent developments

  • that could not have been anticipated by evolution.

  • Those are easy questions. Here are some hard questions.

  • Music. Everywhere in the world people

  • like music. Is this an adaptation for some

  • selective advantage or is it an accident?

  • Steven Pinker, who wrote The Language

  • Instinct that you read before, caused a huge amount of

  • controversy when he argued that music is just an evolutionary

  • accident. He described it as auditory

  • cheesecake, something we like to gorge ourselves on that have

  • no--has no adaptive advantage. Other people argue music does

  • have an adaptive advantage. Sometimes males use violence to

  • coerce sex. Is male sexual violence a

  • biological adaptation or is it an accident?

  • There's more than one language. Is that just an accidental

  • byproduct of the way language works or is there some sort of

  • group or selectionist advantage sketched out in some way of

  • having multiple languages? What about visual art?

  • What about fiction? What about our love for stories?

  • Those are all matters of heated debate.

  • And so, we have to keep in mind some things plainly are

  • accidents. Some things almost certainly

  • aren't accidents. Where the action is in the

  • study of psychology and the study of evolution of cognition

  • is trying to figure out which is which.

  • So, those are the misconceptions we have to avoid.

  • But still, who cares? Again this is an Introduction

  • to Psych course. Why are we talking about

  • evolution? Why should it matter to a

  • psychologist how the mind has evolved?

  • I'm going to talk about evolution now but for the rest

  • of the course I'm just interested in how our minds are,

  • period. S,o why would evolution matter?

  • Well, many people think it doesn't.

  • For instanceand they think it doesn't for different reasons

  • one claim is a metaphysical one.

  • You might be a dualist. You might reject the idea your

  • mental life is the product of your brain and hence evolution

  • is irrelevant to psychology because the brain and the

  • mind--because the brain, which may have evolved,

  • has nothing interesting to do with the mind.

  • Lisa Simpson got it wrong when she said the Pope--She got it

  • half right when she said the Pope favored evolution.

  • It is true. John Paul II,

  • many years ago, made a statement saying that

  • Darwinian theory is not incompatible.

  • Darwinian theory is a view about the evolution of species

  • that is not motivated by any animus,

  • is a genuine scientific theory, and should it turn out to be

  • true, it is not incompatible to truth about man as taught by the

  • Church. And scientists were thrilled by

  • this and they were--they said he's endorsing evolution.

  • But what a fewer people talk about is the fact that after he

  • said this he drew the line. He allowed for evolution of the

  • body but he would not allow for evolution of the mind.

  • So it was--he wrote: If the human body takes

  • its origin from preexisting living matter,

  • the spiritual soul is immediately created by God.

  • Consequently, theories of evolution which

  • consider the mind as emerging from the forces of living matter

  • or as a mere epiphenomenon of this matter are incompatible to

  • the truth about man. So, you might not want

  • evolution to be true about the mind because you might believe

  • that the mind is not subject to the same physical laws as the

  • rest of the physical world. That's one way you could reject

  • evolutionary psychology. Another way to reject

  • evolutionary psychology is to accept that the mind is a

  • physical thing but then argue that all of these instincts and

  • these hard-wired facets of human nature might exist for other

  • animals but they don't exist for people.

  • So, the anthropologist Ashley Montagu in '73,

  • close to when The Six Million Dollar Man was

  • shown, by the way, said:

  • With the exception of the reactions of infants to sudden

  • withdrawals of support and to sudden loud noises,

  • the human being is entirely instinctless.

  • Man is man because he has no instincts, because everything he

  • is and has become he has learned from his culture,

  • from the man-made part of the environment, from other human

  • beings. You might say, "Look.

  • He could believe that in '74 but, of course,

  • all of the infant studies that have come out since then

  • suggested that's not true and nobody would believe that

  • nowadays." But in fact,

  • the view is often hold--held--Louis Menand in a

  • New Yorker article a few years ago wrote,

  • "Every aspect of life has a biological foundation in exactly

  • the same sense, which is that unless it was

  • biologically possible it wouldn't exist.

  • After that it's up for grabs." And this is in the context of

  • an argument that evolution can't tell us anything about what's

  • most interesting about people. Menand is not--is an educated,

  • intelligent scholar. He is presumably well aware of

  • the findings of Spelke and Baillargeon about how people are

  • hard-wired to understand the objects in social life and so

  • on. But his point is just that when

  • it comes to the more interesting aspects of human nature,

  • the stuff we're naturally, intuitively interested in,

  • that's more cultural. And the evolutionary theory and

  • Darwinian theory just doesn't have anything much to say about

  • it, not because the mind is

  • separate from the brain but just because humans are much more

  • cultural organisms, and so biology has little to

  • say about it. There's a third objection,

  • which is you might think, "Okay, the human mind actually

  • does contain instincts. There is a human nature but we

  • should just study it by studying people.

  • How could evolution, the study of evolution,

  • the consideration of evolution tell us anything interesting?"

  • I actually, in my own work, think evolution can tell us

  • some interesting things. And I want to try to make a

  • case for ways in which evolution can inform and enlighten us

  • about the mind as it is. First, I want to make a point,

  • which is although this course is Intro Psych and it is about

  • the mind as it is, still I think by any account

  • the evolution of consciousness, morality and so on,

  • just is intuitively interesting. It's the sort of thing that

  • people are just fascinated by and I think it's a question of

  • interest in and of its own right.

  • But here's how it could tell us about psychology.

  • For one thing, it can tell us what can be

  • innate and what cannot. So, some problems,

  • some evolutionary problems, have been around for a long

  • time and could lead to special biological adaptations.

  • If I told you there is a biological adaptation for

  • talking, mate selection, childcare;

  • maybe it's true, maybe it isn't,

  • but it's not crazy. From an evolutionary point of

  • view, it's a reasonable possibility that it is.

  • Other problems are recent and our brains could not be

  • specialized to deal with them: written communication,

  • interacting with strangers, driving a car,

  • playing chess. If you were to argue that

  • there's a part of the brain devoted to playing chess,

  • I would say you're utterly wrong.

  • You cannot be right because, from an evolutionary point of

  • view, there could be no such part of the brain evolved

  • because playing chess is a recent innovation.

  • As a result, a focus on evolution could help

  • discipline us to make coherent claims about what is built-in

  • and what isn't built-in. Third, we're going to talk

  • about human differences in this course.

  • We're going to devote a class to human differences of the sort

  • of what makes you different from her, different from her.

  • Why do we have different intelligences in this class?

  • Why are some of us arrogant and some of us humble?

  • Some of us like--attracted to men, others attracted to women,

  • and so on. But there's also questions of

  • group differences. And evolutionary theory can

  • help us say intelligent things about what sort of group

  • differences you should expect because evolutionary theory

  • predicts that some populations should evolve in different ways

  • than others. The most obvious example is

  • that children should be different from adults.

  • The evolutionary problems faced by a child are very different

  • from the evolutionary problems faced by an adult.

  • And you can make specific and rather interesting predictions

  • about how children's brains should different--differ from

  • adults' brains. Evolutionary theory

  • predicts--does not make any predictions about racial

  • differences or ethnic differences.

  • Some might exist, but there's no adaptive reason

  • why humans who have evolved in different parts of the world

  • should have profound differences in their mental capacities.

  • What does evolutionary theory say about sex differences?

  • Well, it says some interesting things, and we're going to

  • devote a class to discussing them,

  • but what I think is going to be true--proved to be important is

  • that we'll be able to use evolutionary biology to talk

  • sensibly about what sort of distinctions between the sexes,

  • between males and females, one would expect to find and

  • what sort one wouldn't expect to find.

  • We can make educated predictions.

  • I'm going to have--I want to put here a clip of a man.

  • This is a scene from a movie, the movie "Roger Dodger," that

  • begins with a man making quasi-evolutionary claims about

  • the differences between men and women.

  • And I want to put this as an example of what you could call

  • "barroom evolutionary psychology."

  • And I want us to hold this in our minds because we're going to

  • return to these claims and discuss their validity.

  • I like this for a few reasons. First, I like the backward

  • reference to William James and utility.

  • Second, it is a gorgeous combination of some things that

  • are actually reasonably rational and total bull crap.

  • And--but what evolutionary biology will give us is the

  • tools to distinguish between the two.

  • On the face of it immediately, the ability to read maps,

  • the claim that that has a biological--that differences in

  • that ability have a biological root is crazy.

  • On the other hand, the claim that one--that males

  • may develop a trait not because it's advantageous but to attract

  • females is less crazy. The telepathic stuff is really

  • crazy but--;So, I'm not at this point--We're

  • going to devote a lecture to sex.

  • I do not, at this point, want to make any claims one way

  • or another. But what I want to suggest is

  • that from a biological point of view we could say sensible and

  • intelligent things about what differences should exist and

  • what shouldn't. Finally, and most of all,

  • looking at something from the perspective of design,

  • the perspective of what's it for, can often give you

  • interesting insights as to its current nature.

  • And I'll give you two quick examples, one that's not from

  • psychology, one that is. Women suffer--Often women who

  • are pregnant early in their pregnancy suffer from morning

  • sickness, nausea, throwing up and so on.

  • This has traditionally been viewed as just a breakdown in

  • the system--too much hormones, everything's askew;

  • women get nauseous. Margie Profet suggested an

  • alternative and this won her the MacArthur Genius Award.

  • And this was the claim that maybe pregnancy sickness is not

  • an accident; rather, it's designed,

  • it has a biological purpose. In particular,

  • as the baby develops in the uterus, it is vulnerable to

  • various sorts of poisons or teratogens.

  • Profet suggested that pregnancy sickness is a hypersensitive

  • period where women are extremely sensitive,

  • get extremely nauseous towards the sorts of foods that could

  • damage their baby. Now, if she just ended there

  • it's a story. How do we know it's true?

  • But then she went on to examine it the same way that any

  • scientist examines any claimby making predictions and

  • testing them. And this makes some interesting

  • predictions. It suggests the timing of onset

  • and offset of pregnancy sickness, of morning sickness,

  • should correspond to the period of maximal vulnerability on the

  • part of the developing embryo or fetus.

  • Suggested the types of foods avoided should correspond to

  • those sorts of foods that were most deadly for the fetus and

  • that were deadly for the fetus during the periods where humans

  • evolved. This last qualification is an

  • important one. Women do not develop an

  • aversion to alcohol during pregnancy even though alcohol is

  • extremely dangerous to the developing child.

  • The answer is an easy one. Alcohol wasn't around during

  • our evolutionary history and we could not have evolved a system

  • to protect ourselves from it. And finally,

  • there should be a relationship between miscarriage and birth

  • defects in a surprising direction.

  • For Profet, and she has evidence to back this up,

  • pregnancy sickness is not a glitch in the system.

  • Rather, it's the sign of a healthy act of protective

  • mechanism going on. And in fact,

  • the more morning sickness the more the baby should be

  • protected. Something which,

  • by and large, appears to be true.

  • That's an example of how the question--when dealing with this

  • they say, "Hey. Women throw up when they get

  • pregnant" and then say, "Look.

  • Maybe that's not just a glitch. What's it for?"

  • You could then learn some interesting things.

  • Here's a different example based on the last lecture,

  • this wonderful lecture by Peter Salovey on sex and love where he

  • talked about the "big three." These are the "big three" to

  • remind you of what attracts us to somebody else.

  • You are very attracted to the person next to you or a person

  • that--because of proximity, similarity, familiarity.

  • And there is abundant evidence supporting the truth of this.

  • It's almost always true but the evolutionary psychologist looks

  • at this and says there's something seriously wrong here.

  • There are some cases where that has to be totally,

  • absolutely mistaken. To realize what this is,

  • think for a moment. What humans are you most close

  • to, most similar to and most familiar with?

  • What humans did you spend over ten years of your life with who

  • are genetically and environmentally as close to you

  • as if they were related, who you are intimately familiar

  • with? Are those the humans that you

  • find the hottest? [laughter] No.

  • They're your siblings and they are not hot.

  • [laughter] I was on Google Images this

  • morning. I put up some hot siblings

  • and--but--although we may find them hot, they do not typically,

  • with some rare and bizarre exceptions, find [laughter]

  • one another hot. Why not?

  • Well, this is not a huge puzzle from the standpoint of

  • evolutionary biology. Evolutionary biology posits

  • that humans, as well as other animals, should have incest

  • avoidance. We should love--we should be

  • attracted to those familiar to us, similar to us,

  • close to us, but not kin.

  • Kin are off limits. There is a good reason why.

  • Because if you inter-mate with your kin you have bad offspring

  • [laughter] and so animals should be wired

  • up not to mate with their kin. And in fact,

  • this is what happens. There are--Parents of teenagers

  • have all sorts of concerns. And a lot of the concerns are,

  • in fact, sexual. How do you keep your son and/or

  • your daughter from going out and having sex with too many people,

  • or the wrong people, or unprotected sex?

  • But there are no parenting guides in the world that say

  • "How do you keep your children from having sex with one

  • another?" [laughter]

  • You typically do not need to because they do not want to have

  • sex with one another. Now, this is--actually also

  • illustrates the difference between proximate and ultimate

  • causation. So, you think for yourself,

  • "Eew. Do I want to have sex with my

  • sister?" You don't think to yourself,

  • "I would prefer not to, for the offspring that we will

  • create will be nonviable and it'll be a waste of my

  • reproductive efforts." Rather, you think,

  • "Eew," because at a gut level you respond.

  • And this sort of instinctive response is what you get from an

  • evolutionary analysis of sex. But this story is deeply

  • incomplete because the question that gets raised is "how do you

  • tell?" You don't want to have sex with

  • your kin but how do you tell your kin?

  • People don't carry their DNA markers on strips that you could

  • see. How do you tell who your kin

  • are? And this actually turns out to

  • be a really interesting question.

  • It used--And some research suggests that the answer is

  • simple. You avoid sex with people you

  • grew up with. And these studies actually come

  • from kibbutz studies, studies where people are raised

  • communally on an Israeli kibbutz.

  • They know they're not related, but still, the fact that they

  • were raised together as kids suggests that there's a cue at a

  • gut level not to be attracted to one another.

  • It turns out there's some reason now to believe this story

  • is incomplete. A paper that came out in

  • Nature five days ago reported a series of extremely

  • interesting studies. And they found that the cue of

  • being raised together as a child with somebody--yes,

  • that does diminish sexual desire, but an even bigger cue

  • was "did you observe your parents,

  • and in particular, your mother,

  • taking care of that person?" If you did, that seriously

  • diminishes sexual desire and brings it down to the level of

  • disgust. And again, these are the sort

  • of questions and issues you begin to ask when you approach

  • things from an evolutionary perspective.

  • Okay.

  • For this lecture--the rest of this lecture and then the next

  • couple of lectures, I'll be discussing some basic

  • aspects of human nature that are, to some extent or another,

  • informed by evolutionary theory. And what I want to start for

  • the remainder of this lecture is a discussion of rationality.

  • Now, some of you maybe not want to go into--not want to go into

  • psychology because there's no Nobel Prize for psychology.

  • You might all think, "Hey, if I'm going to go into

  • the sciences I want a Nobel Prize.

  • Think how proud Bubby and Zadie would be if I won a Nobel Prize.

  • Wouldn't that be the best?" You can get one.

  • Psychologists have won the Nobel Prize.

  • Most recently, Danny Kahneman won a Nobel

  • Prize. You win it in economics,

  • sometimes medicine; not a big deal.

  • He won it for his work done over the course of many decades

  • on human rationality. And this work was done in

  • collaboration with Amos Tversky, who passed away several years

  • ago. And this work entirely

  • transformed the way we think about human decision-making and

  • rationality. Kahneman and Tversky caused a

  • revolution in economics, psychology, and the social

  • sciences more generally, by causing us to shift from the

  • idea that we're logical thinkers, who think in accord

  • with the axioms of logic and mathematics and rationality,

  • more towards the idea that we actually have sort of rough and

  • ready heuristics. These heuristics served us well

  • during the time--during our evolutionary history,

  • but sometimes they can lead us astray.

  • And I want to give some examples of these heuristics.

  • And I'll give four examples of heuristics that are argued to

  • permeate our reasoning. The first is "framing effects."

  • This was a classic study by Kahneman and Tversky involving

  • this sort of question. The U.S.

  • is preparing for the outbreak of a disease that's going to

  • kill six hundred people. There are two programs.

  • Program A: If you follow it two hundred people will be saved.

  • Program B: There's a one-third chance everybody will be saved

  • and a two-third chance nobody will be saved.

  • Who would choose program B?

  • Who would choose program A? Okay.

  • And that fits the responses. Most people choose program A.

  • That's--It could go either way. What's interesting is if you

  • frame the question differently, like this, you get very

  • different responses. And instead of focusing on the

  • people who will be saved, you focus on the people who

  • will die and, instead of focusing on the

  • chance that nobody will die and the chance that everybody will

  • die, you'd flip it around,

  • you get a corresponding flip. And this is known as a "framing

  • effect." The idea of a framing effect is

  • that you could respond differently to a situation

  • depending on how the options are framed.

  • And, in particular, this combines with "loss

  • aversion." People hate a certain loss.

  • "Four thousand of these people will die" is extremely aversive

  • and so the framing can influence your decisions.

  • And clever advertisers and clever decision makers will

  • frame things in different ways to give you--give rise to

  • different intuitions. Sometimes this could be fairly

  • simple. So, you have this ad of a

  • hamburger that's eighty percent fat free versus twenty percent

  • fat--You don't have to be a brilliant ad executive to figure

  • out which one to go for. It turns out that this sort of

  • fundamental actthe fundamental role of framing

  • effectsis not limited to humans.

  • So, I want to take a second and tell you some work done by my

  • colleague, Laurie Santos, with capuchin monkeys.

  • And what she does is she takes these capuchin monkeys and she

  • teaches them to use money. She teaches them to use little

  • discs to buy themselves either pieces of banana or pieces of

  • apple. And they like to eat this.

  • And they very quickly learn you can hand over a disc to get some

  • banana or some apple.

  • [laughter] Now, Dr.

  • Santos and her colleagues have done many studies using this

  • method, but the study I'm interested in illustrating here

  • shows framing effects in these nonhuman primates.

  • So, what she does is--There's two options.

  • In one option, the experimenter shows one

  • object to the capuchin and low--and then either gives one

  • or two--half the time gives one, half the time gives two,

  • for an average of one and a half.

  • The other experimenter does exactly the same thing;

  • gives one or two for an average of one and a half,

  • but starts off displaying two. Now, if you weren't a human,

  • how would you feel about these two experimenters?

  • They both give you the same amount.

  • And capuchins are extremely sensitive to how much they get,

  • but it turns out as predicted they don't like the pink

  • experimenter because the pink experimenter is--he gives you

  • two--shows you two and half the time he gives you one.

  • This guy shows you one, and half the time gives you

  • two. And over time they develop a

  • preference for the experimenter that shows them one initially,

  • suggesting that they are being subject to framing effects or

  • choices relative to a reference point.

  • A different sort of demonstration is the "endowment

  • effect." This is a robust and very

  • interesting effect. Here's the idea.

  • I show you something like a cup or a chocolate bar and I say,

  • "How much will you give me for this chocolate bar?

  • It looks like you're pretty hungry.

  • How much will you give me for this chocolate bar?"

  • And you say, "I'll give you two dollars for

  • this chocolate bar." Most people on average give

  • two--the chocolate bar--gives two dollars for a chocolate bar.

  • The other condition's exactly the same except I hand you a

  • chocolate bar and say, "How much money will you sell

  • me that chocolate bar for?" There, people say,

  • "Two fifty," and in fact, what happens is once you own

  • something its value shoots up. And this has mystified

  • economists and psychologists. It makes no sense.

  • The chocolate bar doesn't even have to move.

  • I just leave it on the table and say either "How much will

  • you spend," "How much will you give me for this?"

  • or "Okay. It's yours.

  • How much do you want for me to take it back?"

  • The answer is, it's framing. If you're asking how much you

  • want for it, it's a game. It's just how much will you pay

  • to get something. But if you're being asked how

  • much do you want for me to take it from you, you treat it as a

  • loss. And as a loss it becomes more

  • valuable. Those are framing effects.

  • The second example is base rates.

  • There are seventy lawyers--sorry,

  • seventy engineers and thirty lawyers and John is chosen at

  • random. Let me tell you about John:

  • forty-years old, married, three children,

  • conservative, cautious, no interest in

  • politics, awkward around people. His hobbies include carpentry,

  • sailing, and solving mathematical puzzles,

  • like online dating.

  • [laughter] What do you think John is?

  • A lawyer or an engineer? Who thinks he's a lawyer?

  • Good. Who thinks he's an engineer?

  • Okay. Most people think he's an

  • engineer, but here's the thing. You switch it.

  • Right? Thirty engineers,

  • seventy lawyers? It doesn't change.

  • People--No matter what this number is--these numbers--it

  • doesn't seem to change who you think he is or how confident you

  • are. People look at John as an

  • individual and they ignore the background status of where he

  • came from. They ignore base rates.

  • Base rates are very difficult to think about and I want to

  • give you an example of this. And the example will be on the

  • slides for when you print them out--print it out because you

  • might want to work through it yourself.

  • But I'll give this to you quickly.

  • There's a disease that hits one in a thousand people,

  • a pretty common disease. There's a test for the disease

  • and if you have it, it's going to tell you you have

  • it. It tests for a certain thing in

  • your blood and "boom," if the thing is in your blood the test

  • will go "boom." If you have it,

  • it will tell you you have it. It doesn't miss.

  • On the other hand, it's not perfect.

  • It has a false positive rate of five percent.

  • So, if you don't have the disease, five percent of the

  • time the test will say you have it.

  • So, if the test says you don't have it, you're fine.

  • But if the test says you have it, maybe you have it but maybe

  • it's a false positive. You take the test.

  • It says you have the disease. Without pen and paper,

  • how likely do you think the odds are you have the disease?

  • Who says over fifty percent? Okay.

  • Before people sinisterly shouted the right answer,

  • people will tend--medical students were given this,

  • medical students less savvy than you, and the average is

  • between fifty percent and ninety-five percent.

  • The answer is, as some people quickly noted,

  • two percent. And here's how it works.

  • One percent of a thousand will have the disease.

  • That person will test positive. The test never misses.

  • That leaves nine hundred ninety-nine people who don't

  • have the disease, and we'll say about fifty

  • percent of these people have it. So, for every fifty-one people

  • who test positive, only one will have the disease,

  • giving an average of about two percent.

  • This sort of thing is very difficult.

  • Our minds are not evolved to do base rate computation.

  • And so, any problems involving base rate computation,

  • including real world problems, like what to do when you come

  • back with a positive test, we screw up.

  • And often we screw up in the direction of panic.

  • The third bias is the "availability bias."

  • And this is simply that if you want to know how frequent

  • something is, how available it is to come to

  • mind is an excellent cue. But this could lead to mistakes.

  • A classic example by Kahneman and Tversky is you ask

  • people--one group of people how many English words end with "ng"

  • or what proportion of English words,

  • another group of people what proportion end with "ing."

  • It turns out you get much bigger numbers for "ing" than

  • "ng" though, of course "ng" has to--"ing"--sorry,

  • "ng" would include everything with "ing."

  • It's just a lot easier to think about these things.

  • This can show up in the real world.

  • What are your risk of getting killed--What's your risk of

  • getting killed by a shark? Well, if you ask people what

  • their risk of getting killed by a shark is, they

  • characteristically overestimate it.

  • I will give you the news of what the risk is for getting

  • killed by a shark. Injured in any given year:

  • one in six million. Killed: one in five hundred

  • million. If you live in Florida,

  • which apparently is Shark Central, your chance of getting

  • injured is about one in a half million.

  • People will overestimate the risks because shark attacks are

  • very salient. They are always reported in the

  • news and they're very interesting.

  • What is the chance of getting killed by potato salad?

  • [laughter] Well, food poisoning,

  • death by food poisoning, injury by food poisoning runs

  • to about one in fifty-five, one in 800 for some sort of

  • injury and one in 55,000 killed. Potato salad is 1,000 more

  • times more dangerous than shark attacks.

  • But you get it wrong because you don't think,

  • "Oh, my God, big news story.

  • Somebody dies by potato salad." [laughter]

  • And so, we tend to overestimate the chance of being killed by

  • dramatic effects. How many Jews in the United

  • States, what proportion? Who thinks it's over three

  • quarters of the United States is Jewish?

  • [laughter] I'm kind of anchoring here.

  • Okay. Okay.

  • Who thinks over half? Who thinks over forty percent?

  • Who thinks over twenty percent? Okay.

  • Who thinks over fifteen percent? Who thinks over ten percent?

  • Who thinks over seven and one-half percent?

  • Who thinks over five percent? Okay.

  • Who thinks overall there's more than five percent of the United

  • States that's Jewish?

  • Who thinks over three percent? The answer is somewhere between

  • 1.9 and 2.1%. Most people think--The average

  • American thinks it's twenty percent.

  • There is-- [laughter] If you're curious about

  • demographics, and this map isn't to be

  • entirely trusted because I got it from Wikipedia,

  • [laughter] this is the distribution of the

  • Jewish population, self-identified as Jewish in

  • different parts of the United States.

  • [laughter] New York City is,

  • of course, the most dense population with nine percent.

  • New Haven has 3.5%.

  • Now, why do people get it wrong? Well, there's all sorts of

  • reasons and this is going to come out in the context of

  • social psychology when we talk about how people think about

  • human groups. But one quick answer is people

  • who are plainly Jewish are prominent in positions where

  • people notice them, like entertainment or,

  • in the case of you guys, academia.

  • And this could lead to--this availability-- "Can I think of a

  • Jew? Yeah."

  • [laughter] This availability causes us to

  • overestimate the proportion to which Jews are represented in

  • the population. Final example.

  • Confirmation bias. This is a very nice study and

  • it's very simple. It's--You're in a jury of a

  • custody case. You have to give a child

  • custodyeither a mother or father sole custody.

  • One parent has average income, average health,

  • average working hours, reasonable rapport with the

  • child, and a relatively stable social life.

  • The second parent has an above-average income,

  • minor health problems, lots of work-related travel,

  • a very close relationship with the travel--with the child,

  • and an extremely active social life.

  • Think for a moment. Who would you award custody

  • with? There's no--Obviously,

  • there's no right answer here. Just think for a moment.

  • Who would award custody to parent A?

  • Who would award custody to parent B?

  • Okay. As I think there is in this

  • room, when this study is done there's a slight advantage to

  • parent B. Here's what's interesting.

  • You give another group of people this question.

  • "Which parent would you deny custody to?"

  • You get a slight advantage for parent B.

  • Now, this is to some extent an illustration of framing problem

  • but it's also a more general illustration of the confirmation

  • bias. So, when you're asked to award

  • custody to, you then ask, "Well, what is a good--what is

  • a sign that somebody's a good parent?"

  • And the good parent aspects of B jump out.

  • When asking about denying custody you ask,

  • "Where is a cue that somebody's a bad parent?"

  • And the bad parent aspects of B jump out.

  • In general, when we have a hypothesis we look for

  • confirmations. This makes some things,

  • which are logically easy extremely difficult problems

  • when we face them in the real world.

  • And I'll end with my final example, that of the Wason

  • selection task. Here's the game.

  • And people--I don't want people to shout it out just yet.

  • There is four cards. Each card has a letter on one

  • side and a number on the other side.

  • You have to judge whether this claim is true or false.

  • "If a card has a 'D' on one side, it has a '3' on the other

  • side." How many cards do you have to

  • turn over to test whether that rule is right?

  • Okay. Somebody shout out what one

  • card is you have to turn over. "D."

  • Everybody gets that right. What else?

  • Do you need to do any other cards?

  • How many people think it's "D" and "3"?

  • I'm raising my hand to fool you. [laughter]

  • People answer either "D" or "D" and "3" but think about it.

  • What would make this rule wrong? It's wrong if it has "D" on one

  • side and not "3" on the other. Right?

  • That's what it would be to be wrong.

  • You then would have to check "D" to see if there is a "3" on

  • the other side. You were all right about that.

  • That means you'd check "8" to see if there's a "D" on the

  • other side. "Three's" not going to tell you

  • anything. That's hard.

  • People find this very hard. Okay.

  • Big deal. But what's interesting is you

  • can modify it in certain ways to make it a lot easier.

  • And this is the work of Leda Cosmides and her colleague,

  • an evolutionary psychologist at Santa Barbara who has argued

  • that if you frame these questions in ways that make

  • ecological sense, people are much better at them.

  • And basically, she does studies where she has

  • people who are evaluating a social rule.

  • Imagine these cards. On one side of the card is an

  • alcohol--is a drink. On the other side is a person's

  • age. You are a bartender and you

  • want to make sure nobody under twenty-one drinks beer.

  • Which cards do you turn over? Well, now it's easier but the

  • logic is the same. It's a violation that there's

  • "under twenty-one" on one side, "beer" on the other side,

  • so you need to check the "under twenty-one" here and you need to

  • check the "beer" here. And when you make these logical

  • problems more ecologically valid they turn out to be much easier.

  • Okay.

  • There's a little bit more but I'll hold it off until next

  • class. And I'll end with the reading

  • response, which is to do your own bit of reverse engineering

  • and evolutionary psychology. And I'll see you all on

  • Wednesday.

Professor Paul Bloom: We began the course by talking

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10. 進化、情感與理性。進化與理性 (10. Evolution, Emotion, and Reason: Evolution and Rationality)

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