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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