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 example – the
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 instance – and 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 claim –
by 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 act – the
fundamental role of framing
effects – is 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
custody – either 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.
 
