Professor Paul Bloom:
Sex is really strange.
You ask people,
"What's your favorite
activity?"
and if you ask people,
particularly college students,
particularly just fresh from
spring break – I've seen teen
movies – they'll often answer,
"Sex."
or some word that is synonymous
with sex.
But there's a kind of a puzzle
about how much time we spend on
sex.
And it turns out there is data
on this.
So, people say sex is their
favorite activity,
but it turns out we actually
know how much time the average
American spends on sex.
And the data I'm going to
follow from was summarized in
this wonderful book by James
Gleick:
Americans tell pollsters
their single favorite activity
is sex.
In terms of enjoyability,
they rank sex ahead of sports,
fishing, bar-hopping,
hugging and kissing,
talking with the family,
eating, watching television,
going on trips,
planning trips,
gardening, bathing,
shopping, dressing,
housework, dishwashing,
laundry, visiting the dentist,
and getting the car repaired.
On the other hand,
these same studies suggested
the average time per day devoted
to sex is four minutes and three
seconds.
[As Gleick says,]
This is not much,
even if the four minutes
excludes time spent flirting,
dancing, ogling,
cruising the boulevard,
toning up in gyms,
toning up in beauty parlors,
rehearsing pick up lines,
showering, thinking about sex,
reading about sex,
doodling pornographically,
looking at erotic magazines,
renting videos,
dreaming of sex,
looking at fashion magazines,
cleaning up after sex,
coping with the consequences of
sex,
building towers or otherwise
repressing, transferring,
and sublimating .
And I like this passage because
it illustrates two points,
two important points.
One is we don't actually spend
that much time on sex.
In fact, the four minutes and
three seconds is an interesting
number because when you do times
studies on how much Americans
spend filling out tax-related
forms for the IRS,
it's four minutes and a few
seconds.
But the passage also points out
that regardless of the brute
time we spend on it,
it is extraordinarily
important.
Everything in life follows from
it – marriage,
family, children,
much of aggression,
much of competition,
much of art and music and
creative pursuits.
Much of everything follows from
it.
If we were a creature without
sex, everything would be
different.
And what's interesting is,
there are creatures without
sex.
There are creatures that
reproduce by cloning.
And in fact,
this basic fact about people
– that we fall,
roughly, into males and females
– is an evolutionary mystery.
It's not clear why animals that
are somewhat large have two
sexes.
From a biological Darwinian
perspective, having two sexes is
bizarre because each time you
have an offspring you toss away
half your genes.
My children only have--each of
them have half my DNA.
If I were to clone,
they would have all of it.
And so, it's a puzzle how sex
ever evolved.
This is not a course in
evolutionary biology,
and that's not the puzzle we're
going to be looking at today.
We're going to look at a few
questions.
First, we're going to talk from
first a theoretical point of
view and then an empirical point
of view about how males and
females are different.
Then we're going to talk about
sexual attractiveness,
some research about what people
find to be sexually attractive,
and then we'll talk a very
little bit at the end about the
origins of sexual preference:
why some people are straight,
others gay, others bisexual,
and others harder to classify.
Now, of all the topics I'm
presenting, sex is one of the
sort of dicey ones from an
emotional point of view.
These are difficult issues
because sex is,
by definition,
an intimate part of our lives,
and it matters a lot.
Moreover, sex is fraught with
moral implications.
And since I'm talking about
this from, at least at the
beginning, from a Darwinian
evolutionary perspective,
I'm obliged to start off by
dealing with some of the moral
consequences and moral
implications.
So, for instance,
many biologists – all
biologists I would say – will
have argued that sexual
behavior,
sexual action,
sexual desire is,
to some extent,
a biological adaptation
existing to spread our genes.
From that perspective then,
non-procreative sex –
including gay sex,
sex with birth control,
sex by post-menopausal women
– does not serve this
reproductive goal and,
in some sense perhaps,
is unnatural.
And one might argue then,
"Does this mean it's wrong?"
We'll also be talking about sex
differences, differences between
men and women,
for instance,
in how much you want anonymous
sexual encounters,
differences between men and
women in social intelligence,
in aggression and empathy.
And regardless of what you
think about these differences,
whether you think they're right
or wrong or it doesn't matter,
you'll ask the question,
"To what extent are they
mutable?"
That is, if they exist through
Darwinian natural selection,
to what extent can we ever get
rid of them?
And I want to address those two
issues, the issues of morality
and inevitability,
from the very start.
And I want to start off
with--for each of them have a
quote by a prominent
evolutionary scholar.
So, the first one is by Steve
Pinker in How the Mind
Works.
And he writes, 
Nature does not dictate
what we should accept or how we
should live our lives.
Well into my procreating years,
I am so far voluntarily
childless, having squandered my
biological resources reading and
writing,
doing research,
helping friends and students,
and jogging in
circles--ignoring the solemn
imperative to spread my genes.
By Darwinian standards,
I am a horrible mistake,
a pathetic loser,
but I am happy to be that way,
and if my genes don't like it
they can go jump in the
lake.
Pinker's point,
I think, is a reasonable one.
It is true that certain things
we do exist to serve the
dictates of natural selection,
but that doesn't make them
right?
If you think that something is
only right if it leads to the
generation of more genes,
if it leads to reproduction,
then you're not going to think
very much about birth control.
You're not going to think very
much about any sort of
non-procreative sex.
On the other hand,
if you're--Moreover,
if you think something's wrong
if it's unnatural,
you're going to think much
about flying in a plane or
refrigerating food or surviving
a severe infection.
More generally,
our bodies and brains have
evolved for reproductive
success, but we can use these
brains to choose our own
destinies.
Nothing moral necessarily
follows from the facts of
biology.
That's all I'm going to say
about morality.
But I want you to keep it in
mind when we discuss different
claims about what's evolved and
what hasn't.
What about inevitability?
Here I want to turn to Richard
Dawkins.
Richard Dawkins writes, 
If a child has had bad
teaching in mathematics,
it is accepted that a resulting
deficiency can be remedied by
extra-good teaching in the
following year.
But any suggestion that the
child's deficiency might have a
genetic origin is likely to be
greeted with something
approaching despair.
If it's in the genes,
it is determined and nothing
can be done about it.
This is pernicious nonsense on
an almost astrological scale.
Genetic causes and
environmental causes are in
principle no different from each
other.
Some may be harder to reverse,
others may be easy.
What did genes do to deserve
their sinister,
juggernaut-like reputation?
Why are genes thought to be so
much more fixed and inescapable
in their effects than
television, nuns or books.
I like the nuns.
And the point here is what
causes something is logically
separate from what can reverse
it.
And you can think of clear
cases where something is plainly
genetic but is fairly easily
reversed and where something is
cultural and is very difficult
to reverse.
Here's an example.
My eyesight is quite poor.
The reason why my eyesight is
quite poor is not due to the
patriarchy, television,
culture or "the man."
Rather, my eyesight is quite
poor due to the crappy genes Mom
and Dad gave me.
It is genetically determined if
anything is.
It is also fairly easy to fix.
There are these machines where
they put panes of glass in front
of your eyes and help you to see
better.
More advanced machines known as
contact lenses actually stick
the thing into your eyes,
and at the cost of occasional
infections you come to see
better.
It's biologically caused but
fairly easy to fix.
On the other hand,
take an example of society's
treatment of the obese.
It turns out when we – and
we'll get to this a little bit
when we talk about sexual
attractiveness – how thin
somebody is or how fat they are;
what you think of that is
actually not particularly
hard-wired.
It varies a lot from culture to
culture.
But once it's in a culture,
it is almost impossible to
shake.
So, the point,
there is just that genetic does
not mean inevitable,
and cultural does not mean easy
to fix.
Okay.
That's general background.
Let's start with basic Sex Ed.
What's the difference between
males and females?
Well, don't even think penis
and vagina.
There are a lot of animals that
have neither one.
And the difference actually
runs deeper.
By definition,
when biologists talk about
this, animals that are males
have a little sex cell,
which carries genes and nothing
else – sperm cells.
Animals that are females have a
big sex cell,
which has genes but also food
and a protective cover and all
sorts of other stuff.
Typically, the little sex cell
is much littler than the big sex
cell.
This is the only erotic picture
I'm going to show you today.
It's a bunch of these little
sperm circling around the egg.
It's romantic.
But this raises a puzzle.
I just described male and
female roughly in terms of a
size difference.
Males are the smaller of the
sex cells;
females are the bigger.
Why is it then that for so many
animals males are the bigger
ones, physically,
and the more aggressive ones.
This has been a puzzle that has
occupied scientists for a long,
long time.
And we're pretty--there is now
a pretty clear answer to it.
And the answer goes like this.
It is based on an idea by
Robert Trivers called "parental
investment."
And what parental investment
is, it's defined here as,
any investment that's going to
increase the offspring's chance
of survival at the cost of the
parent's ability to invest in
other offspring.
So, for example,
suppose an animal could create
an offspring by blinking an eye
and then the offspring would run
off?
That would be extremely little
investment.
Suppose another animal had to
work for ten years,
and during those ten years
could not create another
offspring.
That would be a huge investment.
Trivers points out that within
a species, females typically
have a much higher parental
investment than males.
Because females have these big
sex cells, they typically
incubate them internally.
They carry them.
If they're eggs,
they might have to sit on them.
And hence, each potential child
is a huge cost.
For males, which have the small
sex cell, you don't have the
same thing.
For males, it might just be a
few moments of copulation and
that's it.
If you could ask yourself,
for humans, each one of you in
the room, "What is the minimum
effort you can do to create a
child that has half your genes?"
And it's apparent that the male
investment, on average,
is lower than the female
investment.
Males can choose,
or might do better off in some
circumstances by putting a lot
of investment into their
offspring, but females don't
have a choice.
Females, barring technological
advance, have a huge investment
into any offspring;
not investment in the sense or
hard work and effort,
though there's that too.
Investment in the sense that
when you're--when you're
pregnant with one offspring,
you can't have another.
What this does is it has
ramifications that percolate
upwards.
So, it leads to different
psychologies.
Males--and a single male could
fertilize several females,
forcing some males to go
mate-less and giving rise to
competition to see who can mate
with the most females.
For females,
however, females can always
find mates.
So, sheer numbers don't count.
But there's competition to mate
with the right males,
those whose offspring have the
best chance of surviving.
The competition now explains
the puzzle we started with.
It explains why males are
typically larger,
and often why males have
evolved special weapons.
These special weapons evolved
for fighting other males for
reproductive access.
It also explains something else.
Females, biologically,
are choosy.
And so males have to compete
not merely with other males to
get reproductive access but also
to woo females.
And so often,
males have evolved special
displays like this ,
which exist only to be
beautiful, only to be attractive
and to attract mates.
This cold evolutionary logic
was captured in this cartoon,
which really does sum up a
hundred of mate-selection
research.
The logic goes like this then:
difference in the size of sex
cells leads to differences in
typical parental investment,
leading to differences in the
sorts of psychological and
physiological mechanisms that
evolved.
Okay, that's a good story.
What sort of evidence is there
for it?
Well, it turns out this could
explain some otherwise
surprising things.
For instance,
there should be--there are some
cases where the parental
investment is switched,
some cases where it turns
out--where the males end up with
more investment than the
females.
And it--and the theory predicts
that in these cases you should
get an asymmetry.
So, in cases like pipefish,
for instance,
the male takes the eggs into a
pouch and plugs them into his
bloodstream.
The females shoot off.
They have less of an investment
than the males.
In this case,
you would predict,
as is true, the females should
be larger, the females fight
other females more than males
fight males,
and the females try to compete
for the attention of the males.
Recall the movie "March of the
Penguins."
We saw a clip from it,
and this was in the context of
discussing the emotions that
have evolved toward our
offspring.
But remember the story and how
both the male and the female
have to go to tremendous lengths
to protect the egg.
And if one of them fails,
the egg dies and neither one
has it.
You should then not even have
to remember whether male
penguins are much bigger than
female penguins.
You should realize they should
not be, and in fact they aren't.
They're about the same size
because the parental is equal.
You should be able to predict
the size differences and
aggression differences based on
differing parental investment.
So for instance,
elephant seals are four
times--the males are enormous.
They're four times bigger than
the females.
And this is in large part
because elephant seals compete
for harems of females.
It's a "winner take all."
Gibbons are about the same size.
And this is because gibbons are
pretty monogamous;
they raise children together.
This illustrates something,
which is, it's not always the
case that male parental
investment is low.
There are some species,
including gibbons,
where it's in the male's
reproductive advantage to care
for the offspring.
Imagine a situation,
for instance,
where an offspring would die if
both parents didn't watch it for
many years and where the effort
devoted to that offspring had to
be exclusive.
If you focused on another
family or went away,
the offspring would die.
In that case,
you'd have equal investment.
It would matter equally to the
male and the female to invest in
their offspring,
and the cost would be the same.
There's no species--it's hard
to see species that have that
much of an equal system,
but some primates are close to
it.
And this raises the question
then, "What about humans?"
What about us?
What do we know about the
differences between males and
females?
Well, humans are a relatively
polygamous species.
Most cultures--most human
cultures are polygamous.
American culture is what they
call "serial monogamy."
So, we're not like some species
of birds.
We don't mate for life.
We do a series of peer-bondings
for some period of time.
It could be for life,
but indeed may not be and
usually isn't.
Males are bigger than females.
Human males--the size estimates
vary so much,
but the average human male is
about fifteen percent larger
than the average human female.
This suggests that there's
some--there's been,
in our evolutionary history,
some male-male competition for
access to females,
which suggests,
in turn, that the parental
investment is not quite equal.
Males have smaller testicles
for their body size than
chimpanzees, but larger
testicles than gorillas and
gibbons.
And this suggests that there
was some intermediate amount of
competition for the capacity to
create sperm.
And this is relevant for a
different sort of competition,
which regards the impregnation
of females that have multiple
mates.
And this suggests that over
evolutionary history women were
not wantonly promiscuous,
but were not entirely
monogamous either;
so much so that it paid from an
evolutionary point of view to
evolve--males to evolve the
capacity to produce more sperm
than other males.
Aggression.
Males are meaner.
I mean I'm summarizing here.
Meaner is not a technical term.
Yes, females can be meaner,
but males are at least more
physically violent.
They're more violent in the
womb, in utero;
they're more violent as
children, and they're more
violent as adults.
Again, this is not to say that
you can't find violent women or
non-violent men.
It's just on average there is
this difference.
They kick more;
males kick more in the uterus.
As children they're more
involved in play fighting and
violent combat-like sports.
And as adults,
wherever you go you will find a
prison.
And wherever you go you will
find that prison is mostly full
of men.
They are far more likely to
kill one another and to harm one
another.
Male sex hormones,
like testosterone,
are not the sort of thing one
would want to inject in somebody
unless you want them to turn
kind of mean.
They increase aggressiveness,
both in humans and in other
primates.
What about sexual choosiness?
Do male humans and female
humans differ in the extent to
which they will favor anonymous
sex?
And this is relevant from an
evolutionary perspective,
because the parental investment
theory predicts males should be
more receptive to anonymous sex.
Because for males,
to impregnate somebody else
might fortuitously lead to
another offspring;
it might be good for you and
doesn't carry the sort of harm
that females,
on the other hand,
have to be very picky.
Because they have to choose
carefully.
Remember, these systems evolved
before birth control and
vasectomies and so on.
So, what do we know
cross-culturally and
psychologically?
Well, prostitution is a
universally, or near
universally, male interest.
There are male prostitutes,
of course, but contrary to some
various fantasies and sitcoms,
they cater to male customers.
Pornography is a human
universal.
In every society,
males have done some sort of
depictions of naked females for
the purposes of arousal.
Often they carve them into
trees or do sort of sculptures.
One of the weirdest findings in
the last decade or so is that
this extends as well to monkey
porn.
And so, some scientists at Duke
set up a situation where monkeys
could pay in fruit juice,
by giving up fruit juice,
to look a picture either of the
female's hindquarters or of a
celebrity monkey,
a socially dominant monkey,
some sort of combination of
People Magazine and
Penthouse.
And so, there's some interest
in this even by non-human
primates.
What about actually preference
for sexual variety?
Well, you can get at this in
different ways.
There is what biologists
describe as the "Coolidge
Effect."
I have this here.
And the Coolidge Effect is
based on President Calvin
Coolidge.
And it's a story about Calvin
Coolidge and his wife,
who were being shown around a
farm separately.
And the person showing around
his wife pointed out that there
were a lot of hens;
she noticed that there were a
lot of hens but only one
rooster.
And she asked the guy showing
her around, "Is one rooster
enough?"
And the guys said,
"Well, you know,
the rooster works very hard.
The rooster has sex dozens of
times a day."
And she said,
"Well, be sure to tell that to
the president."
The story goes,
the president went around,
the guy tells the story to the
president.
The president asks the man,
"Huh.
Has sex dozens of times each
day.
Same hen every time?"
The guy says,
"No, different hen every time."
And he says,
"Tell that to Mrs.
Coolidge."
Now, there are two responses to
this sort of story,
and they're both kind of
negative.
One thing is,
"Well, everybody knows males
prefer anonymous sex with
strange women.
Duh."
The other response is,
"That's sexist claptrap."
You might think--you might be a
male and say,
"That's not me."
You might know males and say,
"The males I know are not like
that."
So, how do you find out?
Well, there are indirect
measures, such who goes to
prostitutes.
But there are also fairly
direct measures.
One fairly direct measure is
you could ask people in
anonymous surveys.
So, in fact,
I'll give you some anonymous
surveys.
I'm not going to ask people.
And you just ask them.
So, for instance,
I want everybody to consider
this question.
How many sexual partners do you
want to have in the next month?
What is it--we're coming up to
April.
How many sexual partners do you
want in April?
Next two years?
Take many of you through
graduation.
When you leave Yale,
what do you want--like,
"I had X sexual partners,
and that's what I wanted."
Or your lifetime?
We get people to answer these
questions.
Professor Chun last year in
this course had clickers,
and he got people to do it.
We are not so high tech,
so we'll just do it in our
heads.
But here is the way the answers
come out.
Women say less than one in the
next month.
That doesn't mean they want
less than one;
that means many of them--many
of them say zero,
some say one and so on.
One--four to five.
Men--two, eight, eighteen.
You can ask other questions
from this population.
So, you could ask,
"Would you have sex with a
desirable partner you have
known--so somebody really
desirable--for a year;
women say yes,
six months--unsure,
week or less--no.
Men [laughter]--and with men
you could get a majority going
to five minutes.
This is all Q &
A, pen and pencil sort of
things.
Some brave scientists have
actually done experiments.
And in one experiment
somebody--I don't,
you know, this is the sort of
thing which you probably
wouldn't do nowadays.
This work has been done ten
years ago, where they have an
incredibly attractive man and an
incredibly attractive woman and
they approach people on campus.
They're not from campus;
they're actors brought in.
And they go to people,
to strangers,
and they say,
"I've been noticing you around
campus.
I find you very attractive.
Would you go out with me
tonight?
Would you come over to my
apartment tonight?
Would you go to bed with me
tonight?"
The experiment you wouldn't
think anybody would've done has
been done, and women about--a
very attractive man,
over half of the women
approached say,
"Yeah, I will."
Very few agree to this ["Would
you come to my apartment
tonight?"], and nobody agrees to
this ["Would you go to bed with
me tonight?"].
For men, the data are like
this, they go up to there and
then up to there .
In this study,
the twenty five percent of
males who said "no" apologized
profusely,
and they said,
"Oh, you know,
my fiancé's in town,
and [unintelligible]."
What about behavior?
Well, you--if we're interested
in sex differences,
you can't actually figure out
what people want,
male female differences,
by looking at simply at the
average number of times people
have sex because if males and
females have different
priorities,
then heterosexual sex is a
compromise between two groups of
people with competing interests.
What's a more clear reflection
then is gay sex between two
women or between two men,
because then you get a pure
reflection of sexual desire.
Now, the data here tend to be
very messy.
Again, they're survey studies
but by and large every study
done tends to find a difference
in the expected direction,
which is that females tend to
be--lesbians tend to be much
more monogamous than gay men.
Some studies prior to AIDS –
this was many years ago –
found gay men to be extremely
promiscuous,
often having over a hundred or
over a thousand partners.
You wouldn't find this sort of
promiscuity in females.
And a way to think about this
is, what these gay men are doing
is exactly what your average
heterosexual man would do if he
had that degree of willing
females who were as willing as
he was.
And this all suggests that
there's some sort of difference
along lines expected in sexual
choosiness in humans.
What about sexual
attractiveness?
What about mate preference?
What do we find attractive?
Well, unlike the choosiness
studies, here we actually have
some pretty good cross-cultural
data.
So one study,
for instance,
was done in 10,000 people from
thirty-seven countries,
asking people,
"Who do you want to be with?"
And there are different
studies, some of them asking,
"Who do you want to marry?"
Other studies,
"Who do you want as a mate?
Who do you want as a sexual
partner?"
And one main finding is kind of
reassuring, everybody likes
kindness and intelligence,
or at least everybody says they
like kindness and intelligence.
These are valued pretty highly.
But at the same time,
there are sex differences.
Females focus more on power and
status and more on interest in
investing in children.
And think about that from an
evolutionary point of view and
it makes sense.
It doesn't matter hugely,
from the standpoint of
reproduction,
how old the man is.
The difference between fifteen
and twenty-five and thirty-five
and forty-five may matter a lot
for his status in the community,
his physical strength,
his lifespan but from the
standpoint of his sperm it
doesn't matter hugely.
Later on there's a drop off and
it does begin to matter,
but it doesn't matter hugely.
What does matter is his
interest in being a good father,
in protecting you from
predation,
from murder,
from assault by other people,
and in taking care of the kid.
Women's brains are wired up to
find males with those
properties.
Similarly, males focus a little
bit differently.
They're more interested in all
of these things,
but also on the ability to have
children.
So, from an evolutionary point
of view, there's actually a very
big difference between a
twenty-year old and a fifty-year
old,
from a male standpoint looking
at a female, because the one can
have offspring and the other
cannot.
So, this is a difference.
But what I want to focus more
on right now is back to another
similarity.
Everybody likes beauty.
And I want to devote a little
bit of this lecture to talking
about physical beauty.
Physical beauty,
as these beautiful people say,
is a curse.
So she--she's like a big model,
a supermodel,
maybe even a
super-supermodel--points out the
arbitrariness of finding her
devastatingly beautiful.
Famous actor points out how
frustrating it is that people
only ignore his accomplishments
and focus merely on his physical
beauty.
This is very frustrating.
So what is beauty?
What does this mean we say we
find--you know,
yeah, they really are very
attractive people.
What is it about that that
makes you look and say,
"Yeah, that makes sense?"
Well, we kind of know the
answer.
We know some universals.
Beauty seems to signal two
things.
Beauty seems to signal youth--I
mean, not pre-school youth,
but youth like sexually mature
but young.
And so the cues we find
beautiful are cues to that –
large eyes, full lips,
smooth, tight skin.
Beauty signals something else.
Beauty is a marker for health.
And so what we find beautiful,
things like the absence of
deformities, clear eyes,
unblemished skin,
intact teeth – that's very
big – and an average face.
And that last part might seem a
little bit strange.
What would be so good about an
average face?
And there are different answers
to that, but one answer is,
an average face,
on average, should be
considered attractive because
any sort of deformities are
variations from the average.
And if you average every face
together, you get a face
that--where nothing bad has
happened to it.
There's no distortion,
there's no deviation.
As one gets older,
the face gets less symmetrical
and so on.
Average-ness seems to factor
out all the bad things that
could happen.
Good theory.
How do we know it's true?
Well, there's a photo roster
that comes--that I have access
to for this class.
So, I can look at each of your
pictures, and I will make you a
bet about who has the most
beautiful face in this course.
The bet is it would be all of
you.
Aw.
Wouldn't it be funny if I
shouted out somebody's name?
And you know,
A) I don't have the energy to
do this, and B) it would
probably violate four hundred
different privacy laws or
whatever.
But if I took all those faces
and morphed them together,
I would get a very pretty face.
And how do we know this?
Well, people have done this.
They've done it with--so look
at the faces from here to here.
And if you are like most
people, you see as you're going
to the right they're looking
better and better and better.
It's subtle,
but it's actually not so subtle
that babies don't notice it.
The same researchers who
constructed this--these
face--these average Caucasian
faces,
male and female,
have shown these faces to
babies and find that babies that
prefer to look at average
faces--suggesting that our
preference for averaging is not
the product of culture but
rather is to some extent
hard-wired.
These two people don't exist.
They're computer composites.
They're a heavily averaged male
face and a heavily averaged
female face, both from a
Caucasian data sample.
They don't look bad right?
They're good faces.
They don't cheat.
So the hair,
for instance,
is identical--so they
don't--you can't use hair cues.
But they're pretty attractive.
But the story of attractiveness
does not end there.
How do you get a better than
average face?
What can you do to these faces,
these average faces,
and make them look even better?
Well, I'll have a vote.
Who's prettier?
Who says the one on the right?
Who says the one on the left?
Left is average face,
and there might be variation in
this class.
There are definitely variations
in what people favor.
This is a feminized version of
the average face where certain
prototype features were made
more feminine than average to
cue this as more of a sexual
object.
This is more complicated.
Who thinks face A is more
attractive?
Who thinks face B is more
attractive?
Okay.
Most people like face B.
The exception is,
and this has been statistically
replicated, I think,
now in three labs.
Face A is preferred by women
who are ovulating,
and the story about why is
complicated and will take us
beyond the scope of this class.
But currently the idea is that
this is a really handsome guy;
he's young, he's healthy,
he looks strong,
good provider;
this guy is really hot,
and he may not be a good
provider and everything,
but I'm sure he has wonderful
genes.
So, the idea is that one should
have sex with him and then have
him raise the kids.
We've talked so far about
things, about sex and sexual
attractiveness largely from a
biological perspective,
looking at universals.
And in fact,
there are some universals in
what men and women have in
common and what distinguishes
men and women.
And in some of the sex
differences, particularly
related to aggression and mate
preference, seem to be
universal.
They seem to show up to some
extent across every culture you
look at and, hence,
are likely candidates for
biological adaptations.
But there are other sex
differences that people are
aware of where the origins are
far less clear.
And I think that intelligent,
reasonable people could
disagree about this,
but I am personally quite
skeptical about the extent to
which these reflect biology.
I'll mention them to capture
the debate, but the thing to
keep in mind here is that
biology,
natural selection,
is one reason why the men in
this class might differ from the
women in this class.
But of course,
there are other,
social, factors.
Babies are treated differently.
There have been many studies
where you take a baby and
swaddle it in blue and describe
it as a boy versus swaddle it in
pink and describe it as a girl,
and people treat it differently
when they think it's a boy than
when they think it's a girl.
You're treated differently too.
It matters a lot--and there's
study after study suggesting,
for instance,
that when you send an email or
a job application or a paper to
a scientific journal,
it matters whether it has the
name John Smith on it versus the
name Joan Smith.
It matters because people have
different expectations and
different reactions to males
versus females.
Some if you may have firsthand
experience with this if you're a
man with a name that could be
taken as a woman's name –
friend of mine is named Lynn,
and often people think he's
female – or if you're a woman
who has a name that could be
taken as a man's name,
or if you have a name
sufficiently foreign to Western
ears that people can't easily
tell.
You'll often find people
saying, "Oh," people are
high-fiving each other there
--you'll often find some degree
of surprise and some degree of
people saying,
"Oh my, I didn't know you were
a man.
Now I will treat you
differently."
And so, these social factors
could play a role in explaining
some male and female
differences.
Also, there are the facts of
gender self-segregation.
So here something very
interesting happens
developmentally.
Males segregate with other
males;
females segregate with other
females--for a period lasting,
it depends on the culture,
but say from age four to age
eleven.
This self-segregation might
exaggerate and enhance sex
differences.
It might be,
for instance,
as Eleanor Maccoby has
proposed, that boys are slightly
more aggressive than girls.
But then boys go into groups of
boys, and that enhances and
exaggerates their aggression
while the girls' non-aggressive
behavior is enhanced and
exaggerated in different ways by
them falling into girls' groups.
So, what sort of differences
are we talking about when we say
we're not sure of their cause?
Well, one difference is one in
empathy.
So Simon Baron-Cohen wrote a
wonderful book called The
Essential Difference where
he argues that men are by nature
less empathetic,
women are by nature more
empathetic, and that this is a
core sex difference.
So, what do you know?
Well, what's the source for
this?
One thing is men are more
violent.
Simon Baron-Cohen describes
violence as the ultimate
act--murder as the ultimate act
of a lack of empathy.
There's some relationship
between how much testosterone
you have in your system and how
social you are – more
testosterone,
less social.
Boys tend to be less empathetic
than girls, and there's some
evidence, though it's not
conclusive,
that boys do worse than girls
on social cognition theory of
mind tasks.
That's what I have here,
though that is quite debated.
And the biggest effect,
which isn't debated at all,
is problems with empathy,
problems of social cognition,
are much more frequent in men
than in women.
So, these disorders like
autism, Asperger's Syndrome,
conduct disorder and
psychopathy are predominately
male.
And Simon Baron-Cohen suggests
that--basically,
he has this slogan where he
says, "To be a man is to suffer
from a particularly mild form of
autism."
That males are just socially
clueless relative to women.
Final bit of trivia--This is
Simon Baron Cohen,
who is a very famous
developmental psychologist,
but his cousin Sasha Baron
Cohen is far more famous.
Another debate is a debate
concerning sex differences in
the capacity for math and
science.
A few years ago there used to
be a president of Harvard known
as Larry Summers.
There are so many reasons to
hiss at this point.
And Larry Summers is no longer
president of Harvard for various
reasons, but one reason was this
quote,
which included in his
speculations about sex
differences, "...in the special
case of science and engineering,
there are issues of intrinsic
aptitude, and particularly of
the variability of aptitude..."
He argued, or suggested,
that the under-representation
of women in the sciences in
academia is because of an
intrinsic aptitude difference;
women are, on average,
less biologically predisposed
to do this sort of reasoning.
The variability point is that
he wasn't suggesting that
there's just a difference on
average.
In fact, he agreed that the
average skills of men and women
are identical.
The claim is that males show
more variation.
This means that there are more
male retarded people and more
males who are just horribly bad
at this, but it also means there
are more male geniuses.
And he suggested that this
plays a role.
This, as you can imagine,
proved to be an extremely
controversial claim,
and rather than go through it
– because it would take me a
class to treat the pros and cons
of this argument responsibly –
I'm going to refer you to a
wonderful debate between Steve
Pinker,
who was quoted earlier,
and Liz Spelke who's one of the
big infant cognition people.
And we spoke a lot about her
work earlier on in the course.
And they have a wonderful
debate between two of the
smartest people I know on The
Edge,
which was done at Harvard about
a year ago and is on video here
.
So, if you're interested in sex
differences and different
theories about the mechanism of
sex differences,
this is where you should go.
Finally, and a final topic,
some of us, about 98%--and the
numbers are very difficult to
pin down.
Maybe it isn't 98%;
maybe it's ninety-seven,
maybe it's ninety-nine.
Let's say 98% of women are
sexually attracted to men.
About 96% of men are sexually
attracted to women.
And the numbers vary and it's
very difficult to estimate it
properly.
As you could imagine,
there are all sorts of problems
with this sort of research.
But there's some proportion of
the population that's
exclusively homosexual--some
proportion of the population of
men who are only attracted to
other men,
some proportion of the
population of women who are only
attracted to other women.
When people talk about sexual
orientation here,
it's important to realize we
are not talking here about
behavior.
There are all sorts of reasons
why somebody might have sex with
somebody of the same sex.
You know, they might be bored.
You may, you know,
be experimenting,
be whatever.
The question is,
"What do you want to do?"
All things being equal,
what sort of person--if you
could be sexually or
romantically involved with any
person, who would it be?
And most people are
heterosexual.
There's a considerable amount
that varies cross-culturally of
people who are bisexual.
But the real puzzle is
exclusive homosexuality.
So, why?
Well, nobody knows.
We know some reasons,
some answers are probably not
right.
It is not the case,
almost certainly – maybe
there are some exceptions –
but it is not the case that
people choose their sexual
orientation.
I'm not going to do this in
this room, but if you asked
people to raise their hands as
to how many people decided who
to become sexually attracted to,
very few people would.
Part of the issue rises in the
fact that people who are gay are
often extremely discriminated
against, and they have no wish
to be gay.
They might even think it's
morally wrong for them to be
that way.
That makes it implausible that
their sexual orientation is a
conscious choice.
What about experience after
puberty?
So, there is a view that keeps
coming up over and over again in
the literature that people who
are gay have in some sense been
seduced by people,
by other people--or something
happened to them afterwards.
This seems unlikely.
There are in particular the
seeds of sexual orientation
later on in life seem to show up
quite early in life.
Again, the studies are sort of
suspect, but there's some reason
to believe that people who are
gay and people who are straight
are different long before they
hit puberty with regard to their
sexual and romantic fantasies.
You would now expect me to say,
"Well, being gay and being
straight is built in.
It's hard-wired.
None of these stories seem
right.
It seems to be built in."
And the answer to that is,
sort of.
So, if you do the standard
behavioral genetic tests,
and you by now know how to do
them--you'd look for differences
between monozygotic and
dizygotic twins,
you'd do the adoption
comparison--you know adopted
siblings and biological
siblings.
The answer is yes,
you find that there is some
sort of genetic predisposition
towards homosexuality.
But it can't be entirely
genetic.
One reason why it can't be
entirely genetic is,
if I'm gay and I have an
identical twin,
the odds that my identical twin
will be gay--it's about fifty
percent.
Those are very high odds
compared to the average in the
population.
But if it was truly genetic,
entirely genetic,
what should the number be?
A hundred percent – he's my
clone.
He should be exactly as I am.
And it's not.
So, we know then that some sort
of experience,
possibly prenatal experience,
is what explains it.
Why is it so – I said before
this is a huge puzzle – why is
it such a huge puzzle?
Well, exclusive homosexuality
is an evolutionary mystery.
Again, do not think that this
carries any moral weight to it.
What it does mean though is
that it doesn't seem to follow
as a biological adaptation.
The puzzle is not why is it
that some men have sex with men.
That's not a big puzzle.
Maybe they have sex with men as
some sort of recreational things
or pair bonding or whatever.
That's not the puzzle.
The puzzle is why are there
some men who don't want to have
sex with women?
Similarly, why are there some
women who don't want to have sex
with men?
From an evolutionary adaptive
standpoint, you would think that
the genes that give rise to such
a behavior would be weeded out
because creatures with that
behavior typically,
putting aside modern
technology, don't have
offspring.
And that's what makes it such a
puzzle.
So, your reading response for
this week is "solve that
puzzle."
I know I said early on in the
course that reading responses
would be really easy and just
require you reciting back
things,
but that proved to be too
boring.
So, just solve this deepest of
all puzzle.
The thing in brackets at the
end is very important.
Your account,
whatever it is,
should bear some relationship
to the facts as discussed in
lectures and readings.
We have about five more minutes.
Any questions or thoughts?
Yes?
Student:
I like your leather jacket.
Professor Paul Bloom:
Thank you very much.
She likes my leather jacket.
Any questions or thoughts,
just like that one?
No.
Yes?
Student:
My question's not exactly like
that one, but in other animals
do they--is there similar data
on other species?
Professor Paul Bloom: On
sexual preferences?
That's a very good question
because certainly your answer to
the origin – give me two more
minutes – certainly your
answer about the origin of
sexual preference in humans will
be informed by the question of
cross-species data.
What we do know is that there
are many animals that engage in
homosexual behavior;
they engage in sex with members
of their own sex.
What I don't know is whether
you get exclusive homosexual
behavior.
So, I don't know what the rate
is in nonhuman primates,
for instance,
of primates who do not want to
have sex with members of the
opposite sex.
Okay, I'll see you all
Wednesday.
