August 21, 2023 • 46 mins
Why do briefly glimpsed people appear to be more attractive? Why did portrait photographers put Vaseline on their lenses, and what does that have to do with Instagram filters? Why are thirsty people more likely to perceive something as transparent? And what does any of that have to do with mating, optimal decision making, puberty, frogs, and movie stars? In this episode, Eagleman gets us to view the familiar as strange as we examine beauty, instincts, and what drives us.
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Speaker 1 (00:04):
Why do briefly glimpsed people appear to be more attractive?
Why did portrait photographers used to put vaciline on their
lenses and what does that have to do with Instagram filters?
Why are thirsty people more likely to perceive something as transparent?
And what does any of this have to do with
(00:25):
mating or optimal decision making or puberty or frogs or
instincts or movie stars. Welcome to another episode of Inner
Cosmos with me David Eagleman. I'm a neuroscientist and an
author at Stanford and in these episodes, we sail deeply
(00:45):
into our three pound universe to understand the relationship between
our brains and our lives. Throughout this podcast, we're gonna
try to gain a better understanding of ourselves by practicing
the technique of viewing the familiar as strange. We'll look
(01:09):
at instincts, things that we do naturally, so naturally that
we never even think to question them. But digging in
on these things is how we come to develop a
deeper understanding of ourselves. And today's episode is about the
absolutely fascinating topic about how our brains determine for us
(01:31):
what we find beautiful. So beauty is found all around us,
in nature and in art and in music, and a
good life is full of beautiful moments like a sunset
or a compliment or a child's smile. But our interest
today is in people, and specifically on the notion of attraction,
(01:52):
So the notion of the movie star whose next movie
you just can't wait to see, mostly because you find
that person just so magnetically good looking, or the work
made or the neighbor or the person you knew from
your childhood who's just so amazingly attractive. So what is
going on in the brain here, What are the signals
(02:13):
that tell you that person is attractive? And what does
all that have to do with the propagation of the species.
So let's get started. There are hundreds of ways that
a person can be attractive to you, based on their
with or their brawn, or their kindness or their dedication
to a cause or whatever. But what we're going to
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zoom in on today is about the first glimpse of someone,
the rapid assessment that takes your breath away, and that
magic moment is actually the end result of a great
deal of computation that your brain is doing under the hood. Now,
(02:55):
to start off, there's plenty of variation in what any
given person finds beautiful, and there's some amount of variation
across cultures too, in terms of how people dress and
how they act, and their bone structure and their facial
structure and all that. But what's interesting is that attractiveness
is not all in the eye of the beholder, and
(03:17):
beyond the personal and the cultural variations, some of the
most salient elements of attractiveness are hardwired. When researchers study attractiveness,
even cross culturally, they find a surprising concurrence in what
gets rated highly. There are particular things that draw us,
(03:40):
and mostly this has to do with largely unconscious signals
of health and fertility. And in a sense, you already
know this. Just look at the massive popularity of Instagram
and TikTok filters, which are used around the world. These
beautification filters aren't random. Instead, they move things in a
(04:00):
particular direction such that the photos look better to us,
and they work so much so that many young people
are totally unwilling to post photos without these filters in place.
So why what are these about? Let's look at this
from the point of view of biology. When you open
(04:20):
a biology textbook or watch a David Attenborough special, you
see bower birds or lions, or frogs, or butterflies or fish,
and you see these elaborate mating rituals. And of course,
being members of the animal kingdom, we can't pretend that
we don't have neural circuitry devoted to the same thing
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as well, because one of the most important drives for
all creatures, including humans, is mate selection. How an animal
chooses who to reproduce with. And we see this all
across the animal kingdom, with feathers, with colors, with pheromones,
with behavioral displays, all all creatures are trying to do
things to make themselves more attractive to mate with. Now
(05:05):
the question is how does this play out in humans.
Needless to say, the reason you exist is because every
single one of your ancestors successfully mate it. That's the
single reason that you are here. Our species is so
successful at reproduction that we've taken over the entire planet
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and the whole history of our species. Reproduction is driven
by attraction, judgments and issues of mate choice. Now, the
very first thing that blows my mind is how these
algorithms for finding something attractive get programmed into the genes,
which unfold the wiring of the brain and allow us
(05:47):
to grow up and have this attraction and sexual drive.
Because the weird thing is we inherit this psychological drive
for sexual interaction, but it doesn't kick in for years.
Is like thirteen years. So somehow the psychological machine code
is pre programmed genetically, but it gets archived for years
(06:11):
and years. So let's think about that. Everything that we
study in biology happens on the scale of milliseconds. You've
heard me talk about electrical spikes and neurons these last
one millisecond, and gene expression and chemical reactions and cells
and the CREB cycle and so on. All these things
are trucking along at the nanosecond time scale. So the
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idea of programming something out of this material that takes
thirteen years to unpack is mind blowing. Now, how do
we know that sexuality isn't something that's learned? Well, Sometimes
young children get damage to their brains, usually via an
infection that leads to encephalitis, and then they end up
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doing things that look like sexual acts, even though they're
too young to understand what they're doing. They end up
expressing these programs too early. And that's how we know
that these programs are in there, just waiting to be unpacked.
So for everyone else, for whom this program unpacks at
the right time. Once we've hit puberty, suddenly kids find
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themselves paying attention to body parts that they never paid
much attention to before. If you draw a curvy line
and show it to a seven year old boy and
ask him to describe what he sees, he'll describe it
as mountains or an ocean wave or something. But show
him this exact same curved line when he's thirteen, and
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he can't help but interpret the line as breasts and
buttocks and so on. Nothing changed in the outside world,
but his brain changed on the inside such that the
interpretation of the world changes. So we are hardwired. We're
preprogrammed to, at the right time be attracted to others,
like frogs to smell or by, or flies to colors,
(08:01):
or bower birds to a good nest and so on,
And suddenly it sucks up a lot of our mental energy.
And I'm stating the obvious here. This is because there
are few pressures as important as the evolutionary pressure to mate. Now,
something that's wild about this pre programming is that it
is very species specific. You don't find a horse's lips
(08:24):
kissable or a monkey's eyes something that you want to
gaze into romantically. But from a biologist's point of view,
they're not that different. They accomplish the same function using
the same machinery running on the same biological program. So
what's the difference. The difference is that you are pre
programmed to be mesmerized by the equipment of your own species,
(08:49):
and not by the wrong keys to a different lock,
even though they're so similar biologically. Now, note that to
the frog or the monkey or the turkey vulture, their
mate is the most magnetic thing in their world. You
could stand all day naked in front of a frog
and it just wouldn't care at all. It would have
zero interest in you. But if you stick the right
(09:12):
frog in front of it, that's the most wonderful, magnetic,
dizzying thing in the world, and they'll expend great effort
to get over there. So this notion of attractiveness drives everything,
But you typically don't have conscious access to the details
running under the hood. I mentioned in an earlier episode
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about the unconscious brain. An experiment in which men were
asked to rank the attractiveness of different women's faces and photographs.
So the men flipped through all these photographs and ranked
each one from one to ten. Unbeknownst to the men,
in half the photos the women's eyes were dilated, but
in the other half they weren't, and the men were
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consistently more attracted to the women with di dilated eyes.
But the men didn't have any insight into their decision making.
None of them said, oh, I noticed that her pupils
were two millimeters larger in this photo than this other one. Instead,
they simply felt more drawn towards some women than others,
for reasons they couldn't put a finger on. In the
(10:18):
largely inaccessible workings of their brains, something new that a
woman's dilated eyes correlates with sexual excitement. Their brains knew this,
but the men did not, not explicitly. They also presumably
didn't know that their feelings of attraction are deeply hardwired,
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steered in the right direction by programs carved over millions
of years of natural selection. So when the men were
picking up their pencil and making their choices, they didn't
know that the choice was not theirs. Really, but instead
the choice of successful programs that had been burned deep
into the brain's circuitry over the course of hundreds of
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thousands of generations. The great psychologist William James was one
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of the first to really point to the hidden nature
of instincts, and he suggested that we coax instincts into
the light by a simple mental exercise. Try to make
the natural theme strange by asking the why of any
instinctive human act. So I'm going to read you an
incredible passage that he wrote in eighteen ninety, and it
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goes like this quote, Why do we smile when pleased
and not scowl? Why are we unable to talk to
a crowd as we talk to a single friend. Why
does a particular maiden turn our wits so upside down?
The common man can only say, of course we smile.
Of course our heart palpitates at the sight of a crowd.
(12:08):
Of course we love the maiden, that beautiful soul clad
in the perfect form, so palpably and flagrantly made for
all eternity to be loved. And so probably does each
animal feel about the particular things it tends to do
in the presence of particular objects. To the lion. It
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is the lioness which is made to be loved to
the bear, the she bear to the bruty. Hen the
notion would probably seem monstrous that there would be a
creature in the world to whom a nest full of
eggs was not the utterly fascinating and precious, and never
to be too much sad upon object which it is
(12:49):
to her. Thus we may be sure that, however mysterious
some animal's instincts may appear to us, our instincts will
appear no less mysterious to them end quote. So our
most hardwired instincts have usually been left out of the
spotlight of inquiry because we don't think to ask them,
(13:11):
and because psychologists have spent a lot of time working
to understand uniquely human acts like higher cognition, or how
things go wrong like human mental disorders. But the most automatic,
effortless acts, those that require the most specialized in complex
neural circuitry, they've been in front of us all along,
(13:33):
and in the case of today's exploration, that's the notion
of sexual attraction. Now, before I get back to that,
I want to make a general neuroscience point. The more
obvious and effortless something seems, the more we need to
suspect that it seems that way only because of the
massive circuitry that's living behind it. Take something like seeing,
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the active seeing is so easy and rapid precisely because
we have so much circuitry dedicated to it. About a
third of the brain is devoted to vision. The more
effortless something seems, the more we can be pretty sure
that there's a lot of cycles being burned under the
hood to make it appear so. And the same principle
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applies to our sexual attractions. Our lust circuits are not
driven by the shiny faced frog because we cannot mate
with frogs and they have nothing to do with our
genetic future. On the other hand, we do care quite
a bit about subtle human body language, or the dilation
of eyes or the fleshing of skin, because those things
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broadcast important information about something that could impact our genetic future.
We live inside the fish bowl of our instincts, and
we typically have as little perception of them as the
fish does of its water. So our sense of beauty
and attraction is burned deeply and inaccessibly into the brain,
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all with the purpose of accomplishing something biologically useful. So
think about the most beautiful person you know, just magnetic,
just some shouldn't say kuhah. When that person walks into
the room. The geography of the room changes a bit
as everyone turns to look. Our brains are exquisitely honed
to pick up on those signals. Simply because of small
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details of symmetry and structure, that person enjoys a destiny
of greater popularity and faster promotions and a more successful career.
Our sense of attraction is not something just to be
studied by the pens of poets, but instead, our sense
of beauty results from specific signals that plug into dedicated
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neural software the key in the lock. So I'll share
with you some data, and this is all research that
scientists have performed in the laboratory and published peer reviewed
papers on. I will say that there seems to be
more literature on what males attractive. But keep in mind
that even though it's often said that males are more
visually driven, much of this research goes the other way too.
(16:08):
And if you hear this data and you think, well, wait,
what about our gay friends, keep in mind that the
drive of attraction is deeply built into our psychology, and
sometimes the gender someone is attracted to can switch, but
the fundamental drives in the brain remain the same. This
is because the drive to reproduce is really the most
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ancient brain circuitry we have, So even if someone does
not reproduce personally, they're still equipped with and driven by
the same circuitry which drives them towards sex. So let's
return to what I said at the beginning, which is
that the signals driving us are generally correlated with signals
of health and fertility. So until puberty, the faces and
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body shapes of boys and girls are essentially similar. But
the rise in estrogen in pubescent girls gives them fuller lifts,
while testosterone and boys produces a more prominent chin and
a larger nose and a fuller jaw. Estrogen causes the
growth of breasts and buttocks, while testosterone encourages the growth
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of muscles and broad shoulders. So for a female, full lips,
full buttocks, narrow waste. This broadcasts a clear message I'm
full of estrogen and fertile. For a male, it's the
full jaw, the stubble, the broad chest. This is the
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kind of stuff that we're programmed to find beautiful. The
external signs tell us something about the internal, and our
neural programs are so ingrained that there's not much variation
across the population. Researchers have measured a surprisingly narrow range
of the female proportions that males find most attractive. The
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optimal ratio between the waist and hips is typically between
point sixty seven and point eight. Back when Playboy centerfolds
were a thing, researchers studied those and found that their
waist hip ratios remained at about point seven over time,
even over the decades as the average weight of a
centerfold moved up or down. As women grow older, their
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features change in ways that depart from these proportions, their
middles sticking, their lips thin, their breasts sag, and so on,
all of which broadcasts the visual signal that they are
past peak fertility. So a young man ends up being
less attracted to an elderly woman than to a young
adult woman. His neural circuits have a clear mission reproduce,
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and his conscious mind receives only the need to know headline,
she's really attractive, and nothing more. All these computations are
performed unconsciously. Now, males are often more visually driven than females,
but women are nonetheless subject to the same internal forces.
They are drawn by the attractive features that flag the
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maturity of manhood. Now, an interesting twist is that a
woman's preferences can change depending on the time of month.
Women prefer masculine looking men when they're ovulating, but when
they're not ovulating, the data suggests that they prefer softer features,
which presumably flag more social and caring behavior. Although the
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programs of seduction and pursuit run almost entirely unconsciously, the
endgame is obvious to everyone, and this is why millions
of people shell out billions of dollars for facelifts and
tummy tucks and implants and light bosuction and botox. They're
working to tap into that strong correlation in other people's
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brains between their external and internal. They're working to maintain
the keys that unlock the pro programs in other people's brains. So,
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as I've said, we have almost no direct access into
the mechanics of our attractions. Instead, visual information plugs into
ancient neural modules that drive our behavior. Recall that experiment
that I just mentioned when men ranked the beauty of
women's faces. They found the women with dilated eyes more
attractive because dilated eyes signal sexual interest, but the men
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had no conscious access to their decision making process. Now
I'll give you another piece of data which is sort
of mind blowing and demonstrates how deeply and unconsciously we
pick up on signals. First, consider this strange fact that
human females are unique among primates and that they participate
in mating year round. They don't broadcast any special signal
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to publicize when they are fertile, and this is totally
different from other primates who have these periodic cycles of
being in heat. All other female mammals give off clear
signals when they're in heat. For example, in female babboons,
the rear end turns bright pink, which is an unmistakable
and irresistible invitation for a male baboon. Human females just
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don't give off signals like this, or don't they. It
turns out that a woman is considered to be most
beautiful just at the peak of fertility in her menstrual cycle,
about ten days before mensi's. This is true whether she
is judged by men or by women, and it's not
a matter of how she acts. It's perceived this way,
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even if people are just looking at her photograph, so
her good looks broadcast her level of fertility. Her signals
are more subtle than the baboons, but they only need
to be clear enough to tickle the dedicated, unconscious machinery
of the males in the room. If the signals can
reach those circuits, the mission is accomplished. The signals also
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reach the circuitry of other females. Women are quite sensitive
to the effect of other women's cycles, perhaps because this
lets them assess their competitors when competing for mates. It's
not yet clear what the tip offs for fertility are.
They may include some qualities of the skin, or the
fact that a women's ears and breasts become more symmetrical
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in the days leading up to ovulation. Whatever the constellation
of clues are, our brains are engineered to latch on.
Even while the conscious mind has no axis. Your mind
simply senses the almighty and inexplicable tug of desire. The
effects of ovulation and beauty are not not just assessed
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in the laboratory. They are measurable in real life situations.
Some years ago I'm not making this up. There was
a study by scientists who counted up the tips made
by exotic dancers at the local strip clubs and correlated
this with the menstrual cycles of the dancers. And what
they found is that during peak fertility, dancers raked in
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an average of sixty eight dollars an hour. When they
were menstruating, they earned only about thirty five dollars, and
in between they averaged about fifty two dollars. So although
these women were presumably acting flirtatiously throughout the month, their
change in fertility was broadcast to hopeful customers by changes
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in body odor, skin, wasted, hip ratio, and possibly their
own confidence as well. Now, interestingly, dancers on birth control
didn't show any clear peak in performance and earned only
a monthly average of thirty seven dollars per hour versus
an average of fifty three dollars per hour for dancers
not on birth control. Presumably they earned less because the
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pill leads to hormonal changes and cues indicative of early pregnancy,
and so the dancers were presumably slightly less magnetic to
the customers in the club. All this research drives home
the point that the pulls we feel are built deeply
into our neural machinery. We don't have conscious access to
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the programs and can only surface these issues with careful studies.
And the part that's always amazed me is how subtle
these signals are. The brain is picking up on these
really small signals. So think again about that really attractive
person you know, and imagine that you measured the distance
between his or her eyes and nose length and lip
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thickness and chin shape and so on. If you compare
those measurements to those of a a not so attractive
person you know, you would find that the differences are
really subtle, like a centimeter here, a centimeter there, But
it makes a big difference in your final judgment. So
imagine you took these two people, one attractive, one not
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so attractive, and showed them to a space alien. That
two humans would look indistinguishable to the alien in the
same way that attractive and unattractive space aliens would be
difficult for you to tell apart, But the small differences
within your own species, these have a great deal of
effect in your brain. As an example of tiny differences,
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just consider that some people might find the site of
a woman in short shorts intoxicating, and a male in
short shorts less attractive. Even though the two scenes are
hardly different. From a geometrical perspective, male and female legs
just don't look that different. Both are built on the
same architecture. They're both hinged limbs made of femurs and
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knee caps and skin and so on, and the differences
between them are swamped by the similarities. I mean, if
I showed you a female hawk and a male hawk,
you really couldn't tell the difference between them. But other
hawks are exquisitely sensitive to these differences. With all these animals,
they're so similar that you really have to train up
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to see the differences. And this is the point I
want to make. We are so exquisitely tuned to the
differences in humans, and we don't even realize it. Our
ability to make subtle distinctions is exquisitely fine grained. Our
brains are engineered to accomplish the clear cut task of
mate selection. In pursuit, all of the computation lives under
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the surface of conscious awareness. We get to simply enjoy
the lovely feelings that bubble up. And I'll give you
another example of this attractive misjudgments are not only constructed
by your visual system, but they're influenced as well by smell.
So odor carries a great deal of information, including information
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about a potential mate's age, sex, fertility, identity, emotions, health.
The information is carried by a flotilla of drifting molecules,
so in many animal species, these compounds drive behavior almost entirely.
In humans, the information often flies beneath the radar of
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conscious perception, but they nonetheless influence our behavior a bit.
So imagine we give a female mouse a selection of
males to mate with. Her choice is not random. Instead,
it's based on the interplay between her genetics and the
genetics of her suitors. But how in the world would
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she have access to that kind of hidden information about genetics.
While all mammals have a set of genes known as
the major histocompatibility complex or MHI, these genes are key
players in our immune systems, So given a choice, the
mouse will choose a mate with dissimilar MHC genes. Because
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mixing up the gene pool is almost always a good
idea in biology. It keeps genetic defects to a minimum
and leads to a healthy interplay of genes known as
hybrid vigor, So finding genetically distant partners is useful, But
how do mice who are largely blind pull this off
with their noses? An oregon inside their noses picks up
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on pheromones, which are floating chemicals that carry signals through
the air, signals about things like alarm or food trails,
or sexual readiness, or in this case, genetic similarity or difference.
Now do human sense and respond to pheromones the way
mice do? This is an area of debate in the
signe literature, but recent work has found receptors in the
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lining of the human nose just like those used in
pheromonal signaling and mice. It's not clear if our receptors
are functional, but the behavioral research is suggestive. So in
a study at the University of bern researchers measured and
quantified the MHCs of a group of male and female students.
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The males were then given cotton T shirts to wear
so that their daily sweat soaked into the fabric, and
then later back in the laboratory, females plunged their noses
into the armpits of these T shirts and picked which
body odor they preferred. The result was exactly like the
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mice they preferred the males with more dissimilar MHCs. So
apparently our noses also influenced our choices, again flying the
reproduction mission under the radar of consciousness. And I'll just
note that beyond reproduction, human pheromones may also carry invisible
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signals in other situations. For example, newborns preferentially move toward
pads that have been rubbed on their mother's breast rather
than clean pads, presumably based on pheromonal cues, and the
length of women's menstrual cycles may change after they sniff
the armpit sweat of another woman. So again, although pheromones
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clearly carry signals, the degree to which they influence human
behavior is unknown. Our cognition is so multilayered that these
cues have been reduced to bit players. Whatever other roles
they have, pheromones serve to remind us that the brain
is continuously evolving. These molecules unmask the presence of outdated
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legacy software. So all this led me to run some
studies on attractiveness in my laboratory, And this puts us
back to the question that I posed at the beginning,
which is what is going on when you first look
at a person and make some rapid judgment about their attractiveness.
Human faces carry an enormous amount of information about emotional
state and physical well being, and we are programmed to
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read faces like books. And in this light, it is
not surprising that we rapidly form initial impressions about someone
after a brief exposure. And one trait we extract unbelievably
quickly is facial attractiveness. And you've probably noticed that sometimes
a person passes by you for just a moment and
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your brain screams out that that person is highly attractive,
and then you turn and you take a closer look
and realize that your first judgment was actually wrong, and
your attractiveness rating goes way down. So I started asking
a number of people about this years ago and found
that this was a common experience if you pay close
to tension to your perception. So I started to wonder,
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is a briefly glimpsed person always more attractive, and if so,
what is that about from an neural point of view,
Because there's obviously less visual information that's harvested from a
brief glimpse. So my student Don Vaughan, and I started
researching this because here's the question. It is not at
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all clear why the brain would consistently AerR in one
direction in its attractiveness judgments. In other words, why would
a briefly glimpsed face tend to be interpreted as more
attractive instead of less. After all, in most tasks of
information processing, less information translates to less confidence and less value.
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You wouldn't pay more for a car that you knew
less about. So we had fifty nine people participate in
the study, half female, half male. Average age was twenty
eight years old, and everyone rated photographs of either seventy
five female seventy five mails. So you look at the
computer screen and a photograph is flashed, and all you
need to do is rate the photograph on a scale
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from one which is least attractive to ten most attractive,
and then you see the next one in the next one,
and you do this through all the photographs in random order.
But here's the thing. First, you do this with twenty
five photographs to just acquaint you with the rating scale
and for us to gather your average ratings. You get
to look at each photo for as long as you
want no time pressure. Then in the second block, we
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use twenty five new photographs, and here you keep your
eyes fixed on a red dot in the center of
the screen, and after a random delay, a photograph gets
flashed in the center of the screen for about a
quarter of a second. Bang, real fast flash, and you
register your attractiveness judgment. Then in the next block, you
rate the same photographs, again presented in a random order,
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but this time with no time constraints. You can look
for as long as you want. Then to recreate the
effective catching a glimpse from the corner of your eye,
we also ran a block where we presented photographs in
your peripheral vision. So we use twenty five new photographs
and it's the same as before, where you're keeping your
eye on the red dot in the middle, but now
we flash the photograph in a random position somewhere on
(34:15):
the screen. Bang. What was that? By the time your
eyes get there, it's gone, and then you register your
attractiveness rating. Then in the final block, you rate those
same twenty five photographs represented in the center in a
random order with no time constraints. Okay, so what was
the result? Briefly glimpsed photographs are rated as more beautiful
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everyone this, male and female rated attractiveness higher when they
were just catching a glimpse, whether that was in the
middle or on the periphery, so we summarized this result
as the glimpse effect. For example, when a male saw
a flash of a female in the periphery, he rated
her on average almost a point higher than when he
looked for as long as he wanted. And as a
(35:01):
side note, although both females and males show the glimpse
effect when judging photographs of either gender, the effect is
most pronounced in males rating female photographs. And by the way,
this is true no matter what your initial rating was,
it goes down when you have a longer chance to look. So.
In other words, if you catch a glimpse of someone
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rounding the corner or driving past quickly, your perceptual system
will tell you that they are more attractive than you
would otherwise judge them to be. Men show this effect
more strongly, presumably because men are more visual in assessing attraction.
When you catch a brief glimpse of someone, you believe
you have just seen something amazing. Then when you go
(35:43):
around the corner you find you were mistaken. So the
glimpse effect is clear and measurable. But why does it happen.
Why should the visual system, given just a bit of
fleeting information, always err on the side of believing that
someone is more attractive in the absence of clear data,
Why wouldn't your visual system simply strike for the middle
(36:04):
and judge the person to be average or even below average.
So one way you explain these results is to think
about what's called spatial frequencies. Something with high spatial frequency
is changing a lot across space, while low spatial frequency
doesn't change much. So think about it like if you
had a lot of wrinkles, All those sharp lines provide
(36:25):
a lot of high spatial frequency, but if your face
is totally smooth, that's low spatial frequency. Anyhow, it's long
been known that faces that come across as smoother are
rated as more attractive. We don't really like the high
spatial frequencies, the sharp lines and so on, and the
visual system actually takes more time to process the fine lines,
(36:49):
while the low frequency stuff is processed very rapidly. So
when we flash of photograph really quickly, your visual system
doesn't have access to the fine features that decrease ratings
like skin blemishes, because your visual system is just processing
the general shape of the smooth stuff going on. And
this explains something about the way that portrait photography used
(37:11):
to be done, especially in the earlier part of last century.
How did photographers make people more attractive by putting vaciline
on their camera lenses that created a soft focus effect
that blurred the image to create what people regarded as
a romantic look. But of course what they were doing
(37:32):
was taking away information, taking away the sharp lines, in
particular the high spatial frequencies, and just leaving the soft,
dreamy stuff, which we find more attractive. Now we don't
use vacline on lenses anymore, or don't we. That's exactly
the trick with these Instagram filters. What these filters generally
(37:53):
do is simply take away the high spatial frequencies. It's
like the vaciline on the lens. No more little imperfections.
Now you just have perfectly smooth skin for completeness. Soil
also mention that these filters often do other things as well,
like make lips bigger, because fertile women have full lips,
but they don't when they're kids. Or elderly. Okay, so
(38:17):
back to the big picture of the glimpse effect. We
know that in a brief presentation you see less of
the fine lines, and so maybe that's the explanation. But
we also suggested there may be something to understand that's
even a little bit deeper. So we proposed a second,
non exclusive possibility, and this hypothesis pivots on the demands
(38:39):
of reproduction. If you believe that a briefly glimpsed person
is beautiful, and let's say they actually weren't, it only
requires a double take on your part to correct the mistake.
It's not much of a cost. But on the other hand,
if you mistake an attractive mate for an unattractive one,
you can say cyonara to your potentially rosy the genetic future.
(39:01):
So it behooves your perceptual system to serve up a
story that a briefly glimpsed person is attractive. So the
idea is that the glimpse effect results from the combination
of your sensory information with the utility of that information
for the cognizanty. This is known as a Bayesian risk model.
(39:22):
As an example of this sort of thing, imagine looking
at a square of a certain color that's against squares
of other colors, you might conclude that the square has
a certain color, or you could equally conclude that the
square is transparent and its color is being determined by
the squares underneath it. So if you're asked, is this
(39:45):
transparent or not, there's no single right answer. But it
turns out what's found in the laboratory is that if
you are thirsty, you are more likely to perceive it
as transparent. Your visual system has a bi towards determining
transparent things like water when you're thirsty. If you're not thirsty,
(40:06):
you're not seeing water everywhere. Why it's because thirsty people
have an increased utility for water. Finding water becomes more
valuable to your brain, and if you accidentally see water
when it's not there, what's called a false positive that
doesn't matter so much. In other words, it behooves a
thirsty brain to have a bias towards perceiving things that
(40:27):
are water like. And this is the same idea here
with the glimpse effect. Your brain doesn't want to miss
its genetic future, so it has a bias towards seeing
things as attractive. If you're interested in this topic. There's
a field known as Bayesian decision making, and the idea
is that your brain is not seeing maximum likelihood, as in,
(40:51):
how likely is that driver next to me super attractive? Instead,
it's aimed at maximizing expected utility. How useful is it
for me to see things in this way? So in
this framework, an ideal observer chooses the interpretation that's the
most important rather than the most likely. So what we
(41:11):
get is an increase in perceived attractiveness when you have
limited information. And again, this is because the cost of
an overestimate is cheap you just look a second time,
but the cost of failing to identify an attractive potential
mate is high. So what I told you about vacoline
and Instagram filters is explainable just by getting rid of
(41:32):
the high frequencies the sharp lines. But I think more generally,
this issue of limited information is an important part of
what's in play here because during the pandemic I talked
with a lot of colleagues who work at the Stanford Hospitals,
for example, and it turns out that the world ran
a very interesting natural experiment from twenty twenty to twenty
(41:54):
two in the form of wearing masks. The masks don't
changeange anything about the high and low frequency information, but
they take away all the information about one half of
the face. And I heard from a lot of people,
both male and female, that they sometimes met coworkers whose
face they had never seen completely and stead they only
(42:15):
ever saw the top half, and they felt that the
person was really attractive. And at the end of the pandemic,
when the masks finally came off and they finally saw
the whole face, they were often a little disappointed. Now,
was this because everyone had ugly mouths? No, it was
because the brain of the viewer made assumptions about the
(42:37):
half of the face that was not seen. I've informally
quizzed dozens of people about this, and it wasn't that
they assumed something in particular, something they could articulate about
the other person's mouth. It's not like they were looking
for a specific shape of the mouth. It's just that
they assumed that it would be better. Again, when there's
(42:57):
a lack of information, the brain it seems to make
a judgment that's biased in the positive direction. It just
assumes there's something better hiding behind the curtain. It's all
about anticipation, and in an upcoming episode about prediction, I'm
going to talk about why the most attractive person on
a nude beach is the one who still has their
(43:20):
clothes on. If you've ever been on a clothing optional beach,
you'll know that everyone, men and women end up gazing
towards the new person, the man or woman who's just arrived,
because there's anticipation about what is going to be found there.
There's a lack of information because they still have their
clothes on, and so your brain assumes the best. But
(43:42):
moments after that person disrobes, everyone's sort of over it.
The internal positive assumptions have been replaced by reality. And
we can see the same issue of this optimistic judging
with the size of photographs. A lot of people find
that when they're looking at some is Twitter profile or
TikTok profile or LinkedIn photo, you think they look quite attractive,
(44:05):
and then you click on the photo to make it bigger,
and your assessment goes down. I've run some initial studies
on this with small photographs and large photographs, and this
is what we find. If a photo is small and
you can't work out any details, you judge it as
being higher in attractiveness. Now, this may again have to
do with your inability to make out the small details
(44:27):
in a small photo, but it also amounts to the
same thing in space as the glimpse effect. In time.
The lack of information leads to more dependence on your
internal model, and our models tend to be hopeful. So
let's wrap up. We know that across the biological kingdom
there is a constant broadcasting of signals that most often
(44:50):
we don't even have conscious access to. But as we
dive deeper and deeper over the course of these episodes
into all the computations happening under the hood that we
don't have access to, we will see this vast empire
of instincts that we've perhaps never even thought to question.
We all find that it's obvious that we are more
(45:10):
attracted to someone versus someone else. Of course, we're attracted
who wouldn't be, And as William James pointed out, presumably
every animal feels this way about the particular things that
tends to do. As he said to the lion, it
is the lioness which is made to be loved to
the bear, the she bear, but the technique that allows
us to really see ourselves is to be able to
(45:33):
view the familiar as strange. With a little bit of work,
we can step outside our internal models and see ourselves
from a new angle. Today we talked about the instinct
of attraction, and in future episodes we're going to see
how deeply our instincts drive us in other domains, and
how invisible these things are until we scratch the surface.
(45:57):
Making the familiar strange is perhaps the only way to
really come to understand ourselves and to illuminate the enigmas
inside our three pound inner cosmos. To find out more
and to share your thoughts, head over to eagleman dot
(46:17):
com slash podcast. Send me an email at podcast at
eagleman dot com with questions or discussion, and I'll be
making an episode soon in which I address those. Until
next time, I'm David Eagleman, and this is Inner Cosmos.
Why do briefly glimpsed people appear to be more attractive?
Why did portrait photographers used to put vaciline on their
lenses and what does that have to do with Instagram filters?
Why are thirsty people more likely to perceive something as transparent?
And what does any of this have to do with
(00:25):
mating or optimal decision making or puberty or frogs or
instincts or movie stars. Welcome to another episode of Inner
Cosmos with me David Eagleman. I'm a neuroscientist and an
author at Stanford and in these episodes, we sail deeply
(00:45):
into our three pound universe to understand the relationship between
our brains and our lives. Throughout this podcast, we're gonna
try to gain a better understanding of ourselves by practicing
the technique of viewing the familiar as strange. We'll look
(01:09):
at instincts, things that we do naturally, so naturally that
we never even think to question them. But digging in
on these things is how we come to develop a
deeper understanding of ourselves. And today's episode is about the
absolutely fascinating topic about how our brains determine for us
(01:31):
what we find beautiful. So beauty is found all around us,
in nature and in art and in music, and a
good life is full of beautiful moments like a sunset
or a compliment or a child's smile. But our interest
today is in people, and specifically on the notion of attraction,
(01:52):
So the notion of the movie star whose next movie
you just can't wait to see, mostly because you find
that person just so magnetically good looking, or the work
made or the neighbor or the person you knew from
your childhood who's just so amazingly attractive. So what is
going on in the brain here, What are the signals
(02:13):
that tell you that person is attractive? And what does
all that have to do with the propagation of the species.
So let's get started. There are hundreds of ways that
a person can be attractive to you, based on their
with or their brawn, or their kindness or their dedication
to a cause or whatever. But what we're going to
(02:35):
zoom in on today is about the first glimpse of someone,
the rapid assessment that takes your breath away, and that
magic moment is actually the end result of a great
deal of computation that your brain is doing under the hood. Now,
(02:55):
to start off, there's plenty of variation in what any
given person finds beautiful, and there's some amount of variation
across cultures too, in terms of how people dress and
how they act, and their bone structure and their facial
structure and all that. But what's interesting is that attractiveness
is not all in the eye of the beholder, and
(03:17):
beyond the personal and the cultural variations, some of the
most salient elements of attractiveness are hardwired. When researchers study attractiveness,
even cross culturally, they find a surprising concurrence in what
gets rated highly. There are particular things that draw us,
(03:40):
and mostly this has to do with largely unconscious signals
of health and fertility. And in a sense, you already
know this. Just look at the massive popularity of Instagram
and TikTok filters, which are used around the world. These
beautification filters aren't random. Instead, they move things in a
(04:00):
particular direction such that the photos look better to us,
and they work so much so that many young people
are totally unwilling to post photos without these filters in place.
So why what are these about? Let's look at this
from the point of view of biology. When you open
(04:20):
a biology textbook or watch a David Attenborough special, you
see bower birds or lions, or frogs, or butterflies or fish,
and you see these elaborate mating rituals. And of course,
being members of the animal kingdom, we can't pretend that
we don't have neural circuitry devoted to the same thing
(04:42):
as well, because one of the most important drives for
all creatures, including humans, is mate selection. How an animal
chooses who to reproduce with. And we see this all
across the animal kingdom, with feathers, with colors, with pheromones,
with behavioral displays, all all creatures are trying to do
things to make themselves more attractive to mate with. Now
(05:05):
the question is how does this play out in humans.
Needless to say, the reason you exist is because every
single one of your ancestors successfully mate it. That's the
single reason that you are here. Our species is so
successful at reproduction that we've taken over the entire planet
(05:25):
and the whole history of our species. Reproduction is driven
by attraction, judgments and issues of mate choice. Now, the
very first thing that blows my mind is how these
algorithms for finding something attractive get programmed into the genes,
which unfold the wiring of the brain and allow us
(05:47):
to grow up and have this attraction and sexual drive.
Because the weird thing is we inherit this psychological drive
for sexual interaction, but it doesn't kick in for years.
Is like thirteen years. So somehow the psychological machine code
is pre programmed genetically, but it gets archived for years
(06:11):
and years. So let's think about that. Everything that we
study in biology happens on the scale of milliseconds. You've
heard me talk about electrical spikes and neurons these last
one millisecond, and gene expression and chemical reactions and cells
and the CREB cycle and so on. All these things
are trucking along at the nanosecond time scale. So the
(06:33):
idea of programming something out of this material that takes
thirteen years to unpack is mind blowing. Now, how do
we know that sexuality isn't something that's learned? Well, Sometimes
young children get damage to their brains, usually via an
infection that leads to encephalitis, and then they end up
(06:53):
doing things that look like sexual acts, even though they're
too young to understand what they're doing. They end up
expressing these programs too early. And that's how we know
that these programs are in there, just waiting to be unpacked.
So for everyone else, for whom this program unpacks at
the right time. Once we've hit puberty, suddenly kids find
(07:16):
themselves paying attention to body parts that they never paid
much attention to before. If you draw a curvy line
and show it to a seven year old boy and
ask him to describe what he sees, he'll describe it
as mountains or an ocean wave or something. But show
him this exact same curved line when he's thirteen, and
(07:38):
he can't help but interpret the line as breasts and
buttocks and so on. Nothing changed in the outside world,
but his brain changed on the inside such that the
interpretation of the world changes. So we are hardwired. We're
preprogrammed to, at the right time be attracted to others,
like frogs to smell or by, or flies to colors,
(08:01):
or bower birds to a good nest and so on,
And suddenly it sucks up a lot of our mental energy.
And I'm stating the obvious here. This is because there
are few pressures as important as the evolutionary pressure to mate. Now,
something that's wild about this pre programming is that it
is very species specific. You don't find a horse's lips
(08:24):
kissable or a monkey's eyes something that you want to
gaze into romantically. But from a biologist's point of view,
they're not that different. They accomplish the same function using
the same machinery running on the same biological program. So
what's the difference. The difference is that you are pre
programmed to be mesmerized by the equipment of your own species,
(08:49):
and not by the wrong keys to a different lock,
even though they're so similar biologically. Now, note that to
the frog or the monkey or the turkey vulture, their
mate is the most magnetic thing in their world. You
could stand all day naked in front of a frog
and it just wouldn't care at all. It would have
zero interest in you. But if you stick the right
(09:12):
frog in front of it, that's the most wonderful, magnetic,
dizzying thing in the world, and they'll expend great effort
to get over there. So this notion of attractiveness drives everything,
But you typically don't have conscious access to the details
running under the hood. I mentioned in an earlier episode
(09:34):
about the unconscious brain. An experiment in which men were
asked to rank the attractiveness of different women's faces and photographs.
So the men flipped through all these photographs and ranked
each one from one to ten. Unbeknownst to the men,
in half the photos the women's eyes were dilated, but
in the other half they weren't, and the men were
(09:56):
consistently more attracted to the women with di dilated eyes.
But the men didn't have any insight into their decision making.
None of them said, oh, I noticed that her pupils
were two millimeters larger in this photo than this other one. Instead,
they simply felt more drawn towards some women than others,
for reasons they couldn't put a finger on. In the
(10:18):
largely inaccessible workings of their brains, something new that a
woman's dilated eyes correlates with sexual excitement. Their brains knew this,
but the men did not, not explicitly. They also presumably
didn't know that their feelings of attraction are deeply hardwired,
(10:39):
steered in the right direction by programs carved over millions
of years of natural selection. So when the men were
picking up their pencil and making their choices, they didn't
know that the choice was not theirs. Really, but instead
the choice of successful programs that had been burned deep
into the brain's circuitry over the course of hundreds of
(11:01):
thousands of generations. The great psychologist William James was one
(11:23):
of the first to really point to the hidden nature
of instincts, and he suggested that we coax instincts into
the light by a simple mental exercise. Try to make
the natural theme strange by asking the why of any
instinctive human act. So I'm going to read you an
incredible passage that he wrote in eighteen ninety, and it
(11:46):
goes like this quote, Why do we smile when pleased
and not scowl? Why are we unable to talk to
a crowd as we talk to a single friend. Why
does a particular maiden turn our wits so upside down?
The common man can only say, of course we smile.
Of course our heart palpitates at the sight of a crowd.
(12:08):
Of course we love the maiden, that beautiful soul clad
in the perfect form, so palpably and flagrantly made for
all eternity to be loved. And so probably does each
animal feel about the particular things it tends to do
in the presence of particular objects. To the lion. It
(12:28):
is the lioness which is made to be loved to
the bear, the she bear to the bruty. Hen the
notion would probably seem monstrous that there would be a
creature in the world to whom a nest full of
eggs was not the utterly fascinating and precious, and never
to be too much sad upon object which it is
(12:49):
to her. Thus we may be sure that, however mysterious
some animal's instincts may appear to us, our instincts will
appear no less mysterious to them end quote. So our
most hardwired instincts have usually been left out of the
spotlight of inquiry because we don't think to ask them,
(13:11):
and because psychologists have spent a lot of time working
to understand uniquely human acts like higher cognition, or how
things go wrong like human mental disorders. But the most automatic,
effortless acts, those that require the most specialized in complex
neural circuitry, they've been in front of us all along,
(13:33):
and in the case of today's exploration, that's the notion
of sexual attraction. Now, before I get back to that,
I want to make a general neuroscience point. The more
obvious and effortless something seems, the more we need to
suspect that it seems that way only because of the
massive circuitry that's living behind it. Take something like seeing,
(13:54):
the active seeing is so easy and rapid precisely because
we have so much circuitry dedicated to it. About a
third of the brain is devoted to vision. The more
effortless something seems, the more we can be pretty sure
that there's a lot of cycles being burned under the
hood to make it appear so. And the same principle
(14:16):
applies to our sexual attractions. Our lust circuits are not
driven by the shiny faced frog because we cannot mate
with frogs and they have nothing to do with our
genetic future. On the other hand, we do care quite
a bit about subtle human body language, or the dilation
of eyes or the fleshing of skin, because those things
(14:37):
broadcast important information about something that could impact our genetic future.
We live inside the fish bowl of our instincts, and
we typically have as little perception of them as the
fish does of its water. So our sense of beauty
and attraction is burned deeply and inaccessibly into the brain,
(15:00):
all with the purpose of accomplishing something biologically useful. So
think about the most beautiful person you know, just magnetic,
just some shouldn't say kuhah. When that person walks into
the room. The geography of the room changes a bit
as everyone turns to look. Our brains are exquisitely honed
to pick up on those signals. Simply because of small
(15:23):
details of symmetry and structure, that person enjoys a destiny
of greater popularity and faster promotions and a more successful career.
Our sense of attraction is not something just to be
studied by the pens of poets, but instead, our sense
of beauty results from specific signals that plug into dedicated
(15:45):
neural software the key in the lock. So I'll share
with you some data, and this is all research that
scientists have performed in the laboratory and published peer reviewed
papers on. I will say that there seems to be
more literature on what males attractive. But keep in mind
that even though it's often said that males are more
visually driven, much of this research goes the other way too.
(16:08):
And if you hear this data and you think, well, wait,
what about our gay friends, keep in mind that the
drive of attraction is deeply built into our psychology, and
sometimes the gender someone is attracted to can switch, but
the fundamental drives in the brain remain the same. This
is because the drive to reproduce is really the most
(16:28):
ancient brain circuitry we have, So even if someone does
not reproduce personally, they're still equipped with and driven by
the same circuitry which drives them towards sex. So let's
return to what I said at the beginning, which is
that the signals driving us are generally correlated with signals
of health and fertility. So until puberty, the faces and
(16:50):
body shapes of boys and girls are essentially similar. But
the rise in estrogen in pubescent girls gives them fuller lifts,
while testosterone and boys produces a more prominent chin and
a larger nose and a fuller jaw. Estrogen causes the
growth of breasts and buttocks, while testosterone encourages the growth
(17:14):
of muscles and broad shoulders. So for a female, full lips,
full buttocks, narrow waste. This broadcasts a clear message I'm
full of estrogen and fertile. For a male, it's the
full jaw, the stubble, the broad chest. This is the
(17:34):
kind of stuff that we're programmed to find beautiful. The
external signs tell us something about the internal, and our
neural programs are so ingrained that there's not much variation
across the population. Researchers have measured a surprisingly narrow range
of the female proportions that males find most attractive. The
(17:57):
optimal ratio between the waist and hips is typically between
point sixty seven and point eight. Back when Playboy centerfolds
were a thing, researchers studied those and found that their
waist hip ratios remained at about point seven over time,
even over the decades as the average weight of a
centerfold moved up or down. As women grow older, their
(18:21):
features change in ways that depart from these proportions, their
middles sticking, their lips thin, their breasts sag, and so on,
all of which broadcasts the visual signal that they are
past peak fertility. So a young man ends up being
less attracted to an elderly woman than to a young
adult woman. His neural circuits have a clear mission reproduce,
(18:45):
and his conscious mind receives only the need to know headline,
she's really attractive, and nothing more. All these computations are
performed unconsciously. Now, males are often more visually driven than females,
but women are nonetheless subject to the same internal forces.
They are drawn by the attractive features that flag the
(19:08):
maturity of manhood. Now, an interesting twist is that a
woman's preferences can change depending on the time of month.
Women prefer masculine looking men when they're ovulating, but when
they're not ovulating, the data suggests that they prefer softer features,
which presumably flag more social and caring behavior. Although the
(19:30):
programs of seduction and pursuit run almost entirely unconsciously, the
endgame is obvious to everyone, and this is why millions
of people shell out billions of dollars for facelifts and
tummy tucks and implants and light bosuction and botox. They're
working to tap into that strong correlation in other people's
(19:52):
brains between their external and internal. They're working to maintain
the keys that unlock the pro programs in other people's brains. So,
(20:23):
as I've said, we have almost no direct access into
the mechanics of our attractions. Instead, visual information plugs into
ancient neural modules that drive our behavior. Recall that experiment
that I just mentioned when men ranked the beauty of
women's faces. They found the women with dilated eyes more
attractive because dilated eyes signal sexual interest, but the men
(20:47):
had no conscious access to their decision making process. Now
I'll give you another piece of data which is sort
of mind blowing and demonstrates how deeply and unconsciously we
pick up on signals. First, consider this strange fact that
human females are unique among primates and that they participate
in mating year round. They don't broadcast any special signal
(21:11):
to publicize when they are fertile, and this is totally
different from other primates who have these periodic cycles of
being in heat. All other female mammals give off clear
signals when they're in heat. For example, in female babboons,
the rear end turns bright pink, which is an unmistakable
and irresistible invitation for a male baboon. Human females just
(21:34):
don't give off signals like this, or don't they. It
turns out that a woman is considered to be most
beautiful just at the peak of fertility in her menstrual cycle,
about ten days before mensi's. This is true whether she
is judged by men or by women, and it's not
a matter of how she acts. It's perceived this way,
(21:54):
even if people are just looking at her photograph, so
her good looks broadcast her level of fertility. Her signals
are more subtle than the baboons, but they only need
to be clear enough to tickle the dedicated, unconscious machinery
of the males in the room. If the signals can
reach those circuits, the mission is accomplished. The signals also
(22:17):
reach the circuitry of other females. Women are quite sensitive
to the effect of other women's cycles, perhaps because this
lets them assess their competitors when competing for mates. It's
not yet clear what the tip offs for fertility are.
They may include some qualities of the skin, or the
fact that a women's ears and breasts become more symmetrical
(22:40):
in the days leading up to ovulation. Whatever the constellation
of clues are, our brains are engineered to latch on.
Even while the conscious mind has no axis. Your mind
simply senses the almighty and inexplicable tug of desire. The
effects of ovulation and beauty are not not just assessed
(23:00):
in the laboratory. They are measurable in real life situations.
Some years ago I'm not making this up. There was
a study by scientists who counted up the tips made
by exotic dancers at the local strip clubs and correlated
this with the menstrual cycles of the dancers. And what
they found is that during peak fertility, dancers raked in
(23:24):
an average of sixty eight dollars an hour. When they
were menstruating, they earned only about thirty five dollars, and
in between they averaged about fifty two dollars. So although
these women were presumably acting flirtatiously throughout the month, their
change in fertility was broadcast to hopeful customers by changes
(23:45):
in body odor, skin, wasted, hip ratio, and possibly their
own confidence as well. Now, interestingly, dancers on birth control
didn't show any clear peak in performance and earned only
a monthly average of thirty seven dollars per hour versus
an average of fifty three dollars per hour for dancers
not on birth control. Presumably they earned less because the
(24:10):
pill leads to hormonal changes and cues indicative of early pregnancy,
and so the dancers were presumably slightly less magnetic to
the customers in the club. All this research drives home
the point that the pulls we feel are built deeply
into our neural machinery. We don't have conscious access to
(24:32):
the programs and can only surface these issues with careful studies.
And the part that's always amazed me is how subtle
these signals are. The brain is picking up on these
really small signals. So think again about that really attractive
person you know, and imagine that you measured the distance
between his or her eyes and nose length and lip
(24:54):
thickness and chin shape and so on. If you compare
those measurements to those of a a not so attractive
person you know, you would find that the differences are
really subtle, like a centimeter here, a centimeter there, But
it makes a big difference in your final judgment. So
imagine you took these two people, one attractive, one not
(25:15):
so attractive, and showed them to a space alien. That
two humans would look indistinguishable to the alien in the
same way that attractive and unattractive space aliens would be
difficult for you to tell apart, But the small differences
within your own species, these have a great deal of
effect in your brain. As an example of tiny differences,
(25:36):
just consider that some people might find the site of
a woman in short shorts intoxicating, and a male in
short shorts less attractive. Even though the two scenes are
hardly different. From a geometrical perspective, male and female legs
just don't look that different. Both are built on the
same architecture. They're both hinged limbs made of femurs and
(25:59):
knee caps and skin and so on, and the differences
between them are swamped by the similarities. I mean, if
I showed you a female hawk and a male hawk,
you really couldn't tell the difference between them. But other
hawks are exquisitely sensitive to these differences. With all these animals,
they're so similar that you really have to train up
(26:21):
to see the differences. And this is the point I
want to make. We are so exquisitely tuned to the
differences in humans, and we don't even realize it. Our
ability to make subtle distinctions is exquisitely fine grained. Our
brains are engineered to accomplish the clear cut task of
mate selection. In pursuit, all of the computation lives under
(26:44):
the surface of conscious awareness. We get to simply enjoy
the lovely feelings that bubble up. And I'll give you
another example of this attractive misjudgments are not only constructed
by your visual system, but they're influenced as well by smell.
So odor carries a great deal of information, including information
(27:05):
about a potential mate's age, sex, fertility, identity, emotions, health.
The information is carried by a flotilla of drifting molecules,
so in many animal species, these compounds drive behavior almost entirely.
In humans, the information often flies beneath the radar of
(27:27):
conscious perception, but they nonetheless influence our behavior a bit.
So imagine we give a female mouse a selection of
males to mate with. Her choice is not random. Instead,
it's based on the interplay between her genetics and the
genetics of her suitors. But how in the world would
(27:48):
she have access to that kind of hidden information about genetics.
While all mammals have a set of genes known as
the major histocompatibility complex or MHI, these genes are key
players in our immune systems, So given a choice, the
mouse will choose a mate with dissimilar MHC genes. Because
(28:12):
mixing up the gene pool is almost always a good
idea in biology. It keeps genetic defects to a minimum
and leads to a healthy interplay of genes known as
hybrid vigor, So finding genetically distant partners is useful, But
how do mice who are largely blind pull this off
with their noses? An oregon inside their noses picks up
(28:40):
on pheromones, which are floating chemicals that carry signals through
the air, signals about things like alarm or food trails,
or sexual readiness, or in this case, genetic similarity or difference.
Now do human sense and respond to pheromones the way
mice do? This is an area of debate in the
signe literature, but recent work has found receptors in the
(29:03):
lining of the human nose just like those used in
pheromonal signaling and mice. It's not clear if our receptors
are functional, but the behavioral research is suggestive. So in
a study at the University of bern researchers measured and
quantified the MHCs of a group of male and female students.
(29:25):
The males were then given cotton T shirts to wear
so that their daily sweat soaked into the fabric, and
then later back in the laboratory, females plunged their noses
into the armpits of these T shirts and picked which
body odor they preferred. The result was exactly like the
(29:46):
mice they preferred the males with more dissimilar MHCs. So
apparently our noses also influenced our choices, again flying the
reproduction mission under the radar of consciousness. And I'll just
note that beyond reproduction, human pheromones may also carry invisible
(30:08):
signals in other situations. For example, newborns preferentially move toward
pads that have been rubbed on their mother's breast rather
than clean pads, presumably based on pheromonal cues, and the
length of women's menstrual cycles may change after they sniff
the armpit sweat of another woman. So again, although pheromones
(30:32):
clearly carry signals, the degree to which they influence human
behavior is unknown. Our cognition is so multilayered that these
cues have been reduced to bit players. Whatever other roles
they have, pheromones serve to remind us that the brain
is continuously evolving. These molecules unmask the presence of outdated
(30:55):
legacy software. So all this led me to run some
studies on attractiveness in my laboratory, And this puts us
back to the question that I posed at the beginning,
which is what is going on when you first look
at a person and make some rapid judgment about their attractiveness.
Human faces carry an enormous amount of information about emotional
state and physical well being, and we are programmed to
(31:19):
read faces like books. And in this light, it is
not surprising that we rapidly form initial impressions about someone
after a brief exposure. And one trait we extract unbelievably
quickly is facial attractiveness. And you've probably noticed that sometimes
a person passes by you for just a moment and
(31:40):
your brain screams out that that person is highly attractive,
and then you turn and you take a closer look
and realize that your first judgment was actually wrong, and
your attractiveness rating goes way down. So I started asking
a number of people about this years ago and found
that this was a common experience if you pay close
to tension to your perception. So I started to wonder,
(32:02):
is a briefly glimpsed person always more attractive, and if so,
what is that about from an neural point of view,
Because there's obviously less visual information that's harvested from a
brief glimpse. So my student Don Vaughan, and I started
researching this because here's the question. It is not at
(32:23):
all clear why the brain would consistently AerR in one
direction in its attractiveness judgments. In other words, why would
a briefly glimpsed face tend to be interpreted as more
attractive instead of less. After all, in most tasks of
information processing, less information translates to less confidence and less value.
(32:46):
You wouldn't pay more for a car that you knew
less about. So we had fifty nine people participate in
the study, half female, half male. Average age was twenty
eight years old, and everyone rated photographs of either seventy
five female seventy five mails. So you look at the
computer screen and a photograph is flashed, and all you
need to do is rate the photograph on a scale
(33:08):
from one which is least attractive to ten most attractive,
and then you see the next one in the next one,
and you do this through all the photographs in random order.
But here's the thing. First, you do this with twenty
five photographs to just acquaint you with the rating scale
and for us to gather your average ratings. You get
to look at each photo for as long as you
want no time pressure. Then in the second block, we
(33:30):
use twenty five new photographs, and here you keep your
eyes fixed on a red dot in the center of
the screen, and after a random delay, a photograph gets
flashed in the center of the screen for about a
quarter of a second. Bang, real fast flash, and you
register your attractiveness judgment. Then in the next block, you
rate the same photographs, again presented in a random order,
(33:53):
but this time with no time constraints. You can look
for as long as you want. Then to recreate the
effective catching a glimpse from the corner of your eye,
we also ran a block where we presented photographs in
your peripheral vision. So we use twenty five new photographs
and it's the same as before, where you're keeping your
eye on the red dot in the middle, but now
we flash the photograph in a random position somewhere on
(34:15):
the screen. Bang. What was that? By the time your
eyes get there, it's gone, and then you register your
attractiveness rating. Then in the final block, you rate those
same twenty five photographs represented in the center in a
random order with no time constraints. Okay, so what was
the result? Briefly glimpsed photographs are rated as more beautiful
(34:39):
everyone this, male and female rated attractiveness higher when they
were just catching a glimpse, whether that was in the
middle or on the periphery, so we summarized this result
as the glimpse effect. For example, when a male saw
a flash of a female in the periphery, he rated
her on average almost a point higher than when he
looked for as long as he wanted. And as a
(35:01):
side note, although both females and males show the glimpse
effect when judging photographs of either gender, the effect is
most pronounced in males rating female photographs. And by the way,
this is true no matter what your initial rating was,
it goes down when you have a longer chance to look. So.
In other words, if you catch a glimpse of someone
(35:22):
rounding the corner or driving past quickly, your perceptual system
will tell you that they are more attractive than you
would otherwise judge them to be. Men show this effect
more strongly, presumably because men are more visual in assessing attraction.
When you catch a brief glimpse of someone, you believe
you have just seen something amazing. Then when you go
(35:43):
around the corner you find you were mistaken. So the
glimpse effect is clear and measurable. But why does it happen.
Why should the visual system, given just a bit of
fleeting information, always err on the side of believing that
someone is more attractive in the absence of clear data,
Why wouldn't your visual system simply strike for the middle
(36:04):
and judge the person to be average or even below average.
So one way you explain these results is to think
about what's called spatial frequencies. Something with high spatial frequency
is changing a lot across space, while low spatial frequency
doesn't change much. So think about it like if you
had a lot of wrinkles, All those sharp lines provide
(36:25):
a lot of high spatial frequency, but if your face
is totally smooth, that's low spatial frequency. Anyhow, it's long
been known that faces that come across as smoother are
rated as more attractive. We don't really like the high
spatial frequencies, the sharp lines and so on, and the
visual system actually takes more time to process the fine lines,
(36:49):
while the low frequency stuff is processed very rapidly. So
when we flash of photograph really quickly, your visual system
doesn't have access to the fine features that decrease ratings
like skin blemishes, because your visual system is just processing
the general shape of the smooth stuff going on. And
this explains something about the way that portrait photography used
(37:11):
to be done, especially in the earlier part of last century.
How did photographers make people more attractive by putting vaciline
on their camera lenses that created a soft focus effect
that blurred the image to create what people regarded as
a romantic look. But of course what they were doing
(37:32):
was taking away information, taking away the sharp lines, in
particular the high spatial frequencies, and just leaving the soft,
dreamy stuff, which we find more attractive. Now we don't
use vacline on lenses anymore, or don't we. That's exactly
the trick with these Instagram filters. What these filters generally
(37:53):
do is simply take away the high spatial frequencies. It's
like the vaciline on the lens. No more little imperfections.
Now you just have perfectly smooth skin for completeness. Soil
also mention that these filters often do other things as well,
like make lips bigger, because fertile women have full lips,
but they don't when they're kids. Or elderly. Okay, so
(38:17):
back to the big picture of the glimpse effect. We
know that in a brief presentation you see less of
the fine lines, and so maybe that's the explanation. But
we also suggested there may be something to understand that's
even a little bit deeper. So we proposed a second,
non exclusive possibility, and this hypothesis pivots on the demands
(38:39):
of reproduction. If you believe that a briefly glimpsed person
is beautiful, and let's say they actually weren't, it only
requires a double take on your part to correct the mistake.
It's not much of a cost. But on the other hand,
if you mistake an attractive mate for an unattractive one,
you can say cyonara to your potentially rosy the genetic future.
(39:01):
So it behooves your perceptual system to serve up a
story that a briefly glimpsed person is attractive. So the
idea is that the glimpse effect results from the combination
of your sensory information with the utility of that information
for the cognizanty. This is known as a Bayesian risk model.
(39:22):
As an example of this sort of thing, imagine looking
at a square of a certain color that's against squares
of other colors, you might conclude that the square has
a certain color, or you could equally conclude that the
square is transparent and its color is being determined by
the squares underneath it. So if you're asked, is this
(39:45):
transparent or not, there's no single right answer. But it
turns out what's found in the laboratory is that if
you are thirsty, you are more likely to perceive it
as transparent. Your visual system has a bi towards determining
transparent things like water when you're thirsty. If you're not thirsty,
(40:06):
you're not seeing water everywhere. Why it's because thirsty people
have an increased utility for water. Finding water becomes more
valuable to your brain, and if you accidentally see water
when it's not there, what's called a false positive that
doesn't matter so much. In other words, it behooves a
thirsty brain to have a bias towards perceiving things that
(40:27):
are water like. And this is the same idea here
with the glimpse effect. Your brain doesn't want to miss
its genetic future, so it has a bias towards seeing
things as attractive. If you're interested in this topic. There's
a field known as Bayesian decision making, and the idea
is that your brain is not seeing maximum likelihood, as in,
(40:51):
how likely is that driver next to me super attractive? Instead,
it's aimed at maximizing expected utility. How useful is it
for me to see things in this way? So in
this framework, an ideal observer chooses the interpretation that's the
most important rather than the most likely. So what we
(41:11):
get is an increase in perceived attractiveness when you have
limited information. And again, this is because the cost of
an overestimate is cheap you just look a second time,
but the cost of failing to identify an attractive potential
mate is high. So what I told you about vacoline
and Instagram filters is explainable just by getting rid of
(41:32):
the high frequencies the sharp lines. But I think more generally,
this issue of limited information is an important part of
what's in play here because during the pandemic I talked
with a lot of colleagues who work at the Stanford Hospitals,
for example, and it turns out that the world ran
a very interesting natural experiment from twenty twenty to twenty
(41:54):
two in the form of wearing masks. The masks don't
changeange anything about the high and low frequency information, but
they take away all the information about one half of
the face. And I heard from a lot of people,
both male and female, that they sometimes met coworkers whose
face they had never seen completely and stead they only
(42:15):
ever saw the top half, and they felt that the
person was really attractive. And at the end of the pandemic,
when the masks finally came off and they finally saw
the whole face, they were often a little disappointed. Now,
was this because everyone had ugly mouths? No, it was
because the brain of the viewer made assumptions about the
(42:37):
half of the face that was not seen. I've informally
quizzed dozens of people about this, and it wasn't that
they assumed something in particular, something they could articulate about
the other person's mouth. It's not like they were looking
for a specific shape of the mouth. It's just that
they assumed that it would be better. Again, when there's
(42:57):
a lack of information, the brain it seems to make
a judgment that's biased in the positive direction. It just
assumes there's something better hiding behind the curtain. It's all
about anticipation, and in an upcoming episode about prediction, I'm
going to talk about why the most attractive person on
a nude beach is the one who still has their
(43:20):
clothes on. If you've ever been on a clothing optional beach,
you'll know that everyone, men and women end up gazing
towards the new person, the man or woman who's just arrived,
because there's anticipation about what is going to be found there.
There's a lack of information because they still have their
clothes on, and so your brain assumes the best. But
(43:42):
moments after that person disrobes, everyone's sort of over it.
The internal positive assumptions have been replaced by reality. And
we can see the same issue of this optimistic judging
with the size of photographs. A lot of people find
that when they're looking at some is Twitter profile or
TikTok profile or LinkedIn photo, you think they look quite attractive,
(44:05):
and then you click on the photo to make it bigger,
and your assessment goes down. I've run some initial studies
on this with small photographs and large photographs, and this
is what we find. If a photo is small and
you can't work out any details, you judge it as
being higher in attractiveness. Now, this may again have to
do with your inability to make out the small details
(44:27):
in a small photo, but it also amounts to the
same thing in space as the glimpse effect. In time.
The lack of information leads to more dependence on your
internal model, and our models tend to be hopeful. So
let's wrap up. We know that across the biological kingdom
there is a constant broadcasting of signals that most often
(44:50):
we don't even have conscious access to. But as we
dive deeper and deeper over the course of these episodes
into all the computations happening under the hood that we
don't have access to, we will see this vast empire
of instincts that we've perhaps never even thought to question.
We all find that it's obvious that we are more
(45:10):
attracted to someone versus someone else. Of course, we're attracted
who wouldn't be, And as William James pointed out, presumably
every animal feels this way about the particular things that
tends to do. As he said to the lion, it
is the lioness which is made to be loved to
the bear, the she bear, but the technique that allows
us to really see ourselves is to be able to
(45:33):
view the familiar as strange. With a little bit of work,
we can step outside our internal models and see ourselves
from a new angle. Today we talked about the instinct
of attraction, and in future episodes we're going to see
how deeply our instincts drive us in other domains, and
how invisible these things are until we scratch the surface.
(45:57):
Making the familiar strange is perhaps the only way to
really come to understand ourselves and to illuminate the enigmas
inside our three pound inner cosmos. To find out more
and to share your thoughts, head over to eagleman dot
(46:17):
com slash podcast. Send me an email at podcast at
eagleman dot com with questions or discussion, and I'll be
making an episode soon in which I address those. Until
next time, I'm David Eagleman, and this is Inner Cosmos.
Host
David Eagleman
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