Stanford University. --started. See some exam-related
announcements. First off, there are the
statistics, mean and median, which, in terms of
numbers and what they mean-- what
they mean in my book is that people are doing
a good job in here. So, good going. Also having done an amazing
job are the TAs, who, other than coming to
class here, have not been allowed out of
the conference room since you left your
exams with them. They have screamed with the
repetitiveness of grading the same question 550 times. And they worked really hard
to get this back to you guys in time for
decisions about pass, no credit-- that sort of thing. So these guys did yet
another amazing job. [APPLAUSE AND CHEERS] Yay, TAs. Let's see. The other thing is, the
exams will be outside, at the end of class. A to M is upstairs, and
the rest of those letters are downstairs. So start figuring
out which you are. The TAs will be flinging boxes
of exams around out there, so go get yours afterward. Again, people did a good job. OK, picking up on our by now
sickeningly familiar time core strategy thing, here,
we left off on Friday, way to the left, in our very
last area of sexual behavior and the logic there is--
ooh, somewhere along the way we mentioned genes,
or we mentioned a hormone, or a receptor,
or whatever, and thus were immediately talking
about the evolution thereof, all the way back. What does natural
selection theory tell us about the evolution
of sexual behavior? And what we've been
doing is bouncing between the two genders,
in terms of strategies, starting off with
the basic asymmetry of caloric expenditure on sperm
versus an egg plus a pregnancy, plus, in most species,
raising the offspring. All of that giving rise
to the famed promiscuity on the part of males-- the
lower levels of pickiness. What we saw was the role
of male-male competition and making sense
of behaviors that are involved in passing
on more copies of genes. We have also seen all
sorts of male strategies for decreasing the reproductive
success of competitors and, in the same
process, decreasing that of females for the future. And female counterstrategies
in a lot of those cases. What we also then
transitioned to was what female choice
was about, even in species that were tournament species. And what we transition
to now is looking at aspects of
female-female competition, in terms of sexual reproduction. What you see is--
predominantly in species that are pair-bonding,
that are monogamous-- what you see is the
potential for a great deal of female-female competition
for access to males. That ironic turn
of events where, if the whole system
works-- where you give birth and
the guy who believes he's the father is going to
be taken care of the kids, and what you want is
someone who is good at that, is confident at that, can act
maternal in a convincing way, and thus is subject to a
whole lot of competition on the part of females. And thus what you get
is selection pressures in those species-- New World
monkeys, for example-- a lot of bird species--
selection pressures. Where, if anything,
it's the females who wind up being more
aggressive than the males. The females who tend
to have the larger body size, who have the
more pronounced secondary sexual
characteristics. What's that about? It's females competing with
females for males to pick them, exactly the opposite scenario
as in most of the species we've been hearing about. OK. What this then brings us to
is the next great question, which already I've
had a lot of people ask me during breaks-- all
the way back way there, in terms of making
sense of the evolution of this type of sexual
behavior and that type and the other type, in terms of
passing on copies of your genes and you and your
relatives-- all of that. Which brings you, inevitably,
to the question of, well, what about the evolution
of homosexuality? Because this has
always been the puzzle in the book of zoologist,
evolutionary biologist, et cetera, trying
to make sense of all of this in the
context of adaptation and passing on copies of
genes, especially when you see how widespread this
is in lots and lots and lots of other species. What's up with that? Because, up until
relatively recent times, across virtually every
culture out there, gay men had a much fewer
number of copies of genes, on the average, that
they were passing on. How could this trait
to be so universal? And best estimates are 5% to
20% rate in every human culture ever looked at. So what's the
selection for that? Or why hasn't that
been selected against? Basically, there's
been three theories that have floated around. And all of them are predicated
on one very simple fact that still is not all
that factual, which is that there is a
genetic component to one's sexual orientation. And we already heard all
sorts of bits of evidence about prenatal endocrine
environment that argues in other directions. We have already heard that there
have been those studies which find covariance of
sexual orientation in identical twins
versus nonidentical-- finding a genetic marker,
but one that nobody else is able to replicate. So everything now is
predicated on the notion that, well, genes have at
least a little bit of something to do with it. So, three theories that
have floated around, first one being the
heterozygotic-vigor argument. Lots of folks will
recognize that from other realms of genetics. That's the deal where you
can have certain traits which can be in the homozygotic form
or in the heterozygotic form. And people who are
new to this, go back and check your notes from
the Mendel genetics catch-up sections. And what you see is,
with lots of diseases you get an extreme version
is indeed a disease and a partial version
is, in fact, adaptive. And the classic example
that always gets trotted out is sickle-cell anemia--
full-blown homozygotic version, horrible hematological disorder;
partial, heterozygotic version, resistance to malaria and a
gazillion diseases out there. And what's done
is metaphorically running the same argument of
saying, whatever gene genes are relevant, maybe the
homozygotic form is the one that produces a
behavioral phenotype which decreases reproductive success. But there's some
heterozygotic form which has some huge advantage
and enough of one to outweigh the one-fourth of the
relatives who wind up with the homozygotic version. So that's one model, for which
there is very little evidence. Next one. Next one is a gender-dependent
genetic argument, as follows. It is a trait. It is a genetically
influenced trait which, when expressed
in one gender, is maladaptive and decreases
reproductive success. But when it is expressed
in the other gender, it is highly adaptive and
increases reproductive success. And you can immediately run
your numbers argument there that, as long as the benefits
for the other kind of sibling or gender is larger
than the detriment here, this is going to
be selected for. What would that look like? Where is the evidence for that? What one would predict is that
you would see, for gay men, that their sisters have
a higher-than-average reproductive rate. And that is absolutely
there in the literature. So the people who push
for this view would say, aha, there is some sort
of trait which, in a male, increases the likelihood,
manifesting as homosexuality in a female, as some
route by which there is increased reproductive success. The third model is the
"helper at the nest" model, which is that the individual
who traditionally is not passing on copies
of their own genes directly-- instead,
what they're doing is expending resources on
helping their siblings. OK, so that kind of sounds
like the second model, also. What's the difference? The second model says
that sisters of gay men should have increased
reproductive rates. What the third model--
the "helping at the nest" model-- suggests is,
both sisters and brothers should have increased
reproductive rates. And that's actually
what's mostly been seen. So, support for this "helper
at the nest" kin-selection kind of argument. OK. What else does one look
for in a mate, besides all of the stuff that males
are competing about and females in
pair-bonding species? What are some of the
characteristics that pop up over and over again,
when it's getting around to who looks good to you, if
you are a damselfly trying to pick out a mate, and in
all these other species? One initial
characteristic, which is the famed role of facial
symmetry in attractiveness. This has an interesting
history, and this goes back to the 19th century. And there was some
guy-- who was it? It was Francis Galton. Was it? Maybe. And it was Francis
Galton, I think, who was having--
no, it couldn't be. They didn't have-- forget that. Don't write that down. There was some guy in
the 19th century who was a famous criminologist and
was pushing a classic nonsense theory of the time, which is
that there is a criminal face and that people who are really
skilled police people could to look at somebody's face
beforehand and immediately predict that this is
someone who is going to commit a criminal
act, inevitably, at some-- all sorts of nonsense. Genetic determinism and
racism and [INAUDIBLE] biases of all sorts
running through there. Complete nonsense-- yet one
of the dominant intellectual models in criminology
in the 19th century was that there are facial
characteristics that are typical of criminals. So this was this individual
who decided to come up with the archetypal face of
what a criminal looks like and managed to get photographs
of the faces of a whole bunch of different criminals,
pulling them out of the jail or whatever and taking a picture
with the newly invented camera. And, through some technique that
clearly was some proto Adobe Photoshop sort of
ancestor thing, was able to overlap the
faces in order to come up with a composite face. And this composite face
was now going to tell you, this is the most
criminal-looking face that anybody has ever seen. And that's not what happened. Instead, everybody
looked at that face and said, hey, that guy's
kind of good-looking! That guy is, in fact,
really good-looking. And had just stumbled on
this interesting thing that, when you average faces, when
you toss them all together, that when you merge
them, they look more attractive
than the individuals that they came from-- when
you make composite pictures. And this has kept all sorts of
people happy doing experiments where they do mixes and
matches of starting with 100 different pictures of people
and combine subsets of them and having people rating
attractiveness and stuff. And it's this absolutely
bizarre thing-- that the more faces that go
into a composite, the more, on the average, people perceive
them as being attractive, amid incredibly
subtle differences between a composite picture
of 50 faces versus 25, all of that, people are able to
pick up the differences-- not necessarily consciously. So what is that about? And what became clear,
many decades later, is that what happens
when you make a lot of faces all
into one composite is you get a highly
symmetrical face. And this seems to be the
key thing that comes through in that realm of attractiveness. Which is that, when you average
in a whole lot of faces, one of the things you average
is the averageness of the face. And you get rid of asymmetries. And everyone knows that-- who
would you want to mate with? [LAUGHTER] OK, so, thereby
proving the point. And what you've got is,
symmetry is apparently a good, reliable
marker of health. Wildly asymmetric
faces are typically the result of complications--
developmental ones-- health sort of issues. So the general interpretation
is that symmetry is attractive because it is a
marker of health. And every single
article you will ever read in sort of the
lay press-- or even in some of the science
journals, which should be above
this sort of thing-- will have the picture of some
famously attractive somebody or other, with
the face up there, and all the little caliper
markings, and showing the same sizes, and then
some poor schnook who's chosen to be the asymmetric
face who's stuck up there. Did the Newsweek article wind
up being in the readings? No, it wasn't-- yes. OK. Lyle Lovett-- is that
the face they had there that they were making vicious
fun of and pointing out lip asymmetries and such? Something about the symmetry
seems to be a marker for health and is considered
more attractive. And people can pick up
astonishingly subtle asymmetries in faces. Babies, at two
months of age, show-- when you are doing
morphed faces, composite faces, where you
can very minorly adjust the degree of symmetry or
asymmetry in the face-- babies, at two months of
age, are already preferring to look at pictures
of more symmetrical faces. You find this in lots of
other species, as well. When you look at
animals lever-pressing-- rats, for example,
getting access to other rats of
the opposite gender. And you will see there's
a bias for symmetry there. There is a bias in
nonhuman primates for more symmetrical faces. How's this for a
nutty study that was published about five
years ago, in Nature? And this one reported that
people who had symmetrical faces were better dancers. OK, let's work through that one. What was that one about? And they did-- it
was a bizarre study, but somehow, nonetheless,
it was irresistible. Here's what they showed. They filmed all sorts
of people dancing. And, no doubt, they
did perfect controls and they, like,
made sure everybody danced to the same
thing, which was, like-- oh, I don't
know-- something-- a scientist rapping
to something or other. And people dancing away, there. And then they used
this amazing technique, which I didn't understand
in the slightest, with some sort of
camera-capture technique that would make everybody
dancing look like Gumby. So you took out all the
individual features-- anything at all. And people would then
rate them on the dancing. And it would turn
out that people who were rated by both
genders, of either gender, as being a better
dancer, when you then went and checked out
their faces afterward, with your slide rule, turned out
to have more symmetrical faces. Whoa! Isn't that bizarre? My guess would be that this is
one of those indirect routes that we've already
seen some examples of. My guess would be,
more symmetrical faces are thus more attractive,
and thus such people are treated better and
are more confident in life and more extroverted and
more comfortable dancing when they knew that
they were going to wind up looking like Gumby. So that is probably what
the indirect route is. But running through all of
this is this symmetry business. And it's there in
species after species. And humans are amazing at
picking up subtleties at it. One additional finding in
the symmetry world-- women at the time that
they are ovulating have their faces become ever
so slightly more symmetrical. [COMMENTS AMONG STUDENTS] OK, well, that's
going to get people all nutsy in the
coming weeks, no doubt, trying to figure out
what that's about. I did not see a good explanation
as to what that was about, but that has been observed
in the literature. So the first thing,
in terms of what one looks for in
a mate, if you're some basic social animal-- first
set of features, this business about symmetry. Next realm-- this whole
world of secondary sexual characteristics. Why is it that female
peacocks like male peacocks to look like male peacocks,
and all that sort of thing? What is that about? And people have been working
with this one for years. And there is a
zoologist named Zahavi who has been very influential--
Israeli zoologist-- who came up with what is called
the "handicap principle." As follows. Why is it that secondary sexual
characteristics are appealing? Characteristics that exaggerate
the difference in appearance by gender. Why is that appealing? Because, in effect, the bigger
and more garish and the more over-the-top your secondary
sexual characteristic is, the more you were
communicating to the world, I have so much energy on
board, and I am so healthy, that I can afford to squander
massive numbers of calories on these asinine neon antlers
I'm walking around with. That it's an argument
there that this is a display of, in a sense,
conspicuous consumption-- the ability to put energy into
these large secondary sexual characteristics. That these are markers of health
and of good immune systems. Lots of evidence for this. And this is, by now, a whole
field that people have studied. One version of it. These were studies done
with marsupial mice. And there was
something having to do with their marsupialesque
reproduction that made this the species
to do this with. But it was doing sperm
insemination of females. And what was done was
that they took the sperm from these male marsupial
mice, after measuring some secondary sexual
characteristics in them. I believe that they
don't have antlers, but I don't remember what
the actual thing was. And what they were
able to do was to now have sperm from
males of differing degrees of exaggerated
secondary characteristics. And what they showed
was that the males who had the more dramatic secondary
characteristics-- their sperm were more fertile. So that was a first big vote
in this handicap principle that things like
secondary appearances, secondary sexual ones,
can be a marker for health and/or fertility. Now why should that be? What you essentially are seeing
there is, it is a display. It is a potlatch. It is a display
of how much energy you can afford to waste
and thus how much you must have on board. It is a marker of health
and good immunity. This has been shown
in lots of studies. Along the lines
of, the same sort of signals that give rise to the
secondary sexual characteristic are markers of immune function. A well-functioning
immune system will be generating some
molecule which exaggerates facial coloration. And that's the secondary
sexual characteristic-- that there is an explicit
link between immune function, immune competence,
and these markers. Interesting. A study that just
came out recently, looking at women from,
I believe it was, about 20 different
industrialized countries. And what was shown was
that, in general, women have a preference
for faces of men that have strong pronounced
secondary characteristics-- which is, big, jutting
jaw, high forehead, lots of muscle stuff going on. And what they showed was that
the longer the life expectancy in the particular country,
the better the economy, the better the quality of life,
the less women in that country had a bias towards
male-looking males. Which is extremely interesting. What's the comparison there? It was all those, like,
Scandinavian countries. Thank god for the
Scandinavian countries, because they always provide the
extreme of these distributions. So, in those
Scandinavian countries, like, there has not
been a guy who's been, like, selected for a date
because of the height of his forehead, in centuries. Whereas what they showed was,
in a lot of other cultures-- which were the ones who were
most extreme on the list, I am not remembering,
which is not very helpful. But a very different
sort of end of things. And there, much stronger
selection for what are viewed as traits, as
markers of fecundity and health. More evidence about this. What you see is, all of this
is a signal-- all of this is a signal, not only in terms
of who you want to mate with, in terms of who you are
passing on your copies of genes in cooperation with,
but also the possibility that the other individual
is infectious with something or other. And throughout the
world of social beasts, nobody likes getting sexually
transmitted diseases. And a lot of what this whole
handicap principle is about, a lot of this advertising about
what a great immune system you have, is a way of
advertising, I do not have a communicable disease. All sorts of
species-- individuals are extremely good at
detecting the smells in the others of
parasitic infections, of all sorts of
other infections, and avoiding them
like the plague. A common theme in lots
and lots of species. Rodents, where it's been most
studied-- a remarkable ability to smell out the health
of another individual. And this is someone you want to
stay away from-- that they're going to give you an STD. So that's part of it, as well. So, of course, what
you start getting are individuals trying
to cheat at all of this. And this is suddenly
the world of selection to uncouple your secondary
sexual characteristics from your health. Is there a way to cheat? Is there a way? And what is seen in
some bird species is, you've got some guy on
his deathbed, there. And what's he doing with
his last 3 and 1/2 calories worth of energy? He's expending it
on wing coloration or whatever the secondary
characteristic thing is, there, that he's got four
minutes of life left, and maybe there's
one more chance to pass on copies of his genes. You get cheating, as well. You get cases of
disproportionate shunting of caloric investment
towards some of these markers amid animals being sick. So, of course, you have
to have counterstrategies. And we have yet another
world of coevolution between some sort of
exploitative strategy and a counter one to
try to detect that. Then you've got one problem with
this whole literature, which is, there is a certain way to
frame things so that you never, ever can get a
finding that disagrees with your general stance. OK, here's how it goes. Here's the version
that we've just heard of this handicap
principle, which is, what you have to have
is your secondary sexual characteristic-- the intensity
of it has to be reflective of the quality of
your immune system. And in lots of species,
facial coloration is generated molecules
from the immune system in a linear relationship, there. Yes, that is a way
of advertising, I've got a great immune system. But get this. Meanwhile, you can have
exactly the opposite case, which is, you can have your
secondary sexual characteristic driven by an infection
that you have. And what you are presumably
communicating is, if I'm still able to do this ridiculous
courtship dance, despite the fact that I'm
teeming with parasites, I've got the greatest
DNA going around, there. Hey, how about it? Where you see this
is in vultures. And the mere notion that
vultures having sex, and let alone them having sex
based on thinking some of them are more attractive
than others, leaves me breathless with admiration. But what you see
is, in vultures-- I'm forgetting which
species-- sexually dimorphic-- the males have more
colorful faces. They tend to have these orange
faces made out of carotenoids-- these pigment things. These carotenoids. So one version that
we've heard already is, OK, where are the
carotenoids coming from? They're produced in
the immune system. And the happier your immune
system, the more carotenoids you pump out. That would be the first
scenario we've heard. In vultures, you see
exactly the opposite. Which is, where-- this is going
to go downhill really fast, now. So where do you get
carotenoids, if you are a vulture in the
plains of East Africa? You get them by
eating ungulate feces. Which vultures are perfectly
happy to do, if it's fresh-- or even if it's not so fresh. And what that will typically
contain are lots of parasites. Consuming a whole lot
of ungulate feces, rather than, say,
ungulate muscle, increases the likelihood that
you have some sort of infection that you've picked up. What's the interpretation there? Yet here I am, bouncing around
happily and energetically. Just imagine how
great my genes are, if I'm able to do that amid just
teeming with parasites, because of my unlikely sort
of dietary habits. So you've got it, here,
that it can go both ways. Ooh, dramatic secondary
sexual characteristic is a marker of a
good immune system-- I can fight off disease. Dramatic secondary sexual
characteristic as a marker of, look how well I'm
functioning, here, despite teeming
with some disease. You get it both ways. It remains very,
very controversial-- for the three and a half people
who deeply care about this. One additional version of that--
and the "there's no free lunch, and there is no free
ungulate"-- whatever-- OK, one additional version of that
are studies now showing that in lions what you get is--
highly tournament species, and thus a highly dramatic
set of secondary sexual characteristics. The manes. The manes on the lion. And what everybody
knows from The Lion King is that they can be very
big and dramatic-looking and thus make you
very attractive. Unless you're hanging
out with hyenas. But what is clear, also,
is, it comes with a price. What is the most attractive
sort of male lion you can see? It's a black-maned male. Because that is one
that is most expensive, in this
handicap-principle sense. But there's a
downside, if you've got a black mane, which is,
your head heats up more, sitting there in the African sun. You've got to spend more
energy on thermal regulation. There's a downside to it. All of these things,
where you're balancing. What else? What else, in terms
of attractiveness? So we've now got,
lots of species, the symmetry business
as a marker for health. The secondary sexual
characteristic nonsense stuff as a marker of
health but interpretable in a number of different ways. Then there are the secondary
sexual characteristics that are more directly
markers of fertility. And what we've
entered into, here, is the world of primate
species, where females have external swellings
when ovulating, when there are visible signs
of estrus, of going into heat. Humans are concealed ovulators. And we already know some
of the theories about that. But all the other primates get
explicit, observable estrus swellings when it is time
that they're ovulating. And all you need to
do is look at baboons. And beginning somewhere
around junior high, when they start hitting
puberty, some females have bigger swellings
than other females. And it turns out, these
stupid, shallow male baboons prefer the ones with the
big swellings to the ones with the small swellings. You can even show, with
captive male baboons, that they will
lever-press more to get to see pictures
of female baboons with big swellings instead
of middle-sized ones or little ones. There you go. Somewhere out there, there
is a magnificent reality show to be set up
along those lines. What you see with that is,
what's the swellings about? It is a marker of
estrogen levels. It is a marker of-- the
higher the estrogen levels, the more the swelling. And what you wind up
seeing, in various studies by now, replicated,
showing that, among female nonhuman
primates, those females with larger swellings have
a better infant survival during the first year
of life of the kids. It's a marker of greater
fertility and greater health. And there's maybe some element
of a handicap principle there, because by the time
you get female monkeys with the biggest
swellings around, they now weigh about 25% more than they
weigh the rest of the time, all because of the
water retention. And presumably
part of the signal there is, if I can
be running around in my female-in-estrus
sort of way, despite 25% more weight sloshing
around at the end of me, just imagine how strong
and healthy I am. So that, as a source
of attraction. Meanwhile, over at the
male end of things, in terms of looking for
other markers of attraction in females-- by the
time you get to humans, we are not, again,
external ovulators. But what you have with humans
is the famed waist-hip ratio measure. And this one has been endlessly
studied and argued about. The notion that the larger
the size of the hips, relative to the size of
the waist, the greater the waist-hip ratio--
no, the lesser the-- flip that
around the other way. OK. The bigger the hips are,
relative to the waist-- this is a marker of fertility. That is a marker of
childbearing pelvises. That is a marker of all
sorts of developmental health that augurs well for having
a baby pass through the birth canal. In culture after
culture, men find women to be more attractive
who have a higher-skewed ratio of hip to waist. So that's been studied
all over the place. What you have, though, as
the central controversy in that field is, if every
single culture that that's been studied in has been
contaminated by their exposure to westernized culture
and its pervasive values, which may be the source of that. So, among the hip-waist
sort of zealots, what has been the Golden
Fleece to go after, what has been the
equivalent of getting identical twins separated at
birth, what is the thing they go after, is to find
a population of humans who are having their first
contact with the outside world and have had no exposure
to the westernized world. And thus you are able
to rush in there, quickly master their
language, and, once you've done that, you get to ask
them the first question in their entire content with
the westernized world, which is, so, which of these
look better to you? Asking the guys, there. And, at this point--
not surprisingly, there is not a huge
literature of asking people, on the first encounters, about
hip-waist ratios-- what you see is, the literature is mixed. When you look at more
traditional societies, you do not necessarily
see as strong of a hip-waist-ratio
set of opinions. But nonetheless, at
least some of that is universal in every culture
that's been looked at. Again, as a marker of fertility. Meanwhile, over at the
female end of things, you've already heard
what some of the things are that are looked for,
in terms of responsiveness to secondary
characteristics in males, which is jutting jaws, big,
high foreheads, and muscle mass. And all of these are
assays indirectly of testosterone
levels or testosterone exposure or sensitivity
during adolescence. Those are preferred. Interesting thing. Studies showing that,
when you give women a choice of faces of males
that have been manipulated, changing the
dramatic-- how dramatic the secondary characteristics
are-- like forehead and jutting-jawedness and
angularity of face and stuff-- what you see is an
interesting dichotomy. Which is, in these studies,
women on the average rate the rounder-faced
pictures of men, such men, looking more likable, more
honest, more trustworthy, and less desirable. OK. So this is hopeless. And what do you know? Those-- well, I won't
go there, either. What those show is
separable traits, there. Separable traits,
in terms of what's attractive-- what information. And, again, when you
look at these studies, the differences are, like, 5%
difference in nostril width and things, when they're manip--
these are extraordinarily subtle differences, where
people are not consciously aware of them. Which face looks
more attractive? Which face would you like more? Which face would you trust
more if they told you to vote for somebody or other? An interesting
separation, there. OK. One additional one
is that, in women, when women are
ovulating, they prefer more sexually secondary,
secondary-sexually characteristically
dramatic male faces. At the time of ovulation, women
rate as more attractive male faces with the juttier jaws
and the greater muscle mass and the forehead stuff going on. What we see here is this theme
of, at the time that estrogen levels are at their highest
in humans and lots of realms, in addition to other
species, detection of pheromones from males
is the most sensitive. Ability to pick up
subtle differences in facial symmetry or secondary
sexual characteristics are at their best. And the preferences
are derived from that. This is, in some cases, some
rather substantial effects. OK. So, what other things? There's one problem that runs
through this entire literature. OK. So here's the deal. You are a-- uh--
you're a gazelle. You're a female gazelle, and
you have read lots of zoology and you know all about
this handicap principle. And you know the fact that
big, dramatic secondary sexual characteristics on
guys is a marker of better immune systems
and more fertile sperm and all sorts of great stuff. So you go out of your way to
go and find one of those guys. You mate with him. And you've just given birth. So, knowing what you know, what
you, of course, now realize is, you've got a great
kid on your hands that have all these
terrific genes from that jutting-jawed
antelope guy you mated with. And you better make
sure this kid survives, because they have an
enormous potential for having a big reproductive
success later on. What do you do? You expend more calories
in taking care of them. This has been shown in
all sorts of species. Mate various birds in various
bird species-- mate females with males who are more
attractive versus mating them with less attractive,
and what you see is that the females
who have mated with the more attractive males
give birth to bigger eggs. That's interesting. OK, so you're seeing the
evidence of the good genes coming from the guy. Male genes have nothing
to do with egg size. It is how much
protein the mother puts into the egg production
and the egg development. And what you see is, she
makes this a self-fulfilling prophecy. In a lot of species,
now, it has been shown that when females mate
with more attractive males they put more effort into
having the offspring survive. The offspring survive better. And yes, what do you know? You really do want to mate
with guys with big antlers and that sort of thing. This big problem with
self-fulfilling stuff. So that's a confound that
has run through the field. Another confound--
and here is one that shows how many species
are far less distant from us than one might think. This was work by a
guy named Lee Dugatkin at the University of Kentucky. And what he does is study
ospreys or some kind of bird thing that runs around. And what he does is, he first
gets a male and female osprey, and he introduces
them to each other. And what he looks
for are circumstances where the magic does not occur. There is no chemistry
between them. The female rejects the guy. And, at that point, what he
does is, in the next round, he makes the male appear
to be very popular. He puts the male here,
and he takes a whole bunch of stuffed female birds
and puts them around in a circle around him, gawking
at him with rapt admiration and just frozen in their
place at the wonders of, like, the coloration on his bill from
eating who-knows-whose feces. And what you see
then is, the female who spurned him is
now more likely to do solicitive courting
gestures with him. In other words, she's
jumping on a bandwagon. And this has now been shown
in a number of species. What's the logic of this? This is exactly what secondary
sexual characteristics are about. I don't understand
why anyone considers that to be attractive. This individual
does nothing for me. But if it appears to be the
case that those traits are very popular, and thus those
traits are predictors of being able to pass on
many copies of your genes, I sure want my kids
to have those traits. And thus this bandwagon effect. So all of these are
versions of just shallow, shallow,
horrible-values versions of who one looks for in a mate. But then, of course, we go to
all the pair-bonding species. And as we heard from
many lectures ago, the rituals in lots of those
species of male courtship built around showing that
they are a competent parent. Showing that they can do some
rough approximation of acting like a mother to these babies. What's that about? And that's the whole world
of male birds doing courtship by bringing worms and feeding
the mother and showing, look, I know what kind
of things we eat. I know how to bring a worm. By the time you get to
pair-bonding species, the rituals and what is
attractive are often markers not of fertility but of
parenting skill-- parenting competence. Flipped the other way, in
most nonhuman primate species that have been looked
at, when are females most attractive to males,
independent of the size of their estrus swelling? When they've already
had a couple of kids. Females, the first-time-out
rounds of ovulating, are less preferred
than females who have had a number of kids already. If it is the same thing going
on, what she has already proven is she's competent
enough that she didn't kill the kids by
dropping them out of the tree at various points. This being as a marker,
again, of competence. OK. Final realm of what one
looks for in a mate, across lots and lots
of different species. Which is not only
someone who appears healthy and symmetrical,
and these exciting secondary characteristics that are
markers of lots of fertility, and also whatever everybody
else thinks is attractive, you suddenly do as well--
the last thing that tends to be a theme through
lots and lots of species, and in every human
culture, is being attracted to someone who's
kind of just like you are. Being attracted to
someone who is similar. And the term for
this is "homogamy." Homogamy, polygamy, monogamy. In this case, homogamy--
mating with someone who is homogeneous, who is
similar in traits of yours. And across cultures, including
in the United States, people are extremely homogamous
in who they wind up marrying. Here are the statistics. When you look at
couples in this country, there is better than a
90%-chance likelihood of them sharing the same religion, of
being within three years of age of each other, of sharing the
same race-- the ethnicity-- sharing the socioeconomic
status of their childhood-- did they both grow up
poor, wealthy, whatever-- and sharing political views. More than 90% concordance
in this country on those traits-- markers
of homogamous preference for someone who
is just like you. Stepping down a bit-- not in
this range-- but more than 40% homogamy for a couple
having IQs that are within, I don't know, five points
of each other-- having similar levels of education. Those are very
homogamous traits. Then a whole bunch
of weirdo minor ones which, nonetheless, are still
statistically significant. A 20% to 40%
likelihood of couples being the same height--
not the same height, but say, for example,
in the top 10 percentile of height
for their sex-- scaled to what's within gender. Weight, hair color. And then you get into this
bizarre world of lung capacity, of width of nostrils,
of width of eyes. People have studied these,
and these are traits that show significant homogamy. In this fairly low range,
but nonetheless significant at a higher-than-expected rate. What are these weird
things being about? These are probably
surrogate markers for preferring people of
similar race, similar ethnicity. That's probably where those
numbers are coming from. So what's this about? This is suddenly barreling
us back into the world from many lectures
ago of, you don't want to mate with
someone who shares half their genes with you--
the dangers of inbreeding. But you also don't
necessarily want to mate with someone who
is so unrelated that there is no drive of kin
selection for cooperation. We have now heard, from
bird species to humans, you get the optimal
fertility somewhere around third to fourth cousins. You get the optimal
fertility, under circumstances that select for a fair
degree of homogamy across different cultures. And historically, this
is no surprise at all-- that there is a great
deal of homogamy. Various studies have shown
that your average traditional hunter-gatherer winds
up being married to somebody who grew up
less than 40 kilometers away from them. Studies show that people
in traditional agricultural villages in the
developing world wind up being married to someone,
on the average, less than 10 kilometers away from them. You are getting an awful
lot of people winding up being married with individuals
who look a lot like them. And back to that issue
of partial relatedness-- third to fourth cousins. Yes. But couldn't it just be that
I know a lot more people who are the same age as
me, the same race, the same socioeconomic
status, and so on? OK, well, though,
look around the room. This is a very
heterogeneous corner of the planet we've
come up with, here. Yes, it's very
different when you look in more homogeneous
societies, there. But when you begin to look
at the increasingly diverse Western European ones,
you see a fair amount of homogamy going on. Very interesting data. Iceland-- yet another of
our good-old Scandinavian-- is Iceland technically
Scandinavian? Or are they just,
like, good guys who should be Scandinavians? They're so dull and
healthy and sensible. OK. So in those sensible,
non-Scandinavian Icelandics, who have, like-- I
don't know, what? --300,000 people in the whole
country, and all of them are no more than sixth
cousins apart, and all of them have just fanatically clean
records, going back centuries, as to who was married
to who, studies have now been done, looking
over the course of 200 years, in Iceland of how closely
related different couples were. And what you see is, optimal
fertility, optimal number of children who
survived into adulthood, you get from third- to
fourth-cousin marriages. Recent studies showing that. One additional,
interesting version of this homogamy stuff, which
is, in the United States you see something
slightly different. You see an age factor
coming in here, which is, people are more likely
to make less homogamous choices as to their mates, the younger
they are when they get married. What's that a surrogate for? The incredibly depressing
fact that, on the average, people get more and
more closed-minded as they get older. You see the greatest
heterogamy in marriages-- the greatest likelihood
of people marrying someone with a very different
background, the younger they are. In the early 20s is
when you find the peak for a lot of these traits-- when
you find the least homogamy. One interesting exception to
that, or a partial exception, which is with religion. And what you see is, you
look at people getting married in their early 20s. This is the likelihood
of marrying somebody from a different religion. And then it goes way
down in the 30s and 40s. And somewhere between
50 and 60, there's another little
blip that goes up. And this has been documented
in a number of studies. What's that blip about? Any theories? Oh-- OK, somebody
[INAUDIBLE] there. Um-- fewer options for mates? Fewer options for mates. That's one depressing
possibility. And just wait until you're in
the nursing home and, like, anything that moves
you imprint on. Yes, theory? They're not going to
have kids anymore, so they don't need to
worry about passing down [INAUDIBLE] to their kids. OK. So the issue of-- if you
do that, if you have waited long enough that you're not
going to have kids, that you're not going to have
all these fights of, are you going to be a, you know,
a Mac family or a PC family or all those sorts of things
that can tear people apart [INAUDIBLE]. OK, so that's a possibility. How about another one? Yeah. You're reflecting
your mortality. OK, you're reflecting
on mortality, and you're deciding,
enough of that nonsense. Who cares? This is someone who matters. Yes, that's a possibility. What else? Was that an idea? Midlife crisis? Midlife crisis. So it's either you
get a convertible or you marry someone
from, you know, Tierra Del Fuego or something. So all of those
seem to go into it. One additional one, which
I find to be absolutely, like, wonderful, in terms
of just how bizarre it is. Which is, when they
interview people, what you also see is, the ones
who tend to have this peak, they have been in
long-term relationships with the individual. What was that about? They're waiting for
their parents to die, so they don't kill them
by marrying this person. [LAUGHTER] That appears to be
part of that scenario. Which is, once they're dead,
then we can go get married. Because I couldn't possibly
do this to them before then. And that appears to be
part of this peak, also. OK. Finally-- finally, a
study-- famous study that was done
about 15 years ago, by an evolutionary biologist
named David Buss, who's now at the University of Texas. He wasn't, at the time. And he did one of
these sorts of studies that we recognize by now, which
is sort of questioning people, questionnaires of people from
a lot of different cultures, all over the planet. And this was this massive study
of I don't remember how many different cultures. But it ranged from
non-westernized, nomadic pastoralists, non-westernized
agriculturalists, socialist countries, communist
ones, capitalist ones-- everything in between--
individualistic societies, communalist societies--
all of that. It was tens of thousands
of people in the study. Where he gave all these
people a list of traits. And he would say,
which of these traits are most important to you,
in terms of who you marry? And what came out in
every single culture looked at-- as follows. In every culture
looked at, women are more likely than men to want
a mate who is older than them. In every culture looked at,
men, more common than women, looking for someone
who's younger than them. In every culture looked
at, women more than men citing the economic
prowess of this individual as being part of
what constitutes the desirable traits. In every one of them
that's been looked at, men having a greater preference
than women for markers-- health markers-- of fertility in the
person they would wind up with. This was so depressing,
because this is every culture on this planet
coming up with this cliche. Everybody learned
about the study, and how remarkably
disturbing it was in terms of all of those
stereotypes across so many different cultures. Women are looking for older
guys who have lots of money, and men are looking for
younger women with big hips or who knows what. And this came through
in every single culture. But what everybody
always misses when they discuss this study
was one additional one. And this is, like,
enough for, like, Hallmark cards-- all of that. What everybody knows is,
across these cultures, these traits were more
likely to be rated highly by one sex
versus the other, but in every single one of
the countries, what you find is both sexes had an equal
preference for the number one thing on the list, which
is winding up with somebody who's nice to them. OK. On that note,
let's take a break. We now switch to
our next second half of the course topic,
which is going to follow the exact same strategy. And where we're
shifting to, here, is going to be a whole bunch
of lectures on the large, sprawling,
interconnected subjects of aggression, violence,
competition, cooperation, empathy. And what we will be
doing there is wrestling with all sorts of features
of the complexities of these and where the
underlying biology is-- enormously important
social implications, in a lot of these cases. And, of course, what we
need to start off with is, what's the behavior about? How objectively do you
describe these things? And it struck me-- a good way of
starting that, not only giving a sense of the range of
what aggression can be like, but also a very important point
that's going to come through in this entire lecture-- it
struck me that a good thing to be would be to describe a
relatively recent exposure I had to human aggression. Which was me being
aggressive to somebody else. This was, now, a
couple of years ago, before my back
disintegrated on me. I used to play soccer
two, three times a week. And I had been doing
this for decades. And I'm actually
totally lousy at soccer. And, like, I'm short
and I'm old and I'm not particularly coordinated. And [INAUDIBLE]. So this has never
been something that was, like, one of the things I
was going to go to the Olympics with. So, a number of years ago,
there was consistently this one guy who seemed
to always wind up on the other side, and who
somehow always wound up guarding me, who was a
total son of a bitch. This guy, he was-- he was
a lot younger than me, and he was a lot more athletic,
and he was a lot taller than me, and he was a lot
more skillful in this game. And, on top of everything else,
he was a really dirty player. And this was driving me crazy. Every time the ball
would get near me, he would elbow me in my ear,
and he would do something like-- [LAUGHTER] --that he wasn't
supposed to be doing. That sort. And one day, we
were out playing, and somebody passed
the ball to me. And, as per usual,
he effortlessly knocked me out of the way--
crudely and illegally, which no one seemed to notice--
and then stole the ball. And I was pissed. And this guy quickly
passed it to someone else. And the two of us
were sort of running towards a corner of the field. And momentum was carrying us. And I sort of realized
that the ball was now kind of elsewhere in the field,
and thus everybody's attention was kind of elsewhere
in the field. So we're running along, and I'm,
like, a half step behind him, and I just stick my foot
in front of his ankle and send him rolling and-- [LAUGHTER AND SCATTERED
APPLAUSE] --sprawling, and this
was the best-- heaven. This was during the summer. And it turned out there
was a mud hole there. It hadn't rained in six months. This was wonderful! So he goes-- and I didn't even
go through the pretense of, oh, are you OK? Sorry about that. It was just-- yeah! [LAUGHTER] I had to restrain
myself from ripping his stomach open with my
canines, at that point. So I felt wonderful! This was, like,
the best thing that had happened to me in months. [LAUGHTER] Nelson Mandela. [LAUGHTER] Nelson Mandela. Now in his 92nd
year, frail-- frail. An icon of all that is good
and wonderful about humans. This man on his last legs, now. What if I had been playing
soccer with Nelson Mandela and I did that to him? You'd be horrified! Nobody would be on the edge of
applauding that sort of thing. This would be
unspeakable, if I had done that to delightful
Nelson Mandela at age 92. So what we see here is
a very important thing that is going to run
through all of this topic. Which is, very little about
the social, the environmental, the learning aspects
of aggression have to do with learning
how to be aggressive. It's all about when. It's all about the appropriate
social context for it. Because that speaks
to something that is absolutely clear
for 99.9% of us. We do not want a world
without violence. We love violence. We get excited by it. We will pay good money
to see the right displays of competitive violence. We will barely
restrain ourselves from leaping in and joining it. It is all so wonderful
and exciting. We love violence-- when
it's the right kind. When it's in the right context. And a huge percentage
of wrestling with this is built around the
fact that, in some settings, the exact same behavior gets
you medals, gets you promotions, gets you differential
reproductive success. And the exact same patterns of
what you do with your muscles in another setting is some
of the worst things you could do as a human to another human. And it's the same behavior. And what we're going to
be wrestling with, over and over and over, in the
subject, as we march back, here, is this whole issue of,
very little about the biology of violence,
competition, all of that, is about how to
do the behaviors. It is all about
appropriate context. And what we will
see is, all sorts of realms of neurological
diseases, where things go majorly wrong, in terms
of control against violence-- very rarely will it be that it's
the magnitude of violence which is wrong. What you see is, it's
in the wrong context. Because if it's done
right we love it, and we elect people who
have been good at it, and we differentially mate with
them, and we pay to see it. It's got to be in
the right setting. There are very few of us who
viscerally are truly, truly pacifists, all across the board. We just don't like violence
in certain settings. So that will be part
of the challenge, here-- making sense of the
biology of social context. And we've already
gotten some hints about that in the last topic. So, of course, what we
have to start off with is, like, definitions. And it's never
more in this realm that you get the "I don't
know how to define it, but I know it when
I see it" sort of notion in dealing with terms
for aggression and violence. Probably a great
starting point is, just as with the
sexual-behavior subject, starting off with,
well, what aspects of violence and aggression
are unique to humans? And what the theme has been
there, for decades now, is all sorts of domains that
used to be thought to be unique to humans no longer are. We've already heard
some of these examples, way back in the
sociobiology lectures-- all of those wildlife films
where, somewhere in there, somebody with a very deep voice
has to intone about how "only man kills for pleasure"-- while
watching some beasts throwing the old wildebeest
into the river, there, and misinterpreting it. And that was always
the theme-- we're the only species that kills. And that went down the
tubes, way back when, as soon as people started
seeing competitive infanticide. That was first seen--
again, I think I mentioned-- in langur monkeys. A primatologist
named Sara Hrdy, who was at Harvard at
the time-- and she was the first to report this. And-- this could not be! That male langur monkeys
were killing babies? This was impossible. And the interpretation was that
this was a psychopathology. This was because of increasing
habitat degradation, human populations getting
closer, crowding them in. These were populations
of langur monkeys in some urban areas in India,
where she was studying them. This is not normal, because
no other species kills. And now that it's up to
20, 25 different species or so that does
competitive infanticide, it is quite clear we are not
the only species that kills. And we are not the
only species that kills in some premeditated,
strategic, Machiavellian, good for numbers of copies
of our genes kind of way. We are not the only
ones-- Jane Goodall by now having documented lots
and lots of cases of murder between chimps, females
killing each other's babies, males killing other
males quite frequently. And, once again, we are
not the only species. What's also become clear
from more recent work with chimpanzees is,
we're not the only species that makes weapons. Chimps have now been observed
to take large, heavy branches and break off the
ancillary branches, there, and smooth it out
and use it as a weapon, to try to hit another animal. This is tool use
and tool production. This is another species
making a weapon. We are also not the only species
that has organized violence. And this is back,
again, to chimps. Something mentioned way
back when in the lectures-- the facts that chimps
are female-exogamous, that business that,
at puberty, it's the females who pick up and
move to a different group. All of the adult
males in a chimp group are relatively
related to each other. They are relatives. And what you get, then,
is cooperative aggression among males from a
particular group. What you will see
is border patrols. Goodall was the first to use
this term to describe it. You will get-- the
males of the group will get into an
extremely agitated state with each other-- a state
of emotional contagion, where they build up this very
high level of excitation. And they then go and patrol the
territory between their group and the next group over. And what Goodall was the
first to document was, if they encounter a male
from the other group, they will kill him. And what she also documented was
cases of groups of male chimps systematically killing all of
the males of the neighboring group. What is it that we've just
seen, now, in another species? Genocide-- the notion of killing
an individual not because of who they are but because of
what group, what population, they belong to, as
part of a desire to eradicate a
population as a whole. We are not the only
species that has something resembling genocide,
if it's termed that way. So where is a domain
where we might be unique? Lots of people still
argue that humans are the only species that
psychopathologically confuse sexual behavior with aggressive
behavior-- world of sadism and masochism and all of that. That appears to be
something resembling a human-unique trait. OK. Now flipping to the more
cheerful side of things-- the cooperation,
the empathy stuff-- what aspects of those
behaviors are unique to humans? And what people
used to think was an exclusively human
ability-- yeah? Are there any instances where
certain troops of monkeys will not only just kill all
the males in a different troop but kill all females
and infants, too, as in [INAUDIBLE] genocide? Yeah. They will kill the infants,
out of competitive infanticide stuff. And they will then happily
hang with the females. And do more than
that, with any luck. In terms of-- oh, a very
familiar historical strategy with humans, seen
again and again. Good end of things. Used to be the rule
that the humans were the only species that
showed reconciliation-- that showed increased likelihood
of affiliative behavior between two individuals
after they have had an aggressive interaction. In the aftermath of
it, increased odds of doing something affiliative--
making up-- reconciling. Doing something
along those lines. And what has emerged
in the last 20 years or so is a huge literature
showing reconciliative behavior in a couple of
dozen other species. First person to report
this-- primatologist Frans de Waal, first reporting this
in rhesus monkeys, I believe. But lots of other species
since then, including dolphins, including whales. And what you see is-- in
the aftermath of a fight, you see two individuals are
more likely-- in gorillas, for example, to do social
grooming in the aftermath-- than at any other time. An increased rate of that
happening-- reconciliation. What's remarkable is some
of the subtleties in it. And this was work that was done
by Marina Cords, at Columbia. And what she showed was,
the odds of reconciliation increase when it's
a more important, valuable relationship
that you have. How was she showing this? These were studies
with macaque monkeys. And what she did was
set up circumstances-- these were animals
that were caged. And there were
circumstances where she put food on a tray outside
that could be reached for. Where, in one setting,
an animal could get the food in all on its own. And in another
setting, the only way to get the food tray
close enough to the cage was if both of them cooperated. And this was what they
were doing habitually. So what's the difference, there? In the second case,
you have formed this cooperative relationship
with this other individual. You need them, and they
need you to pull off this getting the food
close to the cage business. What she showed was
significantly higher rates of reconciliation
between pairs that have a history of cooperating. What could that
be interpreted as? More of a game-theory
history of cooperation behind you-- more
willingness to forgive. Another way of framing it,
as she does in her work, is, this is a more valuable
relationship that you don't want to screw up. You are more willing to do
something reconciliative afterward. You can see, in baboons,
reconciling behavior in females. No male baboons ever reconcile. Showing gender
differences, there. In bonobos, you
see reconciliation is different from all
these other species, where, in all the other ones, it's
built around social grooming or chimp hugs or whatever. There, of course, as you
guessed it, it's sex. Because with the
bonobos, anything that happens, and
it's time to have sex. But an interesting
thing, in terms of this picture of bonobos
being this incredibly peaceful species out there in this
commune and all of that-- you can't have reconciliation
unless you have aggression. They do have aggressive
interactions. Otherwise, there would be
nothing to reconcile afterward. Even the beatific bonobos have
a certain degree of aggression-- very high and varied
rates, varied abilities, to pull off reconciliative
behavior afterward. More things that used
to be just about us. Empathy. And a literature now coming
out, showing the building blocks of that in
other species, as well. First example in chimps,
second example in lab rats. Chimp example. Again, this was work
done by Frans de Waal. And wonderful study. What he showed were
two circumstances where a male chimp
would get pummeled. First circumstance. You've got this low-ranking
male who goes up and threatens and starts a fight with
a higher-ranking male and gets pummeled
into the ground. Second circumstance. Low-ranking guy
is sitting there, minding his own business. High-ranking guy
is in a bad mood and pummels him into the ground. What's the difference? In the first case,
this kid started it, by challenging the guy. And in the second case, he
was an innocent bystander. And what de Waal showed
is, in the half hour after these incidents, the ones
who were innocent bystanders were far more likely to be
groomed by females there in the group than the
ones who had started it. They were able to distinguish
between not just that this is an individual
who just got pounded but whether it was their
fault or not, or whether they were a victim. And considerably more grooming
when it was an individual who had been a victim. Something resembling some
proto empathy happening, there. Remarkable study, published
in Science a couple years ago. A group from McGill. And what they showed was
arguing this is something resembling empathy in rats. Here's what they
showed in the study. What they had was, they-- let's
see, how were they doing that? They would have one rat
that was restrained. And rats don't like it. And they would be giving
off ultrasonic alarm calls. Now you put a second
rat, and you give them a pain-threshold test. Which is to say, you put them
on a perfectly cool surface, and you begin to
warm it up, and you see at what temperature
do they first lift up one of their paws. And, quick, take them
off at that point. And what is their
temperature threshold for beginning to
find this aversive? And what they showed was that
rats would have a lowered threshold, would be more
sensitive to this pain stimulus, if they were next
door to another rat giving off alarm vocalizations. But it was more
subtle than that. That would be easily described
in terms of, OK, alarm calls, and stressful, and just putting
me in a more agitated state. What they showed was,
this only worked when it was rats that were cagemates. If it's rats that knew
each other, hearing the other rat in distress made
you more sensitive to a pain stimulus. If it was a strange rat,
it didn't work at all. Some crude version of something
resembling empathy, there. So we're not the
only species with it. What's clear, though, is we
are the only species that could take it to
just domains that are utterly unrecognizable. We are the only
species that is moved by people on the other side
of the planet who have just been in some catastrophe. We are the only species moved by
artwork that depicts suffering, by movie characters, by
fictional characters in books. We are taken into realms
that are unmatched elsewhere. There's this wonderful video. This was an
advertisement for Ikea. Has anyone seen this one, where
the light gets thrown out? Is there anyone
who hasn't seen it? OK, this is-- opens up. It's this stormy, like,
dismal, drizzling night, there. And it's clearly freezing. And you see-- coming
into an apartment, you see an old
lamp sitting there, with sort of a
neck-type lamp thing. And it's sitting there. And suddenly this person
appears, picks it up, and walks outside into
the rain and puts it down next to the garbage can. Oh! It's being thrown out. And now, thanks to brilliant
photography and angles that are shot just
underneath the lamp, there, you see it leaning there,
looking miserable in the rain and all alone with its
light thing, there. And you see, from this
angle in the background, there's the
apartment, where it's warm-- lights, and all of that. And then you see the
most heartbreaking thing. You see the person come by the
window, there-- the armchair-- and put down a new lamp--
a new lamp that's nicer. And they even show the person--
just to really get the edge, there-- briefly
caressing the new lamp. And then you get a shot
back out again in the dark, and it's pouring, and
it's drizzling out. And you're sitting
there, feeling terrible for this damned lamp, there. How does this work? And then, just to sort of
show it, suddenly this person appears in the screen
and says, in effect, what's wrong with you? It's a lamp. It's a lamp, and the
new one works better. And then on comes
"Ikea," which I suspect is not actually a good strategy,
because you think of them as heartless
individuals who advocate the abandonment of child lamps. But, like, no hippo
would know what the deal is, while you're
sitting there feeling sorry for this piece of metal, there. We have empathy--
not the only species, but in very distinct
and unique realms. What else? We are ostensibly
the only species with a sense of justice. Again, that's not
necessarily the case. Again, work by Frans de Waal,
whose name keeps coming up, who is one of the best,
most creative primatologists in the universe. This is work, now, where, again,
chimps-- two chimps-- where circumstances were,
either it takes one of them to pull
a tray of food over, or both of them to cooperate
in order to get the food. And what he shows is, after
the cooperative relationship has been established
with them, if you change the workings of it
that it requires both of them to pull the food in
but the food winds up going to only
one of the chimps, that champ is more
likely to share the food with the
other individual than if they didn't have a
working-together relationship. That chimp, on some Frans
de Waal sort of level, was feeling bad for the other
guy getting a rotten deal. Under those circumstances, if
it was a chimp that you already had a cooperative
relationship with, you were more likely
to share with them after they had gotten something
aversive occur to them. What else? What else, in terms of making
sense of other species-- what are unique, what are not? Dominance hierarchies. And if you come from a
certain school of sociology, humans are the least
hierarchical species out there. We are not territorial, in the
sense of lots of other species. We do not have
strict hierarchies. And what you see
in other species are hierarchies can mean
very different things. And the broad
dichotomy that's made is between top-down
hierarchies and bottom-up ones. Top-down, you have a single,
dominating, most aggressive individual who is
up there on top. And the characteristic
of this-- it's also called a "despotic"
hierarchy-- is extremely unequal
distribution of resources enforced by violence or
threats of violence from above. That's baboons. That's chimps. That's rhesus monkeys. Then you look at
vervet monkeys, and you see a bottom-up, what is
also termed "egalitarian," hierarchy. There is a hierarchy, but the
number one individual there is only there with the
cooperation of everyone else. If that individual becomes
abusive, they are overthrown. So hierarchy does
not, in other species, automatically mean abusive,
aggressive, dominating, unequal-distribution stuff. What it is is, it
varies by species. What also becomes clear,
by the time you're looking at other
species, is it gets really hard to figure out what
does indeed count as violence. Example-- East African primate
called a "patas" monkey. Go and study patas
monkeys, and spend 40, 50, 60 years doing it,
and what you will see are virtually no instances
of male patas monkeys having fights with each other. Wow! That's a pretty
unaggressive species. That's kind of nice. Put two male patas
monkeys in a cage, and not only will they start
fighting soon afterward, they will fight to the death. Because they have no signals
of terminating aggression. What's the deal with that? This is a species where the
level of male-male tension and male-male
aggression is so high that the entire social
structure of these species are built around keeping males
as far apart as possible. You don't see male
patas monkeys having fights, not because
they're not aggressive but because they live in
these dispersed patterns. So is this an aggressive
species, or not? This isn't an aggressive
species; you never see a fight. This is an insanely
aggressive species; the central feature of
their social structure is keeping violent males
away from each other. What does it count as? What does it count as
when you see an animal leap on top of another
animal and rip it to shreds? Sometimes that's
aggression, sometimes that's getting dinner. Once again, as with the
sexual-behavior realm-- this whole realm, back
to the limbic anatomy of, are you looking at aggression? Are you looking at predation? These are totally different
biological phenomena. That takes some work. What has always been
one of the big questions in the field is,
so, what's the deal with rough-and-tumble play? What's play about? Because you see it in
endless species out there. A lot of studies show that
during periods of famine, for example, one of
the last behaviors that disappears from kids is play. It is really, really
hard-wired in there. So when you see aggressive
play, is this truly aggression, or is this practicing
the building blocks for the real stuff that
will come later on? What a lot of the
primate studies suggest is, it's not
practice, it's not play, it's already establishing
some of the asymmetries that will be there later in life. OK. So, all sorts of ways
in which aggression can pop up in other species,
in unexpected realms, in which cooperation,
all sorts of things like that-- what are some
of the unique human ones? Nonetheless, amid all
those similarities, we do things that are
completely unprecedented. We are perfectly
capable of being as violent as a chimp, when
it comes to cudgeling somebody over the head. But we're the only
species that could be violent by doing nothing
more physically taxing then pulling a trigger or looking
the other away or releasing a bomb from 30,000
feet up in the air or being passive-aggressive
or damning with faint praise. And we're suddenly doing
all sorts of much more subtle things with aggression. Here's three examples
of human aggression-- and I've heard
about-- which shows just how complex of a
phenomenon this could be. First one. This was the child
of a friend of mine, when she was about
five years old and she was in kindergarten
or pre-K or something. And there was another kid
there that she was not getting along with. And this was around Easter, and
they were painting Easter eggs. And some tussle came
up between them. And my friend's daughter broke
the other kid's Easter egg. Tears, hysteria, teachers
swooping in to say, you're not a bad child but
you've done a bad thing, and you can't do
stuff like that. And you are going to paint a
new Easter egg, to give to her, to make up for the
one that you broke. So my friend's kid proceeds
to go to the corner with this new egg and
some paintbrushes. And what becomes apparent
after a while is she's sort of, like, looking over her shoulder
and working away on something, here, and glowering
back at everybody. And finally she comes
up to the other kid and says, here's your stupid
Easter egg, Happy Easter, and gives her an egg that
she's painted completely black. [LAUGHTER] OK. What's with the
aggression, here? Easter eggs--
pastel colors, bunny rabbits-- all that
sort of thing. Easter eggs are not supposed
to be one solid color and certainly not jet black. That's not what-- what
was she doing, here? She was cooperating with
the letter of the law while doing as much violence
to the spirit of the law as possible. What she was saying
was, she is making me paint this egg for you, and
I don't like you one bit more than 30 minutes ago. And, showing that
the other kid fully understood what this human
bit of passive-aggression was about, she burst into tears
as soon as she saw the egg. Next example of the subtlety
of human aggression. And this one involved my wife. OK. [LAUGHTER] So this was-- occasion. We were, like, driving
around somewhere-- minivan, with our kids. And some total jerk,
like, cut us off. And-- you know, he could
have killed us and our kids, and-- [GROWL OF FRUSTRATION]. My wife was driving. And we sort of get past
what should logically have been about five seconds
of cursing the person. And she suddenly says,
I'm going after this guy. [LAUGHTER] And she proceeds
to trail the guy and trails him for
about two miles, while I'm sitting there
getting increasingly distressed and panicked. And eventually
he, like, realizes he's being followed
now and is taking sort of evasive maneuvers. And eventually we get
him on this street where there's a red
light, there, where there's a car in front of him. And then we're behind him. So it's not like he
could, in a panic, go through the red light, there,
because he's trapped there. And we happen to know this
was a very long red light. While I've been sitting there,
for the last five minutes, saying, um, do you
think this is really a good-- [VROOM] go
around another corner, tracking him down. So we're sitting there. And suddenly my wife says,
I'm going over there. And she grabs something from
between the seats and storms out. While I say, um, do you
really think that's a good-- [LAUGHTER] She's gone. So I, like, get out,
and I run over there. And I see the window's
down in the car. And she's yelling at the guy. And she says, anybody
who could do something like that needs this. And she flings something at him. So she comes back to
the car, at that point. And the light has changed. And this guy, like,
slinks off into the-- if it is possible for a car to
look sheepish, moving, like, four miles an hour, heads
off into the sunset, down this dark,
little block, there. So, sitting there. And she's milking this
for all it's worth. And turn-- what did
you put in there? And she looks totally
delighted with herself. And she's, like, euphoric. And I said, well, what
did you say to him? You-- what was
that-- and she said, anyone that could do anything
this mean needs one of these. And I said, what
did you do then? And she said, I threw
a lollipop at him. [LAUGHTER] I said, whoa! You killer, you! You-- I was so proud of her. My god, the violence
intrinsic in that! No other species would know
what was that going on, there, in terms of the intrinsic
passive-aggression and all of that. We're the only ones
who could come up with something like that. Third example. Every day, out in
Nevada, in a town there, there are men who get
up to go off to work, and they kiss the
family goodbye. And they've got to get reminded
to pick up the dry cleaning. And they get in the car, and
they're a little bit late, and there's a lot
of traffic, and they get all stressed
about the traffic jam. But they get there
to work on time. And they're a little
bit relaxed there. And they finally can come in. And they sit down
in a chair in what is a model of the cockpit
of a fighter plane. And what they do is
control drone airplanes on the other side of
the planet, in Iraq. And they spend the
day, sitting there at their work shift,
controlling planes that release bombs and missiles
and destroy people 12,000 miles away. So they spend the
entire day, sitting there in this air-conditioned
room in Nevis Air Force Base, just outside Las Vegas. And they spend the
day doing that. And at the end of the
day, they pick up, and they tell everyone
they'll see them tomorrow. And they go pick up
the dry cleaning. And they go to their little
daughter's ballet concert. And afterward they
hug her and can't believe they could love
somebody this much. And then the next
morning they go back to spending their
day killing people on the other side of the planet. There is not a whole
lot of species out there who could do that, either. So by the time
you're getting to us, we have ways of being awful to
other members of our species that are simply unmatched. And we have ways of
being empathic, as well. As we begin to wrestle,
here, with the neurobiology and endocrinology and
finally walking our way back towards the left, we're going
to have this huge problem of the context of aggression and
this even huger problem of just how complex aggression
and empathy are, when you leave it to humans. Examples at the empathy end. Human versions of it. The things we are
able to reconcile. We are a species
who has invented truth-and-reconciliation
commissions in South Africa, in the Balkans, in Rwanda,
where people face the person who did that to them, the person who
destroyed their life, destroyed their family. And going through what is by
now a fairly well-worked-out process that all sorts
of people have studied. And, in some of those cases,
there is reconciliation. There is even forgiveness. How can this possibly happen? We have a world where we
try to have individuals foster peace through the
most unlikely of rationales. I will let no man spoil my
soul by causing me to hate him. That is a psychology
that is unprecedented. We have the world of people like
this Catholic nun, Sister Helen Prejean, who has spent
her entire career ministering to the needs
of men on death row in a maximum-security
prison in Louisiana. She was the person who
was featured in the movie way back when, Dead Man Walking. And what she spent a
lot of her time doing is having incredulous
people, often the relatives of the
victims of these murderers, come up and say,
how can you do this? How could you spend your life
devoted to people like these? And she comes up
with an answer that is so definedly human, that no
other species could come near. No matter how much
they groom victims, her answer always is, the
less forgivable the act, the more it must be forgiven. The less lovable the person,
the more they must be loved. And suddenly we're in a world
that the more something cannot be, the more it must be, as
a moral sort of act to do. Whoa-- nobody out there
in the animal kingdom is going to have a
clue what we're up to. This is very complex
terrain we are going to deal with, here,
as we now shift over to the biology of it. OK. So, starting now
with our strategy-- a violent act occurs. An empathic act occurs. Any in these categories. What was going on in the
brain, one second before? And, of course,
what do you know? We're going to immediately
going to land is, right in the middle
of the limbic system. And, just as the Kluver-Bucy
syndrome from the 1980s, as we heard about last
week-- just as that syndrome, when you destroy
the limbic system, you get completely inappropriate
sexual behavior in primates. What those studies
also showed was, you get completely inappropriate
aggressive behavior. OK. So, with 80-year-old
research, we've now landed in the limbic system. What are the subregions
that are relevant? The area that comes in
at the top of the list, immediately, that we've already
heard a fair amount about, is the amygdala. The amygdala and
its role in fear, its role in anxiety--
that strange role, in males, of sexual motivation. But what the amygdala
is most renowned for is its role in aggression. And, as I emphasized
last week, it is mighty interesting,
I think, that the part of the brain which is most
responsive to when you are scared is the part
of the brain that generates the starts
of aggressive behavior. Again, in a world in which
no neuron need be afraid, we're going to have a lot fewer
aggressive amygdalas out there. What's the evidence? You know the drill by now. You go and you destroy
the amygdala in an animal, and you are incapable of
eliciting aggression from them. You go and you do the
same thing in a human, and you get the
exact same result. One of those dark,
horrible chapters in the history of
science-- another realm of legally enforced
psychosurgery. This was a trend that
was very, very popular in the '60s and '70s--
court-ordered amygdalectomies of people. And this was a
technique where people would go in with a lesioning
syringe into each side-- the amygdala is a bilateral
structure-- there's two of them, way
deep in the brain-- and go in and destroy
the structure. And this would
decrease aggression. This would decrease
all sorts of stuff. This wound up on the front
page of the New York Times when, around 1970, three
neurosurgeons at Harvard wrote a letter to the New
York Times, pointing out there's this great
surgical technique which they were the
pioneers of where you could take aggressive
humans and make them less aggressive with
no other side effects. You could make them
less aggressive. And haven't you been noticing
that our inner cities have been burning and rife with violence? Maybe it's time to start
thinking about doing some of these preemptively. This was a letter
from these three guys from Harvard Med School. No surprise, not
everybody sort of thought this was the swellest
idea that they had ever heard. This generated this huge fight
over the psychosurgical use of court-enforced
amygdalectomies. And before it was over with,
it had just as bad of a history as frontal lobotomies. People subjected
to amygdalectomies because they were argumentative,
because they, as teenagers, didn't listen to their parents. They didn't listen
to their teachers. Thousands of cases of these. The one thing that was
clear was that, yes, indeed, aggressive behavior would
decrease in these individuals. There would not be a whole lot
of a person left afterward. So, lesioning evidence. Stimulation evidence. You know the flip
side of that by now. Now stick an electrode
into the rat's amygdala and stimulate, electrically
stimulate, there. And you produce wildly
aggressive behavior. And you see two equivalents
of that in humans. And in both of these
cases, stupendously rare. First is a very,
very, very rare type of epilepsy, where
what you get is the epileptic focus, the place
where the seizure begins, is in the amygdala. What you see is, with
most types of epilepsy, the place where it starts
in the brain, a seizure, tells you a whole lot about
matching with the behavior. People, just before the
onset of the seizure, will get olfactory
auras-- two or three seconds of
hallucinating an odor. That's a seizure that's
starting somewhere down in the olfactory part
of the limbic system. You see all sorts of cases. There have been documented
cases of epileptics who see a mathematical
equation for two seconds before the seizure hits. And that's an area of the
cortex where it turns up. Auditory seizures, where they
hear two measures of music-- the same two measures
before it hits. What you see when you've got
these rare epilepsies, where the seizure begins
in the amygdala, is, two seconds before, the
person becomes furious. They-- I can't bel-- I am so
ang-- and then it happens. So, uncontrolled stimulation
in the amygdala, and you get some aggression there. The next thing that
you see is evidence of the amygdaloid stimulation. OK. Anybody ever hear of a
guy named Charles Whitman? Hands-- oh, what are they
teaching you guys, here? OK. Charles Whitman was once
America's record-holding mass murderer. And he was the best
that we could come up with in the early 1960s. And, oh, his records
have been eclipsed by so many people since then. But he was once our
gold-medal mass murderer. This was the guy who,
in 1962, I think, climbed up the famed clock tower
at the University of Texas, Austin, campus and opened
fire on people below. And then killed
himself, afterward. This was the first of the
rounding up the neighbors to say, oh my god, he
was such a quiet guy-- he was such a nice neighbor. This was the first of the
literal choirboys-- my god, where did this come from--
no hint of anything. On postmortem, he was found to
have a tumor in his amygdala. Another rare case of that. During the 1970s, there was an
extreme leftist terrorist group in Germany called the
Baader-Meinhof gang. And these were the two
people who began it. And one of the two stupendously
violent people-- one of the two found, on postmortem, to
have a tumor in her amygdala. So these very, very
rare cases of this, fitting with this
theme-- circumstances that increase the
metabolism in the amygdala. Out comes aggressive behavior. More evidence. Now, another strategy
from the limbic lectures. Put in the electrode. This is one that responds
to electrical signaling. Show somebody
something that evokes aggression, and their
amygdala has gotten activated. Do the same thing,
now, with a human. Put them in a brain
scanner, and show them something that evokes anger. And the metabolic rate in
their amygdala activates. So you see all sorts
of circumstances where you can document the
amygdala as playing this role. Interestingly, the amygdala
gets bigger, as we've heard, in people with posttraumatic
stress disorder. And what you see there
is also increased frequency of violent behavior. More evidence that the amygdala
plays a role-- and this was a very subtle finding. This was from-- oh my god,
the clock in the back! Turn around and
look at that clock. [LAUGHTER] Everybody run! [LAUGHTER] OK, well, now that
it's almost done, I'll mention the very
last thing, here. These were studies
done showing-- OK, people with amygdaloid
lesions, they are very bad at detecting faces
expressing angry emotions. They are more trusting of people
than average individuals are. They are more likely to forgive. They are less capable of picking
up on any of that information. And a wonderful study done by
this guy, Antonio Damasio-- again, one of the lead
figures in the field. What he did was eye tracking on
people with amygdaloid lesions. You get someone with this
part of the brain destroyed, and they don't look at
the eyes of other people. When they examine faces,
they're looking at the nose. They're looking at the chin. They're not directing their gaze
to be able to pick up accurate information about emotions. So what do we see, here? The amygdala not only
responds to aggression and fear-provoking stimuli. The amygdala is able to
direct you to look for it. And what we will
see on Wednesday is, one of the things
testosterone does in males is it makes them look harder. It lowers their
threshold for deciding that ambiguous
information is, in fact-- For more, please visit
us at stanford.edu.
