17. Human Sexual Behavior III & Aggression I

Transcription for the video titled "17. Human Sexual Behavior III & Aggression I".


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Introduction To Topic

Intro (00:00)

Stanford University. >> Started. See some exam related announcements. First off, there are the statistics, mean and median, which in terms of the 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 a 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 past no credit, that sort of thing. So these guys did yet another amazing job. 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, and the TAs will be flinging boxes of exams around out there, so go get yours afterward. Again, people did a good job. Okay, picking up on our by now, sickeningly familiar time course 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 we're immediately talking about the evolution there of 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 counter-strategies in a lot of those cases.

Exploration Of Beauty And Female Choice

What is Female Choice? (02:26)

What we also then transitioned to was what female choice was about, even in species that were tournament species, and what we transitioned 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, then the guy who believes he's the father is going to be taking care of the kids, and what you want is someone who is good at that, is confident 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 characteristic, what's that about its females competing with females for males to pick them, exactly the opposite scenario, as in most of the species we've been hearing about. Okay, 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 be so universal at 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 and identical twins versus non-identical, finding a genetic marker, but one that nobody else is able to replicate. So everything now is predicated on the notion that genes have at least a little bit of something to do with it.

Heterozygous vigor argument (05:50)

So three theories that have floated around. First one being the heterozygotic vigor argument, which 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 resistant 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 a 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 is 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.

The Helper at the Nest Model (08:15)

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 are doing is expending resources on helping their siblings. Okay, so that kind of sounds like the second model also. What is the difference? The second model says that sisters of gay men should have increased reproductive rates. What the third model, the helping of the nest model suggests is both sisters and brothers should have increased reproductive rates and that is actually what is mostly been seen. So support for this helper at the nest can selection kind of argument. Okay, what else does one look for in a mate besides all of the stuff that males are competing about in females and pair bonding species? What are some of the characteristics that pop up over and over again when it is getting around to who looks good to you if you are a damsel fly trying to pick out a mate and all these other species, one initial characteristic which is the famed role of facial symmetry in attractiveness. This has an interesting history. 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 were really skilled police people could 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 rambiuses of all sorts running through their 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 criminology, 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.

Rectangular Faces (10:50)

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 is 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 combined subsets of them and having people rating attractiveness and stuff.

Symmetry and beauty. Peoples subliminal ability. (12:05)

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? Okay, so thereby proving the point. And what you've got is symmetry is apparently a good reliable marker of health. And 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. And with the face up there and all the little caliber markings and showing the same sizes and then some poor snuck who's chosen to be the asymmetric face who stuck up there. Did Newsweek wind up, the Newsweek article wind up being in the readings? No, it wasn't. Yes. Okay. Lyle loved it. Is that the face they had there that they were making vicious fun of and pointing out oolip 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 and faces. Babies at two months of age show when you are doing morphed faces, composite faces, where you can very carefully, 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's a bias in non-human primates for more symmetrical faces. How's this for a nutty study that was published about five years ago in nature?

Beauty, dance, symmetry and attractiveness 70-80 yr-olds. (15:07)

And this one reported that people who had symmetrical faces were better dancers. Okay. 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, I don't want to know, some famous scientist rapping to something or other. And people dancing away there and then they used this amazing technique, which I didn't understand the slightest, with some sort of camera capture technique that would make everybody dancing look like gumbee. 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. And 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 like this. So that is probably what the indirect route is. 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.

Women ovulate when they are closer to a man that is asymmetric. (16:52)

One additional finding in the symmetry world, women at the time that they are ovulating have their faces become ever so slightly more symmetrical. Okay, 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 is business about symmetry. Next round, this whole world of secondary sexual characteristics. Why is it that female peacocks like male peacocks that 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 is very influential Israeli zoologist who came up with what is called the Handicap principle.

Handicap principle. Secondary sexual characteristics are markers. (17:55)

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 are 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. There are 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 marsupial esque reproduction that made this species to do this with, but it was doing sperm insemination of females. What was done was that they took the sperm from these male marsupial mice after measuring some secondary sexual characteristic in them. I believe that they don't have antlers, but I don't remember what the actual thing was. What they were able to do was to now have sperm for males of differing degrees of exaggerated secondary characteristics. What they showed was that the males who had the more dramatic secondary characteristics, their sperm were more fertile. 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 pot latch, 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. That is 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. 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. 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.

Perhaps sexually transmitted diseases. (21:19)

Which is extremely interesting. What is the comparison there? It was all those Scandinavian countries. Thank God for the Scandinavian countries because they always provide the extreme of these distributions. So in those Scandinavian countries, there has not been a guy who has been selected for a date because of the height of his forehead and 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 they're 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, 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 if 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.

The Handicap Principle Explaining Secondary Sexual Characteristics (23:30)

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 three and a half 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 and mid animals being sick. So of course you have to have counter strategies 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 got one problem with this whole literature which is there's a certain way to frame things so that you never ever can get a finding that disagrees with your general stance. Okay, 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 teaming with parasites, I've got the greatest DNA going around there. And how about it? Where you see this is in vultures and the mirror 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.

Main masculine mating displays: beautiful mating displays (25:44)

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, okay, 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 heard. In vultures, you see exactly the opposite, which is where it is. 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 likelihood that you have some sort of infection that you've picked up. What's the interpretation there?

Discussion About Mate Selection And Marriage

White-Manus Lions Estrogens (26:40)

Yet here I am bouncing around happily and energetically, just imagine how great my genes are. If I'm able to do that, I'm just teaming with parasites because of my unlikely 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 is a marker of look how well I'm functioning here. Despite teaming 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 there's no free lunch and there's no free ungulate. Whatever. Okay, 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 mains, the mains 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. And 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 mains male because that is one that is most expensive in this candy cap principal 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 thermoregulation. 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.

Well-Formed/Genitals Estrogen Swellings (28:43)

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's 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 non-human 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.

What women prefer in a mate and how men determine mates (30:18)

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 could be running around in my female and estrus sort of weight 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 opulators. 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 that flipped it around the other way. Okay, the bigger the hips are relative to the waist, this is a marker of fertility. That is a marker of child bearing pelvis is that is a marker of all sorts of developmental health that augers 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 were 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 of asking the guys there. And at this point, not surprisingly, there's 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, a 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 and males, which is jutting jaws, big high far heads, 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 that of males that have been manipulated, changing the dramatic, how dramatic the secondary characteristics are, like far ahead and jutting jaudness and angularity of face and stuff, what you see is an interesting dichotomy, which is in these studies, women on the average rate the round or faced pictures of men, such men looking more likable, more honest, more trustworthy, and less desirable. Okay, 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 and nostril width and things when they're menip, 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. Okay, 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's rate is more attractive, male faces with the juddier jaws and the greater muscle mass and the far ahead stuff going on. What we see here is this theme of at the time that estrogen levels are at their highest end, humans and lots of realms, addition to other species, detection of pheromones for 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. Okay, so what other things? There's one problem that runs through this entire literature. Okay, so here's the deal. You are a, 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 made it 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 and various bird species, mate females with males who have, who are more attractive versus mating them with less attractive and what you see is that the females who have made it with a more attractive males give birth to bigger eggs. That's interesting. Okay, 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. But 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 is 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 worked by a guy named Lee Dugotkin at 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 wrapped abdoration and just frozen in their place at the wonders of the coloration on his bill from eating who knows who's feces. And what you see then is the female who spurned him is now more likely to do the solicitative 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 parabonding species and as we heard from many lectures ago, the rituals and 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.

Homogamy (40:01)

What's that about? 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 parabonding species, the rituals and what is attractive are often markers not of fertility but of parenting skill, parenting competence." Flip the other way, in most non-human 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. 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 in 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, 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 married. Here are the statistics. When you look at couples in this country, there is better than 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 child, did they both growing 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 people 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. Could you just see that I know a lot more people look the same age as me, same race, same socioeconomic status and so on? Okay, 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 Scandinavian? They're so dull and healthy and sensible. Okay, so in those sensible non-scandinavian Icelandic who have like, I don't know what, 300,000 people in the whole country and all of them are no more than six cousins apart. 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 homogeneous choices as to their mates the younger they are when they get married.

Random Variation in Wife Selection Among Printer People (46:40)

What's that, what's that a surrogate for, the incredibly depressing fact that on the average people get more and more clothes minded as they get older. You see the greatest heterogamy and marriages, the greatest likelihood of people marrying someone with a very different background, the younger they are in the early twenties 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 twenties, this is the likelihood of marrying somebody from a different religion, and then it goes way down in the thirties and in the forties, 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? Somebody stick there.

Marriage and Mortality (47:43)

Fewer options for mates. Fewer options for mates, that's one depressing possibility, and just wait until like you're in the nursing home and like anything that moves you in print on, yes, theory. Okay, so the issue of if you do that, if you've waited long enough that you're not going to have kids, that you're not going to have all these fights of, or you're going to be a Mac family or a PC family, or all those sorts of things that can tear people apart, recording. Okay, so that's a possibility. How about another one? Okay, 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? Is that an idea? Midlife crisis. So it's either you get a convertible or you marry someone from, you know, from 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 had 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. That appears to be part of that scenario, which is, you know, 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. Okay, finally, finally a study, a famous study that was done about 15 years ago by an evolutionary biologist named David Bus, 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, questioners 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, socialists, 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 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 this 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.

Examination Of Human Aggression And Violence

Of Human Aggression, Competition (51:50)

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. Okay, 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 sort of the range of what aggression can be like, but also a very important point that's going to come through 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 was 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 I'm old and 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 wind up guarding me, who was a total son of a bitch. This guy, 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 of 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 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 the 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 it, and I just stick my foot in front of his ankle and send him rolling and 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 been rained in six months. This was wonderful. And I didn't even go through the pretense of, "Oh, you okay? Sorry about that." It was just like, I had to restrain myself from ripping a 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. Nelson Mandela. Nelson Mandela. Now in his 92nd year. Frale, frail and 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.

Violence (56:37)

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 also 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 that what you do with your muscles in another setting. And 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 differ and surely 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 of dealing with terms for aggression and violence. Probably a great starting point is just as with the sexual behavior, it's 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 were somewhere in there. Somebody with a very deep voice has to entone about how only man kills for pleasure when watching some beasts throwing the old will to beast into the river. They're misinterpreting it. And that was always the theme where 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, with Langer Monkeys, a primatologist named Sarah Herde who was at Harvard at the time, and she was the first to report this and this could not be. That male Langer 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.

Are we the only ones? (59:55)

These were populations of Langer Monkeys in some urban areas in India where she was studying them. This is not normal because no other species kills. And now that is up to 20, 25 different species or show 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.

Chimpanzee Border Patrols (01:01:06)

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. The business that is 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 a group. We'll 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.

Going Beyond Humans (01:03:02)

That appears to be something resembling a human unique trait. Okay, 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 exclusively human ability, yeah? Are there any instances where certain troops among these people would not have just killed all the males in the infantry, but killed all the males in the infantry, and then sent to the genocide? Yeah, they will kill the infants at a competitive and fantasized 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 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. And 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, reconcilative behavior in a couple of dozen other species. First person to report this, primatologist Franz Devalle, first reporting this in re-system 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 guerrillas, for example, to do social grooming in the aftermath than at any other time, an increased rate of that happening, reconciliation.

Empathy & Understanding Genesis (01:04:57)

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 get in 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 reconcilative afterward.

Understanding Human Emotions And Behavior

Bonobos (01:06:24)

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 reconcilative 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 Franz de Voll 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 guys sitting there minding his own business, high ranking guys 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. In the second case, he was an innocent bystander. What de Voll 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. The remarkable study published in science a couple of years ago, a group from McGill, and what they showed was arguing this is something resembling empathy in rats.

Being moved by empathy, panic, and pain (01:09:00)

Here's what they showed in the study. What they had was, 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 did they first lift up one of their paws and quick take them off at that point. 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 okay alarm calls and stressful and just putting me in a more agitated state. What they showed was this only worked when it were rats, when it was rats that were cage mates. 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 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're not the only species that could take it to just domains that are utterly unrecognizable. We're the only species that is moved by people on the other side of the planet who have just been in some catastrophe. We're the only species moved by artwork that depicts suffering by movie characters, by fictional characters in books. We are taking 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? Anyone who hasn't seen it? Okay. This 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 on the dark and it's pouring and it's drizzling out. And you're sitting there feeling terrible for this damn 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.

Justice, Cooperation, Aggression, Violence, Play (01:12:52)

What else? We are ostensibly the only species with a sense of justice. Again, that's not necessarily the case. Again, work by Franz Duvall, whose name keeps coming up, who is one of the best, most creative primates in the world. Most creative primatologists in the universe. This is work now where again, chimps, two chimps were circumstances where 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 chimp 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 Franz Duvall 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 averse of the curt of 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, our 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 a 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 pattis monkey. Go and study pattis monkeys and spend 40, 50, 60 years doing it, and what you will see are virtually no instances of male pattis monkeys having fights with each other. Wow, that's a pretty unaggressive species. That's kind of nice. Put two male pattis 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 pattis 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 hardwired in there.

Why are humans so unique? (01:17:34)

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. Okay, so all sorts of ways in which aggression can pop up in other species and unexpected realms in which cooperation, all sorts of things like that, what are some of the unique human ones? Nonetheless, in 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 cudgling somebody over the head, but we're the only species that could be violent by doing nothing more physically taxing than pulling a trigger or looking the other away, or releasing a bomb from 3,000 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.

Passive Aggression (01:18:38)

First one, this was the child of a friend of mine when she was about 5 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 she broke. So my friend's kid proceeds to go to the corner where there's new egg and some paint brushes, and what becomes apparent after a while is she's sort of like looking over her shoulder and working away in 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. Okay, 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's 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, and 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. Okay, so this was occasion we were like driving around somewhere in a minivan with our kids and some total jerk like cut us off, and you know, it could have killed us and our kids and 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." 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's 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 pan and 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, "Do you think this is really a good... I'm going around another corner tracking him down."

The Violence of Parting (01:21:43)

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, "Do you really think that's a good..." And she's gone, so I get out and I run over there and I see the windows 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 slinks off, and 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 its worth in terms of, "What did you put in there?" And she looks totally delighted with herself, and she's euphoric, and I said, "What did you say to him?" "What was that?" And she said, "Anyone who 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." I said, "Whoa, you killer you!" You guy was so proud of her. The violence and trinsic in that. No other species would know what was that going on there in terms of the intrinsic passive aggression and completely, 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 that 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 with 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 pugger 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.

Insights Into Aggression And Fear Recognition

Tour of Duty (01:23:30)

There's 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 are 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 species who has invented truth and reconciliation commissions, and South Africa and the Balkans and 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.

What can we do to redeem ourselves? (01:24:58)

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 Prijon, who has spent her entire career ministering to the needs of men on death row and a maximum security prison in Louisiana, she was the person who was featured in the movie Wayback 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 defiantly 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. Okay, so starting now with our strategy, a violent act occurs, an empathic act occurs, any of these categories, what was going on in the brain one second before?

The role of anger in aggression (01:27:25)

And of course what you know where immediately you get a landing is right in the middle of the limbic system. And just as the clover-busey syndrome from the 1930s, 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. Okay, so with 80-year-old research, we've now landed in the limbic system. What are the sub-regions 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 may be afraid, we're going to have a lot fewer aggressive as amygdala's 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.

The warning signs of violent behavior (01:28:54)

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 amigdilectomies 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 swelest idea that they had ever heard. This generated this huge fight over the psychosurgical use of court enforced amigdilectomies. And before it was over with, it had just as bad of a history as frontal lobotomies. People subjected to amigdilectomies 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 rats amigdile 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 amigdile. What you see is with most types of epilepsy, the place where it starts in the brain is 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 the olfactory part of the limbic system. You see all sorts of cases.

The role of the amygdala/fear recognition (01:31:56)

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 out. 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 believe I am so am." And then it happens. So uncontrolled stimulation in the amygdala and you get some aggression here. The next thing that you see is evidence of the amygdala stimulation. Okay, anybody ever hear of a guy named Charles Whitman? Any hands? Oh, what are they teaching you guys here? Okay, 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 choir boys. "My God, where did this come from? No hint of anything." On post-mortem, 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 Baden Meyerhof gang. And these were the two people who began it and one of the two stupendously violent people, one of the two found on post-mortem, to have a tumor in her amygdala. So these very, very rare cases of this, fitting with this theme, circumstances that increase the metabolism and the amygdala outcomes aggressive behavior. More evidence. Now another strategy from the limbic lectures put in the electrode. This is one that responds to electrical signaling, shows 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, and 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 post-traumatic stress disorder. And what you see there is also increased frequency of violent behavior.

The Amygdala gets bigger (01:34:59)

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.

Aspects Of Physical Activity

Lets all Run! (01:35:10)

Everybody run! Okay, well now that it's almost done, I'll mention the very last thing here. These were studies done showing, okay, people with amygdala ad 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. In 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 amygdala ad lesions. You get someone, 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.

Concept Of Unreal Threat And Fear Response

Threshold for Unreal threat/ Scary Sounds (01:36:31)

And what we see here is that the amygdala is their threshold for deciding that ambiguous information is in fact scary. For more, please visit us at stanford.edu.

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