16. Human Sexual Behavior II

Transcription for the video titled "16. Human Sexual Behavior II".


Note: This transcription is split and grouped by topics and subtopics. You can navigate through the Table of Contents on the left. It's interactive. All paragraphs are timed to the original video. Click on the time (e.g., 01:53) to jump to the specific portion of the video.


Intro (00:00)

Stanford University. >> Let us get started here. So picking up from the other day, where have we gotten, not very far, behavior, full range, variability of sexual behaviors, fixed action patterns, is this kind of dark here? No. Seeing in some ways what's interesting is the conservative nature of sexual behavior across species, other ways the sheer variety, trying to make sense of what aspects of human behavior are unique, all of that. Then beginning to marching backwards, what goes on in the nervous system, one second before sexual behavior occurs, and marching through the relevant limbic structures, some of which have strong sex differences, some of which, that don't, seeing some ways in which neurotransmitters in the whole world of dopamine complicates things enormously marching through there. Where we had then gotten to was asking, okay, so what sort of bits of information in the environment, what sort of ethological releasing stimuli can trigger the nervous system to do its thing, and you've got the drill by now. So what we had done was look at a couple of different sensory systems, and we had just started to wallow in the world of pheromones, a pheromone communication. What we ended with was, number one, the hormone dependency of generating sexually meaningful pheromones, and that business being that males have to have sufficient testosterone, females have to have ovaries on board to be producing pheromones that carry sexual meaning. What is the reason for that, the fact that a whole lot of the actual chemicals that constitute sexually meaningful pheromones are made out of some sex hormone breakdown products, and the sheer bizority, but eventual wonderful clarity of what's up with perfumes. Then transitioning at the very end to the business about how your endocrine status has a lot to do with your perception of pheromones from the other sex. That women who are over-erectomized, the low estrogen levels have trouble being able to differentiate the smell of males and females, men and women, and estrogen replacement takes care of that, the exact same thing when you take away testosterone for men, and what we were just about to get to before we had to stop was one additional thing, which is one's opinion about the pheromones that you were smelling. And this goes back to a literature, a really interesting one, showing that not only are women better at differentiating between the smell of men and women, gonadally intact men and women, not only are they better at doing that around the point of ovulation, but their preference for the smell of males gets more dramatic around the time of ovulation. Meanwhile, over at the male end of things, something rather similar in terms of what you make of the pheromones, and this was a famous classic study in which women volunteers had their armpit swabbed at different points in their menstrual cycle and put into little seal jars and all sorts of male volunteers, sniffing them and raiding their pleasantness. And what you found was on the average, the odorants were rated in the unpleasant direction, but they were rated as least unpleasant around the time that women are ovulating.

Understanding Sex And Gender Dynamics In Nature

The Gender-Sex Nexus (03:29)

And I think once we get past the world of armpit smells and little glass jars, one can get into the more ethologically relevant world of men prefer pheromones derived from women around the time of women are ovulating, once again, a testosterone dependent phenomenon. What we now begin to look at are some of the physiological effects of sexual pheromones between sexes within sexes. One example you heard about in the very first lecture, which is that whole business that wellsly effect the ability of females of all sorts of different species, including college freshmen, human females, to synchronize each other's cycles, this being done with pheromones, intersectional perception of pheromones, so the wellsly effect. What's also shown in a number of rodent species is the pheromones, the smell of an adult female will delay the onset of puberty of younger females. And how might one frame that? That is utterly a gene competition sort of strategy there. This is reproductive competition. If you arrest the development of the other females around you, you are going to leave more copies, etc. Meanwhile, a literature of intramail physiological effects.

The physiological effects of pheromones between species (05:04)

What happens to the physiology of males in various species when smelling the pheromones of other males? What you see, first off, is it depends on who the other guy you're smelling, the dominance rank. And lots of rodent species and some primate species as well. Males are able to differentiate between smells of very high ranking males and very low ranking ones. And what do you know? They're not all that upset about the low ranking ones. What you see in terms of the physiological effects in the number of species when males are smelling the pheromones of big, healthy, strapping androgenic other males, in some cases, it drives down their testosterone levels. They're totally physiologically intimidated, this being some great competitive strategy for males who could pump out just the right kind of suppressive pheromones. In other species, though, what you see is a sudden burst of sperm production. And what's that about another version of the same logic? This is a counter strategy. If males have come up, evolve the means in various rodent species to generate pheromones that will drive down testosterone levels and opponents, what males also want to have evolved with some mechanism of when smelling those sorts of pheromones to try to counter that by increasing sperm production. What we have here is a co-evolutionary arms race. In terms of interactions of pheromones between the sexes, and what I've been doing here is describing all this without making use of this.

How the smell of a dominant male can reduce testosterone and increase sperm (06:33)

So what you see is physiologically when the female is the pheromone donor and the other recipient is a female in terms of, say, puberty, decreasing puberty onset. And what we just saw with male as donor versus male is in some ways suppressing some endpoints testosterone in some ways, increasing sperm production. What you see in lots of rodent species when you're looking at between genders, when males are the source of pheromones among rodents, it accelerates puberty onset in the females. And when you've got females as the donors, it increases testosterone level and sperm production in the males of lots of different species. So all this makes wonderful, wonderful sort of sociobiological sense in terms of this should work. Elaborations on this, of course. What you also see is not only puberty onset and being regulated. You also see in all sorts of species where you can induce ovulation by sensory stimuli. What you see is the smell of a female will decrease the likelihood of induced ovulation. Female, the smell of a male will increase the likelihood of ovulation. There are all sorts of species that do not have automatic rhythms of ovulation cycles of that way, but rather they are induced. And one classic example of that are pigs. Pigs are inducible ovulators, if you've always wondered whether that's the case or not. And you can go and recreationally by a variant of pig pheromone, this known as bormate, and no doubt that's not only patent-pended, but somewhere out in the Midwest, there's all sorts of TV jingles about bormate. And bormate is a pubret, is a ovulation inducer in female boars and involving a same male derived pheromone, which are found in truffles, truffles which somehow have stumbled on the means to induce female pigs to ovulate and no doubt that's explaining some very interesting species interactions.

Heres the evidence that females can be universally induced ovulation (08:23)

So that being another realm, inducible physiological changes, in this case, one classic demonstration of it. In this case, probably pheromones of female causing an indirect measure of testosterone levels in a male. This is a classic paper. And you will note that I didn't say females and males saying a female and a male. This was a classic paper in nature some 30 years ago or so, which was written by the very famous and well-known doctor Anonymous. The author's name was not published there. And this was a researcher who did research in an unspecified hemisphere with an unspecified species, but involved long stretches of being at a research facility completely on his own in isolation from other humans and all sorts of people in the business for decades afterward have been speculating on who the author is and it's generally understood. And what this person noted was every now and then he would pick up and go to the city that was a three hour sea plane flight away or some such thing where, among other things, he had a highly significant, significant other with a great deal of physical intimacy and all that stuff from kind of the right side of the chart. And what he noticed was what he perceived to be an extraordinary difference in what he was subjectively interpreting as testosterone driven mood and level of energy and all of that, depending on where he was. Not quite being the type of field ethologist that took blood from himself, what he did instead was take an indirect assay building on the well-known fact that testosterone has something to do with the rate of beard growth. And what he wound up doing was very soon having a razor there in every day, shaving and getting a little bit to stubble and weighing it. Waying it is an indirect assay of testosterone levels. And what was shown was sit out there by himself with whatever ungulates he was obsessing over in this sort of rate of beard growth, go back to the rest of the world and it does this in this square wave going on like that. This as a very, OK, what are all the confounds here? It's not clear if it was pheromones. Maybe it was actually being in proximity to the newspaper in the town that he returned to now and then maybe there was a confound of whatever after shave he was using that was doing something rather to his testes. Nonetheless, generally interpreted as this being a really interesting indirect and equals one example of induction of physiological changes in human males by pheromones from females. So if you ever meet Dr.

Pheromones (11:30)

Anonymous who interestingly has been publishing papers for about 300 years or so now and then congratulate that individual on the research. OK, so pheromonal stuff now elaborations of it, which you should be able to derive all on your own from some of our principles by now, which is what if, for example, you are a female donor and female recipient and the whole logic here being decreased the likelihood of ovulation delay the onset of puberty. What if these are siblings if these are two sisters and you are often running with that one, it will not work as effectively easy kin selection argument. So all sorts of aspects of relatedness. You will not have your testosterone levels driven up if you are a hamster and you are smelling your sister, all that sort of thing that makes perfect sense by now. OK, now switching over one last piece of business though in terms of the pheromonal tractiveness stuff, a handful of studies showing that among homosexual men, what you have is it's the smell of men who are preferred to women and it's when men have higher testosterone levels that they are preferred. And what we've got there is a exact same physiology and a somewhat going in the opposite direction, flipping of things that sure argues for some interesting psychological underpinnings. One final thing, women not only prefer the smell of men when they around the time that they are ovulating, their noses selectively become more sensitive to such smells and estrogen has all sorts of receptors on olfactory neurons. So that makes sense.

Gustatory (13:21)

OK, leaping over to other sensory systems, gustatory stimuli. This is not one of the more exciting outposts unless you're something like a giraffe, in which case you take part in what is called flemening, a good old Germanic ephological term, which is you want all sorts of interesting reproductive information on somebody else and you just don't have the time to sniff the air for pheromones. So what you do is you go over and lick the individuals private parts and suddenly you know, oh, so much about their personal lives. In this case, gustatory information being passed. We've already heard about examples of auditory priming, inducible ovulation and various moose-like species in the wilds of Minnesota where what the stags have these roaring fixed action patterns, which will induce all sorts of ovulatory responses and females around. So this is another domain. Remember also that interesting fact, and when this was mentioned previously that in human females, voices get a little bit higher around the time of ovulation and in a way that is detectable, something important in terms of all this pheromonal stuff in humans. What has been shown over and over and over again is these are all subliminal processes as in the humans are not consciously aware of, wow, this one smells more like my gonadily intact second cousin who was adopted away to Bolivia for a while when I was a kid. There's not the consciousness, but nonetheless, you force people to make these choices and implicitly you get insight into these same sort of influences. But of course, by the time you get to humans and you talk about sensory releases and all of that, you get, of course, the point endlessly emphasized by Cosmo and God knows where else that ultimately the most erogenous organ in humans is the brain thought as a release or thought as a more powerful humans are not a particularly old factory species.

Environment (15:02)

We are not a particularly great auditory one, etc, etc. An awful lot of the sexual priming in humans coming by way of thought by passing this whole ethological world. OK, more environmental factors, acute environmental factors that can affect all of this and what you've got is a very reliable way to drive down libido is to make an organism terrified, fear as suppressive of reproductive behavior. What you also have is extreme rage doing the same stress in general stress is interesting because what you get is a dichotomous outcome, chronic stress. So now we're not talking about an acute stressor, but all the way back, chronic stress is extremely suppressive of reproductive physiology and behavior, which you will be finding out when you read the relevant chapter in the Zebra's book. But what you see is short term, there's a lot more variability, particularly among males. What you see is a lot of variability as to whether short term stress stimulates arousal or inhibits it. And people have pointed out all sorts of horrific bits of evidence showing circumstances of extreme arousal and stress, say, during warfare where that produces all sorts of violent sexual behavior, no shortage of horrible historical precedents for those. OK, so a difference between chronic stress versus acute stress more affects around here.

Coolidge Effect (16:52)

One final interesting bit of releasing stimulus stimuli, whatever a bit of stimulus is, and one that transcends a particular sensory system is something called the Coolidge Effect. And the Coolidge Effect probably accounts for like 49 percent of the misery encapsulated in human literature and movies and all of that. What is the Coolidge Effect in species after species after species? You take an individual who is sexually sated, which is to say that, for example, you've got some male rodent who's been mating with the female rodent there and has gotten to the point where he has had enough, enough on some physiological level or some deeply emotional what matters to be in my life, a rudential sort of level. But in any case, the male is sated, has stopped having sex with the female. And what the Coolidge Effect is about is you put in a different female and everything start all over again, variety as wildly stimulating of sexual arousal. And the Coolidge Effect sure works in humans and accounts for all sorts of misery. Coolidge, by the way, was not the scientist you first described at, but Coolidge refers to Calvin Coolidge. And as far as I know, this is the only anecdote ever to occur about the guy, something where he and his wife were being shown some chicken farm and they were breeding roosters and when they would get sick of breeding with this pen, they would stick a new one in and Mrs. Coolidge made some sarcastic remark and he made one back and before you knew it, it was the Great Depression. So I actually have no memory of what they said, but in terms of wittiness, you get what you can when you have Calvin Coolidge. So OK, we hurdle on. We hurdle on here now beginning to look at an entire missing category here in my rush. Now we have what's going on with hormones, longer term hormonal stuff, not the hormone levels that you have influenced as a result of sexual behavior, not the hormone levels just right around the time of all this neurobiology happening, but now beginning to talk about hormone levels like over the last 28 days or so in a female. And what one immediately barrels into is this issue of how much is sexual behavior in women a function of where you are in your cycle. What's the reason even to suspect that the entire world of other species that will have females coming into estrus, coming into heat, having elevated estrogen levels, only at very demarcated times of the year. And what you see is in lots of species, a large number of them.

Sexual proceptivity Differs among Days Before Ovulation (19:44)

In fact, what you see is you only get reproductive behavior. You only get sexual behavior in females around the time that they are ovulating. You only get active female proceptive seeking of sex around those times. By the time you get to nonhuman primates, it depends on the species you're looking at. But in general, it's not quite as tight of a relationship. So if you had some rodent and across a year, this was all the points of ovulation, your pattern of sexual behavior of a female would look like this, likelihood of mating with a male. By the time you get to nonhuman primates, in most species, it looks more like that. It's not quite as dramatic. And thus, of course, the question becomes, where do humans fit in on this? And a classic study extremely influential in the early 70s was the first to look at this, which was females, humans, women reporting their levels of sexual activity, as well as the likelihood of orgasm per sexual bout, if that's the right word, and where they were in the cycle. So this is what you wound up seeing. And this by any measure likelihood of having sex, whatever, the curve looked like something like this. And what they reported was a big increase around the time of day 14 and a secondary increase around day 28, not as large of one. And when you looked at the likelihood of orgasm, it was basically doing the same exact thing. OK, day 14, that's just a somewhat less restricted version of the exact same phenomenon, never down to zero. But nonetheless, this is another version of this exact same phenomenon, libido sexual proceptivity, increasing in women and human females around this time of ovulation. But no other species shows this one going on here. So what's up with that? Any speculation why you have the secondary increase around day 28? Oh, come on, somebody's got a... Yes, you're right. That's exactly what they found. That's exactly what they found and good for you, feeling comfortable speaking up in class, all in unison like that. OK, what that tends to be is that women are more relaxed about fear of pregnancy around the time of their period and thus sexual behavior increases somewhat around that point. But the thing that everybody most importantly came away with was just like every other mammal out there that has regular cycling or only seasonal ones. High estrogen is when you get the most sexual behavior. OK, instead of high estrogen is the only time you get sexual behavior. Instead, you simply get the most around that. In the years since, lots of people have done versions on the study and it is frequently difficult to replicate this phenomenon in terms of a change in levels of sexual activity in women around the time of ovulation. What has remained very clear in the literature, though, is that sexual arousal increases around the time of ovulation in women. Very reliable effect. And what that is interpreted as is behavior here may not be telling you anywhere near as much as motivation, arousal, proceptivity at that time. And that's a more pure measure of what's going on physiologically there. What's going on in the brains fitting with that is a very interesting literature suggesting that women act a little bit differently in terms of proceptive sexual signaling around the time of ovulation. Studies showing for example that women as assessed by both women and men, women on the average wear more provocative clothing around the time that they are ovulating. Yes, people go and study things like this for a living. These were not big effects. But the all time bizarre study I've ever heard of in this domain was actually published with a straight face by this guy and he's a evolutionary psychologist. University of New Mexico, a guy named Jeffrey Miller, who reported the following and you know what he was spending his time doing, which he reported was that around the time of ovulation, lap dancers get larger tips. OK, that has since been replicated in E. coli and in various yeast species. And you know, I'm not going to try to unpack that one in any sort of way.

Specific Effect of Luteinizing Hormone on Sexual Proceptivity (24:47)

But nonetheless, this was reported and shows you just how wonderful it could be to be a scientist. Can you imagine that money was being spent on that? You know, research dollars instead of strafing people in Kandahar province or something. OK, so we have a peak there. This general issue of what does hormonal cyclicity in a time scale of weeks to months, what does that do to sexual behavior in various species? What does that do to sexual arousal? Proceptivity. What are some of the building blocks of that estrogen as estrogen levels grow up? Estrogen increases the expression of receptors for progesterone. So you can immediately begin to piece that apart in at least two different ways. First one being estrogen, thus increasing the sensitivity in the brain. This is a brain effect sensitivity to progesterone, which has something to do with the rewarding aspects of sex. You can also translate that into molecular biology, estrogen being a steroid hormone is going to bind to its receptor and do the whole transcription factor translocation sort of thing telling you that upstream of the gene for the progesterone receptor is a promoter that's responsive to estrogen and estrogen receptors. You know how this one works by now.

Circulating Testosterone Increases Sexual Behavior (26:10)

More pieces of it. Estrogen when rising here also increases the synthesis of oxytocin back to all that social bonding stuff and what that suggests I don't know if it has been studied, but that women will feel more affiliative with someone they've had sex with if around the time of ovulation than at other points. That is certainly the case with a vol, but that is certainly the case because they don't mate the rest of the time and because male vols suddenly are expressive around their own terms of their feelings. OK. So more building blocks of it. Estrogen is not only having effects in the brain, but it's also having effects throughout the body at those times in terms of lowering the threshold of certain tactile receptors. What does that mean? That means around the time that women are ovulating thanks to estrogen. They are more sensitive to touch and I'm sure this has been studied in consenting hamsters, but my bet is that more sensitive to tactile stimulation in some parts of the body over others. What estrogen also is doing, as we just heard, is working on the old factory system, lowering thresholds for detecting the smell of males. So we've got all sorts of ways within the brain and in the periphery to bias towards more arousal at that time. Wonderful evolutionary biology, no problem at all. One additional piece of the female story, which is effects over the course of this kind of time span weeks to months, the years or so, the effects of those androgens, those male sex hormones that females are releasing. And what you see there is that plays a role in proceptivity, increasing sexual arousal, sexual motivation. Meanwhile, on the other side of the road, we got males. And what does testosterone, testosterone over this time span? What does it have to do with sexual behavior in males? Well, on first pass, it sure looks like it has a lot to it. Lot to do with it. What sort of evidence? Initially, correlative evidence. Well, the time of year in various species where males do their mating is the time of year when testosterone levels are elevated. Over the lifespan, testosterone levels go up around puberty and from about age to age to age to age to age to age to age.

Sex Drives Testes & Vasopressin Dominates Inseminated Rodents (28:39)

And what you see there is a similar profile in terms of sexual behavior. That does not tell us much. These are correlations. Furthermore, correlative studies in humans, a handful showing more sexually active men tend to have higher testosterone levels. And for what it's worth, a number of studies have documented a dramatic drop of testosterone levels in men right around the time that they become fathers. OK, so figure that one out. Also an increase in vasopressin levels at that time. You know how to interpret this one by now. So we've got testosterone and higher levels of male sexual behavior going hand in hand. Are we looking at any causality here? First off, we already know about one piece of causality, which was the other day. Sexual behavior in men in males increases testosterone levels. So that's one reason why they may go hand in hand. And that scenario, testosterone has nothing to do with increasing the likelihood of behavior. So does testosterone actually have a causal role in increasing the likelihood of male sexual behavior? And the answer is yes. And how do you show it with the most simple classic way of doing something in an endocrine study, which is get rid of the guy's testosterone. And you castrate the male, your rodent male, your non-human primate male. And what you see is there is a big drop in levels of sexual behavior. And this could range from male level, and lever pressing to get access to a female, to courtship displays, to extent of pomating of hair or something in the right neighborhoods. And whatever the measure is, this is when normal testosterone levels are on board. And this is, after castration, a very, very dramatic drop. Now to fulfill the second, you know, iron-clad requirement in endocrinology, the last thing you need to do now is after the subtraction experiment to do a replacement one, artificially give back the normal levels to the castrated individual and levels of sexual behavior go back to there. Whoa, OK, that proves it. We have a causal relationship here, not so fast. First thing to note, which is zero percent testosterone and sexual behavior goes way, way down, it doesn't go to zero. And every species looked at starting with the embarrassing sexual behavior of everyone's pet dogs when they were six years old, even after being neutered.

Experiments And Insights From Animal Studies

A Household Standards Experiment with Male Rats (Israeli Celeb (31:15)

What you see is there's a level of residual sexual behavior, rodents, dogs, primates, including humans. This is a critical point. How much residual sexual behavior is there after castration? The more sexual experience before castration, the more there is going to be retained afterward. In other words, on a certain, like, totally artificial level, this amount of sexual behavior is being driven by testosterone. This amount, which persists here, is being driven by social experience. It's got nothing to do with the hormones. Yes, this is ridiculous dichotomizing into this, but the fact that it doesn't go to zero and the fact that the more sexual experience pre-castration, the more residual behavior, this is a vote for just how much role social experience, social conditioning plays. Next thing that takes away from the yes, it's all caused by testosterone. Now you do an elaboration on the study. You castrate a male and now, instead of replacing with 100 percent of normal levels, you give 10 percent of normal levels or you give 200 percent of normal levels. And what do you wind up seeing if testosterone plays a strictly causative role, even in this range, you are going to get something that's going to be lower than 100 percent and this is going to be higher. That's not what you see. Instead, it is something like that.

The Shape Is so Strong ... (32:59)

You get roughly the same reinstatement of sexual behavior with when you replace return testosterone levels over anything roughly approximating the normal physiological range. What does that tell you? The brain circuits we learned about the other day involved in sexual motivation. It requires testosterone around to work fully, not entirely, but to work fully. But those brain regions are not really all that concerned with the exact level of testosterone. Rough approximation of normal, rough approximation of normal has the exact same effect. If you were seeing a tight relationship in a male between the amount of sexual behavior and testosterone levels, it's not because every little smidgen bit of more testosterone is going to drive more sexual behavior. It's because every little additional smidgen of behavior is going to drive higher testosterone levels. So we've got this really important observation. Yes, testosterone is needed in species after species, including humans for the normal range of sexual behavior. Just as importantly, castration never drops it down to zero. The more social experience that whole song and dance. And very importantly as well, the system is not sensitive to little differences in testosterone levels, stating that a different way. If some guy has one and a half percent more testosterone on board than the guy sitting next to him or then he had last week, is that going to mean he is going to be more sexually motivated, more aroused, no, not at all. Within the normal range, the system doesn't distinguish it. The relevant brain regions are sensitive to testosterone and require it, but do not care a whole lot about the levels. One exception, which is if you instead of say 200 percent push testosterone levels like a thousand percent, tenfold higher than normal, this is super physiological, which means it's out of the normal range, which means no bodies normally generate those sorts of levels, put it up in that range and you will get an increase in sexual behavior and sexual arousal. When do you see this? The idiots who go and abuse anabolic steroids for their weightlifting or whatever. People doing that are not pushing up their testosterone levels into the higher range of what human bodies can generate. They are pushing it way above the normal range and that range you do see an increase in sexual proceptivity. In a week or so, what we will see is the exact same story. It will be the exact same chart here when asking the question, what does testosterone have to do with aggression? And what you see is the exact same conclusions. What are we beginning to see here that testosterone is not playing a strictly positive role? It is playing one of the words that should be becoming repetitive here and clearly really important. Testosterone is playing a modulatory role. What testosterone does is sensitize you towards stimuli that are evocative of sexual arousal, it lowers the threshold. And that could be shown in all sorts of studies, but where its most clear is what is in this case, does testosterone cause the sexual behavior? No, but when it is on board, it facilitates it, it modulates it. Theme again and again and again. And that obviously has tons to do with individual differences. One last hormone to mention in this realm of hormone levels over the last couple of weeks, month, seasons or so, the hormone melatonin. And I think that's the only time melatonin is going to be mentioned in class.

Season Does Not Bin Mating in Samples of USA Prenatal Records (36:57)

Melatonin has something to do with telling the body what time of year it is. It is responsive to the amount of light you were exposed to. What is melatonin about? It is one of the driving forces on seasonal mating. Those species where you suddenly get on one afternoon each year, all the will to beast ovulate, the same afternoon kind of thing. It is almost certainly a whole pathway in the brain sensitive to the amount of light and the amount of light per day over recent weeks, which by way of melatonin triggers the onset of the mating season. Do humans have a seasonal mating pattern? There's a smidgen of evidence for it. If we've got it is a very, very weak echo of what you see in some other species. OK, now we shift over to getting really way back then instead of over your last three days or over the last three seasons, now beginning to look at perinatal factors. Perinatal before birth, prenatal after birth, postnatal, very early development. First off, focusing on early environment, environmental factors, having something to do with adult sexual behavior, what we can translate that into is ways in which early environment affects every single one of these subsequent ones. What does early environment childhood have to do with shaping of sexual behavior? A theme that's also going to come out in every topic we're going to hear of after this buzz words that should beginning to be keeping you awake at night, and modulatory, contingent, if then, all that stuff. Here's another one.

The evidence (38:37)

Here's another concept that comes through. The evidence shows that there is very little about early life experience, which influences the quality, the way in which an organism goes about having sex. What's another way of stating it? This is a pretty set in stone, bunch of fixed action patterns. Early experience is not about learning how to be sexual. Early experience is about learning the appropriate social contexts for being so. And that is shown in species after species. That is what experience is about, not how to do it, but when to do it and who you should not in your right mind try to do something proceptive to. And things of that sort. This is what early experience is about. And what we're going to see in a week is the exact same boring paragraph. Early experience does not teach organisms how to be aggressive. It teaches organisms the appropriate context for being aggressive. So what's the sort of evidence for this for these early effects? One example, a whole literature that emerged that is covered somewhat in the zebra book in another domain, but this whole literature that emerged in the 1950s work looking at captive primates. What are the consequences of growing up in a certain degree of social isolation? What happens to behavior and eventually people studying behavior and physiology? What happens to behavior in adulthood if you are a young rhesus monkey who grows up only with peers and no mother or grows up only with a mother and no peers or grows up with mother being present only intermittently or at the most extremes growing up with neither mother nor peers or any other member of your species around. You will see in the book a whole discussion of the ethics of these studies, but what does your early social environment have to do with things like sexual behavior? And what you see coming out the end is when you looked at these adult primates, since replicated over and over, they go about the sexual behavior, the plain old way that everybody else does, but they do it in totally socially inappropriate context. And thus you have these males who were raised in some degree of isolation early on growing up and carrying out perfectly normal sexual fixed action patterns on the towel in the room, on the bowl of food, on the who knows what wrong context you have, trying to do things with animals. You should not go anywhere near in terms of social dominance and such inappropriate context, early experience, shaping not how, but when what the if then clauses are. More issues of early experience shaping adult sexual behavior, arousal, pro-sensitivity, etc. We already heard one example of this with humans. That's the whole kibbutz literature. That was that whole business that if you spend lots of intimate time with somebody, we for age six, what you will do is in some subliminal imprinting way, decide forever after this individual does not feel like a potential mate. This individual feels like a sibling. That was the example in the recognizing a relative lecture of showing that hooray, we are such a cognitively sophisticated species. We can figure out who somebody's fourth cousin, three steps removed as by thinking. And that's how we make our mating decisions showing instead in those studies, there is this non-conscious level.

Sexual orientation (42:17)

One of the rules that humans have is lots of exposure intimately to somebody early on in life and you are not going to be very likely to get that proceptive behavior stuff going on later, part of turning them into a pseudo kin because of that early exposure. One additional domain I will touch on here in terms of early experience, which is what does early experience have to do with sexual orientation? And depending on which decade you are asking this question, the answer would range from everything to virtually nothing. Going back to the virtually everything time, which was dominating sort of the first half of the 20th century, how people thought about the subject, what you had were two broad models for what sort of early environments increased the likelihood of boys becoming gay as adults. And these were the two models. The first one was the absence of a father figure model. And this was one straight out of monkeys learning who they should try to pelvic thrust with or some such thing. This was the argument that what do father figures provide a proper training for appropriate context for proceptive sexual behavior growing up absent a father, figure increasing the likelihood of being gay. The other model was having this totally pain in the neck neurotic screwed up mother, who as basically said between the lines makes you crazy when you grow up. And thus you have circa 1950, psychiatrically certifiable disorder of having a different sexual orientation. Obviously where I'm going to head right now is there has not been a slight shred of evidence over the years either for the missing father figure model of sexual orientation or the neurotic mothering style model complete nonsense. Nonetheless, dominating thinking about what was going on there. OK, so what we are now ready to shift to is what's going on with hormones around this time period.

Organizational effects (44:25)

Let's take our five minute break and then we'll resume. Looking at what perinatal hormone levels have to do with adult sexual behavior. And you already know the answer. You know it in your hearts by now, which is, well, it depends on what species you're looking at. And what we will see is a very similar thing to the rule there, which is in lots of species, rodent species, prenatal or perinatal hormonal environment has everything to do with adult sexual behavior. And by the time we get to humans, what we'll see is maybe kind of sort of more research needed. What we begin with here, implicit in that is a dichotomy that runs through all of endocrinology when thinking about behavior. The effects of hormones back when you were little jargon in the field, an organizational effect of the hormone. And what that is about is explicitly is what are hormones doing at a time in terms of organizing what kind of brain you're developing there. Effects of hormones instead in this range or so, what you are talking about is an activation hormonal effect. So this is a very sort of consistent dichotomy that people in the business use. Early, early hormonal environments having organizational effects on the nervous system, hormones forever after having activation effects. So what you see is in rodent species that perinatal hormone exposure has massive organizational effects that dramatically influence sexual behavior. What you also see is it's not so dramatic and clear cut. A whole literature initially suggesting that, for example, male rodents, if they are not exposed to testosterone perinatally, will have a different male rodent sexual orientation later on, a dichotomous outcome. What a huge literature now shows is something that is evident to every sort of human sexologist for centuries, which is it's not a dichotomous function. It is on a continuum in terms of sexual orientation and 300 different species have been documented by now to have both heterosexual and homosexual behavior at different times in naturalistic settings. So perinatal hormones having organizing effects on adult sexual orientation, what you see is these are not all or none properties at all. What else? OK, what you see specifically in non-human primates is perinatal period, expose a female monkey fetus to high testosterone levels. And what you will do is masculinize the brain. Masculinize the brain, having thus an organizational effect. What does masculinization then manifest itself as an adulthood? If nothing else is different, it has no effects at all. On the other hand, if you inject a female monkey who is masculinized perinatal if you inject her with androgens with testosterone, you get a wild burst of male fixed action patterns. In other words, you've got an if-then clause. If and only if there was prenatal masculinization, then testosterone will have an acute activation effect on sexual behavior. OK, translating this. OK, pre. OK, so in the absence in a normal female monkey in the absence of prenatal androgens or adult androgen levels, this is the amount of male fixed action pattern sexual behavior. Now prenatal androgenization, normal low androgen levels in adulthood. Same low levels. Now, no prenatal androgenization and exposure to androgens in adulthood. Same low levels, prenatal exposure and acute activation effects. And suddenly you get high rates of male typical fixed action patterns. So what we've got here is a contingent organizational effect, yet again, one of our if-then clauses. This one not being a if this physiology is going on only in this social environment. Then this is if this early life endocrine environment occurs coupled with this acute adult one, then yeah, question. That is a great question and as you're about to see the answer is so insanely complicated, you are going to regret having asked that question for days, but you were going to find out about it anyway.

Determining And Influencing Sex Identity

Perinatal Maternal Effects & Male Or Female Behavior (49:13)

Apropos of that, I just forgot a great question during the break, which is OK. When you've got those weightlifter folks, they're abusing their steroids, their anabolic steroids, their testosterone drive drugs, when you push things up into the supra physiological range, higher than the body normally ever comes up with, do you see a phenomenon from last Wednesday, does the body downregulate the number of testosterone receptors? And you see exactly the case, but you could never downregulate them low enough to compensate for the huge screaming testosterone signal. It is a partially successful compensatory response. OK, what have you got in terms of humans in terms of perinatal and drawogenization of females and people used to know exactly the answer to it? First off, when do you get human females as fetuses and is predominantly in humans pre-natal rather than postnatal effects, it depends on sort of how fast how much of development occurs before birth. But in humans, when are circumstances where female fetuses will get heavily and drawogenized historically to circumstances? One is in the case of a disease where there is something wrong with the adrenal glands and they pump out tons of testosterone. You remember, if I actually did say this and if I didn't, I hope you're not remembering it hallucinotarily, but you'll remember that the adrenal glands make a certain amount of testosterone. In females, it pumps out maybe 5% of levels that males do. When you have this disease of an overactive adrenal system, you pump out way too high of levels of testosterone, a disease called congenital adrenal hyperplasia. Hyperplasia, the number of cells, OK, come up with a limb trick about that one, I dare you. Is it possible to come up with a haiku? How many syllables are there in congenital and adrenal hyperplasia? It depends if we're talking about rodents or not. So congenital adrenal hyperplasia, a genetic and inborn error of metabolism in the adrenal glands and you pump out huge amounts of androgen. So suddenly, there is a world of the occasional girl who was born suffering from this disorder or the mother suffering from it during pregnancy, who has been prenatally and drawogenized. The other population, thanks to a drug that was very popular in the 1950s, a drug decreased the likelihood of miscarriage that was very heavily used to points around then, drug called diethylstylbestoral DES. And in a subset of women, their biochemistry was such that a lot of the DES was converted to androgens. So you had kids who were prenatally and drawogenized girls, either because of this congenital adrenal hyperplasia or because of DES exposure. So then the question immediately becomes, OK, so what are they like afterward? And this prompted the great, large massive set of studies on the CAH, the congenital adrenal hyperplasia, on the CAH girls as they grow up. And you knew exactly what the expectation was straight out of primates here, non-human primates, which was this was going to have mass givenizing effects on their behavior. And what was shown was in adulthood, there were all sorts of differences.

What we can take away about taking sex change (52:55)

Not just in adulthood, starting around adolescence, there were all sorts of differences in the behaviors of these girls. And as we'll see next week, a whole cluster of them were thought to fall into the realm of aggressive behavior. But what was seen here was eventually a higher likelihood of becoming a lesbian in terms of sexual orientation. Whoa, what we've just shown is prenatal androgens and you produce lesbian later on. So there was a little problem with these studies, a slight confound. And one that's going to be very pertinent next week as well when talking about the aggression stuff, the confound being, if you were prenatally androgynized, you would get born with kind of weirdo genitals. And you would have sort of intersectional genitals in all sorts of ways. And all of these girls typically had to have gone through a dozen rounds of reconstructive plastic surgery over the first decade of your life. These were not girls were the only thing different about them was what sort of hormones their brains were marinating in back when they were fetuses. These are also grow up with this really interesting part of the body that all sorts of people seem kind of creeped out about. The doctors are endlessly examining and all sorts of painful surgeries. And this literature was completely confounded by the fact that there was all this masculinization of genitalia and a whole world of surgeries often confusion about gender, assignment early on in life. Things were not merely a change in the hormone levels. So it remains relatively unclear. There's by now at this point, weak evidence of prenatal androgynization increasing the likelihood of a woman being gay as an adult. I'm seeing here in my notes, I have the words indonesia, tomboy, Hobson, Jopson, and I have an clue what that's about. So we will just skip over that. OK, what we begin to see here is another feature of early experience. What does sreary prenatal, endocrine environment have to do with sexual identification, which is different than who you were sexually attracted to, but rather what sex you feel yourself to be. And what we heard the other day with the transsexualism example, is you could have gender being dictated by your chromosomes and which which organ, which go now and types of gonads you have in hormones and all of that. But that is not enough to determine it. There are clearly other things that can happen that could produce a very, very different gender identity. What also was seen from that literature of individuals who were born intersectional, where they have sexually ambiguous gender ambiguous genitalia, is it is far from clear which decision to make, whether that was made circa 1950s by the surgeon with no consultation with the parents or fortunately, these days, a very different scenario in terms of how successful the assignment is by the individuals in the outside world, what's going on in terms of sexual identity inside. Now, what this begins to bring up is the most miserable, irritating, confusing thing about the effects of steroid hormones in the brain, which is where your question came from. And this is where you're all going to start to regret this, but it actually is necessary in terms of an important point. OK, so you got testosterone. And what does testosterone do?

Determinants of Sex Identity (56:35)

We know already it binds to testosterone receptors. OK, testosterone receptor. And does its steroid hormone transcription factor deal? Throughout the 1970s, there was a astonishing amount of confusing irritated research done showing the two following things. In some parts of the body, testosterone has its effect as testosterone. It binds to the testosterone receptor. In some parts of the body, there is biochemical conversion of testosterone to something called dihydrotestosterone. OK, it's not testosterone is a little bit different chemically. It binds to the same testosterone receptors. It works a little bit differently. OK, we can live with that. The thing that had people jumping off buildings was the discovery at the time that some of testosterone's actions are due to it being biochemically converted to estrogen, which then binds to estrogen receptors and causes male typical behaviors. OK, it's at this point that about half the people in the field quit and went to business school because this was so confusing and impossible in all of that. This consumed years of labor of people trying to sort this one out. It goes as follows. Once testosterone enters a target cell, if this is the scenario that's going to happen, it's inside the cell that testosterone is turned turned to estrogen. In other words, this weirdo phenomenon has no effect on circulating testosterone levels. It's only in target cells that have the enzyme that could do that conversion. OK, so it's an intracellular phenomenon. If this is leaving you totally in the dust, don't worry about it except for a small point coming in a while. But if you want to devote the rest of your life to figuring this out in more detail, there's something wrong with you. But what you've got here is normal circulating levels, but different effects throughout the body. In general, what is found is the effects of testosterone in the brain involve this turning it into estrogen. It's symbolized meaninglessly by that asterisk throughout the genitals or throughout the body and secondary sexual areas of skin and such testosterone exerts its effects by being turned into dihydrotestosterone. And whatever parts are left over that brain testosterone just does its regular old thing. OK, so this is incredibly confusing how this can be. Immediately or not so immediately, two things should come to mind. OK, so prenatal testosterone levels are going about their normal prenatal organizational masculinization effects. And part of it is on how the brain organizes.

How Sex Identity Is Assigned: A Brief Detour (59:27)

So what we just saw was prenatal neurobiological masculinization requires testosterone to be working like estrogen in the brain. OK, why don't all the female fetuses then get indrogenized since they're not generating estrogen right on site there within the cell, but they're getting estrogen through some other route as their fetal ovary start to work. Why isn't mom and her estrogen and homogenizing every single fetus out there? How is it possible to ever get a female? And the answer to that is there is a protein which occurs during pregnancy that occurs in the circulation. And what it does is it binds estrogen and it takes it out of action. It leads to estrogen being degraded. In other words, estrogen in the bloodstream of a fetus never has an effect on any of the cells in the body. Estrogen whether derived from the female fetus beginning to get her ovaries going there or from mom's circulation, the estrogen has no effect. In other words, the only fetuses that ever have estrogen inside their neurons are fetuses that are male where the estrogen came from testosterone. So you have to have this protein and it's something called alpha-feto protein. It only occurs in fetal life. This winds up being the solution. What is implicit in that? You do not get the organizing, organizational feminizing effects of hormones prenatally because of estrogen because you've just guaranteed that doesn't happen. You're getting androgynizing effects that way. You don't get prenatal feminizing effects from estrogen. Where does the brain feminization come from? The irritating answer back when was this was always sort of the same phrase was always used, that the female brain is a default brain. You have to actively and a muscular, excited, you know, chopping down the trees and clearing the prairie sort of way. You have to actively do something hormonal to masculinize a brain. And in the absence of that, you just kind of wind up with one of them female brains. What's clear now is this default model is not really the case. It's other hormones that are doing that there. OK, so this totally confusing, irritating thing that everybody had to assimilate at the time of testosterone having different effects, having being converted to different messengers in different parts of the body. And that having to produce this whole complex, you know, rube Goldberg sort of solution as to how to ever get a female.

Sticky Mark Fur Females (01:02:11)

Now, one additional interesting implication. Back to you, you remember the other week. Remember actually, did I talk about it or was it two years ago or? Geez, OK, I think I mentioned to stickular feminized males. Yes, good. OK, thank you for the grounding. To stick, you remember what those folks were about. This was someone who was phenotypically a girl and would not hit puberty, would not start menstruating until every other kid in her grade had. And it still hasn't happened, still hasn't happened. And you take her to the doctor and what is discovered is that she is not female. She is a testicular feminized male. And we went through exactly what the building blocks were of that. The individual is chromosomal email has testes on the center. Testes is producing tons and tons of testosterone. What was the problem there? We know already it was the mutation in the testosterone receptor. So if testosterone is not able to send a signal to the testosterone receptor, you don't get a male phenotype. And you get an individual whose sexual identity is female because these are people who are girls and grow up to become women, women who simply can't reproduce. And otherwise, the sexual identification is female. This should be really puzzling now because what we've just seen is if you have this mutation in the testosterone receptor, you're not going to get any signaling mediated by testosterone. You're not going to get any signaling mediated by dihydrotestosterone. But you're going to get perfectly normal masculinization of the brain by a way of estrogen. In other words, people who are testicular feminized males who in terms of their sex identification have been female from day to day one and will be for their entire lives. Nonetheless, prenatally, they had masculinization, organizational effects on that brain. What does that tell you? All of this great hormone stuff, in some cases, doesn't hold a candle to social sex identity assignment, which is when you have somebody growing up with a certain gender's genitals and all of you treat that individual as a girl, it turns out that virtually 100 percent of the time, it doesn't matter that you still had this pathway working prenatally, all the social queuing produces a female sexual identity. So we've just gotten a big, big vote here for this is doing all sorts of exciting endocrine stuff there, which nonetheless may not hold a candle to some social environmental factors at this end. OK, what else do we have here? Something I don't want to talk about. OK, so hurling on now, we are ready to move back another box here, which is genetics.

Genetic Masculinization (01:05:20)

What is the genetic makeup of an individual, not of a population or species? What do genes have to do with sexual behavior? And the answer is lots of things, starting with the fact that genes determine which gonads you make as a fetus. And thus that determines which sex hormones you were secreting. And thus that determines what sort of genitals you wind up with and secondary sexual stuff and off you go running with that. And we've seen that nonetheless, that can be blunted by, depending on the environment, the testicular feminized male pathway here showing that. OK, so genes play a role in terms of just sheer sex determination. What is known about genes and sexual orientation? This has been studied a lot because this is one of those irresistible subjects that people just can't get enough of. What's up with that? What does the literature show a certain degree of heritability of sexual orientation? And you should be able to leap up right now and say exactly what that means and doesn't mean here's the sort of evidence. Twin studies. Twin studies, when you look at monozygotic twins, identical twins, there's approximately 50% concordance of sexual orientation. Translated into the terms that people are usually focusing on in those studies, which is to say, if somebody is gay, their identical twin has a 50% chance of being gay. Dizygotic twins, nonidentical twins, what is the number? Instead, it's 22% covariance. What's the number with other siblings? 9% covariance. So what do we see here? We see a suggestion that the more genes you have in common with somebody, but also the more prenatal environment you had with your nonidentical twin. All of that stuff, the greater the likelihood of sharing a trait of sexual orientation, and you can be often running right now about the limitations of that interpretation because obviously this suggests genetic effects. It also suggests the whole world of identical twins being treated differently than nonidentical ones. One additional piece in that story, and this was another one of those front page stories in time, news week, etc. And this came a couple of years after Simon Lave's finding of that sexually dimorphic nucleus in the brain, that whole deal there. And this was the reporting of the first genetic markers for sexual orientation. And this was reported by a geneticist at National Institute of Health, a guy named Dean Hammer, who was a very well respected geneticist. And what he reported was that he was finding genetic markers for sexual orientation.

Genetic Factors And Social Evolution

Roy Hammer, The Gay Gene Discovery (01:08:12)

In other words, certain gene locations that were more likely to be shared between gay siblings were both regay than between partially gay siblings or non gay siblings or however that one runs. You know that one by now. Beginning to find genetic markers going with this. This was really interesting and no surprise what the newspapers were screaming about within days was scientists announced today they have discovered the gay gene. OK, great. Maybe we shouldn't let people learn any science out there. OK, so scientists have discovered the gay gene goes all the newspapers and the writers digest and if I recall at the time Ronald Reagan as well, but he was completely demented at that point so I won't hold it against him. But the people at Newsweek should have known better. So we have cover stories about the gay gene. Obviously you can rip this to shreds right now. Number one, this was not a gene. This was a genetic marker. You remember the other week, the difference there. Number two, there was no consistency in this. What do I mean by this? This pair of identical twins would tend to share a certain genetic marker, which was predictive of sexual orientation. And the next pair over, it wasn't the same area of genes that showed that covariance. It would be a completely different area that they had in common. And another pair, a completely different area, you got this genetic covariance in various twin pairs, but it wasn't the same gene marker in all those cases. All of them were different, which makes zero sense in terms of the genetics. The biggest problem with it is that since then all sorts of people have tried to replicate the finding and it has never been replicated. Nonetheless, Hammer became quite famous for this. He is gay and he used this sort of politically, some of the same ways that Simon Levey did with his study, which is don't tell me about choice. Don't tell me about my neurotic mother anymore. We are looking at a very hardwired biological trait, what sexual orientation you have. Levey's finding I have found quite convincing in terms of replications. Hammer's nobody else is replicated and the actual genetics that he reported made no sense at all. So great limitations in what you could make of this. OK, this allows us to make our great final leap to the left with this thing. The logic that's going to run through everything we talk about, which is the second you're talking about genes, you are implicitly talking about the evolutionary history that brought about the existence of those genes. And that you're also talking about the proteins made by those genes and early environment changing the epigenetic state of transcribing those genes.

Picking Up and Transitioning into Evolutionary Changes and Exceptions (01:10:59)

Yes, yes, that whole song and dance now. So now we have to transition to what does evolutionary biology tell us about sexual behavior. So the first thing that tells us is absolutely obvious, which is organisms have sex for the good of the species. OK, so that one's out of the way. So now we go to what is much more logically in terms of contemporary evolutionary thinking, contemporary starting circa 1965 or so, the whole notion of maximizing the number of copies of your own genes, all of that translated into sort of the economic terms of having on copies of genes, what that basically states is sexual behavior is about reproduction. And people who would study phenomenal like these and various rodent species or will to be to ovulating the same afternoon, all of that would say, yes, indeed, you only have sexual behavior when it's around the time when females are ovulating and yes, reproductive behavior is about reproduction. It's about passing on copies of genes. What soon began to fall apart was not only making sense of us with our having non-reproductive sex, all sorts of times was the discovery that we're not the only species that does that and far and away the flagship species as a sort of emblem of that are bonobo chimps who are according to almost all prime biologists out there, the coolest primate species there is. OK, bonobo chimps, they were historically known as pygmy chimps, which is to say that when people first discovered them in terms of scientists, they were viewed as, well, these are chimps, but they're just kind of weirdo atrophied chimps, which I don't quite know how you come up with the pygmy atrophied chimp, but that was the view and not very interesting what eventually became clear is they are a separate species of chimp and bonobo chimps are utterly different from your standard issue Jane Goodall chimps. The Jane Goodall chimps we have a tournament species with extreme high levels of male aggression as we will hear about next week, you have chimps who are building weapons, you have chimps that form something resembling organized warfare. And meanwhile, over as it turned out on the other side of the Congo, which is where the main division occurs, you only find bonobos in one area of the Congo basin and they clearly have been reproductively isolated from all the rest of the chimps heading there east all the way to the Indian Ocean by way of the Congo. There go on the other side of the river, you got the bonobos and bonobos are totally different. Bonobos, unlike chimps, have virtually no sexual dimorphism.

Sexual Promiscuity Becomes a Form of Social Cohesion (01:13:50)

So you're often running with that one, we know exactly what that means. But no boat chimps have female dominance rather than male. All bonobo chimps play the guitar and sing soulfully. What else? And we have astonishing amounts of sex. Wait a second, we just went off the rails here. A species with low degrees of aggression, because they have virtually no aggression whatsoever, species with low degree of aggression and with no sexual dimorphism and body size, what we're looking at is a pair bonding species, a monogamous species. Bonobos are not monogamous species. Bonobos make, I don't know who, look like a pair bonding species in comparison. Bonobos are the most sexually promiscuous species on earth. Bonobos have astonishing amounts of sex with every other type of bonobo they could run into. They have sex in order to reproduce. They have sex in order to decrease tensions. They have sex in order to celebrate having decreased tensions. They have sex because it's an even number day of the month because it's odd. Every variety and the vast majority of it being non-reproductive, non-reproductive because it's not at a time when anybody's ovulating or because it's with someone of the same sex or it involves sexual behavior, which traditionally does not result in eggs getting fertilized and all sorts of variants that people only dream about from buying books and trying to get lessons and this sort of thing. And you have perhaps having something to do with that astonishingly limber, spinal columns, but what you've got is a totally different picture. Wait a second. They're very low aggression and they have no sexual dimorphism, but they're as far from pair bonding as you can get. And instead, you have a highly promiscuous social system, female dominated, and they're all just so cool and wonderful. You can't believe it. And every time people go to primatology meetings, if you study some dumb old stupid species like a baboon, you spend the whole time basically feeling like you're some sort of immature jerk because you're not hanging out with bonobos, they are the kings of primatologists these days, the people who study bonobos as the sound bite goes, chimpanzees are for Mars, bonobos are from Venus. OK, so that's what the t-shirts say from the bonobo people with the conferences there, totally different systems. So what we already see is violating our simple rules of what predicts our tournament species and what predicts a pair bonding one. What's most striking here is yes, we productive behaviors for reproduction for passing on copies of the genes not for the good of the species, but we know individual selection kits. And here's these guys having sex with 14 other bonobos while they're all upside down or who knows what and it's not just for passing on numbers of copies of genes, huge, huge exception there and huge exception in lots of other species. And the ecologist, Joan Ruffgarden here in the biology department has made an argument there is far more non reproductive sex that goes on in lots of different species, weakening the classic Darwinian concept from three, four weeks ago of sexual selection being a very important driving force. What sex is very heavily about is one gender choosing who they were going to meet with the other one and it's all driven by that of seeing instead if the world of bonobos, there's not a whole lot of evolutionary drive being built around sex equals reproduction. So bonobos are really interesting. What's the sex there about? One of the common themes that comes through is it's about promoting group cohesion and one of the things that people emphasize or focus on with bonobos is you look at all sorts of other primate species and what do they do when they're upset about something they groom each other. What do they do when they're happy? What do they do? Social grooming as as termed the social glue, the social lubricant of society. You get a troop of baboons that have just gotten a bad scare from a lion and as soon as the coast is clear, everybody comes down and spends the next 30 minutes grooming each other and sexual behavior in bonobos appears to be serving a very similar role, all about social cohesion as well as decreasing individual tensions, reconciliation, things of that sort. Now this flies in the face of a dominant theory that was around in the last century, the first part of it. And this was due to one of the grand poobas in this field, a guy, this Brit named Solly Zuckerman.

arguing that the Zuckerman stance is wrong (01:18:23)

Solly Zuckerman who eventually became Sir Solly Zuckerman, which probably didn't help him in society at all, still despite that. But old Zuckerman there was for his time the embarrassed wind Edwards. He was the Lamarck of the earliest part of the 20th century. The people who will only be remembered for coming up with Lamarckianism, old Lamarck are coming up with something as idiotic as group selection. What Zuckerman came up with was the notion that sexual behavior is purely for promoting group cohesion and for decreasing violence. And all you need to do is go to half the movies out there or study half the species on earth and what you will see is sexual behavior or inability of or required or whatever vanquished is the cause of the majority of aggression in organisms out there and various mammals and that argues very strongly against it. So what you see in most species that had been studied, it's a strong argument against the Zuckerman stance. Nonetheless, you see in some species like the nobos and rough gardens argument, lots more species than people traditionally think where instead you see sexual behavior often serving a non reproductive group cohesion sort of role. OK, what else does evolution have to tell us about sexual behavior? One critical issue and one that was touched on the first couple of lectures is what does it cost you to reproduce? And there we get the hugely important asymmetry, which is sperm don't cost a lot, whereas eggs and pregnancy and postnatal care and all of that is hugely expensive. What is that the driving force on according to all the sociobiological thinking, the fact that in species after species, females are more selective about who they will mate with than males. And as usually the case, the males are not selective in the slightest. And what you got instead is just a couple of sperm that it cost you and that's not ideal, increased female selectivity, higher levels of it than males, argument being that it is all about the differential costs of pregnancy.

exception to the cost of pregnancy asymmetry (01:20:31)

What we also saw was not a pregnancy, but a reproduction and raising of kids. What we saw was the interesting realm where you got the exception to that, which were the pair bonding species. The marmosets, for example, and what we saw back when was the male does as much child care as the female does and the females always twin. So around the time that the kids are born, the female has put in far more of the investment, she's gone through the pregnancy in terms of caloric expenditure. The males do anything more of the child rearing in terms of carrying the kid around when foraging all sorts of costly stuff like that. And eventually what you see is the curves. Don't do that, but at some point, the cumulative amount of calories that the male has expended is greater than the female. That's when you see that cock-oldry business. That's where females will potentially pick up an abandoned and because the male has made the greater investment at that point, that has seen very frequently in bird species with pair bonding.

Whole world of male competition (01:21:41)

So we've got here an exception to the argument that the cost of reproduction and child raising is always great for females and thus will always produce greater female pickiness for mates than you find in males. Nonetheless, you see that an awful lot. What else do you see? A whole world, not only a female pickiness, but a whole world of male attempts to control female reproductive behavior. And this found in species after species after species and obvious interpretation there in terms of male, male competition, decreasing the ability of females to mate someone else. And that ranges from primates who are in concert ships where the male will do what is often termed mate guarding, which is he tries to keep the female from going near any other guy to all sorts of other stuff as well.

Human Reproduction & Sexual Strategies

human inventions; clitoridectomies, chastity belts, arguing for extended absence (01:22:23)

And you certainly see this in the human realm. What are two cultural inventions humans have come up with to decrease the likelihood by men, to decrease the likelihood of women being sexually active outside that relationship? The first one is cliterectinies and something else that serves a very similar function, which is inventions of things like chastity belts. What's up with that? What you find are cultural inventions like those in groups that tend to have occupations where males disappear for long periods. For example, nomadic pastoralists were depending on the time of year. You pick up with your camels or your cows or whatever and you, the guy, are going to send the next three weeks at the grazing area that's good five miles west of there. And what this is about, the argument culturally for the cliterectinies is it decreases female pleasure, decreases the likelihood of her having sex with someone else when you were elsewhere. What were chastity belts about when the guy picked up and decided to spend the next six years trying to liberate Jerusalem from the Ottomans or whatever, often the United States, and just so you don't have any ideas over the next half decade why go die from the plague somewhere in Eastern Europe, that's when those were again a model of cultures where there are extended periods of men being away from women. You have very often elaborate cultural inventions for men trying to control the reproductive access of women. What that also winds of doing is explaining what was thought to be the dominant models of reproductive success and reproductive choice and all sorts of other species. And seen for example in something like Baboons, what you had was termed the linear access model of reproduction. It goes as follows. You have a social group, for example, a Baboon social group, and there's only one female who is an estrus, only one female who is ovulating, who winds up mating with her, the alpha male in the troop. Now instead there's two females who are ovulating, who gets the two females, numbers one and two in hierarchy, three females, numbers one, two and three get the female, and in person and that is the activeness implied in the word get, the passive lack of choice of the female end of things.

linear model of reproduction (01:24:39)

This was the linear access model in which male dominance rank was entirely predictive of male reproductive success. So that's what people thought lots about then.

Learn lesson four. (01:25:10)

That was the original thinking about the relationship between male dominance rank and reproductive success as we will see shortly. It's not quite so clear. Lots of other species where you see males attempting in the evolutionary sense, attempting to limit female access to other males. This is the whole world of copulatory plugs. Lots of dog canine related species where a semen plug is left there in the vagina of the female, which soon hardens into a plug and like nothing else is happening there. You see that. There are other cases. There are fly species where the male's penis is barbed and. Oh, I heard a. I'm not drawing that. What are you thinking? Where it's barbed and where the barbs, in fact, go in the opposite direction, point back at the male. What's that? You get the penis in there and it's not coming out again. It's like one of those, you know, those you put your things. Well, it's actually not like one of those, but you get the point. And what's that about? The male leaves his penis in there, which he manages to do without afterward because they can make new ones. And this is a very different world you've got here. Then you've got the whole world we've already heard about about sperm competition. Of sperm from one male and various fly species containing toxins that will kill the sperm of another male. Then there's a whole interesting world that goes on, which is when males mate with a female, they do something biochemically which decreases the sexual attractiveness of the female subsequent to that. In a number of fly species, males with mating release a chemical, which decreases mating pheromone production in the female. And suddenly nobody else is interested in her. Or there are other fly species where males release a chemical, which decreases sexual proceptivity in the female viciously clever ways for males to control female reproductive behavior after they've left male male competitive strategies. So what do you see at the female end of things? No surprise. You'd see female counter strategies.

Female counter strategies. (01:27:31)

One brilliant one that evolved in humans is this relatively unique human phenomenon of hidden ovulation. Yes, all that pheromone stuff and smelling people's armpits and things that don't happen much in the real world. But what you see for the most part is that humans are not terribly aware of where somebody is in their cycle. Humans have invented hidden ovulation. What's that meant to do? Decrease paternity certainty. And one argument is that's a good mechanism for decreasing the likelihood of competitive infanticide. The other is it decreases male attempt to control female sexual behavior because it's less clear when you need to be doing that. So counter strategies, more examples. This is argued that in some species that have non reproductive sex throughout the cycle, that is a female counter strategy to again fool the male when their population is actually occurring, increasing the likelihood that at such time she can get somebody else's genes. Other strategies, we've already heard about one whack in the competitive infanticide one, which is that whole world of females that can fake being an estrus that go through pseudo estrus.

What about human males? (01:28:37)

All of this meant to be ways of keeping males a little bit less certain of when they should be trying to control female sexual access. And thus she has more choice in the matter. What that brings us to is the. Oh, that's something interesting that I left out. Yeah, it's not that interesting. OK, so back to male male competition. This was first looking at male and lots of species. Male attempts to regulate female sexual behavior, female counter strategies. What's up with male male competition in terms of evolution and sexual behavior. Most obvious one being is male male competition for reproductive access and the standard old models being that linear access model one female lines up with number one male two and so on. What that thus begins to explain is when you look at all social species out there, the leading cause of aggression is male male aggression built around female access. And as we'll see by next week, that is the case as well for every human culture ever looked at. You also see, of course, the sperm competition.

Something about human males? (01:29:50)

And once again, we have one of those issues with humans, which is where do we fit on the spectrum there? If you have monogamous species, males tend to produce only small amounts of sperm and tend to have small testes. When you have polygamous species, males want to pump out insane amounts of sperm to increase the likelihood of out competing. Some other guy's sperm if it shows up on the scene or for making a sperm bug and what you wind up getting there in those species are large testes. So you look at the various primates and chimps have gigantic testicles per body size, gorillas do not gorillas that have a very different world of male male come. What about humans once again, the same exact thing? We are about halfway in between. When compared to other primates, we are intermediate between a tournament species and a parabonding species in yet another domain. We've been hearing about this again and again. Something really interesting that has been shown in humans, which is... No, I'm not going to tell that. It's too hard to explain, but it was great. You would really wish. So now what we have is also looking at evolutionary aspects of female choice in there and in what cases do you get female, female competition? First off, the answer was obvious in terms of looking at traditional tournament species, which is that females have no choice who they're mating with. It's linear access models. One female winds up with the alpha male, two females and so on. And this was the dominant model in all of primatology starting in the 60s. And then by around 1980 or so, it was recognized that in fact, there's virtually no evidence for strict linear access models of the main determinant of who a female mates with is who's the winner of male male competitive interactions. People discovered at the time that in fact there was this strange, strange violation of all these models because it turned out the models were not based on behavior and this generally was discovered around that time because that was around the time that the majority of primatologists on earth suddenly became female and started looking at the female end of things and discovered that this linear access stuff is not in fact what occurs. And out of that came a completely shocking concept that ran through primatology like a bolt of lightning. The notion that there was this, this is the technical term, some degree of female choice. Oh, whoa, that's kind of bizarre where females have something to do with who they mate with and there's been a whole world of primatology studies since then showing what female choice is about. First off, how does female choice occur in a typical tournament species? You got this problem with primates, for example, you wind up with a parabond concert with a concert ship between a male and an ovulating female. And because it's a tournament species, the male is twice the size or has big, huge canines or whatever stuff he's got there. He is physically able to dominate the female quite readily. You do not see female choice in those cases being exerted by the female beating up on the guy and her getting to go mate with who she's interested in. What you see is much more clever behavior on the part of the female. She will, for example, exhaust the guy. Every time he sits down to feed, the female gets up and starts walking and he has to jump up and pile together to the picnic and go running after every time he tries to take a nap. She goes walking or what you find with baboons is the most clever thing that females do is they go walk and lead the male right in front of his worst rival or then they'll do it again and again and again and get the guy totally haired out and crazed. And at some point, those two males will have a fight. And what then happens is she runs off to the bushes and has what is technically called a stolen copulation with the guy she's actually interested in. Maybe it's not so bad to be a female baboon. So now what this brings us to insofar as this alternative female strategy is available, we now come to this absolutely critical question, one that has run through the ages, which is what do female baboons want? Who do they want to mate with? And people are not positive, but there's some suggestion in the data. It needs to be replicated more. There's this trend, but there's the suggestion that female baboons like to mate with male baboons who are nice to them. No, are they sure? Are they certain that they've done their statistics right as a big they go and they mate with guys who groom them a lot, guys who play with their infants, guys who when they're in a bad mood, don't beat up on them, but beat up on somebody else. I mean, this counts as a prince of the male baboon. This is someone you take home to meet mom when he's in a bad moody pummels. Someone else, not me. This is someone you want to mate with. And in the mid 1980s, excellent primatologist, Barbara Smuts of University of Michigan came up with a very jargon, a scientific term that all sorts of non-human primates have intersectional friendships, and that's not an anthropomorphic term. What it was though was people sort of snickering at it and that the initial notion was that these were just friends. These were platonic monkey relationships. They were not about reproduction and it was not until people got good enough and they had to go to the hospital data to start picking up on all those stolen populations to see that the females were picking up and mating with their nice guy. Oh, we're just friends. I could never see him. Whoa, and they're suddenly in the bushes with him and it suddenly turned from the yeah, nice guys finished last. OK, they do lots of grooming, but let's count number of copies of genes to becoming a parent that the being a nice guy was a viable alternative reproductive strategy as long as there was this thing of female choice. The alternative to the alternative alternative strategy in part because you're not mating anywhere near as much.

Alternative Reproductive Strategies

Alternative strategy (01:36:00)

If you were a low ranking, affiliate is male with a female, you're not rating anywhere, maybe anywhere near as much as the high ranking males, but you're not burning out. You're not getting injured. You're not having the male male fighting. You live a lot longer and this keeps happening. There's a problem though, which is suppose you are a female baboon. And you want to mate with this nice guy. And one of the things that he's nice about is he's nice to your kid who's now about three, four years old. And there's a very good chance that where that affiliative relationship started with him, got jump started was the fact that he was the most likely father of that kid and has developed somewhat of an affiliated relationship with the kid and hangs out with them and hangs out with you. And so you've established this is a nice guy I want to mate with. But there's a problem, which was if he was the likely father of your now three, four year old offspring, the odds are that three, four years ago, he was a pretty high ranking male. And what that means now three, four years later is he's likely to be some age and guy over the hill whose rank has been dropping. In other words, not someone who is going to be very effective at male male competition and you get this horrible sort of tension there going on between the male male competitive world generates some Arnold Schwarzenegger jerk, who's the one who's supposed to where she wants to mate with Alan Aldo or whoever. And what you have then is he's not up to the male male competitive stuff because he's some aging guy and you instead have the world of stolen copulations. So isn't that great?

Alternatives (01:37:44)

Isn't that heartwarming a whole world of what are now called alternative strategies? If you're some skinny male baboon wanting to pass on as many copies of your genes, you may decide the really manipulative thing to do is to be nice to some female and groom her more than she grooms you, which is a very rare thing for a male baboon to do. So great alternative strategies, very heartwarming, not so heartwarming because there are other other alternative strategies available in some species, alternatives where male sexual behavior is not the outcome of explicit male male competition, but instead takes an alternative strategy. And you see one example of this in orangutans.

Specific Species Study: Orangutan Males

Orangutan males (01:38:26)

Orangutans, great apes, and they've got a very interesting bizarre social system. But what you have is your basic nonetheless, sort of familiar picture of male male competition, the large percentage of orangutan male aggression is built around the reproductive access to females, and you've got a whole world of very peripheralised low ranking males who never mate. And there's an interesting physiology that goes along with it. That was the picture that everybody used to have. And then in the 1970s, pioneer researcher in this Buruti Galdecost, who has studied orangutans for decades out there in Indonesia, she noted something really disturbing, which is low ranking, non-reproductive male orangutans have an alternative mating strategy. What do they do? They rape females. And this was the first introduction of that term into zoology, and that is not an anthropomorphism. If defined as a violent process of mating with a female against her will, this is what goes on in orangutans, a certain percentage of reproduction is low ranking guys who have no direct access to females as a result of male male interactions. This is not the nice guy alternative, so there's precedent for this also. And this is by now very well documented behavior among orangutans. Then if you want to come up with something very subtle and clever, there's apparently this whole world of fish species where low ranking males can pretend to be a female and take on female coloration and pretend to be just friends and someone they could pour their heart out to. And then suddenly one day they have a penis and weird back come from and everything suddenly changes there. OK, so we have the very strict boring models. Females invest more calories than males, and thus they are much more picky. Males mate with females entirely as a function of male male competition. And thus evolution is driven by male aggression and all of that. Let me just see as people are clearly about to run out the door. For more, please visit us at stanford.edu.

Could not load content

Great! You’ve successfully signed up.

Welcome back! You've successfully signed in.

You've successfully subscribed to Wisdom In a Nutshell.

Success! Check your email for magic link to sign-in.

Success! Your billing info has been updated.

Your billing was not updated.