#1264 Steve Stewart-Williams: A Billion Years of Sex Differences

00:00 Ricardo Lopes: Hello everyone. Welcome to a new episode of The Dissenter. I'm your host, as always, Ricardo Lops, and today I'm here with the return guest, Doctor Steve Stewart Williams. He's professor of psychology at the University of Nottingham, Malaysia. And today we're going to talk about his new book A Billion Years of Sex Differences, How Evolution shaped the Minds of Men and Women. There it is, the printed version. So Dr. Stuart Williams, welcome back to the show. It's always a pleasure to talk with you. Thanks, Ricardo.

00:31 Steve Stewart-Williams: Thanks a lot. It's great to be back.

00:33 Ricardo Lopes: OK, so let's start with some basic questions here because, you know, this topic of sex differences and sex and gender, uh, there's lots of confusion sometimes when people have these discussions. So uh what do you mean by sex differences in your book?

00:55 Steve Stewart-Williams: Uh, WELL, I'm talking about sex differences, um, I'm talking about average differences between biological males and biological females, and I'm making no assumptions about the, uh, the origins of those differences. So if I call a difference a sex difference, I'm not implying that it's, uh, due to nature or nurture or any combination of, of those things. Uh, MOST of the time it is due to a combination of both, at least for the, the particular sex differences that I discussed, but, um, but there's no assumption there, uh, inherent in that labeling, um. And yeah, the kind of differences that I talk about in the book, um, include sex differences in sexual behavior, uh, and mate preferences, sex differences and aggression, risk taking, sex differences in parenting, personality, uh, career-related interests, health, mental health, etc.

01:46 Ricardo Lopes: And how do you deal with the topic of gender, because there are scientists that distinguish between the sex and gender. That's very common, for example, among anthropologists, uh, I mean, particularly cultural anthropologists, but many biological anthropologists also distinguish between sex and gender. I mean sex being basically uh what we could call biological sex. I mean biological differences between males and females and gender being the social, uh, expression of, uh, what we usually call men and women. Of course, there could be in certain, uh, at, at least in certain societies, different gender categories that it's not just men and women, but, uh, for gender, for example. So how do you deal with gender in your understanding?

02:45 Steve Stewart-Williams: Um, WELL, I typically, I don't find it a hugely useful concept. So I tend not to use it too much, um, for several reasons. Uh, ONE major reason is that, um, I think that the concept of gender isn't really just one concept, it's multiple concepts. Um, SO people mean different things by gender, uh, when, when they use the term different people mean different things, the same person will often mean somewhat different things by gender at different times. So sometimes it means, like you said, the social expression of um of, Like male female categories or sometimes multiple categories, um, or perhaps sort of clusters of personality traits that are associated with male or female, but then maybe you have other categories as well. Um, SOMETIMES people just use it as a synonym for biological sex. Uh, SOMETIMES people are referring to the social roles of the culture or stereotypes of the sexes. Sometimes people will describe a male-female difference as a gender difference. If they're trying to imply that it's a learned difference rather than a difference with, you know, like a, like a natural or evolved difference. So multiple different definitions makes it really quite tricky to know what people are talking about when they use the term. Uh, THAT'S one problem with it. Uh, ANOTHER problem is that a lot of the, Specific definitions that people use, I think have problems of their own. So if we're gonna label a male-female difference, a gender difference, if it's a result of, of learning, socialization, and culture, well, well, for a start, people often label it as a way to, um, To make the point that it is learned rather than innate without actually showing that it is the case. It sometimes seems to be a way to settle that argument without actually providing arguments and evidence. Um, AND most of the differences that are of interest to us and that I talk about in the book, uh, most of the differences are partly due to nature and partly due to nurture. And therefore, if we're going to use the, the sex as biology. Gender is social learning, uh, way of thinking about things, that means that we're going to have to call most male-female differences part gender difference and part sex difference. And that's a really awkward way to construe things. I think it's much easier just to label them as sex differences, as an average differences between biological males and females, and then with, like, like I said before, without an implication that they're due to either nature, nurture, or a bit of both. And then to address the nature nurture question separately. And actually, things as we were talking about the, um, the notion of gender as sort of clusters of personality traits, um, I also think that's a little bit of a problematic definition as well, given that, um, The kinds of differences that we're talking about with that definition, so, so like people will say, like men are typically assertive and, uh, domineering, uh, for instance, women, women are typically nurturing and caring, for instance, um, we're talking about that, well, really we're talking about personality, and there's so much variation in personality in every single individual. That if we're going to define gender that way, basically every different individual is their own unique gender, and really we are talking about personality, rather than talking about anything necessarily connected to sex.

06:08 Ricardo Lopes: Mhm, I understand. I guess that we will come back to some of what you said there when we talk about cross cultural evidence for sex differences and how people interpret and deal with that evidence, but let me ask you now, why do you think it is important to study sex? Differences, I mean, uh, for you, uh, do you think it's just, uh, I mean, it's just science, it's just intellectual curiosity, it's just a matter of knowledge, or can it have other sorts of, for example, social, political implications?

06:46 Steve Stewart-Williams: Well, I think both, for me, uh, first and foremost, the reason I'm interested in the topic is that I just find it deeply, deeply fascinating. I just, um, find it enthralling really. I remember when I first, uh, came across evolutionary psychology, it was in a book called The Moral Animal by, uh, by Robert Wright, and it was really the explanation for the evolutionary explanation for sex differences in humans and in, and other species. That's what really grabbed me and really, uh, turned me on to evolutionary psychology. And, uh, I remember it was, it was a lot like when I was a kid. Uh, AND I first understood how the phases of the moon worked. And You just suddenly understand. This phenomenon, just suddenly all clicks into place and you understand it, and you have that kind of uh exhilarating rush of, of insight. Um, IT was the same thing when I understood the evolutionary explanations for sex differences, and, uh, you know, I had that rush of insight, uh, that they were click, and if anything though, I guess it was even more exhilarating in this case because it was about something that It's really relevant to people in their everyday lives. We all, we all notice the sex differences around us. We all interact with both sexes, so it's a very uh very relevant topic for, for people in general and for myself. And suddenly there was this way of shedding light on some of the differences that we all notice between men and women. So that's, that really is the main reason. That said, I do think that all knowledge is useful. Knowledge about a topic that is so important to so many people could be particularly useful. Uh, USEFUL in our personal lives, uh, useful as well for, uh, steering policy and, and, uh, and the like, as I'm sure we'll come to later.

08:29 Ricardo Lopes: Yes, we'll come to that, we'll come back to that topic later. Uh, AND what do you think are the most rigorous ways of studying sex differences? And establishing to what extent they are the result of nature or environmental factors, learning, and so on, or on the other hand, the result of nature, I I I think I said nature earlier, I meant nurture, or on the other hand, nature and more the result of biology and perhaps pointing to some innate differences between the sexes.

09:10 Steve Stewart-Williams: Yeah, uh, well, there are, there are a few different lines of evidence that I think can shed light on this question of, um, the extent to which the differences are due to nature versus nurture. Um, I, I named six in the book, and, uh, let's see if I can remember what they are. So, uh, the first one is the developmental timing of the differences. So often you'll find that a sex difference appears very, very early on, um, and often so early on that it becomes somewhat implausible to assume that it's just down to socialization. At, at least it sort of shifts the balance of probabilities to the idea that maybe, There's an innate push as well, if it, if it turns up really, really, uh really, really early, aggression, for instance, turns up, uh, the sex difference in aggression turns up, as soon as kids are mobile enough, that aggression is an option, uh, greater energy levels, sort of greater physical activity, um, Like, like, it's tends to be somewhat higher among boys and girls, that appears very, uh, very early as well, um, and also puberty, so some, some traits, Are they either don't appear very, very early on, or they're quite small early on, but often sex differences will get larger or, or first appear at puberty, and that can be a result of socialization, of course, but it's also a telltale sign that maybe, um, that it has an evolutionary origin because a lot of male-female differences appear at puberty, and in fact, that's part of the definition of puberty.

10:35 Ricardo Lopes: So if something, if something is the result of, uh, evolutionary pressures and they are, and we're talking about adaptations, it's not necessarily the case that they have to come online from birth, right? I mean they can come online in later. Later stages in life, but if they consistently show differences between men and women, boys and girls, and they come online more or less around the same time period, then they can still refer to or be adaptations.

11:11 Steve Stewart-Williams: Yeah, they can do, and there is, of course, I, I can hear people saying yes, but they could also be. Due to, uh, different socialization pressures at, you know, during the teenage years as well. And, and that is true. So I think that is suggestive, but we need other evidence as well. Um, SO another line of evidence is that, uh, a lot of sex differences are very, very consistent across, across historical periods. So for instance, uh, the sex difference in, uh, sex differences in mate preferences. Uh, WHICH I'm sure we'll discuss later on. They, uh, have been found consistently throughout the 20th century and into the 21st century. Um, THEY have just remained intact, like within the US, for instance, despite the, the radical social changes during that time. So too have sex differences in, in interests and career-related interests, um, they, which I'm sure we'll also discuss later on. These are some of the more important things that we discussed, that I, that I discussed in the book, um. And that persisted throughout time, and that, that as well as suggestive evidence that we're dealing not with just a social phenomenon, uh, but with something that's deeper seated and sort of harder to shift. Uh, ANOTHER, um, effect that we find is that a lot of these sex differences persist even in the face of social pressures, pushing in the opposite direction. Uh, SO for instance, um, typically, like in most societies, parents and teachers and, and other authority figures, they tend to clamp down on aggression, they tend not to think that, they tend not to encourage it. Um, BUT to clamp down on it instead, and they're actually more likely to tell boys that they shouldn't be aggressive than to tell girls that they shouldn't be. It's not because they approve more of girls' aggression, it's just simply because boys are more aggressive, that they're more often aggressive and therefore, uh, we more often tell them off for being aggressive. Uh, DESPITE the fact though, that there's more pressure on boys than girls not to be aggressive, boys are consistently more aggressive across all cultures, um. So that's the 3rd line of evidence, 4th line of evidence is, uh, associations between hormonal exposure and behavior. Um, THE links between blood levels of hormones and behavior, like current blood levels of hormones and behavior, you know, aggression, risk-taking, people think that that means high testosterone at the time, those links are actually very, very weak. Um, WHERE there is much stronger evidence is that there seem to be associations between prenatal hormonal exposure and later behavior. So higher levels of exposure to testosterone in the womb tend to be associated with higher levels of aggression and, and risk taking, uh, among, among adult, adult humans, um, adult other mammals as well, um, and, and lower levels of parental care, and various other findings along those lines. Uh, THE fifth line of evidence is cross-cultural universality or, or cross-cultural near universality in some cases, depending on the sort of strength I guess of the innate push. Um, AND a lot of these sex differences that we've been talking about and that I discussed in the book. Across cultural universals, basically, so I like aggression, the aggression sex difference is just found wherever you, wherever in the world you look, uh, the risk-taking sex difference found wherever in the world you look. Sex differences and mate preferences are found in most places where we've looked, some of them in all places, some of them in most places, uh, and, and so on, but the fact that women provide more of the parental care is found in all known cultures, including modern cultures where we actually have an alternative. Uh, WAY that women could, uh, women or, or guys could, uh, feed the young, other than nursing them, we have, you know, we have baby formula, and we have ideals, uh, of both sexes, both parents pulling their own weight, and so even in our own culture, we still find, uh, that sex difference. Uh, AND then the final one, which is maybe my favorite, uh, my favorite one is, uh, cross-species evidence. So for a lot of these sex differences, you also find the same differences in many other species. You don't find them in all other species, um, but I think quite importantly, you find them specifically in species that have been subject to the same selection pressures as our species has over evolutionary time. Um, WHICH I'm sure we'll discuss those selection processs later, uh, but yeah, you find them particularly in those species, which I think is very, very meaningful. Um, AND, and, uh, and yeah, really points to an innate contribution in our species as well. It just seems unlikely if you find this a difference in aggression, say, or in parenting in many other species, then you find the same difference in our own species, just seems unlikely that it's purely due to, The social causes in our case, whereas you know, it's obviously in other species, it's due to natural selection, but then, uh, for some strange reason, we coincidentally have the same differences in our species, but for a completely different reason. This seems uh logically possible but unlikely.

16:08 Ricardo Lopes: Yeah, we will certainly discuss in more detail some of those, or at least most of those sources of evidence that you pointed out there. Let me ask you, uh, in the book at a certain point you call some people minimizers of sex differences and other people exaggerators of sex differences. Of course I'm not saying that most people. Following one camp or the other. There are also people who have a more balanced view of sex differences, and we're going to talk about that. But what do you mean by those terms, minimizers and exaggerators, and what do you understand as being someone who minimizes sex differences or on the other hand, someone who exaggerates sex differences?

16:55 Steve Stewart-Williams: Well, someone who minimizes them is somebody who Uh, tries to play down the extent to which men and women differ from each other. Um, IF not to sort of deny that there are differences. If there's, if there, you know, small differences, then maybe you could actually make the case that the difference doesn't really exist, that it's just a stereotype. Um, AND I think they, they seem to be particularly uncomfortable. With any suggestion that any differences that we find have an innate basis, that they're not just 100% due to socialization. So it tends, I think, to come out of a discomfort with male female differences and a sort of desire to minimize them, maybe even deny them, but certainly to deny that they have, uh, evolved roots. Uh, THE exaggerators on the other hand, um, they, they do the opposite, and they are inclined to think that men and women are from Mars and Venus, they're just massively different from each other. And there's little if any overlap between them, um, and sometimes they'll also hold, not only that the differences are really, really big, but that they should be big, and that men should be like this and women should be like that, and that it's kind of going against nature or going against God to have, to have exceptions to the rule. Uh, SO, yeah, that's what that means by minimizers and exaggerators. I think clearly I think that the truth is somewhere in between, that most human sex differences are, they're not huge, they're also not non-existent, we're sort of modestly dimorphic. Compared to most other, uh, compared to most other mammals, but we are somewhat dimorphic, there are some degree of, of, evolved sex differences in our species.

18:30 Ricardo Lopes: Mhm. Yes, and later we're going to talk about what are some of the big sex differences, some of the smaller sex differences, and the ones that fall more or less in between. Uh, BUT before we get into that, uh, I think that it's also important for us to address. He, uh, 4 different biases that you talk about, uh, in your book. You mentioned the alpha bias, the beta bias, the gamma bias, and the delta bias. Could, could you explain each of those biases and why it's important for us to keep them in mind?

19:05 Steve Stewart-Williams: Yeah, sure. Um, SO the alpha bias is the tendency to exaggerate sex differences, um, and that is found among, I guess, sort of, uh, In traditional religions, that's quite common, uh, modern day conservatives, that's quite a common approach, you exaggerate them. I have to say that, um, within my own field of evolutionary psychology, I think we've sometimes been guilty of overstating the size of the differences in our species, and those are all examples of that, of the alpha bias. Um, THE beta bias is the reverse, so that is the tendency to, to minimize or deny sex differences, uh, and that I think is, Very, very common, it's very, very common in academia and in journalism and in education, um, and I guess, you know, it's very, very common in the, the Western world, the, the weird world, if you like. I think it's historically quite an obelisk, um, but it does seem to be pretty common and, yeah, pretty common, uh, in among the chattering classes, if you like. Um, I think in some ways it's a response to the alpha bias. Uh, AND, and the harm's done by exaggerating sex differences and moralizing sex differences, some folks have gone in the other direction. Um, SO it's more common among progressives, generally, so the beta bias generally more common among progressives, but there are exceptions, so when it comes to things like the pay gap, for instance, um, progressives are likely to, uh, flip from the, the beta bias to the alpha bias, if you see what I mean, so they downplay most sex differences, but then, uh, when it comes to, Certain politically relevant differences like, like the gender pay gap, uh, there, there they don't play them down, if anything they play them up instead. So it's alpha and beta, the gamma bias is another one that you find among academics and journalists and the like, um, commonly, and that is the tendency to highlight sex differences where women do better than men. And play down sex differences where on average men do better than women. Um, AND also to highlight differences where women are disadvantaged and need help, and play down differences where men are disadvantaged and need help. Uh, AND I think that's a reaction to the fact that we've kind of done the opposite through a, through a lot of human history. Um, WE have sort of painted males as great and awesome and as superior to females, and this is kind of, um, trying to set the record straight, but arguably going, uh, doing so by, um, introducing, by, by not getting rid of bias, uh, but instead by sort of reversing the bias and just focusing in on areas where women do better. And it comes out of, I think, of a protectiveness of, of women, uh, as well. Uh, AND then the final one is, is the delta bias, and that is a tendency, again among certain progressive circles in particular, to really try to highlight anything that goes against traditional sex differences. So, for instance, um, the delta bias, you would see that for instance if people. Uh, KIND of cheerleading, uh, females, women sleeping around while, uh, criticizing men for sleeping around. So sleeping around's great if women do it, very, very bad if men do it. Being a stay at home parent, great if men do it, that's really cool, but it's a bad thing if women do it. Um, SO it's just kind of the traditional things but turned on their head and we're trying to emphasize the opposite in reaction to the traditional ways.

22:29 Ricardo Lopes: Mm. And in the book, you also, when it comes to the nature nurture debate surrounding sex differences, you identify five different kinds of positions that people can have. So I mean, I mean their names, they are more or less self-explanatory, but you can explain them further if you want. So the first one is basically what we commonly call biological. DETERMINISM, so it's a nature only position. Then there are people who fall more in the camp of mainly nature position. And then there's the nature and nurture as equal partners, so more or less 50/50 nature and nurture. And then the mainly nurture position and then what we could call environmental determinism, which is Which stands at the opposite end of the spectrum from biological determinism and it's the nurture only position. So, I mean, would you like to explain them a little bit better and uh why do you think that we should keep these positions in mind that people might have when we think about sex differences?

23:39 Steve Stewart-Williams: Uh, YEAH, so that's, yeah, that's how I laid it out. So, spanning everything from the nature only to the nurture only. Um, I think that a lot of folks assume that evolutionary psychologists like myself take a, a nature-only position on sex differences. Um, BUT I think that basically none of them do. I think almost no one takes a nature on your position these days. Uh, THE position would be basically just sex differences, uh, largely set in stone. Largely set in stone, you know, and, and without brain surgery or some, or a blow to the head or something like that, basically they're going to be, um, We're gonna find them no matter what, and the size is going to be invariant across cultures and variant across different uh social influences. So yeah, I think, I think almost no one holds that view. The one exception I guess would be that, um, that most people, I would say take a uh nature only view for sexual orientation. And so if they're thinking for instance about same-sex sexual orientation, um, they would tend to say that that is. A nature only difference or or something close to it. Um, THEN, yeah, and then at the other end of the spectrum you've got the, the nurture only position. Now some people will say that's a straw man view, uh, and that no one holds that view either. I personally think that that's not the case. I've sort of, I say in the book I've got 3 stock responses when, when that claim is made. So sometimes I'll argue, like I'll, I'll argue online or, uh, In a journal article that here's, here are these lines of evidence, the six lines of evidence I mentioned before, that a given sex difference is not just due to nurture, and a common response is, well, no one says it's all due to nurture. And that's just a straw man, just like it's a straw man to say that, uh, evolutionary psychologists think it's all due to nature. Uh, MY first response to that is, OK, great. So you're, you're agreeing with me that it's partly due to nurture, cool. So, so we're, we're in agreement. Perfect. Uh, MY second response, Is that even if that were true, even if it were true that everyone agrees that every single sex difference that's worth talking about is partly due to nature, I think we should still make the case that that is, that that is true. We shouldn't just accept it without arguments and evidence. Uh, BUT then my third argument is that I just don't think that it actually is true that, No one claims, uh, that certain sex differences are just basically due to nurture rather than nature. You know, sometimes people will explicitly say this difference is due to nurture, it's got nothing to do with nature. Uh, SOMETIMES people will. Kind of agree that yeah, sure, nature and nurture is involved in everything, no worries, but then they'll just only focus on the nurture side of the equation, as if, um, they'll they'll tacitly act as if it's all down to nurture. Uh, SOMETIMES people will say, uh, well, the nature nurtured dichotomy is not a, you know, it's a, it's a false dichotomy and we can't split it into those two things. I, I do notice though that they only do that when somebody mentions a nature explanation. They don't do it when somebody mentions a socio-cultural explanation. They don't say, well, well, well, well, hold your horses with that socio-cultural explanation, uh, because actually the nature nurture dichotomy is, is false. They only do it for the one, not the other. Uh, SO those are the two extremes. In between is where I think, uh, almost every sex difference is going to be found, um, you know, I think possibly there, I'm sure there are some cases of nurture only sex differences. Maybe the names that, that people have, individuals have within a given culture, probably not innate contribution to that, right? But in general, the sex differences that are, are of interest to us and that are focused on in the books, and the book, um, I think are just due to a combination of nature and nurture. Um, NOW, yeah, so it's spanning within that range, right, the the more realistic range it's spanning from mainly nature to equal partners to mainly nurture. And I'm sure, I guess one thing I should emphasize is that these are not five positions that people can take on every single sex difference. I think actually that um we would apply different ones to different sex differences. Now, for the ones that I'm discussing in the book, like uh sex differences and sexual behavior and mate preferences, aggression, risk taking, Uh, parenting and so on, I think that I would, I would say that most of those are mainly nature. Or nature and nurture as equal partners. The reason I say that, so, so the mainly nature position is that, Culture can shift things around and it can expand or contract sex differences, but they're really quite sturdy, and they're sturdy enough that you're gonna find them basically in every culture or in the vast majority of cultures. It's gonna take really quite a cultural push to get rid of them, so we're gonna find them in most cultures. Uh, AND I think that's true of most of these uh sex differences that we're talking about. They, they do seem to be very, very persistent across cultures. So I would say yeah, so, so most of these sex differences. Mostly, mostly, uh, mostly nature or at best nature and nurtures equal partners. I think there are many fewer where it's mostly nurture. And uh maybe just one other thing I, I'll add is that the mostly nurture category would be that you, you see people staking that claim when they say, OK, sure, there might be a little bit of a push, a little bit of an innate push early on in life. Um, BUT then it's, it's amplified by culture. Um, AND it doesn't have to be, it could just as equally be minimized by culture or even completely eliminated by culture.

29:02 Ricardo Lopes: Mhm. Uh, SO do you think that from a scientific perspective, all of these five positions can play a role or be useful to some extent depending on the sex difference we are looking at?

29:19 Steve Stewart-Williams: I do, I do think they can be. Um, I just think that. Uh, IT'S gonna sort of cluster around mainly nature and nature and nurtures equal partners. I think there'll be more sex differences that fall into, into those camps, but there'll be some that fall into all the different camps.

29:34 Ricardo Lopes: Mhm. So, there are two sources of evidence that you point to in your book that I would like to discuss a little bit with you. So at a certain point you talk about behavioral genetics, and I would like to ask you this because I've had conversations on the show over the years with prominent behavioral geneticists like Robert Plomin, Eric Turkheimer, and others. Others and I mean they told me that when it comes to group differences, particularly behavioral genetics is not a very good tool to study those because what people do in behavioral genetics is that they study individual differences among a particular population in a given environment. So the behavioral genetics would not be a very good tool to study differences between groups of people, but rather be across individuals in a given population. I mean, uh, do you also have that understanding or and if not, uh, in what ways do you think that it can still be useful to study sex differences?

30:53 Steve Stewart-Williams: I do have that understanding. I think they're. Almost always, it's almost always the case that uh behavior genetics applies to individuals, um, and, and to explaining the nature and nurture of individual differences, rather than average differences between groups, um, or nations, uh, and, and that would generally include the sexes as well. Um, BUT the one place where I do think that it can shed some light on sex differences concerns a, a generalization that's come from behavioral genetics research, which is, uh, named by Eric Turkheimer, the second law of behavior genetics. So the second law, uh, states that the effect of sharing a home, sharing a family home as a kid, um, has less impact on, uh, individual differences. Um, THAN the effect of the genes. Genes have more impact in shaping individual differences than sharing a home does. Um, AND more specifically, um, the, the finding is that sharing a family home doesn't make people much more similar than they would be if they hadn't grown up together. So get a couple of identical twins, uh, they grow up in the same home, compare them to a couple of identical twins who are separated at birth and grow up in separate homes. You'd expect that the ones who grow up together would be more similar to each other because they've been separate to all the same, uh, or, or many of the same, uh, family, uh, you know, uh variables and and situations. Um, IN childhood they often are quite similar to each other, or like more similar to each other, but by adulthood they're often not much more similar, or depending on the variable, they're sometimes no more similar at all. Um, AND the lesson there basically seems to be that within the normal range, so we're not talking about neglect or, uh, abuse, within the normal range, um, the family home has less impact in shaping how we turn out than we typically think. That applies to individuals, but I do think that, It has implications for the discussion of sex differences as well, because among the most common explanations for sex differences are that they're a product of the family home, of, of parenting practices and the like. And the reason that the second law of behavior genetics is, is important here is that it kind of says, well, It seems that parenting doesn't have a big impact on how people turn out, and that just sort of undercuts the idea that parenting has a big impact in terms of how males, males and females turn out. You know, it's a, it's an extrapolation from that, it doesn't directly come out of behavior genetics, but um it seems to me to be a plausible extrapolation from it that suggests that more than likely, in the normal range, parenting behavior is not gonna have a huge impact in terms of how, uh, the, the differences between boys and girls and especially men and women.

33:46 Ricardo Lopes: Mhm. Yeah, but, but then you acknowledge that behavioral genetics when it comes to the study of sex differences is not one of the best tools out there for the reasons we discussed here.

34:00 Steve Stewart-Williams: Yeah, I do, I do think so, because it's looking for the, the nature and nurture of individual differences, and what they typically find is that, um, individual differences are shaped. By nature and nurture in both sexes and to usually to a roughly similar degree.

34:18 Ricardo Lopes: So, and when it comes to the cross cultural evidence, I mean, one thing I would like to say and for you to comment on is, uh, do you think that we've studied or people looked at enough data across all the societies that we've studied because we've had We've been basically studying thousands of different human societies for the past, roughly the past 5 centuries or so. And for example, there's an ethnographic atlas with more than 1200 societies covered there. And I mean, at least what I hear from anthropologists. IST s is that when it comes to knowing through this sort of evidence, cross cultural evidence, whether sex differences are universal versus culturally variable or for example, socio ecologically variable or contingent that no one really. There has done the work of digging through those tens of thousands or thousands of ethnographic reports to really conclude one way or the other. I mean, what do you think about that?

35:43 Steve Stewart-Williams: Yeah, that's interesting. Um, I certainly think that, uh, you know, more, more work could be done, and systematically looking at that. Um, I definitely had the impression though that, well, well, a few things, so I think that um, There's a ton of variability across different cultures in, in every way that you care to name, including in the exact details of how men and women, women behave and, and the way, the ways that the roles are divvied up between men and women. A lot of variation, um, Especially in the specifics, but when you get into uh sort of more general categories of behavior, things like aggression and parenting, for instance, I think, I don't think anyone's made a compelling case, despite, I think a lot of people wanting to be, to be able to, that the differences are found in some cultures but not others. I think uh those differences, in particular, that that is found very, very consistently. There's no culture on record that uh where for instance, Women are more aggressive than men, where women band together to form war parties to go off and attack other groups of women and, and, um, kidnap the men, which is a common thing that happens in, in reverse, in the uh anthropological record. Uh, NO plausible cases of cultures where it's the men who are the primary caregivers consistently for, for the kids, um. You know, these, these things just recur again and again and again, and occasionally you will, you'll hear claims, uh, anthropologists for instance, will make claims about some society, some exotic society where things are, are very different and things are done in a very, like the reverse of how we're used to seeing them in Western societies. But almost inevitably they just fall apart on closer examination, and you find that actually, we do find that at a deeper level, we do find the same sex differences. Um, NO, like you said, there's, there's more work to be done, uh, in going through all these, um, hundreds and hundreds of ethnographies. But a lot of work has been done already, there are, there are people who have looked across um ethnographies. And they've done so with all sorts of theoretical ideas and political preferences in mind, and they have consistently found these kind of sex differences that I'm talking about. There's no, no sort of realistic exceptions to the, to the big ones like aggression, parenting, differences in sexual behavior and the and the like.

38:01 Ricardo Lopes: Yeah, but I mean, I think you understand the worry from some anthropologists when they say that at least in their understanding when it makes to claiming or making claims of universal sex differences that Perhaps we haven't gone through enough, uh, ethnographic or people haven't looked through enough ethnographic studies to make those claims, or, or is that something that you don't think is a plausible argument to make?

38:35 Steve Stewart-Williams: I think that they're right that we shouldn't be, we shouldn't be too confident. Um, BUT the question is how confident is too confident. I think if we just had the cultural record, then perhaps we'd be being too confident in saying, yes, it's, it's a cross-cultural universal. I think though that because we also have evidence from other species, we've got very, very strong theories from evolutionary biology, uh, predicting some of these differences, uh, theories that have been corroborated with multiple other species, um, and we've got the various other lines of evidence as well that I've mentioned. I think that, you know, we, we should of course always leave room for doubt. And be willing to uh say that this is a tentative conclusion, but I think it's a strong tentative conclusion, and I think that, I don't think we're being overconfident to suggest that uh many of these differences are just part of human nature, rather than uh creations of some cultures but not others.

39:30 Ricardo Lopes: Uh, WHEN it comes to cross-species evidence, what kinds of models, animal models do you think are the best for us to look at or compare ourselves to when it comes to studying the the evolutionary basis of sex differences, because, uh, uh, yeah, let me just add. When it comes to, for example, um, discussions or talks I had with primatologists, my understanding is that, for example, when it comes to certain differences where we compare sex differences where we compare ourselves to chimpanzees. THAT there's been some exaggeration when it comes to their, for example, proclivity toward aggression and violence, because unfortunately, and this has been something recognized by people like Jane, the late Jane Goodall, it seems that a few decades ago, In certain places in Africa where they studied male aggression, for example, that it was very much due to the fact that we were interfering with their ecological conditions in the sense that we are providing them with bananas for them to approach the researchers and then Uh, I mean, the fact that we, uh, the fact that there would be bananas in their environment, then they would start fighting for those, for that resource, for example, and on the other hand, when it comes to bonobos, it seems that we are, we have underestimated their rates of Violence and actually they are more violent than we tended to believe. So I mean, what do you think are the best ways for us to approach cross-species evidence when it comes to sex differences?

41:30 Steve Stewart-Williams: Yeah, that's a great question. Um, I think the way we shouldn't approach it is to say, to look at any one particular species like chimpanzees, and say, well, chimps are aggressive, therefore human aggression is innate, um. Or to say that bonobos are not aggressive and therefore that challenges the idea that humans are innately aggressive. I don't think we should do that, I don't think we should choose any one species as a model of human beings. I think the way to use the cross-species uh evidence is to look for general trends in big groups of species, uh, and the general kind of thing that you find is that in species where, Males can potentially have more offspring than females. Certain kinds of sex differences uh become common. So basically, where males can have more offspring than females, any male that is one of the lucky few that has a lot of offspring, rather than one of the many that has few offspring or even no offspring, any traits that propel that male into that category of having heaps of kids, those traits are going to be selected, and those traits include things like uh aggression. So, um, like male male aggression, males are more likely to fight each other than females are likely to fight, uh, one another in these species where males are, um, where there's competition on the males to be among the few that have many, many females, and therefore many, many, um, many, many offspring inheriting their traits. Um, SO I look like across the broad swathe of the animal kingdom that, that we find that tendency. And then we look at human beings and we say, um, well, we have that same selection pressure acting on us, it is the case that men can potentially have more offspring than children. We know from various sources, genetic sources, anthropological sources, sociological sources that some men have always had more offspring than even the most reproductively prolific women, and therefore there would have been a selection pressure acting on us. We then find, same as we do in other species, that males on average are more aggressive than females are. And it makes sense in light of the general trend in the animal kingdom that. That we're part of that trend, and therefore that the difference has an evolutionary genesis in our species, just as it does in in other species. Yeah,

43:45 Ricardo Lopes: and I think that perhaps other sources of evidence we can look into, particularly when it comes to mating, for example, has to do with penis size and the size of the testicles, right, because I mean that that. Points to, uh, particularly the size of the testicles, points to the sperm competition and perhaps a more more intra-sexual competition in that case, uh, among males for, uh, female mates,

44:16 Steve Stewart-Williams: right. Exactly right, yeah, and that's, you have very high levels of that chimpanzees and bonobos. So in terms of their sexual, but not among humans. So I think in humans we have probably some degree of sperm competition in our past, but our relative testicle size is that we, we don't have anything like what you find among chimps and bonobos. So in that respect, they're actually very different than us, and the fact that they're closely related is, uh, is irrelevant really, um, for testicle size, they're just not good models for human beings, or they're not like human beings, um, we're more like, uh, Sort of socially, we have our testic relative testicle size, it's more like that of socially monogamous, uh, species like, like gibbons. So I think probably we're in that respect, we're a little bit more like them. Not exactly like them, you know, we, we live in bigger groups and so there's probably more sperm competition, there's probably, there's more, you know. Uh, SPLITTING up and, and, uh, forming different relationships and having kids with sometimes with multiple partners and, and cheating and that kind of thing. I don't want to give the impression that these things are massively common in our species, but I, but I think that they are more common than they are in, in gibbons. But you take my general point, right, is that we need to look at the specific species, the specific, um, mating arrangements, and parenting arrangements, um, and that's more important than looking at the degree of relatedness, uh, of the species to us.

45:37 Ricardo Lopes: Mhm. Uh, SO, uh, just to clarify this point, I think that you've already ended up mentioning these differences, but what are the most scientifically robust sex differences that we know of in humans?

45:53 Steve Stewart-Williams: Yeah, uh, well, the ones that I'm most persuaded by are the ones which, um, they have, uh, 3. Uh, YOU know, 3 features Uh, one is that we've done a ton of research on them over the last century or so, so they're very well documented. There are, you know, literally dozens or hundreds of studies showing the differences. Uh, THE second thing is I'm most persuaded by ones that are predicted by well established theories in evolutionary biology. Uh, SO theories like sexual selection theory and, uh, parental investment theory and, and sperm compensation theory. Uh, AND then the third, uh, thing is if, if these, uh, differences have also been found in other species. Subject to the same selection pressures as us, that makes me more confident that they are, Real in human beings and genuinely shaped at least in part by natural selection, so, so you know, the examples would be sex differences in sexual behavior, sex differences and sexual choosiness, the fact that uh women are often choosier, or rather females are often choosier than males about their mates, uh, sex differences in aggression, risk taking, parenting. I'd say those are the main ones.

47:02 Ricardo Lopes: Mhm, uh, BUT I mean, uh, the females tend to be choosier, but when it comes to mate selection, uh, I mean, we tend to have that model of, uh, males compete, females choose, but it seems that the more correct one is mutual mate choice.

47:22 Steve Stewart-Williams: Or am I wrong? No, no, no, you're right, I completely agree, um. I wrote a paper on that exact topic and, and with, with Andrew Thomas, I think you've had him on the show as well, right? You've had Andrew, yeah, yeah, yeah, yeah, that's right, yeah, yeah, so we worked on um. On a paper where we coined those terms, uh, males compete, females choose, and, uh, the mutual mate choice model, and the males compete, females choose, uh, model that characterizes a lot of species, so the males do most of the competing for mates, the females do most of the choosiness, the most of the choosing of mates, um. Doesn't quite apply to us though, um, and that is because, so, so you know I mentioned that sex differences emerge out of, um, the sex difference in terms of the maximum offspring number. So the fact that males can have more offspring than females, like the maximum number for males is higher. Um, THE main reason for that is because females usually invest more per young, so per offspring they invest more. Um, WITH mammals, that's because they're the ones that get pregnant, they're the ones that give birth, they're the ones that, that nurse the young, whereas, whereas in principle, all a male needs to contribute is just the sex act. Um, NOW, in humans. The theoretical minimum is that, so theoretically to produce one offspring, females need to get pregnant, give birth, and until very recently, they would need to nurse as well for a few years, whereas the males in principle only need to, um, Uh, have, have sex with a female. Uh, THAT'S not the typical, uh, level though, not the typical level of investment, um, for males. Typically males invest quite a bit. And when that happens, the maximum offspring number for males comes down and gets closer to the maximum offspring number for females. As it does that. The sex differences in general get smaller in the species, that's why we have quite modest sex differences, um, but also what happens is, because males are forming pair bonds. Like quite durable pair bonds, and then investing them quite heavily in the young, they become choosier about their uh long-term mates, for exactly the same reason that females are choosy, which is just that um, they're having fewer offspring and therefore each offspring counts for more. So they become choosier about their mates, uh, in that, in that context. Um, AND so it's mutual mate choice, and both sexes compete for desirable members of the other sex. Because both are investing, rather than only the males competing. Mhm

50:00 Ricardo Lopes: Since we're talking about specific sex differences here, what do you make of the literature on educational and occupational sex differences? I mean, uh, at this point in time, uh, do you think that there's good enough evidence to say that there's a, An evolutionary basis, a biological basis to them, or that perhaps there's more of an environmental input into those differences.

50:32 Steve Stewart-Williams: Yeah, there, it's an interesting, it's an interesting puzzle really, isn't it, because there's no obvious immediate evolutionary rationale for there being differences in education or occupations, given that we didn't have schools throughout most of our, the course of our evolutionary history. And people weren't studying mathematics and they weren't studying languages and uh the humanities and sciences and so on. Uh, AND exactly the same problem with the occupational preferences. Like, we don't, all our modern occupations are evolutionarily novel, so why would men and women be inclined in different directions? It's nowhere near as obvious as some of the, some of the other, other differences that we talked about. Um, BUT nonetheless, there are well established sex differences in both of those domains. There are educational differences. And occupational differences, so an educational difference is basically unless women, uh girls rather, unless girls um, Denied an education They just, they tend to do at least as well as boys and often better than boys at school and at university. Um Other sort of differences, it's not much of a math step, but, you know, the, the stereotype is that boys are better at maths, and there are some, um, some nations where that's the case, uh, but it's less often the case today than it used to be. It seems that since we've educated both sexes, right, right across the board, including in mathematics, there are some societies, some nations where you find no difference there, some nations where you find that women are doing better, that girls are doing better. So, um, I don't think there's actually a strong, Innate push there necessarily, that said, there does seem to be a strong trend where, among the small minority of people who are particularly good at mathematics, more of them seem to be uh male than female. Women on average, and girls on average, they tend to be uh slightly better with language. They are, uh, you know, slightly more gifted verbally than boys, and develop faster verbally. Uh, SO that's another difference. Um, AND then in terms of interests, there are interests that appear at school and then later in, in the occupational sphere. Uh, THE big one is that, uh, boys and men on average, are more interested in things and things related professions. Whereas girls and women on average are more interested than boys and men in people, and people related professions and, and helping people. Those differences are found very, very early, um, like I said, there's no obvious evolutionary rationale for the occupational preferences per se, but it does seem that there's, there's pretty good evidence that they're not 100% due to socialization, and the evidence is, like, first of all, They, those differences have been there for as long as we've been measuring them. We've been measuring them since the early 1900s, and they have just persisted right throughout that period. Despite efforts to try to get more girls and women into traditionally male occupations. Um, THEY seem to be, there seems to be a correlation between prenatal hormonal exposure and interest in things, so, so more testosterone is associated with greater interest in things within both sexes, um, and, and like girls who have congenital adrenal hyperplasia, CAH, they're exposed to high levels of testosterone in the womb, and they typically, uh, as girls have more, um, Sort of interest in things related things and things related topics and less in people related topics, and as girls, as women, they're more likely to pursue traditionally male careers. And the final line of evidence is, is cross cultural. It, the people versus things difference are, are massively, uh, cross-culturally universal. So the one study found them in a study of 200,000 participants and found it in 53 out of 53 nations. Another more recent study found that, I looked at 500,000 people, half a million people, and found those differences in 80 out of 80 nations, which is just unprecedented level of cross-cultural uniformity and, and does point to the idea that probably this is not just a social, a socialized thing.

54:40 Ricardo Lopes: Uh, BUT I mean these differences, they are not huge, right? Or, or are they?

54:46 Steve Stewart-Williams: Uh, WELL, they're not huge, um, there's, there's overlap, but the people versus things difference, that's, um, the effect size there is about, about 1. Cohen's D equals 1, and what that means is there's, there's about 1 standard deviation between the mean for males versus the mean for females. So that is actually, that, that, there's still a lot of overlap, um, so I wouldn't say it's a huge difference, but I would say that as, as human sex differences go, that's a, that's a pretty big one. And maybe, maybe surprisingly big, given that there's no evolutionary rationale for the difference in the first place. Some of the other differences I mentioned though are not, are not so big at all. Um. Women do, uh, girls and women do better than boys and men at school and university. Uh, IT'S consistent, but it's not a massive difference. Girls are somewhat better with language than boys, it's not a massive difference, it's, uh, again, it's consistent but not massive. I would call it a small difference, maybe 0.2 of a standard deviation between the female mean and the male mean. There's also 11 to mention is that, um, On average, boys do slightly better, and men as well do slightly better on spatial, most spatial tasks, uh, and depending on the task that spans between a small difference of about 0.2, in some cases it's, it's a medium difference of about 0.5. Occasionally you'll find out an estimate, uh, for like for mental rotation, for instance, it might be 0.5, might, might even be as high

56:13 Ricardo Lopes: as mental rotation of 3D objects, correct.

56:16 Steve Stewart-Williams: Exactly, exactly right, yeah, men, men and boys seem to have a, um, Significant, non-trivial, but also not huge, uh, advantage there on average, and again, tons of overlap in all of this.

56:31 Ricardo Lopes: Uh, BUT I, I mean, I, I was just going to ask you because this is something that, uh, people, sometimes people identify as feminists, other times they don't necessarily identify as feminists, but they, uh, look at sex differences more from a nurture perspective or environmental perspective. I mean, do you, do you think that, uh, there's maybe, or at least to some extent the risk that Uh, some of these differences that even we can find cross-culturally that we are attributing a biological basis to them when perhaps there would be more of an environmental influence on them in the sense that, for example, and this is just an example, of course, uh, I mean, before the second wave of feminism, particularly in countries like the US, the UK, and so on. Many women tended to stay at home. They didn't work outside the home, and then when they got access to jobs outside the home and to tertiary education, I mean, they were, were able to go to university and so on. That some of the fields like, for example, that we tended to associate with males, like for example, being a school teacher, being a university professor, being a medical doctor, and so even nurse and so on. I mean those were male dominated fields, but I mean since women got access to those. Opportunities over the past few decades, I mean, they turned things around and now medical doctors, nurses, school teachers, and so on tend to be female dominated fields. So I mean what I'm asking you is, uh, do you think that there's a possibility that we for some of these differences. We just haven't given them enough time for them to uh become smaller and perhaps some of you, some of it could be as some feminists argue, uh, the fact that we have inherited, uh, a patriarchal culture and that perhaps some of it could be still influencing those differences. I mean, how likely do you think that is?

59:02 Steve Stewart-Williams: Uh, IT'S a great question. Um, AND I do think that there is, there is a risk there. Like if people had assumed that all the, all the occupational sex differences that we saw 50, 100 years ago were due to nature, they would have been wrong. And, and people did assume that actually, didn't they? They thought, well, being a doctor is an inherently male thing, just look at the numbers. And they were just completely wrong about that. And as soon as the, uh, doors were, uh, flung open, uh, women very, very quickly, um, flooded into basically all fields. They went into all fields, um, but some of them more than others. Now it is possible that, uh, That like you say, it's just a matter of time before some, some, some of the ones like physics and computer science and mathematics, where there are nontraditional, you know, there's, there are a lot of women in those fields, like a non-trivial, uh, subset of individuals in those fields are, are women. Um, IS it going to be the case though that eventually that they will come to some something closer to parity and it's just a matter of time? I think it's possible, and I think that it would be risky to assume otherwise, just in case doing so, um. It operates as a self-fulfilling prophecy. It means that women who might otherwise enjoy going into those areas, uh, don't. Um, AT the same time, we also need to, uh, think about the fact that maybe, maybe that's not the case, and maybe, um, they will just, As long as the doors are open. Fewer women than men will go into certain professions, and, and also uh fewer men than women will go into others like maybe the health sciences. And that, that is possibly not just due to socialization and the weight of history, and, and bias and discrimination, but it could just reflect. Average differences in men and women's interests, and uh, And, and, you know, so, so I do agree that there's a risk in. Jumping too readily to the conclusion that the way things are today, reflects nature and it's the way that, therefore, you know, this reflects people's preferences, but there is also a risk in the other direction. So that if we assume that, Average Uh, evolved sex differences play no role in shaping the occupational landscape, then we're going to assume that any differences are direct evidence of bias and discrimination, and we're going to try to, um, get, get to par, to, to correct for it exactly. And if that's wrong, if it's not due to discrimination, or a big chunk of it is not due to discrimination, there are costs to doing that. So for instance, um, If we attribute it all to discrimination, first of all, we're going to create a lot of resentment, and if that attribution is, is not correct, then that is needless resentment, um. It means that we're going to throw a lot of time and effort and and money at trying to eliminate the differences rather than just eliminating bias and barriers, but eliminating the differences, um, and we're going to be targeting, Uh, the wrong causes, things that don't actually explain the gaps, um, it could mean that we use, um, coercive tactics to try to eliminate the gaps, um, Because if, if, if it is due to preferences that are really quite deep seated, then we're gonna find that, uh, less coercive tactics don't do the job, you know, they, they, more women come into a field, but then it sort of stabilizes, so we're gonna start using coercive, more coercive tactics, um, Nudges, uh, sort of, uh, bribes, uh, pushing pressure. Uh, A quota system, for instance. Um, In doing so, we might actually end up instead of eliminating discrimination, we may accidentally reverse the direction of discrimination and end up, and actually there's some evidence that we are doing this already, when it comes to hiring, uh, for instance, in STEM fields, it seems that, Rather than preferring males in the STEM fields, we prefer females, even if otherwise identical, um, uh, CVs. Uh, WE tend to have a bias towards hiring the females these days rather than the males, which seems like a reversal of the old, um, of the old bias rather than successfully having eliminated that bias. Uh, AND then finally, I guess if we paint a picture of STEM and other male dominated fields as being. Just hotbeds of sexism. We run the risk of putting off some girls and women who might otherwise be very interested in going into those fields, um, but then just think, well no, I don't want that, I don't want to be constantly, uh, Under an onslaught of, of sexism from these patriarchal males, so they, they might, we might actually ironically put them off by um exaggerating the extent to which the differences are, are due to discrimination. And actually, you know what, I think there's one other thing I would say, a good reason for acknowledging the sex differences. Is that It might help us pitch STEM fields. To, to women Um, so, like I mentioned, uh, women on average tend to be less interested in things than men, more interested in people than men. Um, BUT a lot of STEM fields that are basically thing-oriented fields, they actually do involve working with people and helping people more than we might initially think, more than the stereotypes suggest. And so if we were to, to emphasize the ways in which these jobs involve working with people and helping with helping people, that could just attract, um, Some women who would love working in that, in those areas, but just aren't aware of that.

1:04:47 Ricardo Lopes: Mhm. Uh, AND by the way, when it comes to educational, educational and occupational sex differences, and because earlier we've also talked about the exaggerators, right? So, do you think that if people put too much of an emphasis on uh those sex differences or them being the result of evolution and having a biological basis to them. There could be a risk in the other direction that perhaps I don't know, let's say that a man has a particular nurturing kind of psychology and he would like to go to a field like nursing and or a woman who tends to be particularly interested in mathematics would like to go to a field like physics that if we exaggerate. Those sex differences and put too much of an emphasis on them that we would be dissuading those people from making those choices because they just will think, oh, OK, so I'm a man, I have, I, I cannot have anything to do with nursing or I'm a woman. I mean, I'm not someone who is welcome or or physics is not for me, something along those lines.

1:06:06 Steve Stewart-Williams: I think there's a major danger of exaggerating the differences. And also of uh moralizing them, so exaggerating them, men do this, women do that, but then moralizing them and thinking men should do that and men and women shouldn't do that. And I think, um, yeah, so that's one of the risks of talking about sex differences, is that people will exaggerate them. Um, AND I think though what we need to do about that is Uh, you know, I, I think we need to talk about sex differences anyway, even though the risks are real, uh, partly because it just simply is the case that men and women differ from each other, and we can't just lie about that. I think what we need to do instead, we need to tell the truth carefully and really emphasize that the exaggerated versions are exaggerated, that actually men and women aren't identical, but, They're also not from Mars and Venus. They are, uh, modestly dimorphic, and that there's tons of overlap, which means that there are plenty of women who are much more mathematically inclined than the average man, and plenty of men who are much more nurturing than the average woman. We just need to try to get that right. Uh, AND also the, the other reason though for talking about sex differences, even though there are some risks attached with it, is the fact that, There are also risks and dangers associated with minimizing sex differences and denying sex differences. So there's no, no way out of, no, no way to avoid the risks by just not talking about one side of the equation. I think the risks on both sides, and what we really need to do is just be careful and responsible and just try to get it right and accurate, and also respect. Individual differences, uh, respect people's decisions about what they wanna do with their lives, even if it's gender atypical.

1:07:48 Ricardo Lopes: Mhm. And what are some of, uh, could you give us some examples of what are the most modest sex differences? I mean, the ones where there's all, uh, uh, I mean, lots of overlap and perhaps in some of them almost complete overlap.

1:08:06 Steve Stewart-Williams: Well, one example is IQ. So the, the best estimate I think of um the sex difference in IQ is an effect size of 0. At the average there's basically no difference. Uh, EXCUSE me. Um, SO yeah, so no difference. Um, PEOPLE often respond to that when you say that, people will often say, hang on a minute, isn't that just because IQ tests have been designed so that the average is the same for men and women. And that is true of some IQ tests, but there are some where, where it hasn't been designed that way, and they nonetheless give, Uh, basically equal, um, estimates of IQ in representative populations. Now there are some papers that say, oh, actually men have a slightly higher IQ, but what I think is going on there is that very, very low IQ men are more likely to just sort of fall off the grid and disappear than very, very low IQ women. So you have fewer of the very lowest IQ men in the data, in a lot of data sets. And that means that the, the average for men goes up slightly, because it's not being pulled down as much as it, as it should be if everybody were included in the data, it's not been pulled down as much as the, the IQ for, for women. Um, SO, but I think yeah, when you get representative data, Uh, my reading of the evidence is that there's, there's just basically no difference. Um, OTHER small ones, OK, so self-esteem is one that I find, I find it quite interesting. Everyone can guess the direction of the self-esteem sex difference, and, and that is, of course, that on average men have somewhat higher self-esteem, uh, than men. I think I would have guessed that that was, say medium effect size, like a 0.5, uh, Cohen's D, uh, 0.5, half a standard deviation between the means, uh, but actually, uh, the best estimates, I think, put it lower than that, and it's only about 0.2 effect size. So there is a ton of overlap there. There were just many, many. Women who have higher self-esteem than many, many men, uh, the stereotypes are directionally accurate, but I think they overstate, they often overstate the difference. Uh, WHAT else, what are some of the other low ones, uh, the language sex difference is, is another small one, about 0.2, um, so again, it's real, people notice it, but when you see stereotypes like that, Most women are, are fantastically articulate, whereas most men are like, uh, as articulate as chimpanzees. That is, that's not actually, not actually the case, you know. I mean, for a start, there's a range in both sexes, uh, but the average difference isn't, isn't huge either.

1:10:39 Ricardo Lopes: Uh, AND, and even, uh, uh, I mean, when it comes to breaking down, uh, IQ tests into different kinds of tasks, I mean, sometimes people emphasize that there are, but you've already mentioned one of them there, that women tend to score better when it comes to the more language-related tests and men tend to score. Better when it comes, and this is something that you've mentioned already, when it comes to uh spatial uh kind of intelligence. I mean, for example, mentally rotating 3D objects, those kinds of differences, I mean, if I, if I'm reading the literature correctly, are also not very big or are they?

1:11:26 Steve Stewart-Williams: That's right, um, they're not, they're not massive. I think that the, um, the verbal one is pretty modest. The spatial one depends on the particular task, but it, it's, um, I would say most of them are small to medium with a spatial, with the occasional, um, study will show a larger sex difference, but that is true, uh, and that is, That's good news in a way. I mean, it's, it's good news on just in real in life, uh, but it's also good news in, in the sense that this is quite a controversial topic at the best of times. So it is very good news that when it comes to cognitive sex differences, sex differences and specific cognitive abilities, they're very, very small, they're much smaller than sex differences and sexual inclinations, uh, sex differences and occupational preferences, those are quite big cognitive differences. Men and women are much more alike than different.

1:12:16 Ricardo Lopes: Uh, SO, uh, before I move on to another top, uh, to another topic related to sex differences, let me just ask you this. Do you think that the study of sex differences can be compatible with feminism, and I'm asking you that because, I mean, usually, not always, but usually, Feminists tend to prefer a more environmental approach to sex differences, and they tend to emphasize things like patriarchal culture, the effects of culture on sex differences or differences between men and women, but do you think that it can actually be compatible with feminism or

1:13:00 Steve Stewart-Williams: not? I think it can. It does though depend exactly what you mean by feminism, and there are different streams of feminism. To the extent that a feminist worldview involves, like you say, the view that sex differences are entirely shaped by, by nurture and socialization and patriarchy. It is inconsistent with that, an evolutionary perspective, but by definition, it's inconsistent with that, and that it just just claims that as important as those factors might be and in many cases clearly are, they're not the whole story, and there's also an an innate push. But there are plenty of feminists who, Don't hold to a nurture only view, there are plenty of feminists who think, yeah, there's, you know, there's an innate nudge as well, they're, they're quite at ease with evolutionary psychologists, uh, with the evolutionary psychology, and actually there are plenty of evolutionary psychologists who call themselves feminists, uh, and I think like another approach to feminism that is perfectly compatible with an evolutionary perspective, uh, would be to say that feminism is the movement which is, Uh, seeking to, uh, increase fairness for women, to make things fair for women, and to, um, uh, fight for women's rights and the like. All of that is completely compatible with the idea that average differences between the sexes are not 100% due to nurture, and my sort of favorite slogan for that point is to say, uh, that we can treat men and women equally and fairly, and we can be just in how we, how we treat them. Even if average differences between the sexes are not 100% due to socialization.

1:14:37 Ricardo Lopes: Mhm. So, I mean, we've been talking a lot about sex differences, but I actually want to ask you more about the evolutionary rationale behind them, because it's one thing to study the, the differences, but the theory and in this particular case, the evolutionary theory behind them. It is another, it is a complete, is a different subject. So, what, what do you, what would you say is the evolution, the evolutionary rationale behind sex differences? I mean, evolutionarily speaking, what is really at the bottom of that?

1:15:15 Steve Stewart-Williams: Well, the main thing I think is the sex difference and reproductive variance. Um, OR in other words, the sex difference and the maximum offspring number, uh, that I mentioned earlier. So in most species, the average number of offspring per male and per female has to be the same, as long as the sex ratio is the same. Uh, BUT the variance can be greater for one sex or the other. So in other words, you know, you can have more. Uh, MORE individuals from one sex have many offspring, uh, than the other sex, and more at the other end of the as well having no offspring or few offspring. Um, NOW usually in most species, the males have greater variability in offspring number than the females do. So there are more males having a ton of offspring, um, than females, and then more males having no offspring, and where that is the case, What you have is you have selection for any trait that is likely to put an individual male into that category of one of the lucky few that hits the reproductive jackpot and has tons of kids, rather than being one of the, the individuals, the unlucky males that has few kids or no kids. Um, AND the traits that that selects for can vary across species. One of them that, that I mentioned already is male-male aggression. Um, OR, or, or same-sex aggression, so that's aggression, either aggression directly, so, so, so males fighting each other directly for females or males fighting each other for the status, uh, or the resources or the territory that are prerequisites for female attention. And that is stronger in the males than the females, selection for same-sex aggression is stronger in the males than the females, because of the fact that males can potentially have more offspring if their aggression is successful and they get to the top of the pecking order. Um, SO I touched on that already, but another example would be, well, another example would be that because of the sex difference in maximum offspring number, uh. Actually, let me just mention before I go on, why that sex difference exists. The main reason it exists is because males in on average in most species, they invest less in their offspring per offspring than females do. Um, AND for that reason, they can have. Uh, OFFSPRING with multiple females, whereas females, uh, can't have offspring with as many males. But it's not, it's not symmetrical. Uh, GET, let me get a concrete example to make that clear.

1:17:45 Ricardo Lopes: And does that have, uh, let me just ask you, does that have to do, uh, at the, at the basis of it, is it, uh, reproductive biology, I mean, the fact that, Males, uh, across, uh, I mean, I guess most species tend to produce, uh, the smaller gametes, uh, usually sperm and females tend to produce the larger gametes, usually eggs. Is that it?

1:18:12 Steve Stewart-Williams: That's the starting place, um, but it's actually more parental investment overall. So if, so in species where they only produce sperm and eggs, that's the extent of parental investment. And that's what determines the differences. But for species like ourselves, sperms and eggs are just a tiny part of the contribution to, to the offspring, and they're, they're greatly, they're overwhelmed by other forms of parental investment, uh, like pregnancy, parturition, and, uh, and nursing the young. Um, THOSE are all physio like reproductive, they're built into reproductive physiology, and they mean, for instance, that, um, that a man who had to have, say, 3 sexual partners in a year could potentially have 3 offspring at the end of that. Uh, WHEREAS, uh, a woman that had a woman that had 3 sexual partners in a year, probably gonna have no more offspring than she would if she just had 1 sexual partner. Um, AND so that creates a selection pressure on males. To uh seek multiple mates, and so, and so that's another, um, consequence of the sex difference in the maximum offspring number, is that males are often going to be selected, and often are selected in many species to seek multiple mates to a greater extent than females are. We see that in their own species, uh we see that in many others as well. And then another difference is that um because Males invest less Females invest more and females are often choosier about their mates. And for that reason, they select males for signs of signs of health and vigor, good genes perhaps, other things like that. So males evolve to, uh, basically to show off to females, either behaviorally or with, you know, the peacock's tail, that's the classic example of a way in which, uh, a male evolves to try to seduce the females with this fantastic tail that he has this colorful, ornately patterned tail, uh, and the females choose it on the basis of that tail which male they want to mate with. Uh, AND in our own species, we see, I would say that, you know, again, both sexes choose, so both sexes compete for mates and both sexes kind of show off. To try to attract the eye of the other sex, but I think it's fair to say, and I don't think most people disagree with me about this, uh, that, that men tend to do more of the showing off than women do, and the more extreme forms of, of the showing off, uh, which fits quite nicely with evolutionary predictions. So yeah, so that's, so the evolutionary rationale is basically maximum offspring number, sex differences, maximum offspring number, due to parental investment, there's a whole cluster of different sex differences. In fact, most of the sex differences that we've been talking about.

1:20:54 Ricardo Lopes: Yeah, that bit about the showing off, let me ask you a little bit more about it because I, I find it curious, uh, because, I mean, of course, Uh, I'm, uh, I don't think that's necessarily a human universal what I'm going to say next, because, for example, in our more, uh, Western industrialized societies, uh, women tend to be the ones who use makeup, for example, right, and use more, uh, let's say body ornamentation, but of course I'm saying that is. It is probably not a human universal because there are lots and lots of traditional societies where men do lots of body painting and body ornamentation. So, uh, uh, in those societies, it goes the other way around. But, uh, what, what do you mean exactly by men doing more showing off than women? In, in what ways do you think that is?

1:21:53 Steve Stewart-Williams: Um, QUITE a few ways, but, but let me address the, um, the body ornamentation piece first. I think that's the big exception really to this rule that males tend to do more of the showing off. Is that when it comes to physical appearance, um, women tend to do more of it. It's a very interesting exception, I think, to the rule. Um, WHEN it comes to physical attractiveness and ornamentation, it seems that, uh, the females in, in our species have reversed the usual trend, and they, they have the bigger peacock's tail. Um, And I do think that that is a cross-cultural universal when it comes to Uh, like the daily. Daily ornamentation as opposed to ornamentation on special occasions. So there was a study recently, for instance, um, of I think it was 90 nations, and they found in every single nation that women spend more time trying to enhance their appearance than men do, even though both sexes do it. Um, WOMEN did it, did it more in every case. And then, yeah, when, oh,

1:22:52 Ricardo Lopes: so, so perhaps when I was mentioning earlier in traditional societies or some of them men using body paint, I mean, perhaps that is for special occasions or special rituals when they go to war and so on.

1:23:08 Steve Stewart-Williams: Uh, YEAH, I think it might be both of those things separately. So I think there are, um, I'm actually picturing, as you talk about the body ornamentation and the men, I'm picturing. An African group, uh, tribal group, I can't think of the name of it, but the men are all painted in red, and on special occasions they do, they jump up and down and do these impressive physical feats trying to attract, uh, women. Um, AND I think the war painters may be a different thing where they're trying to dress up and hype themselves up and scare the other side. Yeah, yeah, sure, yeah. Uh, SO, but, yes, as far as I know, and anthropologists have, at least some of them have claimed this as well, that it's, that it's a general trend that the women generally spend more time on, on their appearance, and, um, and I argue in the book actually that it's not just about ornamentation, that actually because men place more weight and, and good looks in a long-term mate, that actually women in our species have evolved to be better looking. Um, SO in terms of their physical appearance, they really do have a larger peacock's tail. Uh, SO that, that, but that's going in the opposite direction to what I would say is the general trend, the showing off trend, where I, I think that men are a lot more concerned about status and broadcasting status, and I think that that is, uh, like a big part of that is the fact that women place more weight than men on status in a long-term mate, status and resources in a long-term mate. And so they put men under selection pressure throughout our history. For two things, one, a motivation to attain status and to broadcast status. Um, YEAH, well, to do those two things, they put men under selection to do that. Um, SO yeah, uh, the specifics of the showing off vary from culture to culture. Uh, SO in some cultures, and, and some subcultures within a given nation, for instance, it might mean you can dress up in a really nice suit with a very expensive looking tie and convey, I, I, I earn the big bucks, um. It might mean picking up a guitar and trying to learn how to play songs that are going to impress people. It might mean, uh, picking up a skateboard and trying to get really, really good with, uh, doing fancy moves on the, on the skateboard, uh, it can involve sort of risk taking, uh, just, just all sorts of things, I think, um. It is interesting that there's a great example I think of something we touched on earlier, which is that at the level of the specifics, you just have a ton of cross-cultural variability and variability within cultures and across times, um, but at a, at a deeper level, it does all seem to come out of the fact that men seem more desperate to master something and broadcast how cool they are and how high status they are to the world.

1:25:48 Ricardo Lopes: Yeah, even though I imagine that nowadays we have to be a little bit more careful with honest signaling because I mean, we can rent a nice suit, we can rent a nice car, you know.

1:26:01 Steve Stewart-Williams: Yeah, and, and I, I think you're absolutely right, and I wonder if actually that changes what signals people pay the most attention to. Like it seems to me, I was actually thinking as I was talking about suits as a status display, I was thinking, I don't think that that is as much of a status display these days as it might used to have been. Yeah, well, your social circle as well, but, yeah, yeah.

1:26:22 Ricardo Lopes: OK, so let me just ask you about sexual selection because I would imagine that sexual selection from an evolutionary standpoint also has played and plays a big role in driving the evolution of sex differences. So, is it, is it possible for us to really distinguish between, uh, the role. THAT intersex competition versus intersex selection might have played in driving sex differences. I mean, is it possible for us to know how much of it has been the result of competition within sex or intersex selection?

1:27:08 Steve Stewart-Williams: Sometimes it is, I think sometimes it's a, the lines are a bit blurry, and I think actually that there are some traits that are favored by both forms of, of selection, by mate choice and uh same-sex um competition. I guess that's sometimes it's pretty clever. So I do think sometimes it's clear, I do think that, hm, what's an example? I would say aggression in humans, in human beings is pretty clearly a product of intersexual selection rather than intersexual selection. So in other words, aggression is, is about competition between males rather than aggression as a way to try to impress females. And the reason I say that is that often females, this is, this isn't just humans actually, there are quite a few species where the females don't actually seem to like the aggression, they don't seem to just, They don't see a fight and then just fall for the winner and think that that winner's so hot, the way that he beat up that other person. So I think it's more likely that that is about same-sex competition for status and rank and resources, and that, but that is the status and rank, that is what females are, are interested in rather than aggression per se. Um, AND in some traits like the peacock's tail, I don't think that plays a big role in terms of male-male competition. They, they have leg spurs though, so they do actually fight, the males fight each other as well. And I think the leg spurs kind of like built-in knives on their legs. Basically, I think those are products of intersexual selection, but that um the tail itself is almost completely a product of intersexual selection, so, um, the fact that the females like them, and uh, and they choose the male based on the impressiveness of their tail. Uh, IN humans, I think a lot of traits like male upper body, uh, Upper body strength, yeah, exactly, and muscularity, um, I think that those, it's pretty good evidence and arguments that those are largely a product of intrasexual selection, um, because they tend to be more threatening to other males than they are attractive to females, but they are also often quite attractive to females, so they're probably they're they're a product of both. Um, BUT maybe more intra than intersexual selection. And then a lot of women's, uh, secondary sexual features like, you know, uh, breasts and, uh, the, um, hourglass shape, things like those that appear at puberty, those are largely products, I think of intersexual selection. So in other words, a, a male mate choice, rather than being about intersexual conflict among females.

1:29:47 Ricardo Lopes: Yeah, I don't know if you would agree with me, but I think that particularly when it comes to the male body, I mean, what attracts women, it seems to me that it tends to be not so much the trait itself, but more the sense that the trait is a proxy to status because for, for example, in the 60s, 70s, there There were lots of, I, I, I mean, I, I think that the majority of them were like this, that many er famous musicians were really, really, really skinny and female female females were very attracted to them, but it's, uh, I, er, but it was because er er that was a signal of their status as musicians, as people who probably have lots. Of social status, lots of money, and so on. And nowadays, perhaps with this trend of, for example, male actors being more muscular in terms of their upper body, perhaps the muscularity is more of a proxy to those same kinds of things like social status, money, and so on. I mean, would you agree with that, or

1:31:01 Steve Stewart-Williams: maybe, let me think. Um, THE only counterargument I can think of. Is that, I think it's possible that women are interested in a whole bunch of different things, and, and men as well, um. So they're interested in status, interested in resources, but also interested in physical attractiveness. And I guess it's possible that those 60s and 70s scrawny rock stars might have been, might have been even more attractive if they'd been a little healthier looking and didn't have the sort of druggy look or whatever it was, you know, um, they're just spending all their nights out partying look. Um, AND, and yeah, so possibly. They found them attractive despite their scrawliness rather than because of it. And uh yeah, and. Yeah, it's interesting, isn't it? It's the fact that Women can be attracted to scrawny guys and quite muscular guys, I guess it does suggest that, I mean obviously they do, obviously women just like men have physical preferences. But I guess unless they're really extreme, like extreme muscularity, I don't think is considered too attractive because it's too out of the norm, and extreme scoringness I'm sure would not be attractive either. Yeah,

1:32:13 Ricardo Lopes: and extreme muscularity also at a from a certain point on it becomes the body becomes sort of dysmorphic, right? I mean, it doesn't, it doesn't look good at all and sometimes it doesn't even look like, uh, oh my God, what's that kind of trait that people always like in terms of the body as symmetry. It doesn't look symmetric.

1:32:35 Steve Stewart-Williams: Yeah, yeah, true, yeah. Um, BUT within the normal range, within quite a wide range, it seems like it's not a, a deal breaker to be, to be some, you know, it seems to be quite a wide range of acceptable. Healthy-ish kind of bodies, and yeah, especially it was trumped by other things like uh wealth and status and, Playing cool guitar licks.

1:32:59 Ricardo Lopes: Yeah, so, uh, let me just, uh, when it comes to mating, I mean, we've already gone through most of it, but there's another aspect that you also tackle in your book that has to do with, uh, preference for people from a particular kind of, uh, age bracket. OR not necessarily age bracket, but them being younger or older than you. So, and in the book you make the claim that men prefer younger women, whereas, whereas women prefer older men, but not always. So could you explain that?

1:33:34 Steve Stewart-Williams: Uh, THAT'S right. And actually, you know, that, those, the sex difference in age preferences is actually quite a big sex difference as, as human sex differences go. And yeah, so for people, for men and women and their. In the twenties, Uh, early to mid-twenties in particular, that's where most of the research has been done. The general finding is that men do tend to prefer somebody a couple of years younger, whereas women do tend to prefer someone, About their own age or maybe a couple of uh couple of years older, um. But that's not always the case, and the exceptions to that rule, I think actually point quite nicely to the validity of the evolutionary explanation for these differences in the first place. Um, SO what you find is among teenage boys, they're not actually most attracted to, to girls who are younger than them. So if they're like 16, they're not most attracted to 14-year-old girls, they're more attracted to women who are older than themselves. So women, women in their early 20s, um. Which, which the key thing here is that that's the age of peak fertility uh in females, and the physical features that men typically find the most attractive are those associated with fertility. Um, Now what happens is that And that's actually true for both sexes, is that both sexes find traits associated with youthfulness to be, to be attractive, but men place more of an emphasis on youthfulness than women do, and the evolutionary rationale for that is that women but not men, have menopause. So women have a narrower window of fertility than men do. And men place more emphasis on youthfulness in a mate than women do, because youthfulness is more key to female fertility in women than in men. So yeah, so yeah, so it's a stronger emphasis on youthful traits, um, now as people get older, uh, moving through their life in their 20s, 30s, 40s, 50s, uh, it's not the case that, that men, Always would prefer a mate who's in the, who's in her early twenties. Um, THE purely physical features that they might find the most attractive, maybe those associated, they are those associated with women in their early twenties. But, uh, we don't just choose mates based on, on looks, contrary to the stereotypes of men, uh, there are very few who only choose on the basis of looks. Looks are part of it, but also compatibility is very, very important as well. People tend to be more compatible with people of their own age, they have more, more in common with them. So what seems to happen is that as men get older and older and older, the um age of their ideal mate gets older as well. But The age of the ideal mate doesn't go up as fast as their own age does, and it seems to be the, the age of the ideal mate is like a compromise between the age of peak physical fertility and their own age, sort of somewhere in the middle. Um, WITH women on the other hand, as they get older, they. Just continue to prefer somebody of roughly their own age, you know, that there's a range of some somewhat older than themselves to a slightly younger. Within that range, the average is slightly older than themselves, but it is not, uh, not massively discrepant. And, and let me just add that I think, um, when people hear about this, they sometimes think that it's just, Uh, wishful thinking on the part of older guys who just think, oh yeah, you know, women like older guys, this is great. Um. Uh, AND that's not the case, right, so it's not the case that women are primarily attracted to older guys, let alone old men. You know, if it were, you'd look at their, at, uh, teenagers, teenage girls, bedroom, uh, walls, and they would post up pictures of, you know, politicians or, or older guys rather than boy bands. They, they tend to prefer someone of around their own age. Um, SOMETIMES you do get pairings where you have a, an older guy with a much younger woman, but I think when that happens, that's usually, uh, despite the guy's age, rather than because of his age. It's usually because he's got other stuff going on, like wealth and status.

1:37:46 Ricardo Lopes: Could it be that, for example, the fact that some guys and I mean we can see lots of that in the porn industry now with the MILF category. I mean, since the release of American Pie in 1999, I mean, it became a thing. I mean, could it be the case that perhaps what we tend to associate with the MILF cat. Category and guys feeling attracted to some older women has to do with the fact that many of them, the thing is not that they are older, but that they look younger than they really are. I mean, because many of them actually retain some of these more neotenous features, right, even in their, even in their 40s sometimes.

1:38:34 Steve Stewart-Williams: Yeah, agreed. I think that is a big part of it. I think that, uh, our lifestyles these days are in many ways cushier than they used to be. So, a 40 year old man or woman today, woman or man, is probably going to look, uh, younger than a lot of 30-year-olds or maybe, I don't know, maybe even 20-year-olds in hunter-gatherer times. So you look younger because of cushier lifestyles. Um, ALSO, a lot of MILFs, I read somewhere that, um, the average age of women who classify themselves as MLFs, it's, it's actually surprisingly young, it's not actually, like 40s is relatively uncommon. Um, IT'S more likely to be in the 30s, I think, you know, maybe even the, maybe even the late 20s. Uh, SO yeah, so I think it's really about, it's not the, it's not about the age per se, it's about features statistically associated with age throughout most of our evolutionary history. And, and yeah, a lot of, uh, older, older women. Who are still found very attractive, it's because they still retain those features and, and also there's cosmetics and cosmetic surgery, and then I guess on top of all of that, I think that, uh, a lot of the women who go into that kind of work or who are considered very, very attractive models or actresses, They're atypically attractive anyway, so, um, so that's sort of, that trumps a lot of,

1:39:50 Ricardo Lopes: uh, yeah, some of it, some of it perhaps is even genetics.

1:39:55 Steve Stewart-Williams: Yeah, yeah, yeah, exactly. Mhm.

1:39:58 Ricardo Lopes: OK, so I have just two more topics that I would like to discuss with you and, uh, I mean one of them has to do with how we should deal with all of these in terms of how we approach gender roles, but Before that, er, what do you make or how do you approach er intersex people or people with differences of er sexual development, trans people, and non-binary people? I mean, generally speaking, people who tend to or apparently fall outside of the sex or gender binary.

1:40:36 Steve Stewart-Williams: Yeah, um, it's an interesting topic, right? And I think it's one where, um, a lot more research is needed. I touched on it in the book, but I don't say too much about it. And really, the reason for that is that there's, there's not a heap of evidence on the topic. Um, I discussed same-sex sexual orientation in some depth, because there is quite a bit of research there. But yeah, what I, what I think's going on. Uh, ONE of the things going on with trans and non, non-binary individuals is that, well, I think there are some. Biological males who are somewhat shifted in a, in a more typically feminine direction, and some biological females who are um somewhat shifted in a more masculine, uh, direction, and that's probably, I would, I would say probably due to sex atypical prenatal hormonal exposure. And some of those individuals who are shifted in that kind of atypical direction. Would just see themselves as being feminine men or masculine women, um, but some on the other hand, Identify with the other sex instead, or, or don't identify with either sex and would classify themselves as being um non-binary.

1:41:51 Ricardo Lopes: Yeah, because, because during intrauterine development, the brain can develop independent from, uh, the other, uh, the goal nuts, for example, right, and the uh for example, the, the um, The regions of the brain which we know tend to develop in somewhat sexual dimorphic ways in certain people, they can develop, uh, for example, even if they have male. Genitalia and produce male gametes and have male gonads, their brain can develop in the opposite direction when it comes to the structures that tend to influence gender identity.

1:42:36 Steve Stewart-Williams: That's exactly right. And, you know, at least to some degree, they can be shifted in that direction, and that's just because, uh, the time period within the womb where, uh, Sexual differentiation of the brain takes place is difficult, is uh different from when uh other aspects of sexual differentiation take place, um, so, so yeah, so I think that's probably a big part of what's going on. And I think that, uh, so those are the facts, right? Um, THEN there's the ethical question, and, uh, the ethical question for me, I just think people should be, people should be able to just live the lives that they wanna live and lead, uh, and, and identify the way that they want to identify, and of course not be mistreated, uh, because just because they identify in an atypical way, um, that's not any great hot take, I think a lot of people have that view. But I'm just saying I, I completely agree with them on that. Um, NOW in terms of intersex people, that's slightly different. That's when you have a, a mixture of male typical and female typical traits, uh, like physically that come about. So, so some people have argued that the, um, trans people and maybe, um, non-binary people are psychologically intersex. Um, YEAH, but, but they're not intersex in the traditional sense of the term and that they don't have, um, ambiguous physical features.

1:44:05 Ricardo Lopes: Mhm. Yeah, because people who we tend to call intersex, that in the medical field nowadays we call people with differences of sexual development, uh, many times, uh, they tend to have ambiguous primary sexual characteristics, right?

1:44:24 Steve Stewart-Williams: Yeah, indeed, yeah, it's just, uh, intersex people in that sense are a sort of subset of people with, um, uh, Disorders or differences of, of, uh, sexual development. Mhm.

1:44:36 Ricardo Lopes: OK, so one final question and I guess that you've already at least part, partly answered it, but, uh, toward the end of your book, you talk about three different, uh, sort of gender role approaches that we can have to all of these differences. I mean, you talk about gender role traditionalism. Which I think it's pretty much self-explanatory and gender role progressivism and gender role individualism, but I, I mean, uh, explain a little bit each of them, and uh I mean, in your opinion, I mean, do you have a preference for any of them, or do you think that one of them is more ethical than the others? How do you approach this question?

1:45:21 Steve Stewart-Williams: Sure, so the, so those are the three different ways that I stake out that we can potentially react to, uh, sex differences in society, uh, and, and actually even in our individual lives. So the first one, gender role traditionalism, is the idea that men and women are, are very different, and they're very, very different by nature. And not only that, they should be. So they are different and they should be different, and if men and women, Start straying away from the traditional gender roles that have been bequeathed to us by God or by nature, we should try to correct that, in exactly the same way that if somebody breaks their arm, we would try to correct that by putting their arm in a cast. Um, GENDER role progressivism is the view that most sex differences are almost completely due to discrimination or sexist socialization, and therefore that in an ideal society, we would expect and hope that they would just disappear completely, and, and that's what we should try to do, we should try to get rid of sex differences or maybe even reverse them to make up for past roles. And then the third approach is gender role individualism, which is that, We shouldn't take a stand on the gender outcomes. We shouldn't be aiming for massive differences or or getting rid of differences. We should just instead, um, get rid of bias and barriers, try to create, to the extent that we can, try to create an even playing field. But then let the, the gender gaps and sex differences and sex similarities set themselves as a result of different individuals making informed choices about what they most want to do with their lives. Um, NOW, the way I've described that, I think it's gonna be pretty obvious to everybody that I do have a preference,

1:47:12 Ricardo Lopes: and it's, it's the leather one.

1:47:13 Steve Stewart-Williams: Exactly, exactly right, yeah. That is the one that I prefer. And, and that's the one that I think is the most ethical approach, and I think it's the most ethical, because I think it's the way that is most conducive to increasing individual happiness and also people's freedom. You know, so I do, one thing I don't like about either of the other two. Is they seem to be trying to make decisions. You know, about what other people should do with their lives. So in one case they're trying to push people into gender roles, and in another case they're trying to push them out of them, whereas I would much prefer to just really try to give, empower everybody to make the decisions that suit them best, and then it's just up to them what they do and we'll just let the cards fall where they may. And some sex differences may be bigger and some maybe smaller and it just doesn't matter. What matters is that people, um, are not subject to unfair treatment or bias and that they uh have the, the resources to try to make up their life what they want to make.

1:48:10 Ricardo Lopes: Also, I think that both general traditionalism and general progressivism are not very accommodating of variability even within men and within women, because I mean, general traditionalism for very obvious reasons, I mean, is not very accommodating for, I mean, more masculine women or more feminine men or and even trans people, non-binary people, and so on, and gender progressive. I mean, sometimes it seems like any kind of difference between men and women, and I guess even to some extent variability with, particularly within women, because I mean some women might be more conservative, others more progressive, and so on, that many times it's also not very accommodating to that sort of more I guess political variability.

1:49:10 Steve Stewart-Williams: I completely agree, and that's one of the things I like best about gender or individualism, um, is the fact that I, I just think it's the most tolerant approach. Tolerant of individuals, it says it's completely fine if you buck the trend, and if you're very, very different than the, the average man or the average woman. But, but it's also completely fine. If you don't buck the trend, and you just fall in with the traditional ways, that's fine too, whatever, whatever suits you best. Yeah. As long as it doesn't harm other people. Sorry, just an extra thought, as long as it doesn't harm other people, you know, I think, um, and as long as it's, as long as the differences are not a product of injustice or mistreatment, and as long as they don't, they don't create harm, I think we should basically let, live and let live and let people be themselves. My favorite example of where we shouldn't do that so much concerns male violence. So male violence, there's an obvious sex difference there. But male violence is the cause of a lot of completely unnecessary suffering in the world, and so I think for that reason, even though it's perfectly natural, we have every reason to try to seek unnaturally low levels of male violence. And, and in doing that, we're going to shrink the sex difference. But the problem with aggression, it's not the sex difference that is the problem, it's the violence that is the problem, and um, what we should be aiming to do is reduce harm, increase freedom, and the effect that has on sex differences, well, you know, what whatever effect it is, it doesn't matter. Uh, WHAT, what matters is harm and freedom rather than getting rid of sex differences or magnifying sex differences. Yeah.

1:50:45 Ricardo Lopes: OK, great. So, let's end on that note, Doctor Stuart Williams. It's been a great conversation and the book is again, a billion Years of Sex Differences, how evolution. The minds of men and women. There is the cover in case people are interested in buying the printed version of it. So Dr. Stuart Williams, thank you so much for doing this. And by the way, apart from the book, would you like to tell people where they can find you and your work on the internet? Yes,

1:51:15 Steve Stewart-Williams: and thank you as well, uh, Ricardo. That was great. I really, really enjoyed that conversation. Other than the book, you can find me in uh two places. My favorite place at the moment is, is sub stack, and I have a sub stack called the Nature nurture, Nietzsche newsletter. So you can find that, you can Google Nature, nurture, Nietzsche, or you can just Google my name. I think it's one of the 1st, 1st things that comes up is my, my sub stack page. Uh AND also I'm on Twitter, and my Twitter handle is at Steve Stewwill. So at Steve S T E V E S T U W I L L. You me, Dave as well.

1:51:51 Ricardo Lopes: Oh, and by the way, I will, of course, also link to our first interview about your other book, The Ape That Understood the Universe, which is also very fascinating, fascinating, and thank you so much for taking the time to come on the show again. It's been really fun to talk with you. Yeah,

1:52:07 Steve Stewart-Williams: thank you, Ricardo.

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