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A
There's this phenomenon called the gender equality paradox, which reflects the fact that for many, many traits, including career related preferences and job choices, it's the exact opposite. And you just find that the more gender equal and the wealthier and more individualistic a nation is, the larger those sex differences become rather than the smaller. Very counterintuitive.
B
And now the good fight with Yasha Mon. Well, today I decided to tackle one of the age old questions. What are the differences between men and women? Are they downstream from nature or from nurture? How do these differences shape our society? And what are the different kind of biases that we bring to understanding? From traditionalist biases like thinking that people should act like their sex, to perhaps other biases that try to correct for those that try to deny sex differences that really do have a biological root. To talk about this I invited onto the podcast Steve Stewart Williams. He is a professor of psychology at the University of Nottingham, Malaysia. He is the author of a new book called A Billion Years of Sex How Evolution Shaped the Minds of Men and Women and he's also the author of the Accident Nature, Nurture Substack. We talked about all kinds of fun and potentially controversial things for from differences in the appetite for casual sex, mate choosiness, the tendency towards aggression. In the last part of this conversation, which is reserved for paying subscribers, we talked about how philosophical liberals should think about all of this. How do we take the science seriously? How do we avoid falling into the camp of people who deny things that are very clearly scientifically established without becoming sex essentialists, while continuing to fight for a society in which every man and every woman is able to make their own choices about how to live, what profession to pursue, and so on? And how does that relate to perhaps the hottest of the hot potatoes in this area, which is research about the differences in aptitude at the extreme ends of men and women. To listen to that part of the conversation to support the podcast, to get all of our full episodes into your inboxes, into your favorite podcasting apps without ads, go to writing.ashermonk.com and today I'm throwing in my best offer I ever give. 30% off your first year of subscription, which brings us down to to about a dollar a week. You can afford that. You can help us go to writing.yashamonk.com 2026writing-monk.com 2026. Steve, welcome back to the podcast.
A
Hello Yasha. Thanks very much for inviting me again.
B
So last time we spoke you gave a really great introduction to how to Think about the influence of evolution on human nature and human psychology. You are now out with a book that speaks more specifically about sex differences and how those are rooted in biology. Let's go through some of the sex differences that the literature establishes relatively decisively. One way you break this down is to say, you know, some sex differences are just, you know, completely dimorphic. Women give birth, men do not. Others are more, you know, statistical variances. Tell us a little bit about how to think about the kinds of sex differences and what some of the most common ones are.
A
Sure, no problem. Yes. So the new book is called A Billion Years of Sex Differences, and that is the COVID right there. And yes, I start by listing what I call standard issue sex differences. Just a list of very well established sex differences in our species. Like you say, they range from the very, very large and the strictly dimorphic and categorical to the not so large and just sort of. They range at the other end to just statistical differences like relatively modest discrepancies in the average scores of massively overlapping distributions. So at the. The larger end of the spectrum, we generally just have physical differences between the sexes. So reproductive differences, the reproductive organs, the capacity to nurse versus not being able to do that, capacity to give birth versus not being able to do that. Those are all very large differences. The difference in upper body strength is quite large. Well, actually very large. There's very little overlap there. Very little overlap either in voice pitch. So voice pitch is another quite large sex difference. Moving down the scale, I guess the only. When we talk about psychological sex differences, the only one that's even remotely in the ballpark of those physical differences is the sex difference and the primary target of sexual attraction. So most men are primarily attracted to women. Most women are primarily attracted to men. And there are exceptions, of course, but nonetheless, that's a very, very large psychological difference. And it shows, I think, that natural selection can create large levels of dimorphism.
B
And that's interesting because in the first category you're talking about, certainly we're not going to get into the whole translator, but for purposes of this conversation, we're talking about biological sex. Men can produce sperm, women can produce eggs versus just completely different biological processes. Dimorphic. Here we're talking about most men are attracted to women, most women are attracted to men. But then there's these subcategories of. Of men who are strongly attracted to men and women who are strongly attracted to women. So that's a kind of very, you know, it's sort of a very different kind of distribution.
A
It is, yeah, it's, it's a different kind of sex difference. And even though people attracted to the same sex, they are exceptions, but they are a minority. But they're not a trivial minority. There's a, there's a non trivial number of exceptions, whereas that's not the case for the first, the first sex differences that I named.
B
Not to go down a rabbit hole, but a lot of people are going to have in their mind this idea of a Kinsey scale that actually most people know, fall somewhere on a long spectrum between complete heterosexuality and complete homosexuality. And so actually it's not that most men are attracted to women when a few men, some significant percentage of men happens to be very attracted to men. Is that really we all fall on the spectrum along the line? Is that compatible with modern science? Is that something that scientists today believe, or how does what you're saying fit onto that kind of model of McKinsey scale?
A
Well, I was thinking of that Kinsey scale when I, I framed the exact wording. So my exact wording there is that most men are primarily attracted to women, most women are primarily attracted to men. So that's accepting the fact that there is some degree, it's not uncommon at all for there to be some degree of attraction to the same sex among people who are primarily attracted to the other sex.
B
So broadly speaking, McKinsey scale has been borne out by more recent research.
A
Yeah, yeah. So there are differences in the degree of attraction to each sex that people, that individuals have. I guess one thing is that people often understand it to mean that there's a spectrum of people that distributed fairly evenly across it. Whereas you do actually have clustering toward the two extremes of the continuum that is primarily attracted to the other sex versus the same sex. But especially with men, actually. So with men you do get quite strong clustering, either primarily attracted to the other sex versus the same sex. With women, it's a little bit, the distribution is a bit sort of more even across that scale.
B
So if you're picturing the scale from left to right, what you're saying is that one big mountain, I'm picturing it on the left where it's attraction to the opposite sex and then a smaller mountain on the other end of the scale when it's really primarily attracted to the same sex. And then in between, there are all kinds of people who fall at all kinds of points in between. But those are not going to be big, local, maximum.
A
That's exactly right. With just the one proviso that There are fewer men in the in between category than there are women in the in between categories.
B
So the mountains are going to look. The peaks are going to look higher for men than for women.
A
Yes, slightly higher. Slightly higher for men. Yeah.
B
Interesting. Okay, great. So we're here. And that was the second kind of category. Now the third category, which I think is sort of where most of the interesting debates lie, because the first category, the biological differences, those are relatively straightforward and uncontested. You know, the second category is super interesting and important, but I guess applies to slightly fewer characteristics. Perhaps a lot of the things that we really have big social debates about are the third category. Right. Is it true that men have an innate attraction to certain kinds of forms of professions, to certain kinds of forms of socializing, to certain kinds of ways of thinking about the world or not? Right. All of that contested stuff lies in the third category of minor statistical differences. But that might make a really significant impact on the world. So tell us about those.
A
Sure. Yeah. And that's exactly right. So the vast majority of psychological sex differences in our species are in that third category, which is statistical sex differences, or what I call fuzzy sex differences, where you have differences in the average of highly overlapping distributions. And I think probably that a big part of the reason that there are so many debates about it is because they do awkwardly fall into that middle ground where a lot of them are small enough that you can sort of question whether they actually exist, but they're large enough that also they trouble us. So sort of in that awkward middle ground where you can deny them, but so they do have real world effects to some degree, span a range of different magnitudes as well. So among the larger ones that you find. So you mentioned career related interests, that's actually one of the larger sex differences that you find in this category. There's usually about a standard deviation difference between the mean for men and the mean for women in career related interests.
B
Cash out a little bit for lay listeners and readers, what that means both in terms of if you have a different professional preference, how strongly does that mean drive professional choice and so on, and roughly how big, in effect is a standard deviation?
A
No worries. So, yeah. So talking about career related differences, the key differences are that on average, men tend to be more interested than women in things and sort of how machines work and mathematical formalized kind of things that are sort of impersonal than women do and more interested in careers involving those things, whereas women on average tend to have a greater interest in people and how people work and in People related professions, professions that involve helping people and interacting with people. The difference is. So yeah, so the difference is about a standard deviation between the means for the two scores. And that is considered to be quite a large effect size. There are still heaps of overlap. So what it would mean if you were to choose two people, one man and one woman at random, and every pair that you chose with an effect size of one, probably about a 70% chance that. So for interest in things where men score higher, random people, there'd be about 70% chance that the man would score higher than the woman. So 30% of the time it'd be the other way around. And the converse for interest in people. And about 70% or thereabouts of the randomly chosen pairs, the woman would score higher than the man, but then there'd still be a very non trivial minority of cases where the man scored higher than the woman.
B
And so that's, I think, a little bit of what makes this awkward. Let's cash this out talking about this relatively uncontroversial example and then we can think about how that applies to more controversial examples. Because what you're saying is that in the literal sense, stereotypes about this are right. There's a stereotype that men love their machines and their tools and they go into the man cave and they potter around in the workshop. And women love to engage more social professions or exchange, pejoratively speaking, gossip or whatever. You can make a negative caricature of each of those things. Or positive, positive is the man likes to build things and get things done and, and the woman loves to, you know, be a connector in the neighborhood and make sure that people are doing well and, you know, cared for. Or you can have a negative start about each. Right. The man is just like locking himself away, you know, like an incel in his workshop working on things of a woman is engaging in mean girl gossip behavior or whatever. Like you, you can sort of like spin each of them positively or negatively. But the point is that, you know, that is a stereotype we hold in society. And what he's saying is there is some real empirical grounding for it. And yet of course, if you apply that to everybody, if you were hiring in an engineering firm and saying, well, this is a female applicant, surely she doesn't actually like machines, then you would not only be perpetrating an injustice towards that woman, but a lot of the time you'd be wrong because a good number of women is interested in these kinds of things. And probably out of women who are applying for this position, it is most of them who are exactly.
A
Yeah, that's exactly right. And I think that it is true that this stereotype and a lot of stereotypes are on the right track. At the very least, they're on the right track. They're a response to something real. And the danger is this, if you exaggerate the magnitude of them, which is what you're doing, if you say, well, this is a woman applying for a male typical job involving machines, that's just impossible. It couldn't be the case that she would be interested in them or good at working with them and vice versa. For men applying for people related jobs, you'd be exaggerating the strength of the sex difference. And I think that's a big reason why people are nervous about talking about sex differences is that they worry that people are going to do that. They worry that if there's any acknowledgement that actually there is some truth in these sex differences, people are going to misunderstand that, blow it out of proportion, and that it will be a justification for discriminating or a cause of discriminating against one sex or the other. And I do take that concern seriously. And in the book I discuss that as a serious thing that we do need to concern ourselves about. But I nonetheless think that it's really worth exploring the topic for two reasons. One is, whether we like it or not, there are average differences between the sexes in many different areas and we can't just lie about them. And then the second reason is that even though there are dangers of talking about sex differences and there are dangers associated with exaggerating them and moralizing them, there are also dangers for the converses. There's also a danger in minimizing them and ignoring them and moralizing the absence of sex differences instead. So I think really the only responsible solution to that little conundrum is to just see what the data say, try to convey it accurately, but also talk about sex differences responsibly and be careful to talk about them, but talk about them carefully.
B
Motivate where the dangers here lie. So the danger of the first kind of error is relatively straightforward, right? It's that I'm a hiring manager at an engineering firm and an excellent female candidate applies. And I say, well, come on, she's a woman, she's not really, really going to want to be doing this kind of job. And I don't hire her even though she's, you know, an excellent, well qualified candidate. So that's a very straightforward danger. Where does the danger lie in not Talking about these sex differences.
A
Yeah, there are quite a few and there are actually other dangers as well with exaggerating sex differences. Like if we get a sort of mental image of how what men are supposed to do and boys are supposed to do and what girls and women are supposed to do, then we might pressure people to, to fall into stereotypical definitions of the sexes, which is, which is bad for people who don't fit in with the, with the norm.
B
That's a slightly, I mean, it's obviously related, but it's subtly different. Right. Because here we've gone from, you know, if I'm a hiring manager at an engineering firm, I may not have a belief that it's wrong for women to want to be engineers or something like that. It would be great if women were like us, Amanda, were super into engineering. Right. But sadly they all aren't. So I'm not going to look at this candidate seriously. Right now we've gone to a slightly different thing, which is because there are some statistical sex differences in the world that is in fact what men and women should be like. And so now let's say I'm a dad and my daughter's interested in engineering, say, well, that's not for you, you should really study psychology. Right. So here we've sort of gone to the danger of ignoring the fact value distinction or the is ought distinction or something like that.
A
Exactly, yeah. So there are dangers with just exaggerating and that one I just mentioned is a danger of exaggerating and moralising the sex differences. But there are converse dangers, to answer your earlier question, converse dangers with minimizing sex differences and moralising the absence of sex differences, one of which is directly symmetrical with the problem of trying to force men and women into traditional gender roles is a sort of danger of trying to force them out of them, of not accepting the fact that although there are always going to be exceptions, there are going to be some people who are just going to fit with the sort of gender typical norms and roles and preferences and people sometimes have a tendency to think that that's a bad thing and a product purely of sexism, or if it's their kids, they might feel guilty that they've done something wrong in the parenting, that their kid falls into typical patterns and boys are engaging in rough tumble play and girls love pink and dolls and the like. So I think that's, that's one danger. Another is that if we ignore sex differences in things like preferences, career related preferences, that means that when we find discrepancies in the sex ratios in different professions, we're going to assume that it is 100% due to discrimination and sexist socialization. And while it's very probably partly due to discrimination and sexist socialization, it's not necessarily. In fact, it's not even likely to be the case that it's only due to those factors. Given that men and women do have, on average, these different preferences. It seems very likely that part of the reason that we have different sex ratios in some professions is a result of the fact that we have these different statistical. Statistical differences in preferences. And not just that. Actually, it's not just that. It seems likely. I think it seems very unlikely. Unlikely, given that we have those different preferences. That wouldn't be one of the causes of the differences.
B
There seems to be some preliminary evidence that men aren't just more interested in tools, they're also interested in a specific tool, which is artificial intelligence. If that turns out to be the case, at a moment in which it seems very likely that AI is going to fundamentally reshape our society, is that going to be to the detriment of women? Are we entering a technological age in which you might see some of the professions that a lot of women are in, like human resources, become relatively less lucrative? And some of the professions, like helping to create these new AI systems in which men continue to be overrepresented, really dominated?
A
That's a very interesting question, and I think that is possible. One reason though, that I think that is not necessarily going to turn out that way is that the interface between people and AIs is quite a social activity. It doesn't feel like tool use in a traditional sense. It sort of can feel quite a social thing. You're interacting with something verbally. And I was at a festival recently, the how the Light Gets in festival out at hey on Y. And I met a few AI people who work in AI, and one of them was. Met a couple. So one was looking at how AI can be used in the medical sphere. That's Charlotte Bleez. She's very interested in applying that in the medical sphere to help people. And in that area you might actually find predominance of women over men being interested in that in that question. And then somebody else I met was very interested in the use of AI for psychotherapy. And again, that's a field where currently women predominate over men. And it's possible that if AI moves into that area in a big way, that actually likewise there'll be a predominance of women over men and the AI applications of psychotherapy.
B
And let's make a simple prediction here, right? If you think that women professional choice is really down to socialization, social pressure, informal prohibitions on men becoming hairdressers or women becoming engineers, then you would expect that the more gender egalitarian a country is, the less pronounced those gender differences in professional choice. So you'd expect that in a relative traditional society like Egypt, there would be a huge difference where very few women are engineers and very few men are hairdressers or whatever. In that society is a more female coded profession. And in Sweden, or whichever country is relatively gender egalitarian, that's not to say that any society is totally gender egalitarian. You would expect those differences to be relatively more minor. My understanding, Steve, is that that is not in fact what the evidence shows.
A
Yeah, your understanding is correct. So I would have made that same prediction before I saw the data. Even accepting that there's an innate contribution to preferences and the like, I would have thought that in cultures where they treat people more differently and they have stricter gender roles, sex differences would be even bigger. So if there's even innate contribution, it'll be amplified and then it'll be smaller in more gender egalitarian societies, more individualistic societies, and wealthier societies where people are freer to pursue their own interests. But yet, like you say, there's this phenomenon called the gender equality paradox, which reflects the fact that for many, many traits, including career related preferences and job choices, it's the exact opposite. And you just find that the more gender equal and the wealthier, more individualistic a nation is, the larger those sex differences become rather than the smaller. Very counterintuitive.
B
Yeah, really interesting finding. I had an interesting episode that touched on that with Alice Evans on the global gender paradox. Among other things, I find that one of the things that makes this conversation often unproductive is that different, and that is, I think, true, not just of this conversation, but of many conversations, is that different people kind of have different audiences in mind and that drives them to talk about different things in slightly different ways. So I'll give you a totally different example. A lot of social science disciplines, like sociology, for example, love to make this move where they're saying this thing actually turns out to be socially constructed. And I find that that is good for an intro undergraduate class in the sense that I think a lot of 18 year olds come in thinking that something like, say, the United States Constitution is just this God given thing and it is objectively correct and there's no reason to question it and put it in a historical context. And to say, no, these are particular people who built this at a particular moment and they were brilliant people doing something important, but they also had their shortcomings and their blind spots is a sort of helpful thing. I don't actually know how many 18 year olds still come to college today having that kind of naive view of a constitution, but certainly I see where that kind of comes from. But I think there's a danger in both overagging what it means for something to be socially constructed, which is the general pet peeve I have, but also in sort of making your whole academic career invested in pointing out this thing actually is not natural and God given. And you're kind of speaking to an audience where everybody already agrees with that. Right. And I think when you talk about these gender differences in a similar way, I think there's sort of a lot of people who, for understandable reasons sort of think, oh, you know, there's a danger of there being stereotypes and prejudices in society and they coerce men and women to these gender roles and then obstacle to women advancing in certain professions. And so that's really what we got to be on the lookout against. And so you coming in and writing this book about sex terms is really damn unuseful. Steve. What? What on earth are you doing? Right. And there's others who say, well, no, but actually there's a kind of like a higher level thing where the whole mainstream has become so concerned about that real danger that it's overshot the mark and gone the other direction. That's led to all kinds of other confusions. And so that's really what we should be setting ourselves up against. So you call this alpha bias and better bias talk, Talk us through it.
A
Yeah, so those aren't my terms, but those are, I think, very useful terms. So the alpha bias is the tendency to exaggerate the magnitude of sex differences and the beta bias is the opposite. There's a tendency to minimize and downplay and maybe deny them. And yeah, I think that there is a tendency to do both. There's quite a strong tendency toward the beta bias in media and academia, sort of in the mainstream and among the chattering classes. I think that the alpha bias is perhaps the historical starting point. And I think also, though, that the alpha bias does exist in some small areas of academia and probably journalism as well. So I think the alpha bias tendency, that is to exaggerate sex differences, I would have to say, does sometimes exist in my own field of evolutionary psychology. I think perhaps because we are responding to the beta bias that we find elsewhere in academia and have maybe spun to the opposite degree to some extent. But yeah, what I am trying to do with the book is trying to respond to both and critique both and try to walk a happy medium between the two, which I would love to think means that people on both sides will agree and take my point and maybe come to a truce. But of course, another thing that could happen is that I'll just annoy people on both sides of that debate. But yes, that is what I'm trying to do, strike a nice balance.
B
So just to make things more complicated, you then add two different biases, the gamma and the delta bias. Right? What are those?
A
Well, the gamma bias, first of all, is the tendency to highlight sex differences that put women in a better light than men while downplaying those that put men in a better light than women. And I think that's a response to, basically response to historical anti female sexism. So basically response to the reverse, where we really highlighted men are better when men highlighted men are better at this. Women are not as good as men in this way and that way and the other. So it's kind of an attempt to set that right and be protective of women. I think the delta bias, on the other hand, is a tendency to highlight and favor sex differences that go in the opposite direction to traditional sex differences. So traits like, I don't know, devoting everything to your career and putting family lower down the list might be frowned on if men do it, but it's a great thing if women do it. That's one example. Sleeping around, for instance, is sometimes considered to be a bad thing if men do it, but a good thing if women do it. And I think that's a response to just traditional social norms.
B
That reminds me of one of the very early viral Internet controversies of the Duke Fuck list, if you remember that.
A
I don't remember that. What's that?
B
It was, I guess, some senior, I believe it was, at Duke University, who had made a kind of joking PowerPoint that was in the style of like a senior thesis or something like that about all the men she'd slept with and in college. And in a way it was kind of like, you can see how it's kind of a fun, charming idea. The slides themselves were quite demeaning and objectifying. They were ranking all of these men in all kinds of ways and so on. And some people thought, well, this is really demeaning and just a mean way to interact with people and to write about people, to identifiable people and so on and so forth. And then Jezebel and the sort of early Internet feminists were defending this as this great act of, of female empowerment. And obviously it's obvious that the same people, if it had been a man partizing his fuck list and grading the genitals of women he'd slept with in similar ways, would have found it to be terrible. But because they felt that there had been this historical, that this was typically thing that men did but not women did for a woman to do it, it was empowering.
A
Yeah. And I think that's a good example of the Delta bias and also a good example illustrating where I think it comes from, which is that there are different standards applied because of the history, because it's turning the tables. So I think that is a good example of that. So yeah, so those are the four biases that I think make the discussion a bit harder and make it trickier to research sex differences and talk about sex differences without it getting heated. There are these biases and these preferences that people have for what kind of sex differences they want to see.
B
It has been a long winter, but now finally summer is here. As I'm recording this in New York, it really feels like mid July and I'm trying to figure out what to wear. When I'm just going to the gym, I usually just wear a Persuasion T shirt which looks pretty good. But when I want to go to a social occasion and look nice but not overly formal, I always struggle to figure out what I should wear. Well, I have started wearing really nice linen pants and shirts from a company called Quince. They are perfect for the summer season. They are really nice and soft but lightweight. And everything at Quince is priced 50 to 80% cheaper than comparable brands. A few weeks ago I got a lovely 100% European linen relaxed long sleeve shirt. It's really casual but elegant and I've been wearing it through our Mini Heatwave. I strongly recommend it. If you want to look good without spending a fortune, Quince is the way to go. Elevate your summer wardrobe. Go to quince.com Good fight for free shipping on your order and 365 day returns. Now available in Canada too. That's Q-U I N C E.com Good fight for free shipping and 365 day returns. Quinn.com Good fight. Great. So I think we've done a lot of the preparatory ground to really think about sort of how do we approach these questions? How do we Think about them. Let's go a little bit deeper into how we should think about particular sex differences. In light of this, why don't you tell me the three most juicy ones we should talk about for the next 20 or so minutes.
A
How about the sex difference in interest in casual sex, the sex difference in choosiness about sexual partners, and the sex difference in aggression? That sounds juicy enough.
B
Sounds sexy. Let's start with casual sex.
A
Casual sex. Okay, so the difference here you'll be very surprised to hear is that on average, men are more interested in casual sex and no strings attached sex and sexual variety than women are. And that is a pretty big difference as human sex differences go. So depending on exactly what you ask about, the difference is about like a 0.8, 0.8 of a standard deviation between the men, the means for men and women, with men scoring higher. And that means that again, to use the analogy of plucking two people at random, one man and one woman for that sex difference, you'd find about 2/3 of the time that the man would be more interested in casual sex than the woman would. Again, there was significant minority where it would be the other way around. So it is a real sex difference and it is pretty substantial as human sex differences go. But yeah, it's not quite as big as people sometimes make it out. Actually, I was going to mention this earlier. This is an interesting point about sex differences in general. That even when you have a sex difference that's fairly modest at the mean, when you go out to the extreme of the distribution, the difference will typically get a lot bigger. So if you go to the extreme of the distribution for interest in casual sex, you'll find that even though it's like 0.8 or one standard deviation at the mean, roughly where most people are out of the extreme, there are many more men than women. So if you think about the extremes of interest in casual sex, a lot more of them are men than women. And I think probably a lot of our stereotypes come from thinking about the extremes rather than people closer to the mean.
B
And this is where it would be helpful to have a visual aid, but perhaps we can put one in the podcast transcript. But that is just a function of how normal distributions work, right?
A
Exactly.
B
Where if in a normal distribution, depending on how high the maximum is, you can have a relatively small difference at the median where the top of the distribution is, it may really be quite minor. But even that relatively small difference then leads to the fact that once you're free for standard distributions out where you're talking about the people at the extremes. For people who are most smart or least smart, for people who are most interested in casual sex or least interested in casual sex, when people are most violent or least violent, that small difference in the mean condensate into 4, 5, 10 fold difference adverse extremes.
A
Exactly, exactly.
B
So now we've established those kinds of statistical properties, how does that shape social behavior and things like casual sex?
A
Well, the fact is that it's often going to be the case that men are pursuing it to a greater extent than women are. Now I'll tell you one mistake that people often make when they hear about that sex difference is they think that the claim is that men are interested in casual sex or more so than women, whereas women are more interested than men in long term relationships. But actually men and women have similar levels of interest in long term committed relationships. It's really only within the domain of casual sex that we do find the sex difference and that again that men are more interested. I guess actually there are two differences. So one is that men are more interested in casual sex just on average. But then the second difference is that when it comes to casual sex, when it comes to low commitment relationships and also early courtship, women tend to be choosier about their mates than men are sort of choosier about who they're willing to have a, a short term thing with, basically.
B
So on the first topic, before we get to the sex choosiness, what do lesbian and gay relationships tell us here? Because you know, obviously there may be certain ways in which lesbian women sexual behavior is different from heterosexual women's sexual behavior and gay men's sexual behavior is different. You know, not just in terms of the object of attraction from heterosexual men's sexual behavior, but presumably that is at least a suggestive field of study to see what happens if you, if you take two people who have male sexual preferences and put them in a relationship together and two people have more female sexual preferences in a relationship together. And obviously there's going to be a huge range from very monogamous gay couples to very open gay couples. But do we see these systemic differences between lesbian and gay couples? And what does that tell us?
A
Yeah, we do, we do see differences and the differences stem from the fact that with same sex relationships, people are not having to negotiate with the preferences of the other sex. So they can typically express their own preferences to a greater degree with less compromise. And so it provides, looking at the sexual behavior of gay men and lesbians can provide a clearer window into the sexual preferences of men. And women in general. And what you find is that with men, with gay men, that they typically engage in a lot more casual sex than straight men because they're interacting with other guys who typically have similar preferences. Whereas lesbians typically have less casual sex than straight women, again because they're not having to interact with the average preferences of the other sex either. So it fits very nicely with the idea. It's a good piece of evidence for the idea that there are these average differences between the sexes and the interest in casual sex.
B
It's interesting because you were saying about men that they don't necessarily have less of an interest in long term committed relationships, but they do have a much greater interest in casual sex. And so if you just know those two things, you would predict that you'd end up with a bunch of couples that are open to each partner having casual sex, which is certainly not the universal norm among gay couples. But true of many gay couples.
A
Yeah, and I think it's true of more gay couples than straight couples. And it is interesting because in straight couples, you know, like some guys do want that, but I think often jealousy, sexual jealousy, gets in the way. And a guy might think, well, it'd be great if I could sleep with other people, but I don't want my partner to be sleeping with other people and so I'm going to content myself with mammogamy. Whereas that, for some reason seems to be less often the case with gay men. I'm sure many do fit that description. But does seem that there are more gay couples where jealousy doesn't seem to be quite such a big issue as it is in straight couples. It's the impression I have.
B
Anyway, just to up the level of intrigue here I've read, I'm not sure if this is true, that there's significantly higher rates of divorce among lesbian couples than among gay couples. Why is that?
A
I have read the same thing. There are good data on that. Why it is, I'm really not too sure. I'm really not too sure if it's a selection effect or something about. I mean, I guess it could be related to the fact that among straight couples, around 2/3 of divorces are initiated by the woman rather than the man. Maybe it is a sort of offshoot of women's greater choosiness about their mates. Our next juicy topic. But I'm not 100% sure about that.
B
Well, so let's go to choosiness about mates. There's two things here you say that are striking. The first is that evolutionary theory Would suggest that women are more choosy about the mates than men because they invest more in offspring, if only through a process of pregnancy and often beyond that. And that is true throughout the animal kingdom and it is true for humans as well. The other thing that is often forgotten, I know which bias that is. You'll have to remind us of Greek numerical for it, of a Greek designation for it, is that actually humans are relatively. The difference in humans between the two different sexes is relatively smaller than it is in most other animals in this regard.
A
Yeah, it is. At least for long term relationships, it's smaller. So we're doing. When we think of women being choosy and men being not choosy in the short term context, short term mating, casual mating, that certainly has some truth.
B
So 2am In a club, humans are like, what are the animals? The man is happy to go home with whatever woman, but the woman says, even though I might enjoy casual sex, I'm still going to be quite picky. But when it comes to long term relationships, suddenly the men become picky.
A
Yeah, both sexes tend to be pretty picky and maybe similarly picky. So you get the alpha bias, the exaggeration of sex differences when it comes to the long term context. It's a general truth actually, is that sex differences in sexual psychology are a lot smaller when it comes to long term committed relationships than to short term relationships. Casual sex, early courtship, it's an early courtship and low commitment relationships that the sexual differences are a lot bigger.
B
And is this a challenge to evolutionary free. Or is this simply downstream from the fact that humans procreate in very different ways from most animals because they invest in their offspring for so much longer?
A
Yeah, I think that it's not a challenge to an evolutionary perspective. I think that it fits very, very nicely with an evolutionary perspective. Because according to the evolutionary perspective, the greater female choosiness that we see right across the animal kingdom directly follows from the fact that women invest more in each offspring that they produce. Did I say women? I meant female. So female animals in general invest more in each offspring they produce than male animals. And because they invest more, they can have fewer offspring in their lifetimes. Males, on the other hand, they typically invest less in each offspring. And therefore, in principle, they could have many, many more offspring than any female could. That creates different selection pressures on both sexes, creates a bunch of traits in males that increase their chances of being one of the lucky few males that has many offspring, rather than one of the many males that has no offspring or just a handful of offspring. So that's where most sex differences come from, the difference in the maximum offspring number. And we have some of the same thing in our species. But in our species, because of the great dependence of our young, we've evolved a system, sort of reproductive system, where we fall in love and we form pair bonds and we engage in high levels of biparental care, much higher than you see in most mammals. And when males are investing heavily in the young as well as females, that reduces the sex difference and the maximum offspring number that each sex can produce. So it brings down the ceiling number of offspring that men can produce, with a few exceptional examples that we can think of notwithstanding. But for most men, it brings it down. And as it brings it down, it has led to the evolution of reduced sexual dimorphism in our species. And one area where that's evident is in the sex difference in choosiness. So sex difference in choosiness is a result of the fact that females invest more. But in a long term context, both sexes are typically going to be investing quite heavily in the relationship and then in any offspring that result from the relationship. And for exactly the same reason that females evolved to be choosy when they can only have a relatively small number of offspring. Males evolve to be choosy as well. Men evolve to be choosy as well when they are only going to in a context where they're only going to have relatively circumscribed number of offspring.
B
I once leafed through a book that was arguing, very interestingly, that when we compare humans to other animal species, we fall somewhere towards the middle of the range on the extent to which we're wired to be monogamous. So I think the argument was that some species that are strongly monogamous, many species, perhaps most species, are not monogamous at all. And when you look at a whole set of physical characteristics of humans, they tend to fall somewhere in the middle between those. And I think the book was arguing that we're kind of semi monogamous. And that is how to think of us and how to explain a lot of literature, a lot of conflicts in social life, the fact that we both have this tendency towards pair bonded, long term committed relationships, but also the tendency towards going beyond that. Do you find that to be a helpful way of thinking about this topic?
A
Yeah, I do. And actually I don't suppose you remember the book. Is there any chance that it was my last book, the Ape that Understood the Universe? Because in that book I do make, I basically make that argument, oh, Interesting.
B
I mean, I did also know, I think it was a different book, but I know that you also talked about it in the last book. Yeah, yeah, yeah.
A
So I do find that useful. I think it's true, really. We have a strong tendency toward pair bonding and bi parental care, but it's not like gibbons and some birds. We do also have an interest in sexual partners other than our main partner. Often that's not uncommon. And it kind of nudges us toward arrangements other than strictly monogamous pair bonding. Men have a desire for sexual variety. I mean, some members of both sexes do, but men typically have a stronger desire for sexual variety. And so that sometimes translates into polygyny where one man has more than one partner. Pair bonding is the most common relationship type that we find in basically all human societies, including in polygynous societies. So even in societies where men can take more than one wife if they want to, it's a minority activity. It's not like with gorillas where basically either the male has a harem of females or he's a bachelor. With humans, most men who have more than zero mates only have one. But then there are a small number who have multiple mates. Herbon is our main reproductive approach, but we're very flexible. We do all sorts of other stuff as well.
B
So we've talked about our first two controversial topics. Talk us through referred.
A
So the third one is aggression. And the finding here is that at least when it comes to direct aggression or face to face aggression, men on average do more of it. So that includes verbal aggression where it is a medium effect size, I would say medium effect size. So about half a standard deviation between the means for men and women. So not a massive sex difference when it comes to verbal aggression. But then as you go up the scale toward more and more intense forms of aggression, when you go to physical violence, pushing and shoving, more extreme forms of physical violence, the gap gets bigger and bigger. Men come to predominate more. And then when you get out to the extreme of one on one violence, which would be homicide, men massively predominate in that. So about 90% of homicides plus right throughout the world are perpetrated by men. Of course, only a minority of men do that, but among the minority who do, it's massively skewed towards men. Now when it comes to. So that's direct aggression. When it comes to indirect aggression. So things like the mean girls phenomenon, or you know, gossip, spreading rumors about a person, that kind of thing, where it's aggressive as in you're Trying to harm the person, but you're not doing it to their face. There we find either no sex difference, so both sexes do it about evenly, or we find that it's slightly more common among women than men. But for most forms of aggression, men predominate.
B
So this is another area where stereotypes seem to hold up to some degree. Now, I think when you talk about the extreme forms of violence, that difference is very obvious in the statistics and it's sort of easy to understand, right? We know that men are more likely to murder, men are more likely to be soldiers, men are more likely to be in criminal gangs and so on. Right? Prisons are much more full of men than. Than they are of women. When you don't talk about the extremes, when you talk about people towards the middle of the distribution, how big is that difference in standard operating procedure? Is it that the average guy probably is not particularly violent, but perhaps once or twice in their life has gotten into a small scuffle at a bar or pub or something like that? The average woman is not particularly violent, but when she engages in a form of social aggression, it really is this kind of rounding up a few people to ostracize somebody in the friend group that they have beef with. To what extent are those kind of stereotypes true about the middle of a distribution? Is that a helpful lens to understanding society? I mean, as an evolutionary biologist, do you feel like. And psychologists, do you feel like you can watch Cruel Intentions or, you know, whatever high school movie and sort of check, check, check, you understand better what's going on when somebody without that training? Or do you think that it doesn't in fact help to illuminate social reality in that kind of way? Is the alpha bias of a better bias more tempting here?
A
That's a good question. I think maybe with low level aggression, the alpha bias comes in more and people exaggerate. I think people are maybe a little surprised when they hear that the difference isn't larger for just verbal aggression and the like. I think the way you describe it, I think is pretty accurate for modern Western societies. So modern Western societies, most men are not especially aggressive. They maybe get into an occasional scuffle in their lifetimes, a handful, or maybe more commonly an occasional sort of verbal aggressive interaction in which there's a kind
B
of implicit threat of minor physical violence. But that doesn't usually come to pass or something, right? Like you get into each other's face or something like that?
A
Yeah, yeah, exactly. Yeah, exactly. And that's less common, I think, with women. So they might have as many or a similar number of aggressive interactions verbally, but with, I guess, less of the sense of there's a physical threat there and that this could turn into actual violence. So, yeah, I think that's accurate in the West. I do think, though, that we have successfully tamed our aggressive impulses to quite a high level in the west, and that in other cultures and more traditional cultures there were higher levels of violence. And I would say, especially among men, and just, I guess that the culture sort of brought it out more or at the same time the culture's suppressing it somewhat in modern populations, Western populations, which I personally think is a good thing. And I'm not sure there's any. Most people I'm sure would agree with that. It's an example, I think, of a case where we have a natural tendency that society is pushing against, but it's a tendency that is generally not a good thing, it's generally a bad thing. So it's a good thing that we're sort of able to engineer unnaturally low levels of aggression.
B
And I do think that one benefit of thinking about the world in evolutionary terms is to see you have a dangerous life for society. I think one very fundamental insight from evolutionary biology and evolutionary psychology is the human tendency to split into in groups and out groups. And now you could form the naturalistic fallacy and say, therefore we should encourage people to really stick to their tribe and hate the other. But no, we've learned from history that that is a disaster. And the whole of civilization, the whole point of working positive some institutions is to mitigate the impact of the in group and the outcome. I think the way to do that is to channel it, right? It's not to not give people any kind of outlet for it, but it is to channel it into productive directions. That is why, you know, you have sports rivalries in high schools. That is why, you know, think of Harry Potter. You split a private school or a boarding school into different houses so that they can compete with each other. And there's dangers with that. Sometimes they come to blows. But the main point is to make people within each house sort of aspire to work really hard to make the house pride, right? There's all kinds of ways. The city of Siena is split into 20, I believe, contrade parts of the city that compete against each other in this huge horse race as a way of instilling solidarity within each part of the town. And they hate each other and they compete against each other. But it also has historically actually strengthened the ability of Siena As a whole to work together because it instills this really strong civic identity. In terms of aggression, you might think that's similar in terms of, for example, sports, right. When you're playing American football, rugby, or even a less violent sport like basketball or whatever, that is a way of channeling aggression into something that is socially non harmful.
A
Yeah, agreed. A way of what Freud would have said, sublimating those potentially destructive desires. Yeah, I think that's true and interesting. And I think that in a way, evolutionary biology and psychology, when you study the fact that we're so prone to in group and out group biases, I think that that rather than saying, okay, it's natural, therefore it's good, you could equally well argue that by showing it's just an evolved tendency, it kind of punctures it. So you might genuinely think my in group really, really actually is great and that out group actually really genuinely is terrible. But if you realize that we have this built in tendency in human nature to divide the world into in groups and out groups, it can make us challenge that, make us think, well, maybe I'm just falling prone to this evolved illusion and it's not actually true that we are superior and great and angelic and they are genuinely terrible and anti monarch.
B
Thank you so much for listening to this episode of a good fight. In the rest of this conversation, Steve and I try to think through what the implications of all of this is for society and for public policy. How do we grapple with take seriously some of these sex differences without running the risk of imposing one particular vision on life, on individuals? Steve gives what I think is a broadly philosophically liberal answer, and of course I broadly agree with him. But I also push us to challenge ourselves. To what extent are some of the negative trends we see, like the greater and greater gulf separating young men and young women downstream from philosophical liberalism? Or to what extent are they to blame on traditions that precisely put ideological commitments over the science in a way that does not flow from these commitments? Finally, we also talk a little bit about differences in aptitude regarding sex and how it is that philosophical liberals should deal with that challenging field of scientific research. To listen to that part of the conversation to support the podcast, please go to writing.yashamonko.com and today I'm throwing in the best discount we ever give around here. 30% off your first year of subscription. That brings it down to one coffee from a coffee cart in New York in 2003. A week, about a dollar a week. Go to writing.asher munch.com 20 26.
A
Sam.
Host: Yascha Mounk
Guest: Steve Stewart-Williams (Professor of Psychology, University of Nottingham, Malaysia, author of A Billion Years of Sex: How Evolution Shaped the Minds of Men and Women)
Date: June 6, 2026
In this engaging and controversial episode, Yascha Mounk and Steve Stewart-Williams dive deep into one of the oldest questions in human society: What are the real differences between men and women? Are these differences rooted in biology, or do they primarily emerge from cultural influences—nature or nurture? Beyond the science, the discussion explores the moral and policy challenges that come with acknowledging sex differences, the pitfalls of exaggeration and denial, how biases inform both, and the uneasy balance between acknowledging data-driven realities and fighting for individual choice and equality.
The conversation maintains an engaging, curious, and rigorously scientific tone, with moments of humor and self-awareness about controversy. Mounk brings skeptical, often philosophical framing; Stewart-Williams offers careful scientific reasoning and reflects on social implications candidly.
This episode provides a nuanced, evidence-based guide to what we know (and often misinterpret) about sex differences, the complex role of stereotypes, the perils of both exaggeration and denial, and the perennial challenge of crafting an open society that takes human nature seriously without succumbing to determinism or discrimination. The discussion is rich, careful, and timely for those wanting to understand the science—and the cultural crossroads—of sex differences in modern society.