The Truth About Sex and Gender: What Nature Can Tell Us About Who We Really Are with Dr. Nathan Lents
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This is Smart People Podcast, a podcast for smart people, where we talk to smart people, but not necessarily done by smart people. Hello and welcome to Smart People Podcast, conversations that satisfy your curious mind. Chris Semp here. Thanks for tuning in. It is rare that I prepare you for one of the top 10 conversations we have ever had on the show. Maybe five, maybe top three. And I think you'll feel the same.

In this episode, we're talking about a topic that's at the center of heated political debates today. That is gender and sexuality. And these things often are weaponized to divide us. Everything from trans bathrooms to drag shows at the Kennedy Center to gay marriage and more.

And when you listen to these arguments or discussions, what you'll often hear is people trying to say we should follow what is natural. The social norm should be based on nature. But what if many of these claims being thrown around aren't even remotely close to being rooted in biology or even evolutionary truth?

In this episode, I sit down with Dr. Nathan Lentz, author of The Sexual Evolution, How 500 Million Years of Sex, Gender, and Mating Shape Modern Relationships. This conversation is about facts, not fear. If we're going to have the discussion, let's make sure it's rooted in reality.

Some of the important takeaways we will discuss: Number one, the power of diversity. The built-in evolutionary necessity for us to all be different. Number two, gender versus sexuality versus relationships and how it actually shows up in nature. And then third, and perhaps most enlightening, is the end of the binary.

The idea that there are only two sexes or genders is actually a human construct, not necessarily a biological fact, even down to the argument of women make babies and men do not. In a world where misinformation around sex and gender is rampant, this episode focuses on the science. It's about stepping back from the politics, looking at the evidence, and understanding what evolution really has to say about who we are.

I hope this information can make it into the public discourse. It is much needed for today. If you agree, send it to a friend, a colleague, a loved one, because this isn't political. This is curiosity. Let us know what you think. We're at smartpeoplepodcast.gmail.com. If you are as moved by this episode as I was, please consider sharing it on social media or somewhere out in the public to get it in others' hands. Let's get into it.

Our conversation with Dr. Nathan Lentz about his new book, The Sexual Evolution. Enjoy. Throughout human history, we've often discussed sex in a way that is shameful, hidden, judgmental, reproductive.

And yet your book and your work challenges that narrative. How do you think we got it so wrong as a species? And how should we look at it? Right. It's a good question. And anthropologists have wondered that for a long time because we are the only species that tends to have sex in private.

We tend to do it behind closed doors and that's pretty cross-cultural. So, so we don't really know exactly where that comes from, but it's deeper than that even because we're also peculiar among mammals that we also conceal our ovulation, like the fertile period of a woman's menstrual cycle. Most species advertise their fertility with estrous cycles and, and, you know, visible conspicuous signs of their fertility. So humans are,

definitely have something in us where the sexual activity is a little bit private. And of course, once you've gone sort of gone down that path, what you end up with are taboos. So taboo and shame and, you know, stuff being sort of illicit and not really, you know, allowed and polite company.

That's really the effect of culture. And that's when you see, for example, foraging societies and hunter gatherers, they don't have much shame and taboo and hangups like we do, but they still do have sex in private. So it is a bit of a conundrum why we do that and why we conceal our ovulation and why we do have sex in private. I know there's something there. There's got to be a reason, but we don't really know for sure why that is.

I've actually never thought about the fact that anything done where everyone on the planet, for the most part, make sure it's out of sight naturally will have a connotation to it. Yes, right. That's where taboos come from.

And what's interesting, though, is that taboos also create the opportunity for something to be titillating and or a kink or a fetish. And in fact, actually, if you if you look at sort of people's porn search habits in different parts of the world, you can predict what is taboo in a culture by looking at their porn search history. You do kind of seek out those taboos when it comes to fetishes and kinks and things.

And so anytime we try to make something shameful, you know, people are going to actually be drawn to it. The analogy of that is if you want to sell a lot of books, get it banned, get your book banned. Yeah. It'll really sell a lot of books. It's sort of the same psychology is involved there, I think. Yeah. No such thing as bad press type. Right.

Exactly. This is what I found so fascinating about your work. It's like things that are hiding in plain sight that change the way you think. And that's going to be a theme of actually this conversation, because the patterns that lead our lives without focus and that fertility one caught me off guard as well. Never thought about it.

Yeah. No, it's true. Gender, sex, and sexuality is one of these areas where a lot of diversity, a lot of variety was kind of staring at us in the face, and we just didn't see it for whatever reason. We didn't want to see it. And that's a bias. We do have a bias against sort of a lot of sexual truths and gender diversity.

The example I use in the book, I chose a non-controversial example to sort of open the discussion so that people would see where I was coming from. And then I get into more controversial things. But the example I use at first in the book is the study of bird...

monogamy or pair bonding in birds. So birds are prolific pair bonders. They're really the stars of monogamy when it comes to their life history. Most migratory birds will form dyads. So they form pair bonds.

Two individuals get together for at least a season. It can be many seasons. And they build a nest together. They tend the eggs and watch out for them. They incubate them together, taking turns. They get food and they feed each other. So they sort of share resources, territorial resources, food resources, and then they feed the chicks together until they're off and flying on their own. If it's in warmer climates, they might have time to do this two or three times a

per year in colder climates that you really just get one annual cycle, but they're monogamous. Now, the scientists who studied birds for about two centuries assumed that they were also sexually monogamous or sexually faithful, you might say.

Because that's they sort of squinted hard to see in nature what they valued in humans, in human society, which was this lifelong, you know, faithful, sexually exclusive marriage. And that's what they wanted to see when they looked at birds. And I don't think anyone there wasn't like a conspiracy where they all decided that they were going to interpret it this way. It was just this implicit bias, this program that was running in their brain.

that that's why they saw it. And it was really only the invention of DNA paternity testing in about 1987. The first results came from DNA testing in birds and one species after the other, after the other, after the other, we discovered that none of them are sexually faithful because the eggs that they're incubating, at least some of them are not the progeny, the genetic progeny of the male.

It turns out some of them are not the progeny of either of them because birds can lay eggs in each other's nests and try to take their- Scandalous birds, man. Yeah, they really try to steal parental care sometimes. That's called brood parasitism. And that was another thing that we knew happened, but we had no idea the scope of it, the scale of it until DNA testing. But anyway, to return it to monogamy. So that sort of forced ornithologists, those are the biologists that study birds, to rethink what monogamy means.

because they do pair up. They do share resources. They build a nest together. They feed the chicks. They are each other's life partner, you know, and main social partner, all of that. But it doesn't come with sexual fidelity or sexual exclusivity. It's just not part of bird monogamy. And in fact, it's not common in any form of monogamy. About 9% of mammals also have pair bonding and they also are not sexually fidelitous usually.

And so it forced the field to rethink this. But this was a bias that was in place for hundreds of years. And so in the book, with each of the chapters, I often give some of the examples of how scientists themselves really missed what was going on because they were already thinking about

the world in these very categorical ways. Males do this, females do this. There's only two, two sort of modes to reproductive behavior, male and female, and anything that didn't fit the bucket, the, you know, the dominant bucket, you know, the stereotype was either ignored or

underappreciated at the very least. And so that's what my book is trying to tear down is some of these biases and trying to encourage non-scientists as well as scientists to look with a more open mind, to open our eyes to what we might be missing because of bias. It's almost like a Trojan horse. I mean, yes, your book is really targeted towards this idea of gender and identity and sexuality, but

Did you ever zoom out and say, you know, this is my area of expertise. It's also interesting to what I know, but really far zoomed out. It is to help

show people that so much of what we do and think is shaped and constructed by the world in which we live and the things we want to believe. Right. So there's several things to unpack there because what I think about day in and day out is human beings and why we are the way that we are. And as individuals, as a society culture, how we got this way. Because

We are a very unique creature on planet Earth. And there's a lot of things about us that really

that really are complex and worth exploring. So let me tell you how this book came about. So I have been teaching about sex and gender, the biology of sex and gender, that's the name of the class, for about 15 years. And I kept coming across this, what I consider bias, how scientists themselves talk about the animals in such categorical ways, and they were really missing the diversity that was right there in the data. I mean, I'm talking about the research articles themselves. I could see

from the articles that they wrote that they were missing things right in their own work. But I just kind of, you know, put that aside and just kind of, you know, grumbled about it. And, and, and I didn't really have the idea for the book right away. What happened was about five, well, no, I guess now about seven years ago, um, there was kind of an explosion in pop culture of, of young people being, um,

non-monogamous or polyamorous, as well as gender non-binary. And more and more people were identifying as heteroflexible or pansexual or demisexual, all these new labels, these new categories, these new labels, either for gender expression or relationships or attraction. All of those things associated with sex and gender were sort of being called into question by young people.

And what I was seeing was the older generation, especially even scientists, kind of freaking out a little bit and being like, this isn't natural. This is crazy. You know, society is built on all these ideas that young people are throwing out away, all the traditions when it comes to this stuff. And I, having taught sex and gender and animals for so long, was like, no, no, no, no, no. What's happening is a rediscovery of

of a more expansive, less restricted relationship with sexuality that we used to always have, that our ancestors had, that other animals have, that because whether we're talking about prehistorical humans or our animal cousins,

They're not bound by these strict categories regarding their gender, regarding their gender expression, even gendered behaviors. And even sexed bodies in animals come in different forms. There's not just one kind of male or one kind of female in most species. You actually see a lot more variety than most people realize. And so...

I saw among young people what I've been seeing among animals, which is less categorical approach to all of this, a more of a free for all in the sense of diversity was flourishing. And that's what I see in the animal world. So I was really kind of pushing back against the reactionaries to say, hold on, you know, it's not such a big deal. This is normal. This is natural. We see it in other animals and we shouldn't be afraid of it. We, of course, we should try to understand it. It's an important sociological phenomenon.

phenomenon, whatever its impacts are going to be. We should, you know, you know, have our eyes open about that, but it's nothing to be scared of. And it's certainly not unnatural. So that's really what made me finally decide to get, get my thoughts together enough to write this book. Here's the first thing I want to recap. We have things that humans are doing specifically, let's call it the last 10 years. And now even more so in the current administration, it's this, um,

misunderstanding of sex and gender identity. And so there were or are intelligent people who have been saying that is unnatural.

As an expert, somebody who's been doing this and teaching this, you came in and said, look, if we're going to have the discussion, let's at least make sure we're discussing it based off of reality. So far, so good? Yeah. Thank you for clarifying that. It's a good point. Okay. And so the question becomes...

Why do so many smart people miss it? And why is it such an issue if really it is who we are? Like, why would we try so hard to not just ignore it and get it wrong, but then feel normal about that? Right.

Well, so there's this idea of received wisdom, received ideas, you know, and your mind is much more open to new and fresh ideas when you're younger, you know, and so you because you're learning kind of everything for the first time. So our brain has a lot more plasticity. That's the word, the neurological word for plasticity.

A young brain is plastic, meaning it can move around. It can change. You can change your thinking on major issues even while you're young. Much, much harder to do that when you're older.

And so what happens with sex and gender is this very categorical way of thinking, male, female, heterosexuality, sexually exclusive monogamy, that these were all the ways that humans were supposed to be. And it jives very well with religious instruction and almost all the world's major religions kind of have the same ideas on that.

Although there's much more variability there than most people realize too. But it all kind of coalesced into this cultural meme. A meme is a cultural unit of inheritance, something that gets passed on. And so if you don't question it, it just stays with you. And there's lots of ideas that were just never questioned for generations and generations and generations. And it's really only when you're forced to

with data to rethink it, that the old prejudices, and they are prejudices, that's when they start to come apart. And so, like I said, with the advent of DNA testing, the field had no choice but to look at bird bonding differently than they had been. They had no choice, you know, because if it was one species or two species, well, that would be weird. But if it's all of them, then maybe we didn't understand monogamy correctly, for example. Yeah.

And the same thing would apply to sexuality. And that's one where we're a little bit more in front of that one than we are, for example, gender expression. Diverse sexuality and sexual attractions is something that most biologists, the vast majority of biologists now accept as normal and natural diversity. But if you go back 30 or 40 years and you look at the literature, they did not. So biologists were not leading the way when it comes to talking about the natural nature of sexuality.

of same-sex attraction or whatever you want to say, diverse sexualities.

biologists kind of came kicking and screaming to that reality but that one was just you know a couple decades out in front of for example gender diversity and once again they were forced by a couple of early studies that showed same-sex activity and then same-sex bonding long-term same-sex partners in other animals and that's again when biologists had no choice but to say okay well we

We can't ignore this anymore. We can't say it's unnatural. I mean, for example, you know, between one fourth and one third of albatross couples, albatross is a very large seabird. They're same sex. They do same sex bonding almost as commonly as opposite sex bonding. And are you going to go up and tell them that they're unnatural for doing that?

You know, of course not. It's ridiculous to consider an animal behavior as unnatural. And so unfortunately, that's what it took for people to see human same-sex sexuality as natural is that we saw it in animals. I mean, it ought to have been enough.

That humans, you know, it ought to have been enough. But but animals, there's this sense that animals can't be doing it for any other reason than it's in their nature. So we can believe it. So I get that. That's what I was just thinking. And now I'm going, well, wait, let's go off this argument, which is OK. I give you some leeway that, yeah, maybe some animals have same sex or something.

All the different types. I don't even know what they are. But you just alluded to the fact that humans are the ones that get to get to choose, get to almost override their biology. And given that the purpose of sex is to procreate and we are the top of the food chain and all this, haven't we done it right? Right.

We have procreated to a way where we can control all other animals. Therefore, that means the monogamous and two gender pairing is the right one. So we've outsmarted our natural instincts and they're all wrong now.

I mean, I'm assuming a lot of people say that, especially from the reproduction argument. Well, there's there are people who say that, that humans are at the apex of creation or evolution or whatever you want to say. I mean, when we're the ones doing the judging, it's not surprising that we come in first. Right. Because we judge everything based on our values of what is a winner and loser, for example.

But I mean, the fact that we can control and dominate other species, that's a really human way of defining success. Right. And kind of a violent one, if you think about it. I love that point. And then and we have spread all over the globe. And that does really speak to our flexibility and adaptability and how humans really are the ultimate generalists. Right. We're not we're not.

strictly adapted to life in the desert or life in the tundra or life in the grasslands or life in tropical rainforests. There are even seafaring people or people that live almost exclusively at sea. There's no other mammal that comes close to us when it comes to being able to live in different environments. And what that speaks to is the fact that we don't just react to the environment. We build and construct environments.

what we need to survive and thrive in a diverse environment. So why can we survive in the tundra? Is because our bodies have adapted to extreme cold? No, because we build houses and put on clothing and build fire. We do what you need to do to survive up there. And it's the same thing with every climate that we've

We've, you know, marched into and with diet to like we people eat a wide range of diets and are perfectly healthy because we are not really built for any one specific way of life. But apply that same logic to gender and sexuality. Now, we're not built for any one kind of relationship. There is no one correct way to pair bond. There is no one correct way to build a family. Right. There's no one way to organize our societies anymore.

And that's also what we see when we look at pre-agrarian human culture. So agrarian meaning farming and sedentary life, where we started to really get tied to specific locations and livestock and all that. Well, before that, we were foraging. We were hunter-gatherers. And there are contemporary hunter-gatherers today. And if you look at their social structures, they're all different.

They're all different. And some of it you can kind of predict by their climate. You know, harsher climates, you know, have a certain pattern and more generous climates have, you know, have more more of a free for all. And so if you consider if you think and I do that, if looking at foraging lifestyles helps to get at what we're really built for.

then we're not built for any one specific thing. And that's the conclusion I come to, is that humans really are the ultimate generalists. And that includes gender expression. That includes sexuality. That includes sexual relationships. And so there's really nothing to be afraid of with this experimentation. It's actually in keeping with our evolutionary history to do that. The idea of diversity is something that stuck with me based on your work. And I want to spend some time there discussing

Before we do, though, I think it's fair to set some ground rules or things that people might be considering that would nullify this, which is first is this idea of gender. And admittedly, I'm tolerant of it, but I still don't fully understand it. Specifically, things like transgender or I don't know what it's called when you like don't identify. The common refrain is, look, we are born with certain chromosomes. You can tell us like it's an X and a Y or two X's or something like that, whatever it is.

And so that is your biological sex. You can't deny that. So let's just say what you're born with is your gender. So we have some consistency across the board.

Okay. No, it's not that simple. I wish it were. Scientists always wish to find simple explanations, but when we don't find them, we have to admit that the reality is more complex. So let's break this down. You have sex and you have gender, right? Sex refers to bodies. It's a physical property of bodies. A body is sexed, male or female, for example.

And then gender is how you express either your sex or your reproductive behaviors or however you want to think of that. Gendered behaviors. So behaviors are gender and physical property is sex. Well, neither one of those reduce down to just two buckets. They just don't. Let's talk about sex. That's the one that's a little bit more controversial for me to say this. But here's the thing. The only way that you really get to a strict binary

is if you're only looking at sperm versus eggs.

Because it's almost unheard of that there's someone who produces both. So that one, but every level you go on top of that, it's not binary anymore. It's bimodal. And what a bimodal difference is, is when you have sex differences across a spectrum, a continuous spectrum, but with two major peaks, male and female. If you take about, if you look at the height of women and the height of men, they'll have different peaks, but

but there'll be overlap in between. So that's a bimodal, continuously bimodal distribution. There are some women who are taller than some men, even though there's an average difference. You can keep going with that though. If you go to basal metabolic rate, men is pretty substantially higher than women on

on average, but you will find women who have higher ones than some men. If you look at breast size, that seems really, really dimorphic, but you can find men who have larger breasts than some women, right? Yeah. Right? If you look at waist-hip ratio, if you look at the size of the corpus callosum, if you look at the ratio of gray matter to white matter, if you look at red blood cell count, white blood cell count, these are all things that show average sex differences, and every single one of them

all throughout your body shows a continuous bimodal distribution, not binary. So it's a lot harder to simplify things down to two buckets when you consider the whole body.

I see. Okay. Wait, before you keep going, question, what about reproductive organs? Would that fall into the egg sperm argument or no? Beyond the eggs and sperm, there's a lot of difference there too. So if you, let's concentrate just on genital anatomy. Once again, you will find people that don't perfectly fit in their bucket. Something like 1% of babies that are born have anatomy that is atypical for their sex, right? And then something has to

You know, so what happens is you look at the whole body and you start making decisions. OK, well, this is mostly female. This is mostly male. But as they get older, then, you know, these are intersex individuals, right?

And generally the thought now is, is we don't interfere. You know, you don't do any medical intervention until they're old enough to decide on themselves. And by the way, a lot of them choose not to correct anything. Interesting. You know, the idea of surgical alteration to make your body more palatable to others, not everybody's up for that. And the thing is, is the intersex community now has grown into something where they, you know, they have community of solidarity. And so, so, you know,

Yeah, there's really, it's not binary. Sex is not binary unless you center the gametes, the sperm and egg above everything else. And here's why I refuse to do that. That doesn't matter to you very often. What, what, how often does it matter that you make sperm rather than eggs? But I'll tell you what does matter. Your basal metabolic rate, your red blood cell count, right? Your, your, the likelihood that you'll get Parkinson's disease. It's two and a half to three times higher as a man.

Whereas women are nine times more likely to get lupus, right? You name it. There's all kinds of diseases that really, so those differences matter. I mean, eggs and sperm, how often does that matter? But all these other things really do. So that's why I refuse to allow gametes to be the way that we decide sex because it ignores all the very important sex influenced biology throughout your body. You're, you're,

You know, hormone ratios. There's everything in your body almost has... It responds to your sex. Isn't that more important than what's between your legs? Yeah. And I'm assuming from a hormone perspective, there are men...

with higher maybe estrogen levels than women? I don't know that, but is that true? Absolutely there is. Yes, it is an overlapping range. Of course, there is an average difference, but it's an overlapping range. There are men with high estrogen, there are women with higher testosterone. And of course, the ratio is really what's most important. So it's not as much absolute levels as it is ratio. So yeah, those things do overlap. There are people who don't fit the mold and there's nothing wrong with them, right? They're

they're perfectly healthy. In most cases, they're fertile. You know, actually the hair on our face, if you're a man, is one of the most beautiful,

bimodal things there is because most men do have hair on their face and most women don't. But even that you start to lose as you get older. Right. And it's not entirely binary. Yeah. Binary nature doesn't traffic in binaries. It just doesn't. Well, and that's what I do. That's where we're going. I just, I'm trying to kind of get out some of the things, because I think in order for people to recognize how much this can change your thinking,

You have to first hear the cold, hard facts, which a lot of it is what your book does. Yeah. What about the reproductive argument, which is like women can have babies, men cannot. And given as a species, we assume evolutionarily our goal is to continue the species birth reproduction, pretty important part. So we need to determine sex or gender because of that.

Okay. So first of all, not every member of a species needs to be reproductively capable in order to be valuable to the species. And in fact, if you have in the social insects, for example, ants and termites and bees and things, a very small number of the individuals have participate in reproduction at all, right? You have a queen and you'll have a few males and then millions upon millions of sterile males called drones.

you know, that are doing the work of the species without directly participating in reproduction at all. So first of all, great point. Yeah. Wait, you can't just gloss over this. All right. I keep bees. So I know this stuff, but essentially what you're saying, I've never thought of.

Again, let's get rid of the bias that the point of being a sex is to have the ability to procreate. It's not as long as what's built into the species is the ability to procreate effectively. That's right. And there are some, there are some traits that that's exactly right. There are some traits that make you more likely to help others, uh,

and their reproduction. Assuming you share, you know, a large number of genes with them, it can be selected for that's called kin selection. So sometimes a gene doesn't make you reproduce better, but it makes you more social towards your group and towards your family. And that has a value to all of us, you know, and here's the thing, we are not running out of people anytime soon, right? There's like 8 billion people on this planet, we've got enough

And I think there is a certain responsiveness to that, that as overall population density gets high, the desire to procreate goes down because, and you see this in other species too. Like, for example, one of the examples I talk about in the book is the clownfish. And I talk about the clownfish mostly because it's so interesting because they can switch sex, right? They start off male and then if they live long enough, they'll switch to female. But another part of that

that I sort of just barely gloss over in the book is that they control their own reproduction very carefully because they live in symbiosis with poisonous sea anemone, right? So a sea anemone, which is very poisonous, but they have a resistance to it. And then they feed the anemone with scraps of food and their own waste and all that. So they have this delicate balance. But here's the thing.

If there's too many clownfish per sea anemone, it'll kill the sea anemone. It'll poison it from their own waste and so forth. So they control their own reproduction to make sure that they don't over reproduce. So there are plenty of examples out in nature that just making more individuals isn't always the best way, right? So it can be, but there's lots of cases where if you eat all of your food, nobody's left to survive. So restraining your own growth

And in fact, there are animals in that same chapter, I talk about eels and a few other animals that can switch sex based on population density. So if there's a whole bunch of them, they switch to male. And if there's very few, they switch to female. The reason why is, again, females are the productive sex. But males, why would you want a bunch of males? So that they compete against each other and you improve your gene pool.

right? So you let the males bear the brunt of all that competition and the females bear the brunt of reproduction and together they make the species better, more adapted, more resilient and so forth. And actually resilience is something that I hope we'll talk about because that's a bit. Well, and actually I think that's where we're going because you just made me realize something, right? Let's use the same logic that I kind of came into, by the way, I think the listeners know this, but I'm not saying it's my logic. I'm trying to walk us through, but the

that reproduction is the primary goal or resilience of a species is the primary goal, which I'd say there's probably a lot of truth to that. Let's say that's true. The key component here, though, is when you talk about diversity, diversity is what serves resilience. It is not the binary. So

When we say there are only two genders and they have these purposes and that helps us with resilience your argument your research is showing it is actually Almost the exact opposite right that blows my mind So tell us a little bit about how what is diversity when we look at kind of the animal kingdom and then us as yes, that's

You set it up very well. You summed it up probably better than I could. So diversity is often referred to as our insurance policy against a changing environment, an unpredictable future. So what we mean by that is if every animal does exactly the same thing, lives the same way, and it fits the environment fairly well, that's fine. But as soon as it changes, no one's left to conquer the next challenge. So nature...

is constantly generating diversity and variability. We call them variants or morphs or whatever. They're different varieties of almost every feature you can think of. That's why not all animals are the same height or the same, you know, almost any feature you can measure about an animal, you're going to measure a variety, a range. And in fact, that was one of Darwin's big insights is he noticed that

There's variety. They're not all identical. And that that those differences are usually heritable. So they're genetic in nature. And then whoever survives, those traits will be enriched in the next population and so on. Survival of the fittest. That's not the words you use. I don't I don't particularly like those words, but that's sort of the idea of evolution by natural selection. Right. So diversity is the best. You can't know what the future holds. Right.

There's no way to predict. Evolution doesn't have any goal-oriented nature to it, right? It's just kind of random. But the best way to make...

Like to have insurance against this unpredictable future is to have a lot of diversity in your gene pool, to have different forms of the animal, to have different behaviors, different, you know, maybe being fast is really important one year, but next year being drought tolerant, you know, is much more important. And then the next year, you know what I mean? So if you have all this variety, that's your insurance policy against a changing environment. And the thing is, is that's not controversial. Scientists have recognized that for a long, long, long time.

at least 50 years, maybe 60 years. Diversity as a bulwark against a changing environment, that's been very well established. But it's only now being recognized as applying to sex and gender. And I think it's kind of funny that we've accepted it in all the other areas, but except sex and gender, even though sexual reproduction is where this variety comes from, right? So we should expect more variety, right?

and sex and gender than we do in the others because it's the source right that's why we have sex by the way i don't know if you that's an even more fundamental let's talk about that yeah yeah so you have asexual reproduction and sexual reproduction asexual reproduction is much faster much cheaper much more efficient less costly like risky all that kind of thing asexual reproduction beats sexual reproduction in a head-to-head competition every time but it produces clones

Right. It produces just copies. And once again, no variety. So as soon as the environment changes, you've overfit the conditions that you have now. And then you're screwed when those conditions change. So the reason why all plants, all animals, most fungi, most protists, all the more complex creatures on the planet.

They all favored sexual reproduction because of that diversity, because short term gains, you know, aren't aren't what lasts. Right. So asexual reproduction is about short term gains. Sexual reproduction gives you long term gains. And so now we're finally looking at gender as something where diversity, you know, wins. Diversity pays off, right?

So hopefully, are you ready to have that conversation? I am. But I got to say, man, we've now talked for like two hours and it is amazing at how many things you say that mess with my head, which is, so we are now picking and choosing which aspects of human diversity we like in the moment. By the way, not even as a culture, like literally in the decade. Yeah. Yeah.

Well, I mean, think about this. Think about skin tone. Let's go. Let's get controversial for a second. Let's get controversial for a second. So skin tone, obviously our ancestral skin tone is very dark, right? Because we evolved, you know, almost exclusively in Africa for millions of years. Well, as humans migrated north, there was there needed to be a re...

to lighten up the skin in order to absorb more sunlight to activate vitamin D primarily was the main, the main reason why Europeans and Asians and other, other groups lightened their skin. I don't know if you know this, there's a really good correlation between latitude that an ethnic group is native to and their skin tone. It's almost a perfect correlation with one interesting exception. I'll talk to you about it if you want.

Anyway, you – but if there was no variety as the humans started migrating northwards, there would have been nothing to select. If all the individuals were perfectly the same skin tone, how would it have ever gotten lighter? You –

But there was a variety because nature always produces variety. So the lightest skin tone folks would be less susceptible to rickets because that's what you have if you don't get enough vitamin D. So they persisted better. And then the next generation had variability again. And the lightest individuals kept reproducing as the population moved northwards. The light skin people outproduced the dark skin people because of rickets.

You know, the darker your skin was, the less UV light you could absorb, which means you weren't activating vitamin D. Without vitamin D, you don't absorb calcium, your bones become brittle, etc. So skin tone correlates really, really well with latitude because of the need for sunlight to activate vitamin D. But if there hadn't been variability to begin with, there would have been no selection that could have taken place. So that's the point. Diversity.

in skin tones in this example, was important to the species as they migrated into different climates. So that's the thing is we understand that about all kinds of other things about our bodies. But for some reason, our sexed bodies and our gendered behaviors has sort of escaped that logic. And I'm here forcefully to bring that logic back into that conversation. It's funny. I was listening to one of our own episodes on a walk the other day. And I don't do that often because I don't like listening to my own voice. And I remember thinking,

Chris, like when I'm in these conversations, I'm so it's singular, but other people are doing other things. So I got to pause and do a quick, not recap, but like, why in my mind is this conversation so core to what we try and do on this podcast? And it's the following. I don't think many people listening are shocked by the fact that like the idea of diversity, not the way you talk about it, but the idea of it is beneficial. However,

The nuance is like, great, you know that. Then why are there certain aspects of diversity that you not only don't like, you disagree with? And many people, especially societally, are trying to force that diversity out through negative means, right? Through everything from, you know, historically in humanity, killing off the diversity to just...

social pariahs and things like that. That I think is so foundational to this. Is that how you think of it? Yes, I do. And I think that society has a lot of tendency to enforce social controls.

Because we have a narrative about how our society should be built. And there's a lot of should, you know, we like to should on people, right? You know, we're constantly telling people what they should and shouldn't do, right? And social control is at its most central when we talk about gender and sex, because it really violates

our sense of order because we want two sexes because that's simple. It's easy to understand. It's categorical. We like categories with clear definitions and hard labels and boundaries and all of that. Nature doesn't work that way, but humans do. We really like that. And in fact, it all comes down to, I think, some of the same features that make us racist and xenophobic and in fear and hatred of other

And that comes down to also to our evolution. Unfortunately, evolution doesn't always produce happy ends. Evolution has made us xenophobic because humans were evolving as small groups in competition with one another. And so one group would work very well together if they had strong in-group identification. OK, so that's called social cohesion, where a group really the members are so dedicated to each other as a concept that they'll die for the group.

Right. As individuals, they will sacrifice their own lives in order to for the good of the group. But that only works if you have strong in-group identification. And that only works if you identify an out-group because not everybody can be in the in-group.

Or else it's not an in-group, right? There's a tautology that says, like, if everybody's in the community, there isn't a community, right? Community always means a subset, right? So in-group means us and not them. And partially what defines us is that we're not them, right? So you have, in order to have an us, you have to have a them. And so our ability to identify, you know, in that way with social cohesion is,

is what led to social controls. So you would have a society that collectively enforces certain rules, certain labels, certain identifiers in order to keep that clear. Because if you violate the social order, you risk social disruption, which is the loss of cohesion. So there is a reason why we're racist and xenophobic by nature. And we are. We have to just admit that.

that we all have a tendency towards that and we have to work to undo it because in our evolutionary past, it was advantageous to be xenophobic. Unfortunately, I wish I weren't too, because now we're dealing with the negative consequences of it, obviously. Then the argument could be, look, if nature makes us identify outgroups,

xenophobia, racism, whatever you want to call it. Let's apply that same logic to what we're talking about here, which is sex and gender. And so by stigmatizing differences, I'm just doing what we're supposed to do. I'm I'm creating in groups and out groups. Nathan, like, I don't understand.

Okay. Well, the creation of in-groups and out-groups is what leads to warfare and homicide. And, you know, I think we've decided as a larger culture that we don't want to live constantly at war with our neighbors, right? So in-group, out-group identification is good for social cohesion, but it's really bad for world peace and harmony and general flourishing because you're picturing a

us as winning all of these battles, but what if we lose them, right? The losing end of all of this xenophobia and racism is often, you know, death and destruction and famine and squalor, right? So because, you know, when there's a war, there aren't winners, right? We talk about winners, but there really isn't a winner. You know, who won World War II? How many tens of millions of people were slaughtered in World War II? There weren't winners there. We escaped with our democracy intact, but there

It's hard to say that there was a winner when considering how many Americans did we lose in World War II? Something like half a million, something like that. Yeah. Russia's lost like 12 million. And those are the winners. Russia's won, supposedly, on the Eastern Front. But they lost more people than Germany did. So there aren't winners in war, right? So that's what I mean by in-group, out-group identification. It is natural. It's part of who we are. But we do really well to work against it. You know what else is natural? Greed.

And the desire to steal, that's totally natural also. We do well to prohibit that, I think. And I think that's what I'm talking about, where just because something is natural doesn't mean it's okay, right? That's not what I'm saying. When I look at gender diversity in animals, I'm not saying, hey, since they do it, we're fine to do it because they do some awful things to each other. But what I am saying is, if you want to enforce social controls on someone's gender expression, you're going to have to convince me without telling me it's unnatural, right?

because it is natural. Now, you might say, well, so is murder. Fine. It's not murder, though. That's the problem is it doesn't hurt anybody. And that's my point is that, you know, consenting adults living their gender and sexuality the way they want doesn't actually hurt anyone. It hurts your sense of social order. And I would rather we challenge that

rather than victimize people unnecessarily. We're not saying that what the bonobos do or what the birds do is right. We're just saying if we're going to talk about creating a civilization, human civilization, the animal we are,

and we're going to use various data points, in this case, what's natural, then let's make sure we're getting that right first to base our argument against. So we can say gender diversity is natural, murder is natural. Great. Which one do we want to enforce or impose or leverage? And which one do we not? That should be the starting point. What you're saying is we're not even starting from the right spot.

Right. Exactly. Because the argument has always been that it's unnatural. And that was the same argument that was used against the gay community as they started to assert themselves and ask for at least tolerance, if not equality. They were said, but it's unnatural. It's aberrant. You know, of course, that's one step away from saying evil, sinful and all of that, which they say that, too. But they're going to say that more in church than they are in civil society. So.

You know, it's a code word, right? You know, what they really mean is that it's, you know, it's a violation of God's will or whatever. And which you're perfectly fine to think and believe. No one's going to go in and tell churches that they have to teach differently. Of course not. In fact, I would defend a church's right to define these things for themselves also because I want to live in a society where you're free to do that.

So freedom means you have to give somebody who disagrees with you the same freedom you expect for yourself. So I would, and I work with churches on, on evolutionary theory sometimes. And I do tell them like, I disagree with you guys on a lot of stuff, but I will fight for your right to say it and believe it and act accordingly. Just remember that it's an opt in system religion. It's,

Your rules apply to your members and not to people outside of it. Right. Not to anybody you control. Yeah. Yeah. And that's the thing. And I say the same thing when it comes to gender and sexuality. You don't have to go to a drag show. You don't have to cheer any of this stuff on. You can live in whatever world that you want. It's just, will you allow your neighbors to be themselves without being molested by the government, basically? Yeah.

Man, but you know what I just realized? I think I now understand the fear. I've never really understood the whole, like the drag show thing is the, is the hilarious one. I'm pretty sure I don't follow it that closely, but I'm pretty sure like that's why Trump wanted to be the chairman of the Kennedy center because there was like drag shows or something. Are you familiar with that? I didn't hear that, but I'm not surprised. I'm not surprised. I think that's what it was. So let's just assume that's true. And y'all can, my point is,

As you alluded to, humans are very societally malleable. So somebody who wants to dress in drag or somebody who's gay or somebody who, whatever, if that is not them, then that's an out group. Then they say, so my children being exposed to that could be

give them that social pressures to turn them into that, which is an out group. So now my child who's an in-group is I might view as an out group. Okay. Well, uh, okay. So that might be where the fear comes from. Yeah. I mean, I would just say that, um, I don't think there's any drag Queens that recruit,

I recruit other drag, like kids to become drag Queens. Right. So that's, I think that's a misplaced fear, but what they're really afraid of is that their kids might see nothing wrong with drag Queens. And that's the problem is that they're trying to teach them a certain value set and

And drag queens living their lives in peace, you know, violates their that value set. All I will say is, listen, you always will have the right to teach your kids whatever you think is best. You'll always have that right. They're going to be exposed to the world around them. We live in a multicultural society. They're always going to be exposed to other ideas that aren't your own. I'm sorry to tell you this. The kids are on the playground with other kids. They're hearing stuff that you don't approve of no matter what.

Right. So, yeah. So, and also if your ideas are better than what are you afraid of? Right. Only someone who's really insecure about their beliefs would, would think that they have to shield people from even hearing something different in order to maintain. If you can't tolerate hearing the other side without immediately adopting it, then maybe your ideas aren't as strong as you think they are. Right. And it's,

And it's also assuming if you're what we'll stick with kids in this example, if your kids are hearing it to your point and if they like it or enjoy it, then they're going to do that. And you're scared of it, which is funny because one of the things I've got three kids and I always think of the quote slash idea, which is the kids are.

born like a seed in that you cannot change what that seed turns into. If you plant a pine cone, it's going to turn into a pine tree. It's not going to turn into a maple, right?

Right. Your job is to help that seed then become the strongest one. And so by that logic, your pine cone is not going to turn into a maple because it saw a maple and thought it was pretty. You know what I mean? That's exactly right. And when it comes to gender, gender expression, sexuality, all of these things, we don't know that much about how it comes about. That's what I was wondering. But what we do know is that it's not.

driven by what you're exposed to necessarily. It's certainly not homosexuality. So there were thoughts that it was a product of sex abuse. People thought that, that if you were molested as a child, then you were much more likely to become gay. And there was a study that claimed that.

That study, and I mentioned this study in chapter seven or eight of the book, all the incredible flaws with it. But fortunately, we have done the studies properly to determine that. So, and in fact, it's a colleague of mine at John Jay College has been running. And this is, if you want to have her on your podcast, I strongly think you should. She's wonderful. Listen to this study that she's had going now for over 30 years. I think we're close to 40 years now. So she studies a group of children who were abused.

And there's, I mean, it's a large number, like five, 600 children. And she has a control group from the same, you know, zip code, socioeconomic background, you know, education, race, that she's factored in everything she can. So she has a perfect control group of,

unabused kids. So you have these two groups going through life and she can ask all kinds of questions about what happens differently. So the first thing that she discovered, which won her the Stockholm prize, which is like the Nobel prize for criminology is that being abused does not make you more likely to become an abuser yourself because that was always what was thought.

was that this idea of hurt people, hurt people, right? Exactly. Called the cycle of violence or cycle of abuse. And she just proved that. And she showed between these two groups, there were no more likely. When you factor in all of the other things, like for example, socioeconomic background, that does affect, you know, having a parent in prison. There's lots of things that do predict

your likelihood of becoming an abuser. But the fact that you were abused does not make you more likely to become an abuser. So that was important. Where am I going with this? Well, she had the perfect data set to ask,

well, what about if you were sexually abused, are you more likely to become gay? And do you know what she found? No difference whatsoever in terms of the likelihood of you becoming gay. But she did find one interesting difference. Children who were sexually abused were more likely to have at least one same-sex experience or dalliance.

you know, experimentation. And because it's been known that people who are abused, particularly as children, often do undergo a phase or a period of their life of sexual experimentation. And the reason why is, you know, there's lots of ideas, but one of them is they're trying to reclaim their autonomy, you know, their social autonomy. And one of them is just a coping mechanism or misplaced

You know, there's lots of theories about why that is, but it's not like a lifelong necessarily change, but generally. And so during that exploratory period, it included some same sex activity, but it did not necessarily make them more likely to be gay, which I think proves the point twice in a sense, because one, it proves that the abuse didn't make them gay, but two, even experimenting didn't make it gay. Yeah.

Exactly. Right. So there's a far cry from just hearing it on the playground. Exactly. Exactly. So they've, they've tasted the ice cream and decided they don't like that flavor. Right. Yeah. So that's what we know. We don't know exactly where attraction comes from. It seems to be largely kind of random actually, because twins correlate a lot, but not always. So there seems to be some randomness built into the system, which by the way is also how nature works. Nature loves variety and randomness. Um, so what we know is that you're not really, really, um,

influenced, but that much by what you see in here, whatever, in terms of where your attraction will land. Now you will absorb some beauty standards from the culture, which I think that's interesting too. Like if you look at what's attractive, that changes over time, it changes in different locations. You know, sometimes like big boobs were like really attractive. And then other times really flat chests were really attractive. You know, it's just very, you know, that's what's weird is how does that work? How do you absorb that stuff?

You know, you made me aware of that. It blew my mind because the way we act specifically when it comes to like sexual attraction and things feels so different.

It is so, it is not malleable, at least for me. I don't, I guess I can't speak for everybody. And I think a lot of people, right? Yes. It's part of you, right? Yeah. Like there is a certain type that I like and I don't care if I grew up in the, in the 1800s, it would be that type. That's what I say. And you're like, no man. Chris, that is not true. Crazy. If you grew up in a different time and place, so,

so many things would be different about you. That's crazy. Yeah. You can't tell me if I was Roman that I'd, that I'd be, you would be different. You would be, you would be unrecognizable to your current self. That's so many things about you would be different if you grew up in a different time and place.

And your attraction to various modes of femininity, we'll say, that's the least of the differences that you've experienced. That's incredible. I would sort of put it this way. You're not you. You're the sum total of everything that's happened to you. Yeah.

Including molecules and genes and things. But yeah, we are. I'm sorry to say the self is a very useful illusion. And I guess to wrap it up, it's saying that the purpose of these discussions is to use the best parts of our humanity, which is our brains and our prefrontal cortex and our social interactions to determine how do we create the best environment for our species. Right.

And you're not saying, I know the right one. You're just saying, can we at least make sure what we do know is being factored into the discussion? Right. Just make the decision with the best possible information and data. That's it. And we can choose to decide what society we build. And I just hope we build it thoughtfully. And for example, one of the values that we have, particularly in the West, is the idea of personal freedom and autonomy.

That's not universal by any means. There are plenty of cultures that are very repressive on what individuals can and can't do, even in the modern society. Right. There are countries where you can be locked up just for thinking certain things. Right. So we have valued personal liberty and autonomy as something that is worth everything.

the negative consequences that come from it. And there are negative consequences, right? We disagree a lot. There's discord and the government swings back and forth from parties to parties. There's a lot of downside to having all that freedom and autonomy, but we've still decided that it's worth it. Right?

So that's what I mean when I say we get to decide. We take all the information. We know what communism is. We know what totalitarianism is. We know what all these different things is, and we've decided this is the way that we want it. So that's where I'm coming from when it's gender identity expression is.

learn about what it is, learn about how natural diverse genders are in other creatures. And in my book, I talk about gender diversity in other animals. And so learn about that. And then we can all decide, well, do we want to include that

in that general scheme of personal liberty, freedom, autonomy, you know, about what consenting adults do to me, it's a kind of a no brainer. I want you to be able to live your truth with your gender expression and your, your approach to marriage. I would never say that I should be in charge of other people's marriage rules, like how you live with your wife, Chris is you too, and enjoy the freedom of being able to craft it in the way that you want. But just give,

Give that freedom to everyone else, please. You know, that's kind of where I'm coming from. To wrap this up, the book is The Sexual Evolution, How 500 Million Years of Sex, Gender and Mating Shape Modern Relationships. And you said something there that I want to make sure listeners know, which is by telling things about these animals, I mean, our misconceptions about the strength of, say, lions or the monogamy of birds or the all those things, they help you just break thought patterns and

that once broken forced you to ask what other thought patterns do I have that are based on some kind of fiction, which is literally what this podcast is about. Right. I have two questions for you to finish it up. One is tell us about your work as, as a whole, because this book would lead people to believe like, Oh, he deals with like gender identity specifically, but it's not that it's

you have other books which are just as fascinating. So can you tell us a little bit about that? Yeah, so I'm a scientist who studies human beings. That is broadly defined. So actually right now, I'm a molecular biologist by training. So right now I'm studying gene expression differences among humans, Neanderthals, Denisovans, which are kind of a variety of Neanderthal. And also in comparison to the other apes, which are gorillas, chimpanzees, orangutans. The reason I do this is that

I don't know if you know this, but we've actually found very little different among our close relatives when it comes to like the main genes, like the protein coding genes. So there's this search for like, okay, so why are, why are we so different when we have almost all the same genes and even the same versions of those genes in most cases? So what my lab studies is how we use those genes, how they get turned on and turned off. Like epigenetics?

It's epigenetic. Unfortunately, we can't do a lot of epigenetics with Neanderthals. But yeah, it's epigenetics. It's that layer on top of the sequences themselves about how those sequences are regulated. So epigenetics is one way. The way that we study has to do with what's called microRNA. So microRNAs are little small RNA molecules that can turn other genes up or down. They're like little hands on the dials that go around and just kind of tweak the

gene expression. And what we found is small tweaks there can lead to large changes in the physiology of an organism. And so that's what we study. So that kind of tweaks of gene expression. And again, my main interest though is how did we get this way? Why are we different than Neanderthals? Why are we different than chimpanzees? And because very little of it comes down to regular genes. It comes down to how the genes are used. And that's why we're studying. That's insane. Yeah.

You can't keep doing this to me. I got to let you go. What's great about it is like this work wasn't even possible a decade ago because we didn't have full Neanderthal genomes.

Oh, shit.

And most people don't realize this, but when we built the Neanderthal genome, we had to have the human genome as a template. Like if you imagine like you're putting a puzzle together, if you didn't know what the puzzle was going to look like,

it would be hard. So we had to see the human genome as a reference. And then we built the Neanderthal pieces together because they were such small pieces because it's so old. But our ability to do that gets better and better all the time, actually. So you might be surprised at some of the creatures we eventually get DNA out of. I mean, we won't get dinosaurs or anything. That's way too old. But for example, they're talking about bringing back

the woolly mammoth and yeah yeah i've heard a more recently extinct species we might get enough dna to do that i'm not saying it's a good or bad idea again that's a judgment that other people can make but um yeah that's what i really dna is what i'm i'm almost always focused on dna and how it

works. You mentioned, like, I know we have the same DNA genetic code. You tell me as say a monkey or something, right? It's like 99, 98, 98 and a half, something like that. Similar. Yeah. So if I'm hearing you correctly, you're saying one of the primary things you study is if we're only one and a half percent different there, how are we relatively indistinguishable? And you're saying it's these like

micro RNAs? That's one, one rate. That's the one I study. Yeah. There's a, there's a variety of mechanisms that affect gene expression. And that's the one that my lab happens to study because we basically, because we stumbled upon some interesting differences in that area. And then I started a project to understand it.

This project started about 2018 when I was looking at human chromosome number 21, which is the smallest one. And I was just kind of lining it up, looking at this compared to chimpanzees. And I found this big chunk, about 1.8 million base pairs big, that was really human unique. Apes didn't have it at all. And what I found in there was a bunch of microRNA genes.

Well, it was a bunch of junk mostly, but there were, but there, you know, sprinkled in there were some micro RNA genes that we don't share with the other apes. So that was a clue of, okay, so these genes are like little switches that the other apes don't have and they turn other genes up and down.

Have you looked at health and wellness, like the impact of that on health and wellness disease and stuff? Is that where you're going? Well, so a lot of people who just study humans, just human health and disease are studying micro RNAs and they're rolling. They are. Okay. Oh yeah. I've never heard of it. That's what's crazy. If you Google micro RNA and like,

Cancer or Parkinson's or Parkinson's isn't one that they know there's a role there. A lot of different kinds of cancers. Yeah. So that's how micro RNAs are most often studied. But I'm doing cross species comparisons because I'm interested in evolution. Yeah.

I'm going to send you an email. I I'd love to know anybody else who like does similar work. I now just want to interview people that do your stuff. This is great people for your podcast. Yeah. I know. Very good. Very, very, um, cutting edge, um, you know, paleo geneticists and other things like that. Yeah. You might talk to, but talk to Kathy Whittem. That's the one who did that study on the cycle of violence. You can tell her I sent you, she's a colleague of mine at John Jay.

Okay. Um, yeah, she's like a member of the national Academy. She's very famous for this long-term study of child abuse. That's so insane. I will do that. Uh, Nathan, where can we find you? We will link to the book for people as fascinated by this as I am aside from reading all your books, actually, where else are you these days? Um, I'm easy to find online. Nathan Lentz. There's, I'm the only one, I think, uh, the only one that has, uh,

a public profile, I guess. So Instagram, Facebook, all those, I, I, I'm not that active on social media cause I don't like social media. I don't think you're busy, but, um, I do respond to DMS. There you go. There you go. But also, um, just email me. I mean, my email is easy to find online too. So, and in fact, I have a link tree. Maybe I'll send you a link to that and all my socials and email and stuff are on that. So that'd be perfect. All right. Thank you so much. Thank you. I had a great time talking to you.

Thank you to this week's guest, Dr. Nathan Lentz. The episode was hosted as always by Chris Stemp and produced by yours truly, John Rojas. Dr. Lentz's book, The Sexual Evolution, How 500 Million Years of Sex, Gender, and Mating Shaped Modern Relationships is available wherever books are sold.

And now for the quick housekeeping items. If you ever want to reach out to the show, you can email us at smartpeoplepodcast at gmail.com or message us on Twitter at smartpeoplepod. And if you want to stay up to date with all things Smart People Podcast, head over to the website smartpeoplepodcast.com and sign up for the newsletter. All right, that's it for us this week. Make sure you stay tuned because we've got a lot of great interviews coming up. We'll see you all next episode.