'Eve' author says medicine often ignores female bodies. 'We've been guinea pigs'

TONYA MOSLEY, HOST:

This is FRESH AIR. I'm Tonya Mosley. Back in 2012, writer Cat Bohannon went to see the movie "Prometheus," Ridley Scott's prequel to the movie "Alien." At the time, Bohannon was a grad student at Columbia University, and one scene in the movie stood out. An archaeologist played by Noomi Rapace was impregnated with an alien. She asks the spaceship's surgery pod to help her remove it. And here's what happens next.

(SOUNDBITE OF FILM, "PROMETHEUS")

AUTOMATED VOICE: (As Computer) Please verbally state the nature of your injury.

NOOMI RAPACE: (As Elizabeth Shaw) I need cesarean.

AUTOMATED VOICE: (As Computer) Error. This med pod is calibrated for male patients only. Please seek medical assistance elsewhere.

MOSLEY: That was a scene from the movie "Prometheus" and one of the motivations behind Bohannon's new book. It's called "Eve: How The Female Body Drove 200 Million Years Of Human Evolution." Bohannon says the movie scene points out a stark reality. For over a century, the female body has been left out of biological and medical research. And when scientists only study the male norm, we're getting less than half of the picture of human evolution. Bohannon's book attempts to trace the evolution of women's bodies and how that evolution has shaped our lives. The book reads like a user's manual for the female mammal, taking us through the Jurassic era to modern day, exploring everything from why we menstruate, are more likely to get Alzheimer's and why we live longer. Cat Bohannon is a Ph.D. from Columbia University where she studied the evolution of narrative and cognition. Her writing has appeared in various publications, including the Scientific American, Science and The Georgia Review.

Cat Bohannon, welcome to FRESH AIR.

CAT BOHANNON: Thanks. Thanks. Nice to be here. You make me sound so fancy. I love it.

MOSLEY: Well, you know, that "Prometheus" scene is make believe, of course, but it is such a powerful example of how the male form is centered. You write about how in biological and medical sciences there's something called the male norm. Can you describe what that is?

BOHANNON: Oh, absolutely. And this is something I only learned when I was a grad student, because, you see, in the work I did, which was mostly with computers, I didn't actually have to, well, breed a bunch of mice and then make choices about what happens and who I would use in my research, right? I didn't work in mouse. I worked with computers. So that means that I didn't know that the majority of studies that use mice are only studying the males, which is this really kind of weird thing if you're not in biology, right? And you're like, OK, why is this happening? It's not that there's some kind of evil cabal, like, rubbing their hands together saying, muahaha (ph), I will understudy females. It's actually that when you conduct a scientific experiment, you want to control for as many factors as you can. You want a clean experiment. So what you do is you try and reduce confounds, reduce what's complicating what you're seeing.

Well, usually, the ovary is thought of as an unfortunate complication because in all mammals, there's an estrus cycle. There's this cycle of hormones that rises and falls, right? Some of us do it more quickly, like every month for people like you and me, maybe, and, you know, others, it takes longer if you're, say, a mouse. But nevertheless, your hormones, they're going up and down, and so that's complicating the experiment. So a decision was essentially made by many different people in biology a long time ago that, well, maybe we just won't study the females because the guys don't have that.

MOSLEY: This is so interesting. The male norm is such an issue, you write, that many papers don't even mention they only use male subjects.

BOHANNON: Yeah. Absolutely. It's so assumed that there isn't this urge to say, yes, I did this thing that we're all doing. Now some things are finally starting to change. There's been a big push at the National Institute of Health. There's been a big push in a number of different scientific bodies that say, oh, wait, wait, wait, we're not studying the females. That's a problem. Things are working differently in female bodies. Now you need to actually say whether or not you're including them. But the thing is is that the NIH only controls about 2% of the money that's funding a lot of biomedical research in the United States. So they have a big public place, but they don't push the bar as much as the journals who decide whether or not to publish a paper. That's where the real change is going to come from.

MOSLEY: That's really interesting. So just to go back a little bit, in the 1970s, regulators strongly advised do not use female subjects in research to be of childbearing age for many of the reasons you mentioned because of menstrual cycles and you can't really get a sample of women who are all having their menstruation at the same time and their hormonal shifts are happening at the same time. The National Institutes of Health managed to update some of the regulations in 1994, but you're saying that such a small sliver. Can you give us another example of maybe how the male norm plays out in medicine, and what are the implications of not studying women's bodies?

BOHANNON: Yeah. Absolutely. Well, I'm going to cover one thing quickly, and then I'll do that. So the reason we stopped studying women of reproductive age in clinical trials is because we didn't want to screw up babies, OK? It wasn't simply because of controlling for the neatness of science, because...

MOSLEY: I see.

BOHANNON: ...Once you're dealing with human bodies, there is a potential that that body could become pregnant. And there is a problem with testing drugs on a body and not knowing what it might do to the fetus. So it's actually a shift, then, that happens in advising scientists that are doing biomedical research, don't study women of reproductive age out of a good heart, right? But unfortunately, being of reproductive age is, well, anywhere from, like, 12 or 13 to in your early 50s. So that's the majority of our lives, and that's a big gap. So one of the ways that this ends up playing out in medicine today is that the vast majority of medicines that we end up taking - prescription medicines - right? - may not have been tested on female bodies at all - right? - because these regulations only recently shifted. It takes a certain amount of time to go from clinical trial to release to the public, and you're not obliged to go back and redo your experiments if you were already cleared to release your drug to the public. So effectively, we've been guinea pigs.

MOSLEY: Right. OK. So if males are only used in the trials, are doctors basically relying on anecdotal knowledge when prescribing to women, based on body weight and age?

BOHANNON: Like I say in the book, that's often the case. Thankfully, we're starting to rewind. We're starting to learn a little bit more about this sort of free-for-all experiment wherein women take drugs in the public and then you see the effects afterwards. And we now know that opoid drugs are now famously processed different in typical female bodies, right? It often takes us longer to recover from side effects and-or we clear it from our systems too soon and then we feel like we need more. Opoids are common prescription painkillers, OK? And that's where you get into a danger zones for things like addiction.

A common pattern for addiction is to frontload a whole bunch of painkiller and then keep norming your body to it until you feel like you need more and you need more and you need more, right? So the thing is, in a female body that's taking opoid drugs, the way that her liver is metabolizing this drug will naturally make her a bit more prone. So while it's true that more men are addicted to opoids because that's a general addiction pattern, women are specially vulnerable, and it can really, really, really influence things like pregnancy and postpartum recovery and, well, anything in our lives, really.

MOSLEY: I'm astounded by this. You gave another example - sex differences for general anesthesia research only began - it really only began in 1999 for women?

BOHANNON: This is the moment at which somebody was conducting a study and it was a bunch of different research hospitals. So for once, they actually had a bunch of men and women included in this study. So that's great. But they didn't set out to test sex differences. They just wanted to know, is this new special EEG machine - it's a kind of monitoring machine - yeah? - is it usefully influential in monitoring anesthesia effectively? And it turned out, yeah, sure, the machine was kind of fine. But what they really found out is that women come out of anesthesia faster, no matter - even if they're the same weight as the guy - right? - they still need a different profile treatment in anesthesia. And it's actually true that women are more likely to wake up on the surgery table, which, to me, not a great thing.

MOSLEY: Well, of course, of course.

BOHANNON: (Laughter) Not what I'm looking forward to in the day.

MOSLEY: I was actually wondering about some of the current day health disparities we see in men versus women. We know that more women are known to die from heart disease, for instance. Can these types of disparities be linked to evolution or discrepancies in health care or a little bit of both?

BOHANNON: I always assume a little bit of both because, you know, yes, our bodies evolved over hundreds of millions of years, but we also live in the societies we live in with the disparities we face. So it's absolutely the case that you can take two relatively identical bodies, but then make one body suffer more through various types of injustice and medical inequity - right? - and then you should not expect to see the same outcomes in a body that didn't have to go through that same sort of suffering, right?

So that's inevitably going to be the case. Both are going to be a factor. But it is true that the typical male cardiovascular system is, in a word, a bit more crap than the female, actually, across its lifetime. That's something that male bodies really struggle with, and it's a characteristic pattern in aging, right? As male bodies get older, they have known problems with cardiovascular disease. One of the main reasons that heart disease can be such a killer for so many women is that our symptoms can be different, right?

And that's something that, thankfully, has gotten some more airtime lately, because awareness saves lives, right? So you know, when you have what we would call a heart attack in women, it may - instead of feeling, like, that pressure on the chest, that classic model, it may feel more like severe indigestion. Some women report just feeling weirdly anxious, with no history of anxiety in their lives, you know?

MOSLEY: Right, so this is not an evolutionary thing that has happened in women's bodies that we're more prone to heart disease. It's just that the symptoms show up differently and we've centered the male norm in understanding what heart disease might look like.

BOHANNON: I think you're absolutely right, I really do. There are some ways in which women's - most women's cardiovascular systems are slightly more vulnerable. We're slightly more likely to get strokes. So that's tied to how we live longer. You know, but for the most part, what's going on, I think, in how vulnerable women are to heart disease today is absolutely that disparity in studying sex differences, which also means that we're going to end up having even less the more awareness is spread, right? Which means, effectively, the contrast between men and women will become more severe as we improve treatment for women.

MOSLEY: You break the book down by categorizing several Eves, not just one, starting 205 million years ago with a mammal called Morgie all the way to Homo sapiens, which evolved roughly 300,000 years ago.

BOHANNON: Yep.

MOSLEY: Morgie is a cross between a weasel and a mouse. Why is Morgie important in understanding the evolution of what we now know as the human female?

BOHANNON: So Morgie is an exemplar genus. That's very scientific words. She's not exactly our direct ancestor, but she's an animal a lot like our ancestor that we know a lot about. We found a lot of her fossils over time. We can infer a lot about her behavior. And the really interesting thing about Morgie is that most think this is kind of the dawn of milk. The reason so many cisgender women have breasts is because we evolved to make milk, and this is just sort of the way we do it.

But we had milk way before we had breasts, we had milk before we had nipples. We used to kind of sweat it out through these little hairy patches, right? So when you think about why milk is the way it is and how that pattern of child care and that pattern of body development evolves over that mammalian line, well, then you have to think, OK, where is this coming from? What's useful about lactation? What's good here?

MOSLEY: You actually say that breast milk isn't solely about nutritional value, it's about infrastructure. Can you say more about that?

BOHANNON: Yeah. So milk is something that the newborn mammal, including our own, uses to go through that early phase of development - right? - because you're not even supposed to give water necessarily - like, little bits - to newborns. You're supposed to just give them more milk, ideally - right? - because if their bellies get too full, then they might think, oh, I'm not hungry. They're not very smart when they start out. This is true of all mammals. When we start out, we're kind of, like, useless - OK? - some more than others.

So you give this newborn milk. And the thing is, is that we think the baby's hungry, but primarily that baby is thirsty. Milk has a huge amount of water in it, and that helps control for infection. And infection is the big story of milk because the thing is, where you get your water shapes how likely you are to be infected by something, especially when your immune system is really naive and sort of starting out, yeah? So if you're getting your water from mom, well, that controls your infection related to water because you're not getting - the only infections you'll get are ones that her body is already dealing with.

But the really cool thing about human milk is we have a huge number of really, really special sugars in milk that aren't actually for the baby to digest, they're for her bacteria, OK? So there are these special sugars, oligosaccharides. And they're meant to help basically fertilize the garden in that kid's intestines because some of our very friendly bacteria in our guts, which will then help that baby digest milk, among other things, really like some of these sugars a lot. And the less friendly ones might be negatively impacted by these sugars or just by competing with the good guys, right?

So in other words, when you're giving that baby milk, you're really setting up an entire structure in that kid's microbiome. You're selecting for the bacteria that will aid and you're helping give that kid extra ways of fighting off the things that are bad.

MOSLEY: One of the more interesting theories that I've heard before, I think, but not in great detail, is that breastfeeding is a predictable sort of birth control. It's nature's birth control. How so?

BOHANNON: Well, first of all, for all your listeners, please use modern forms of birth control because this is not reliable, OK? Anybody who has become pregnant in a few months after giving birth will tell you, well, that did not work. That did not work. I was still breastfeeding. Yeah, so bodies are variable. Please use modern birth control. OK, but it is absolutely true that across mammals, when a mother's body is making milk, when she's lactating, she is far less likely to ovulate. And that makes perfect sense. It's really expensive to breastfeed. I mean, in all the modern ways, it's expensive - our time, the actual equipment. But also, importantly, for ancient mammals, it's expensive in terms of how much energy she's using to nurse her baby. It's also very energetically costly to be pregnant. So doing both at the same time - not a great idea. Not hard to imagine how that would be selected against in deep time.

MOSLEY: Let's take a short break. If you're just joining us, my guest is Cat Bohannon, author of the new book "Eve: How The Female Body Drove 200 Million Years Of Human Evolution." We'll continue our conversation after a short break. This is FRESH AIR.

(SOUNDBITE OF WOOKIE'S "SCRAPPY")

MOSLEY: This is FRESH AIR, and today we're talking with writer Cat Bohannon, author of a new book centering the role of the female in human evolution. The book is called "Eve." Bohannon completed her Ph.D. in 2022 at Columbia University, where she studied the evolution of narrative and cognition. Her writing has appeared in several publications, including the Scientific American and Science magazine.

OK, Cat, we left off talking about the female body and how it drove 200 million years of human evolution. And you shared with us a little about Morgie, a mammal from millions of years ago that also gives us a lens into how lactation was formed in the earliest eves. Now I want to talk a little bit about how the evolution of the female womb and live births came to be. There is a powerful statement that you make in the book about this that milk started under the feet of dinosaurs, but live birth took hold in an apocalypse. Say more about this.

BOHANNON: Yeah. So this thing that we do, this giving birth to live babies, seems normal because all human beings do it. But it's actually pretty nuts. It's actually kind of crazy not to lay eggs. That's still the dominant way in which we have offspring, OK? So that mammals are all giving birth to live babies is just incredibly innovative. There are also some squamates, there are some lizards, there's some sharks that do it, OK? But for the most part, this is a mammalian story. And the moment at which we really start saying, OK, this is what mammals are going to do and we're going to do it the way we do it is right around the apocalypse, right around when the asteroid takes out the vast majority of dinosaurs, and all that are left are some disgruntled birds, right? So this is the moment at which that happens.

So the placenta is evolving before then, but our body plan and the body plan of marsupials are kind of head and head at that point. We're all just kind of weird, little beasties doing our thing. But whether or not the majority of mammals end up like marsupials, who end up giving birth to teeny, tiny, little things and then finish it out in a pouch, or whether we're going to do it the way we do it, which is, you know, longer gestations, bigger babies, that kind of thing - it's head and head. And we don't know exactly why, but more marsupial ancestors died off in that massive fallout after the apocalypse than our ancestors. And that's why we have the kinds of uteruses and placentas that we have - uteri, I prefer, but it could be either way. And it's also why we only have, for most of us, one vagina instead of two or more.

MOSLEY: Somewhere after this apocalypse, women began to have periods. I wanted to slow down here because why? And what is the theory on what was happening before then?

BOHANNON: The uterus is a diverse thing. There are many different sorts. They're all over the mammalian populations of various types. But the way that we have a menstrual cycle is actually less about the fact that we shed the blood externally, although I also would be perfectly happy for that to stop, but I'm stuck with it, right? But it's also that the lining of our uterus, the endometrial lining, starts building up before it even gets the signal that a fertilized egg's coming down the tube, OK? And this is actually what's really unusual about us. And there are only a handful of species that menstruate the way we do - in other words, that start building up this lining, whether or not there's an incoming potential baby. And the thing that's common among all of those is that all of these species, like us, have incredibly invasive placentas, right? Some placentas are kind of shallow. They kind of sit on the top of the lining of the uterus. No big deal. Some of them are medium.

Ours are the most deeply invasive kind. They penetrate all the way into the mother's bloodstream in that uterine wall. And having it like that has massive impacts throughout the female body. Our pregnancies are more invasive. They're more challenging, and that means our bodies are basically bracing for impact whether or not it's coming, because basically that's the safer way to do it. And that's true in our species, and that's true in others that have invasive placentas like ours. But humans are among the most invasive. So that means that pregnancy isn't really like kind of a soft cuddle, you know, like a nice warm cushion and then the baby comes out. It's more like trench warfare.

MOSLEY: Our guest today is Cat Bohannon, author of the new book "Eve: How The Female Body Drove 200 Million Years Of Human Evolution." I'm Tonya Mosley, and this is FRESH AIR.

(SOUNDBITE OF ERIC DOLPHY'S "MRS. PARKER OF K.C. (BIRD'S MOTHER)")

MOSLEY: This is FRESH AIR. I'm Tonya Mosley, and my guest today is Cat Bohannon, author of a new book centering the role of the female in human evolution. The book is called "Eve: How The Female Body Drove 200 Million Years Of Human Evolution." Her work attempts to trace the evolution of women's bodies and how that evolution has shaped our lives. Bohannon completed her Ph.D. in 2022 at Columbia University, where she studied the evolution of narrative and cognition. Her writing has appeared in several publications, including the Scientific American and Science magazine.

OK, Cat, there is a chapter in this book that you explicitly say you did not want to write, and that is the chapter on the brain.

BOHANNON: (Laughter) Yeah.

MOSLEY: Why were you so hesitant to write about the possible differences in brains of male versus females?

BOHANNON: Oh, gee, Tonya, can you imagine (laughter)?

MOSLEY: No, I know. Let's get into it, yeah?

BOHANNON: I mean, look, I am a queer woman sciencing (ph) in public, all right? That's kind of like what I'm doing right now, which, you know, has a history of already being a complicated thing to do. And now, because I'd set myself up with the project of this book, I can't ignore the evolution of hominin encephalization - that our brains got bigger, in other words. You know, our brains got very much bigger. It's very much a story of where we come from. It's also like the seat of how we think about what makes us human, right? It's like, who am I? Well, I am definitely in my brain, right? I am absolutely a human being because I have the brain I do. And then I need to go and say, OK, are there sex differences, you know?

So, like, for at least a year, I am digging into the research, and I am bracing myself because I have to. I have to be ready to find answers that I don't like, right? I have to. It's my job. Like, I would be doing a bad job if I didn't. So I am a hardcore feminist. It's pretty obvious, you know? And I'm just, like, gripping the edge of the desk like, all right, science, what do you got for me? And I was so, so grateful. After a year of, like, rage writing - right? - after, like, a year of, like, pulling back and saying, OK, what's here? What's really, really, really here? You know, to see, oh, man, if you hold two brains in your hands - now, don't go, like, stealing them from hospitals. But, like, if you manage to have two cadaver brains in your hands - human brains - you actually will not be able to tell which is male and which is female. And that's true by almost any measure.

Even if you are using microscopes, even if you are using the most careful instruments, the only way to actually do it is to sluice the whole thing down in a blender and sequence the DNA and look for the Y chromosome, because the brain is actually made of many, many different regions. And there are some typical sex differences in some features, in some regions. But the differences are so subtle. And even a brain that might have a so-called female-typical, you know, region would then end up having a male-typical other region, you see? You end up with a mosaicism. You end up with a kind of mosaicism. And that means that, like, OK, OK, what human brains really evolved to be is remarkably similar - more similar in many ways, both in structure and in overall functionality, than they are for other mammals. And that's actually really interesting.

MOSLEY: Well, if our brains are basically the same though, why is there a cultural belief that they're different?

BOHANNON: Why do people believe that women are a certain way and men are a certain way? I mean, I don't know. The roots run kind of deep.

MOSLEY: Because there does seem to be differences - absolutely, they do. And, I mean, based on what we know culturally, it seems to be true that our brains are different or maybe the way that they work different or the way that we perceive the world is different.

BOHANNON: One of the most distinctive features of the human brain actually isn't necessarily its composition. We do have a hugely expanded frontal cortex, OK? That is a big deal. But, like, the really interesting thing about the evolution of human brains is the evolution of human childhood, right? We, unlike the ape, spend decades in brain development. And the chimpanzee, you know, our most closely related other ape, non-human primate, is only going to spend, like, a handful of furry years - OK? - before that brain is fully developed. Some of that is tied to our longer lifespan, but actually not all of it. We famously have this long period of brain development that is closely tied to social learning, which is to say when it comes to brains, it's not just how big it is, it's how you build it, you know? It's how you learn over time.

And so many of the things that you see in very, very subtle - I got to make this clear, too, because it's true in the chapter. The differences in functionality in male and female brains are incredibly subtle. It's really safer to say they're more functionally similar than different. But there are some. There are some. But it's mostly going to be a thing that happens through the development of childhood.

MOSLEY: Right.

BOHANNON: Right?

MOSLEY: Right.

BOHANNON: In other words, we're - we train ourselves to be the way we are by growing up in the social environments that we do.

MOSLEY: But to push back or challenge that a little bit, I mean, as someone who is a parent, it feels like there are differences in just the way - from the moment that a child is born, the - what they gravitate towards in the way of toys and the way of interests. But what you're saying, it's also what we're putting in front of them that also makes the difference.

BOHANNON: It's absolutely true. So actually, I'm going to say both are true. So in early child development - now, I have a boy and a girl - or at least so far as I know, they are. They have all the relevant bits, and I happen to know their chromosomes because we did DNA testing in the womb. Anyway, so I have a boy who's about to turn 5 and I have his little sister who just turned 3. So I have - I've been in it in this pandemic, right?

MOSLEY: Yes.

BOHANNON: Yeah, I've been in it. And I've absolutely been curious - I wrote the book that I did - whether or not there would be differences there. But again, I have a sample size of two, OK? So that's - like, that's not good science. That's just parenting, right? And it is absolutely true. However, in the lab, they've shown that maybe male babies like to do a little bit more rough and tumble play, right? There's a little bit of difference in gross motor movements. And it's absolutely true that female babies meet a number of cognitive benchmarks - you know, language acquisition and a number of other things - a bit sooner than a male boy will.

And so there are some in the field that think female cognitive development might be slightly more accelerated. There's debate around that. No one's really sure. But, you know, the numbers kind of maybe support it, you know, that girl babies just can do things - smart things, if you like - a little bit faster than a male baby will. But they catch up. The boys catch up, and then they're fine. They still walk roughly the same time. I think it's true. I think you're absolutely right that what we put in front of them, because they're the super smart social primates they are, is shaping the choices they make.

MOSLEY: Let's take a short break. If you're just joining us, my guest today is Cat Bohannon, author of the new book "Eve: How The Female Body Drove 200 Million Years Of Human Evolution." We'll continue our conversation after a short break. This is FRESH AIR.

(SOUNDBITE OF THE BAD PLUS' "THE BEAUTIFUL ONES")

MOSLEY: This is FRESH AIR, and today, we're talking to writer Cat Bohannon, author of a new book centering the role of the female in human evolution. The book is called "Eve." Bohannon completed her Ph.D. in 2022 at Columbia University where she studied the evolution of narrative and cognition. Her writing has appeared in various publications, including the Scientific American and Science Magazine.

You pose a very hairy question, and that is did men evolve to be smarter than women. On the face of it, that question feels sexist and rooted in patriarchy, but you felt it was important to pose it. Tell us...

BOHANNON: I've...

MOSLEY: ...What you found.

BOHANNON: Oh, well, I mean, again, that same thing about, like, oh, God, I didn't want to write this chapter. You know that, like, I felt like - I felt obliged. I felt obliged because not only the massive debate around the thing, but also because it seems to be driving how we think about what women are capable of in intellectual spheres is just, you know, it just felt like it was a sexist as hell question, and I had to, like, dig into the research to answer it anyway. So I did the best I could. And I would say it probably depends what you mean by smart.

So there's this famous thing around math. There's this idea that the female brain is somehow less capable of math. Now, I was on, you know, the math team. I was a little mathlete, mostly 'cause they gave me donuts in high school. You know, I woke up early in the morning, I did some trig problems and they gave me sugar. I was like, this is a good deal. But, you know, I understand outliers, what a - blah, blah. It's actually not the case that the female brain is innately less good at math. For one thing, there's only some subsets of math-related cognitive behavior that shows any reliable sex differences. It's around spatial logic.

So if you picture a box in your head and then you try to rotate that box in your head and how fast you're able to then come up with an answer that's related to how you rotated that box in your head, basically, well, that's spatial logic. And a typical male being tested will do it a little bit faster. It's not the case that the female, given slightly more time, will not come up with the right answer, though, right? So the underlying theory is that she may be using slightly different cognitive strategies to get there based on her very, very slightly different wiring, which again, is about statistics and norms and under the curve, right? But it's absolutely not the case that the resulting functionality is so profoundly different that we can then say chicks are bad at math. Like, that's just not what the research shows.

MOSLEY: And as you said, it also really challenges what we actually deem as smart. Yeah.

BOHANNON: Absolutely. I mean, well, there's the broad sense, of course, too. Any professional athlete is incredibly intelligent. That brain doing what it does on whatever field, whatever sport, is incredibly involved in what's happening, OK? It's actually very classist and periodically racist, but mostly classist, you know, how we think that smart is related to this very specific subset of things that happen in a university. Actually, human brains are more complex than that, and our smarts are spread over a very wide array of functionality, you know? But it's also true that if you put a girl or an adult woman in a test taking environment and prepare her by letting her know in one way or another that girls are bad at math, then she will perform worse on a test involving math than she would if you hadn't so prepared her.

Now, that preparation could be like you told her that, you know, like, which is just, like, straight up sexist throughout, OK, fine. It could be that she saw a poster nearby that kind of, like, implied it, right? But this is not just true of these sexist realms. Like, if you take a boy or an adult man - usually, most of these studies are going to be done with undergrads, so most of that's, like, 18-year-old guys. Anyway, if you take a boy and you tell him that boys are worse at recognizing emotion or that boys are less emotional, they will then perform less well on a test of recognizing facial emotions on a screen with different faces. And if you tell someone in a study section that, for example, Black Americans are less good at engineering, you know, then that person will perform less well on the subject exam, right?

So across many, many, many different areas, this idea of stereotype threat, that you would change how you behave totally subconsciously because you internalize these messages about who you are and what you're capable of, is kind of everywhere in the psychological literature. This is not - if you're a psychologist, this is not actually a challenging idea. But for the general public, people may not realize that there are many things going into how you perform on a test.

MOSLEY: Cat, the thing that ultimately makes us human, you write, is our ability to love. This was a really interesting portion of your book. How did humans evolve to love each other, and what role did women have in that evolution?

BOHANNON: Oh, that's a big question.

MOSLEY: It is.

BOHANNON: One of the things that's really wonderful about primates - and we are primates, but is especially true of us - is that we take this innate thing where we care for members of our group, and we extend it outwards and identify other people who might be genetically unrelated to us and treat them as if they were members of our family. This is called extended kinship, yeah? And one of the really beautiful things that humanity is capable of, which comes from that sort of basic primate behavior, you see some of it in big troops of baboons. You see some of it in chimpanzees, but you really see it with us. The thing that we're able to do to build these huge, complex social groups that we have, these things we call societies, is to take how much we innately love people who are genetically related to us and say, ah, but I will love you, too, you person who is so different from me. That's not to say that we're doing it really well all the time. Actually, we can often suck at this problem, right? But we're capable of it, yeah? And there are ways in which even the chimpanzee isn't quite as capable of it as we are.

MOSLEY: You write that no one really agrees when it comes to sex and love, what is most natural for us. And you talk about polygamy versus monogamy, for instance. And it just got me thinking that so many of our cultural conversations about love and relationships is actually about whether it is an evolutionary trait that men, for instance, have a hard time being monogamous than women. I know this is a complex topic, but what's a detail about this that you found the most plausible when it comes to women in this scenario and us being monogamous?

BOHANNON: There are two different ways. I'll come - I'll dig into it however I can, because it's a whole chapter, but all right. So like I do in a lot of the book, I try to look for evidence of our past, of our evolutionary path, in the body itself because our past is written on the body. Our bodies are made of where we came from and what happened along that path, yeah? So there are things that are very characteristic of other primates who have mating patterns that are more, you know, harem style or more promiscuous. Harem style - think a gorilla. Promiscuous - think, like, the chimp or the bonobo, OK?

So the chimp male is massively larger than the chimp female. But compared to a gorilla male and that size difference, not so much, right? So a human male is only slightly bigger than the female. So that's one of those things that really says, oh, maybe our ancient males weren't competing with each other so much for mates, which is something that you find in a harem style, right? When you have one guy and a bunch of females, he's defending his access to having sex with those females, like, constantly. And one of the common strategies is to build a really big body. You know, you picture King Kong, you beat your chest.

MOSLEY: Right, right.

BOHANNON: That's a gorilla, right? OK. A chimpanzee is also bigger because he's also fighting with other guys for access to females, but because they're having sex with kind of everybody. If you didn't know that about chimps, you know, you're welcome. That means that, like, you know, they're going to have to have a number of different strategies. Body size, which is an expensive thing to build and maintain, isn't going to be sufficient, right? That isn't - you're going to have to have a number of ways of controlling who you get to have sex with, and she's probably going to be having sex with a bunch of people.

But more to your point, the thing we often forget when it comes to monogamy, which is a really neat way of reducing male aggression and male-male competition - right? - because if he's sure that he can have babies with that one, then he doesn't have to do as much with his body to defend his right to have sex with that one, right? There's a kind of, that's just what they're doing, right?

So if we evolved to be monogamous, OK, cool. There is actually a lot of evidence in the primate line to show that that might be the case, as I write in the book. However, what we often forget about monogamy is, when compared to the chimps, it's actually incredibly dangerous for the female. This isn't a good deal for her at all - right? - because in chimps, you have something called paternal uncertainty. If you're having sex with everybody, nobody has any idea who the dad is.

MOSLEY: Right, right.

BOHANNON: OK? Which is really, really important because unfortunately, among chimps, there's a significant amount of infanticide, right? So the way to keep males from being potential baby killers in part is to not have them know if that baby is theirs, right? From a biological perspective, you know, you don't want to kill your own offspring, so then, OK, cool, it keeps them slightly safer.

But in a monogamous scenario where everyone knows who the dad is, that's actually dangerous for the female and her offspring in this chimp model, I mean, which one presumes, at some point, our ancient ancestors were very much like them. So if everyone knows who the dad is, that means that that child is vulnerable to infanticide from competing males. Because if a competing male kills your offspring, then you potentially come into fertility sooner. It's an ugly truth of the animal world.

MOSLEY: Let's take a short break. If you're just joining us, my guest is Cat Bohannon, author of the new book "Eve: How the Female Body Drove 200 Million Years Of Human Evolution." We'll continue our conversation after a short break. This is FRESH AIR.

(SOUNDBITE OF YO LA TENGO'S "WEATHER SHY")

MOSLEY: This is FRESH AIR. And today we're talking with writer Cat Bohannon, author of a new book centering the role of the female in human evolution. The book is called "Eve." Bohannon completed her Ph.D. in 2022 at Columbia University, where she studied the evolution of narrative and cognition.

I want to talk a little bit about sexism in modern culture, because you say at the core of sexism is this massive set of rules that work to control reproduction. It creates cultural rules around when and where males get access, essentially, to female bodies and creates punishments for those who break these rules. I guess my question is, is sexism a cultural norm that we can eliminate or an evolutionary feature of being human?

BOHANNON: There is nothing in your genes that codes for how long your skirt should be, OK? So that's an important thing. When we say what is evolved and what isn't, we can't say that specific sex rules now - you know, like, only at a certain age should a girl wear makeup, right? You know, specific sex rules now that we have that are normed in one culture or another are going to be recent, complex, creative innovations that we have in our culture now. I think what may be an evolutionary feature is this drive to create societies and, as a subset of that, create rules that generate norms in those societies and, as an important feature of that, to create sex rules.

MOSLEY: Got it.

BOHANNON: In other words, I don't think there's a specific kind of sexism that evolution has selected for. If sexism is, by the way I'm describing it, to create rules around access to female bodies and female fertility, then there isn't one way to do it, right? I think we may have an innate drive to create these rules and then deeply care about them in the same way we create any cultural rule and then deeply care about it. It's just in evolutionary terms. Sex rules have more impact on whether or not your society is going to survive and thrive in ancient times, right? Does this rule help keep more women and babies alive, right? That's the deep question.

And right now, in our modern world, in our great diversity of cultures, with many of us creating all kinds of different rules around sex and access to female bodies, you know, it's unclear that really any of them are providing the same deep benefit that they used to, right? If they used to keep us more alive by, for example, limiting when you could become pregnant - because pregnancies are innately dangerous. Modern medicine is awesome. That's why our pregnancies are more survivable now. They didn't used to be, OK, right? And likewise for our births and our postpartum recoveries. You know, nowadays, modern gynecology is so very, very good at serving that purpose of keeping more biologically female bodies and their offspring alive that sexism - maybe it's worn out its welcome.

MOSLEY: That's so interesting when you say sexism has worn out its welcome. More generally, there's so much that we learn from this book about how the female body has driven evolution over the millions of years. But what do you want readers to take away from this book?

BOHANNON: We all live in these bodies, you know? Whether you're male or female or any of the many ways a person could be intersex, we live in these bodies, right? And they come from somewhere, right? They actually come from millions and millions of years of evolution. We are just this little dot on the line at the very end of something that started a very long time ago. And it can feel - because our bodies are weird, because our bodies are complicated, because our bodies are problematic, you know, it can feel like you're at sea sometimes, living in these things, right? So I find it very satisfying to have some window into where they came from.

For me, it gives me new ways of talking about my experience because we're all the best authorities on what it's like to live in our bodies. No one knows better than you what it's been like to live in that body of yours from when you were born. That's your experience, right? That's your authority. But it is absolutely true that some of those experiences can be hard to describe. Some of those experiences can be hard to kind of situate in that larger body of knowledge of where humanity comes from, you know what I mean? And so I would hope that reading this book would give a reader new ways of thinking about his or her or their bodies, new ways of saying, this is where this comes from or, wait, I thought everyone knew this, but it turns out we don't know this - right? - that it gives us new language.

MOSLEY: Cat Bohannon, thank you so much for this conversation and this book.

BOHANNON: Thank you.

MOSLEY: Cat Bohannon - author of the new book "Eve: How The Female Body Drove 200 Million Years Of Human Evolution." On the next FRESH AIR, growing up in a devout Rastafari family in Jamaica, we talk with poet Safiya Sinclair, author of the new memoir "How To Say Babylon." Her father, a reggae singer, ruled the home, and everyone who wasn't Rasta was considered heathen. A turning point for Sinclair's life was when she cut off her dreadlocks. I hope you can join us.

To keep up with what's on the show and to get highlights of our interviews, follow us on Instagram @nprfreshair. FRESH AIR's executive producer is Danny Miller. Our senior producer today is Sam Briger. Our technical director and engineer is Audrey Bentham. Our interviews and reviews are produced and edited by Amy Salit, Phyllis Myers, Roberta Shorrock, Lauren Krenzel, Heidi Saman, Ann Marie Baldonado, Therese Madden, Thea Chaloner and Susan Nyakundi. Our digital media producer is Molly Seavy-Nesper. Seth Kelley directed today's show. For Terry Gross, I'm Tonya Mosley.

(SOUNDBITE OF SONG, "COMING IN FROM THE COLD")

BOB MARLEY AND THE WAILERS: (Singing) In this life, in your life, in your life, it is a sweet life. We're coming in from the cold. We're coming in, we're coming in, we're coming in, we're coming in, we're coming in , we're coming in, we're coming in, we're coming in We're coming in from the cold. It's you, it's you, it's you I'm talking to. Well, you, you, you I'm talking to now. Why do you look so sad?

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