Is Gynecology the Best Innovation Ever?

Hey there, it’s Stephen Dubner. This is the time of year we share with you some of the other shows we’ve been making at the Freakonomics Radio Network. Today: the show that, around here, we call PIMA; full name: People I (Mostly) Admire. It is an interview show hosted by my Freakonomics friend and co-author Steve Levitt, who is an economist at the University of Chicago. The episode you’re about to hear is a fascinating and wonderfully weird conversation with Cat Bohannan, an evolution researcher and the author of a new book called Eve: How the Female Body Drove 200 Million Years of Human Evolution. My guess is that after hearing this episode, you will want to go right to your podcast app and follow People I (Mostly) Admire … so if you want to do that now, I’ll give you a second …

Okay, nice job. One more thing: in this episode of PIMA, there is a goodly amount of frank conversation about various sexual and reproductive topics; if that is a problem in your household, you might want to hit the pause button. And here now is Steve Levitt with a special episode of People I (Mostly) Admire.

*      *      *

My guest today, Cat Bohannan, describes herself as a “researcher, scholar, author, and freak.” She’s written a book called Eve: How the Female Body Drove 200 Million Years of Human Evolution.

Cat BOHANNON: We are by no means the perfect model of a success story. If you dropped a Martian down, they wouldn’t be like, “That’s the guy.”   We were by no means the top of the food chain. And we were not necessarily even the most clever either. Apes are really clever. We’re just another ape.

Welcome to a special episode of People I (Mostly) Admire, with Steve Levitt.

I did not expect to like this book. I’m generally just not that interested in things that happened 200 million years ago, or even 10,000 years ago. I tend to be much more excited by modern events. But in chapter after chapter, Cat Bohannon offers such a fresh and surprising perspective that I couldn’t put the book down. And over and over, I found myself bringing up these stories in conversation. Are her hypotheses right? I have no idea. You’ll have to form your own opinions on that. But one thing I’m pretty confident about, you will not listen to Cat Bohannon and say she’s boring.

*      *      *

LEVITT: I have to confess, I wasn’t familiar with your work. The first description I found about you mentioned your Ph.D. in evolution of narrative and cognition. And of course, I didn’t know what that meant. And then it mentioned that you’d published a wide range of essays and poems. And I’ve got nothing against poets. I just have no idea what I’d talk to a poet about. And it said you’d written a book about the female body. That was the sum of everything I knew when I opened your book — that it was a book by a poet about the female body. And can I honestly say, rarely have I been caught so off-guard by a book because right from the beginning, it’s clear that you have deep knowledge about an enormous range of scientific subjects. And this isn’t just a repackaging of the standard popular-science stories. On subject after subject that I thought I knew something about, you brought forth facts and ideas that were totally new to me, that were fascinating, and it changed my view of the world. And I don’t think as a writer, you could have hoped to do anything more than that.

BOHANNON: Thank you. I’m glad I pulled it off. It wasn’t easy, but I did the best that I could. The book used to be longer. My editors did a heroic job of helping me trim it down. I cut out a lot of jokes because not all my jokes land, but also they were worried about the tone. They wanted to make sure I seemed like a serious person.

LEVITT: How long did it take you to write the book? It seems like a book that took a big chunk of a life to write.

BOHANNON: I think that’s the right way to say it. We got the book deal back in 2012. It was the exact same month, actually — October, 2012 — when I was supposed to be studying for and passing my quals exams for my Ph.D. at Columbia. And for people who’ve never passed quals exams, that is hard. But then, of course, I had a whole decade to both finish the Ph.D. and do my research for this book and write it up. And I also had a couple of kids and they’re still alive, amazingly. I had a life, and this book was running deeply in and alongside that life.

LEVITT: It probably makes sense for you to give the two-minute version of what the book is about more broadly.

BOHANNON: The book is called Eve: How the Female Body Drove 200 Million Years of Human Evolution. So that’s going to be the milk that makes us mammals, the womb and placenta that makes us placental, eutherians. It’s going to be the primate sensory array, and it’s going to be the tool use and the big brains that distinguish us as hominins and as humans. And at each step of that journey, I dig into the scientific literature across a number of different fields to say, Okay, where did this thing come from? Is there something specific and interesting and useful about it from what we’ve learned about the biology of sex differences? Is there a female story here, in other words? And how does that story continue to influence our lives today? I try and really get at: what have we been getting wrong? And where can we be getting it better? How could we make it right?

LEVITT: Okay, so one of your first chapters is on the subject of milk, mother’s milk. And I’ve got a lot of kids, I’ve been around a lot of breastfeeding, and what seems totally obvious to me, and I think to everyone, is that the main point of breastfeeding is to get calories into the baby. But you argue that story is far more interesting and complex. Could you explain what the true evolution of mother’s milk was?

BOHANNON: Milk starts before we even give birth to live young. We’re still laying eggs when we start sweating milk out of these furry milk patches along our abdomen.

LEVITT: And when you say “we,” we’re talking about, like, a squirrel-like creature or something like that, right? 

BOHANNON: We’re talking about our ancient, ancient proto-mammalian ancestors that are still laying eggs, that are still crawling around on their bellies under the feet of dinosaurs, digging little damp burrows and having their pups, but their pups are hatching from eggs. But even though they hatch from eggs, they are licking milk off our bodies. And one of the most useful things about it — well, first is that it controls where you get your water. Because milk is mostly water. Land animals really need water. And once your bodies are big enough that you can’t get it just by drinking droplets off of a burrow wall or absorbing it through your skin the way some earthworms and insects still do, now you have to drink water. Well, water is laden with bacteria, and if you have to leave the burrow, you might get eaten on your way to the water. So having milk come out of mom solves a lot of problems for newborns. It controls infection levels. It gives you a little bit of the mom’s immune system. It gives you a usefully controlled way of getting water into your body, kick-starting your immune system, and then as an add-on perk, it gives you some calories and other stuff. But interestingly, especially for human beings today, what it really gives you is prebiotics. So, probiotics you’ve heard of. You get it in yogurt. But prebiotics are what the bacteria in your guts need to survive and thrive. So you’re just up s*** creek without a paddle if you don’t have prebiotics with your probiotics. Okay, so there’s a lot of special milk sugars that are effectively prebiotics in human breast milk, and they’re not actually digestible by the baby. They’re for the gut bugs in that baby’s intestines. It helps the right kind of bugs grow and help that baby digest the milk. And the interesting thing about human bodies and human milk is that we have some of the most dense and diverse of these sorts of milk sugars of any primate. And it’s because we’re urban. It’s because we have this history of getting infected a lot, and our human milk evolved to compensate, to help our newborns fight all of these new infections that they have, living the lifestyles that we do.

LEVITT: What also was surprising to me was the deep confusion in more modern history about mother’s milk, and in particular colostrum, the first, really thick milk that comes out right after a baby is born. There was some point in time where a supposed expert’s belief was that you shouldn’t give colostrum to babies, but rather you should have it sucked up by young wolves?

BOHANNON: I know! Because, you know, you have all of these nearly moral attributes assigned to mature human milk — that it is white, that it is pure, that it is the grace of God given through your boob. And then the early stuff that comes out, the colostrum, this is thick and yellow and a little bit sticky and looks a little bit like pus. So it’s not a reassuring thing to see coming out of your own boob if you happen to have them. And the idea is like, well, do I give this to my baby? It’s the only thing that’s coming out. And there was a time that they thought maybe you shouldn’t. Maybe you pass the kid off to a wet nurse or a goat or, I don’t know, anything but the mom, who should somehow get this stuff out of her boobs. Now, Metlinger recommended — he wrote one of the first pediatric textbooks in Europe many hundreds of years ago — and he recommended, for some reason, that every new mother find a young wolf to suck at her boob. Just find one! Just find a wolf pup — which I’m sure the wolf mom would be fine with — and then just stick it on your boob, which definitely would not go badly in any way, and just have the pup suckle it out of there. And of course Metlinger makes no comment about how wolf pups eat regurgitated meat and may well chew on your boobs, so this is definitely not a good idea. But no, colostrum is super, super good for your baby, actually. It primes that kid’s intestines, and helps prime that kid’s immune system.

LEVITT: So people always laugh at me when I admit this, but with every one of my kids, I tried repeatedly, when they were babies, to get them to latch on to my breast. I partially wanted to see what it would feel like, and I was also interested in the baby’s reaction, but not one of them would ever latch on to me. Somehow my nipple was completely repulsive to them. So I was amazed and surprised to read in your book that not only do babies latch on to some men’s breasts, but that male breasts can actually sometimes produce milk.

BOHANNON: Oh, absolutely. Many male nipples can produce milk — biologically male nipples. One of the most interesting things that I learned when I was working on the book was that trans women — so, biologically male people, so people with a Y chromosome who identify as women and who want to breastfeed a new baby that they themselves have not given birth to — take the same medical protocol as cisgender women with two X chromosomes who want to breastfeed a child that they themselves did not give birth to, whether through a surrogate or whether a different adoption route — that the series of basically pills that you take over time, the same set of hormones, are given to you whether or not you have a Y chromosome. And the milk that these trans women produce is biologically identical to the milk that a body with two X chromosomes will make, given the same protocol. Now, they won’t make colostrum because it seems that the placenta is somehow involved in triggering the production of colostrum. And obviously if you don’t have a uterus, well, you’re not having a placenta. But it’s not right to say that the male nipple is vestigial. It’s more like: we’re freaking mammals. So that means we are ready to go with the right hormonal signal to start making milk. We’re just hardwired for this. So why do males still have nipples? Probably because in the developmental sequence in the womb, you might mess up your torso build by not having a nipple — we don’t know exactly what controls that — but also because it’s just so fundamental to what mammals are, that it’d be weird if men didn’t have them.

LEVITT: There’s so many arguments you make in the book that sound completely absurd to me when you first make them, but that actually seem plausible once you’ve fully stated your case. And one of those related to mother’s milk is that you argue wet nurses played a critical role in the viability of early cities, and the resulting population explosion. Do you want to explain the logic behind that?

BOHANNON: In many ways it’s a thought experiment, because populations are complex systems. There are many factors that influence population growth. But the thing I always found weird when we talk about ancient cities, and we talk about population growth, is how often we fail to remember basic human reproduction — that these are the bodies that make the babies. And to grow a population, you have to literally grow it, right? You have to actually make the damn things, and then keep them alive. It’s a numbers game. So here’s the thing: breastfeeding is an ovulation suppressor. In other words, it’s an imperfect kind of birth control. Now, imperfect is a really key word here, right? As anybody who’s been breastfeeding and then got knocked up will happily tell you — please do use condoms, ladies, if you’re having heterosexual sex and breastfeeding — anyway, when you have a wet nursing scenario, that means that you’re giving your baby to somebody else to nurse the kid sooner than you would complete nursing on your own. The ovulation control starts to get a little wobbly as the kid takes in food and isn’t nursing as often. But in a wet-nursing scenario, your ovaries are going to come online sooner than they would otherwise. That means you’re going to be having more babies if you’re having someone else nurse your kid. Okay, that all makes perfect sense. But you’re like, “Oh, but wait, the wet nurse, they’re not having kids, so whatever.” Except “imperfect control,” which means she may well get pregnant and give birth. Maybe not quite as often as she would otherwise, but in general, for every woman and wet nurse, you’re still ending up with more babies between the two of them than you would have, had both of them simply nursed their own kids. If you have a huge class of women doing this in an ancient urban environment, well, it’s not hard to imagine that you’re going to end up with a lot of babies fairly quickly. This is a thought experiment. Of course, you’re still going to have early infant mortality. Of course, there’s going to be disease. Of course, many things will blunt that growth. But it is true that in the same era, the golden city of Jerusalem, this is King David — that city’s population was only about 2,500, something like that. And Babylon is 60,000, okay? Babylon has a practice of wet nurses, and culturally speaking, the ancient Hebrew folk in Jerusalem nurse their own kids. And that’s the thing, when you put the female body back in the picture, it changes how you think about the stories we tell of where we come from. As soon as you think about the mechanics of human reproduction, then there’s stuff that we’ve been missing.

Coming up after the break:

BOHANNON: The human reproductive system is a flaming garbage pile. It’s terrible, the way that we do this. 

More of Steve Levitt’s conversation with Cat Bohannon, in this special episode of People I (Mostly) Admire. 

*      *      *

LEVITT: Alright, here’s another mechanical argument you make that I had not at all expected. The question is why women have a period. I could have come up with a variety of theories, but I absolutely never would have gotten to the explanation that you offer.

BOHANNON: And indeed scientists and anthropologists over decades and decades, probably centuries really, have been trying to come up with reasons for it.

LEVITT: And the argument against having a period is that it’s super costly in terms of blood and nutrition and health. It seems wasteful to have a period from an economic perspective.

BOHANNON: Oh, absolutely. Not to mention the raw inconvenience. So, the real trick about our estrous cycles, our menstrual cycles, is that we start building up the lining of our uterus before our body even gets a signal that a fertilized egg is coming down the tube. So it’s not so much that we shed it externally versus absorb it internally; the real trick is when we start building it. And we start building it as soon as possible. And the other species that do this all have one trait in common: we have incredibly invasive placentas. It actually penetrates the mother’s bloodstream. You have these blood vessels which are interwound with one another. Other species, the placenta is more shallow, easier to keep a safe barrier between the mother’s body and the placenta and subsequently the fetal body. So the reason we get periods the way we do, the best argument going, is that we have to. Having a deeply invasive placenta is a s*** show. It’s dangerous, okay? It means that you have to have more of a buffer to try and accommodate such a pregnancy, so that it won’t kill the mom. The human reproductive system is a flaming garbage pile. It’s terrible, the way that we do this. Human pregnancies are longer and more dangerous, more prone to complications, and generally just more difficult than they are for most other primates. We suck at this. It’s simply so costly to build our giant babies with their hugely invasive placentas that it affects us all along the chain of female development, from how the female immune system works, from how our placenta is built, and yes, unfortunately, the fact that we get periods the way we do.

LEVITT: People have this romantic idea of the fetus growing inside the mother, and this wonderful symbiotic relationship, but the truth is more like a war. Can you describe the true relationship between the fetus and the mother, as opposed to the idealized ones that we have in our mind?

BOHANNON: I love my children. I love them very much. I’m very glad that they exist, and I’m very happy to never choose to be pregnant again. There’s such a thing as maternal fetal competition. If you think of the uterus as an environment, the placenta is long evolved to get as many resources as it can because it has this window of time to accomplish this arguably very difficult process of development. You have to build actual bones inside a body. It’s not easy. So you want to get as many resources as you can. Meanwhile, the mother has long evolved to survive, especially in mammals, where mom’s job doesn’t just end when she gives birth. So that means that in the space of the womb, over the course of a pregnancy, you have effectively two competing agents. One trying to survive and not give too much, and the other trying to get as much as it can. And so what you really have is a kind of trench warfare, where both sides are just holding their line as best they can, and a successful pregnancy is a stalemate that lasts, well, roughly nine months, where neither side wins too much — otherwise one or both will die or be crippled by it. And so, this is a common idea in evolutionary biology. It’s a common idea in biology. It’s not a common idea in the public, and it’s not hard to see why — because we love our kids, and that’s not how we want to think about our kids. And pregnancy’s hard enough. You definitely don’t want to think about that while you’re pregnant. “This thing is trying to kill me,” even though somehow intuitively in the back of your mind, you know it’s trying to kill you.

LEVITT: If you ask people’s opinion about the most important discoveries that humankind has made, common answers might be harnessing fire, agriculture, the advent of language, but you give a different answer — one that sounds completely crazy to me — and that’s gynecology? How can gynecology be our most important human invention?

BOHANNON: You have to remember that tool use is all about the study of behavior. The only reason that stone axe matters is because that person is thinking about the relationship between this object, its user, and its environment. Tool use is all about manipulating something in your environment to overcome some inherent problem. And so that means that when you’re thinking about, okay, what was our most important innovation in our ancestral line? Well, what were our biggest problems? In evolutionary biology, there’s something called a hard selection. That’s when you have problems with your reproduction because evolution, of course, works by generations building over time, literally making babies, having them survive to have their own babies, and maybe produce more bodies that have this trait that your body has. Well, if you have something that messes up your reproduction, if it’s hard for you to make a baby, then your line is probably headed for extinction. If human pregnancies are the absolute s***show that they are that is hard selection. That is our biggest problem. A chimp mom — chimpanzee, one of the animals that we are most closely related to, both obviously and genetically — a chimp mom’s labor is about 40 minutes. A first-time human mom is about 12 to 16 hours. Can be longer. Mine was. Okay? And that’s before we even try to start squeezing out the actual giant headed babies that our species likes to make. It’s also true that our pregnancies are longer than you would expect for an animal our size. And it turns out, the threshold for when we give birth is not necessarily how big the head gets, to get out the small lemon-sized hole, which as we know is problematic. No, it’s actually a metabolic threshold. At what point would building this body any further actually be deleterious to the mother’s body because it’s simply too costly to keep doing it? In other words, we give birth, we go into labor when we do, typically at full term, because doing it any longer would kill us.

LEVITT: Yeah, marginal cost becomes greater than marginal benefit. It’s interesting how biology and economics are basically the same thing.

BOHANNON: Yeah, exactly. So if it’s the case that you end up with a lot of moms that are crippled for life, that die in the process, that offspring die in the process — well, at some point, and generally we seem to think this happened around Lucy, around the australopithecines — around 4 million years ago, she had a midwife. Lucy had a freakin’ midwife. But it isn’t just the moment of giving birth that matters for the advent of gynecology, because there’s a long ramp of reproductive history that comes before, and a long tail of a woman living in a female body that comes after. So even before we’re anything like women, when we’re really just furry, little, very ape-like creatures just walking around, we’re helping each other give birth, and we’re manipulating our reproductive strategies. In other words, the most important thing we ever did was get our hands on the levers of reproduction to overcome our most basic problem, which is that we suck at making babies. We should be like the giant panda. We should be a curiosity in somebody else’s zoo. We should never have gotten to eight billion people in the world. But we did. And the only way we did, to be honest, is by building societies that could support the kind of interdependence that helped females give birth in ways that didn’t kill them and cripple them.

LEVITT: How do we know that Lucy had midwives?

BOHANNON: The reason we assume Lucy had a midwife is that she had the so-called obstetric dilemma, which is to say she made big babies and her pelvic opening was small. Her offspring had to do that weird rotating thing that ours do, where the head comes into the birth canal and then they have to rotate to get the damn clavicles out. And it’s not hard to get stuck. So if you have the obstetric dilemma, you have this obvious need to have someone help you get through that thing.

LEVITT: A study came out really recently in the journal Science that really reinforces the importance of what you’re talking about. The claim that these authors made was that the population of human ancestors, it crashed around 800- or 900,000 years ago. And they estimate that there were only 1,280 breeding individuals still alive in the world. Our human ancestors were that close to extinction that we — all of us today — came from those 1,280 breeding individuals who had been part of a population that was, I think 100 times bigger not that long before.

BOHANNON: There is a big debate in the field about whether this “population bottleneck” — that’s what it’s called — whether that happens because of a massive population collapse, some kind of horrific event that’s global, that just kills a lot of us off. It could be infection. It could be climate change. It could be volcanoes exploding. Or whether it’s actually “founder’s effects,” wherein you have these small breeding groups that form essentially a reproductive island in a new environment, only breeding with themselves, build up enough of a population, and migrate again. Because that also naturally shrinks down your genetic diversity. So I got to go read that paper. It sounds really cool. Going to do it.

LEVITT: We’re so dominant as a species these days, it’s really difficult to remember that this wasn’t inevitable. At least it doesn’t appear to be biologically preordained that we were the best and we were going to rule the globe. We were incredibly marginal for almost all of our existence. Is that right?

BOHANNON: Absolutely. We are by no means the perfect model of a success story, once you get a few million years back. Even 300,000 years back at the dawn of our species, if you dropped a Martian down, they wouldn’t be like, “That’s the guy. That’s the city builder right there. That’s the one.” No, absolutely not. For most of our hominin history, we were prey species. We were by no means the top of the food chain. And we were not necessarily even the most clever for most of it either. Apes are really clever. We’re just another ape. There are a number of different things that came together in our body plan, in our societies, in our cognitive shifts that make us more of a success story. But it’s always that behavioral stuff, that collaboration, that gets us where we are. And the most important thing we had to collaborate on for a good long time was we suck at making babies. And then when our babies are born, they’re really useless. They can’t even hold up their own damn heads, right? This is very obviously the big deal that we need to get past in order to survive and thrive.

You’re listening to a special episode of People I (Mostly) Admire with Steve Levitt and his guest Cat Bohannon. After the break, they’ll discuss whether our ancestral societies were patriarchal, matriarchal — or both.

*      *      *

I want to finish our conversation by talking about what strikes me as one of the most radical and potentially important ideas in Cat Bohannon’s book.

LEVITT: Now virtually every modern society, every society we know, is patriarchal. Men have much of the power. But you argue that there are clues in the human body that suggest that for much of our evolution, human society must have been matriarchal. Can you explain how you come to those conclusions?

BOHANNON: If you look at chimp society, female bonds are not very tight. In that arguably patriarchal model of a super-social ape, when a female gives birth, she usually goes on a “maternity leave.” She leaves the troop to give birth and hesitates to come back with the newborn and is very careful, in those initial days, who she introduces her newborn to. Why? The other females may kill the thing and eat it in front of her. That’s actually a thing in chimp society. So are you going to let another female help you give birth? In that society, that’s not a given at all. Now, if you look over to the bonobos, you may have a better chance. They’re not chimpanzees, but they are very closely related, and we’re equally genetically related to them as we are to the chimpanzee. They are a matriarchal society, but a free-love society. Little too free love. They’d have sex with everybody. We won’t get into it. But anyway, so there they are. They have very tight female bonds. You don’t mess with the females and you don’t mess with the kids because if you do, then an entire gang of closely bonded females are going to chase you out of the troop. There is this one male bonobo who started acting up — getting a little handsy, as it were, with one of the females — and there’s this amazing story from a primatologist where a gang of females violently chased him off. And they found him later. Luckily, he kept his penis, it was a close call, but he was missing a toe. I don’t know if I want to live in that kind of society. But it is true that in that society, it’s safer to give birth. No one hesitates to introduce their newborns to the group, because there isn’t a lot of infanticide. There isn’t a lot of female-to-female violent competition that isn’t quickly resolved. And those are the sort of conditions that you would need for an advent of human-type gynecology, particularly in midwifery. You’re going to need tight female bonds and deep trust between the females of the group because this is a vulnerable moment and our offspring are vulnerable. So you need to not have a threat of infanticide from an alpha female you don’t get along with happening in the middle of labor. You need to not have to go hide when you give birth, basically.

LEVITT: So you believe for us to have succeeded, gynecology was really important. And you think that gynecology would have been unlikely to have emerged unless we had matriarchal societies. That’s one line of argument. What can we learn from the body? I know some primates have huge testicles, and some have tiny ones. Is there evidence in the human body that also supports this idea that humans might have been matriarchal?

BOHANNON: Yeah, so it sounds like you read the love chapter, where I do indeed get into it. And I talk a surprising amount about penises for a book about the evolution of the female body. But because the penis and the vagina co-evolve, naturally we’re going to have to talk about dong. There are a number of different places to look for what our ancient mating strategies might have been. Now, it’s tricky with matriarchal versus patriarchal because you can have various mating strategies and various power strategies. But for the mating strategies that we have, there’s always this question: Was it like King Solomon and his many wives? Is that the ancient ancestral state of human mating? Was it more like chimps, where we just had sex with everybody? It was just like a weird orgy all the damn time? Or was it more like monogamy? Like the later parts of the Bible, where you have the one man and the one woman and they do the thing and then they have the babies, they raise the babies, and that’s the model of how we mate? When you look at other primates, there are signs in their bodies for the different mating strategies that they have because mating strategies tend to reward certain body types and vice versa. So, testicles. Very large balls in primates usually indicate a lot of male competition. So that’s not a good model for either harems — because presumably if you have your harem, you’re just occasionally defending it from interlopers. You’re mostly the guy having the sex. And it’s not a very good model for monogamy either, because again, the idea is you’re not competing as much for the right to have sex with whatever ancestrally counts as your wife. So if you have big balls — just real, honking testicles — it’s probably because you have to make a lot of sperm, because your sperm is in competition with other guys’ sperm, potentially even in the same damn vagina you recently had sex in. So, gorillas: big bodies, tiny little balls, like peanuts. Chimps, very large testicles. Not very large penises, actually, but very large testicles. And humans have medium sized balls — kind of Goldilocks, not too big, not too little, given our body size. That’s a good indication that we probably didn’t have harems and we probably weren’t, at least at some point in our ancestral line, super, super competitive for mates. There are other signs too. So, male gorillas have huge bodies, and they are massively larger than the females. In the female and male human, what’s interesting is we have a much smaller size difference. We’re actually pretty similarly sized, and that isn’t something you would expect to see in a society with a lot of male competition. So again, that’s a count against the harems. That’s a count against super promiscuity. It’s a good argument for monogamy.

LEVITT: If it’s right that human society used to be matriarchal, and now it’s patriarchal, somewhere along the way it flipped. What do you think the mechanism was that took us from matriarchy to patriarchy?

BOHANNON: First let me clarify and say, I don’t know when those possible matriarchal societies occurred in our ancestral line. It may well have been before we had human bodies. We can’t pinpoint an exact moment when that flip happened. And we also, importantly, don’t know how many times it flipped back, or flipped halfway, or what have you. What humans are known for is behavioral innovation. But one of the ways it could have happened is something that we actually see in some matriarchal baboons. The males are still big, they’re still violent. But if you make friends with a female and her offspring and you do generous things with the offspring — you give it extra food, you play with it, you protect it — then you may have a leg up in that society versus guys that aren’t friends with any of the kids. You start to establish relationships with those females, and you might get more sex, which is a perk, because then more of those offspring become yours. But imagine then, if that starts to become exclusive. Imagine that becomes a model of relations in a society wherein you start to have more exclusive sex with a female because, for whatever reason, she and her kids are getting more benefit from it. Maybe she has conflicts with other females, and this helps. But at some point, if it becomes such the norm that you’re having more monogamous relationships within larger societies, then that starts to become more of a problem because now males know who their kids are, and now males can inherit social status in ways that previously only females could. And so you can see how this could become problematic pretty quickly.

LEVITT: One thing that’s unusual for me reading your work is that you come with an explicitly feminist viewpoint. And in my field, economics, whatever one’s actual ideology or biases, we write as if we’re bias-free, that we’re simply purveyors of truth or data or mathematical theory. And my sense is that science writing is also very self-consciously striving for the illusion of being ideology-free. But your choice to deviate from that norm is obviously one that’s carefully thought out. What were you thinking behind that choice?

BOHANNON: Well, interestingly, my dissertation — which is mostly unrelated to the book — had none of that. It was not ideologically-driven at all. And when it came to this book, I actually tried very hard to chase down hard questions that my feminist position might not eventually agree with, particularly in the brain chapter. Oh God, I hated writing that chapter. Look, I’m a feminist, obviously. I’m sciencing in public. Any of us who do that and have a biologically female body are automatically pretty feminist. But it’s also true that, usefully, many of the things that I found did end up aligning with some of my more feminist principles. “Is it true that women are somehow innately less smart than men?” And that was not a fun question to ask. But I dug into the literature. I did the best I could. And thankfully, after ten years, I was able to say, “Seems unlikely. Seems cognitive functionality is pretty similar,” but I did go through it to do it. And likewise for the love chapter, I opened the story with how I was very nearly a prostitute. I put it in there and I use it as that frame in that chapter to say, “Okay, is this the story of womanhood? Is it true that we’ve simply always been patriarchal?” And I just looked for evidence in the body.

LEVITT: You can’t come on a podcast and say, “I was very nearly a prostitute,” and not finish the story.

BOHANNON: It is the early aughts, and I am broke as hell. And I am in a summer break from my college, and I am looking for work. I see an ad in a paper for a person to answer phones. Now, I’ve been a telemarketer. I don’t know if you noticed, but I can have a sexy voice. So I’m like, “I can do that job. All right.” And I drive in my half-broken car to the outskirts of town, where I apply for a job for the phones. And it’s only about halfway through the interview that I realize, “Oh, I’m applying to work the call-in center for an escort agency. Ah, I see.” And there’s cubicles and headsets, set up to, like, answer calls from johns. And so anyway, I’m interviewing with what I now realize is a madam to answer phones, and my head goes all over the place. And I’m like, “Well, it’s a job.” And as I’m walking out the door, she essentially offers me the job for the phones, but she’s like, “I think you’d be great as one of our girls.” And I’m like, “Well, what does that mean?” And she’s like, “Well, it would pay 200 an hour.” Nowadays, that would be quite a bit more. Remember, this is early aughts. “And you have a website, but we have drivers and we have people who arrange everything and you have a security guy outside the door and you go on dates and sometimes they want to take you on vacations. And there are a couple of guys who like to bring girls onto their yachts.” And she’s saying all this stuff very casually, of course, but she’s meaning to convince me. She’s meaning to paint a portrait of a life which could be glamorous. And I’m hearing this job, and first I’m sort of amazed that such a job exists because I am so naive. I have just gotten out of my teens. And I go home and I think about it. I even go so far as I’m all set up and I’m about to have my first date, my first gig. So I tell my boyfriend at the time what I’m going to do, and bless his heart. He’s like, “If you do this, I will break up with you” — which is a perfectly reasonable position for him to have. I’d love for there to have been some feminist revelation —  bell hooks with a halo and robe floating down to tell me what to do — but I was just in love with the guy. And so I ghosted the madam, I didn’t show up. And then my life gets a lot fancier after that — I get this scholarship, I finish my undergrad education out in the U.K., I ended up at an Ivy League school, and I go to fancy parties, and there are a lot of rich guys around. And some of the women are hired to be there, but not me. There’s no woman, cis or trans or otherwise, that isn’t affected by the simple fact that for some portion of our lives, the most economically rewarding thing we can do is put our vaginas up for rent. Every woman and non-binary person in the world is shaped by this on some level. And even though my editor actually — my Canadian editor, Anne, didn’t want me to include that story because she was worried for me —  she didn’t want that story to get out — and I’m like, how the hell can I write a book about the evolution of the female body, about the evolution of what became women’s bodies today, and not mention that I was very nearly a prostitute? Not mention how normal it is? Not mention that, of course, at some point nearly all of our lives we reckon with that? It makes you see the world a little differently. It makes you see your body a little differently. It makes you move in society in slightly altered ways with slightly altered steps, simply knowing that’s true.

At the top of the show, I made a prediction: you would not find Cat Bohannan boring. I still feel pretty good about that prediction. What I’m much less sure of is whether her original and exciting conjectures are actually correct. I generally get surprisingly few negative emails from listeners, but a notable exception is whenever I have a guest on who tries to explain the entire history of the world. I’m thinking of guests like Jared Diamond and Yuval Noah Harari. I got lots of positive feedback about those episodes, but also historians who study specific time periods or societies — they wrote me in droves criticizing the conclusions those two come to, saying they cover too much ground to get the details right. Well, few people cover more ground than Cat Bohannon in her book Eve. So I suspect our email inbox will be quite busy. I’m eager to hear what you think — whether you’re an expert in the subject matter or just someone like me, who isn’t very familiar with the topic, but loves to think about new ideas. Our email address is PIMA@freakonomics.com. That’s P-I-M-A@freakonomics.com, and we read every email that comes in.

*      *      *

Hey there, it’s Stephen Dubner again, and I hope you enjoyed this special episode of People I (Mostly) Admire. You should probably go right now and follow the show on your favorite podcast app.

*      *      *

Freakonomics Radio and People I (Mostly) Admire are produced by Stitcher and Renbud Radio. This episode was produced by Julie Kanfer and Morgan Levey, with help from Lyric Bowditch. Our staff also includes Alina Kulman, Eleanor Osborne, Elsa Hernandez, Gabriel Roth, Greg Rippin, Jasmin Klinger, Jeremy Johnston, Neal Carruth, Rebecca Lee Douglas, Sarah Lilley, and Zack Lapinski. Our music is composed by Luis Guerra. If you would like a transcript or show notes, that’s at freakonomics.com, where you can also sign up for our newsletter. As always, thank you for listening.

BOHANNON: As you walk through your life, you’re just going to throw away most of the sensory information you encounter, or else you’re going to go nuts, right? You can’t remember every freaking bit of garbage on the sidewalk, especially in New York.