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From KQED in San Francisco, I'm Alexis Madrigal. You know, over the last couple of decades, many of science's understandings about biology, particularly our attempts to simplify the complexities of living organisms, have fallen to empirical evidence. Brains, genetics, development, evolution, it's all more dynamic and complex than anyone could have imagined.
In a new book, Princeton biological anthropologist Augustine Fuentes brings new scientific understanding of human reproductive biology and sex variation to demolish most of the old men are from Mars, women are from Venus type thinking, along with much of so-called evolutionary psychology. He's coming up next right after this news.
Welcome to Forum. I'm Alexis Madrigal. It's probably not worth dancing around the context for today's conversation. The Trump administration has attacked the concept of gender identity and pushed hard to enshrine what it says is a more scientific view of sex difference.
This is a direct attack on transgender people, but it's also a much broader assertion of what our reproductive organs mean as human beings. It's a way of saying gonads and genitals are science and fact. Gender is Judith Butler and humanities.
In a new book, Sex is a Spectrum: The Biological Limits of the Binary, Agustin Fuentes, a Princeton biological anthropologist deeply versed in the science of human difference, provides an important corrective for our times.
Fuentes writes any effective examination of the human experience in relation to sex biology is always contingent on two things the sex biology variation in play and the specifics of the culturally structured gender system and
he calls this the quote biocultural framing and instead of separating out sex and gender uses the term increasingly used by researchers in this field which is gender sex to denote a rejection of these nature nurture type binaries
This is going to be a fascinating conversation. I've read a lot of things in this realm of research and culture, and this book is bringing something different and new to what has felt like a poisoned and difficult discourse. Welcome, Augustine. Alexis, thank you for having me.
So when you say sex is a spectrum, I kind of got into it a little bit in the intro, but how would you, what would you say that means? Well, first of all, I love the intro. That was great. You should do that every time I give a talk anywhere. So let's think about it this way. Most people tend to sort of default to this binary notion of sex. So imagine a one and a zero, right? Those are both numbers, but they're different numbers. They're a binary, a one or a zero, two different things.
That's not the way humans are. Right?
When you say male or female, you're actually talking about variations on a theme of bones, of tissues, of DNA, of chromosomes, of blood systems, of circulatory patterns, of organs. And so when we say sex is a spectrum, we're not saying males and females are the same. We're not saying there are many sexes. We're saying that these categories, male and female, are variations, ranges of different assemblages and similar assemblages of everything that makes us human.
How would you sort of apply this way of thinking to talking about human variation? Like, you know, an example you use a lot in the book is height. Right. So let's think about this. So if you take just the population of the United States, which is very large, and you measure 10th.
thousands and thousands of people, you would find that there's a sort of a range from, you know, about four foot eight to six something on average. And then if you divided that by folks who identify as male and folks who identify as female or the folks you are identifying in either way, you'd see that all of those folks overlap by about 78%.
That is, at the very highest, there's more folks that are going to be male. And at the very lowest end, there are more folks that are going to be female. But 78% of everyone overlaps in height. So if you said, you know, well, of course, we all know men, males are taller than females. But then you use just height to categorize someone as male or female. You'd be wrong 7 out of 10 times. Yeah.
There's another really important point here, though, and that's not just height. It's think of all our body systems, right? So when you're like, okay, well, males and females are different. Are kidneys different? No, there's no such thing as a male or female kidney. Now, kidneys change in your bodies as you grow, but they're not different kinds. They're not different kinds of livers or spleens or even hearts or even brains. Yeah.
The brain facts are some of the most interesting things in this book, right? Because people have spent an enormous amount of time over the last few decades trying to identify like structural, not just decades, centuries, structural differences between men's and women's brains. And yet the study that you cite in the book says that 1% of variation in human structures in the brain is explained by...
you know, the male-female binary. Yeah, so Lisa Elliott and her colleagues published an amazing large overview study called Dump the Dimorphism, which clearly demonstrates that there are, you know, there's average size differences. Different size bodies have different size brains. But really, there's one or two small structural differences. They're very minor. And if you look at
all of the morphology of the brain, only about 1% of that variation is explained by male or female, rather, in those categories. Rather, 99% of the variation is explained by inter-individual variation. And that's really important. That's not to say...
That if you just grab a 25-year-old man and a 25-year-old woman off the streets and you put them in an imaging machine, that their brains would react the same. Humans' brains react depending on how we've grown up and what our lives are like and all those kinds of things. So the brains themselves are not patterned by sex. That is, there's no male brain and female brain. But they are patterned by our individual experiences within the society in which we live in.
And that seems to me to be really the heart of this biocultural analysis, right? Like we're building on these evolved systems of biology and then we've layered over, you know,
really an enormous amount of learning, right? That's really what we're talking about, learning at every level and for every function in the body. So I think, Alexis, I would even challenge a little bit. We don't layer on, right? We grow together culturally and biologically, right? From the get-go, from when you're in your mother's body developing
Her cultural behaviors, who she's interacting with, what she's eating, all those kinds of things actually impact the way in which your body grows. And so I think it's really important, what I'm really trying to push here is that we really have to understand what do we know about the biology of bodies? And when we look at that, this sex as a spectrum idea and concept maps closer to what we know about biological variation. I mean, take the male-female thing. Not everyone fits into those categories. That's part of the regular variation that we see in our species.
I mean, you know, sometimes when people describe people who have variation in their gonads or in their genitals that falls outside of a male-female binary, people sometimes say, oh, it's a tiny percentage of the population. One of the things that you note is probably say 80 million people living on Earth right now who
who are living in that type of body. Yeah, exactly. So, I mean, that's sort of a conservative estimate of intersex individuals that have sort of a variation on that spectrum that doesn't map clearly to a male or female category. But even more importantly, within those categories of male and female, there are hundreds of millions of people who don't quite fit what they expect or the norm that that society wants or what they think is right.
My point with this book is not just about sort of small –
clusters of humans that maybe differ from the typical patterns. My book is about all of us. If we really understand what the distribution of biological variation looks like in dialogue with our cultural variation, then we're better fit, capable, or, you know, to engage with all the kinds of stuff that we see today. In the intro, you talked especially, you made some example to references why understanding of sex and gender and biology is so important right now. Yeah.
You know, in unfolding your argument, you first kind of go to the animal kingdom to point out these kind of variations, you know, worms that...
are intersex hyenas that have like ova but also a pseudo penis fishes that can like change their sex assignment as they go through their lifespan. And I thought it was really interesting because of a cultural context which you kind of note but I think that people should have at the front of their mind that
We have kind of grown up in this culture thinking like male big, female small, right? There are these things that we have placed on the animal kingdom that turn out to just not be true or at least to have tremendous variation is probably a better way of putting it.
Yeah, the variation is it. So the comparative approach, right, looking at trying to understand humans by looking at other animals is really important because to understand what's distinctive about humans, we got to know what's the stuff out there. Like, what's the world of biology and animals look like? And I don't even get into plants. Plants are fascinating and mess with everything. But anyway.
Why look at other animals? Well, the thing is that, yes, there are patterns, typical patterns in sexually reproducing organisms. But across the animal kingdom, there's lots and lots and lots and lots of ways to do that. And that doesn't mean, right, that there's lots and lots and lots and lots of ways to do sex biology in humans. No, there's this interesting pattern of variation. But different species have different patterns of variation. And the bottom line is there's not one way to
to do sex or to do biology across the animal kingdom. And I mean, if you really get back to the evolution of sex itself, right? For the first billion years or so of life or maybe a little bit less, things didn't sexually reproduce. They just copied their DNA and divided themselves. If we look at the evolution of sex, the most common hypothesis for why sex evolved at the beginning
is that we needed more variation to have a better chance of making it in the world. So at the very heart of sex is variation. What about people who look at our closer relatives, you know, the primates and they make...
Some inferences about how humans should be or are as a result of what they see, say, in gorilla or chimp or bonobo communities. Yeah, I mean, that would be a really bad mistake, right? So humans, chimpanzees, bonobos, gorillas, we're all sort of contemporary evolved organisms. And we have different evolutionary histories. All of us split, you know, 10, 12 million years ago into different lineages.
But it is amazing because we can look at our closest relatives, the great apes, right? Gorillas, chimpanzees, bonobos, orangutans. And what we can see is that the actual biological patterns vary a bit
But the behavioral patterns vary even more. That is, even in chimpanzees and bonobos that are almost identical biologically in regards to their sex biology have really, really different ways of living in the world around sex and sex roles and things like that. The bottom line.
is that the comparison with other primates or other animals just reemphasizes that there's just a lot of variation out there. And so we should actually, instead of trying to force humans into a very, very sort of cluster of two distinct kinds of things, we should ask, what is the biology? What is the culture? And what does the history tell us? Yeah, and that there's not a simple kind of determinism at play there. Yeah.
We're talking with Princeton biological anthropology professor Agustin Fuentes about his new book, Sex is a Spectrum, The Biological Limits of the Binary. We would love to hear from you. What are your questions for Agustin Fuentes? What are your reactions, sort of what you're hearing about this biocultural approach? You can give us a call. The number is 866-733-6786. That's
866-733-6786. The email, of course, is forum at kqed.org. You can find us on social media, Blue Sky, Instagram, etc. We're KQED Forum. And of course, there is the Discord that you can check out. I'm Alexis Madrigal. Stay tuned for more right after the break.
Support for Forum comes from San Francisco Opera. Experience the soaring highs and heartbreaking lows of bohemian life this summer in John Caird's beloved production of La Boheme. Puccini's most adored opera transports us into the heady bohemian world of 19th century Paris as we follow a circle of starving artists falling in and out of love, living for the moment. La Boheme runs June 3rd to 21st. Learn more at sfopera.com.
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Welcome back to Forum. Alexis Madrigal here. We're talking with Princeton Biological Anthropology Professor Agustin Fuentes about his new book, Sex is a Spectrum, The Biological Limit to the Binary. It is out today. What are your questions for Agustin Fuentes? You can give us a call. The number is 866-733-6786, forum at kqed.org. I want to talk a little bit now about our human ancestors and sort of what we can learn from them.
our evolutionary past. I want to start first by saying, asking you to talk a little bit about this field that has coalesced that calls itself evolutionary psychology, in part because there are people doing very real and serious work in that world. And then there's a lot more other people who I feel like are drawing on kind of caveman stories to talk about how modern humans should act.
Yeah. So evolutionary psychology in theory should be great. That is to think about human evolution, think about the past and to sort of use core concepts in psychology and other disciplines to recreate how our minds work to sort of how we evolved cognitively, behaviorally and things like that. So in concept, it's fantastic. And there are some really good people doing work there. But there are also some people who are taking contemporary racist, sexist
and other kinds of biases and transplanting them to the past in an attempt to justify contemporary patterns or sometimes just making assumptions that are just completely disconnected from the actual fossil and archeological evidence we have. So the field of human evolutionary studies is amazing and reconstructing behavior, psychology of the past is difficult and I think a lot of people overstep the bounds.
I mean, you have a great example of, you know, when people are found in burial situations and then sexed based on what they're buried with. Sometimes we get it wrong, right? Yeah. So, I mean, in the last decade, there's been all these things, you know, this great Viking burial with a sword. It was a guy. And then you go back and like, oh, maybe it wasn't.
I think what happens is that we assume a very sort of strict and rigid gender dichotomy in the past. And so we impose contemporary understandings of gendered relations in economic, political framings in the past. So we dig up a grave. We find a sword. We find some grave goods that look like they're associated with prestige. We take a general look at the skeleton. We're like, yeah, I mean, this, the pelvis, the skull looks pretty male. This must have been a guy.
Interestingly though, now we have proteomic that we can test the proteins and in some cases genetic from paleo DNA stuff. We're able to document that at least chromosomally they don't fit XY. They may have been XX. And so how then do we think about that? The bottom line is that we have to be very careful when talking about the past not to impose our contemporary ideas about the way the world is right now, especially when it comes to gender, politics, and power. Yeah.
One of the things you think we can learn from the past, though, is the way that we evolved to do child care. And not just child care, but care of all kinds and cooperation in human groups. At one point in the book, you write that coordinated and extensive compassion was a major element in the success of our genus.
Why can we say that but maybe not some of the other things people want to say about the past? Well, I love working in human evolution because it's just fascinating and incredible. But I also hate it because it's very frustrating in the sense that you can't, without a time machine, really go back and tell everything. So you have to take hints. You take hints from fossils, right? The bones. You take hints from the archaeology, the things that these folks or ancestors left behind.
So what we do now, and this is a convergence of massive amounts of evidence, is that over the last two million years, our lineage, the genus Homo, really excelled at cooperating and collaborating, at working together to solve all the challenges that they face. That's our sort of big superpower, if you will. And it also turns out that that collaboration and cooperation enabled us to do something really marvelous, and that is to have infants
whose brain is only about 40% developed. That means we have infants who are born who take years to be able even to walk. I mean, think about a giraffe or something like that. A giraffe out on the savanna, the mom gives birth, the giraffe drops down, 15 minutes later, it's sprinting across the savanna. Humans don't even run effectively until five or six years old.
That's generous.
When we talk about human evolution and gender roles or sex roles in reproduction, we have to recognize that humans have evolved a multi-individual reproductive system. That is, it's not just about a sperm and an egg getting together or one female, one woman gestating, right?
It's about multiple individuals caretaking for the infant when it's born, about collaboration, facilitating, taking away some of the energetic costs to mothers. And so what we really see when we talk about sex and reproduction in humans is a system that has evolved to –
displace all of the costs of reproduction across multiple individuals in the group. And that's really important because a lot of people want to say, well, males and females are totally different, right? Females have kids and males run around and hunt. And it's not that simple at all. Also, there's a line of thinking that suggests that sort of men and women pair because this is sort of an evolutionary psychology story. You know, women need a strong male partner. Men could choose multiple partners, but there was sort of value to them and pairing.
How do you read these kind of stories about why it is that...
humans have these deep and long-lasting pair bonds. I mean, that'd be a whole show in and of itself, right? I spent the last 25 years writing about this, but I think it's really important. When you see people who are like, no, there's one way to be human. It's only this way. You got to ask about like, how did they grow up? What were their experiences? That's sort of weird because anyone who's been a human for a while recognizes that there are multiple ways to have relationships. There are multiple ways to develop families. There's multiple ways to care for kids. So
But what I think people try to focus on is this monogamy package, right? Well, male and female get together, have a kid, and that's the center of human existence. So the fossil, the physiological, and the contemporary ethnographic evidence, right, studying the past and the present,
show that that's not actually that typical for humans. We do pair bond, though. We do form these incredibly tight relationships between individuals, heterosexually, homosexually, with sex, without sex. And that's fascinating. And that probably comes from this incredible capacity to collaborate and coordinate and to be together, a kind of compassion that's incredible.
So we pair bond, but the idea that monogamy or the nuclear family is the sort of natural state of being for humans, it's just not true. You know, what if someone is listening to you talk and listen to the show and they're saying, "But you know, I know a lot of men and I know a lot of women and they just seem different to me." That person would be right. So here's what we have to really recognize.
Man is not the same as male. Woman is not the same as female. If we're talking about male and female, we're talking about biological patterns. We talk about man and woman, we're talking about gender sex, we're talking about gender roles, we're talking about histories. So in any given society, yeah, it's not strange to say, well, I know a lot of men, I know a lot of women, they don't seem to be the same. There's also not strange to say, well, you know, I know a lot of women and they're really variable or I know a lot of people that don't fit into the man-women thing.
It's also not strange to say, yeah, I know that kids and 60-year-olds are pretty different.
The bottom line is because we have categories or clusters of variation, doesn't mean they're two different kinds of things. And really when we talk about men and women, we're usually talking about masculine and feminine. The whole thing is a complex bundle of biocultural stuff. And I know that's an unsatisfactory answer, but you got to step back and ask, why are you asking that question? Right? And if you were to say, man,
Are men and women really that different? And you thought about all your relations with the people who identify in those ways. Is there more overlap or more difference? And I think that's a really important question. Jeff writes in to say...
And you talk about this study, so I'm bringing it to you. NIH study observed that men's brains on average have 13% more cerebral cortex neurons than women's. This seems to represent a greater sexual dimorphism than your guest stated, 1%. So I assume, well, I'll let you answer.
So that's a really good thing. So it depends on what we're talking about. That overall size, remember, on average, those categorized as males have like 9% larger brains than females. That's about the sort of body size variation. And so that accounts for some of these larger volumes with neurons or different kinds of things. There's a huge debate. Again, I encourage people to really read Lisa Elliott and colleagues article, Dump the Dimorphism.
It does a great overview of all these studies and shows in comparison. So the bottom line is Jeff is right. There's some difference in size on average, but that doesn't correlate anything to function and the overlap in size is enormous. Let's take caller Mark in Dublin. Welcome, Mark.
Hi. Those of us in the Judeo-Christian world tend to be influenced by the biblical story of creation, which would lead one to believe that the generic sex is a male, right? Because first God created man, and then Eve came out of Adam's rib. In actuality, from an embryological point of view, all male embryos start out as women.
And in order to become a male in utero, it requires that there be certain receptors on the fertilized egg and that there's a certain surge of testosterone which causes the embryo to develop into a male.
And this is one of those really quite fascinating, interesting facts that one learns when you study embryology and biology or medical school curriculum. Hey, Mark, thank you. No, it's a great – let's bring that.
Yes, go ahead. This is fascinating, Mark, and thank you so much for bringing this up. So I'm going to challenge this a little bit. So it turns out if you look at Genesis, right, Genesis is actually written in two parts in the Christian Bible. So if you look at Genesis, there's two actual stories of Genesis, right? There's, I think, 1 through 20 and then 20, 22. So Genesis, in fact, has two stories. One,
probably the earlier one, is that God created them. So both male and female, Adam and Eve, are created at the same time from the dirt. In a second version of Genesis, which many scholars think comes a little bit later, Eve is created, Adam is created first, Adam looks around on all the animals for a mate and can't find one, and then God puts him to sleep and pulls out the rib and creates Eve. So in fact, the earliest version
the Judeo-Christian sort of framing has sort of a complexity there to Genesis. And the second thing about embryology, I think it's really important because that's still taught in a lot of intro bio classes. But it turns out through the first six weeks in humans, for example, for the first six to eight weeks of development, you're neither. You're not male or female. None of those things have developed yet. And the default is not female. In fact, you have to have a whole suite of genetic
and developmental dynamics have to turn on and interact in the right ways for you to develop towards sort of female reproductive tract or towards male reproductive tract.
So the idea that everyone is basically female, that's an old idea. And it was understandable when we knew less about embryology. But now that we know more, it turns out that no, both male and female are active developmental trajectories that have to be initiated. And because they share that same thing for the first six to eight weeks in humans, that's why you see so much overlap and variation in those developmental processes.
Does that mean there kind of is no default state? No default. The default state is human.
We're all variations on the theme of human. Now, there are typical patterns, right, that we call male and female. But there's variation, tons of variation in male and in female. And there's lots of variation that falls between those. And I think that's really, really important. There is not a default pattern. The default pattern is us. And then the developmental trajectory goes typically or atypically and shows up with humans.
Let's talk about an area that you note that does have particular difference between people, and that is pregnancy. Pregnancy and the ability to gestate a child do require quite different bodily functions and processes. How do you think that that has been incorporated into sort of like gender sex as you would think about it?
Well, I mean, that's a huge area. And I just want to be really, really clear. When I say sex is a spectrum, right, I'm not saying males and females are the same. They aren't. And I'm not saying that biological variation related to sex biology, to reproduction, doesn't matter. It does. Of course it does. It's just that it's not really two kinds of humans. But let's take those individuals with the uterus and the fallopian tubes and producing ova can get pregnant, right, and they can gestate, that is, develop ova.
with the fetus there, and then once birth happens, usually can lactate as well. And that's distinctive, right? That is only, you know, a little over half of humanity has the physiological capacity to do that. But what's really interesting is that all those with uterus and fallopian tubes and all of that, not all of them do.
get pregnant and give birth. And it turns out, and this is really fascinating and needs to be studied much more, and it has been studied a lot recently, but under the contemporary NIH rules, who knows if it still will be, is the variation that happens to women's bodies
when they undergo pregnancy, right? There's actually some substantial changes that happen between those with a uterus who have been pregnant and those who haven't. And that's actually really important to understand that variation. And so my big point here with the spectrum is not to say that, you know, females are
aren't capable of gestating and lactating, but rather to understand what does that variation look like in there and how do we understand that as a sort of pattern of human variation rather than saying all females are this way and all males are that way. Stephen writes down saying, you know, this all boils down to the particular chromosomes found in each of us, right? There's more than just XX and XY and this belief is the reason for approximately 2% of the human population
being intersex this is interesting because the way that you deal with this in the book is to basically say that there are kind of three G's right there's the genes the gonads and the genitals and they work in a sort of dynamic way to produce the sort of center of the distributions that we're talking about here right yeah I mean this is a long and complicated things let me do it really quickly okay some people want to just define them this traditional biological classification of sex
The organisms that make the large gamete, the ova, the egg, are female. And the organisms that make the small gamete, the sperm, are male. That's actually a fine classification if what you're interested is gametes, right? Getting sperm and egg together and studying the sperm and egg. If you're actually interested in organisms like whole beings and their bodies and lives and ecologies, the gametes actually don't tell you that much.
So then people are like, well, it's chromosomes. Chromosomes contain some of the instructions for developing this stuff. The problem, for example, in humans is that we're XX or XY or some variation on that. And there's a lot of variation that can have some really deleterious effects. There's other variation that doesn't have that major deleterious effect.
deleterious effects. And just because you're XX or XY, XX is what we usually say female, XY usually male, doesn't mean that all the developments, all the genes are going to turn on the same way and all of the tissues are going to develop in the same way. So you can be XX but not be typically female and you can be XY and not be typically male. In other words, there's not a one-to-one correlation. So the chromosome stuff isn't that. It's better, but it's not great and it doesn't cover all of the things that bodies and lives actually do. Yeah.
So finally, I go to 3G, which is a better biological categorization. That is, there's typical clusters of genes, a set of genes, a set of gonads, and a set of genitals. And those are typical patterns. They don't include all humans, not even close. But they allow us at least to sort of understand the entire body and reproductive dynamics rather than just talking about gametes or chromosomes, which actually don't tell us much about organisms and their daily lives, especially when we're talking about humans. Hmm.
Yeah, a couple of different listener reactions. Chris writes in to say, I say labels are used to divide people. Your side on a continuum is refreshing. I'm looking forward to hearing more from you. Another listener on Blue Sky writes, a lot of people, especially the current administration, don't know how to navigate ambiguity. And I think there is a lot of, in the current realm of biology, ambiguity.
The dominant theme is, wow, we still don't know a lot of things. I think that's been my read of the field. You know, it's like we thought we had a lot of things figured out. And now it turns out even, you know, what a gene is, for example, has a much more complex answer than anyone would have said before.
you know, some decades ago. So we are talking with Princeton biological anthropology professor Agustin Fuentes about his new book, Sex is the Spectrum, the Biological Limits of the Binary. Love to get your questions for him. The number here is 866-733-6786.
That's 866-733-6786. The email, of course, is forum at kqed.org. And you can find us on Blue Sky, on Instagram, all the other places. We're KQED Forum. I'm Alexis Madrigal. Stay tuned for more right after the break. ♪
Support for Forum comes from San Francisco Opera. Experience the soaring highs and heartbreaking lows of bohemian life this summer in John Caird's beloved production of La Boheme. Puccini's most adored opera transports us into the heady bohemian world of 19th century Paris as we follow a circle of starving artists falling in and out of love, living for the moment. La Boheme runs June 3rd to 21st. Learn more at sfopera.com.
Greetings, Boomtown. The Xfinity Wi-Fi is booming! Xfinity combines the power of internet and mobile. So we've all got lightning fast speeds at home and on the go. That's where our producers got the idea to mash our radio shows together.
Through June 23rd, new customers can get 400 megabit Xfinity Internet and get one unlimited mobile line included, all for $40 a month for one year. Visit Xfinity.com to learn more. With paperless billing and auto-pay with store bank account, restrictions apply. Xfinity Internet required. Texas fees extra. After one year, rate increases to $110 a month. After two years, regular rates apply. Actual speeds vary.
Welcome back to Forum. I'm Alexis Madrigal. We're talking with Princeton biological anthropology professor Augustine Fuentes. New book out today, Sex is a Spectrum, the Biological Limits of the Binary. Okay, Augustine, let's get to a topic that I'm sure listeners have been thinking about. Stephen writes, Augustine's description of the spectrum of human variation makes perfect sense, but how do trans people fit into this? That is the sense they have of being in the incorrect body.
So, I mean, this is, I think, a really important topic. I think discussing intersex, trans, and a wide range of variation in human gender sex identities is a central part of today's world. And I think the attacks on intersex and trans individuals and a variety of other sexual minorities is horrendous and highly problematic.
But we've talked about everybody, right? We're talking about the species and biological variation. And so what I want to make very, very clear is that what we have to understand is that humans today are not just our biology. We are gender sexed. That is, we have gender roles, we have societal expectations, we have individual experiences of our bodies and our sexualities.
And so what we have to recognize is that in a given cultural context in the world, right, as we grow up, as we mature, we as individuals, right, don't always fit. We don't feel that we fit necessarily and we don't fit in our own senses of the bodily self. Maybe our body doesn't feel right or our connection with expectations.
Expectations that people put on us about gender and about sexuality because of our body doesn't feel right. And it doesn't feel right because there's multiple successful ways to be human.
Sexual identity, identity and connection to body and gender roles is highly variable even within classic traditional gender roles. Think about the range of masculinity and femininity and think about how everyone you know, right, maps to different areas in that. That's not something that comes from your genes, right? This is something that comes from the biocultural experience of growing up as a human. Yeah.
I mean, as a biological anthropologist too, you know, studying people across cultures, across time, what kind of perspectives does that give you on this topic?
I think it's really important to point out that this idea of a sort of heterosexual, masculine associated with particular male bodies, feminine associated with female bodies and a real division of say gender roles or social roles in context, we know that that is not consistent across time even today. And in the deep past, it doesn't look – clearly there were gender roles or some patterns but they weren't the same as they are today.
What does that tell us? That tells us that this notion, let's take here in the US, this big fight about gender identity and things like that. The idea that there's a clear, let's say, binary gender reality is simply wrong. That is refuted by the ethnographic evidence, all the data on human populations today and in the recent past. And then we look at the entirety of the human experience and we see that variation and different ways of successfully doing human is the norm. That's not to say
That is not to say that there aren't some typical patterns that we see across many societies. But the power, right, of political culture and economic imposition over the last few centuries has had a huge impact on reducing the variation and variety of ways of being human because of the sort of power of politics and economics that have been imposed. Let's bring in Owen in Sacramento. Welcome, Owen.
Hi, Dr. Fuentes. I really appreciate the research that you've done and understand what you're pointing out. Halifax is a spectrum and this is very fluid and these assumptions can be problematic.
I'm wondering what are the implications of your research on how we best care for young people? So I think a lot of folks, especially recently, like you mentioned, have been concerned about creating confusion, causing children to feel like they need to explore more than they may actually need to. It seems to make sense that creating more clear structure can lead them to having more comfort and a more...
thriving more at that stage of life, but how are you seeing it? What are the implications of your research on how we care for children?
Thanks for that, Owen. Oh man, Owen, thank you. That's a really important question. Let me just clarify one thing. It's really important when you hear the word fluid and when I say spectrum, it doesn't mean that individuals biology is changing across their lifetimes necessarily, right? I think that's really important to point out. But when it comes to kids, so developing, I think we have messed up kids a lot.
Recently, I think it's very hard to be a kid growing up in the world today. I think over time, things have changed a lot. But the way in which we expect children to behave or the way in which we structure it, let me give you an example that's related to this. Sports.
Think about sports. Think about where we emphasize bodily activity, running around, rough and tumble play, or even participation in things like football or soccer and baseball or basketball. We're seeing increasing sort of activity
invitation for more kids to play, but we still see those categorized as boys. We see boys sports and men's sports really heralded, really supported, and girls and women's sports not as much. And what we know but don't pay attention to is that pre-puberty, a lot of these sports, we don't need to differentiate by gender. And so we have to ask the question, what are we imposing on kids right now? But, Owen, your question probably had to do with sexual identities.
and that sort of flourishing of different kinds right now. And I think a big part of that is understanding that human sexuality is incredibly complicated.
and that it varies with individuals and even across the lifespan in some cases. And so allowing individuals a freedom, a flexibility to understand that, but recognizing that it isn't fixed always at birth and that it's acquired or changed and that people experiment. I think that's really important, but that doesn't mean that we can't understand
the diversity of ways of successfully being human. A couple of science questions here. Kay writes, "Your guest mentioned that for the first six weeks of gestation, an embryo is human but not female or male. Certain chemical reactions have to occur to create a female or male. Can you clarify what's happening during the IVF process when a doctor tells you the gender of an embryo before placing it into the uterus to grow?" So what's really amazing is the doctor is not telling you the gender of the embryo. The doctor is telling you whether or not it's XX or XY.
That is whether or not the embryo has two X chromosomes or an X and a Y chromosome. And that is predictive of a particular developmental trajectory, but not 100% so. So really what's interesting, the doctor might say gender, but it's not gender because gender is acquired, you know. And it isn't even 100% biologically characteristic because all they can tell you is what chromosome showed up and then they have to wait and see what the development is.
Yes. You know, one of the things that I think I want to draw out of what you've been saying in this hour is that, you know, in biology, there are so many variations that sometimes the variation actually becomes the norm, right? Like people say, well, okay, well, there's a small variation here. There's a small variation here. There's a small variation here, a small variation here. And it's actually those variations which become the significant thing to focus on, right? Because...
There are so many exceptions to these rules that we keep creating. Yeah, and I think understanding how biology works is really important. People tend to think, well, genes sort of structure. That's the blueprint. It's not a blueprint, right? There's not like a set of instructions to build the body. It's a dynamic collaborative across all of development. And so I think variation is really important here. When we think about how your diet affects how your long bones grow, how your femur grows, which will affect your ultimate height.
That variation is enormous, but it's dependent on who you are, where you're growing up, what you have access to, what you have access to relative to other folks. The variation in most parts of our lives is pretty substantial. And to ignore it and try to pretend that there are just sort of clear, distinct things doesn't always work. Not that there aren't things that are clear patterns.
Sue writes in, this is an interesting question. You're going to like this one, I think. My understanding is that within every male and female, there are varying degrees of testosterone and estrogen. Since these hormones are factors in determining the sex of a person, wouldn't this in itself define a spectrum in sexual identity?
I mean, the short answer is yes, but it's actually much more complicated. And a lot of my biology colleagues will yell at me if I don't make it very clear that all humans have the same hormones, right? There are no such thing as male and female hormones, right? We all have testosterone, we have estrogen, we all have progesterone and a bunch of other stuff.
But the relative levels, the frequencies of these hormones change across the lifespan with particularly post-puberty levels of testosterone, for example, on average being much higher in those that are classified as males or at least those with gonads than those classified as females or those with ovaries. So there's big fluctuations. However, amongst those with gonads, the fluctuating levels of testosterone can be as much as 300%.
And in females, testosterone receptors might function a little bit differently than they do in males because of different exposure to different levels. That's all very confusing. The punchline here is that there's no such thing as a sex hormone, but different levels and frequencies of hormones vary in some typical patterns and some atypical patterns across humans. And so studying them that way, as opposed to saying, well, testosterone is male and estrogen is female, that's just not true. Estrogen, testosterone, and progesterone are human.
I mean, just to draw one implication of what you said there, if the receptors for testosterone for females are in
different or are working in concert with other hormones in a slightly different way, a smaller amount of testosterone might lead to larger effects than would be expected in a different body. Right. And so this is when people take external testosterone that can change some of the responses. So how's your body grows up? And that's what I tried to say really early on. So as your body goes up, let's say, for example, there's no such thing as a sexed liver, right? A liver isn't male or female. Liver is a liver.
But as you grow up, what you eat, what you drink, what experiences you have in your life actually do impact your liver and the receptors for the different hormones and other things in that liver. And it turns out that gendered roles being man or woman in our society
actually experience the world slightly differently. And so those gender, those cultural patterns can actually shape your body as you grow up. So I'm not saying that there aren't these patterns of differences, but that those differences don't come from some innate biology most of the time. They come from gender sex. And of course, this extends beyond gender and sex. If you're interested in this approach, you can check out Augustine's other book, Race, Monogamy, and Other Lies They Told You, in which many of these same people
sociocultural factors are at play as well.
I mean, biology and culture, right, aren't separate for humans. And I think that's really important. That is, there is no such thing as nature and nurture because the two don't exist without one another. So as humans development, our bodies, our lives, our ideas, our ideologies, our languages, our day-to-day experiences meld with one another and make us who we are. And that's wonderful. It's super complicated and confusing, but it is wonderful. Yeah.
Yeah, it's always, you know, it's interesting. There's always a kind of form of headline that's like, such and such phenomenon in the world changes your brain. And it's like, well, yeah, because every single thing that happens in this world that you experience as a brain, as a mind, that's what's happening. That's how you know it's occurring. But it's not ultimately variable, right? There are constraints. We can't do anything or flex into anything, but
But those patterns, that comes back to what you said, we keep looking at historically typical patterns. We're like, okay, well, we understand 80% of what's going on. We'll just ignore the other 20%. And now in the world of biology, at least, it's becoming really evident that that other 20%, that's really important. Understanding the variation across the 100% of our biology is central to understanding who and how and why we are what we are.
Another listener writes, you know, I'm curious about how the guest thinks about medical research. If we focus on humans who congestate versus women who congestate, does that help women? Women's issues are so under-researched. I wonder if we say, hey, this is human research, not just women's research. More money will be spent. Or does this viewpoint erase women? Like, it's a little scary to think that women will be erased by this view.
No, that is not my position at all. And in fact, there is a huge harm done to women by the medical establishment by under focus on them for decades and by continued discriminatory focus. So increased research on women and women's issues and on females and on those humans with uteri as an expanded category, I think is really, really important. But
What we have to make sure we do when we're studying human health is not always assume that we have two kinds of humans, a man and a woman, a male and a female, because many health issues don't map in that specific way. And so if we divide our samples, our study populations, always into male and always into female at the beginning,
we might be missing, and there's good evidence this is true for a lot of conditions, we might be missing some important human variation and potential patterns. So I'm not saying reduce study on women. No, please expand it because it's very, women's issues are incredibly diverse and varied and very, very understudied. But we have to understand that male and female are not two different kinds of human. And that it's that very type of thinking that the,
that male mice could stand in for, for everybody, everything, uh, every mammal, um, is what got us into a lot of this trouble in the first place, right? It was sort of like separating people out and saying, this one is typical and then women are a deviation or female mice are a deviation from the male mouse standard. Yeah.
Yeah. And this whole idea that males are less variable than females. Females are really confusing. So we'll just study males and sort of extrapolate out. That was a long held medical assertion. It's completely wrong, but it's important and it has led to a lot of harm to women. Yeah.
Casey over on the Discord writes, "Sex, like gender, is not a clean binary. There's this idea that social processes like gender are too squishy for good science, but then those same people don't have a good understanding of how complex sex is. Irksome to say the least, studying puberty was eye-opening for me in this regard. It's like the perfect subject for thinking about how both gender and sex contribute to what we see in adolescence. My wife studies menopause, very similar in that regard."
That's absolutely correct. And I think it's really important. And puberty is a great place to study because it is so complicated. And I highly recommend Kate Clancy's book, Period,
about menstruation is absolutely fantastic biocultural analysis of this incredibly important and yet poorly understood by most people process. No, puberty is amazing and it's totally crazy and we've all gone through it. Like all of us humans who've gone through puberty, we know that it's not clear cut. We know that it's really complicated and yet folks still want us to believe that there's one clear cut, one way to do this thing. Clearly there's not. Yeah.
And I also, I do think, yeah, menopause and perimenopause has also had this incredible flowering of research and discussion and...
I think the realization by many people that all kinds of perspectives have been left out of the discussion of how menopause is, what it is, how it works, the effects, etc. Yeah, no, and really aging is extremely important. And we've really understudied aging on biological systems. And part of this is that binary view. They're like, well, women stop reproducing, therefore, you know, this is what happens. That's
That's a very simplistic thing. To define women only by their reproductive capacity or not is a bad medical, bad evolutionary, and bad biological approach. So I think the understanding of the seriousness and the incredible complexity of perimenopause and menopause in humans today is a great area where they should be doing a lot more work. Last couple of comments here. One listener on Discord writes,
Think so many people are frightened by heterodoxy when you hear someone saying it's obvious there are men and women and that's it They're displaying a fear of deviating in their beliefs from what's comfortable for them very comfortable They're very uncomfortable being challenged this way and unfortunately combined today with attempts to undermine expertise science research and honest curiosity about what's new or new
Greg writes, "Please work into the discussion of the lag between science discovery by researchers and the inclusion of that research into textbooks for high school and college students. I'm tired of politicians citing 'what we learned in high school as if scientific knowledge was frozen in amber' four to six decades ago."
Both of those comments are fantastic because they reflect what we actually know about those of us who do science. So the scientific process is largely a refutation of previous stuff, right? We keep pulling hypotheses and trying to prove ourselves wrong or maybe find some support and try to get closer to good answers. And I think what most people don't understand is science is an ongoing process. So there was always complexity. There's going to be lag getting it out there. But that's why I wrote this book. Yeah.
Because there's a lot of information and people should have access to it. The book is Sex is a Spectrum, The Biological Limits of the Binary. It is out today. Princeton Biological Anthropology Professor Augustine Fuentes, thank you so much for joining us. Alexis, thank you so much for having me. Thank you to our listeners for their comments and calls as well. Thanks, y'all. I'm Alexis Madrigal. Stay tuned for another hour of Forum Ahead with Mina Kim.
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