Agustín Fuentes, bioanthropologist: ‘Saying that human beings are binary is a failure; it’s not biology, it’s philosophy’

Agustín Fuentes passionately recalls his summers spent in Spain witnessing the birth of La Movida, the cultural period that followed the end of the Franco dictatorship. “I remember – when I was young, in Madrid – gravitating toward Rock-Ola (a music venue), observing the changes in dress, behavior, dancing…”

He doesn’t recall this out of nostalgia. Rather, he compares it to the situation in the United States today, but in reverse. This 59-year-old Princeton University professor – born in Santa Barbara, California – explains that the U.S. is going through the opposite of what Spain experienced when it emerged from Franco’s regime. “They’re trying to curtail freedoms, to eliminate the possibilities of existence for many people. Just look at the situation of trans people. And the next step will be to eliminate gay marriage, I’m sure,” laments this academic, who is the son of the Madrid-born Hispanist Víctor Fuentes. He’s also a regular contributor to the prestigious journal Science.

His training as a biologist, zoologist and anthropologist (he even studied the macaques of Gibraltar) brought him success with the 2017 book The Creative Spark: How Imagination Made Humans Exceptional, in which he pointed out this crucial human difference from the rest of the great apes. Now, he has just published Sex is a Spectrum: The Biological Limits of the Binary with Princeton University Press. The 200 pages are bursting with biological complexities, entering into a debate that many – starting with Donald Trump – want to inflame with the use of broad brushstrokes.

Fuentes, who wants to regain Spanish citizenship for fear of the political degradation in the United States, answered questions from EL PAÍS via video call from his home office in Princeton, New Jersey.

Question. What did you want to contribute with this book?

Answer. Right now, there’s a wave of interest surrounding the topic of sex… but there’s also a lot of confusion, conflict, fear, hatred and pain. Also, unfortunately, there’s a lot of misunderstanding and ignorance about biology, especially in this context that we can call “sex biology.” There’s a lack of awareness about how diverse and varied human beings are. Everything about us is a super-complicated mix of culture and biology. We need good information so that we can get together at a basic level in this conversation.

There’s a lack of awareness about how diverse and varied human beings are

Q. You assert that sex is a biocultural issue… but many of the people reading this interview will think that sex is about biology, not culture.

A. That depends on how you define “sex.” If you’re speaking only about gametes, everyone understands that [an] egg isn’t a woman and [a] sperm isn’t a man. We have to rethink a little about what we’re talking about. Just think about our feet, which are biological traits. But at the same time, look at your foot and look at the foot of a person who has never worn shoes. The two are almost distinct: the structure of the bones, the muscles and the skin changes. When I discuss sociocultural contexts, we’re talking not only about the embodiment of culture, but the mutual exchanges between experience, perception, bones, muscles, digestive systems, vascular systems… there’s a lot of interconnection between our physical body and the world and the experiences we have. There’s always more intermingling and a bit more complexity.

Speaking of biological sex, what exactly are you talking about? Masculinity or femininity? Are you talking about genitals? Sexuality or identity? All these things are different. In English, we have the words male and female, as well as man and woman. In Spanish, we have hombre and mujer, or masculino and femenino… but we don’t say macho and hembra (the words used to describe male and female animals in Spanish, respectively) when we talk about human beings. In Spanish, when you talk about people, you say hombre and mujer, which are biocultural terms, not biological ones.

Q. You write about how the concept of “sex at birth” isn’t very rigorous, because it can mean many different things. You talk about the “three Gs.”

A. In the biological context, we’re talking about typical categorizations based on three factors: genes, gonads and genitals: the three Gs. A 3G woman would be one who has ovaries, clitoris/vagina/labia, and XX chromosomes. And a 3G man would be one who has testicles, penis/scrotum and XY chromosomes.

The importance of using 3G is the range of variation: it’s a spectrum that has standard groupings. We assume that, by looking at the genitals, you’re sure to have the other two Gs. And it’s true that they’re highly correlated, but not absolutely correlated, not 100%. We must understand, biologically, that these categories don’t contain all the variation in human beings; there’s variation beyond that. And, among the 3Gs, there are people – more than we think – in whom one of those Gs is a little different. If we use only the genitals at birth, or the chromosomes or the genes, we’re leaving out a lot of extremely relevant information.

Q. This 3G explanation doesn’t reflect the biological reality of 1% of humanity, as you state in the book, which is at least 80 million people. But if it reflects that of the 99%, so isn’t it natural for many people to say, “Well, 99% is almost binary, isn’t it?”

A. But what is binary? I’m not saying there aren’t things that are binary in human beings. Gametes are binary: sperm and eggs. But saying that human beings are binary is a failure. It limits us too much when we’re thinking about the full range of variation between human beings. A binary relationship is that of one and zero. They’re completely distinct. This concept is used in computer science, because there’s no overlap in any element: either you have a one, or you have a zero. But human beings – our bodies, our ways of being – aren’t like that. There’s nothing between men and women that makes them totally different, like one and zero, because they come from biological materials that overlap on that spectrum of variation in our bodies.

To say that we’re binary is philosophy. It’s not biology. It’s declaring oneself essentialist: there are [men and women], two types of humans. But our biology doesn’t validate that position. Yes, there are binary things in our biology, but to say that human beings come in two different types is false. And we can prove it. Genitals, hormones, brains, organs… when you understand the range of variation between our bodies, it becomes very clear that human beings don’t come in binary, but in typical sets.

Q. You argue that this binary concept emerged recently, given the obsession with categorizing men and women.

A. In ancient times, the Romans and the Greeks thought of males and females as hierarchically ranked versions of one human form, with males above females. And then, starting in the 17th century, they began to put men and women into different categories altogether – categorizing them as different types of human beings – and to look for a true binary trait between the two. But this binary thinking comes from a philosophical context, not a medical or biological one. At first, they opted for genitals… but when you look at genitals, there’s a spectrum. Of course, there are typical genitals: men have penises, women don’t. But if you look at millions of people, there’s a huge spectrum of genital development. They aren’t binary.

Then they settled on gonads: testes and ovaries. But when you really break it down, they’re not binary either, because there’s a lot of overlap. And then, finally, at the beginning of the last century, they found the 23rd chromosome: XX and XY. But there are several versions of these as well… a spectrum of impact, effect and genes. Biologically, there’s no single trait that defines human beings in a binary way. It’s a very powerful philosophical concept.

Q. Listening to you talk about the centuries-old search for a single trait that can be used to classify people, I find it similar to the current search by sports authorities to find a trait to determine who qualifies as a female athlete. At the moment, they’re using testosterone, which, obviously, isn’t a binary factor. They previously failed with chromosomes. Fortunately, we no longer force athletes to strip...

A. Here, in the United States, they’ve started with that again.

Q. We’re going back to the 19th century in many ways.

A. That’s why we need to improve these narratives. In sports, they followed the same path. Genitals: no, it doesn’t work. Then, genes: well, this also doesn’t work. There are many female athletes with XY chromosomes. Well then, hormones, testosterone… and no, this doesn’t work, either.

To say that there are only two distinct types of human beings is wrong

Q. The world of sports has become the place where we define what a woman is, or what a woman should be like. It happened to Imane Khelif at the Olympics and, before that, to Caster Semenya. There are people who say, “She can’t be a woman with that body, with that face.”

A. That’s ignorance about the range of distribution of human bodies. Look at Ilona Maher, a famous rugby player [who was harassed online for being trans]. What body does she have, right? She’s completely female, but she’s bigger than me. If you take 1,000 people – 500 women and 500 men – and line them up by height, there’ll be more men among the tallest and more women among the shortest. But there’ll still be a big mix… and that variation distribution is what’s important. People who say “that body isn’t feminine” are talking nonsense, because there’s a huge range in female bodies.

Q. There’s a clear attempt to impose one way of being a woman and one way of being a man on society. When Donald Trump signed his executive order banning trans women from competing in sports, he was surrounded by many women, but there was only one type of woman: long hair, skirts, high heels...

A. Thin, blonde...

Q. Is this an attempt to invoke science to justify a model for people? A model for society and a model for women?

A. Trump isn’t using science; all of his executive orders are a total scientific failure. Science – by pointing out the range of biological variation in human beings – shows us that there are indeed several ways to be human. And that’s the important thing. In any country, in any culture, there’s a range in bodies and sexualities, but our cultures, our governments, diminish the possibilities of expressing [ourselves] and living within that range. We’re always on an average; we’re bits and pieces of the full range of human beings. And the main thing is to at least know what the possibilities of that range are… to understand that this is what being human is all about: variation, not a standard.

Our culture is always controlling where we can express ourselves. We’re biocultural organisms: there’s always a greater range of variation than what’s culturally accepted. And that’s the difficult part. Because many people are certain that “this is a woman and this is a man.” But if they start thinking, “My cousin has a slightly different body,” they then realize that there’s greater variation. We all know people who are outside the typical categorization, be it behaviorally or biologically, of what we think women and men are.

In the US today, publishing a book about our biology is a political act

Q. Are you afraid that your book will cause you problems in your career? That your research projects will be canceled?

A. I’m part of one of the large research groups whose funding has been frozen by the National Science Foundation, even though our projects are extremely successful. The government isn’t going to support my research, but my university for now is supporting me. And the students are interested. I’m at Princeton, one of the best private universities in the world, with a lot of money. But I fear for all my colleagues at public universities. That said, whenever I leave the United States and return, I always keep in mind what’s happening. I want to have Spanish citizenship, in case I have to go live in Spain.

Q. Did you expect to have to defend your book in such a hostile context?

A. There were already a lot of problems here in the United States a long time ago, ever since I started writing the book under the first Trump administration. But it’s a bit strange to publish a popular book and then – as soon as it’s published – find that it contradicts five or six executive orders. Everything this book tells us shows that what the government is saying is false. I’ve already had several promotional events canceled. In the U.S. today, publishing a book about our biology is a political act.

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