Sex and Sensibility

23 Feb, 2025

This is a transcription of Forrest Valkai's video "Sex and Sensibility" by Whisper and organized by gpt-4o.

Introduction

Hello there! My name is Forrest Valkai, and I'm a biologist who teaches at the prestigious University of the Internet. About three years ago, I released a video on why sex and gender are different things and why neither one of them is a binary. Unfortunately, as this was my very first video essay, it was riddled with poor editing and loud table thumping, and I left out a lot of cool details and responses to common counterarguments that I would normally include in a video now. So today, I've decided to remake that video with more detailed information, new concepts, and more than one looping background track.

Overview

In this video, we're going to cover a wide range of topics and talk about a lot of different species. This is because the concept of biological sex is usually taught to new learners in a grossly oversimplified way for the sake of brevity and absorption. Now, this is no different than the way that almost any topic in biology is taught at an introductory level, but in this case more than most, that simplism can lead people to make unfair judgments about other people who fall outside of the watered-down binary model in their heads. If we want to understand sex and gender in a real and meaningful way, we're going to need to turn over a few more stones than just a couple of clinical studies in humans, so expect to hear a lot of information over the course of this video, and don't hesitate to pause, walk away, and come back for more when you're ready.

Topics Covered

In this video, we'll learn about the concept of sex from a broad lens, sexual development in humans, why sex is a spectrum rather than a binary, the concept of gender, why self-identification is a necessary part of gender identity, a little bit about sexuality, and most importantly, what all this stuff actually means in the real world, why you should care, and how to handle this information going forward. So settle in and get ready to learn some biology as we dissect the science of sex, gender, and why life is so much more interesting than you might have thought.

The Basics of Biological Sex

Humans as Animals

Let's start with the basics. Humans are animals. We are living things, and we are not plants, fungi, protists, bacteria, or archaea. We are simply animals, and we obey the same laws of nature as every other animal. I'm mentioning this right at the outset because it's shockingly controversial among new learners. Lots of people think that humans are somehow inherently special and that we have some privileged place in the world that makes us separate from all other life. We're not, and we don't.

Cells and DNA

Cells are the most fundamental units of life. They are the smallest things that we can call alive, and every living thing is made up of at least one cell. Your body is made up of tens of trillions of cells of all shapes and sizes, and they do all manner of different things. Cells make tissues. Tissues make organs. Organs make organ systems, and organ systems make organisms like you and me. Almost every single cell in your body contains DNA, or deoxyribonucleic acid. DNA is sort of like an instruction manual that your body uses to do most things, mainly making proteins. A long stretch of DNA that codes for one particular thing is called a gene. A massive stretch of DNA containing lots and lots of genes can be tightly wound around proteins called histones to form a thick rope called chromatin, which is then further coiled and compacted to form a chromosome.

Chromosomes and Genotype

Most humans have 46 chromosomes that are broken up into 23 pairs, usually with one of each pair coming from each parent. The last pair of chromosomes are called allosomes, or more commonly, sex chromosomes, which differentiates them from the other 44 chromosomes, which we call autosomes. The full complement of genetic material that an organism contains is called its genotype. However, it's important to remember that just because an organism has certain genes within its genotype, that doesn't mean that all of those genes are going to be expressed in the same way, or at the same time, or in all cells, or even at all. The actual observed characteristics of an organism, whatever its genotype may be, are collectively called its phenotype.

Sexual Dimorphism and Dioecy

Lots of species have different sexual phenotypes for males and females, a condition that we call dimorphism, from the word "di" meaning two and "morph" meaning shape. And dimorphism can occur in varying degrees from species to species. The term for a species having separate males and females in the first place is called being dioecious, which means two houses, and that's what separates those species from the monoecious, or one-house species. Other words for monoecious and dioecious are hermaphroditic and gonochoric, although depending on where you're from, those words may be more or less common. In my training, I heard the words hermaphroditic and dioecious way more than the words monoecious or gonochoric, and I have plenty of friends with the exact opposite experience. That sort of thing is very common in biology.

Understanding Biological Sex

What is Biological Sex?

Now that we know a little bit about the associated terminology, let's talk about what biological sex actually is. In biology, sex is not just the term for the act of reproduction through the reassortment of genes and the blending of genomes. It's also the way that we categorize individuals of a sexually reproducing species. To make this distinction clear over the course of this video, I'll be sure to use the term sexual reproduction to refer to the formation of genetically distinct offspring, and the term sex to refer to the sexual phenotype of individual organisms.

Gametes and Sex Differentiation

Sex is a complex thing, with a number of different factors going into it, that we'll cover over the course of this video. But in the world of biology, the most common way to differentiate between the sexes of an individual species is by looking at the size of their germ cells, otherwise known as their reproductive cells, or more commonly, their gametes. If you have lots and lots of very small mobile gametes, we call those sperm and we call you a male. If, however, you have relatively few very large and immobile gametes, we call those eggs and we call you a female.

Challenges in Defining Sex

Right away, you can notice there's a pretty big problem here. What if you don't have any gametes? What if you haven't started producing them yet? What if you're infertile? Surely that doesn't mean that you just don't have a sex, right? The thing that you have to understand about science, especially biology, is that nature is what nature is. It has no definitions and very few clear boundaries. So one of the ways that scientists are able to organize information and make analyses is by looking for patterns out in nature and drawing little boxes around them. But that doesn't necessarily mean that the boxes or even the patterns are actually real.

The Concept of Species

Consider, for example, the concept of species. Understanding what a species is and where one species starts and another begins is really important in biology. But there is no definition for the word species. Nor is there any concrete way to say what a species is and isn't. We have several species concepts, but they all have their own flaws, and there isn't a single one of them that's universally applicable. And the same sort of thing is true for other big concepts in biology, like homology or novelty. These are things that have different meanings for different sub-disciplines of biology in different circumstances and sometimes just in different contexts. But we're still able to work with these concepts despite the fact that we don't have a single operational and universal definition for them.

Sex as a Spectrum

The point is, sex is not unique here. Life makes all the rules and breaks all the rules all the time. And no matter what we're talking about in biology, there's almost always some wiggle room and some gray area. And the fact that I have to explain that at the beginning of this video should give you a pretty good indication as to how the rest of it's gonna go. Ignoring the fact that an individual of a dioecious species may not have any gametes at all, the generalization of sex as a function of gamete size simply doesn't work on a broad scale any more than any single concept of species does. Which is why when we talk about sex, we usually break it down into several sub-categories. We could be talking about anatomical sex, or phenotypic sex, or chromosomal sex, or genetic sex, or hormonal sex, or gonadal sex, or we could be lumping several of those together into typological boxes for pure convenience. We'll talk more about all of that as we move along.

Sex Determination in Nature

Mechanisms of Sex Determination

Right now, let's talk about sex determination, the mechanisms by which sex is established in the first place. And take a look at some of the diversity of sex determination throughout nature. We'll begin with reptiles, which exhibit some of the widest variety of sex chromosome structure and sex determination mechanisms out of all vertebrates. Lots of species of reptiles, and also lots of species of fish, but we're not talking about that right now, have temperature-dependent sex determination. That means that the anatomical sex of the animal is determined by the temperature at which the eggs are incubated, at a critical period of embryonic development known as the thermosensitive period.

Temperature-Dependent Sex Determination

So, for example, in leopard geckos, if an egg is incubated at 30 degrees Celsius, the resulting lizard will be female. But if it's incubated at 32 degrees Celsius, the resulting lizard will be male. And if it's incubated at 34 degrees Celsius, it switches back around to female again. Those are known as hot females, and they're known to be especially aggressive, and I think that's great. And of course, this isn't a perfect system. No matter the temperature, the sex of an embryo isn't guaranteed. One temperature is just more likely to produce a certain sex than another. And somewhere in the middle, you get a temperature where you get more or less a one-to-one ratio. And all of these temperatures are different for each reptile species that uses this system.

Sex Chromosomes in Reptiles and Birds

Of the reptilian species that do rely on sex chromosomes for sex determination, it's a toss-up as to whether or not the homozygotes, the ones with two of the same allosome, will be the males or the females. Birds, for example, have Z and W allosomes instead of X and Y. The major difference between the X, Y, and the Z, W systems is which sex has homologous, or the same kind, of allosomes. So in the Z, W system, those with Z, Z allosomes are usually male, and those with Z, W allosomes are usually female. The exact opposite of what you would expect in mammals, where X, X usually means female, and X, Y usually means male. And when you remember that birds and mammals share an amniote ancestor, this all becomes beautifully relevant from an evolutionary perspective.

Platypuses and Sex Chromosomes

I mean, we like to pretend that mammals are very cut and dry about all this sex stuff, but they are super not. I mean, just think about the fact that platypuses have ten sex chromosomes. Ten! Many of them share homologies with the avian Z chromosome, and none of them have an important mammalian sex-determining gene called SRY, which we're going to be talking about later. How wild is that?

Genetic Sex Differences Without Sex Chromosomes

And while we're on the topic of sex chromosomes, there are even other ways to get genetic sex differences without sex chromosomes at all. Consider, for example, ants, which use a sex-determination system called haplodiploidy, in which any egg which gets fertilized now has two copies of its genome, just like you do, and will automatically develop into a female. Any egg that is left unfertilized, on the other hand, will automatically develop into a male. This system has some really cool implications, the first of which being that male ants can never have male children, because as soon as they fertilize an egg, it will develop into a female. They can have male grandchildren, because one of their female children can lay an egg that goes unfertilized, but there is no unbroken chain of males in this system, at least not in the same way that there is in our system.

Haplodiploidy in Ants and Other Species

And that brings me to the other thing. This is a very different sex-determination system than the one that we rely on, and it occurs in way more taxa than just ants. But even if we were just talking about ants, there are several times more species of ants alone than there are species of mammals total. And when we factor in all the other things that use the haplodiploidy system, bees and wasps and a lot of beetles and a lot of arachnids, we're talking about millions and millions of species that disobey pretty much everything that most people learn about sex in the sixth grade. More importantly, however, we need to remember that even this system, which sounds at face value to be pretty darn binary, there are exceptions. Sometimes an unfertilized egg will still develop into a female, and that female can even go on to lay eggs of their own. We call this parthenogenesis, or reproduction without the assistance of a male, and there are plenty of other species, including lots of vertebrate species, that can do that. There are even some species, like the whiptail lizards in the southwestern U.S., which are entirely female and only reproduce this way.

Sequential Hermaphroditism

But let's back up a little bit. I said at the beginning of this section that the most common way to determine sex is through gamete size. Big means female, small means male. But even that raises a lot of issues. First of all, the whole idea that being either male or female is a persistent condition, which is understood from birth, is deeply flawed, to say the least. There are plenty of species out there that are hermaphroditic. They make both sperm and eggs. And there are plenty more species out there which are sequentially or serially hermaphroditic. They start off as one sex, and then at some point in their life, they switch. If they start off male and then become female later, we call that protandry. If they start off female and then become male later, we call that protogynie.

Slipper Limpets and Sex Determination

There are other species, like the slipper limpet, an adorable species of sea snails that live in stacks on the ocean floor, that are sequentially hermaphroditic, but they have no guaranteed starting point. Their sex is determined by where they are on the stack, with those on top being male and those on bottom being female. So even if one of them has been a male for a very long time, all it takes is another limpet climbing on top and it'll just turn into a female. There are also plenty of species, like the stoplight parrotfish, which are sequentially hermaphroditic, but don't have to be. They only switch sexes if they can't find a mate, and there are even other species which are bidirectionally hermaphroditic, meaning they can swap back and forth. All of these situations constitute massive evolutionary advantages, because these individuals get to pass their genes along, regardless of what sex they have to be to do it, and the other members of their population get to do the same.

Isogamous Species

All that is to say, sperm versus egg production is not a bad way to talk about sex. It's just important to remember that it's not always the full story. In all those examples I just gave, there are species which produce sperm at one point in their lives and eggs at another point in their lives, meaning their sex is neither fixed nor immutable, and asking for their sex is about as useful as asking for the time. But even with all that in mind, we could still say that these species are producing either one type of gamete or the other or both at any given time, and because there are still just these two types of gametes, this is still ultimately a binary system. The problem is that only applies because we're talking about an isogamous species here. Species which have more than one size of gamete. And there are plenty of species which are isogamous, meaning they have only one size of gamete. So what are we supposed to do with them?

Mating Types in Isogamous Species

And to be clear, being isogamous isn't the same thing as being hermaphroditic. These species still differentiate into mating types, which you can kind of think of as males and females, only we would call them plus and minus based on who's giving and who's receiving the gametes. And of course, if we were to try to define everybody that way, then animals like seahorses would have their sexes swapped, because the females deposit eggs into the males, who then fertilize them and give birth to live young. And then there's Tetrahymenothermophila, a radical little protozoan with seven distinct mating types, each one of which can reproduce with any of the other six, but not with its own.

Multiple Gamete Sizes

There are also some species out there that have more than two gamete sizes. For example, there's a species of fruit fly, which has one size of egg and three different sizes of sperm. So if size is really all that matters, we should be saying that there are four sexes here. Or at the very least, there's two, but one of them is broken down into three subcategories, one of which violates this whole system anyway, because its sperm is bigger than the egg. And that's not even mentioning the situations where the sperm is bigger than the entire fly! There's also a genus of green algae, which can reproduce in a variety of ways, some asexual, some sexual. And one of the sexual ways that it can reproduce is to divide itself up to 64 times until it becomes its own gametes. Each of the daughter cells grows a flagellum and becomes a gamete of a variety of sizes. And then there's the genus Pandorina, which lives in colonies of 16 cells, which then divide into eight large and eight small gametes. Only any of those gametes can fuse. Two big, two small, one big, one small, you name it.

Plants and Gametes

Some plants also have sperm and eggs, although they do things a little bit differently. Looking just at the angiosperms, the flowering plants, they can be either monoecious or dioecious, but even within those two categories, there's a lot of variation. When a flower has both male and female parts, we call it a perfect flower. Apricots are a great example of a monoecious species with perfect flowers. When a flower has either male or female parts, we call those imperfect flowers. So you could have a dioecious species like aspen trees in which each tree is either male or female. But you could also have imperfect flowers within a monoecious species. Walnut trees, for example, are monoecious and have both male and female flowers on the same tree.

Fungi and Mating Types

And then there are fungi, which also have different mating types, which are sort of analogous to the sexes in plants and animals, in that they each possess a particular set of genes, which conveys a particular sexual phenotype. The difference is that in some fungi, like yeast, there are two mating types. And in other fungi, like splitgill mushrooms, there are over 23,000 mating types. And even among all those mating types, there are different levels of complexity, with some mating types being unipolar, bipolar, or tetrapolar, depending on how many crossover events there are and how many genes are actually being shared during reproduction. And none of that is even touching on the fact that there are some fungi which are homothallic, meaning they can self-fertilize and reproduce from a single spore, and then there are heterothallic fungi, which need other compatible fungi to reproduce with. Nor is it touching on the fact that some fungi can exist in an anamorphic or asexual form, or a telomorphic or sexual form, allowing them to adapt their reproductive strategy to whatever their local environment requires. And even if you were to really, really try to say that all of these fungi actually exist in a very specific, discrete sexual category, the hyphae, or the roots of the fungus, can have multiple nuclei within the same cell, and those nuclei can contain different genomes of different mating types, which means one single fungal system can have lots of different sexes all at once.

Gynandromorphs and Bilateral Gynandromorphy

And even if we walk it all the way back to strictly dioecious and anisogamous species, there are still individuals which we call gynandromorphs, which means they have some male and some female parts within the same body. There are even some of them which we call bilateral gynandromorphs, because they're split right down the middle, with one half of their body being male, and the other half being female. Bilateral gynandromorphy doesn't really happen in mammals, but it does happen in mammalian gonads. Ovo-testes are organs which have ovarian tissue on one side, and testicular tissue on the other side. That can happen in humans, and in many other mammals, and there are even some mammals, like European moles, where that is the normal ground state of all females.

Sex and Sexual Reproduction

Perhaps this is all just a bit too weird, and you want to try to do away with all this variation, and combine sex and sexual reproduction. Boiling sex down to just the function of genome blend. Unfortunately, if you do that, things are going to get a whole lot weirder. Consider, for example, the fact that bacteria can share genes in lots of different ways. One of those ways is called conjugation, which is essentially bacterial mating. During conjugation, a donor cell connects to a recipient cell and gives them plasmid genes which they can use. The attachment is even done by a structure called a sex pilus. How are you going to talk about males and females in an organism which has no sex chromosomes, no sex organs, no gametes, no more than one cell, and in which any individual could give or receive DNA at any given time? And let's not forget the fact that bacteria can also do this neat trick called transformation, where they can incorporate free DNA into their genomes, and that DNA can be sourced from pretty much anywhere, including dead bacteria. If you really want to say that sex is all just about genome blending, then you'd have to admit that sometimes functional sexual reproduction can happen with dead things.

The Sex Spectrum

Shifting to a New Model

So it's important that we have some sort of structure to this concept of sex. But as we've just seen, that structure is highly variable and can be pretty difficult to pin down. So where do we go from here? Well, it just so happens that this exact issue is why modern biology is shifting to a new model of a sex spectrum. Let's talk about that.

Understanding Spectra in Nature

For a lot of people, the concept of sex being multi-dimensional, dynamic, and spectral can be a little bit daunting. But spectra in nature, even regarding sex, is something that you're almost certainly already more familiar with than you may realize. Consider, for example, human height. We know that male humans are 10 to 15 percent taller than females. But when we look at how that data plots out, the actual distribution of height between sexes, we see that there's a lot of difference between the two. So when we say that males are 10 to 15 percent taller than females, we don't mean that every male is taller than every female. Nor do we mean that height alone is a reliable way to distinguish between sexes. Nor do we mean that any male that's shorter than an average female isn't actually a male, or that there's a height limit to females, or anything like that. We're just talking about a trend in the population. And when you start thinking about almost any sex-based characteristic, even sex-determining factors, you'll find that we're talking about trends, not binaries, a whole heck of a lot.

Multivariate System of Sex

Despite popular belief, there is no single simple switch for sex determination. In fact, the more we've looked at it, the more we've found that sex is a multivariate system. A suite of diverse characteristics, and a whole bunch of different types of characteristics, produced by an array of different factors, no single one of which is solely determinant of the outcome, and no single one of which has only two options. And to better understand what I mean by that, let's look at humans as a case study.

Human Sex Determination

Four Major Steps

Overall, there are four major steps to sex determination in humans. First is the establishment of your chromosomal sex at the time of fertilization. This is usually either XX or XY. Second is the development of gonads, due to the expression of genetic pathways encoded on those chromosomes. This establishes your gonadal sex. Third is the continuation of sex-specific development of your internal and external genitalia, which is what establishes your anatomical sex. And finally, you establish outwardly visible sex characteristics, which is what establishes your phenotypic sex. And while that all sounds very straightforward at face value, when you understand the sheer range of possibilities in each one of those four steps, you'll start to see why it's completely impossible to call any part of this a binary sex.

Chromosomal Variations

Let's start big with the idea that XX always means female and XY always means male. Right away, this has a lot of problems. De La Chapelle syndrome is when a person has XX chromosomes but still develops anatomically as a male. This usually happens because the SRY gene, an important gene for male development, is translocated or moved onto an X chromosome. But this isn't always the case. Because the genes for both testes and ovaries are upstream, so to speak, there are individuals with De La Chapelle syndrome who don't possess any Y-derived genes at all.

Just as De La Chapelle syndrome is a variation in the sex characteristics of people with XX chromosomes, Swyer syndrome is a variation in the sex characteristics of people with XY chromosomes. For example, there could be a mutation on or a deletion of that SRY gene. Without that gene acting on gonads, these people could be chromosomally male but hormonally and anatomically female. And yes, there are plenty of cases of women with Swyer syndrome getting pregnant and giving birth. These are anatomically female, chromosomally male women giving birth to healthy children.

Experimental and Natural Cases

This can be done experimentally as well. Researchers have spliced an SRY gene into mice with XX chromosomes or out of mice with XY chromosomes and caused them to develop anatomies and behaviors that are in stark contrast to their chromosomal sex. And this happens out in nature as well, even in mammals. In African pygmy mice, 75% of females have a Y chromosome and an SRY gene. In the creeping voles here in the US, all males have XX chromosomes. These aren't anomalies or crazy mutations. These are persistent evolutionary changes.

Even humans who have a Y chromosome and an SRY gene still develop in the same estrogen-rich environment as every other embryo. If they don't produce enough testosterone to counteract that estrogen, they could still develop as an anatomical female, no matter what their chromosomes or what their genes look like. But that's getting ahead of ourselves in talking about hormones. We'll get to those in a minute.

Turner Syndrome and Chromosomal Configurations

Going further with just genes and chromosomes, there's also Turner syndrome, which is the condition of having an X and then nothing else. Having just a Y would be lethal, but having just one X is functionally the same as being chromosomally female because when you have two Xs, the second X doesn't really do much. If you recall, chromosomes are made of a thick rope of DNA and proteins called chromatin. When that chromatin is loose and accessible, the genes contained within it are able to be transcribed to make proteins. We call this structure euchromatin. When the chromatin is wound tightly, however, the genes are inaccessible and functionally inactive. We call that structure heterochromatin.

When someone has two X chromosomes, one of those Xs ends up being scrunched down and condensed into a heterochromatic structure called a Barr body, with only about 15% of it being expressed at any given time. Whether it's the first or the second X that gets scrunched up like this varies from cell to cell. You could literally have two cells right next to each other, one expressing the first X and the other expressing the second X. This can be easily seen in calico cats, which have the alleles for either orange or black fur on their X chromosomes. The random distribution of orange or black color within their coats is the result of the random inactivation of X chromosomes in their underlying tissues.

Other Chromosomal Syndromes

So if you think having either XX or XY chromosomes is the only thing that determines your sex, then would someone with Turner syndrome with only one X chromosome have half of a sex? Looking in the opposite direction, triple X syndrome, as the name suggests, is when someone has three X chromosomes, poly X syndrome is when someone has four or five X chromosomes, Jacob syndrome is when they have one X and two Ys, and Klinefelter syndrome is any combination of multiple Xs and one or more Ys. So XXY, XXYY, XXXY, XXXYY, and on and on and on. So again, if you really think that having either XX or XY chromosomes is the only thing that establishes your sex, then would someone with three or more sex chromosomes have multiple sexes?

Mosaicism and Chimerism

The possibilities certainly don't stop there, because there are some ways in which a person can have some cells inside their body which are chromosomally different than others. One of the ways this can happen is mosaicism, which usually occurs following a copying error early in development, resulting in an individual developing from a single egg but possessing two or more cell populations with different genetic makeup. Mosaicism can affect any type of cell and can include whole sex chromosomes as well, resulting in a person with a mixture of male and female cells and subsequently male and female traits.

Mosaicism isn't the only way in which you can have cells with different DNA inhabiting the same body. Chimerism occurs when two different egg cells are fertilized and then at some point in their development, the embryos fuse, meaning the resulting embryo will have two sets of cells with two different types of DNA. Fun fact, this is also called reverse twinning, which is an awesome name. Just like with mosaicism, the tissues that end up being chimeric in these situations vary in each circumstance, depending on which cells are traveling, how they do it, and where they settle.

Microchimerism

Chimerism usually doesn't show any signs or symptoms, but sometimes when these people have children, they find that they are more distantly related to them than they had expected, with a son or a daughter being more genetically similar to a nephew or a niece, for example. How wild is that? And also just like with mosaicism, this can result in a person with a mixture of male and female cells, and the unique proportion and distribution of those cells dictates that person's unique sex characteristics. And all of that is just primary chimerism. Secondary chimerism can be the result of organ transplantation, blood transfusion, or if you've ever been pregnant before, you may have experienced a phenomenon called microchimerism without even knowing it. Microchimerism is when fetal stem cells cross the placenta and implant themselves somewhere in the parent's body or vice versa. If you're chromosomally female and you've ever been pregnant with a chromosomally male child, there's a chance that some of the cells and some of the organs somewhere in your body have XY chromosomes, and some of your child's cells have XX chromosomes, and that's all totally natural.

Conclusion on Chromosomal Variations

The point is, just like with all the different chromosomal configurations that we talked about earlier, if XX and XY are all that matters, how would we classify these people? Do they have multiple sexes at once? Are different parts of their body different sexes? Or can we just admit that some people exist outside this simplified binary framework?

Genes and Hormones

A moment ago, I touched on how defining chromosomal females as having two Xs is really about as useful as just saying that they don't have a Y, but having a Y doesn't really mean anything on its own either. Remember, certain genes are only going to be expressed at certain times, under certain conditions, and in certain tissues, like for example some of the genes that produce sperm, which are only ever going to be expressed in the testes. So if I don't have testes for any of the reasons that we talked about earlier or any other reason, then these genes do nothing, and having them means nothing.

Genetic Interactions

The point is, even if you have a certain sex-related gene, even if you have a whole sex chromosome, you could still be missing any one of a dozen pieces of the puzzle of what sex determination actually is. For example, there was one study back in the 1980s that showed that female wallabies with XX allosomes that didn't have any egg cells at birth actually went on to develop testes even without an SRY gene. And you know why? It's because everybody watching this has the genes for both testes and ovaries. What gonads you get, whether it's one or the other or neither or both, comes down to an incredibly complex set of genetic interactions across several chromosomes, most of which aren't even your sex chromosomes.

Genes Involved in Gonad Development

For example, one of the genes that helps build testes is called SOX9, and it's found on chromosome number 17. If you have ovaries, that's because there's another gene on your X chromosome called NR0B1, which makes a protein called DAX1 that stops SOX9 from giving you testes. Now, chromosomal males have an X chromosome too, but they also have a Y chromosome, which usually contains a gene called SRY, which works by producing a protein which binds to NR0B1 and stops it from making DAX1 so that SOX9 can produce testes again. That's why I have testes at this very moment. It's because a gene made a protein that stopped another gene from making a different protein that would have otherwise stopped a different gene from giving me the testes that I have. How awesome is that?

Pleiotropic Genes

It's also important to remember that some genes are pleiotropic, meaning they are one gene with several effects throughout the body. A great example of that is SOX9, which isn't only responsible for testicle development, but also plays a role in skeleton development. And it's even more important to remember that the three genes I just listed aren't even close to the end of the story. There are plenty more genes at play here, like WNT4, which is important for developing ovaries and kidneys. And even if I were to give you every single gene that I could think of, it still might not be the end of the story, because there's evidence for other unknown genes which play some role in gonad development as well.

Genetic Variations and Outcomes

Now, if you're paying attention, you might be starting to put some pieces together here. Like, for example, that you could have a perfectly functional Y chromosome, but have a mutation on your SOX9 gene, or extra copies of your WNT4 gene, and so you still end up with female reproductive anatomy. Or you could have no Y chromosome at all, but you're missing an NR0B1 gene, or over-expressing an SOX9 gene, and so you still end up with testes. And let's not forget the difference between heterochromatin and euchromatin. You could have all the right genes in all the right places, but they're just wound a little bit too tightly, so they're functionally turned off. And yes, there are other animals, even other mammals, that don't have an SRY gene or even a Y chromosome. And yet they still have genetic sex differentiation, and they still reproduce sexually. None of these factors are guaranteed binary sex switches.

Hormones and Development

But let's ignore all of that. Let's say you have all the right chromosomes and all the right genes and whatever gonads that you like. That still isn't good enough, because it is the hormones that those gonads produce that actually causes you to develop as a male or a female or somewhere in between. And hormones aren't nearly as simple as people like to pretend either. For about as long as we've known what hormones are, the idea of testosterone being the man hormone that makes you aggressive and estrogen being the woman hormone that makes you compassionate has been very popular science fiction. However, all the way back in the 1930s, scientists were noticing that both male and female animals interacted with both male and female hormones in pretty unexpected ways. Male horses were shown to possess striking levels of female hormones, and female rats exposed to male hormones experienced female-typical anatomical developments. Even male-typical and female-typical behaviors seemed to increase when lab animals were exposed to hormones of the opposite sex.

Hormonal Complexity

Just like everything else in biology, hormones got a lot more interesting the closer we looked at them. And yet, to this day, lots of people are still very surprised to find that we all have testosterone and estrogen and all sorts of other hormones in our bodies all the time. And they don't usually do what people think they do. Endocrinology gets pretty complicated pretty fast. So let me give you a very simplified example of a few key hormones so you can understand a little bit of what I'm talking about here. You see, some of the cholesterol in your body can be converted into progesterone. And that's what becomes testosterone, and that's what gives you what some of my anatomy professors would call male internal plumbing. Some testosterone can then be converted into dihydrotestosterone, and that's what gives you male external genitalia. Or testosterone can be converted into estrogen and estradiol, and that's where you get female sex characteristics.

Hormones and Receptors

Sometimes the same hormones can have different effects in different sexes, like the luteinizing hormone, which triggers the ovaries to release eggs, and the testes to produce sperm. Or estradiol, which signals the growth of female internal genitalia and also helps regulate erectile function. All this is to say, these different hormones are not male or female things. Everybody has all of these hormones in their bodies all the time. And your specific hormone levels are as unique as your fingerprint. It's also important to point out that hormones don't actually do anything by themselves. All they can do is bind to cell receptors, and then cause those cells to do things. And those cell receptors are controlled by a totally different gene pathway with just as much room for variation.

Androgen Insensitivity Syndrome

So for example, you could have a daughter who has not had her first period by age 16. So you bring her to the doctor to figure out what's going on, and you find out that she's actually chromosomally male, but she has androgen insensitivity syndrome, which means her cells aren't producing the receptors to bind testosterone. So even though she has XY chromosomes and more than enough testosterone to go around, she is still anatomically and phenotypically female. And if you think that's some wild and fantastical scenario, it's not. Androgen insensitivity syndrome affects one in 20,000 people. That's about the same rate as albinism.

Congenital Adrenal Hyperplasia

And there are some ways in which more or less the same thing can happen in the opposite direction. Like some cases of congenital adrenal hyperplasia, in which a chromosomal female would be exposed to high levels of androgens prenatally, and so develop partially or fully masculinized external genitalia.

External Genitalia and Sex Assignment

But who cares about all these chromosomes and genes and hormones and developmental stuff? At the end of the day, you're either born with a penis or a vulva, right? Well, not always. In Western cultures, sex is typically assigned at birth based on a visual inspection of external genitalia. And for that reason, a lot of people tend to assume that external genitalia are a simple and unambiguous way to indicate sex in one direction or the other. But that is a super narrow viewpoint, and it couldn't be further from the truth.

Indifferent Stage and Genital Development

To understand what I mean by that, let's start by addressing the super common belief that we are all females by default, and it's the Y chromosome that makes someone transform into a male. That is a major oversimplification, and the truth is way cooler. At around three to six weeks of development, regardless of your sex chromosomes, all embryos look the same. In fact, this stage is called the indifferent stage. But that doesn't mean that we're all phenotypically female. There is no male or female phenotype at this stage. At around five weeks, a structure called the urogenital ridge will give rise to the Wolffian and Müllerian ducts. If left unchecked, the Wolffian ducts will eventually develop into the ductus deferens, which used to be called vas deferens, and the Müllerian ducts will develop into the uterine tubes, which used to be called fallopian tubes. So it isn't that we all start out female. Most people start with the fundamentals of both male and female genitalia, and usually one of those continues to develop while the other one is reabsorbed.

Persistent Müllerian Duct Syndrome

However, that isn't always the case. For example, a chromosomal male with persistent Müllerian duct syndrome will have a penis and testicles, as well as all or part of a uterus and uterine tubes, and maybe even the upper third of a vagina, whereas a chromosomal female with Müllerian agenesis will lack those structures. As genitals start forming from what's called the genital tubercle at around four weeks, you would still have no idea whether they're forming a penis or a vulva. That whole region is so undifferentiated at this point that it takes another two full weeks just to separate your urethra and your anus. Before then, you still have a singular lower orifice, basically a cloaca. In fact, the folds surrounding that orifice are even called cloacal folds.

Gonadal Dysgenesis

Actual proper sexual differentiation of the gonads depends on signaling from what are called primordial germ cells. Which means that in order for things to go smoothly, those primordial germ cells have to actually make it to the gonadal region to begin developing into an ovary, a testis, or an ovotestis. Otherwise, you end up with gonadal dysgenesis, where your gonads simply don't develop at all. This usually results in a person who is phenotypically female, but doesn't menstruate, and doesn't develop female-specific secondary sex characteristics at puberty. Sexual differentiation of the genitalia is largely driven by hormones produced by the gonads. So if there's a problem upstream, there's going to be a lot of changes downstream as well.

Secondary Hypogonadism

But that isn't the only place those hormones come from. For example, you could have secondary hypogonadism, which is when your hypothalamus and pituitary gland aren't producing enough androgens, and so you get similar results to androgen insensitivity syndrome, because there simply aren't enough androgens to go around. No matter how it happens, through congenital adrenal hyperplasia, or through androgen insensitivity syndrome, or through secondary hypogonadism, or through any other way, the story is largely the same. Too many, or too few of these hormones can masculinize or feminize the body in ways that may not be congruent with the person's chromosomal sex.

Ambiguous Genitalia

And to blur the lines even further, one in every 2,000 people are born with atypical, or ambiguous, genitalia, meaning that their external genitalia aren't clearly defined, and may not match up with their genetic sex or their other sex organs. Someone could be born with an enlarged clitoris that looks like a penis, with an undeveloped penis that looks like a clitoris, with a fused labia that looks like a scrotum, with an unfused scrotum that looks like a labia, or with an atypically positioned urethra, which greatly enhances the ambiguity of any of those structures. Any one of those situations could easily result in a child being assigned the wrong sex at birth. And to complicate matters further, ambiguous genitalia are usually surgically altered one way or the other, often without the child's consent, which is a whole other ethical bag of worms.

Guevedoces in the Dominican Republic

One of the more interesting examples of the kind of variation we can see in human sexual development comes from a small community in the Dominican Republic, where around one in every 90 children are known as Guevedoces. Guevedoces children are chromosomally male, but they're deficient in an enzyme called 5-alpha reductase, which converts testosterone to dihydrotestosterone, which, as I mentioned earlier, is what causes you to develop male external genitalia. As a result, these children are born with external genitalia that are either ambiguously or completely female, and they're often assigned female at birth and raised as girls. That is, until they hit puberty, and start developing secondary sex characteristics typical of males, and also start growing a phallus and a scrotum and their testicles descend. And that's where the word Guevedoces comes from. It's derived from a Spanish slang word for testicles, and the number 12, which is when these kids usually hit puberty. Guevedoces.

Gender Identity and Guevedoces

Research into this population shows that these children usually grow up to have the gender identity and take on the gender roles of a typical man. We'll talk about what those words mean in a minute. But what's so important here is that if you're talking about chromosomal sex, these people haven't changed at all. But if you're talking about anatomical sex, they just switch their sexes by totally natural means. And no matter what layer of sex you're talking about, there are many sex traits, not just those found in the Guevedoces, which can change over time either anthropogenically or otherwise, which makes sex a very complex and temporally fluid system. And it means basing the entire system of sex assignment off of a casual glance at a baby's giblets is a major problem.

Conclusion on Human Sex Determination

A little while ago, I said that human sex determination could be broken down into four major steps. Establishing chromosomal sex, establishing gonadal sex, establishing anatomical sex, and finally establishing phenotypic sex. And since then, we've talked about how every single one of those steps can be fuzzy and even dynamic. The chromosomal, hormonal, and anatomical variations we've been talking about here all fall under the umbrella of what are known as intersex conditions, or DSDs, differences in sexual development. The occurrence rate of individual intersex conditions varies between one in under a hundred and one in a few thousand. But even at the most conservative estimates, we're talking about tens of millions of people who fall outside of the supposed sex binary. The UN estimates that 1.7% of the global population is intersex. And with a global population of around 8 billion people, we would be talking about 136 million people. That's a population the size of Russia. Imagine the legwork you have to do to hold on to this bizarrely parochial worldview that every single one of the over 8 billion people around the world fall perfectly into one of two distinct and discrete boxes. Unless they're Russians.

Importance of Recognizing Intersex People

Even if we could agree that sex is a simple and uncomplicated thing for 98.3% of all of humanity, that's no reason to gloss over the immense diversity within that last 1.7%. I mean, consider the fact that 99.9% of all atoms in the universe are either hydrogen or helium. That's way more of a binary than human sex could ever be. And yet it's not a reason to ignore the other 116 elements on the periodic table or call them anomalies and variations of hydrogen and helium. There are tens of millions of intersex people out there. Their lives and experiences matter, and they shouldn't be ignored or forced to conform to a strict binary for our convenience.

Conclusion on Biological Sex

All this is to say, simply having an X or a Y chromosome is neither necessary nor sufficient for determining your overall biological sex. There is no standard template for male versus female development out in nature or in humans. As it stands, there are more than enough variations on the sex chromosomes alone to produce a female that is masculine enough or a male that is feminine enough to pass as the opposite sex both in social circles and even just to themselves. The possibilities are simply too broad, and the people they produce too diverse to reduce any part of biological sex down to a simple binary.

Exceptions to the Rules

Even after all of this, it's still very possible that there are still some of you out there that think all I'm doing is throwing out exceptions to the rules. But the thing is, in science, finding exceptions to the rules is often what tells us that it's time to re-evaluate what we thought we knew about the rules in the first place. That's how science has always moved forward. But to understand what I mean by that, you need to take a step outside of typological thinking for a moment. Let me explain what that means.

Different Types of Thinking in Biology

You see, in biology, we're taught to employ different kinds of thinking to approach different challenges and answer different questions under different circumstances. An analogy for this would be like learning kickboxing and military strategy. These are two different ways to think about conflict, and one is going to be more useful than the other in different situations. Similarly, there are lots of different ways to think about biological information, and while thinking in terms of systems may be good for physiology, it's going to yield different results when you're talking about ecology, and it might be better to think in terms of networks.

Typological, Tree, and Population Thinking

There are lots of different types of thinking in this field, but the big three that I want to focus on here are typological, tree, and population thinking. Typological thinking categorizes things into distinct essential groups with exclusive parts and clear boundaries. This type of thinking is great for rapidly understanding major concepts without much nuance. Think about the first time you learned the difference between a plant cell and an animal cell, for example. But it's not as good for areas where things get fuzzy and gray, like protists, which have plant-like or animal-like cells, but certainly aren't plants or animals.

Tree Thinking

Tree thinking focuses on evolutionary relationships and the utility of adaptations. It's great for when you see a new organism with familiar characteristics, consider the evolutionary benefits of those characteristics, and instantly understand a little bit more about that organism's life history and probably what it's related to as well. However, it's not always the best for addressing variations within a characteristic, like wings on an insect versus wings on a penguin.

Population Thinking

Population thinking accounts for and emphasizes variation. It takes the entire population into account and helps to understand the dynamics of that population. For example, when looking at a group of cancer cells and understanding which among them are most likely to metastasize. But it's not great for telling you what cancer cells are or why they exist in the first place.

Applying Population Thinking to Sex

So when we're thinking about biological sex, it can be very easy to want to boil things down into the simplified typological categories that we were first taught, or to use tree thinking to think about it in terms of a reductive binary functionality. But when you consider the full spectrum of sex, looking across hundreds of different species, especially humans who are the most studied animals on earth, these types of thinking are simply not appropriate. In fact, sometimes they're not even useful. We would have so much deeper of an understanding of sex and so much less risk of dehumanizing people if we were to utilize population thinking and take into account all the beautiful variation of our global population.

Conclusion on Sex Spectrum

So far, we've talked about XXXY sex determination, XXX0 sex determination, ZZZW sex determination, environmental sex determination, genic sex determination, and how all of those vary beyond what a simple binary could contain. But more than anything, we've shown that it's next to impossible to talk about sex in a meaningful way without talking about development. And any biologist will tell you that development covers your entire lifespan, not just the point up to your birth. Your genotype stays more or less stable throughout your life, but the way that it's expressed and the environmental factors around you change, and so your sexual phenotype changes as well. And that's no different than any other part of biology.

Understanding Gender

Introduction to Gender

But all of that is only the first part of this video. When you remember that sex is not the whole story of the human experience, all the diversity we've talked about becomes a whole lot broader and a whole lot cooler. I mentioned earlier that when we talk about biological sex, we sometimes need to specify as to whether we're talking about hormonal sex, gonadal sex, chromosomal sex, anatomical sex, phenotypic sex, and so on. The key takeaway from that last section was that no one of those categories necessarily implies any of the others. In this section, we're going to be talking about how none of those categories are the same thing as words like man or woman.

Distinction Between Sex and Gender

Just like how the words theory and guess are used interchangeably in common parlance but have very different meanings in terms of science, the words sex and gender aren't nearly as synonymous as you might assume based on their day-to-day usage. Sex refers to the many anatomical and physiological characteristics of individuals who are male, female, or intersex. Whereas gender refers to the socially constructed roles, norms, behaviors, and characteristics of women, men, girls, boys, and non-binary people. Whereas sex is strictly biological, gender is something that is designed and assigned by the individual experiencing it and others around them based on cultural habits and practices.

Cisgender and Transgender

Because gender interacts with but is fundamentally different from sex, the two are often aligned, but that isn't necessarily the case. When someone's anatomical features match their own internal sense of their gender, we call that person cisgender, from the Latin prefix cis meaning on the same side. When they don't, we call that person transgender, using the Latin prefix trans meaning on the opposite side. Being transgender is not the same as being intersex. These are distinct groups that may overlap, but we should be careful not to conflate the two.

Swyer Syndrome and Gender

However, we can use our understanding of intersex people to help highlight the distinction between sex and gender. Think back to the cases I talked about earlier of Swyer syndrome. Here we have someone who is chromosomally male, but anatomically and phenotypically female. They feel like a woman, they dress like a woman, they act like a woman, they can get pregnant and they can give birth, all while having XY chromosomes. If sex and gender were truly synonymous, then you would have to accept that this person is a man because they have XY chromosomes, which means some men can give birth. Or you'd have to accept that they are a woman because they have female reproductive anatomy, which means some women have XY chromosomes, neither of which is possible within a strict binary essentialist framework. If, however, you simply separate sex from gender, this all makes perfect sense. Being able to become pregnant is not a necessary condition of womanhood, so it has no real bearing here. There are plenty of ways for the different aspects of sex to be incongruent, and none of them necessarily need to line up with gender. That makes this person interesting, but nowhere near outside the realm of possibility. People with Swyer syndrome are no longer anomalous exceptions to the rules, they're just people.

Social Constructs and Self-Identification

A common sticking point for people who are new to thinking about gender in this way is to wonder, if gender is a social construct and is determined by someone's personal identity, then why aren't other social constructs treated this way? Why, for example, would it be inappropriate to self-identify as another race? In order to answer this question, we need only compare any two other social constructs, in order to see that the idea of different social constructs having different rules is something that we're already all familiar with, whether we're conscious of that or not.

Money as a Social Construct

Consider, for example, the social construct of money. There are no wild dollar bills growing out in nature. Money is something that is invented by and maintained by generations of humans. It isn't objectively real in any concrete way, but it does affect our lives. Like gender, money is something that you experience differently based on the circumstances of your birth, and it means different things for different people and different cultures at different times. But unlike gender, it's entirely determined by external factors. Its value is dependent upon group agreement, and your relationship with it can be altered arbitrarily by your and other people's personal choices.

Marriage as a Social Construct

Let's try another. How about the social construct of marriage? Like gender, it's reliant on aspects of your personal identity, in this case sexuality, which usually plays a big role in deciding who you're marrying. But unlike gender, it's not something that relies on self-identification. Instead, it's largely a legal thing, and it has measurable effects on your private property more than your body.

Race as a Social Construct

Circling back to the social construct of race, like gender, it changes throughout history. It's dynamic in its presentation. It impacts your social and political life, and it's contingent upon truly arbitrary categorization systems. But unlike gender, which is rooted in culture and identity, race is rooted largely in ethnicity, despite there being far more diversity within so-called races than between them. These two social constructs, like almost any two social constructs, are intersectional, but not in any way interchangeable.

Conclusion on Social Constructs

We'll talk more about self-identification in a minute, but the point here is that when you stop to think about what a social construct is and does, you'll very quickly realize that just like how everything that's considered to be a vehicle can't be categorized and utilized in the same way, everything that's considered to be a social construct can't either.

Experiencing Gender

It's also important to remember that while gender is being constructed, it's also being experienced. This fact alone makes gender a highly multidimensional concept, because we're not just talking about somebody's gender identity, which is a core part of their individuality, but also their gender expression, their behaviors and appearances, as well as their cultural expectations, social status, how to flaunt secondary sex characteristics, and specific behaviors associated with these gender categories. For this reason, gender becomes pretty non-binary pretty fast, but that's not a new thing for humanity.

Historical and Cultural Perspectives on Gender

When we look across culture and throughout history, traditional gender roles have been linked to things like socioeconomic status and power far more frequently than they've been linked to sex alone. And there are a multitude of cultures across time and space that have more than two genders in their cultural constructs. Even today, after centuries of colonialism and erasure, hundreds of indigenous societies around the world still retain their long-established traditions of third, fourth, fifth, and transgenders, like for example the Mahu of Hawaii, the Hijra of India, the Kwariwami of Peru, the Feminie Yellow of Italy, the Socrata of Madagascar, the Sister Girls and Brother Boys of Australia, and the wide array of trans and third gender identities across the native tribes of continental North America, which we collectively call Two Spirits. These are all diverse gender traditions that live on to this day.

Transgender Figures in History

European cultures have enjoyed and been influenced by transgender people throughout history as well, like Chevalier d'Éon, a celebrated French diplomat, soldier, and spy who fought in the Seven Years War. Although she was assigned male at birth, she lived openly as both a man and a woman at different times in her life, which drew a lot of public attention at the time, and then, starting in 1777, she began to live permanently as a woman and was even officially recognized as a woman by King Louis XVI. Or how about Emperor Marcus Aurelius Antoninus, who ruled the Roman Empire around 218 AD? She regularly wore makeup and wigs, demanded to be referred to as a lady rather than a lord, referred to herself as queen, not a king, and offered great sums of money to any doctor who could change her physically into a female. For this reason, some museums have even rewritten their plaques and information about Antoninus using she-her pronouns, as would have been her preference as someone who is presumably a transgender woman.

Christine Jorgensen and Transgender Activism

Or what about someone closer to home? Christine Jorgensen served in the US Army during World War II before traveling to Denmark to transition. Somehow, a letter to her parents was leaked to the press, and since transgender people weren't really talked about at the time, her return to the US was met with a lot of publicity. She later went on to become an actress, a recording artist, and an activist for transgender acceptance.

Changing Gender Norms

Even in the Western binary framework that most of the world lives under today, concepts of gender have changed a lot over the years. Before the 18th century, when the concept of the cold and stoic man became popular, men were expected to exhibit a wide range of emotions and behaviors that certainly wouldn't be considered very manly today. Men would weep with emotion, faint in distress, they wore high heels and makeup and painted their fingernails, and let's not forget about powdered wigs. The early 20th century saw women rejecting Victorian ideas of femininity, cutting their hair short, smoking, dancing, seeking a more boyish style, all things that wouldn't raise an eyebrow today, but at the time were quite scandalous. Even our traditional nursery colors of blue for boys and pink for girls didn't really come into being until around the 1940s. Before then, dressing a boy in pink would have been all the rage, but today there are men that won't even wear a pink t-shirt, lest it tarnish their masculine image.

Personal Gender Expression

Even in this very moment, I have my hair cut relatively short and I'm wearing dark colors. These are ways in which I can signal masculinity in a way that makes sense to me. But neither of these things make me a man, nor would I be any less of a man if I wasn't doing these things. Nor does it mean that any woman couldn't also cut her hair short and wear dark colors and signal femininity by doing so. Nor does it mean that there aren't plenty of other ways that I could signal masculinity or plenty of other ways that I could use this exact system here to signal any other gender expression. Just like language, gender presentation is personal, contextual, dynamic, fluid, and it's changing all the time.

Conclusion on Gender Norms

And again, all of that is just considering Western gender norms over the past couple of centuries. There are plenty of other cultures out there whose gender norms have become more progressive, more regressive, or who have been colonized and had their gender norms supplanted with new ones. These are all examples of our attitudes, views, and practices surrounding gender changing over the course of multiple generations. None of which would be possible if gender were fixed and binary, but all of which point to the idea that gender is less something that we are and more something that we do, enact, or even perform. Based on our cultural surroundings.

Thought Experiment on Gender Norms

You could even run a thought experiment on your own cultural norms at this very moment. Can a real man wear a dress? Can a real woman fix a car? What about ordering a fruity cocktail or being the primary money earner of a household or knitting as a hobby or having hairy armpits or wearing nail polish or playing sports? No matter what your answers are, how many of them would your parents or your grandparents or your great, great, great grandparents have agreed with? Or what about the simple fact that phrases like real man and real woman exist in the first place? If we can make intragender comparisons, whether they be meant as compliments or insults, for example, saying things like he should man up or he's more of a man than you, then that implies that the manliness in question isn't something innate that you either have or don't based on your chromosomes or whatever, but that it's spectral and precarious and needs to be maintained through performance.

Arbitrary Nature of Gender Roles

When you think about it for more than two seconds, you'll quickly realize that the gender roles and expressions and norms and biases and even definitions that we live under every single day are completely arbitrary. While words like masculine and feminine have a general meaning in biology of pointing towards one of the two most common sex categories, they don't really have a concrete meaning in terms of culture or gender. Because gender includes how a person experiences, expresses, and performs their identity within a cultural context, it's gonna end up being a reflection of that person and their society's expectations, meaning there isn't ever going to be a definitive way to say for sure what it means to have a particular gender because gender varies from culture to culture, from generation to generation, and often from person to person as well.

Debunking Gender Myths

Despite the fact that this understanding of gender has been developed scientifically for about a century now, lots of people still hold on to thoroughly debunked gender myths, like for example the idea of men historically being the hunters and women only being the gatherers and homemakers. We have bountiful archaeological and ethnographic evidence of widespread feminine participation in hunting, tracking, meat processing, and more. One study which surveyed indigenous cultures from around the world found that women participated in hunting in 79% of the society studied, and that wasn't limited to small game either. These were big game hunters who were out there putting in the hard work with the exact same specialized knowledge and skills as their masculine counterparts. And yet, just like the myth of you're either XX or XY, the myth of man the hunter still persists to this day. People look at the gender roles within our own culture and assume that that is the natural ground state of all humanity going back to the beginning of our species. It's a glaring example of cultural bias clouded in scientific thinking.

Conclusion on Gender and Sex

The truth is, no matter how you slice it, gender can neither be boiled down to nor predicted by sex. What Western cultures consider natural behaviors for males and females are not universals among animals, mammals, primates, or even peoples. And if you still don't believe me, let's take a look around the animal kingdom and see just how useless gender would be as a category if it truly were a sex-linked trait.

Gender in the Animal Kingdom

Sexual Dimorphism and Gender Roles

Starting with the basics of sexual dimorphism, there are plenty of species out there where the females are bigger and stronger than the males. And there are also plenty of species where the males and the females are completely indistinguishable. There are even some species where the males can take on several forms, some of which resemble the females. Or species like hyenas, where the females have a fully erectile pseudo-penis, which makes it very difficult to distinguish them from the males unless you dissect them first. Or species like ring-tailed lemurs, where the females have a long and phallic clitoris which is transverse by a urethra, which makes the whole thing look and act an awful lot like a penis as well. And if you think that a phallus with an accessory urethra is an impossibility in human females, you'd be dead wrong. But we already covered that stuff earlier.

Paternal Lactation and Male Caregiving

There are some species, like diac fruit bats, which exhibit paternal lactation, meaning it is the males that produce milk to feed their young. While male lactation is relatively rare at the species level, the ability for any given male to produce milk certainly is not. Even most human males have mammary glands that can be triggered to develop and produce milk under the right circumstances. There are some species where the females deposit eggs into the males and then the males give birth. There are some species where the males, not the females, tend to the nest and watch over the eggs. There are other species where they take turns.

Matriarchal Societies

There are plenty of species, including some of our closest relatives, which are completely matriarchal, meaning it is the females that are in charge and control their whole group. And a strong dominant male would not make it very far. If gender truly was easy to define and linked with sex, then all this variation, which exists well outside of the norms of our own culture, would be impossible to maintain.

Conclusion on Gender in Animals

It's also incredibly common for new learners to confuse gender and sex with sexuality, and to assume that these discussions of genes, hormones, anatomy, roles, identities, and behaviors necessarily implies information about attraction, intimacy, eroticism, and romance. But sexuality is yet another completely different thing that exists on a vast spectrum of preferences and behaviors. And even that spectrum can be further broken down into more specific spectra based on who you're romantically or sexually attracted to, which may or may not line up. For example, an aromantic person is someone who doesn't experience romantic attraction, and that's different from asexuality, which is a lack of sexual attraction.

Understanding Sexuality

Sexuality and Gender

A couple of things that we can say that sexuality and gender have in common is that they're traditionally associated with socioeconomic status and power, and that they display rich diversity across cultures and throughout history. There are plenty of cultures out there which categorized and recognized sexualities in totally different ways than we do today, if they even labeled certain sexualities at all. Our current labeling system for different sexualities is a very modern invention, which doesn't really work outside of our cultural framework, which is why it's sometimes so difficult to pin somebody's sexuality down to just one category within our limited language.

Homosexual Behavior in Animals

Looking across the animal kingdom, we've observed homosexual behavior in over 1,500 animal species. There are even some species which are entirely bisexual, like bonobos, or entirely homosexual, like the parthenogenic whiptail lizards that we talked about earlier. If any other trait, behavioral or otherwise, had been observed to be as ubiquitous across the animal kingdom as same-sex sexual behavior, it would not be the least bit controversial to call that trait ancestral or maybe even advantageous.

Genetic and Hormonal Influences on Sexuality

As far as evolution and development are concerned, we're still not entirely sure where homosexuality comes from, but there's strong evidence that there's at least some genetic component to it. In monozygotic or identical twins, twins that share the same DNA, if one twin is homosexual, there's a significant chance that the other one will be as well, whereas in dizygotic or fraternal twins, that chance drops significantly, and in non-twin siblings, the chance is about the same as it would be for any two random people. But genetics aren't the only factor which appear to be at work in determining one's sexuality. There's some evidence that hormones may be at play here as well. For example, in one study, female zebra finches, which were injected with a common feminizing hormone very early in their lives, were more likely to exhibit male-typical behaviors and choose females as mates. Some of them even develop male-typical color patterns. However, we can't be sure whether these sort of things are due to some change in the structure or function of the brain, or if it's somehow extending the sensitive period for sexual imprinting, or if there's some other factor at play. And none of this rules out environmental influences or epigenetic changes that could be allowing those different factors to take effect. Just like with genes, hormones appear to be a piece of the puzzle, but they certainly aren't the whole picture. It's all just a little bit too complicated for that.

Social Pressure and Sexuality

Speaking of environmental influences, there is an unfortunately common myth that social pressure can influence somebody's sexuality or gender identity, especially at a young age. Now is a great time to point out that there is absolutely no evidence to support that, and strong evidence against it. There is evidence that social networks play a role in the spread of certain sexual behaviors, such as the age, frequency, and level of safety at which adolescents engage in sexual activity. However, there is no evidence that the same kind of social influence and peer pressure can change someone's sexual orientation or gender identity. And that isn't for lack of trying. There is actual scientific research looking for that kind of influence, and there are plenty of horrific, real-world examples of people trying to forcibly change someone's sexual orientation or gender identity. None of it works.

Case Study: David Raymer

One case study into this very thing was a man named David Raymer. He was born in 1965, and due to an equipment malfunction during circumcision, his penis was irreparably damaged. His parents sought the help of Dr. John Money at Johns Hopkins University, who used the boy to test his ideas that people were born neutral in our gender identities and that we were socialized into being the genders that we are. Following Dr. Money's instructions, David underwent full sex reassignment surgery and began to be raised as a girl. But by the time he reached adolescence, it was very obvious that he was having a hard time identifying as a girl. And before long, without even knowing the circumstances of his birth, David began to threaten suicide if his parents wouldn't let him be a boy. Later in life, David learned what happened to him, changed his name, became a husband and a father, and went public with his story in order to discredit Dr. Money's research.

Conclusion on Social Pressure and Sexuality

David's tragic story, along with the consistent findings of modern research, thoroughly debunk the sadly popular ideas that being gay or transgender are examples of social contagions or maladaptive trauma responses. They also categorically rule out the ideas that somebody can be turned gay or straightened out, and they've prompted scientific and medical communities to re-evaluate the ways that they deal with non-binary, transgender, and intersex people, and to develop new measures to prevent harm in children and adults alike who may be struggling with their gender identities. These data fall perfectly in line with our understanding of sexuality and gender as being relatively stable parts of a person's identity, which while not fully understood, are certainly not dependent upon fashion or social conditioning. Which is one of the major reasons that all of these professional organizations, which collectively represent millions of licensed medical and mental health care professionals, have made public statements denouncing conversion therapy as the dangerous, pseudoscientific nonsense that it is.

Research into Sexual Orientation

Research into sexual orientation is incredibly important, but just like the rest of the things in this video, there's a lot that we still don't know, and unfortunately that knowledge can only be gained by people being very honest with complete strangers about really intimate personal information that historically has been seen as pretty taboo. So it may be a little while before we have a more complete understanding of all this stuff. What we already know for sure though is that sexuality is yet another spectrum, so looking for one single cause that produces a clear-cut outcome is a surefire way to miss out on a real understanding of what's actually going on there.

Self-Identification and Gender

Importance of Self-Identification

The cultural dynamics of gender, along with its deeply personal and fluid nature, means that the labels associated with gender identity necessarily rely on self-identification. And this is a major sticking point for people who think that self-identification renders gender overly subjective, recursive, or impossible to confirm. However, self-identification is an inherent part of social identity in general, so it's not like this is a new concept that just came along with gender.

Sexuality as an Example

In fact, we can actually use the spectrum of sexuality as a great example as to why the self-identification model is not only functional, but the most effective way to identify someone's gender. When we talk about sexuality, it's important to remember that there may not be a single, simple, specific term to adequately describe someone's sexual orientation. And the terms that we do use sometimes mean different things to different people. This is because there's simply no way to fully and adequately account for all of a person's feelings about something so complex while simultaneously crushing those feelings down into a single categorical label that can be reliably applied elsewhere. Instead, the terms we use are just tools for self-expression, allowing people to describe their experiences in ways that are meaningful to them. And gender works the same way.

Descriptive Nature of Gender Identities

The terms we use are neither diagnostic nor universal, so each person who identifies themselves using a term like man, woman, boy, girl, or non-binary also defines that term for themselves. These identities are descriptive, not prescriptive, reflecting what matters most to the individual about the roles, behaviors, expressions, or even physiology that they associate with that category. When someone earnestly refers to themselves as a man or a woman, all we know for sure is that they are a person who self-identifies as and aligns their gender identity to the social, cultural, and personal traits that they associate with manhood or womanhood. There is no other way to define these terms so that they include all cis and trans people of one category and exclude all cis and trans people of any other category.

Eurocentric Framework and Gender

It's also critically important to remember that even just the words, transgender, non-binary, gay, bisexual, and so on, are themselves products of a Eurocentric framework of gender and sexuality, which assumes that cisgender heterosexuals are the natural standard and that everybody else's existence needs to be justified rather than accounted for. This perspective ignores the fact that there are plenty of cultures out there that have all had the same kinds of people, but with completely different lines and distinctions than the ones that we're hashing out here. Beyond that, it ignores that nature itself has presented us with a complex and diverse spectrum of chromosomes and anatomies and hormones and behaviors that often defy the rigid, oversimplified categories that humans have created. This is not unique to science, especially to biology, and we need to quit pretending like it is. It is only because we are looking through the narrow lens of our cis-centered and heteronormative culture that we treat diverse genders and sexualities as anything less than yet another exciting part of the rich tapestry of biology.

Conclusion on Self-Identification

As I said in the beginning of this video, we are not special. We're just animals. The one thing that sets us apart in all of this is that we are the only animals that can communicate in great detail what it feels like to have a particular gender or a particular sexuality and what it means to experience those things in the cultural context surrounding us. We should not be afraid of the perceived differences between cis and trans or straight and gay or any of this. We should be excited for the opportunity to learn new information about how life really works rather than just trying to cram things down into boxes all the time. If we want to understand what it means to be human or what it means to be anything, we need to be focused on science and be listening to the people who are living the lives that we want to understand.

The Human Brain and Gender

Historical Perspective on Brain Sex

And we can gain a glimpse of that understanding when we look directly into the human brain. Historically, the concept of sexual dimorphism in human brains originated from observations in other animals, where certain brain regions which were usually tied to reproductive behaviors like vocal control regions in songbirds, for example, showed dramatic differences between the sexes. And so it was largely assumed that human brains would show the same kinds of dimorphism. But when we looked more closely, we found that it wasn't necessarily so easy.

Hormones and Brain Development

For example, one study on quails found that there was a critical period for hormone exposure in the brain. And when researchers gave quail embryos, masculinizing or feminizing hormones at this stage, the resulting adults would behave more like a male or a female based on the hormones they received rather than their chromosomal or anatomical sexes. Fast forward to looking at human brains and we see that the same thing is true. Brain development and function are not solely determined by genetic sex, but are actually influenced by a complex array of hormonal, environmental, and even social factors. And this dynamic dance of stimuli is what creates the complexities of our gender identities, whether we're cis, trans, non-binary, or whatever.

Sex Differences in the Human Brain

While some sex differences do exist in the brain, the magnitude of these differences is far smaller than in other species. For example, the third interstitial nucleus of the anterior hypothalamus, or the INAH3, is around 1.6 times larger in human males than it is in human females, whereas a homologous region in rats is around five times larger in males rather than females. So when we talk about structural differences within the brains of males and females of other species, we're sometimes talking about differences that are so prominent you can see them with the naked eye. In humans, however, we're talking about clusters of neurons that are around the size of a grain of rice.

Brain Regions and Gender Identity

There are other notable regions like the central subdivision of the bed nucleus of the stria terminalis, or BSTC, and the sexually dimorphic nucleus of the preoptic area, or SDNPOA, both of which are usually larger in males than in females. But the key is, because hormones seem to play a bigger role in brain development than sex chromosomes do, the sizes of these brain regions tend to reflect someone's gender identity rather than simply their sex assigned at birth.

Outdated Model of Brain Sex

Through all of this, it's crucial to emphasize that the concept of brain sex, as it used to be understood, is a very outdated model. It is true to say that certain sex hormones play a critical role in shaping the brain during both pre- and post-natal development. However, there are plenty of other factors, like gene expression, hormone receptor distribution, and even individual experiences, which also play a major part in brain development, and can dramatically influence the degree of maleness or femaleness within brain structure and function.

Mosaic Nature of Human Brains

Most of the brain differences, which were once attributed to sexual dimorphism, have since been shown to actually be quite small, with a ton of overlap between sexes. In fact, modern research has shown that human brains exhibit a wide variety of characteristics which were once considered male-typical or female-typical, creating a unique mosaic pattern for each individual and a lot of variation across populations. One review of over 1,400 human brains found that sex differences between the brains were neither highly dimorphic nor internally consistent. Instead, each and every one of the brains was a varied composite of diverse features, putting the brain, along with everything else about sex, on a spectrum.

Volume and Development Time

The most consistent sex difference between male and female brains tends to be overall volume and development time, with male brains being slightly larger, simply because male bodies are slightly larger, and female brains finishing development earlier. But none of that really translates to a major difference in functionality, and all this complexity makes it difficult to say that anybody, not just cis or trans people, have brains that truly completely structurally match their gender identities.

Neuroplasticity and Gendered Experiences

But what does point in that direction is the fact that brains adapt to experiences. The connections between neurons break and build and reorganize all the time, and as they do, whole brain regions can change. We call this quality neuroplasticity. So when we want to look for gender-specific differences in the brain, we often need not look much further than gender-specific experiences which create gender-specific plastic responses. That is to say, as we lead gendered lives and have gendered feelings, we develop somewhat gendered brains.

Phantom Pain and Gender Identity

Let me give you an example. People who have lost limbs sometimes experience what's commonly known as phantom pain, where their brain is so sure that the lost limb is still there that the patient suffers pain in a part of the body that no longer exists. Interestingly, some transgender people have been shown to experience their own kind of phantom pain, only instead of experiencing pain in a limb that they have lost, they feel a part of their body that they've never had before, like breasts or wide hips or even certain genitalia.

Brain Perception and Gender

We can also learn from how our brains perceive our own bodies, like one notable study in which cis and trans people had their brains monitored while they watched computer-generated images of their own bodies morphing to become more masculine or more feminine. And sure enough, the same brain regions lit up in trans people watching their bodies morph away from their assigned sex, as in cis people watching their bodies morph towards it.

Conclusion on Brain and Gender

As it is, the relationship between brain structure and development and their association with gender identity is not fully understood, and more research is needed to draw more definitive conclusions. However, it seems clear that the brain is far more mosaic than dimorphic. The idea of male and female brains oversimplifies a far more dynamic and individualized phenomenon. At face value, there seem to be no more male or female brains than there are male or female hearts or male or female lungs. But there are gendered patterns of brain responses, which are produced by gendered patterns of stimuli in the world around us. And we consistently see that the activation patterns within transgender people's brains match those that we would expect to see in someone with their gender identity, not their assigned sex at birth.

Neurobiological Component to Sexualities

Oh, and by the way, there's a ton of research showing a neurobiological component to diverse sexualities as well. For example, functional MRI scans show the same brain regions behaving in the same way, in homosexual men and heterosexual women observing an image of a man's face. And sure enough, in homosexual women and heterosexual men, the exact same brain regions do the exact same things with a woman's face. There are also other studies which point to certain brain regions which may be larger or smaller in homosexual or heterosexual individuals. And just like with gender, the evidence increasingly points to a vast array of neural factors which may or may not be associated with sexual orientation. All of this makes interpretations of the meanings of these connections just as murky as those drawn from brain differences between sexes.

Avoiding Pathologization

All that being said, as we continue to study these things, it's important that we take care not to pathologize LGBT identities. Not only is it abundantly clear that these are not diseases or disorders, but emphasizing differences in order to explain perceived anomalies can lead to people justifying discrimination. As we work to interpret these data, it's crucial that we also work to temper our social and cultural heuristics surrounding gender and sexuality, so that we don't unduly influence our scientific understanding or risk perpetuating harmful stereotypes.

Conclusion

Recap of Key Points

So, if you've been following along, we've covered a variety of possibilities in chromosomes, in hormones, in internal and external genitalia, in gender, in sexuality, in brains, in culture, and in history. We've talked about how you can have XX chromosomes and still have a penis. We've talked about how you can have XY chromosomes and still get pregnant. We've talked about how you can have ovaries or testes or a penis or a uterus or neither or both or more than one of one or the other, which happens from time to time. And through it all, the point remains, if you really, really want to hold onto this idea that every single person fits into just one of however many boxes, you are very quickly going to have to come up with dozens, if not hundreds of categories, just to hold onto this insanely parochial worldview you're keeping.

Complexity of Sex and Gender

The genetic, chromosomal, biochemical, hormonal, gonadal, anatomical, and physiological characteristics traditionally associated with so-called males and females are far more complex than people tend to assume. Sex is not a binary system, with only two mutually exclusive outcomes. And gender, by its very definition as a social construct, adds yet another layer of infinite variation. And that's why it's not only more scientifically accurate, but just so much easier to say that sex and gender exist on a spectrum. And while it's entirely possible that you're 100% male or 100% woman, whatever that would mean, it is at least equally possible that you fall somewhere along this fuzzy gradient. And that shouldn't bother you. It should make you curious. But to go on spewing nonsense like XX means girl and girls dress like this, or XY means boy and boys act like that is not only preposterously inaccurate, it is cruel and dangerous.

Real-World Implications

Which brings me to why all this stuff matters outside of biology class. Over the course of this video, we've talked about how sex and gender are different things, how they aren't necessarily congruent, and how neither one is a true binary. This is especially true of gender, which by its very nature cannot be expected to reliably present itself in predictable ways. But just because gender is a social construct, that doesn't mean that it has no bearing on reality. Just like other social constructs like law, marriage, race, and money, gender has big impacts and big implications at both the individual and societal levels.

Gender and Healthcare

For example, gender has a direct influence on people's experiences with, and sometimes even their access to, healthcare. Not only because of gender bias and discrimination among healthcare professionals, but also because of systemic gender inequalities within societies. Typically, women and girls experience greater barriers to accessing adequate healthcare than men and boys. These barriers include, but aren't limited to, restrictions on their mobility, lack of access to medical information, reduction or removal of decision-making power, lower literacy rates, discrimination from their provider and their community, and sometimes even lack of training and awareness among healthcare providers of the specific needs of anatomical females. Consequently, women and girls face greater risks of unintended pregnancies, sexually transmitted infections, cancer, malnutrition, vision impairments, respiratory infections, genital mutilations, elder abuse, and much, much more.

Gender-Affirming Care

When it comes to transgender people, this situation compounds due to the tremendous amount of misinformation and fear-mongering surrounding what's known as gender-affirming care, which is specialized medical care which attempts to reduce the incongruence between a person's gender identity and their phenotypic sex. When we talk about gender-affirming care, people often assume that we are talking about extreme surgeries performed only on transgender people. However, that isn't the case. In fact, most gender-affirming care, including things like hair plugs, lip fillers, hormone therapies, laser hair removal, breast augmentation, breast reduction, breast tissue removal, erectile dysfunction treatments, facial feminization or masculinization surgeries, and even puberty blockers, are utilized more often than not by cisgender people, usually to help align their physical appearance with their gender identities, exactly the same as when these treatments are given to transgender people.

Misconceptions and Political Issues

Unfortunately, despite the fact that every major medical association in America recognizes the validity of transgender people and the vital role of gender-affirming care in improving their mental and physical well-being, despite the fact that studies have consistently shown that age-appropriate and evidence-based gender-affirming care protects transgender people from a greater incidence of anxiety, depression, and self-harm, despite the fact that we have standards of care and clinical guidelines which are widely accepted for transgender adults and children alike, which recommend a staged process of transition which allows these individuals to explore their gender identities while keeping their options open, and despite the fact that the regret rate for these interventions is significantly lower than many common treatments and surgeries that nobody takes issue with, people and politicians alike are attempting to demonize or even deny gender-affirming care specifically and only for transgender people because it conflicts with their ideology rather than their understanding of the evidence.

Gender Dysphoria and Mental Health

Gender dysphoria is the distress caused by the discrepancy between an individual's gender identity and their sex assigned at birth. Not all transgender individuals experience gender dysphoria. Sometimes it can be treated with social transition alone. Sometimes medical interventions are necessary. Sometimes it abates with puberty. Sometimes puberty makes it much, much worse. In any and all of these situations, it is imperative that transgender people be allowed to explore their options and to effectively align their genders with their bodies under the safe and supportive care of a physician, because when they are not afforded that opportunity, the results can be exactly as dire as you would expect when a person is forced to live in a way that is in direct conflict with their identity.

Suicide and Mental Health Risks

As of right now, suicide is the second leading cause of death among people from the ages of 10 to 14 and the third leading cause of death among people from the ages of 15 to 24. It outranks all major illnesses. Lots of young people think about it. I thought about it at that time. But LGBT people in those age groups are almost five times as likely to have attempted suicide than their cisgendered heterosexual peers. And what's worse, LGBT youth who report coming from non-accepting or non-supportive families are eight times as likely to have attempted suicide than other LGBT youth. So we're talking about people who are eight times as likely as the people who were already five times as likely as the people who were already at a high risk of attempting suicide. That is a major problem that deserves serious attention. And if there was anything, anything at all that could reduce that risk even a little bit, it should at least warrant your sincere consideration.

Misinformation and Harm

And all of this is hugely exacerbated by the deluge of charlatans, grifters, and pseudo-intellectuals in media and politics who point to these high rates of suicide and depression as evidence that diverse genders and sexualities are tantamount to mental disorders. When all it really demonstrates is that these people don't understand the difference between correlation and causation and that these poor kids are being treated like perverts and freaks for just trying to exist. It also doesn't help anybody to suggest that we should be keeping discussions of gender and sexuality away from children. Not only does it ignore the fact that children are exposed to depictions of cisgender people in heterosexual relationships all the time, whether they be in fairy tales or family sitcoms or history class, it also assumes that LGBT people were never children before. Research shows that these kids know who and what they are long before they have the vocabulary to articulate it. And by denying them the same levels of age-appropriate representation and education that we afford everybody else, we're spreading the harmful message that their thoughts, feelings, and identities are something to be ashamed of and hidden away, as well as fueling the exact same kind of bullying and stigmatization that leads to serious harm in any children.

Gender Norms and Violence

And because of our cultural attitudes surrounding gender, the risks for women, girls, and those with diverse gender identities continue well into the outside world and throughout their entire lives. Gender-based stigma and discrimination puts these people at significantly higher risk of both physical and sexual violence, and when it comes to trans people, those numbers increase dramatically. Trans people across the board, both men and women alike, are over four times as likely to experience sexual assault, aggravated assault, rape, and other forms of violence as their cisgender counterparts. And circling back to self-harm, it turns out when you're consistently the victim of systemic discrimination and normalized physical violence, it takes a toll on your mental health.

Harmful Gender Norms for Men

Even looking beyond trans and gender-diverse people, the gender norms that we live under themselves can be harmful if not regulated, as we see, for example, in men and boys, who are more likely to take unnecessary risks with their mental, physical, and sexual health, abuse drugs and alcohol, smoke tobacco, and even refuse mental and physical health care, all in the interest of appearing tough and manly. And those same emotionless, hypersexual, and dominance-oriented gender norms lead to men and boys being the perpetrators of physical and sexual violence, as well as failing to report on instances in which they are the victims of that same violence. These are all examples of widespread, gender-specific patterns of violence, harm, and death that we could be working to eliminate. But first, we've got to come to grips with the functions and implications of gender and stop pretending like this is all just some modern political ideology.

Reevaluating Priorities

But if the biggest problem you're having in the 21st century is what people's genitals look like and what they're doing with their genitals in the company of other consenting adults, if that is the needle on your moral compass, I strongly encourage you to reevaluate your priorities.

Scientific Progress and Inclusivity

Looking outside of the interests of direct human harm reduction, improving our understanding and attitudes surrounding gender is beneficial to progress as a whole. A lot of scientific research has been done under the outdated binary framework, which often conflate sex and gender together. Having recognized this issue, lots of scientists and even major science organizations are working to establish meaningful ways to measure sex and gender as non-binaries, in surveys, research studies, job applications, clinical settings, and more. After all, if we've been doing research using definitions and dichotomies that are at best ineffective and at worst inaccurate, then how does that research stand up? It's certainly not useless, but it's undeniable that we could be learning new things faster if we were to use more accurate and more inclusive models of sex and gender when gathering and analyzing data.

Moving Beyond Dualisms

The very idea that sex and gender are synonymous and locked in a strict and immutable binary, despite all the evidence of the contrary and the lived experiences of millions of trans and intersex people, exemplifies the kind of unnecessarily rigid and dualistic thinking that impedes both social progress and scientific discovery. However, recognizing the non-synonymous and non-binary nature of things like sex and gender not only opens the door for accepting and celebrating the immense variation we see within human bodies, minds, and existence, it also paves the way for improving the way that we do research into things like evolution and development, as well as how we tackle things like health care, education, social policies, and so much more.

National Academies of Sciences Report

That's why, back in 2022, the National Academies of Sciences, Engineering, and Medicine put out this consensus study report on how to better measure and report things like gender identity, sexual orientation, and sex as a non-binary construct, all to expand our research efforts beyond the restrictive dualisms of male and female, or man and woman, or homosexual and heterosexual. Because, as it says right in the introduction, the use of a single, binary male-female item to measure sex does not capture either the multidimensional nature of this construct or its underlying complexity for those with intersex traits or transgender people, because their sex traits may not correspond to those of a single sex. Introducing a third response category to binary measures of sex, such as transgender or intersex, is thus a poor measure of these populations. Moreover, because gender is socially mediated, binary measures of any dimension of gender are also inadequate for capturing the complex ways in which individuals can identify with, express, or socially experience gender.

Conclusion on Sex and Gender

The reality is that sex and gender are far from clean-cut concepts. We're still learning all the pieces that go into sex determination, as well as where gender even comes from, let alone what it actually is. We should expect to have better, more accurate, and more productive understandings of these things sooner rather than later. But as for right now, as is so often the case in science, especially biology, it's less about getting clear-cut answers and more about asking bigger and better questions. It's about recognizing the assumptions that we're making, sometimes the ones we don't even realize that we're making, and challenging them so that we can better understand nature in its own language. That may sound daunting, but handling concepts with no simple definitions or with context-dependent definitions requires precisely the kind of special care and specific reasoning tools that, as I mentioned earlier, we're used to in biology. Turning old models on their heads and forcing us to dramatically change the way that we think about the entire world is the story of science. It's what science is best at.

Language and Inclusivity

And in the meantime, the least that we could do is try to tidy up our language. We've taken nothing else away from this conversation. You should have at least picked up on the fact that even what you might call normal is a massively diverse group of people. Boiling concepts of manhood or womanhood down to simple physical characteristics like a phallus or a uterus or whatever chromosomes you like is not only unnecessarily reductive, it's wholly inaccurate. For example, as we've already mentioned, not every woman has a uterus, and not everyone with a uterus is a woman, whether you separate sex from gender or not. We all live on a spectrum of sex and gender, and you're not always going to have an easy time navigating it, because people are under no obligation to make sense to you. But none of the variation or fuzziness that I've brought up so far means that we now have to say that chromosomes have nothing to do with sex at all, or that there are 10,000 new sexes and genders that need to be labeled, or that there are no gendered patterns of behavior to speak of, any more than a person occasionally being born without legs means that we can't call humans bipedal anymore. It just means that we should try to be a little bit more specific. Most humans have two legs. Generally, humans have two legs. More often than not, humans have two legs. And similarly, typically, XY means male. Ordinarily, males are boys. On average, boys like sports. Adding just a tiny bit of effort into your language choices makes what you're saying not only more inclusive, but more scientifically accurate as well. In fact, you'll find that if you're being more scientifically accurate, you are almost always being more inclusive, too.

Embracing Change

I understand that it's going to be a little uncomfortable to alter our conceptual frameworks, our heuristics, our language, and our culture around a more detailed model of sex and gender. But hundreds of millions of people are counting on us to pull it together and figure it out, so that they can go on living their lives in peace the way that we all want to. And maybe you still don't believe me on this. Maybe you think that I'm just totally wrong or that I misread or misinterpreted something. That's fine. But there are two important things that I should point out. First is that there's a lot more stuff that I could have put in here, but I mainly specialize in evolution and human biology. While I do have training in genetics and development, I am neither a geneticist nor a developmental biologist. So even if we had hit the limit of what I could have talked about here, there still would have been a lot more information that could have been included.

Final Thoughts

And second is that I am not the only biologist who has reached these conclusions. As I mentioned earlier, plenty of other scientists and scientific organizations are working on this new model, and even modern biology textbooks are catching up. The 10th edition of Campbell Biology: Concepts and Connections, a widely used textbook for introductory biology courses for non-majors, published back in 2022, includes this paragraph on gender and sex:

"The biochemical, physiological, and anatomical features associated with males and females are turning out to be more complex than previously realized, with many genes involved in their development. We now know that sex is not a binary state with just two defined outcomes. Because of the complexity of the genes and proteins involved in sex determination, many variations exist. Some individuals are born with intermediate sexual or intersex characteristics, or even with anatomical features that do not match an individual's sense of their own gender, known as transgender individuals. Sex determination is an active area of research that should yield a more sophisticated understanding in years to come."

This is literally basic biology.

If you're interested in all of this and would like to know more, or if you just want to fact-check anything that I've said today, I've left a link in the description with a detailed reference list of all the books, papers, and studies that I used to make this video. This includes several things that I barely had the chance to touch on and even a few things that didn’t make it into the video. For those of you who don’t want to dig through all that but are curious, here’s a sneak peek. So I guess just read through those and get back to me.

We've covered a ton of material in this video, but the one thing I hope you take away more than anything else is that life is incredibly diverse. And humans, as living beings, are incredibly diverse as well. We do not come in just one or two sizes, shapes, colors, styles, sexes, or genders. We are a product and a reflection of the multidimensional beauty that is life on this planet, and we should respect and appreciate each other as such.

Just as the rainforest teems with tens of thousands of species, and the oceans sparkle with vibrant colors of every hue, humanity adorns the world with expressions of gender, love, and what it means to be alive. Our diversity highlights the beauty of nature, and the way we embrace and celebrate that diversity highlights the beauty of our species. The more we explore ourselves and each other, the more we enrich our lives and societies. As we learn more about the people around us, we find meaning, belonging, and more than a little science along the way.

Biology is just too big for my nerves, and if you ask me, I wouldn’t have it any other way.

And with that, I’m Forrest Valkai. Thank you so much for watching, liking, commenting, subscribing, and all the other stuff you do here on YouTube. Have an awesome rest of your day. Be yourself and never stop learning. Bye-bye!

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