PRAISE FOR COME AS YOU ARE

Goodreads Choice Awards, Top 5 Science and Technology Books

Buzzfeed’s 17 Things that Changed Our Sex Lives in 2015

Book Riot’s Best of 2015

Autostraddle’s Top 10 Queer and Feminist Books

SSTAR’s 2017 Consumer Book Award

This is the best book I have ever read exploring the science of female sexuality. I am a total evangelist for Nagoski’s work…. You think you know how women’s sexuality works? I can guarantee that you do not. Not until you read this, anyway. The book is definitely great for college students and for bright high schoolers as well.

—Peggy Orenstein, author of Girls and Sex

"This is the best book I have ever read about sexual desire and why some couples just stop having sex, and what they can do about it. Come As You Are is an absolutely necessary guide for all couples who want to understand the ups and downs in their own sex life. It is a must-read!"

—John Gottman, Ph.D., author of The Seven Principles for Making Marriage Work

"Emily Nagoski has written one of the most important books about sex any woman (or anybody else) could ever pick up, full of insights that are both fascinating and deeply useful. Synthesizing new research and theory about sexuality with old-school sex-positive information of the sort you didn’t learn in sex ed (unless, perhaps, you are a Unitarian, or Scandinavian, or lucky enough to be in Dr. Nagoski’s class), I guarantee Come As You Are will open minds and change lives."

—Carol Queen, Ph.D., founding director of the Center for Sex & Culture

"Emily Nagoski is worth her weight in TED Talks, and Come as You Are is a master class in the science of sex."

—Ian Kerner, sex therapist and bestselling author of She Comes First

It’s the science of sex, decoded and demystified. Want to be educated on the latest findings about female genitalia? Of course you do. Empowering and sex-positive at best, this informative read makes for an enticing bedfellow.

—Refinery29

Lots of books—and articles and experts—claim to have the keys to transform your sex life. This one actually has it. It isn’t as fast as taking a pill, but it will last a whole lot longer. You will find no hot new bedroom moves—it’s that deeper-level soul stuff. You know, the stuff that actually works.

—Salon.com

Wonderful new language to help us articulate to women (and their lovers) what is going on.

—Huffington Post

Like a punch to the gut. When I read the passage that made me realize—after all these years—that I was not actually broken, I began to cry…. I wished [Nagoski] was someone who was actively in my life, someone I could reach out to for grounding every time I momentarily forgot the lessons in her book.

—Book Riot

"Nagoski’s book deserves plaudits for the rare achievement of merging pop science and the sexual self-help genre in prose that’s not insufferably twee…. [Come As You Are] offers up hard facts on the science of arousal and desire in a friendly and accessible way."

—The Guardian (UK)

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For my students

introduction

YES, YOU ARE NORMAL

To be a sex educator is to be asked questions. I’ve stood in college dining halls with a plate of food in my hands, answering questions about orgasm. I’ve been stopped in hotel lobbies at professional conferences to answer questions about vibrators. I’ve sat on a park bench, checking social media on my phone, only to find questions from a stranger about her asymmetrical genitals. I’ve gotten emails from students, from friends, from their friends, from total strangers, about sexual desire, sexual arousal, sexual pleasure, sexual pain, orgasm, fetishes, fantasies, bodily fluids, and more.

Questions like…

Once my partner initiates, I’m into it, but it seems like it never even occurs to me to be the one to start things. Why is that?

My boyfriend was like, You’re not ready, you’re still dry. But I was so ready. So why wasn’t I wet?

I saw this thing about women who can’t enjoy sex because they worry about their bodies the whole time. That’s me. How do I stop doing that?

I read something about women who stop wanting sex after a while in a relationship, even if they still love their partner. That’s me. How do I start wanting sex with my partner again?

I think maybe I peed when I had an orgasm…?

I think maybe I’ve never had an orgasm…?

Under all these questions, there’s really just one question:

Am I normal?

(The answer is nearly always: Yes.)

This book is a collection of answers. They’re answers that I’ve seen change women’s lives, answers informed by the most relevant science and by the personal stories of women whose growing understanding of sex has transformed their relationships with their own bodies. These women are my heroines, and I hope that by telling their stories, I’ll empower you to follow your own path, to reach for and achieve your own profound and unique sexual potential.

the true story of sex

After all the books that have been written about sex, all the podcasts and TV shows and magazine articles and radio Q&As, how can it be that we all still have so many questions?

Well. The frustrating reality is we’ve been lied to—not deliberately, it’s no one’s fault, but still. We were told the wrong story.

For a long, long time in Western science and medicine, women’s sexuality was viewed as Men’s Sexuality Lite—basically the same but not quite as good.

For instance, it was just sort of assumed that since men have orgasms during penis-in-vagina sex (intercourse), women should have orgasms with intercourse, too, and if they don’t, it’s because they’re broken.

In reality, about a quarter of women orgasm reliably with intercourse. The other 75 percent sometimes, rarely, or never orgasm with intercourse, and they’re all healthy and normal. A woman might orgasm lots of other ways—manual sex, oral sex, vibrators, breast stimulation, toe sucking, pretty much any way you can imagine—and still not orgasm during intercourse. That’s normal.

It was just assumed, too, that because men’s genitals typically behave the way their minds are behaving—if a penis is erect, the person attached to it is feeling turned on—a woman’s genitals should also match her emotional experience.

And again, some women’s do, many don’t. A woman can be perfectly normal and healthy and experience arousal nonconcordance, where the behavior of her genitals (being wet or dry) may not match her mental experience (feeling turned on or not).

And it was also assumed that because men experience spontaneous, out-of-the-blue desire for sex, women should also want sex spontaneously.

Again it turns out that’s true sometimes, but not necessarily. A woman can be perfectly normal and healthy and never experience spontaneous sexual desire. Instead, she may experience responsive desire, in which her desire emerges only in a highly erotic context.

In reality, women and men are different.

But wait. Women and men both experience orgasm, desire, and arousal, and men, too, can experience responsive desire, arousal nonconcordance, and lack of orgasm with penetration. Women and men both can fall in love, fantasize, masturbate, feel puzzled about sex, and experience ecstatic pleasure. They both can ooze fluids, travel forbidden paths of sexual imagination, encounter the unexpected and startling ways that sex shows up in every domain of life—and confront the unexpected and startling ways that sex sometimes declines, politely or otherwise, to show up.

So… are women and men really that different?

The problem here is that we’ve been taught to think about sex in terms of behavior, rather than in terms of the biological, psychological, and social processes underlying the behavior. We think about our physiological behavior—blood flow and genital secretions and heart rate. We think about our social behavior—what we do in bed, whom we do it with, and how often. A lot of books about sex focus on those things; they tell you how many times per week the average couple has sex or they offer instructions on how to have an orgasm, and they can be helpful.

But if you really want to understand human sexuality, behavior alone won’t get you there. Trying to understand sex by looking at behavior is like trying to understand love by looking at a couple’s wedding portrait… and their divorce papers. Being able to describe what happened—two people got married and then got divorced—doesn’t get us very far. What we want to know is why and how it came to be. Did our couple fall out of love after they got married, and that’s why they divorced? Or were they never in love but were forced to marry, and finally became free when they divorced? Without better evidence, we’re mostly guessing.

Until very recently, that’s how it’s been for sex—mostly guessing. But we’re at a pivotal moment in sex science because, after decades of research describing what happens in human sexual response, we’re finally figuring out the why and how—the process underlying the behavior.

In the last decade of the twentieth century, researchers Erick Janssen and John Bancroft at the Kinsey Institute for Research in Sex, Gender, and Reproduction developed a model of human sexual response that provides an organizing principle for understanding the true story of sex. According to their dual control model, the sexual response mechanism in our brains consists of a pair of universal components—a sexual accelerator and sexual brakes—and those components respond to broad categories of sexual stimuli—including genital sensations, visual stimulation, and emotional context. And the sensitivity of each component varies from person to person.

The result is that sexual arousal, desire, and orgasm are nearly universal experiences, but when and how we experience them depends largely on the sensitivities of our brakes and accelerator and on the kinds of stimulation they’re given.

This is the mechanism underlying the behavior—the why and the how. And it’s the rule that governs the story I’ll be telling in this book: We’re all made of the same parts, but in each of us, those parts are organized in a unique way that may change over our life span.

No organization is better or worse than any other, and no phase in our life span is better or worse than any other; they’re just different. An apple tree can be healthy no matter what variety of apple it is—though one variety may need constant direct sunlight and another might enjoy some shade. And an apple tree can be healthy when it’s a seed, when it’s a seedling, as it’s growing, and as it fades at the end of the season, as well as when, in late summer, it is laden with fruit. But it has different needs at each of those phases in its life.

You, too, are healthy and normal at the start of your sexual development, as you grow, and as you bear the fruits of living with confidence and joy inside your body. You are healthy when you need lots of sun, and you’re healthy when you enjoy some shade. That’s the true story. We are all the same. We are all different. We are all normal.

the organization of this book

The book is divided into four parts: (1) The (Not-So-Basic) Basics; (2) Sex in Context; (3) Sex in Action; and (4) Ecstasy for Everybody. The three chapters in the first part describe the basic hardware you were born with—a body, a brain, and a context. In chapter 1, I talk about genitals—their parts, the meaning we impose on those parts, and the science that proves definitively that yes, your genitals are perfectly healthy and beautiful just as they are. Chapter 2 details the sexual response mechanism in the brain—the dual control model of inhibition and excitation, or brakes and accelerator. Then in chapter 3, I introduce the ways that your sexual brakes and accelerator interact with the many other systems in your brain and environment, to shape whether a particular sensation or person turns you on, right now, in this moment.

In the second part of the book, Sex in Context, we think about how all the basic hardware functions within the reality of your actual life—your emotions, your relationship, your feelings about your body, and your attitudes toward sex. Chapter 4 focuses on two primary emotional systems, love and stress, and the surprising and contradictory ways they can influence your sexual responsiveness. Then chapter 5 describes the cultural forces that shape and constrain sexual functioning, and how you can maximize the good things about this process and overcome the destructive things. What we’ll learn is that context—your external circumstances and your present mental state—is as crucial to your sexual wellbeing as your body and brain. Master the content in these chapters and your sexual life will transform—along with, quite possibly, the rest of your life.

The third part of the book, Sex in Action, is about sexual response itself, and I bust two long-standing and dangerous myths. Chapter 6 lays out the evidence that sexual pleasure and desire may or may not have anything to do with what’s happening in your genitals. This is where we learn why arousal nonconcordance, which I mentioned earlier, is normal and healthy. And after you read chapter 7, you will never again hear someone say sex drive without thinking to yourself, Ah, but sex is not a drive. In this chapter I explain how responsive desire works. If you (or your partner) have ever experienced a change in your interest in sex—increase or decrease—this is an important chapter for you.

And the fourth part of the book, Ecstasy for Everybody, explains how to make sex entirely yours, which is how you create peak sexual ecstasy in your life. Chapter 8 is about orgasms—what they are, what they’re not, how to have them, and how to make them like the ones you read about, the ones that turn the stars into rainbows. And finally, in chapter 9, I describe the single most important thing you can do to improve your sex life. But I’ll give it away right now: It turns out what matters most is not the parts you are made of or how they are organized, but how you feel about those parts. When you embrace your sexuality precisely as it is right now, that’s the context that creates the greatest potential for ecstatic pleasure.

Several chapters include worksheets or other interactive activities and exercises. A lot of these are fun—like in chapter 3, I ask you to think about times when you’ve had great sex and identify what aspects of the context helped to make that sex great. All of the exercises turn the science into something practical that can genuinely transform your sex life.

Throughout the book, you’ll follow the stories of four women—Olivia, Merritt, Camilla, and Laurie. These women don’t exist as individuals; they’re composites, integrating the real stories of the many women I’ve taught, talked with, emailed, and supported in my two decades as a sex educator. You can imagine each woman as a collage of snapshots—the face from one photograph, the arms from another, the feet from a third… each part represents someone real, and the collection hangs together meaningfully, but I’ve invented the relationships that the parts have to each other.

I’ve chosen to construct these composites rather than tell the stories of specific women for two reasons. First, people tell me their stories in confidence, and I want to protect their identities, so I’ve changed details in order to keep their story their story. And second, I believe I can describe the widest possible variety of women’s sexual experiences by focusing not on specific stories of one individual woman but on the larger narratives that contain the common themes I’ve seen in all these hundreds of women’s lives.

And finally, at the end of each chapter you’ll find a tl;dr list—too long; didn’t read, the blunt internet abbreviation that means, Just get to the point. Each tl;dr list briefly summarizes the four most important messages in the chapter. If you find yourself thinking, My friend Alice should totally read this chapter! or I really wish my partner knew this, you might start by showing them the tl;dr list. Or, if you’re like me and get too excited about these ideas to keep them to yourself, you can follow your partner around the house, reading the tl;dr list out loud and saying, See, honey, arousal nonconcordance is a thing! or It turns out I have responsive desire! or You give me great context, sweetie!

a couple of caveats

First, there are times when I discuss what trans sex educator S. Bear Bergman calls factory-installed parts—the anatomical details that make doctors declare a baby a girl or a boy. For clarity and simplicity, when I’m talking about those parts, I’ll use the words female or male, referring to the biological categories that can describe many sexually reproducing species, not just humans. When I’m talking about a whole person, I’ll use the words woman or man, referring to the person’s identity and social role.

A further gender caveat: Because this book is grounded in the existing science, most of the time when I say women in this book, I mean cisgender women—that is, people who were born in bodies that made the adults around them declare, It’s a girl! and then they were raised as girls and now feel comfortable in the social role and psychological identity of woman. There are plenty of women who don’t have one or more of these characteristics, and there are plenty of people who don’t identify as woman who do fit one or more of these characteristics. Trans and nonbinary people deserve excellent, science-based, pleasure-oriented sex education, too… and there’s still (still!) too little research on trans sexual functioning for me to say with certainty whether what’s true about cisgender women’s sexual wellbeing is also true for trans folks’. I think it probably is, and as more research emerges over the coming decades, we’ll find out. I am totally sure that people of any gender—including cisgender men—can learn a lot from the existing science, incomplete though it is. But while we wait for more and better research, I want to acknowledge that this book relies on science that is almost entirely based on cisgender people.

Third, I am passionate about the role of science in promoting women’s sexual wellbeing, and I have worked hard in this book to encapsulate the research in the service of teaching women to live with confidence and joy inside their bodies. But I’ve been very intentional about the empirical details I’ve included or excluded. I asked myself, Does this fact help women have better sex lives, or is it just a totally fascinating and important empirical puzzle?

And I cut the puzzles.

I kept only the science that has the most immediate relevance in women’s everyday lives. So what you’ll find in these pages isn’t the whole story of women’s sexuality—I’m not sure the whole story would actually fit in one book. Instead, I’ve included the parts of the story that I’ve found most powerful in my work as a sex educator, promoting women’s sexual wellbeing, autonomy, and pleasure.

The purpose of this book is to offer a new, science-based way of thinking about women’s sexual wellbeing. Like all new ways of thinking, it opens up a lot of questions and challenges much preexisting knowledge. If you want to dive deeper, you’ll find references in the notes, along with details about my process for boiling down a complex and multifaceted body of research into something practical.

if you feel broken, or know someone who does

One more thing before we get into chapter 1. Remember how I said we’ve all been lied to? I want to take a moment to recognize the damage done by that lie.

So many women come to my workshops or to my class or to my public talks convinced that they are sexually broken. They feel dysfunctional. Abnormal. And on top of that, they feel anxious, frustrated, and hopeless about the lack of information and support they’ve received from medical professionals, therapists, partners, family, and friends.

Just relax, they’ve been told. Have a glass of wine.

Or, Women just don’t want sex that much. Get over it.

Or, Sometimes sex hurts—can’t you just ignore it?

I understand the frustration these women experience, and the despair— and in the second half of the book I talk about the neurological process that traps people in frustration and despair, shutting them off from hope and joy, and I describe science-based ways to get out of the trap.

Here’s what I need you to know right now: The information in this book will show you that whatever you’re experiencing in your sexuality—whether it’s challenges with arousal, desire, orgasm, pain, no sexual sensations, whatever—is the result of your sexual response mechanism functioning appropriately… in an inappropriate world. You are normal; it is the world around you that’s broken.

That’s actually the bad news.

The good news is that when you understand how your sexual response mechanism works, you can begin to take control of your environment and your brain in order to maximize your sexual potential, even in a broken world. And when you change your environment and your brain, you can change—and heal—your sexual functioning.

This book contains information that I have seen transform women’s sexual wellbeing. I’ve seen it transform men’s understanding of their women partners. I’ve seen same-sex couples look at each other and say, "Oh. So that’s what was going on. Students, friends, blog readers, and even fellow sex educators have read this book or heard me give a talk and said, Why did no one tell me this before? It explains everything!"

I know for sure that what I’ve written in this book can help you. It may not be enough to heal all the wounds inflicted on your sexuality by a culture in which it sometimes feels nearly impossible for a woman to do sexuality right, but it will provide powerful tools in support of your healing.

How do I know?

Evidence, of course!

At the end of one semester, I asked my 187 students to write down one really important thing they learned in my class. Here’s a small sample of what they wrote:

I am normal!

I AM NORMAL

I learned that everything is NORMAL, making it possible to go through the rest of my life with confidence and joy.

I learned that I am normal! And I learned that some people have spontaneous desire and others have responsive desire and this fact helped me really understand my personal life.

Women vary! And just because I do not experience my sexuality in the same way as many other women, that does not make me abnormal.

Women’s sexual desire, arousal, response, etc., is incredibly varied.

The one thing I can count on regarding sexuality is that people vary, a lot.

That everyone is different and everything is normal; no two alike.

No two alike!

And many more. More than half of them wrote some version of I am normal.

I sat in my office and read those responses with tears in my eyes. There was something urgently important to my students about feeling normal, and somehow my class had cleared a path to that feeling.

The science of women’s sexual wellbeing is young, and there is much still to be learned. But this young science has already discovered truths about women’s sexuality that have transformed my students’ relationships with their bodies—and it has certainly transformed mine. I wrote this book to share the science, stories, and sex-positive insights that prove to us that, despite our culture’s vested interest in making us feel broken, dysfunctional, unlovely, and unlovable, we are in fact fully capable of confident, joyful sex.

The promise of Come as You Are is this: No matter where you are in your sexual journey right now, whether you have an awesome sex life and want to expand the awesomeness, or you’re struggling and want to find solutions, you will learn something that will improve your sex life and transform the way you understand what it means to be a sexual being. And you’ll discover that, even if you don’t yet feel that way, you are already sexually whole and healthy.

The science says so.

I can prove it.

part 1

the (not-so-basic) basics

one

anatomy

NO TWO ALIKE

Olivia likes to watch herself in the mirror when she masturbates.

Like many women, Olivia masturbates lying on her back and rubbing her clitoris with her hand. Unlike many women, she props herself up on one elbow in front of a full-length mirror and watches her fingers moving in the folds of her vulva.

I started when I was a teenager, she told me. I had seen porn on the internet, and I was curious about what I looked like, so I got a mirror and started pulling apart my labia so I could see my clit, and what can I say? It felt good, so I started masturbating.

It’s not the only way she masturbates. She also enjoys the pulse spray on her showerhead, she has a small army of vibrators at her command, and she spent several months teaching herself to have breath orgasms, coming without touching her body at all.

This is the kind of thing women tell you when you’re a sex educator.

She also told me that looking at her vulva convinced her that her sexuality was more like a man’s, because her clitoris is comparatively large—like a baby carrot, almost—which, she concluded, made her more masculine; it must be bigger because she had more testosterone, which in turn made her a horny lady.

I told her, Actually there’s no evidence of a relationship between an adult woman’s hormone levels, genital shape or size, and sexual desire.

Are you sure about that? she asked.

Well, some women have ‘testosterone-dependent’ desire, I said, pondering, "which means they need a certain very low minimum of T, but that’s not the same as ‘high testosterone.’ And the distance between the clitoris and the urethra predicts how reliably orgasmic a woman is during intercourse, but that’s a whole other thing.¹

I’d be fascinated to see a study that directly asked the question, but the available evidence suggests that variation in women’s genital shapes, sizes, and colors doesn’t predict anything in particular about her level of sexual interest."

Oh, she said. And that single syllable said to me: Emily, you have missed the point.

Olivia is a psychology grad student—a former student of mine, an activist around women’s reproductive health issues, and now doing her own research, which is how we got started on this conversation—so I got excited about the opportunity to talk about the science. But with that quiet, Oh, I realized that this wasn’t about the science for Olivia. It was about her struggle to embrace her body and her sexuality just as it is, when so much of her culture was trying to convince her there is something wrong with her.

So I said, You know, your clitoris is totally normal. Everyone’s genitals are made of all the same parts, just organized in different ways. The differences don’t necessarily mean anything, they’re just varieties of beautiful and healthy. Actually, I continued, that could be the most important thing you’ll ever learn about human sexuality.

Really? she asked. Why?

This chapter is the answer to that question.

Medieval anatomists called women’s external genitals the pudendum, a word derived from the Latin pudere, meaning to make ashamed. Our genitalia were thus named from the shamefacedness that is in women to have them seen.²

Wait: What?

The reasoning went like this: Women’s genitals are tucked away between their legs, as if they wanted to be hidden, whereas male genitals face forward, for all to see. And why would male and female genitals be different in this way? If you’re a medieval anatomist, steeped in a sexual ethic of purity, it’s because: shame.

Now, if we assume shame isn’t really why women’s genitals are under the body—and I hope it’s eye-rollingly obvious that it’s not—why, biologically, are male genitals in front and female genitals underneath?

The answer is, they’re not! The female equivalent to the penis—the clitoris—is positioned right up front, in the equivalent location to the penis. It’s less obvious than the penis because it’s smaller—and it’s smaller not because it’s shy or ashamed, but because females don’t have to transport our DNA from inside our own bodies to inside someone else’s body. And the female equivalent of the scrotum—the outer labia—is also located in very much the same place as the scrotum, but because the female gonads (the ovaries) are internal, rather than external like the testicles, the labia don’t extend much past the body, so they’re less obvious. Again, the ovaries are not internal because of shame, but because we’re the ones who get pregnant.

In short, female genitals appear hidden only if you look at them through the lens of cultural assumptions rather than through the eyes of biology.

We’ll see this over and over again throughout the book: Culture adopts a random act of biology and tries to make it Meaningful, with a capital Mmmh. We metaphorize genitals, seeing what they are like rather than what they are, we superimpose cultural Meaning on them, as Olivia superimposed the meaning of masculine on her largish clitoris, to conclude that her anatomy had some grand meaning about her as sexually masculine.

When you can see your body as it is, rather than what culture proclaims it to Mean, then you experience how much easier it is to live with and love your genitals, along with the rest of your sexuality, precisely as they are.

So in this chapter, we’ll look at our genitals through biological eyes, cultural lenses off. First, I’ll walk you through the ways that male and female genitals are made of the same parts, just organized in different ways. I’ll point out where the biology says one thing and culture says something else, and you can decide which makes more sense to you. I’ll illustrate how the idea of all the same parts, organized in different ways extends far beyond our anatomy to every aspect of human sexual response, and I’ll argue that this might be the most important thing you’ll ever learn about your sexuality.

In the end, I’ll offer a new central metaphor to replace all the wacky, biased, or nonsensical ones that culture has tried to impose on women’s bodies. My goal in this chapter is to introduce an alternative way of thinking about your body and your sexuality, so that you can relate to your body on its own terms, rather than on terms somebody else chose for you.

the beginning

Imagine two fertilized eggs that have just implanted in a uterus. One is XX—genetically female—and the other is XY—genetically male. Fraternal twins, a sister and a brother. Faces, fingers, and feet, the siblings will develop all the same body parts, but the parts will be organized differently, to give them the individual bodies that will be instantly distinguishable from each other as they grow up. And just as their faces will each have two eyes, one nose, and a mouth, all arranged in more or less the same places, so their genitals will have all the same basic elements, organized in roughly the same way. But unlike their faces and fingers and feet, their genitals will develop before birth into configurations that their parents will automatically declare to be boy or girl.

Here’s how it happens. About six weeks after the fertilized egg implants in the uterus, there is a wash of masculinizing hormones. The male embryo responds to this by developing its prefab universal genital hardware into the male configuration of penis, testicles, and scrotum. The female embryo does not respond to the hormone wash at all, and instead develops its prefab universal genital hardware into the female configuration of clitoris, ovaries, and labia.

All the same parts, organized in different ways. Every body’s genitals are the same until six weeks into gestation, when the universal genital hardware begins to organize itself into either the female configuration or the male configuration. Description 1

Welcome to the wonderful world of biological homology.

Homologues are traits that have the same biological origins, though they may have different functions. Each part of the external genitalia has a homologue in the other sex. I’ve mentioned two of them already: Both male and female genitals have a round-ended, highly sensitive, multichambered organ to which blood flows during sexual arousal. On female bodies, it’s the clitoris; on male bodies, it’s the penis. And each has an organ that is soft, stretchy, and grows coarse hair after puberty. On female bodies, it’s the outer lips (labia majora); on male bodies, it’s the scrotum. These parts don’t just look superficially alike; they are developed from the equivalent fetal tissue. If you look closely at a scrotum, you’ll notice a seam running up the center—the scrotal raphe. That’s where the scrotum would have split into labia if the chemistry or chromosomes had been a little bit different.

Homology is also why both brother and sister will have nipples. Nipples on females are vital to the survival of almost all mammal species, including humans (though a handful of old mammals, such as the platypus, don’t have nipples, and instead just leak