How Sexism Helped Our Species Thrive

The biologically female human body is an enormously trippy thing. Set aside the whole getting-pregnant-and-giving-birth business: Some female eyes can detect 100 million distinct colours, which is 99 million more than the eyes of your average folk. The female ear hears better at higher frequencies. Female muscle fibres can endure over ultra-long distances, while female lungs and cardiovascular systems are far likelier to outrun disease. Given all that, you’d think modern science might be keen to usher these bodies under a microscope. But you already know what happens instead: It’s the male body, whether mouse or monkey or human, that gets studied in the lab, written about in papers and analyzed in clinical trials. And that’s why there was a long history of women being more likely to wake up in the middle of surgery—we just didn’t bother testing sex differences for general anesthesia until the turn of the 21st century.

Author and academic Cat Bohannon thinks that’s bananas. She knew we needed a no-nonsense, rigorously researched, highly readable user’s guide to the female mammal—and she kept waiting for one to arrive. “I thought, someone is totally on this right now,” she says. “And then I realized that no one was on it, and I had to write it.” And so she did: a process that took 10 years—during which time she also earned a PhD from Columbia University, got married, moved across the country, had two children and lived through a pandemic.

Eve: How the Female Body Drove 200 Years of Human Evolution traces several essential traits (including our breasts, wombs, fatty brains, and menopausal bodies) to their earliest known ancestors. In doing so, the book makes an enormously convincing case that it was women—thank you very much—who paved the way to language, tool use and padding around on two legs. Here, Bohannon discusses when we got milk, why the uterus is a war zone and how the image in your head of the female reproductive system is totally wrong.

(Related: Why Squirting Orgasms Are a (Really) Good Thing—And How to Have One)

You write at the start of Eve that lactation began 200 million years ago, under the feet of dinosaurs—and that beyond nutrition, milk is also about infrastructure. How so?

Milk is 90 percent water, which is maybe not surprising, because our bodies are also very much water. But when you think about milk, you need to think not only about slaking thirst. You need to think not only about nutrition. You also need to think about immunology. Milk initially comes about as a hot dose of immunological aid from the mother’s body to the infant’s body in those vulnerable, early periods of life. So the infrastructure question is interesting, because early milk is really a laxative. It’s there to help you poop out the remainder of all the things you’ve ingested in the womb. It clears the slate, as it were, along the digestive path, and also seeds key populations of friendly bacteria in the gut that will train the infant’s immune system.

Breastfeeding is a dialogue, where the upsuck is telling a woman’s body something important about what’s going on in her infant’s body. How does that mechanism work?

We love the upsuck. It’s so weird. It’s so wonderful. It’s kind of batshit crazy when you think about it, but it’s just physics. Milk starts before the nipple. But once you have a nipple on board, then you have a docking seal; you can clamp the offspring’s mouth around it to form a vacuum. Because the milk is moving back and forth, the offspring’s saliva is sucked back into the mammary tissue, which has ductwork lined with immunoagents and sensors that read that spit like an ancient code and tailor the milk to it. Every species seems to do something like this. So if our baby is sick, we make different milk to suit. That way, milk is a co-produced biological product, because of this communication that’s happening around the nipple.

I want to detour for a moment to the woeful limitations of my grade-school sex ed. Because I did not realize until I saw the diagram in your book that my reproductive organs are so completely smooshed together. What’s going on down there?

Yeah, so: same. We’re taught that classic diagram—this T-shaped thing where you have the womb, and then the little arms of the fallopian tubes hanging out the sides. And almost no one realizes that this isn’t accurate. We have a lot of organs in our lower abdomen just piled on top of each other. I remember very clearly having a transvaginal ultrasound—which is already awkward, right?—and the tech could not find my freaking ovary. I’m like, did I lose it? And she said, no, this happens a lot. It’s just hiding today behind your uterus or behind part of your bowel, because they’re all smooshed.

But the health impacts are many and varied. Many people get used to the weird aches and pains of having ovaries and a uterus. And that signal can be pretty diffuse, because it’s radiating out from one organ and touching other organs and your intestines can come along for the ride. So everything down there feels kind of messed up, and we learn to ignore a lot of the signals. But they’re often the exact same signals of the early stages of ovarian cancer. So please talk to a doctor. But don’t be scared. Not every gas pain is cancer.

But the uterus, you write, is a war zone. How does that explain why we, among only a handful of species, menstruate the way we do each month?

What’s interesting is not necessarily that we shed the lining of our uterus externally. It’s very annoying for us, obviously, but what’s interesting is how we build up that lining in the first place. We don’t wait for a signal from an incoming embryo. We do it pretty much right as the egg itself is starting to develop. The reason we do that is we have crazy invasive placentas—like, they go about as deep as they can into the maternal bloodstream. That means building up the uterine lining is more like a buffer for the maternal body—not to simply cushion and support, but rather to protect itself from this incredibly greedy, incredibly invasive embryo that has long evolved to suck out as much as possible from the maternal body. I love my children very much, but when they were in the womb, they were taking everything they could out of my body, and my body was doing everything it could not to die from the process. We give birth when we do not because the baby gets too big to fit out the hole, but because doing it any longer becomes a metabolic threat. It’s no longer sustainable to maintain this intense transfer of goods and resources across the war zone.

For a global population of 8 billion, we are really garbage at making babies. How is the human reproductive system stacked against us?

I’ll initially flag that if it weren’t for modern gynecological care, oh my god, I’d be so dead. And so would many of my friends. And we are not outliers. But there are many reasons why human reproduction is such a flaming garbage pile, and the big one is the obstetric dilemma: We are trying to fit a watermelon-sized baby out of a lemon-sized hole. The word for that is problematic. The best theory going is that when we evolved to walk upright, the pelvic bowl shifted. Instead of a pelvis that’s shaped more outward, it rotated up to support the different centre of gravity, which shrank the pelvic opening at the bottom. And that makes our labour and delivery a lot longer than it is for our most closely related primate cousins. A chimp mom is usually done in 30 to 40 minutes, while a first-time human mom takes 12 to 16 hours and sometimes much longer; I did. But it’s not just the delivery, it’s the lead up: the super invasive placenta, the long pregnancy that is so metabolically taxing. There’s so much opportunity for something to go wrong. When things do go wrong, they tend to go wrong fast, and the later you go into a pregnancy, the more dramatic those risks can be. We don’t often admit to ourselves how much we’re on the edge of a really big cliff, simply in the act of being a pregnant person.

So modern gynecology is terrific, but how did ancient gynecology help us succeed as a species?

If we have a really risky reproductive system that has so many fail points, that sometimes takes out the mother, and more frequently takes out the offspring, that is not the portrait of a likely success story. Like, if you had a time machine, you would not go back and think, They’re definitely getting to 8 billion. We can’t improve our reproductive success without behavioural workarounds—like the invention of gynecology, which includes not simply obstetrics but also all the interventions we have around a female’s reproductive life. Now, we didn’t have anything like the Pill when we were small, furry things running around Africa. But we do have local plants, which influence fertility cycles. We might cluster our babies at the start of our fertility, or spread it out over time, depending on which environment we’re in. And going all the way back 3.2 million years—so pre-human; still very chimpy—it’s clear from analyzing fossilized pelvic structure across many different hominids that they shared this obstetric dilemma. So it’s very likely they had a midwife. Having that flexibility around reproduction, and helping more people survive that horrible process, is a huge part of how we thrived. Unfortunately, some of that also has to do with sex rules and sexism.

Right, let’s talk about that. How does sexism help solve how bad we are at making babies?

There’s no one way to go about being sexist. Actually, we’re very diverse in our sexism. But what we do have in almost every human culture is a strict set of rules that guides access to female bodies—where they can go in a given day, how much of them can be seen, whom they can interact with. There’s nothing in your DNA that codes for how you feel about how short a skirt is. But we are hardwired to care about how we fit into our local culture and whether or not others are following the rules. And a lot of what these rules do is influence pregnancy rates. They’re very much influencing the circumstances under which you might have sex with a man and whether, or when, that sex is allowed to produce a pregnancy. So those rules are what I analyze as sort of the evolutionary roots of sexism. It’s another behavioural workaround that we generated over deep time to overcome our crap reproductive systems, to work in parallel with gynecology to keep more mothers and offspring alive. But now that modern gynecology is so miraculous, it has way outpaced the benefits of sexism. In fact, modern sexism works very clearly to reduce the health and well-being of biologically female people. It’s killing us.

A biologist would then say, well, it’s just a matter of time before that behaviour changes, because it no longer serves us. But I wonder if doing so requires a shared acceptance of its perniciousness—and that seems harder and harder to come by, as much for something like climate change as for the effects of sexism.

I get a lot of questions about how hopeful this book is. And I am actually deeply hopeful. You ask me, okay, wouldn’t we simply evolve away from sexism? Yeah, maybe, given enough time, but you don’t know how long you’re going to have to wait. Is it 100 years? Is it 3 million? We are only 300,000 years old as a species, which sounds like a lot, but in the scale of deep time, it is very much yesterday. But my hopefulness comes from scale. If you pull the camera back, and you look at the historical trajectory of the last 500 years, it is very, very clear that many human societies have been moving toward sex egalitarianism. And the advances that have been made are obvious. Now, that is not to reduce the very real suffering of so many women and girls and non-binary folk over those many hundreds of years. It is not to discount the fact that my country somehow elected Trump, nor that so many places in the world are so steeped in rape culture. All of that is very real, and we must care. But by pulling the camera back, you can tap into evidence for why we should be hopeful. And then you can recommit, with that hope, to active change.

Next: This Is Why We Need to Talk More About Sex, and Our Intimate Body Parts, at Every Age