Eve: How the Female Body Drove 200 Million Years of Human Evolution

by Cat Bohannon

Cumulatively, these moments—as they often do for other women who do research—affect my ability to feel like a member of a scientific community that includes people like that guy. But the general cost of dealing with sexism as a woman—how these things accumulate, I mean, in the brain, over the course of one’s lifetime—goes all the way down into some basic functional features. And that might finally give us a better definition of the Female Brain.

“Stereotype threat” is real. Psychological research is pretty clear about this. If you tell a woman that girls are bad at math and then give her a math test, she’s not going to do as well as a woman who wasn’t exposed to that threat.

But what if you’ve learned you’re sort of always supposed to smile? Even when it’s not a direct, appropriate emotional response to someone else’s smile? For example, what if you’re a woman walking down a New York street and some guy on the sidewalk yells, “Hey, why aren’t you smiling?” That should count as a stressor.[*33] It’s a reprimand. It’ll probably train you, consciously and unconsciously, to smile more.

I can say that it seems incredibly likely that such mechanisms would involve some or all the parts of the human brain that are known to intersect with general sociality, given that gender—as opposed to biological sex—is fundamentally a set of social behaviors tied to how one’s self and one’s body interact in a social environment.

And yet you can deliver a dense package of information from an organ inside your body into another person’s body.

Not only could he take deeper breaths with his larger lungs, but he had more muscle mass surrounding those lungs, allowing him to better control the release of that pressure over time. Recent research supports this: when we speak, women’s brains send more frequent impulse signals to the diaphragm and “inspiratory” muscles than men’s do. To put it simply, women ask them to work harder and more often, which requires more involved neurological control. It’s possible this bias toward greater control makes us better at fine-grained differences in voice control (more on that in a moment), but in the nuts and bolts of making sure our lungs don’t explode from pressure differentials, the male chest wall has an easier job.

To become truly fluent in your first language, your brain needs exposure as early as the first six to seven months of life. Babies who don’t get such exposure, for one reason or another, struggle with things like syntax for the rest of their lives.[*15] That’s really young. You’re not even crawling yet. Before you’re even mobile, your brain is already figuring out the building blocks of language.

Mom, in other words, is at least half of how language happens. And she’s not passive. Not at all. Human mothers have evolved to be language engines—prodigious users and teachers of language.

Children whose mothers emphasize vowels more—the way you do in motherese—arrive at language milestones faster than other kids. And they perform better at language tests, too. Children of parents who don’t use any sort of motherese lag behind.

Everything humans care about is possible because we have language. The human mind is made for language, yes. But it’s also made of language. The same sorts of logic paths that rule language, that combine known things into new ideas, that puzzle out the code of others’ communication into knowable thoughts and desires, also write stories and build meaning and tease out the finest, strangest features of the universe. They make us what we are.

So I think there was one moment in the evolution of human language that marked a dividing line: before it we were not yet human, but after it we were. It was probably the smallest thing, neither heroic nor grand. More than likely, it was the intimate moment, probably late in the evening, in the low blue quiet before dreaming, when a single human being told the very first story.

If the story of our ancestors is about anything, it’s about survival. Hunger, and migration—the unyielding force of Death, driving us ever forward and out, into the gray line of a long horizon. That is where we came from. It drives us even now.

Hearing about menopause is one thing. Watching your own mother or aunt sweat their way through it is another. But actually feeling your own body change in these ways can be hard to wrap your head around.

There’s no part of the human body that sex hormones don’t touch.

That’s why human menopause is one of the biggest mysteries in modern biology, right up there with why we die.

And for whatever reason, a woman’s ovaries give up the ghost a lot faster than the rest of her. We stop having children, but we keep on living. It’s as if one part of our bodies were aging a lot faster than the rest.

So, what if ancient humans needed grandmothers to stop being fertile in order to succeed? What if, as humans became increasingly social, with increasingly specialized roles in society, new mothers needed more help taking care of their needy, vulnerable offspring? If the child’s father or grandfathers couldn’t (or wouldn’t) do it, maybe the grandmothers could—but only if they weren’t busy with babies of their own.

So maybe, the theory goes, ancient human women evolved to support that kind of society: males doing whatever they’re doing, young mothers tending to their children, and a significantly large, eusocial “grandmother” class assisting in child rearing. Assuming their granddaughters would benefit by such an arrangement, a “menopause gene”[*3] would spread quickly through the population. Over time, it would be so useful that every girl would be born with the genetic code that switched off her ovaries by age fifty.

want the idea that human evolution leads inexorably to my grandmother’s cookie jar to be true.

This is presumably what happened to my friend’s wife. Like nearly every woman on the planet, she was born with roughly a million immature egg follicles. But every year since, thousands of her follicles died off and were reabsorbed by her body. By the time she became a teenager, she had only about 300,000 to 400,000 follicles left. From then on, she lost about a thousand of them every month. If she started ovulating at age thirteen, she was destined to run out of eggs somewhere in her early forties. Which is precisely when most women stop being able to get pregnant without medical assistance. My friend had been on the Pill for many years, which you might assume would have saved some of her eggs. But no—delaying the ovulation process by going on the Pill doesn’t save your eggs. In fact, every year of being on high-dose hormonal birth control seems to move the start of menopause up by about a month.[*5] That’s because the loss of egg follicles isn’t triggered by ovulation. Instead, ovulation saves about 20 follicles a month from early death, of which usually only 1 will go on to become a mature egg and find its way down the fallopian tube. But for those 20 that are saved, 980 die off.

While half of your DNA came from your dad and half from your mom, most of your mitochondria and cytoplasm came from your mother.[*7]

The longer a cell lives, the more chances it has to be damaged by accumulating waste and free radicals. There are mechanisms in place to repair damage, but those mechanisms get less reliable over time. It’s also true that older eggs are more likely to have genetic problems of the sort that can lead to Down syndrome.[*9] For the same reason, older women have more early miscarriages. So maybe ancient humanlike bodies somehow anticipated those problems, discarding all those egg follicles to avoid giving birth to disabled babies.

Scientists figure that when hominins began to walk on two legs, there wasn’t room in their upright pelvises for giant genital displays.[*11] These flaps shrank, but even now a woman’s labia may swell just a bit when she’s ovulating. The inner labia—nearly diaphanous flaps that nestle around the clitoris and its hood—can turn a bit darker with blood whenever we’re particularly turned on, and in a more pronounced way around ovulation. As women age, the inner labia tend to stay darker, a leftover from lifelong cycles of fertility.[*12]

In other words, the deep structure of primate ovaries might be fundamentally geared for a life span of about fifty years. We can live longer, but we won’t be as good at making babies, and the rest of our bodies are also shutting down. If that’s the case, then it would seem that the thing that changed in our Eves might not have been in their ovaries. Instead, women somehow delayed aging in the rest of their bodies, and human ovaries haven’t had a chance to catch up yet.

What grandmothers do, in other words, is remember. Living a really long time as a social mammal is good for two things: reinforcing the social status of adult children, and ensuring the well-being of the group overall in a crisis by remembering how to survive in a world that changes over time.[*15] Maybe, instead of the grandmother hypothesis, we should think about two things: Postmenopausal grandmothers may help their children to maintain their social status and resources over time (call it the mother hypothesis). And maybe grandmothers are also helpful because they’re really good at remembering things. Old people can be valuable because they’re wise.

In 1989, the Russians finally withdrew like a glacier, leaving the land scraped flat by the rollers of war. For a time, Abedo managed to settle down to a more “normal” life back in her village. She even opened a shop, selling goods to people she’d fought with. Her children grew. Though it certainly wasn’t normal for an Afghan woman to live the way she did, she maintained her independence and was well respected by her neighbors. Twenty years came and went. Her children had children. Poppies bloomed in the river valley, pink and white. Then, after another war burned half the cities down, the Taliban started interfering with her business. They told her not to sell to the U.S.-backed government. The government, meanwhile, told her not to sell to the Taliban. She refused to take a side. She’d probably still be living her ordinary village life if the Taliban hadn’t decided to set fire to her shop. After that, with the blessing of the American-backed government, she recruited ten young men for her own paramilitary troop. When I started researching this chapter, she’d survived, a cross between a wizened grandmother and a commandant, continuing to defend the daily life and well-being of her village with well-oiled guns. Given her extensive experience as both a fighter and a military commander, that U.S.-backed government had consulted her for security intelligence and strategy in the region. “Modern-day youngsters in the police and army don’t have experience,” she said to a journal...

Before we could write stuff down, it was especially important to have someone in the group who could remember earlier crises. It’s usually not hard to find someone who can remember a difficult thing that happened ten years ago. It’s much harder to find someone who remembers a difficult thing that happened forty years ago, or how, precisely, the community managed to find a work-around. Oral history provides only so much after the storyteller dies. Living long enough to see a rare crisis happen again is the most reliable way to know whether a piece of knowledge is something the entire group should learn.

Centenarians used to be unicorns. Now the United States has more than fifty-three thousand of them. Canada has nearly eleven thousand. Japan has more than eighty thousand. Italy, nineteen thousand. The U.K., just over fifteen thousand. And by and large, they’re not men. More than 80 percent of today’s centenarians are female.

That’s why, from a genetic perspective, we probably shouldn’t think of human menopause as the result of evolution selecting for nonreproductive elderly females. Rather, whatever helps female bodies live on may simply benefit male bodies less, and losing more males may not cost primate societies that much.

Unlike children in many hunter-gatherer societies, most of today’s industrialized human beings survive childhood. When we don’t die of something stupid, like preventable infections or violence or accidents, we usually die because we get old. But “getting old” isn’t exactly what kills us. It’s the big three: cancer, cardiovascular disease, and lung disease. These are the killers we’re running from. And, as they get older, female bodies are just better at outrunning them.

The male cardiovascular system is more prone to higher blood pressure from an early age. This may be why young men who received some of the COVID vaccines in 2021 were more at risk of myocarditis and pericarditis after their shots—inflammation of the sac around the heart or of the lining of the heart. But, of course, men and boys who fell ill with COVID-19 were also more likely to suffer cardiovascular problems such as these, and likewise were significantly more likely to die during the pandemic than women were.

As for cancer, outside genetics, many different lifestyle choices influence one’s overall cancer risk: eating charred and fatty foods, sugar consumption, exposure to toxic chemicals, alcohol, failing to get enough exercise, stress…Simply knocking back one alcoholic drink a day raises an American woman’s risk of breast cancer by 14 percent. But, in general, more men get cancer, they get it younger, and they are more likely to die of it.

One central reason most researchers think that may be the case is that the Y chromosome is tiny compared with the X chromosome: The X carries about eight hundred genes, while the Y only carries about a hundred to two hundred, leaving large portions of the X un-partnered in the male cell.[*21] The reason that matters, of course, is that in the womb female embryos shut off or “inactivate” one of their two X chromosomes, presumably so they don’t double code for things and gum up the works. Thus, while each cell line carries two X chromosomes in a female-typical body, each living cell is normally activating genes on only one of those two chromosomes.

So if a male has some screwy genes on his X chromosome, his dinky little Y chromosome isn’t going to be able to keep the dampers on potential tumors the way having two X chromosomes would. This problem is so characteristic of men with certain kinds of cancers, in fact, that researchers decided to call the still-active X genes EXITS: escape from X-inactivation tumor suppressors. Across twenty-one different sorts of cancers, five of these EXITS genes were more frequently mutated in men than in women. Being male, in other words, was very much a part of what was killing them. And presumably, as we slowly figure out how to develop treatments for those sorts of cancers, we may well be trying to make those cancer-ridden male bodies essentially more female.

To be a woman in those war years often meant you were a person who loved someone who wasn’t there.[*22]

It’s a very old story: Penelope waiting for Odysseus to come home. There are versions in Sumerian, in Akkadian, in the little cuneiform arrowheads that line ancient clay tablets. Even the story of Inanna, the Sumerian goddess of love and war, resolves with her mourning the death of her beloved Dumuzi.

That’s the real story about menopause. It’s not the night sweats. It’s not the dry vagina. It’s not really about menopause at all. It’s that we outlive the men we love. We outlive our brothers and husbands and lovers and friends. We have to live on, all of us, and watch them go.

There are things you can’t unlearn: when I was twenty years old, I learned that the most money I could make, of anything I could possibly do, was putting my vagina up for rent.[*2]

the thing which makes us most human is our ability to love. To truly love someone.

So if the human penis and vagina evolved in a rape-fueled competition, our current anatomy doesn’t betray that history. If anything, our bodies seem to reveal a lot of consensual sex without very much violent male competition, and maybe even a continually reduced competition over time, with our older ancestors being more competitive, and our more recent ancestors getting less and less so.

While chimp males rarely kill chimp babies in their own troop, when they war with other troops, males regularly kill their enemies’ babies, since babies produced by the enemy males’ sperm are no benefit to them. They also have a habit of raping—or at least violently coercing—their female enemies, presumably to both enforce their dominance and potentially father new kids.[*14] Thus, many argue, the main thing keeping chimp males from killing babies in their own troop is that they’re never really sure the kid isn’t theirs. That’s not true in harem-based societies. Among mountain gorillas, over 20 percent of child deaths happen at the hands of an adult male—gorillas have harems, so paternity is more certain.[*15] That’s the big problem with the monogamy argument.

Picture a group of ancient hominins. Really ancient ones, maybe even before Australopithecus. There they are, having sex, making babies. They’re probably being as promiscuous as chimps, and the fathers aren’t sure who their children are. Then picture a female deciding to be sexually exclusive with a male in exchange for food. That guy better be huge. Because now he doesn’t just have to guard his mate. He has to make sure his kid doesn’t get slaughtered by a rival, because all the other males in the troop know that the kid is his. Not theirs. In other words, when it comes to physiology, if there had been early hominin monogamy—pre-language, pre-culture—it should have turned these hominins into gorillas. Because every single one of our male ancestors had the obvious potential to be a rampant baby killer. That means cooperative culture had to come before monogamy started. You had to have other cultural checks in place before measures to create paternal certainty made sense. You had to have bands of ancient hominins who were interdependent and had created clear and dire consequences for any behavior that threatened children. What you basically needed was a matriarchy.

In promiscuous matriarchies, females would already have more power than female chimps do, so maybe the kids wouldn’t need a lot of protection at first. If a male were to start misbehaving, all hell would rain down on him—female coalitions don’t allow aggression toward offspring. Maybe a few well-positioned males start participating in violent retribution against such transgressors. Maybe they start acting a bit more like thugs, even beating up their female allies’ enemies. Sometimes the enemies’ kids get caught in the cross fire.

you can be born a princess but never a prince. You have to fight for that.[*24]

There are no specific genes for individual sexist beliefs. There’s nothing written in your DNA that makes you approve or disapprove of the length of a woman’s skirt. But you are wired to care about sex. And you are wired to care about social norms. And the consequence of how much you care about sex and social norms is a massive rule book that mostly applies to women, built up over more than a hundred thousand generations.

So basically, it’s relatively chaste, modest, and serially monogamous women who are driving massive outbreaks of syphilis, herpes, gonorrhea, and chlamydia in places with cultures that promote female chastity and masculine promiscuity. The Centers for Disease Control has been tracking them throughout the United States: Minnesota hit a record high for STIs in 2014. Montana more than doubled the rate of gonorrhea transmission from 2013 to 2014. Louisiana, Mississippi, Georgia, and Texas lead the charge in syphilis, chlamydia, and gonorrhea—all states with some of the highest social emphasis on the importance of female chastity (and predictably, some of the lowest public funding for sex education and prophylactics).[*38]

Reducing the number of girls married before they are eighteen by even 10 percent can reduce a country’s maternal mortality by 70 percent.

Presumably every species wants the healthiest mothers and offspring possible, within the resource limits of its particular environment. Allowing maternal mortality to go up? In evolution, that makes no sense at all. If the mother dies because of some local antiabortion policy, that means she never gets to have more children. If she dies because she didn’t have access to good health care and family planning, she doesn’t get to have more children. This is the opposite of optimizing for the greatest number of healthy babies. It’s the biological equivalent of cutting off your nose to spite your face.

In a wide variety of studies, covering cultures ranging from rural America to urban India, women are more likely to allocate financial resources in a way that directly affects the welfare of their immediate households and local community. When given the opportunity, women are more likely to spend a family’s money on food and clothing and health care and children’s education. Men, meanwhile, are more likely to spend it on entertainment and on weapons and—if we’re talking global trends—on gambling or the local equivalents.[*47] Worldwide, girls and women spend up to 90 percent of their earned income on their families. Men and boys spend only 30–40 percent. When women in India were given the opportunity to participate in local governments as ministers and officers, those governments more greatly invested in things like public services and infrastructure, from waste management to potable water and railways—things that, as it turned out, seemed to matter more to female politicians.

Some think these inclinations may be tied to the fact that women do most of the child rearing, and that keeps their focus on local concerns, but the real truth is we don’t actually know what’s driving these differences. Still, even without fully understanding the mechanism, we can say that you don’t have to care about women’s “rights” in order to find good reasons to financially empower women. You can just look at known outcomes. Maybe you can just care about the bottom line of your economy. Many well-regarded economists have written extensively about this: give women more money and give them the power to make decisions about where to spend it, and their communities will generally become more economically productive.[*48]