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

by Cat Bohannon

All living creatures, mammal or not, are mostly made of water. While the adult human body is 65 percent water, newborns are 75 percent. Most animals are essentially lumpy donuts filled with ocean. If you wanted to describe life on Earth in the simplest terms, you could say we’re energetic bags of highly regulated water.

Ugly bags of mostly water

Mammals coevolved with their gut bacteria, because it takes a village.

human milk has the most, and most diverse, oligosaccharides of all our primate cousins’, probably because unlike other apes modern humans have had to deal with cities and high-speed travel. Cities are bacterial cesspools. Humans are not just social primates; we’re super social. By living in such close quarters, day and night, human bodies regularly encounter an onslaught of foreign bacteria.

Some of the science around oxytocin is good, and some of it is so tainted with stereotypes of femininity that we might as well dress it up in a frilly pink tutu: “Oxytocin makes you love your baby.” “Oxytocin makes you love your man.” “Monogamous men make more oxytocin than men who’re going to cheat on you.” While oxytocin does seem to be associated with a number of psychological states in various mammals, and higher levels of oxytocin are associated with more pro-social behaviors, there are simply too many other factors that produce these things to treat oxytocin as a solo player.

When a woman goes into labor, oxytocin is a major player. It’s so important for childbirth, in fact, that it’s listed by the WHO as one of the world’s “essential medicines.”

These sorts of responsive features seem to be true across Mammalia, the particular magic potion varying from species to species—different bodies need different sorts of breast-borne chicken noodle soup—but the overall principle holds true. The resulting effect is so powerful that when many babies grow up, their brains still associate milk-related signals with healing and comfort. Eating fat-dense and/or high-carb foods, especially if they taste sweet—the sort that many humans tend to seek when feeling stressed or lonely—produces an analgesic effect in a number of different mammals. For rat and human alike, “comfort food” can dampen the body’s pain response, a kind of grown-up breast substitute.[*13]

Higher-cortisol milk also tends to be protein heavy, which in principle helps an infant build a lot of muscle, good for running like hell toward safety. Sugar-heavy milk, in contrast, is great for building adipose tissue, creating a comforting energy buffer, and for fueling a growing brain. Brains are, after all, supercomputers that run on sugar.

What’s not normal is letting eggs incubate and hatch inside your body, where they can do all kinds of catastrophic damage. What’s not normal is building a placenta and anchoring a developing fetus to the wall of the uterus, thereby transforming the mother’s body into a kind of H. R. Giger fever dream meat factory. What’s not normal, in other words, is giving birth to live young.

uterus will then rapidly transform into what’s called the decidua, a thick buffer between the mother’s body and the growing embryo. Meanwhile, digging down into the decidua, the embryo will start building its part of the placenta. That’s right: the placenta is actually made of both embryonic tissue and the mother’s tissue—one of the only organs in the animal world made out of two separate organisms.

We seem to be driven to assume that being pregnant is innately good for us—that fetuses give us a “glow,” that they calm us down, that pregnancy is a healthy state for a woman’s body. One can, indeed, have a perfectly healthy pregnancy, and most women do, but being pregnant can also make a woman deeply unwell.

The doctors were astonished she’d made it to the hospital alive. Largely because modern medicine is amazing, she and her new baby survived. Afterward, she told reporters (who’d somehow gotten wind of the “miracle delivery” on the operating table), “I was just happy that I was alive and our daughter was alive….I think that the baby saved my life.” Of course, it was the baby who nearly killed her. But that’s no way to start a relationship with your child. Preeclampsia—a disorder that plagues more than one in twenty pregnancies in the United States, which is what this woman had—is characterized by spikes in blood pressure that cause knock-on effects in the mother’s other organ systems (for example, her kidneys, which start to have difficulty filtering out excess protein in the blood).

Pregnancy is inherently dangerous and can have crippling long-term side effects on women. The safest thing for a woman’s body is to never be pregnant at all.

Pregnant women with malaria are three to four times more likely to suffer from the most severe forms of the disease, and of those who do, 50 percent will die. Ever wonder why the Centers for Disease Control is located in Atlanta? Malaria. The entire reason the United States built the CDC is that malaria was rampant throughout the American South. Malaria was finally eradicated in the United States in 1951. That wasn’t very long ago.

Nowadays, in the United States, only 0.65 out of every 100,000 legal abortions will result in the woman’s death, while 26.4 American women still die for every 100,000 live births. Before Roe v. Wade, 17–18 percent of all maternal deaths in the United States were due to illegal abortions—that stat was as true in 1930 as it was in 1967.

New organs of perception come into being as a result of necessity. Therefore, O man, increase your necessity, so that you may increase your perception. —JALĀL AD-DĪN AR-RŪMĪ, 13TH CENTURY

The biggest shock is that it’s bloody loud. On any given day, it’s louder than a Rio street carnival. The insects thrum and buzz at screaming decibels, their wings and legs rubbing a frenetic jazz. The frogs bellow. The birds caw. And the monkeys, the howler monkeys, like the horns of hell, day and night they call.

Middle-aged and older men also have more trouble following a conversation in a crowded soundscape, especially if it involves a lot of higher-pitched sibilants. That also means they have difficulty hearing women’s voices, with their characteristic higher pitches, but retain the ability to hear men’s voices and other low, rumbly things. Because social power is typically assigned to men as they age, women’s voices are literally not being heard by men in power.

responses to the world are often on high alert, too. Sartre’s Nausea? Paltry. A bored Frenchman. Try a pregnant woman who’s puked twice in one morning, nibbling saltines from a plastic sandwich bag on the subway from Brooklyn to midtown. She can smell every single dead thing that’s ever been in that car.

Cyanide famously tastes and smells of bitter almonds—in fact, almonds would still be dangerous today if ancient farmers hadn’t managed to breed the cyanide out of them.[*24]

Because women are generally born with two X chromosomes, some are actually tetrachromats—they see the world not in three color dimensions but in four.[*34] Like birds, these women can tell far subtler differences between red, green, and yellow wavelengths, potentially making them able to see as many as 100 million distinct colors: a full 99 million more than the average human being.[*35]

As many as 12 percent of all human girls may be born tetrachromats. They have the potential to see a world that no man will ever be able to see. To see a world most women don’t even see. But because they grow up in environments that will never ask them to use it, they’ll never know that they have this ability. It simply won’t develop.

Species don’t really get a harder problem than the one we have to deal with: We’re really, really bad at reproducing ourselves—demonstrably worse at it than many other mammals. We’re worse than most other primates. We’re even worse than our fellow apes, whose bodies are so like our own we’re called “the third chimpanzee.”

Most of the features that make our reproduction such a crapshoot were probably already in place by the time Habilis arrived. And they only got worse for her descendants.

And yet, somehow, there are 8 billion Homo sapiens on the planet right now. That’s not just impressive—it should have been impossible.

Abortion is just one of the things that female mammals do. We don’t know the ins and outs of its mechanisms yet, and they probably differ between species. But if rodents, equines, and primates have all developed some version of the Bruce effect, then we should stop thinking that human abortion is something unique. The way we do it—using human gynecology—is different, but ending a problematic pregnancy in response to social stress is something a lot of mammals do.

The field of research is fairly new, but primatologists have been able to find tantalizing evidence of self-medication. In one case, the medicine in question was the bitter pith and juice from shoots of the Vernonia amygdalina plant. Mahale chimps, sick with parasitic intestinal worms, spend up to eight minutes carefully peeling away the bark and outer layers of the shoots in order to get at the extra-bitter innards. They chew on the pith and suck out its juice. This isn’t tasty. Nearby adult chimps who are not sick avoid the stuff. Primatologists sampled the poo from before and after this pith-eating behavior and found fewer parasite eggs in the post-medication poo. And it just so happens that local humans also had the habit of using this bitter pith in traditional medicine for treating intestinal parasites. As with humans, the chimps presumably learn to treat themselves this way from other chimps.

many biologists and medical professionals have difficulty reconciling the fact that sexed species produce two very different types of bodies. We’re only just now starting to hear voices in the medical community calling for different treatment paths for the sexes.

Men make up only 20 percent of the people who buy and read novels. The numbers improve for history and other nonfiction, but overall book publishers throughout the Americas and western Europe are selling books to women.

For reasons that are still unclear, boys are two to three times more likely to be dyslexic than girls. Furthermore, given that schools aren’t great at identifying these issues—as of 2013, less than 20 percent of students that researchers identified as having reading impairment were categorized as “learning disabled” by their schools—boys are probably not receiving help with their reading problems as they move through the education system.

human babies’ metabolisms burn white-hot. Newborns drink 16 percent of their body weight in milk every day for the first six months of their life. To put that in perspective, an average 150-pound woman needs to eat and drink only about 5 percent of her body weight per day—a third of what newborns need. Babies put a massive portion of all that energy and fat and protein directly into building their oversize brains.

The human brain reaches peak synaptic density—that’s when the most neurons are the most wired to other neurons—when we’re around two.[*24] Then the brain starts violently pruning itself back, like an overzealous master gardener. Glial cells move in and gobble up synapses. Inhibitory cells start damping signals in some pathways, effectively increasing the strength of signals traveling nearby paths, a bit like redirecting traffic. The brain of a standard toddler is effectively rewiring itself, dramatically reshaping the material it just built.

To put it in plainer terms, if your brain produces an experience of identifying as a woman, but your genitals happen to include a penis, does that mean your identity as a woman is less real than another’s? Absolutely not.

We always say the brain is the biggest, the primary sex organ

But wolves are pretty fantastic hunters, do it in groups, come up with surprisingly complex plans for the hunt that depend on members performing diverse roles, and don’t have a lick of language.

She doesn’t actually know that wolves and other animals don’t have language. And let’s note that she hasn’t bothered to actually define language—that’s one of the sticking points in trying to figure out when humans started using it

Much like their dinosaur ancestors, today’s birds have nine different air sacs that function like bellows. They breathe into their air sacs and out through their lungs. That means they have way more oxygen available at any given moment than mammals do, so it’s a lot easier for them to do ridiculously energetic things like flying.[*4] And singing all day long. Singing is, in many respects, a fancy way of holding your breath, much like talking.

If you’re a woman who uses your voice professionally, you’re more likely to see a doctor about your strained vocal cords than a man who does the same work. What’s odd about this is that the female vocal instrument isn’t inherently more fragile than a man’s. We might even have some mechanical advantages—finer control, for example, over our respiratory muscles, faster responses in nerve pathways between the brain and mouth and throat. The problem is probably that women unconsciously train our voices to mimic men’s, especially in the public, political, and business spheres.

Hillary’s? She probably dropped by only a few eighths.

What the hell is an eighth in terms,of voice pitch? The writer does not understand pitch

Language is an infinitely flexible framework for cognition.

Infinitely? Hmmmm, dubious…

Your brain has evolved that ability to learn and create grammar. We’re the only species on the planet who’s ever managed to do that.[*32]

She doesn’t know that and it is almost certainly incorrect

And yet, and yet…Denying temporal succession, denying the self, denying the astronomical universe, are apparent desperations and secret consolations. Our destiny (as contrasted with the hell of Swedenborg and the hell of Tibetan mythology) is not frightful by being unreal; it is frightful because it is irreversible and iron-clad. Time is the substance I am made of. Time is a river which sweeps me along, but I am the river; it is a tiger which destroys me, but I am the tiger; it is a fire which consumes me, but I am the fire. The world, unfortunately, is real; I, unfortunately, am Borges. —JORGE LUIS BORGES, LABYRINTHS Damn, I got out of hand! —BORGES’S MOTHER, ON HER NINETY-EIGHTH BIRTHDAY

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.

And a human being whose life is nurtured in an advantage which has accrued from the disadvantage of other human beings, and who prefers that this should remain as it is, is a human being by definition only, having much more in common with the bedbug, the tapeworm, the cancer, and the scavengers of the deep sea. —JAMES AGEE, COTTON TENANTS

The man has a theory. The woman has hipbones. Here comes Death. —ANNE CARSON, DECREATION

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.

Being in a matriarchal primate society is a bit like spending your entire life in a high school where the popular girls rule. It’s Mean Girls. The top girls form complex alliances that reinforce their own power and keep “lesser” girls in check.

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

think of sexism and gynecology as two sides of the same coin: they’re two behavioral strategies our species employed—and still employs—to try to jury-rig a glitchy system. If pregnancies are dangerous and babies are needy, you need work-arounds. For example, birth spacing to control how often the girls in your troop are pregnant. Gynecology gives you tools for birth control and abortion. But you can also create cultural rules around when and where the males get access to female bodies, and then create punishments for those who break the rules. That’s the core of what sexism is: a massive set of rules that work to control reproduction. The aspects shift from place to place, but every single human culture has rules about what women should wear, where they can go and in what circumstances, whom they should talk to and when, and most certainly when and how and with whom they should have sex.

Human beings care a lot about sex rules, but especially when it comes to women. So how did that happen?

it’s quite possible that it got started inside ancient primate matriarchies, with males trying to get in on female power. And over time, sex rules became a part of how human beings built modern human culture. Maintaining those rules helped us take control of our reproductive systems, but the rules also destroyed the legacy of the matriarchies. Modern female coalitions are scattered, vulnerable, brittle.[*27] But today, no one is really aware that they traded anything, or that we’re continuing to re-up this contract with each generation. That’s because the way human behavior produces human culture isn’t straightforward.

the reason we want to shame women who have affairs with married men isn’t simply that we’ve “internalized” male dominance. Frankly, that gives men too much credit and women too little.

Syphilis rates tripled between 2012 and 2014 in Louisiana, a state where more than 60 percent of the population regularly attends religious services.