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In October, at the Cheltenham Literature Festival in England, Cat Bohannon was sporting a pink latex top and a mischievous twinkle in her eye. She and I shared a stage to talk about our recent books; in my case, Bitch: On the Female of the Species; in hers, Eve: How The Female Body Drove 200 Million Years of Human Evolution. We hit it off immediately.
Eve, Bohannon’s first book, is a sweeping revision of human history that places the female body center stage, instead of just a feminine footnote to the macho main event. Bohannon, a Ph.D. from Columbia University (where she studied the evolution of narrative), with a sideline in poetry and performance, tells this epic tale through a series of “Eves”—presumed ancestors who vaulted various biological hurdles, with pivotal consequences for our evolutionary path.
Talking to Cat Bohannon is like being struck by a tornado of ideas.
Eve begins in the Jurassic period with a small rodent Morganucodon, nicknamed Morgie by the Smithsonian, which laid eggs and lacked nipples but nevertheless became the first mammalian breast feeder. We discover that milk is alarmingly like pus, but with added prebiotics for developing gut health. Next comes Protungulatum donnae, “our womb’s great-grand-rat,” who managed to survive the apocalypse that wiped out the dinosaurs by inventing the placental pregnancy.
By the time we get to our hominin ancestors, with their ever-expanding brains, this internal incubation system is starting to creak—mammalian mothers are at war with their fetuses over limited resources, and hominin heads too big to pass through the pelvis. It is this fundamental biological limitation that shaped our trajectory far more than man the hunter, farmer, or toolmaker ever did. In Bohannon’s myth-busting tale, reproductive choice and the need for midwifery drove the evolution of a matriarchal society, like the one we see in our great ape relative the bonobo.
Eve’s structure reminded me of Richard Dawkins’ The Ancestor’s Tale, but the content, with its female focus, could not be more different. Bohannon shares Dawkins’ gift for compelling science communication but has her own intimate style. The book took her 10 years to write. During this time, she finished her dissertation and became a mother. Twice. Alongside all the Eves, we meet various incarnations of Bohannon herself, from life-drawing model to almost sex worker (during college she interviewed for a job as an escort but decided against putting her “vagina up for rent”). Her personal stories bring grit, humor, and humility to those of her imagined Eves.
Not long after the festival, Bohannon and I spoke over Zoom about the incredible Eve. Talking to her is like being struck by a tornado of ideas.
Tell us how midwives set our ancestors on the evolutionary path to success.
Because this is for Nautilus, and it’s a science credit, I’ll start with a high-minded idea and dig in. Paleoanthropologists don’t give a damn about rocks. That’s not what they’re actually studying. What they really want to know about is the triangulation of an object that is a tool, its user, and its environment. From that you can infer ideas about a creature, its cognitive capabilities, its likelihood of socially shared knowledge, its relationship with foodstuffs. There’s a lot you can learn from rocks.
Tool use is fundamentally about doing something to overcome a basic limitation of your body plan in your environment. How does utilizing a tool get you there? What behaviors are you doing to overcome that limitation? Our biggest problem wasn’t food. I mean, it’s always food. We’re always hungry. Our most important problem was we were crap at making babies.
By looking at fossils, we’ve determined that many in the hominin line share this problem—our pregnancies got longer and more difficult and more prone to crippling and sometimes deadly complications for the mother and child than they are for almost any other primate. In evolutionary biology, that’s a hard problem. You can limp around on one foot, you can have a weird neck, you can be many things in the animal world. But if you suck at making babies, then you are not destined for great success. You’re certainly not destined for massive migration plans that end up in every environment in the world.
Enter the midwife.
Right. If need is the mother of innovation, look at the mothers. The way they innovated is with behavior. Our workarounds are always behavioral. And midwifery is a behavior. But it’s a behavior that requires major shifts in a social organization. You need to have strong female bonds where you can trust someone between your legs when you’re giving birth.
Jane Goodall and many other wonderful primatologists have seen that there’s a lot of female infanticide. When you’re giving birth as a chimpanzee, you’re going off secretly, then carefully reintroducing that newborn to the group, and only to your friends first. If you’re not friends with the alpha female, you’re avoiding the hell out of her because she’s not just going to kill that kid, she’s going to eat it in front of you, while you scream.
But it’s not just about midwifery. Any good OB-GYN will tell you how your pregnancy, birth, and postpartum recovery are deeply dependent on your prenatal care. They’re also deeply dependent on the whole history of your reproductive life and general health before you ever get pregnant. So, given your local environment, and what’s going on around you, it may be healthier to have less children, or have them in a cluster, which is also a behavioral innovation. I’m not the first to say that Lucy [the name for an australopithecine skeleton from over 3 million years ago] had a midwife. She shared our obstetric dilemma.
The traditional model for hominin society has been based on chimpanzees—a patriarchal society where females disperse from their natal group, and don’t have strong bonds with one another. But your midwife argument supports those that see our other great ape relative—the matriarchal bonobo, with her sisterhood of unrelated females—as a more convincing model. You even found evidence of bonobo females supporting one another giving birth, which I found incredible.
The thing that I found most interesting about it wasn’t simply the laboring female was so obviously trusting of the others. It was that they shared the placenta. We’ve wondered about how midwifery might take hold as a regular practice in a species—you need those strong female bonds. Usually, the argument is a mother is helping a daughter, or a sister—you must have that genetic bond. But now there is an immediate reward. I have never eaten a placenta—and have no desire—but that’s a nutritive reward for being around. And the bonobos are passing it and sharing it. And sharing food in primates is a big social bonding thing. So, in other words, you get a meaty bloody treat for helping, and also not harming the child.
I’m not going to say the editor had testicles, but maybe?
Speaking of blood, menstruation is a bit of an anomaly. Humans are part of an eclectic, and unrelated assembly of bleeding female mammals that includes a handful of primates, four bats, the elephant shrew, and a spiny mouse. Why?
We like to focus on the blood and tissue and mucus coming out of the hatch. But that isn’t the most biologically interesting thing. It is probably just an accident of it being less expensive to just shed the stuff rather than reabsorb it. A lot of species just reabsorb it.
What’s interesting about the way that we have a menstrual cycle is that we build up our endometrial lining without any signal from a fertilized egg. Most beasties only start doing that when they get that hormonal signal that a fertilized egg is incoming. Then you get rare creatures like us who have a very invasive placenta that penetrates all the way down into the mother’s bloodstream. This is a partial allograft that’s docking in—the basal plate of the placenta being of the mother’s body, and then the top plate being made of fetal material from the embryo. The placenta is the only organ that’s made of two different organisms.
So, it’s like trench warfare, right? Because there’s maternal fetal competition for resources. That means the mother’s body has long evolved to survive and resist invasion. And of course, the embryo has evolved many mechanisms to get as many resources as it can—our babies are among the greediest out there. So, we have periods because our bodies have evolved to survive our blood-sucking demon fetuses.
That’s just a fantastic way of looking at it. But that hasn’t been the way that many people have thought about periods. Wasn’t there a whole bunch of ideas, largely devised by men, about menstruation? What’s one that made you chuckle?
The thesis that women synchronize their periods in order not to have sex with men, and therefore the men can go out and hunt and get us food, and I don’t know, snacks. And this is the dawn of human collaborative civilization. On the face of it, this is a very bad idea. But it was published in a very reputable place. I don’t know what the editor was thinking. I’m not going to say the editor had testicles, but maybe?
Man the hunter has traditionally driven the story of our evolution. He’s the great hero and many advances are tied to him. One of those is bipedalism. But you see that differently, too.
When you think about what it is to become upright, from a more tree-based life form, you’re thinking about expanding range. And that is usually about food sources. It probably was not hunting big game. We don’t have evidence for that until way later, way later. We’re talking about finding a tasty tuber at the edge of your range.
It’s useful to think about who has the greatest need for nutritive resources. Is that going to be the male with the slightly bigger body plan? Or is it going to be a female, who is the primary caretaker in nearly every primate species? Who is also lactating, which is metabolically costly, and is going to require a lot of food to feed the kid. The dawn of bipedalism to me sounded a lot more like single moms with a hungry kid who needs to expand her range.
She has advantages in metabolic endurance to be able to walk that far. And there is evidence that female bodies in humans are better geared for endurance. Endurance runners have more so-called slow-twitch muscle, and speed runners have more fast-twitch. Well, the sex-differentiated balance is clear, even in so-called untrained bodies. Female-typical muscle cells are also better at tapping into different energy substrates when one runs out, versus male muscles. So it’s all the way down to the microscopic that we have this endurance advantage.
Another gynecological innovation that you write about is the evolution of reproductive choice in mammals, albeit unconscious choice.
It’s always tricky, right? Because what we call choice is so tied to our understanding of human consciousness. So, what does it mean to choose? Well, it seems clear that female reproductive choice—as it’s talked about in biology—is very much a thing. I found it fascinating how many other species of mammals have abortions. And what I’m talking about here is social abortions. Humans can have surgical abortions, or you can have miscarriages. But that’s not a medical term: That is a spontaneous abortion.
There are many species that have a spontaneous abortion in response to a directly observed social change. A mouse is going to do it when she smells the scent of an unfamiliar male while she’s pregnant. And she is extremely likely to end that pregnancy and return to her fertility cycle.
That’s what grandma’s for—she remembers where the good hunting is.
You see it in lions, horses, and geladas. It’s normal. The mechanisms that drive it are probably a bit different, depending on the species. And the gelada was amazing because now we’re in a primate—we’re closer to us. They live in that harem-based reproductive group, and the females will abort when a new male does a coup and takes out the old alpha—80 percent of the time. That’s a hell of a freakin’ signal. And what’s interesting to me is that, it’s usually modelled as fear of infanticide. Because why invest in the baby if it’s just going to be killed by the new guy, right? So that’s a threat response.
In the gelada what’s interesting is there could be infanticide, but it actually seems to be more about social tracking, because that new guy can’t actually succeed in his coup if he doesn’t have the support of the majority of females, right? So, these social abortions are not simply mapping threatened stress in a social environment. Sometimes it is for self-advantage.
Indeed, the gelada females that get pregnant more reliably are those who do have the social abortions. So, there is a reproductive fitness thing there, too. But the idea that it might be tied to social bonding means it’s both threat and reward. It’s a complex space, and that for me, when I think back now to our very messy, complex, cautious, conscious thing of human primates, it removes this idea that abortion is somehow new and unnatural. It removes this idea that intervening on female fertility in a way that down-regulates our fertility, rather than always trying to be pregnant, would somehow not be true of other mammals and is something only we do. I think only we consciously choose the way we do it. But having an abortion response to a perceived change in a social environment, whether for threat or for reward, is something a lot of mammals do.
The female experience has traditionally been wedded to motherhood, as if no other role existed for us. But that’s not always the case. Orcas, for example, are one of the few species that, like humans, go through menopause. The popular theory is that it’s so they can help their daughters care for their offspring—the grandmother hypothesis—but you think that’s not quite accurate. Tell us about your thinking on menopause.
The grandmother hypothesis holds to the idea that not only does spending a portion of your later life not having babies reduce your competition with your daughters, but also, most importantly, you become advantageous to your daughters, because you’re helping take care of the kids. You know, built-in mammalian daycare. It’s a great situation, which as a mother of young children, I have a lot of sympathy for.
But orcas are not particularly taking care of the grandkids more. What they mostly seem to be known for is leading the pod to good hunting grounds, particularly when local food sources are running dry. In other words, in a time of nutritive stress, that’s what grandma’s for—she remembers where the good hunting is. She’s also instrumental in teaching younger members of the pod more difficult hunting strategies like lining up like line-backers and creating a bow wave to knock a seal off an ice flow.
So, in general, we expanded our lifespan. That’s clear from bones and tooth growth. We had a series of mutations that expanded human lifespan to considerably old age. And the story of menopause is the story of how all human bodies started having a benefit from having the elderly around. I assume it probably required some pretty collaborative societies to have the elderly around. Those societies were probably like unicorns for a very long time. But once you had societies that could support the elderly, one presumes they would benefit from the wisdom of older people.
But the tragic thing about menopause is that women outlive males on the average. And we love men, whether or not we have sex with them. We love trans women and people with these biologically male bodies. If we’re lucky enough to live to an old age, we’re going to have to say goodbye to them. I think the great impact of menopause is not the hot flashes, it’s saying goodbye to your loved ones.
That’s definitely the sad side of it. But your emphasis on the fact that menopause is more about a selection for longevity, rather than a selection for a shortening of fertility, is like, boom, yes, that just makes total sense. The idea that I have a role in society for my wisdom, and it was actively selected for, is really empowering. Eve contains a huge amount of wisdom. Well done, you, for plowing forward and writing it. What do you hope will be its legacy?
I hope it gives people more permission to talk about the lived reality of their own bodies. The body is automatically taboo, we are hesitant to speak about it. I hope this book gives readers new frames to talk about what womanhood might be, what parts of it come from where, and what parts don’t. I hope scientists and clinicians take up the call to better study the biology of sex differences, because all women are under-studied and under-cared for. We have the power to change that. 
Lead image: Polina Raulina / Shutterstock
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