A New Book on the Evolution of the Female Body Will Blow Your Mind

In Eve, author and researcher Cat Bohannon turns science's "male norm" on its head, and charts why our bodies are the way they are.

By Nora Biette-Timmons | October 6, 2023 | 9:30pm

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A New Book on the Evolution of the Female Body Will Blow Your Mind

Cat Bohannon’s new book, Eve: How The Female Body Drove 200 Million Years of Human Evolution, opens with a fact so thoroughly detached from beauty myths and the beauty industry that it makes every “body positivity” message I’ve directly or indirectly encountered entirely irrelevant. The “gluteofemoral fat” that develops in women’s midsections and upper thighs is “chock-full of unusual lipids,” she writes. From the end of pregnancy through the first year of breastfeeding (a crucial time for baby brain development), “the mother’s body starts retrieving and dumping these special lipids by the boatload into the baby’s body.” So, some evolutionary biologists are now positing that “women evolved to have fatty hips” because the compounds they contain “provide the building blocks for human babies’ big brains.”

I cracked open Eve while on the train on the way to drinks, and immediately proceeded to share this fact with everyone I met up with (including a stranger I’d just been introduced to). The book is full of information like this—science and theories that get into how weird (and occasionally wonderful) it is to exist in the present-day Homo sapien female body.

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Outrage over the fact of the “male norm” in science is not new, but Bohannon (who has a Ph.D. in the evolution of narrative and cognition) builds upon it in a deeply constructive and fascinating way: She flips that idea on its head and has produced a book about the female norm, explaining along the way how everything from butts to boobs to socialization has made homo sapiens what we are today. (Bohannon is clear throughout that trans women are women. In one of my favorite lines on the subject, she writes: “All atypical sexualities and gender identities are fundamentally ‘natural’ because nothing a body does (including its associated mind, which is itself a product of the body) could ever be unnatural.”)

She’s pulled off an impressive feat, writing a book that is once highly complex—covering literally dozens of academic disciplines—and very readable, while avoiding the behavioral economics pop-science trap of drawing too-neat conclusions. (I did not get Freakonomics flashbacks while reading, and I mean that as a huge compliment.)

It is, however, somewhat difficult to summarize. The titular Eve is broken out into multiple Eves, each one representing a crucial evolutionary element of the female Homo sapien body—Morgie (a nickname for a species found in Wales that lived 205 million years ago), the “Eve of mammalian milk”; Donna, the “Eve of placental mammals” (67-63 million years ago); Habilis (Homo habilis, 2.8-1.5 million years ago), “the Eve of simple tools and associated intelligent sociality.” You get the idea.

“It’s kind of hard to sum up the whole range of research I was reading into,” Bohannon told me over Zoom last week. “I mean, it’s a book about where we come from, and how that makes us what we are, fundamentally, which is always true of books about our evolution. But [it’s also] a survey of some really cutting edge shit that’s going down in the biology of sex differences right now—in part because we were behind in the field, for, like, centuries, maybe forever.”

Overall, she calls the book—which took her 10 years to write, during which she got her Ph.D., was pregnant six times, and gave birth to two children (which she readily volunteers)—“a starter package on this paradigm shift we’re in the middle of.”

Existing as a woman in our increasingly atomized world can be isolating in ways that are hard to even identify. Beyond making me gasp aloud in wonder, Bohannon’s book was an unexpected antidote, delivering a profound sense of kinship with every other woman who’s ever existed (plus those various Eve ancestors). If the paradigm shift is solidarity, shift away.

The following is an adapted excerpt from Bohannon’s new book, Eve, which came out on Tuesday.

When a pregnant woman miscarries, what’s happened is what doctors call a spontaneous abortion. Humans aren’t the only species that do it. Abortion is common across mammals. Some of it is really “spontaneous,” and some of it is more deliberate.

If you put a pregnant mouse in an enclosure with a male who isn’t the father, she’ll abort (this is called the Bruce effect). The consensus is that this capacity evolved as a response to threat since male mice will usually kill and eat pups they don’t recognize as their own. From the female body’s perspective, why invest energy giving birth to pups the new guy will eat? Cut your losses and abort.

Once the scientific community recognized the Bruce effect in the 1950s, researchers started finding it all over the mammalian world. Rodents do it. Horses do it. Lions seem to do it. Even primates do it.

It’s easy to argue that, at least in rodents, the Bruce effect isn’t behavioral, which makes it harder to compare it with what we usually call abortion—an act where human women deliberately and consciously choose to end their pregnancies.

But consider the gelada. On a high, grassy patch of Ethiopia, primatologists have observed a troop of geladas for nearly a decade. They’re a lot like baboons: big, shaggy, smart, and highly social. Within their large societies, reproductive groups are harem-based: one dominant male with a bunch of females, surrounded by roving packs of outsider males who regularly try to challenge the alpha male. If a new male manages to take the crown, a curious thing happens: a full 80 percent of the currently pregnant females will abort within weeks of the new male taking over.

After taking over a troop, the new male may kill any offspring who are still nursing and may even kill the freshly weaned. That’s probably because their mothers will become fertile again sooner than they would if they were tending to these infants. And for the females, like mice, continuing a pregnancy that’s going to end in the death of the offspring is kind of a lousy investment.

But even more tantalizing is the fact that no gelada male will successfully rout a dominant male without the support of that male’s current sexual partners. In other words, it’s not as simple as saying that the females abort out of fear of the new male; some scientists propose the females may even abort to make them better able to bond with the new guy.

These are higher primates—in evolutionary terms, just shy of being great apes. They’re not aborting because of a simple biological trigger, like the scent of a male’s urine. This is something that happens as a result of directly observed social change.

It also looks as if primates use plants to influence their fertility.

Chimps in Sudan have been seen eating leaves from the Ziziphus and Combretum species. This wouldn’t seem too remarkable—chimps eat leaves all the time—except that humans who live in the same area use these plants to induce abortion. If it were the case that selectively eating these leaves detrimentally influenced the chimp population, they would probably avoid them, much as they avoid other toxic plants. But because females—not males—are the ones who eat the leaves, and because the plants are known to have abortifacient properties, that leaves a rather tantalizing question: Are these chimps controlling their inter-birth spacing by selectively eating plants that limit their fertility?

Trying to guess an animal’s intentions is always a tricky business. But given that today’s primates seem to possess a range of knowledge about the plants in their local environment—what’s safe, what’s not safe, and what might be good when you’re sick—it’s probable that early hominins did, too. Habilis was likely taking advantage of whatever she could to influence her own reproduction. Since she didn’t have anything as reliable as the Bruce effect, she would have been driven toward behavioral adaptations to exercise her choice. She was social. She was a problem solver. She was a tool user. Faced with her own faulty reproductive system, she would have tackled the problem as only a hominin could: socially and cleverly, with whatever tools she could manage to invent.