Eve: How the Female Body Drove 200 Million Years of Human Evolution, by Cat Bohannon

A feminist take on evolutionary history might be a bit of a hard sell for ACX readers, it certainly doesn’t help that it made me read the word mansplain two chapters in. But Cat Bohannon’s Eve: How the Female Body Drove 200 Million Years of Human Evolution is an interesting enough book to be well worth enduring a few culture war flashbacks.

As the title would suggest Eve is an exploration of human evolution through the lens of the female body. Which in retrospect seems like the obvious way to look at evolution, given that it’s where 99% of the whole reproduction business seems to be going on. The book structures itself as a journey through time, with each chapter focusing on the history of a particular evolutionary trait and it’s associated female ancestor, or “Eves” as the book likes to call them. These range from the first mammal to produce milk up to modern homo sapiens. Although really Eve is anything but linear. One minute we’re talking about breastfeeding rodents, then wet nursing in ancient Babylon, the next we’re reading about Hillary Clinton and howler monkeys. It’s an evolutionary journey, yes, but one with flashbacks and flashforwards and more than a few diversions along the way. Here’s a far from an exhaustive list of interesting things I learned along the way:

1.   Breasts are A Communication Platform

I was vaguely aware that breastfeeding played a role in building a babies immune system before reading Eve and that breasts were a bit more than just milk dispensation nozzles. But it’s even more complicated than that. Think of breasts as more of an elaborate baby-to-mother docking port where biological information flows both ways. The baby is getting hormonal signals from the mother that convey her current stress level, which in turn shapes the babies behavior. Rats, mice and monkeys fed on milk low in stress hormones are playful and adventurous while those fed on high-stress milk are skittish and antisocial. But the baby’s backwashed saliva also informs the mother what sort of milk they need. A mother’s breast milk will change composition to fight off infections, adjust nutritional needs or work as an analgesic for a baby in pain.

2.  Wombs are Weirder than you Think

You probably know that the human reproductive system is a mess. Narrow, upright walking hips and giant heads led to a protracted and difficult birthing process with a high chance of killing or permanently harming the mother. Eve introduced me to a few new glaring design flaws, like how the downward pressure from standing upright squishes down our organs on top of the womb. Or how the fetus and it’s mother are basically at war with each other over the course of the pregnancy. After implantation, the placenta sends cells called trophoblasts into the uterine lining. These trophoblasts attack the mother’s uterine arteries in order to try to gain more nutrients for the fetus. The mother’s immune system fights back, but the fetus deploys a bunch of clever tricks to get around this, like attacking nearby veins with something called placental protein 13 (Or PP13) which inflames the area and keeps the immune system distracted. Throughout the book Bohannan’s tone while describing the female reproductive system fluctuates between loving and lovecraftian, which having finished the book, doesn’t strike me as too inaccurate.

Our wombs aren't even the weirdest in the animal kingdom. Marsupials have multiple wombs and vaginas, as well as corresponding forked penises to match. The embryos of sharks that give live birth are free to swim between their mothers multiple uteri, feeding on a nutritional mucus instead of a placental connection, even poking their heads out of the cervix on occasion. Birds don’t have penises but instead mate with a sort of ‘cloacal kiss’. Oh except maybe male weaver birds who have a sort of pseudo-clitorus. I’ll let the diagrams below illustrate just how weird they can get.

3.  Get Pregnant, Develop your Brain

During childhood the human brain is continually rebuilding itself, blooming with interconnecting neurons then pruning them back to something more manageable.There are a couple phases in which the brain gets particularly busy, particularly around the phases that tend to be the most emotionally tumultuous, early childhood and adolescence. This restructuring lasts until our mid twenties when things finally start to settle down.  

But there’s a secret bonus phase of brain development that only pregnant women will ever experience. By her third trimester a woman’s brain will shrink by about 5% then slowly rebuild itself over the coming months. This occurs mainly in the parts of the brain related to building emotional attachments, general learning, and memory. It comes with a short-term disruption to memory, emotional regulation, sleep regulation in the same way other developmental phases do.

This seems massively understudied. Bohannon couldn't even find whether this occurred in every pregnancy or just someone's first. I’m very curious if this can be used therapeutically in some way. Readers are invited to get impregnated and report back.

4.  When in Danger, Grab a Friendly Toddler

This, according to Eve, is the origin of human monogamy and patriarchy. You see, at some point our ancestors made the switch from a bonobo-like social structure, which was matriarchal, matrilocal, (females stick around while males ‘marry out’ to other groups), and very very promiscuous, to the typically patriarchal, patrilocal, and monogamous social structures common today. So why did the switch happen? And how? A patrilineal system seems like a non-starter when no one can tell which child belongs to which father.

 There’s a possible hint in the behavior of savannah baboons. Males will befriend the offspring of high-ranking females with gifts of food until the infant starts habitually clinging to them. Next time they get into a fight with another male their tiny bodyguard starts letting out a cry and the other male now has to face the wrath of it’s mother and her entire sisterhood of dominant females. Ingratiating themselves with female hierarchies also makes them a favorable mate for these females and ensures that evolution selects for step-dad behavior. As birthing and childrearing become more difficult and resource intensive, the need to control when and where they give birth lead to a decrease in promiscuity among our ancestors. Combined, all this led to the exchange of sexual exclusivity for protection and provision, setting the stage for a monogamous system.

Homo Gynaecologia

If the above points didn’t make it clear enough, Eve has a lot going on. But if the book does have a central theory it’s this: the critical innovation that drove human success wasn’t fire, or tools or agriculture it was gynecology; our ability to control our fertility, ensure the survival of baby and mother and generally manage the ramshackled mess of a reproductive system we’ve inherited.

Bohannon asks us to imagine the opening scene of 2001: A Space Odyssey but instead of the bone-wielding ape-man smashing up a tapir skeleton and subsequent cut to space station, it’s a pair of ape-women, a birth giver and the first midwife, guiding the baby out, and holding it triumphantly overhead, with a subsequent cut to an orbital Planned Parenthood.  

This innovation begins with a movement away from the chimpanzee-style of birthing, where the pregnant female has to leave the group out of fear that another member will take the opportunity to eat her newborn. But not eating babies is only the first in a long line of gynecological innovations. Dealing with birthing difficulties is the root of a number of social practices, it’s also why we have grandmas and wetnurses.

To elaborate on those last two points, grandmas, or more specifically post-menopausal women, are kind of an oddity. We’re the only species that doesn’t keep reproducing for our whole lives, except, for some reason, orcas. Eve’s theory on why we have menopause, is a variation of the grandmother hypothesis. That being that, past a certain point, it’s evolutionarily beneficial for women to start caring for their grandchildren over making new children. Bahannon adds that grandmothers are also important stores of knowledge, most importantly gynecological knowledge, which might do something to explain why there’s no corresponding grandfather effect and why women enjoy an elongated lifespan.

Wetnurses, too, are a fertility control mechanism. Breastfeeding acts as a weak form of birth control. So the elites of ancient cities like Babylon and Rome would hand over the task of breastfeeding to a servant, since one woman could often provide enough milk for two children. The mother would then be freed up to get pregnant again without waiting for the infant to finish feeding, and since breastfeeding two children isn’t a stronger form of birth control than feeding one, the wetnurse still has the same chance of getting pregnant again. This allowed the elites of early agricultural societies to explode in population. So the wet nursing babylonians could grow their city to 60,000 members by 1,000 BC, while contemporary Jerusalem which favored breastfeeding by the mother lingered at 2,500.    

It’s a compelling theory but Bohannon is sort of her own opponent here since she also peppers in just as many terrible historical gynecological practices throughout history. Like how physicians in the middle-ages advised against letting newborns feed on colostrum, the thick yellowly breast milk mothers produce right after giving birth, which carries a lot of immunoglobulins to help the baby's newly formed immune system. Or the modern practice of neglecting using female subjects for clinical trials and completely forbidding the use of pregnant subjects, even for drugs like pain-killers which women and especially pregnant women use disproportionately often and intensely.  

If I had another criticism it’s that Bohannon’s feminist tendencies did induce a couple of eye-rolls throughout my reading. She gives enough inclusive nods to trans people that I know she’s at least not one of the TERFy variety of feminists but then she goes back to talking about our wombs and the struggles we endure giving birth and it all feels a bit moot. Bohannon seems to very much expect a female reader.

There are some points when this went from quibbles about phrasing to flat out disagreement. Take her chapter on the evolution of the brain, which explores the question of why developmental tests seem to show the female brain on par with its male counterpart, or even ahead of it in some areas, before abruptly starting to lag around puberty.

Bohannon argues that this is something brought on by the stress of girlhood. The grinding strain of years living in a sexist culture and micromanaging how she presents herself shapes the female brain into something specialized for social awareness and too burnt-out to rotate shapes as well as boys can.

“As a term, the “male gaze” means too many different things to be useful here. But this fundamental experience—this moment or loose assemblage of moments, somewhere between ages eight and fourteen, wherein a girl starts to know that being visibly female means being a thing that’s seen differently—rings true for me. When I asked the women I know if they could remember it, the majority said yes, absolutely.”

I can’t speak for the men Bohannon didn’t ask, but I don’t recall my teenage years as being marked by confidence, low levels of stress or a nonchalant attitude about how the opposite sex was perceiving me. I don’t think the theory is implausible but I'd like to see some stronger evidence. Are, for example, women who grow up in more sexist cultures correspondingly more ‘female-brained’?  

There are a couple of moments like this throughout the book, when it strays into becoming the sort of evolutionary herstory one might fear. But ultimately I can’t be too mad at Eve since these moments aren't the norm, and it did leave me with an intense feeling of gratitude at having been born male.