fiefoe

Cat Bohannon offers a long perspective on how female body parts came to be, and it's just so good to know such things.

One-size-fits-all doses of antidepressants are given to men and women, despite evidence that they may affect the sexes differently. Prescriptions for pain medications, too
there’s a massive difference between biological sex—something wound deep into the warp and weft of our physical development, from in-cell organelles all the way up to whole-body features, and built over billions of years of evolutionary history—and humanity’s gender identity, which is a fluid thing and brain based and at most a few hundred thousand years old.
Many researchers default to male subjects for practical reasons: it’s difficult to control for the effects of female fertility cycles, particularly in mammals... as of 2000, one in five NIH clinical drug trials still wasn’t using any female subjects, and of the studies that did, nearly two-thirds didn’t bother analyzing their data for sex differences.
unfortunately, addiction to pain medication becomes more likely the greater and more consistent one’s dosage. In other words, women who take OxyContin are more likely to do precisely the sort of thing that will make their bodies addicted to it: front-loading pills to the point that their bodies “norm” a certain level of drug in their system.
Is it really acceptable that we only bothered to test sex differences for general anesthesia in 1999? Turns out women wake up faster than men, regardless of their age, weight, or the dosage they’ve been given... And that study didn’t even set out to discover sex differences. The researchers simply wanted to test a new EEG monitor during anesthesia.
As it turns out, women’s fat isn’t the same as men’s. Each fat deposit on our body is a little bit different,[*6] but women’s hip, buttock, and upper thigh fat, or “gluteofemoral” fat, is chock-full of unusual lipids: long-chain polyunsaturated fatty acids, or LC-PUFAs. (Think omega-3. Think fish oil.) Our livers are bad at making these kinds of fats from scratch, so we need to get most of them from our diet. And bodies that can become pregnant need them so they can make baby brains and retinas... in the last trimester of pregnancy—when the fetus ramps up its brain development and its own fat stores—the mother’s body starts retrieving and dumping these special lipids by the boatload into the baby’s body. This specialized hoovering of the mother’s gluteofemoral fat stores continues throughout the first year of breast-feeding—the most important time, as it happens, for infant brain and eye development.
liposuction... I was pretty sure... nor the women who had undergone the procedure knew that our adipose tissue and our livers and our immune systems all came from the same primordial organ, called the “fat body.” That’s probably why all three share so many properties: tissue regeneration, hormonal signaling, deep responsiveness to shifts in local environments... Adipose tissue famously regenerates, too. But unlike the liver, the separate fat depots in our bodies seem to be geared for different jobs, each intricately linked to the digestive, endocrine, and reproductive systems. This is why people who do research on adipose tissue have started calling it an organ system... It gives you a reason as to why it’s hard to “get rid” of one’s fat: if adipose tissue is a body-wide organ system that has regenerative properties that go back 600 million years, maybe lopping off a piece of it in one spot naturally triggers a self-protective response that effectively “regrows” it elsewhere.
Bodies are basically units of time. What we call an individual “body” is a way of bounding a series of cascading events that follow self-replicating patterns until finally entropy sets in and enough goes wrong that the forces that keep you from flying apart at the seams finally let go. Species, in a way, are also units of time. But what’s unusual about the body..., is that your basic digestive system is radically old. Your brain is not. Your bladder is a workhorse, doing essentially the same job it’s been doing for hundreds of millions of years... It’s not your bladder’s fault that the mammalian uterus evolved to squat on top of it like Quasimodo. That only happened about forty million years ago. Actually, if we’re talking about the gravity problem, that was only four million years ago.
Whether we are in pain or joyful, abled or disabled, in sickness or in health until death do we disassemble, our bodies and the brains they contain are quite simply what we are. We are this flesh, these bones, this brief concordance of matter. From the way we grow our nails to the way we think, everything we call human is fundamentally shaped by how our bodies evolved.
Twenty-two percent of the world’s species are egg-laying beetles. Seriously. In the history of life on Earth, beetles do really, really well.
Each of our bodies’ features has its own evolutionary story, and we’re still in the thick of it. Evolution works by building cheap upgrades on existing systems. Once one body feature is in place, that newly changed body interacts with its environment, and those interactions influence the rise of other features. Those new features lead to more changes, which often loop back and change the first feature: milk leads to nipples, and the caretaking habits involved in being a nursing mother help enable the development of the placental uterus. The placental uterus then influences our metabolism and the needs of our offspring, so breast milk starts to change. Breast milk changes, and eventually birth canals turn into petri dishes for the bacteria that help newborns digest sugary milk. In essence, the kid is coated on the way out with handy bugs that coevolved with our breast milk.

CHAPTER 1 MILK

The milk and the crap and the egg scraps in that dark little burrow—these are the origins of breasts. Morgie is the real Madonna. Creatures like her nursed their young in a dangerous world, not only to feed them, but also to keep them safe.
Thus, controlling exposure to water and finding ways to ensure that drinking water is clean are two of the better strategies for maintaining the health of any animal. <> Think of Morgie’s body as the Jurassic world’s best water filter.
a hard shell that prevents the liquid inside the egg from evaporating. The eggs of most reptiles and insects, including the haphazard lineage that led to early mammals, were soft... Like anything a body tries to build when making babies, all that calcium has to come from somewhere... (Chickens in industrial egg-laying farms often suffer from osteoporosis, their fragile leg bones breaking under the weight of their own bodies.)
In all likelihood, this was the first mother’s milk: an egg-moistening mucus that Morgie’s grandmother secreted out of specialized glands near her pelvis. When her pups hatched, some of them licked up a bit of this extra stuff, which gave these offspring a serious evolutionary boost. By the time Morgie came along, these glands had evolved to secrete a goo containing more water, sugars, and lipids.
colostrum is especially dense with immunoglobulins: antibodies tagged to respond to pathogens that the mother’s body knows to be dangerous. In fact, before we discovered penicillin, cow colostrum was commonly used as an antibiotic. <> Despite its obvious benefits, human women throughout history have mistakenly believed colostrum to be rotten milk, or what they called beestings.
Bartholomäus Metlinger wrote the first European textbook for pediatrics...: The first 14 days it is better that another woman suckle the child as the milk of the mother of the child is not as healthy, and during this time the mother should have her breast sucked by a young wolf.
Meconium, a baby’s first poop—actually first few poops—is thick, tarry, and alarmingly green-black... it’s mostly broken-down blood, protein, and fluid the fetus ingested inside the womb. But it’s important that the stuff comes out fairly soon, and the laxative properties of colostrum help hurry that along—so well, in fact, that the intestines of a newborn drinking colostrum are wiped relatively clean. <> Before babies start to digest the food that will give them energy, they need to line their intestines with bacteria to help them break that food down. Mammals coevolved with their gut bacteria, because it takes a village. <> Friendly bacteria—present in the mother’s milk, in her vagina, and on her skin—rapidly colonize a newborn’s intestines.
Just in the last decade or so, scientists have come to realize that maybe its nutritional value isn’t the biggest deal off the top. Milk is really about infrastructure. It’s city planning. Some combination of a police force, waste management, and civil engineers.
At some point before marsupials and placentals arrived—somewhere between Morgie’s 200 million years and marsupials’ 100 million years—the Eve of nipples was born. On her holy chest were not just a few sweating patches of fur but thickened bumps of skin that helped her kid latch on.
When an infant begins to suckle, the nerves in the breasts send signals to a mammalian mother’s brain. In response, the brain tells the pituitary gland to produce a lot more of two specific molecules: the protein prolactin and the peptide oxytocin. Prolactin stimulates milk production. And oxytocin helps squeeze the milk out of the glands into the waiting ducts, which are then emptied by suction from the baby’s working mouth. <> These two molecules have roots tied to the evolution of milk itself... the more prolactin you have in your body after sex, the more satisfied and relaxed you feel. This may be because prolactin counteracts dopamine, which your body produces in buckets when you’re sexually aroused. Likewise, if you have too much prolactin in your system, you’re more likely to suffer from impotence.
Oxytocin also evolved to serve multiple purposes. This little peptide has garnered tons of attention lately because of its association with emotional bonding... Sometimes those uterine contractions are so powerful they don’t entirely stop after the event is over, and she’ll experience rather painful aftershocks, like menstrual cramps (which, by the by, also involve the oxytocin pathway, helping the uterus rhythmically and sometimes painfully contract in order to slough off its old lining).
It’s the vacuum, though, that really changed the breast game—being able to seal a kind of docking station between the mother’s body and her offspring’s. Once that evolved, milk stopped being something the mother’s body made on its own and started being something the mother’s and baby’s bodies make together. As the rhythmic rolling of the baby’s tongue and jaw move the focus of the vacuum back and forth, a kind of tide forms between the breast and the mouth. In that rolling wave, the milk flows up over the top while, on the bottom, the baby’s spit is being sucked back into the mother’s nipple, in a kind of evolutionarily purposeful backwash... Lining the mother’s milk ducts, from the nipple all the way to the glands, are an army of immuno-agents. And depending on what happens to be in baby’s spit that day, the mother’s breasts will change the particular composition of her milk.
The majority of human women favor cradling their infants and nursing them from our left breast, which also happens to line our baby up with the side of our face that is more expressive. No, really—and other primates do this, too.
If you live in a very dangerous world, a fact you’re “learning” through your mother’s cortisol levels and other milk content, it’s probably good to be a bit fearful. <> 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... Researchers think that to a certain degree mildly challenging environments inoculate children against the upcoming stresses of adulthood. So maybe it’s better to have a mother’s milk “demonstrate” a moderately dynamic and challenging environment.
There’s a group of people who live in Congo who call themselves the Aka. In this tribe, gender roles are remarkably fluid. Men and women both hunt. Men and women both care for children... And after she gave birth, the father still traded responsibilities day to day, not only the general child care, but suckling the child at his breast.
thanks to Hippocrates, European anatomists were convinced, well into the seventeenth century, that all women had a vein connecting the uterus to the breasts that existed for the sole purpose of transforming “hot” menstrual blood into “cool pure” mother’s milk. Even Leonardo da Vinci, a careful anatomist, drew veins in his diagrams that connected the uterus to the breasts.
We also know that from the dawn of recorded civilization human beings have employed wet nurses. These women, paid or enslaved to breast-feed others’ babies, enabled population booms. In fact, human cities may be Morgie’s greatest legacy. Without wet nurses, city life might never have taken off the way it did... While agriculture might have allowed more humans to live in one place, the problems associated with population density should have provided their own checks against exponential population growth... the average delay in childbirth for a woman who’s breast-feeding is more than double that of women who aren’t breast-feeding, so for every employer and wet nurse, you get an extra two babies. For two women nursing their own kids, you’ll get two kids every 4.7 years. For every urban woman and her corresponding wet nurse, you’ll get three kids—three and a third, to be precise, born an average of 1.3 years apart.
Remember Babylon? That massive, terrifying city, so loathed by ancient Hebrews? Around 1000 bc, its population was roughly 60,000. Meanwhile, the denizens of the Golden City of Jerusalem under King David (same era) numbered a measly 2,500... Hebrew mothers were in the habit of nursing their own, as the sacred texts exhorted them to do. Babylon had wet nurses. Their gods were more urban... It seems, for instance, that the tale of Noah and the ark wasn’t originally about sinful humans; it was about urban overpopulation and birth control... So, a story born in ancient cities beleaguered by too many people, and arguably about the dangers of urban overpopulation and the benefits of birth control, is adopted by the mostly nomadic ancient Semitic tribes who didn’t use wet nurses as often. And those tribespeople repurposed it as a story about urban wickedness... in both the Torah and the Christian Old Testament, Noah originally sends out a raven.

CHAPTER 2 WOMB

There is no holocaust, no natural disaster, no great terror in the history of humankind that can compare with the apocalypse we call Chicxulub... And we know that there, somewhere in the ashfall, is the reason women have periods. In the middle of one of life’s worst disasters, the placenta took hold. Ancient mammals gave birth to live young.
Instead of laying their eggs, some number of ancient creatures started incubating them inside their bodies. Some of them became the marsupials, while others became eutherians like us—the placentals...
But creating a body that can do all those things for gestating little ones also means making some big sacrifices. For example, nowadays, we have only one vagina. More would have been handy. Most marsupials have at least two; some have three or four.
The human uterus is shaped a bit like an upside-down pear, flanked by a couple of tiny fallopian tubes that end in fringed bits right next to the ovaries, which themselves are typically the size of a large grape. These are the leftovers of the old egg-laying system: a place to make the eggs, some tubing for those eggs to roll down, a pouchy gland to secrete materials to create an external eggshell (that gland is what turned into the uterus), and a way for the final product to roll out.
Once in the pouch, most marsupials essentially fuse their tiny mouths with a nipple, maintaining that close connection with the mother’s body as they grow. Think of the marsupial nipple as a lesser umbilical cord: there’s still that two-way communication
Others, like giraffes, are born essentially able to live in the world right from the start, which is good, given that they drop a full six feet from the laboring mother’s vagina to the ground. The force of impact is what breaks the newborn giraffe’s umbilical cord and natal sac and jolts its lungs into action,
when you get rid of the shell, that sort of system could lead to all sorts of bacterial overgrowth on your newborns... So if the evolution of live birth came first, building a more reliable separation between feces and the birth canal should have quickly followed
The marsupial penis coevolved with these respective scabbards, as penises always do (more on that in the “Love” chapter), which is why possums and kangaroos have a forked penis to match their mates’ two vaginas... The marsupial penis coevolved with these respective scabbards, as penises always do (more on that in the “Love” chapter), which is why possums and kangaroos have a forked penis to match their mates’ two vaginas.
there are always trade-offs when it comes to new body plans. In principle, the more recent a feature, the more likely it is to fail—as true of smartphones as body parts. The walls of our modern placental vagina are, being rather new, a kind of “poorly tested product.” If marsupials are any clue, it’s likely that the supporting structures for the relocated urethra, which is now just behind the vagina’s front wall, evolved more recently than the structure that divides the back wall and the rectum. In human women, these structures aren’t as robust as one might hope: as many as one in ten women suffer from urinary incontinence after a vaginal birth... After a difficult birth weakens the deep tissue between the bladder and the front vaginal wall, many women suffer a prolapse, in which their bladder partially falls into the vaginal cavity... Many women will have surgery to tighten the tissue and repair the prolapse. If the prolapse is significant enough—for instance, part of the bladder actually falls out of the vaginal opening, or the uterus does, cervix slumping down past the vaginal walls—some women may even have the vaginal opening surgically closed to support their organs.
Most male birds don’t even have a penis. Cocks, in fact, do not have one. Human language often misrepresents reality.
a female rhino has such a convoluted vagina that the rhino male evolved a two-and-a-half-foot-long penis shaped like a lightning bolt to match it. A long time ago, people in China glimpsed the lightning bolt penis (or perhaps witnessed the typical two and a half hours of mating the rhinos have to go through just to make the darn things work) and erroneously believed that rhinos’ physical prowess could be transferred to humans. Rhino horn—illegally poached, dried, and ground into a powder—continues to fetch a high price for poachers on the black market. That’s why most rhinos are now endangered species; thanks to that complicated vagina, zoos have a difficult time impregnating them to increase their dwindling numbers.
Not everyone who gives birth to live offspring has a placenta like ours. Roughly 70 percent of all living shark species give birth to live pups (and were among the first on the planet to do so)... The sharks... use a range of strategies to keep them fed in utero: secreting a thick mucus from the uterine walls that the pups can munch, firing unfertilized eggs down the fallopian tubes to waiting hungry mouths, or even having the earliest-hatching (and thereby largest) pup eat siblings in the womb,.. Tawny shark embryos are actually known to swim between the mother’s two uteri in search of a meal, and even, occasionally, poke their little heads out of the cervix and through the cloacal opening to take a look around.
with eusocial species, not every individual has a chance to reproduce, but a caste of asexual members is useful, even essential, to the group’s success, most typically by helping care for the young. Ants are some of the most famous eusocial sorts of creatures,
they would have had bigger offspring, which made a more fused uterus necessary. As fetuses grew in size, their placentas became more penetrative—it takes a lot of energy to build bigger bodies, so the more a fetus can draw from its mother, the better off it is…so long as it doesn’t kill her. Each evolutionary step toward a fused womb and greedier placentas makes sense: it’s a dance between what the mother’s body needs and what her hungry offspring need, with each accommodation skirting just on the edge of killing one or both of them.
If a fertilized egg manages to hook onto the endometrium’s functional layer, it will start building a placenta. The functional layer of the 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. One half is built from the blueprints in the embryo’s genetic matter. The other half, the placenta’s “basal plate,” grows out of the mother’s decidua. Two fleshy landscapes, one organ.
The question is why the uterine lining starts building up before it knows a fertilized egg is barreling down the fallopian tubes toward it. Among Donna’s descendants, this trait is exceedingly rare. Yet it has evolved independently three different times: once for higher primates, once for certain bats, and once for the elephant shrew... Like many other mammals with highly invasive placentas, our apelike Eves evolved a strategy for survival. Instead of waiting for a bomb to land, we dig our defenses early. We build up our linings on a regular basis, long before they are needed to protect the mother against the never-ending hunger of a human embryo.
In other words, if a pregnant woman has collapsed and needs CPR, the goal should be getting that baby out of her as soon as possible, because the pregnancy may well be why she’s about to die.
Preeclampsia is the most common of these complications. While only 5–8 percent of standard, singleton pregnancies will suffer from preeclampsia, one in three women pregnant with more than one fetus at a time will develop the condition. This seems to be regardless of whether they are carrying identical twins—which usually share a single, somewhat larger placenta—or fraternal twins, as is most often the case with IVF, each with their own placenta.
But in certain concentrations, these proteins narrow the blood vessels too much, which starts the hypertension cascade of preeclampsia.
If there’s a lot of inflammation in one area—and inflammation is generally what happens when tissue is being attacked—the immune system will fortify its efforts there. Such a focus often means paying less attention to other areas. That’s the feature of the mother’s immune system that the fetus hijacks by way of PP13... They surmise that the placenta produces PP13 to inflame tissue around uterine veins so that the arteries are left relatively unprotected. That way, the trophoblasts can do their thing and the placenta can set up its arterial supply of nutrients while the mother’s immune system is busy fighting all those distracting skirmishes around the veins... Maybe preeclampsia is what happens when the placenta starts losing the war and brings out the nukes.
women who never give birth are less likely to develop autoimmune diseases than women who have given birth at least once... Chronic inflammation is a known risk factor for many types of cancers, so the theory holds, and maybe being pregnant—particularly being pregnant more than once—is a good way of “turning down the heat.”
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.

CHAPTER 3 PERCEPTION

Artists love these broken places. They’re cheaper, for one. They also make time feel slippery, as if the past were always there, ready to be repurposed: fresh coat of paint, don’t mind the ghosts.
To understand human perception, we’ll have to think back to where our face was made. The Bethlehem, if you like, of the male gaze: that crèche of ancient forests. Because those students trying to trace my body on canvas weren’t just mammals but primates.
Some scientists even think primate hands and posture evolved from sitting upright in trees, using their forepaws to delicately handle food... Living in trees does certain things to a mammal’s body: You have to be able to hang on. You have to have good balance and depth perception.
We needed eyes that could see when fruits were ripening and distinguish when leaves were young and nutritious and tender. We needed ears that could hear our children in a loud, leafy landscape high above the ground... we needed noses that could handle a sex life in the canopy.
Howler monkeys can reach 140 decibels—per monkey. They usually roar in a chorus, and they’re not the only beasts roaring.
Primates are able to hear much lower frequencies than many other mammals. And the best theory going for why we can is our move into the forest canopy. It’s actually a physics problem: when you’re at ground level, you can bounce your sound waves off the earth, doubling your signal strength. When you’re in the trees, the ground is too far away to amplify your vocalizations... By lowering the pitch, they automatically gave themselves more distance, since the lower the pitch of a sound, the longer the sound wave, and the longer the wave, the farther it travels... Dogs, on the other hand—who evolved mostly from ground-based mammals—can hear pitches quite a bit higher than we can.
Tuvan throat singers famously manage to sing two notes at once, though that isn’t happening in the larynx—they’re adding strength to some of their vocal overtones by manipulating the back of the throat and mouth above the voice box, making the overtone more audible alongside the primary note. It’s a difficult thing to do. Professional throat singers often sweat when they perform because it takes tremendous concentration and muscle control.
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... Computer fans, however—the ones cooling down the blazing-hot processors—generate a high-pitched whine of their own that bothers women’s ears more than men’s. Blame it on the sex of the designers and testers
All that can really be said is that queer women’s ears often behave slightly differently than straight women’s do, and that the ears of gay and bisexual men don’t reflect a similar difference.
Our hearing and sight sensors don’t require as much room in our heads as our olfactory system, which takes up a good third of the volume of our faces. Because olfaction involves molecules rather than waves of light or sound, and there are millions of different molecules in the air we breathe, being able to smell something requires a big, wet, warm surface area lined with sensors... In the alphabet of our olfactory sense, there are roughly four hundred known receptors in the human nasal tract, and roughly a thousand known genes for odor receptors in mammals, though the majority aren’t functional in the human body. Even setting aside the nonfunctional ones, these genes constitute as much as 2 percent of the mammalian genome—a truly massive number.
Male goats, in a display I can only hope was never part of hominin history, actually urinate on themselves, spraying a thick, musky pee up their belly all the way to the chin. As any goat breeder will tell you, it’s about the most disgusting and instantly recognizable stink a person could ever encounter. It contains putrescine and cadaverine—two organic compounds that corpses produce when they decompose.
The big reason pig farms castrate male pigs is that otherwise, once they reach puberty, their testicles pump out androstenone, which becomes concentrated in their adipose tissue and can make the meat taste like sweat and piss. It’s called boar taint.
Gay men particularly liked the smell of other gay men, as it turned out, but less so the straight guys, whereas women preferred the stinky pits of gay men to those of straight men. And male-to-female transsexuals showed similar hypothalamus activity to heterosexual women.
Human puberty builds a bigger nose in boys in order to provide the oxygen they need to run their larger muscle mass. A typical teenage male will grow a nose about 10 percent bigger than a typical girl his size... And yet women are still better at detecting diluted scents—fewer molecules of the scent, in other words, in any given local quantity of air.
In most of the brain, neurons are wired dendritically... In the olfactory bulb, however, signals are more diffuse. An activated cell tends to radiate the information out in all directions to nearby cells. In that sense, the wiring of the olfactory bulb is less about sparking a chain of events and more about creating a ripple over a pond.
Prey animals usually have their eyes on either side of the head... they’re able to keep watch for predators over an incredibly wide field. What’s directly in front of them matters a lot less than spotting the lion in the grass. Meanwhile, predators—dogs, eagles, snakes, cats—generally have their eyes on the front of their heads... it greatly increases the amount each eye’s visual field overlaps. That overlap—the parallax—makes it a lot easier to see how far away something is from you in space. It’s also easier to make out fine-grained features of items in that overlap zone.
Your brain might have to get bigger, too, since processing a lot of 3-D visual data takes a lot of computational firepower. Indeed, when paleontologists measure primate fossils’ skulls, the more stereoscopic the eye placement, the bigger the brainpan.
And those brains and their corresponding forward-facing eyes became rather useful for our new diets. With our wider parallax, we were able to use our forepaws to manipulate leaves and fruits and seeds close to our faces, with much greater clarity and precision.
your eyes, in other words, help your entire body “understand” what time it is, and the clockwork of your internal machinery responds accordingly. This became only more true as primates became more visual creatures. What our bodies do with eye signals influences pretty baseline stuff. For example, women who work night shifts famously have trouble with fertility
Most placental mammals are dichromatic, meaning they have two primary types of color receptors: blue and green.
Because the tectonic plates that hold Africa and South America were closer at that time, and because so much of the world’s oceans was bound up in Antarctic glaciers, the sea was narrower and shallower than it is now. Scientists assume that primates, living as they are wont to do in trees near good sources of water, were caught up in storms along the African coast and got tossed—possibly along with their trees and the earth bound to their roots—into the ocean, where currents swept them across the sea. Astonishingly, many survived. From these storm-tossed creatures descended the howler monkeys, the spider monkeys, the capuchins. The New World monkeys.
The groups with a mixture of color vision among their members appear to be slightly better at foraging as a group. Humans, like most of our social primate Eves before us, have bodies that work the way they do in large part because they live alongside other humans. Just as we carry the deep past in our differently ancient physical traits—some things old, some things new—our social groups carry the past, too: some things old, some things new.
Consider, for example, what happens when untrained artists try to draw human faces: they forget to draw foreheads. <> Because human beings tend to fixate on the eyes, nose, and mouth—which is to say, where our identifying features are located
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... These girls are like secret superheroes. They have eyes like birds.

CHAPTER 4 LEGS

Tearing a continent apart does a number on the weather. Up in the canopy, our primate Eves were evolving into apelike things. As the planet cooled, wind patterns shifted over East Africa’s rising plateau, separating the continent’s central rain forests from our ancestors’ home ecosystem. By 8 million years ago, it wasn’t raining as often as it used to.[*1] Forests shrank and wide, grassy plains opened up, as fertile and treacherous as the sea.
When we take a step, the stiff bones of our upper foot stabilize the force between our toes and our ankles. Starting at the heel, we essentially roll our weight forward, over the upper and mid-foot, onto our toes, stepping from one forefoot onto the opposite heel. We’ve taken something that originally evolved for grasping and made it a hinged series of levers for bearing weight while walking. Your big toe is basically a short thumb... But it’s worse for women. Stiffening the upper- and mid-foot bones so we can walk means a lot of force is transferred from our ankles to our forefoot. All that force on the forefoot, especially the big toe joint, weakens it over time. Combine that with a female body that tends to “sway” in motion (wider hips, funky knees, more butt fat), and eventually something’s gotta give.
If anything, when it comes to withstanding high heels, male drag queens are arguably better equipped to wear those Louboutins than women... They’ll also never ovulate or become pregnant, lacking both ovaries and a uterus,[*7] so those lower levels of relaxin stay lower, their spine stays nicely fixed, and their hip joints never have to widen to accommodate a newborn’s head and shoulders.[*8] Relaxin will also never mess with the ligaments tying together a drag queen’s foot bones—something every pregnant woman has to deal with.
That’s why older women are encouraged to add weights to their exercise regimen: tugging at the muscular anchors of our bones encourages those anchors to add more calcium, strengthening the bone.
fundamentally, a musculoskeletal system is a set of levers. Lots and lots of levers—things that pinch closed and widen, depending on the task at hand. <> In a few key spots, there are also ball-and-socket joints that allow a wider range of motion, swiveling and rotating,
Instead of just using carbohydrates for energy as they work, mammalian muscle cells shift and start metabolizing fats and amino acids, too. That switch is a lot like the “second wind” endurance athletes talk about... It’s actually about firing up the mitochondria—the powerhouses in each cell. Women of reproductive age may be better at utilizing that metabolic switch... that may be because there’s something in the mitochondrial metabolism in skeletal muscles that’s controlled by female sex hormones.
if females bear a greater need for food—in terms of both having pregnancies and needing to feed their offspring—then it seems safe to assume that added food pressure would be a driver in selecting for evolutionary change. In many mammals, female bodies have evolved to adapt to that food challenge by being smaller than males so that, when they’re not pregnant, they need fewer calories to survive.
Despite less muscle overall, the muscles we do have give us an advantage. <> Skeletal muscles are made up of large bundles of fibrous tissue. Think of them like twitchy rope, all packed together and anchored to the bone by ligaments. These fibers are divided into two primary types: fast-twitch and slow-twitch. Fast-twitch fibers contract very quickly and generate a lot of power, but they tire easily.
astronauts also have conversion, wherein muscle tissue shifts from slow-twitch to fast-twitch. If you’re not constantly asking muscle fibers to work, the way slow-twitch muscles do when we walk around in Earth’s gravity, the muscle will optimize for fast-twitch fibers.
The muscles that run over the tops of your thighs are mostly the quadriceps: two long, bulky ropes responsible for hiking your knee toward your hips. Unless you live in a very hilly place, these don’t get worked nearly as often as the muscles on the backs of your thighs—the hamstrings, which straighten the leg. Think about the mechanics of it: You don’t have to lift your foot very far from the ground to walk forward. But the hamstrings and glutei maximi (your butt muscles) hoist your entire body forward over your foot each time you take a step. If you’re running, that action is even more pronounced.
So at this point, it seems women are at least as good as men, and may even be innately better, at hard-core muscular and metabolic endurance. And there’s one more thing to consider: We may be better at dealing with muscular tissue damage than men. Women recover from exercise more quickly than men do.

CHAPTER 5 TOOLS

Generally speaking, innovation is something that weaker individuals do in order to overcome their relative disadvantage. As a primatologist in Kenya told me years ago, “Women do clever things because we have to.”
The most important human invention—the very reason we’ve managed to succeed as a species—was gynecology.
The pregnancy and birth complication rate—which, again, can readily stop a genetic line in its tracks—shoots up to a full third of human women.
There are two likely reasons why human reproduction is so dangerous. First, the risk of internal bleeding. Our deeply invasive placentas can rupture veins and arteries (rare), can separate from the uterine wall before it’s time (less rare), or can hemorrhage during or just after birth (still rare, but one of the leading causes of maternal death). <> The second reason our reproductive system causes so much trouble is what’s called the obstetric dilemma. Compared with other apes, human women have a really small pelvic opening and human babies have a really big head. When humans evolved to walk upright, the structure of our pelvis had to change,
Chimps labor about forty minutes... While a chimp’s cervix needs to dilate to only 3.3 centimeters,
The modern human birth canal sort of twists, wider in some spots and narrower in others, which means a newborn actually rotates ninety degrees in the middle of the vagina while being born. That’s another gift from hominin evolution: big heads need big shoulders to brace developing neck muscles.
Dominant female chimps are known to kill the offspring of females with lower status. Maybe they do it out of spite or maliciousness, but from a biologist’s perspective it’s probably because it helps them maintain their social position. They don’t just kill the baby. They may even eat it in front of the crying mother.
They just tend to resolve such conflicts with quick bouts of sex. And somewhere in the middle of all that sex, there’s one strict rule in bonobo society: nobody messes with the kids... Did she help with the delivery? We don’t know. We do know that all three females shared the placenta afterward, gulping down pieces of it.
Mallard ducks are constantly raping each other... After her rapists run off, her body will get rid of that sperm as best as it can. Sometimes she’ll even tap her beak against her lower abdomen, helping expel it from her cloaca. The males didn’t take this lying down. The mallard’s penis coevolved with the female’s changing vagina and now has a kind of corkscrew structure—presumably to try to sidestep the trapdoors.
Meanwhile, the dolphin’s penis can actually swivel, feeling around its environment—a bit like a blind tentacle—before hooking itself into a vagina. The whole business can get rather violent. In the wild, gangs of dolphin males can prevent a targeted female from surfacing to breathe
And then there are horses. That’s where things get really behavioral. Domesticated horses are significantly more likely to miscarry than wild mares... The answer was strikingly simple. To avoid these spontaneous abortions, you have to let the mare have sex with a familiar male... That stallion does get first dibs on reproduction, but mares also have “sneaky sex” with outsider males. Then they immediately seek out the stallion to try to have “cover-up” sex with him. If they don’t get the chance to have cover-up sex? That’s when they’ll usually abort.
we can see that social abortion—“miscarriages” that occur as a response to the local social environment, rather than any problem with the embryo itself—is a well-documented part of mammalian reproductive biology. Abortion is just one of the things that female mammals do.
By the time Erectus came around, their placentas were greedy, their birth canals were a gauntlet, and their babies, once safely born, were highly dependent for years and years and years. Maybe that’s why as few as 50 percent of human pregnancies actually produce a human baby... If pregnancies, births, and child rearing are biologically expensive, then you’d expect the bodies that have to do all those things to evolve ways of ensuring that only the pregnancies with the very best chance of success will continue. <> If those sorts of miserable success rates were true of our hominin Eves, too, that’s probably why only a few hominin species ever managed to get out of Africa.
Consider the armadillo: one of the reasons the strange, semi-armored little mammal does so well in its many difficult environments is the simple fact that it’s able to control when it’s pregnant. In the low belly of the nine-banded armadillo, the embryo, semi-miraculously, is able to stop developing... Her embryo also splits into four, producing four identical offspring attached via one placenta—very unusual among mammals, and another reason she’s good at migrating. Armadillos can build up a minimal viable population in any environment fairly quickly.
Here’s a more realistic Genesis: about sixty to a hundred thousand years ago, a population of ancient Homo sapiens finally reached critical mass in southern Africa. <> A small group of them then migrated to eastern Africa. Ten thousand or so years later, they finally flourished enough to enable another band to migrate, moving into the ancient Middle East. From there, it took only about five thousand years for subsequent groups to move into Europe, into central and northern Asia, and finally, only fifteen thousand years ago, into North America.
Pregnant women seem to attract twice as many malarial mosquitoes as nonpregnant women.[*35] And once a woman is bitten, she faces severe consequences. In places where malaria is endemic, a full 25 percent of all maternal deaths can be directly tied to malaria. Pregnant women are three times more likely to suffer a severe version of the disease, and nearly 50 percent of those women will die... Given how much more likely pregnant women are to be bitten by malarial mosquitoes, taking special advantage of pregnant female bodies could be part of the protozoan’s broader life-cycle strategy. We know that the protozoans accumulate in placental tissue. If sequestering in the human placenta allows them to escape detection for longer,
Then we see a fast montage of female reproductive choice: hominins having sex, eating strange plants, having babies, nursing, walking with their offspring on their hips over the ridge to a green horizon. And back to the newborn, who suckles at her mother’s breast as the two females move together toward the troop. Near the watering hole, the mother lies down, exhausted. The older female picks up the newborn and raises it overhead. Its profile clear against the blue sky, the newborn transforms into a human baby in a woman’s arms, the two in profile against the window of a spaceship. We see the thin, bright arc of the planet in the background, the curvature of Earth. In the woman’s free hand, the camera zooms in on a pamphlet: Planned Parenthood: The Best Care in Low Orbit. And The Blue Danube begins.

CHAPTER 6 BRAIN

I can actually report that the oddest thing about our species might be that the female human brain doesn’t seem to be all that functionally different from the male.
(Map test:) A man tends to do a little better than a woman does on that one. But if you include a tiny picture of a person on every corner, women do just as well as men.
Originally, Europeans thought an angry, irritable uterus could actually move, floating upward past the stomach and the diaphragm and into the throat, to somehow choke a woman’s brain. *Though the mobile uterus was disavowed, “hysteria” remained: As late as the 1920s, clitoral stimulation was considered the proper treatment for feminine hysteria. That meant doctors—typically male—were obliged to stimulate moody women to orgasm in clinical settings. Hilariously, most of the doctors seemed to find the task boring and tedious, which drove the invention of the electric vibrator in Paris in the late nineteenth century.
Male brains seem to suffer more extensive inflammation and lesions around injury sites than females’ do. And this might be because progesterone and the estrogens—the classic female sex hormones—have a protective effect on brain tissue, dampening that inflammatory response.
What happens after we’re born is the kicker: the biggest difference is what happened to our ancient ape brain when hominin evolution beefed up that frontal cortex and gave it a superlong childhood... 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.
While female and male brains prune themselves roughly the same amount, males prune later and faster. That might be one reason why schizophrenia hits boys so hard and so predictably in mid- to late adolescence, whereas female schizophrenics don’t typically fall ill until their mid- to late twenties. These shifts are also tied to depression and pathological anxiety—“teenage angst” is a real thing in the brain.
For one thing, kids learn how to point in part because they have to, since unlike chimps they can’t get about on their own until they’re at least seven to twelve months old. If a human baby wants something—an object, or to go somewhere, or to stop being trapped in a high chair—they have to ask others for help.
As we discussed earlier, the transitions between life phases are often dramatic and involve all sorts of bodily reordering. For something like a butterfly, that can mean entirely losing one’s jaw.
The reason that matters for the evolution of human brains, of course, is that pregnant and breast-feeding women just so happen to have brains that are doing very similar things to what human brains do at other major transitions in our body’s life cycle: they violently rearrange themselves. A pregnant woman’s brain will, quite reliably, shrink in volume by as much as 5 percent during her third trimester, followed by a steady rebuilding during the first few months after giving birth... Thus, human women might have evolved to be capable of an extra phase of brain development, of much the sort all humans go through when we’re children: a deep pruning that precedes a massive period of social learning.
The trendy term for this is “microaggression,” but the outcome in any deeply social human brain is easy to name: it’s stress. Like a fine-grit sandpaper, little bits of social stress can wear you down over time. The damage accumulates.
It takes a whole girlhood in a sexist environment to build a brain like that. You have to have gone through puberty as a female in that sexist world. You have to have felt that moment when walking down the street changed because men started to look at you differently. When your understanding of your life’s possibilities began to shrink, and you felt powerless to stop it.

CHAPTER 7 VOICE

Our brains and diaphragms learn how to power our words with our breath when we’re young. Babies can’t do it. Toddlers are better, but still pretty lousy. Mature breath control, the sort adults use to talk every day, doesn’t seem to kick in until age five. *This is why you may find musically gifted children showing their talents by way of an instrument before they are five—Mozart did that—whereas singers don’t start until later. They don’t have the voice control, and they don’t have the lungs.
Men have bigger lungs than women, which means they have more oxygen still circulating while they’re talking. That’s one reason the male Clinton found it easier to deliver his acceptance speech. He simply had more hot air to work with.
Women’s ribs pinch inward at the bottom, just a bit, which is a big part of why women’s waists are narrower than men’s. <> Evolution endowed teenage Hillary with that female rib cage for a good reason: She needed room for future Chelseas.
But because vocal speech requires that you finely control the distribution of that pressure, you effectively bounce it back and forth between the voice box and the lungs. If you didn’t carefully control that moving pressure, you’d be liable to tear up tissue—the force of air in the human respiratory tract when we’re speaking is remarkably high.
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. *Bats manage to pull it off by having a much more efficient method of flying than birds or insects: their stretchy wing membranes and many-jointed wing bones let them make tiny, efficient adjustments to the shape of their wings as they fly
Careful study of the fossils of hominin neck bones suggests we had throat sacs until very recently. Lucy and the australopithecines still had them. And it’s easy to see their legacy in today’s human throat, which has deep folds on either side of the larynx... Still, while a hefty throat sac lets you get loud, you can’t be precise.
At ovulation, both a woman’s larynx and her vagina seem to hit “peak mucus”: the cervix creates extra in order to help sperm swim up and find the egg, and the larynx’s lining and vocal cords become plump and happy and flexible. Across the menstrual cycle, women often favor their own voices around ovulation.
The strongest muscle in the human body, in terms of absolute pressure, is the masseter muscle of the jaw. The uterus is the strongest muscle in the body in terms of constricting pressure. But when it comes to muscles that have both strength and flexibility, the clear winner is the human tongue, which has to roll and push a bolus of mashed food from side to side around the mouth, getting the un-mashed bits better mashed before swallowing, all while dodging the powerful slice and crunch of the moving teeth.
the latest science is moving... toward something a bit simpler, a bit more accidental. A significant part of why ancient hominins were able to invent vocal language may be that our Eves evolved to walk upright. Balancing our skulls on the tip of an upright spine naturally changed the structure of our throats and mouths over time. Not all those changes were beneficial. Choking was a problem. Infected throat sacs, too. The loss of the throat sac might have led to males developing a deeper voice to compensate,
Our capacity for learning and innovating in language is innate, but nevertheless, for the largest gains in intergenerational communication to persist over time, each generation has to pass language on to the next with careful effort, interactive learning, and guided development.[*10] Language, in other words, is something that mothers and their babies make together and is dependent on the relationship between them in those first critical three to five years of human life.
Across most cultures, women are especially prone to using motherese, and we’re also more likely to exaggerate pitches and shift the overall register up... The most obvious reason motherese might help is its higher pitch, which is easier for baby ears to hear and understand... we exaggerate the phonemes—the smallest parts of human speech, like the “fuh” in “far” or the “ah” in Hillary Clinton’s “accept”—to make them more distinguishable. Babies whose mothers put more emphasis on vowels tend to perform better on language tasks later... As much as 70 percent of the world’s languages are tonal
what’s unique about us is that we have a long childhood full of those drives and capabilities, with extended and unique bursts of brain development usefully timed to stages where we need to learn really hard, complex stuff in order to be able to function in our highly social societies.[*30] So in essence the story of language may be about windows of brain plasticity: times in our young lives when our minds can still build those critical pathways, which just so happen to be perfectly timed to coincide with breast-feeding and motherese. <> But it’s not the words that are important, particularly. The real payoff is grammar—the very stuff of human thought.

CHAPTER 8 MENOPAUSE

Most animals keep reproducing until they die. That’s true of primates. That’s true of birds and lizards and fish. That’s even true of most insects. With the exception of orcas, no other species does what we do. <> That’s why human menopause is one of the biggest mysteries in modern biology, right up there with why we die.
So maybe ancient humanlike bodies somehow anticipated those problems, discarding all those egg follicles to avoid giving birth to disabled babies. <> Since most mammals don’t live as long as we do, maybe they don’t have to deal with genetic damage to old eggs. There are some outliers, though, and they kind of punch a hole in that theory.
But, as opposed to human cultural norms, the older the chimp, the sexier the boys find her. The hottest gal on the block is already a grandmother.
In other words, while the mechanisms of menopause are physiological, being a “menopausal” species may be a deeply social phenomenon—you need to have most females routinely surviving to sixty and beyond, living a third of their lives after their reproductive years. Because evolution takes a phenomenally long time to standardize changes in a species’ body plan, it couldn’t be a one-off. Culture changes quickly. Physiology, as a rule, does not.
What the grandmothers are responsible for is teaching the pod in times of crisis. When food is scarce, the grandmothers are the ones who lead the way to places that are more likely to have good food... For instance, creating bow waves to wash seals off ice floes and herding fish. <> 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.
green potatoes contain solanine, a chemical that essentially prompts cells to kill themselves. Nausea, diarrhea, and vomiting are the milder side effects. The nightmares are also survivable. You’ll have a harder time getting past the hallucinations, paralysis, hypothermia, and death... In other words, you are more likely to be poisoned when you eat plants than when you eat a diet of meat.
Such elders would have benefited hunter-gatherer societies, too, but maybe sustainable agricultural societies made societies of the elderly simply more common.
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... 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. <> Presuming she’s born, for the rest of that female’s life, each cell somehow remembers which X was initially shut down in the womb, and instructs all subsequent cells in that line—each time the cell and its progeny divide, for the body’s entire lifetime—to keep shutting down that particular X. This turns out to be true except for about fifty of those eight hundred genes, as researchers just discovered in 2017; some of those genes seem particularly important for cellular DNA self-regulation and metabolism—precisely the things a cancer cell tends to screw up,

CHAPTER 9 LOVE

The man has a theory. / The woman has hipbones. / Here comes Death. —ANNE CARSON, DECREATION
What parts of the body, exactly, are we allowed to sell? If not the genitals, then the mouth? Can we make the body smile, make it say things, put food in it or not, put a fist in it or not, smooth the edges of the voice, drop the pitch, change the rhythm—let them hear it, but not see it; let them see it, but not touch it; let them touch it, but not own it, drag their fingers along it, the way you’d run your hand over the hood of a car.
Is loving a man actually the best thing a woman can do? As for the second, I’d greatly prefer that the story of womanhood not be summed up as elaborate whoring. <> But just as we’ve done with other unpalatable ideas, we need to explore these two threads. How did human beings evolve to love one another, and what role did women have in that evolution? Is it prostitutes all the way down?
Promiscuous primates have gigantic balls... If you want your sperm to win out, you basically have to blitzkrieg the female’s cervix with huge numbers. To make huge numbers, you need huge testicles. <> Gorillas? Tiny little balls. Peanuts.[*6] But silverback gorillas don’t have to worry that much about other males having sex with their harem. What’s more, the females aren’t in estrus for very long—only two to three days a cycle,
Regardless of how they got that way, having medium testicles now does imply that our ancestors weren’t especially promiscuous, or at least not as much as the chimps.
In fact, when it comes to sex, chimp males are typically more cajoling, solicitous, even friendly. Or they employ tactics remarkably similar to what human domestic abusers do. Male chimps will physically and vocally harass females, often in an attempt to socially isolate them, stress them out, and wear them down.
it does seem to be the case that males with significantly less money and social status are more likely to be violently abusive toward their partners than men who don’t have those problems.[*7] So maybe human men have evolved to use violent mate guarding as a reproductive strategy. Or at least, as primates who are incredibly similar to chimps, maybe our bodies and our brains were abuse ready
So what else could the glans be good for? How about sucking out fertile cervical mucus. Though the human penis doesn’t fit so perfectly into the vaginal cavity that it makes a total vacuum seal, most do produce a slight sucking force during thrusting. So each time the penis draws out, a small amount of suction draws away material from the upper vagina down the fluted rim of the penis head and along the shaft. <> The acidic vaginal environment is actually toxic to human sperm... The very best position to be in, actually, is to ejaculate as close to the cervix as possible, with a lot of fertile mucus around and behind the sperm at the moment of ejaculation, shielding that tiny bubble of semen for a few crucial minutes while they swim desperately toward their north star.
It does fit neatly with the fossil record. It also helps explain why human sexual culture is so very different from that of our primate peers. There’s just one problem: monogamy wasn’t such a sweet deal for female hominins. As with other apes, our ancestral promiscuity wasn’t just a pleasurable habit. It was a strategy—a necessary one. See, primate males aren’t just a danger to one another. They’re incredibly dangerous for babies.
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.
One bizarre, if enticing, alternative theory: in a matriarchy, babies make good buffers for aggression. Take savannah baboons. .. But then one of the combatants goes off and picks up a baby, who blithely clings to his chest hair or his back. Then he goes over to the male he was having the fight with. If the baby likes the male it’s clinging to, the kid will scream at his opponent if he acts aggressively. So the other male either backs off or is mobbed by friends of the mother, spurred on by the baby’s cries. It’s so effective, in fact, that some males simply carry a baby around as a kind of adorable bodyguard,... Hanging around helping with the kids also gives him more chances to have sneaky sex while the dominant male is away—call it the monkey world’s gender-flipped version of having an affair with the nanny.
There’s only one mammal we know of where males inherit their mother’s social rank for life: transient orcas. Sons stay with their mothers their entire lives, inheriting their mothers’ rank. They’re matriarchal, too, and the only other species proven to have menopause.
No—sexism is one of the ways our ancestors solved our hardest problem, which, as I’ve already discussed at great length, is that we categorically suck at making babies. <> I 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... 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.
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.
But what happens when sexism turns into a runaway train? What happens when a culture’s sex rules start to reduce the overall health, fertility, and competitive viability of a population?
If anything, the clearest benefits of Christian sex rules went to the church itself—without legitimate children who could claim inheritance from its clergy, the Church remained the uncontested owner of all its property generation after generation.
Maternal age is the single most predictive factor for whether a girl is likely to die simply because she became pregnant. Reducing the number of girls married before they are eighteen by even 10 percent can reduce a country’s maternal mortality by 70 percent.
the data exist: when you leave men in charge, roads and bridges and dams are effectively left to rot. When women are empowered in local governance, for whatever reason, they are more likely to vote for local infrastructure (and health services and local, directly impactful public spending) than male politicians,
Let’s put that in the simplest terms possible: four years of school equals one less baby.
the Prophet Muhammad’s first wife, Khadija—famously his most beloved—was older than him, twice widowed, already had children, and was a widely respected businesswoman when he met her. *According to the Quran, the Prophet Muhammad met her while she was his employer, and it was her idea to propose marriage, not his. He also refused to take on a second wife while she was still alive, quite contrary to local custom for any man who could afford more than one wife
The slow decline of that civilization also happened to start when Islam absorbed Byzantium and became more influenced by Western thought, including the increased seclusion of women and girls, so popular in Persia, and the de-emphasis of the importance of education and “worldliness” of anyone who happened to be female
In part, that’s because sharing and enforcing sex rules isn’t just about making us more competitive baby makers. It’s also useful to be the same sort of sexist as the people around you. Sharing cultural rules helps trick the human brain into thinking your neighbor is your sister.

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