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

by Cat Bohannon

nine is young. The start of menarche has been slipping downward in industrialized countries

Many fear it’s due to hormones in our food and other endocrine-disrupting chemicals in our environment, while others think it has to do with the rise in childhood obesity: girls who are overweight or obese by age seven are significantly more likely to start their periods sooner

Dogon women in Mali found no evidence of menstrual synchrony among women, despite the total lack of (modern) birth control, artificial lighting, or cultural squeamishness about sex,

These women had eight to nine children over the course of their lives and roughly 100 to 130 periods all together (Strassmann, 1997).

the average American woman today is likely to have around 400 (ibid.). So we may not actually sync our periods, but we Western folk are having roughly four times as many...

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.

Purgatorius, the world’s earliest known primate.

Purgi appears in the fossil record roughly sixty-six million years ago, precisely when angiosperms started filling in the smoking holes left in the old conifer forests.

Scientists found her little bones on Montana’s Purgatory Hill in the 1960s, and more of her many sisters throughout the Fort Union Formation: broken jaw...

freaky monkey-squirrel, roughly the size o...

But unlike Donna, the Eve of the modern uterus, Purgi had hinged, rotating ankles, which were especially good for climbing trees and skittering along branches.

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.

The arrival of angiosperm forests profoundly shaped the evolution of tree dwellers, just as tree dwellers shaped the evolution

Other members of Purgi’s family became today’s typical primates: big-brained and flat-faced, most of whom are still in the trees.

When you first visit a tropical rain forest, the dominant emotion is usually surprise—not over the beauty of the place, nor over how hot it is. The biggest shock is that it’s bloody loud.

Howler monkeys can reach 140 decibels—per monkey.

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.

Animals generally adapt to a soundscape in one of two ways: they tweak their pitch range, or they boost their volume.

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.

Humanity’s high end, around 20 kHz, vibrates at twenty thousand times per second, which is comparable to many other mammals our size.

the “silent” dog whistle works—it produces a sound close to 50 Hz that humans can’t hear.

we built a “primate whistle” that dogs couldn’t hear, it would sound like whale farts.

We’re able to produce and hear sounds at greater decibels and lower pitches than is typical for animals of the same size.

Among primates, females and males have slightly different hearing. That might be because the males don’t need to hear everything the females need to.

This is a very common reaction for breast-feeding women: babies cry; boobs leak.

But generally speaking, men’s ears seem to be better tuned to lower pitches, while women’s ears are more sensitive to higher pitches—usually those above 2 kHz. That just so happens to correspond to the standard pitch of a baby’s cries.

Via pathways that are still mysterious, female-typical hearing became tuned to these higher pitches. Most women can hear them better than men even in noisy places. And while typical masculine ears tend to lose their higher range as they age, women’s ears are better at hanging on to those pitches.

is also tied to hardwired emotional response: baby cries alarm women more than men.

these shortwave sounds are greatly diminished by the time they make it all the way down the ear canal to the cochlea, which means the human ear has to “work harder” to be able to focus on them.

that most men over the age of twenty-five are unable to hear noises at 17.4 kHz or higher, which led to the invention of an alarm in the U.K. specially targeted at young people. It’s called the Mosquito. It blares out a horrifying whine at 17.4 kHz precisely, and can be cranked higher than 100 decibels, so that shopkeepers can use it to disperse loitering groups.

Blame it on the sex of the designers and testers: back in the day, televisions and computer monitors used cathode-ray tubes, which regularly buzzed at an obnoxious 15.73 kHz. But with these departments largely staffed by men, no one noticed it before they hit the sales floor. What made the sound was the transformer in the back of the machine, whimpering like a mad mosquito while it strained against magnetic forces.[*10] These

What’s unclear is why women as they age retain their hearing better than men do.

The assumption among scientists has been that women have fewer high-volume, ear-damaging jobs—like

It is a significant factor, but not enough to...

Both men and women are born with roughly twenty thousand hair cells in the cochlea of each ear.

After eighty, both men and women suffer from hearing loss equally. But before seventy, men are more than twice as likely to have hearing loss as women are.

There’s some support for the repair model; as I’ll discuss in the “Menopause” chapter, women’s bodies do seem to be a titch better at fixing themselves than most men’s bodies.

our olfactory system, which takes up a good third of the volume of our faces.

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,

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 ...

the female nose can do this—men’s noses aren’t as good at that kind of granularity.

The theory for why we lost it is that Purgi and other early primates slowly evolved to become more visual and less scent-driven.

Maybe that’s because, for primates at least, life in the canopy made it harder for them to distribute social stink than creatures on the ground.

Whatever the reason, the further along primate evolution you go, the flatter the face. The eyes mo...

Once ancient primates evolved into apes, the olfactory system had massively degraded.

Men also prefer the smelly T-shirts of ovulating women, don’t like the pit smells of menstruating women and women who are less immuno-compatible as much, and almost universally dislike the smell of a woman’s tears, regardless of her reproductive status.

a woman’s sense of smell is more sensitive than a man’s.