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

by Cat Bohannon

From 1996 to 2006, more than 79 percent of the animal studies published in the scientific journal Pain included only male subjects.

In the biological sciences, there’s still such a thing as the “male norm.”[*2] The male body, from mouse to human, is what gets studied in the lab. Unless we’re specifically researching ovaries, uteri, estrogens, or breasts, the girls aren’t there.

Many researchers default to male subjects for practical reasons: it’s difficult to control for the effects of female fertility cycles, particularly in mammals.

the ovary itself is thought of as a “confounding factor.”

As we’ve increasingly learned, female bodies aren’t just male bodies with “extra stuff” (fat, breasts, uteri). Nor are testicles and ovaries hot swappable.

It’s so huge that many papers don’t even mention that they used only male subjects. I often had to email the authors directly and ask. Okay, maybe it’s just mice, I

Thanks to regulations established in the 1970s, clinical trials in the United States, for one, are actually “strongly advised” not to use female subjects who “could be of childbearing age.”

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.

Even if everyone actually followed the new rules, given that it usually takes more than ten years for drugs to move from clinical trial to market, 2004 was the first year any new drug approved for sale would have been tested on significant numbers of women.

While recent research has demonstrated that women require higher doses of painkillers in order to feel the same level of pain relief as men, that knowledge isn’t currently built into dosage guidelines.

For many painkillers on the market today—for example, OxyContin, released in 1996—clinical trials didn’t rigorously test for sex differences,

more…Most clinical studies show that across multiple drug types, women metabolize drugs more quickly than men.[*5]

Is it really acceptable that we only bothered to test sex differences for general anesthesia in 1999?

I’d spent altogether too much time thinking about my fat, but I hadn’t the faintest clue that my adipose tissue is actually an organ, much less that it evolved from the same ancient organ as my liver and most of my immune system.

Some evolutionary biologists now believe that women evolved to have fatty hips precisely because they’re specialized to provide the building blocks for human babies’ big brains.

Meanwhile, we found out just a few years ago—again, someone finally asked the question—that a human girl’s hip fat may be one of the best predictors for when she’ll get her first period. Not her skeletal growth, not her height, not even her day-to-day diet, but how much gluteofemoral fat she has.

Most women’s bodies begin preparing for pregnancy in childhood, not because it’s a woman’s destiny to be a mother, but because human pregnancy sucks, and our bodies have evolved ways to help us survive

This is why people who do research on adipose tissue have started calling it an organ system: that’s not a bit of fat under your chin but a small, barely visible part of your fat organ.

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

your basic digestive system is radically old. Yo...

Actually, if we’re talking about the gravity problem, that was only four million years ago. Before then, our ancestors had the good sense not to walk on two legs, smooshing all our long-evolved organs on top of one another in our trunks (not to mention generally screwing up the spine).

The earliest fossil records of vertebrates—that is, animals with spines—date to 500 million years ago. Vertebrates still represent only about 1 percent of all living species.

Evolution works by building cheap upgrades on existing systems.

You can’t really follow it unless you’re willing to pay attention to more than one major character.

There’s no one mother of us all.

Each system in our body is effectively a different age, not only because the cellular turnover rate differs between cell type and location (your skin cells are far younger than most of your brain cells, for instance),

“Lucy”—Australopithecus afarensis. 3.85–2.95 million years ago.

Australopithecus are both among the best-known hominins (more than three hundred individual fossils have been found so far)

Australopithecus africanus. 3.3–2.1 million years ago.

heidelbergensis. 790,000–200,000 years ago, though she may stretch back to 1.3 million years.

This was the first species to build simple shelters of wood and rock. She had definite control of fire and hunted with wooden spears—the first known hunter of large game (as opposed to scavenger).

As the name implies, her fossils were first found in Germany, and later in Israel and France as well.

“Neanderthals”—Homo neanderthalensis. 400,000–40,000 years ago. Neanderthals coexisted with Homo sapiens as they spread through Europe, and the two interbred.

They seem to have developed more quickly than we did, however; their childhoods were shorter.

“Denisovans”—Presumed to be Homo denisova or Homo sapiens denisova, though not yet formally described. 500,000–15,000 years ago.

Thought to be a small population, Denisovans lived in Siberia and eastern Asia, including at high altitudes in what is now Tibet, potentially passing down a gene that continues to help populations in these regions succeed at that altitude.

Recent legislation in a number of countries has boosted the numbers—for instance, now NIH-funded studies in the United States have to justify why they’re not including women in a clinical trial if they fail to—but there remain enough loopholes in the system to drive all the elephants in a three-ring circus through (Geller et al., 2018; Rechlin et al., 2021).

While a lot of attention is given to the fact that women’s bodies tend to be smaller, the reason we metabolize drugs differently may actually have as much to do with our livers.

One recent study comparing biopsies of male and female liver tissue showed thirteen hundred genes whose mRNA expression was significantly influenced by sex; of these, 75 percent showed higher expression in females

But it wasn’t just the surfeit of beetles that made Morgie so successful. Unlike the Eves who came before her, Morgie nursed her young.

Once they are born, newborn animals face four essential dangers: desiccation, predation, starvation, and disease.

The most important thing infants need after they are born is water.

All living creatures, mammal or not, are mostly made of water. While the adult human body is 65 percent water, newborns are 75 percent. Most animals are essentially lumpy donuts filled with ocean. If you wanted to describe life on Earth in the simplest terms, you could say we’re energetic bags of highly regulated water.

We use that water to transport molecules between cells, between organs, to splice molecules and build new ones, to fold proteins, to cushion our various lumps, to mov...

But mammals seek the ocean in their mother’s abdomen; human breast milk is almost 90 percent water.

There were other advantages in replacing water with mother’s milk. Water is an ideal medium for transmitting disease.

Larger bodies of water are almost always host to millions upon millions of bacteria, some of which can be dangerous pathogens.

Think of Morgie’s body as the Jurassic world’s best water filter.

Like all the early mammaliaforms, Morgie laid eggs.