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

by Cat Bohannon

Morgie was about the size of a modern field mouse.

Even today, newborn duck-billed platypuses lick milk from sweaty milk patches on their mother’s stomach; she doesn’t have nipples.

For the first few days after a woman gives birth, her milk is incredibly special—a hot shot of immune system for her newborn baby.

Each of those fat globules is surrounded by a membrane that contains xanthine oxidoreductase—an enzyme that helps kill a ton of unwanted, dangerous microbes.

The four dangers—desiccation, predation, starvation, and disease—are differently dangerous according to a timetable.

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.

Colostrum doesn’t just clear the path for the early bacterial settlers. It also contains bacterial growth factors that help those colonies gain a foothold.

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 turns out a significant portion of our milk isn’t even digestible.

These complex, milk-specific sugars aren’t even digestible by the human body. We don’t use them. They’re not for us. They’re for our bacteria. Oligosaccharides are prebiotics: material that promotes the growth and generally ensures the well-being of friendly bacteria in the intestines.

(Prebiotics are not the probiotics you’ve likely heard of—bacteria like L. acidophilus that the human body naturally contains. Eating fistfuls of probiotics on their own is a little like planting your garden without fertilizer, or maybe even without soil. You need prebiotics to make the whole system work.)

some scientists argue, the beaver’s children inherit both their parents’ genetic material and a changed environment.

So, if our gut bacteria are in the business of passing on their genes, they’re going to evolve in ways that help their descendants colonize the intestines of their hosts’ babies. In mammals, milk is one of the key ways that happens.

chimps, for example, have markedly different breast milk in the wild than they do in zoos

But what remains consistent in human milk, no matter where we are and what we’re eating, is the extraordinary number of oligosaccharides we stuff in there.

In fact, human milk has the most, and most diverse, oligosaccharides of all our primate cousins’, probably because unlike other apes modern humans have had...

Humans are not just social primates; we’r...

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.

The average nipple has fifteen to twenty small holes that are connected via tubes to the milk glands in the breast.

the infant has a significant role in the type of milk that the mother’s body makes.

There are a few different mechanisms involved, but the most important are these two: the let-down reflex and the vacuum.

they’re full of blood, fat, and glandular tissue.

There’s no bladder in a breast that holds a sloshing cup of milk that empties as the baby nurses and then gradually fills up again,

It’s a lot like what your mouth does when it comes to saliva. Chewing your way through a typical meal produces about half a cup of spit. But you don’t have half a cup of spit in your mouth at all times, ready to go.

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.

Milk with a lot of cortisol tends (at least in rats and mice and certain kinds of monkeys) to produce baby personalities that are less risk seeking, and those traits seem to persist through the individual’s lifetime.

Human infants drink about three cups of breast milk a day in their first year of life.

What isn’t clear is why female breasts have so much extra fat.

From what studies have shown, big, fatty, pendulous breasts are no more likely to make higher-quality milk than “skinny” teacup breasts,

Obese males, too, may develop additional breast tissue—not

Large breasts can, however, advertise an estrogen-heavy phenotype, particularly when combined with a relatively narrow waist, which may be good for carrying babies in general. Like any plump female feature,

In fact, human cities may be Morgie’s greatest legacy. Without wet nurses, city life might never have taken off the way it did.

Breast-feeding, in other words, is a very predictable sort of birth control. It is an imperfect birth control,

Generally speaking, our ovaries stay quiet while our breasts are at work.

So, imagine what happens to a city’s population when you have a large percentage of its mothers employing wet nurses. In principle, that would reduce a woman’s mean birth interval significantly, from 4.1 years to as little as 1.3 years.

Gestation takes about 9 months. You’d be pregnant pretty ...

Meanwhile, wet nurses wouldn’t be pregnant as often as you, but because breast-feeding is an imperfect ovulation suppressor, they wou...

In this imaginary world, where only wet-nursing influences a city’s population, it would seem Hammurabi had a hell of a lot of babies on his hands. No wonder regulations for wet-nursing made it into his written law.

For example, in eighteenth-century France, where large swaths of the middle classes employed rural wet nurses, not just the rich, many infants farmed out to the countryside died, presumably of disease or neglect.

It became such a problem that a nationwide regulatory agency called the Bureau des Nourrices was conceived to help protect the infants and look after the interests of both mothers and wet nurses.

It stayed in business until 1876, and the French continued to employ wet nurses through World War I. In the United States, African American women regularly nursed the white babies of the American South throughout slavery, through Reconstructi...

(there was no bureau to regulate that, of course; it was one of the many degradations of slavery and c...

Ancient Romans formed organizations to regulate the practice;

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 (Noah and the ark), thereby generally screwing women for the next three thousand years.

Breast cancer is common and deadly precisely because mammary tissue evolved to strongly respond to hormonal changes; wherever you have a bunch of cells proliferating and changing and reverting,

you’re likely to find cells that go rogue.

While 1 percent of breast cancers occur in men, breast cancer is a full 30 percent of all cancers in women.

Unfortunately, it’s also the second leading cause of cancer death for women.

There’s still a one-in-eight chance that I, as an American woman, will develop breast cancer at some point in my lifetime, and those stats are similar worldwide.[*35]