Breasts Read online

  One could argue that it doesn’t really matter why we have breasts. We have them, we love them, they can be useful. “They’re pretty, they’re flamboyant, they’re irresistible,” wrote Natalie Angier in Woman: An Intimate Geography. “But they are arbitrary, and they signify much less than we think.”

  But it does matter because, as we’ve seen, the origin stories wag long political, sexual, and social tails. Beliefs about the origins— and thus “purpose”—of breasts can even influence their health and functioning. It’s not just the feminists who are down on the sexual selection stories. Sellen is also, because, as he put it, oversexualizing the breast detracts from infant health and contributes to body image problems in young women. It’s hard enough to get women to breast-feed as it is. “If we keep reinforcing that breasts are exclusively for sex, we’re always undermining the idea that breast-feeding is normative and normal and should be supported. Look,” he said, “the reason humans have a slightly different breast structure has to do with delivering essential nutrients.”

  As a specialist in infant nutrition, Sellen acknowledges his own biases. But the ones governing the work of the Dixsons and the other Morris descendants are stronger, he argues; in fact, they’re rooted in human nature. “Humans will make anything sexy. We can transfer some kind of sexiness to any trait.”

  “Like bound feet?” I asked.

  “Exactly,” he said. “In cultures that start to hide women’s bodies, that can explain why men are attracted to these traits. With breasts, men are just loading culturally a set of symbolizations onto something that really evolved for more direct reasons. We’ve got to be more scientific about it.”

  THESE ACADEMIC FISTICUFFS WERE VERY MUCH ON MY MIND IN Wellington. On my last morning in town, I joined Barnaby and Alan Dixson for coffee. Alan was wearing a pink button-down shirt, suspenders, and a tan blazer. A Maori fishhook made from cow bone hung from a cord around his neck. He was part gracious Englishman, part eccentric Englishman. With his bushy mustache and slightly wild white hair, he reminded me of some of the primates he has spent so many years studying.

  I asked Alan if he thinks it is possible that natural selection, not sexual selection, was driving the evolution of breasts. “I think the two went lockstep,” he answered judiciously. “Laying down the fat is naturally selective, because you need it. Then it becomes a question of where to put it. If you’re a dormouse, you put it in your tail. If you’re a mandrill, you put it in your ass.” Now the coffee was kicking in, and engaging professor mode was fully launched. “If you’re a human, and you put it in your chest, then maybe it’s sexually selected too, because in younger women, you’d have the appearance of healthy physiognomy. Men might prefer women with these attributes. We’re talking about a dynamic process. We’re not talking about the peacock’s tail, which is no bloody use at all. We’re talking about something that displays underlying health and well-being. I imagine there’s something to do with more than just lactation and pregnancy. I imagine breasts have something to do with displaying readiness for reproduction.”

  “Yes,” mused Barnaby, hunkering over his espresso and wrinkling his brow again. “These things may be linked together. It’s a fair point.”

  Ah. It seems we’d arrived at a happy medium. I could go home now. Except, for some reason, I still found myself not altogether satisfied. The more I thought about it, the less it seemed that sexual and natural selection of the breasts arrived in lockstep. In fact, I became increasingly convinced that breasts have been categorically miscast in modern history.

  I kept thinking as my plane thrummed out over the Pacific, which long ago men and women crossed in rickety dugouts following their human dreams of migration and survival. Then, as for all of our history on this planet, they fell in love or in lust, and everyone who could have children did.

  What if instead of men selecting breasts, the breasts selected the men? It’s possible that once upon a time, Early Man loved lots of different specimens of Early Woman, some with no breasts, some with small breasts, some with hairy breasts, whatever. Man, as we all know, is sometimes not that picky. Then, for the reasons described earlier—fat deposition, cranium shape, the development of speech, and the long neck—the women with the enlarged breasts and their infants gradually outlasted the others. That is, after all, the way natural selection works.

  Consequently, the people who could talk and sing and have the biggest, best-fed brains were the ones born of women with breasts. It makes perfect sense that we would grow up to appreciate and enjoy breasts, eventually putting pictures of them in eye-tracker machines in universities.

  Perhaps, all along, the breasts were calling the shots.

  • 2 •

  CIRCULAR BEGINNINGS

  … from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.

  — CHARLES DARWIN,

  On the Origin of Species

  HOPEFULLY NOW WE CAN ALL RELAX AND UNDERSTAND that breasts are, truly, designed for the purpose of feeding infants. With that out of the way, it’s worth exploring briefly how the evolutionary zinger of lactation came about.

  As wondrously unique as human breasts are in their pendulosity, their basic glandular architecture is shared by all other mammals. Our packaging is just more fetching. Other mammals have some notably oddball features. The manatee has nipples under her flippers. The nipples of the aye-aye (a small primate) sit near the mother’s rear end. The gelada monkey’s nipples are so close together that the baby can suck both at once. Spiny anteaters and platypuses, rare egg-laying mammals, have no nipples, but they “sweat” milk to the puggle in their pouches through special glands. I don’t know what a puggle is, but I want one. A hedgehog-like mammal from Madagascar takes the trophy for most nipples, twenty-four, and the Virginia opossum is unique in having an odd number, thirteen. The only male animal believed to lactate is the Dayak fruit bat, but even that is somewhat contentious—it’s unknown if the substance has any nutritional value.

  But we’re more alike than not. Evolutionary biologists point out that the six thousand or so genes governing lactation are among the most strongly conserved ones we have, meaning they haven’t evolved as recently as genes governing, say, hair or toes or the ability to digest Cherry Garcia ice cream. We have protected our primitive lactation genes because they have served us so well. If the ability to lactate is among our most valuable genetic assets, the fat globule is its crown jewel. At its core, lactation is a fat-delivery system, very little changed over millions of years, except for some dietary tweaking. Each mammal has its own proprietary ratio of fats to carbohydrates to proteins. Human milk, for example, contains one-sixth the protein found in that of the quokka (a small marsupial), and one-fiftieth the fat found in seal milk.

  All mammary glands, ours included, serve four basic eon-tested functions: First and most obvious, they provide specialized, highly adapted chow for each little newborn mammal. Second, they provide immune support for same. Third, getting a little more subtle, they produce hormones that work as natural contraception, ensuring that a mother’s births are spaced adequately apart. Finally, they provide a “window of learning” in which young mammals can focus on acquiring skills rather than desperately seeking breakfast. (Note: attracting the opposite sex was never part of the original job description.)

  If it works, don’t fix it. And for millions of years—even hundreds of millions of years—it worked unbelievably well. In fact, mammals’ ability to lactate was crucial to our success. It was an innovation that changed the world.

  The earliest lactating species showed up at the end of the Triassic, about 220 million years ago. Before that, animals popped out of eggs and then immediately had to find food. It was rough out there. Dinosaurs ruled the earth. By the start of the Cretaceous, 135 million years ago, dinosaurs and giant sea monsters still held dominion, and the few mammals scampering around were small and rodent-like. But around 60 million years ago, at the beginning of our Cen
ozoic era, some very dramatic things happened to the earth’s temperature and moisture levels. Maybe a meteor hit the earth; maybe a volcano erupted; maybe the climate simply hiccupped of its own accord. Whatever it was, nearly 40 percent of all creatures went extinct in pretty short order. Dinosaurs? Kaput. Sharks and large marine reptiles? For many, ditto.

  The new world order was cuter and furrier and made up of strong social bonds, a keen sense of smell, and a lot of snuggle time. Mammals owned the Cenozoic.

  The dramatic emergence of lactating species has been something of a thorn in the side of Darwinians, who had a hard time explaining it. Critics of evolution like to point to lactation, along with the development of eyes, as events that couldn’t simply evolve gradually, by accidental mutation, in a way that conferred an immediate survival advantage. How could you have a partial eye or a partial teat? Darwin himself went out on a limb to speculate that mammary glands slowly evolved from sweat glands in brood pouches where some fish and other marine animals kept their eggs. The sweat gave the eggs a little extra nourishment, and the system was off and running.

  It turns out that Darwin hit pretty close to the target. At least so says Dr. Olav Oftedal, the closest thing the planet has to an expert on the evolution of lactation. Oftedal came to his specialty in a circuitous way. The child of a Norwegian diplomat, he grew up chasing snakes and playing in the hardwood forests of Europe and the United States. But in the late 1960s, wanting to be socially relevant, to change the world and improve infant nutrition, he started working for aid programs in the developing world. Oftedal grew discouraged with the pace of policy work, though, and went back to school to study maternal-offspring nutrition, this time in the animal kingdom.

  “It was amazing how Darwin hit on things, and this was before genetics!” boomed Oftedal from his office at the Smithsonian Environment Research Center near Chesapeake Bay in Edgewater, Maryland. Oftedal has built his three-decade career studying the remarkable lactation habits of seals, bears, bats, and monkeys, among others. Weddell seal pups near Antarctica must quadruple their weight in the first six weeks of life, so seal milk is around 50 percent fat, among the fattiest known. A stiff wind might turn it into butter. Lactating seals have unique feeding pressures; in some species, the mother nurses for a few days, then takes off for days or even weeks to replenish her body stores far from home. The pup has to wait for her return.

  Oftedal has tasted this wondrous seal milk, declaring it “fishy.” You might think obtaining a sample is no simple matter, and you’d be correct. He throws a rubbery bag over the mother’s head, and then pumps her teats with a handheld device—all in temperatures around 20 degrees below zero Fahrenheit.

  Oftedal sees lactation as a quintessential competition between mothers and offspring for nutrition. In the case of the Weddell seal, the mother is nearly depleted by the needs of her fast-growing pup. Seen in this light of tremendous costs, lactation wouldn’t have evolved if it were not very, very useful. It also necessitated radical innovations in both the mother’s hardware and that of her young, including different teeth and brains. It was not to be embarked upon lightly.

  First, we had to figure how to make the hardware, the mammary gland itself. Teeth, oddly enough, offered a blueprint. Having developed much earlier, they pioneered a technique for simple bioorigami, showing how two layers of tissue could fold in on themselves and make proteins to build an organ. In a sequence that would make dentists everywhere happy if they knew it, we would never have breasts if we didn’t have teeth. But it was still a long way to get from a molar to a milk machine.

  For one thing, we had to keep upgrading the software. Metabolic activity is regulated by hormones that flow back and forth from the brain to target cells all over the body, including the mammary gland. As mammals evolved, so did the complex hormonal conversation necessary to regulate their changing bodies. Mammary glands evolved receptors on their cells to “listen” for and collect estrogen, progesterone, prolactin, lactogen, and many other hormones. These tell the glands when to mature and when to regress. They reveal when there is a fetus in the oven, when to deploy a glandular growth spurt, when to shut down milk production, even what sex the fetus is in order to fine-tune the composition of the milk.

  “We don’t realize how strange mammary glands are,” said Oftedal. “There are tons of placenta-type structures out there in sharks and lizards, but there’s nothing else like mammary glands. To have a skin gland producing a large flow of liquid rich in nutrients is very strange.”

  Darwin did not have the advantage of being able to date fossils, so he couldn’t know how far back lactation went. It’s very far indeed. Lactation even predates mammals, which now sounds bizarre since it is the defining characteristic of them. Here’s how Oftedal thinks it happened. Once upon a time, long before there were mammals, there were mammal-like reptiles called synapsids. These split off from other reptiles and proto-dinosaurs around 310 million years ago. Instead of scaly skin, synapsids had leathery, glandular skin containing hair follicles. They developed specialized teeth and a unique jaw that would someday evolve into a mammalian palate, nose, and ear bones. Early synapsids looked like giant terrestrial lizards. After thriving for tens of millions of years, the synapsiddescended therapsids were nearly wiped out—along with 70 percent of all creatures—by the Permian-Triassic mass extinction event 250 million years ago. Fortunately for us, a few survived, evolving into small, mammal-like creatures called cynodonts, but they would soon be eclipsed by emerging dinosaurs in the late Triassic and the Jurassic period. Somewhere in here, lactation proper began.

  The proto-mammals had kangaroo-like pouches that transported eggs, then hatchlings. The eggs, said Oftedal, were made of leathery shells with porous, parchment-like coverings. Because they were porous, they lost moisture easily and were susceptible to harmful microbes. But the mother could help solve these glitches. Maternal skin glands in the pouch began to secrete fluids and fight germs. The first fluid was a sort of natural Lysol. It wasn’t much of a leap for nutrients to eventually find their way into the mix. Eventually the happy hatchlings had constant, enriched fast food: Lysol on a burger. It’s worth mentioning again that mammary glands likely first evolved for immune support (stay tuned for more on this in chapter 9).

  Out of the hostile, climate-addled Cretaceous period, only a few small, straggler mammals, about eighteen genera in all, survived. They adjusted their skeletons and airways for better running, and they became nocturnal. They also invested more time and energy in their young and internally regulated their temperatures in ways the reptiles could not. Lactation enabled most of these changes. Endothermy, or body-temperature regulation, for example, wouldn’t be possible in tiny offspring without the fast metabolism offered by specialized, high-fat milk and intensive, snuggling parental care.

  “Little creatures that had become warm-blooded and active and lactating when the world went to hell were in a better position to survive,” Oftedal explained. “The consequence of lactation was that ultimately you could defer becoming an adult, when you have to kill or find your own food.” Consequently, mammals could become much more specialized because they weren’t forced to stay in a habitat that provided kid-friendly food. They could transform adult food into milk. Ruminants, for example, evolved eating stuff that their babies could never handle. Another example Oftedal offered are whales, which spend part of the year getting fat by feeding in the rich polar regions, then migrate to the warm but food-scarce tropics for birthing and nursing. “They do this because they can lactate!” he said, getting more excited now that we were talking about marine mammals. Crocodiles, by contrast, are stuck by the riverbank all day long so the baby crocs can go fishing. Another benefit of lactation is that mammalian babies’ heads can start smaller (because they don’t need teeth) and later grow larger to accommodate more specialized teeth and bigger brains. Being born with a small head and body is also very helpful for the mother’s mobility.

  The key concept here is flexibility a
cross habitats and niches. By the late Paleocene, there were a hundred genera of mammals made up of thousands of species, from saber-toothed tigers to hornless rhinos to flying bats to primates. The largest known mammal, a rhino-like Indricotherium transouralicum, walked Eurasia 34 million years ago. It weighed forty thousand pounds. The bumblebee bat, on the other hand, stands one and a half inches tall. As Oftedal put it, “You can have the tremendous diversity of form of things like cheetahs, buffalo, mice, manatees, seals, all made possible because of lactation!”

  The bonuses continue. Because the young must stay with the mother all day, “you have cultural transmission!” The offspring learns from the mother. Because mother and baby must communicate and “love” in some form, the mammalian brain’s six-layer neocortex evolved (together with a new sensitivity to hormones), making possible an acute sense of touch, sound, and smell, and eventually conscious thought, reasoning, and language.

  Lactation, with its tremendous metabolic efficiencies, made possible the huge difference in brain volume—up to ten times— between reptiles and mammals. The need for suckling drove the development of the palate and tongue muscles. These developments in turn prepared the way for the evolution of speech in certain higher-order primates, namely, humans. Lactation enabled complex communication.

  “You have the evolution of highly social behavior!”

  Oftedal spoke with the enthusiasm of a convert, but, surprisingly, there is barely a mention of lactation in many textbooks about the evolution of synapsids and proto-mammals. No one pays adequate attention to lactation, said a wistful Oftedal, even though it’s perhaps the single most earth-shaking event in mammalian ascendance. “It’s because the field is dominated by men who don’t think much of breasts except as sexual objects,” he laughed.