Read an Excerpt
CHAPTER 1
EVOLUTION AND THE FEMALE BODY
I SPOTTED LUCY, framed and hanging on the walls, in the bowels of the American Museum of Natural History. The three-million-year-old fossilized australopithecine was a creature in mid-evolution between ape and Homo sapiens. She is one of the oldest human ancestors ever discovered.
Having just seen the expansive pelvises of knuckle-scraping apes and chimps in other displays in the museum, I was shocked to see Lucy's pelvis, so tiny and elliptical from hip to hip that it could not have been easy for her to give birth, not even if the baby's head was the size of a lemon. Staring at Lucy's remains, I imagined the agony and ecstasy of birth since the beginning of time. And I thought about the connections between her bones and the advent of midwives, epidurals, surgical instruments, medical malpractice claims, a newborn with a cone head, and virtually every trendy technique that has come and gone throughout the centuries. It was clear that if we had ape-sized pelvises, we'd need no midwifery help, no sterilized stainless-steel paraphernalia, and no Demerol to give birth. But there would be other consequences.
Lucy, unearthed in Ethiopia in 1974, was related to those apes and chimps; she had long arms, short legs, and a face with ape-like features. But she was clearly different in one respect. She walked upright. And there was her compact pelvis to prove it. As an evolutionary entry point, Lucy can help explain not just the physical aspects of human birth, which have become remarkably more difficult since we began walking upright and producing smarter offspring with the requisite larger crania, but also how primitive behaviors that may have existed in her era are still affecting labor and delivery today. Since Lucy's lifetime, the female pelvis has remained narrow, so as to accommodate our walking upright, but it also has evolved in shape to accommodate the newborn head, which has grown in size over hundreds of thousands of years as the brain enlarged. Today, the upper opening of the pelvis is wide from side to side, as was Lucy's; the lower pelvis, however, the baby's exit, is widest from front to back. And therein lies the problem.
The obstetrical consequence of such a design is that human birth is, quite literally, a twisted process. In order to pass through the birth canal, the baby's head — the largest part of its body — must rotate as it descends in a grinding pirouette. A baby monkey, on the other hand, does not need to turn: It emerges faceup, having had plenty of room to simply drop down the chute.
The contrast between human births and those of four-legged mammals is stunning. Women have a much more difficult time than, say, polar bears, or the free-ranging howler monkey — which can deliver in about two minutes — as each has plenty of space in her birth canal. In fact, we are the only mammal species that needs assistance to give birth.
Although most animals seek solitude for birth, almost all women in labor ask for help or surround themselves with company. It's as if somewhere, deep inside our brains, we cannot fathom how that baby's big head can make a graceful exit. It's a notion that causes fear, which triggers a cry for help in labor and delivery. According to American anthropologist Wenda Trevathan, such an impulse to call for aid could be an adaptive response to reduce mortality in a species more prone to obstetrical problems. This behavior probably developed around two million years ago, she says, along with the advent of consciousness. Once our brains were advanced enough to know that birth could be dangerous, the onset of labor made us scared. Fear often leads to the release of the hormone epinephrine, also known as adrenaline, which can stop contractions. To alleviate that fear — to keep labor progressing — women began asking for help from people they felt comfortable with: other women. Monkeys in labor often stop contracting when they know a human is watching them. Women aren't necessarily different. After laboring at home for hours, many find their labor stalls when they arrive at the hospital, surrounded by the unfamiliar. The phenomenon is so common that doctors and nurses self-referentially call it "white-coat syndrome." For women, being among strangers can retard labor.
Around the world, solitary human births are virtually unheard of. The exceptions are those peoples whose cultures support and value the concept. For example, women of the Igbo tribe of Nigeria may have a first birth supervised but a later one alone. Female members of the nomadic Pitjandjara tribe of Australia might deliver by themselves, behind the group, if there is no worry of trouble. So, too, do women of the !Kung San hunter-gatherers living in the Kalahari Desert in northeastern Namibia give birth on their own — for it is a sign of strength, esteemed in that culture. The story of a !Kung woman named Nisa is remarkable because it shows how even an uncomplicated birth among a people who encourage solitary delivery can be traumatic.
In the chilly depths of night, early in the twentieth century, Nisa gave birth to her first child in the bush without any help. When Nisa's contractions had begun, she left her husband's village, carrying only a blanket and an animal skin for warmth, walked a short distance, sat down on the sandy earth, and waited.
I leaned against the tree and began to feel the labor. The pains came over and over, again and again. It felt as though the baby was trying to jump right out. The pains stopped. I said, "Why doesn't it hurry up and come out? Why doesn't it come out so I can rest? What does it want inside me that it just stays in there? Won't God help me to have it come out quickly?" As I said that, the baby started to be born. I thought, "I won't cry out. I'll just sit here. Look, it's already being born and I'll be fine." But it really hurt! I cried out, but only to myself. I thought, "Oh, I almost cried out in my in-laws' village." Then I thought, "Has my child already been born?" Because I wasn't really sure; I thought I might have only been sick. That's why I hadn't told anyone when I left the village. After she was born, I sat there; I didn't know what to do. I had no sense. She lay there, moving her arms about, trying to suck on her fingers.... The cold started to grab me. I covered her with my duiker skin that had been covering my stomach and pulled the larger kaross over myself. Soon the afterbirth came out and I buried it.
Somewhat stunned, Nisa left the baby, still attached to the placenta by the umbilical cord, and ran back to the village. When her husband saw her bloody legs, he shouted for his grandmother to go and help cut the cord. The old woman promptly did just that.
According to Marjorie Shostak, a researcher to whom Nisa recounted her story, an uncomplicated delivery reflects a !Kung woman's full acceptance of childbearing: "She sits quietly, she does not scream or cry out for help, and she stays in control throughout the labor. A difficult delivery, by contrast, is believed to be evidence of her ambivalence about the birth, and may even be seen as a rejection of the child."
Thankfully, being alone during delivery is a rarity for most women today.
OVERNIGHT DELIVERIES
Another obstetrical phenomenon that may be an adaptation from primitive times is that mammals commonly labor through the night. The squirrel monkey begins her labor between dusk and dawn. If delivery does not happen before morning, her contractions will stop and begin again after sunset. Natural selection might favor nighttime deliveries for some animals — like the squirrel monkey — that search for food during the day. A female who stops to give birth during such a busy time risks being left behind by her kin. Delivering at night also gives mother and offspring time to recover without the risk of being discovered by predators — or even those in their own social group who might want to inspect the new arrival. (The schedule is flipped for nocturnal animals: They tend to deliver during the day.)
Humans, as well, seem to prefer laboring through the night. But because delivery takes longer for people than for monkeys, women tend to give birth in the morning. Such a pattern may also reflect Lucy's era, when it was advantageous to deliver with fellow tribe members around to provide assistance and protection. Those giving birth in the afternoon would likely have found themselves alone, as the others would have been looking for food. Also, laboring through the quiet of the night may keep the mother relaxed and therefore able to have faster, less complicated births.
But, as you might suspect, behavior that worked well on the savanna two million years ago may not be advantageous now. Most dilating women today arrive at the hospital during the late shift, when the staff is reduced and the least experienced doctors are working. More senior obstetricians have the privilege of working business hours, while exhausted residents, living on pizza and donuts and the occasional nap on a cot, attend to the overnight customers. Some women might be willing to forgive a resident who yawns through her contractions at 3:00 a.m. or rushes to the bed at the last second to catch the baby and cut the cord. However, the dearth of well- rested, experienced doctors working overnight, and the lack of hospital services that are available only during the day, can have devastating consequences.
Babies born late at night have as much as a 16 percent greater chance of dying than babies born between 7:00 a.m. and 7:00 p.m., a 2005 study found. This spike in overnight infant deaths may be attributed to the quality and number of doctors and nurses during those dark hours.
There are other ways that life in the developed world hasn't mixed well with the ancient biological process of birth. Take, for example, modern eating habits. Easy access to food is yielding bigger babies that, no matter how hard they try, simply cannot fit through the standard-issue pelvis. This imbalance is called cephalopelvic disproportion, or CPD in E.R. language, and is an increasingly common reason for cesarean sections.
Dietary changes affected obstetrics hundreds of years ago, as well, during the period of rapid industrialization and urbanization, which severed populations from fresh milk, green vegetables, and sunlight. Calcium and vitamin D deficiencies led to a bone disease called rickets, which deformed women's already tight pelvises, resulting in countless deaths for mother and baby. The disease was so pervasive that much of the early research and practice for cesareans involved pregnant women with rickets.
Thinking about all this, I peeled away from the display case of Lucy's bones. The sights and sounds of humanity shuffling across the museum floor suddenly reentered my consciousness. I turned and happily saw the throng of well-fed women inching strollers through the café line. Obviously, children — and their mothers — were today regularly surviving birth. How? These women were all taller than Lucy, who stood less than four feet high; their pelvises certainly were somewhat larger. But their babies' heads are more than twice the size of what they would have been in Lucy's time. Proportionately, we still seemed to be losing the battle with evolution.
Back at home, I phoned Owen Lovejoy, professor of biological anthropology at Kent State University in Ohio and of human anatomy at Northeastern Ohio Universities College of Medicine. Lovejoy often can be found brushing through the dirt at fossil excavation sites around the globe, or sitting on the witness stand in high-profile homicide cases.
"Lucy's pelvis was so small!" I said.
Lovejoy laughed and explained that women today are indeed better off than Lucy was, in purely obstetrical terms, but perhaps not by much.
"Because we have her pelvis, we know something about pelvic evolution among humans," Lovejoy explained. "Lucy's pelvis is beautifully adapted to upright walking, but it's poorly adapted to giving birth to a large-brained fetus. And so between Lucy as a starting point and modern humans, we changed the pelvis — not for bipedality but to get that huge cantaloupe through," he explained.
No wonder birth doesn't always go smoothly. The physical frame leaves little room for error. Lovejoy explained that the birth canal became larger, but, more important, it also became different in shape, with the exit now widest between the pubic bone and the tail bone. As a result, the big head is able to descend through a pelvis fine-tuned for walking, though not easily. Assuming the baby is not breech — being born feet or buttocks first — its head must enter the pelvis facing up toward the pubic bone, with the widest part of its head — ear to ear — lining up with the widest part of the pelvis — hip to hip. But, as mentioned, that has to change quickly. The baby must begin to turn sideways, as much as forty-five to ninety degrees, in order to align its body with the widest pelvic outlet, its head emerging facedown, rather than faceup. In most cases, babies can navigate the space unaided. But not always. Sometimes the space is just too small and the head is too big, so the aforementioned cephalopelvic disproportion becomes a factor.
Birthing babies with large crania would not be an issue if humans had pelvises like chimpanzees, our closest genetic relatives. But if we had pelvises like chimps, we would also walk like chimps, rocking from side to side as if wearing snowshoes. The stance would be an uncomfortably wide, inefficient, and exhausting means of getting around.
Although women's pelvises are universally narrow compared with those of other primates, they vary enough in shape that there are four categorizations for them. If she is lucky, a woman has a "gynecoid" pelvis, the most common and successful shape for birth because it is the most spacious and round. The other shapes — android, resembling a funnel or a narrow heart similar to a male's pelvis; anthropoid, a thin oval; and platypelloid, with a mildly deformed kidney-shaped brim — can also accommodate a baby, but only if they are simpatico with the child's size.
Brand-new babies may appear tiny, especially in those first days, when their fingernails are perfect little specks and their knees are as sweet and wrinkled as shriveled figs. But it doesn't matter if they're five pounds or eight: Human newborns — and their heads — are proportionately much larger than what other mammals deliver. Female gorillas produce offspring that average only about 2 percent of their mother's weight, compared with 6 percent for humans. Polar bears, who weigh more than five hundred pounds, give birth to cubs with heads smaller than those of human newborns.
Still, anyone who has ever pushed for hours on end only to have the experience culminate in a grapefruit-sized head tearing her flesh might be surprised to learn that while human babies' crania are huge by comparison with those of other animals, their brains aren't as large as they should be.
Lucy's offspring would have needed a tiny head to pass through her small frame. By the later part of the Stone Age, a couple of hundred thousand years ago, the Cro-Magnons appeared in what is now Europe. Their crania — and those of their offspring — had expanded to accommodate all that newfound intellect used to invent religion and draw deer on cave walls using berry juice.
"Brains appear to have gotten bigger progressively throughout the last two million years," said Lovejoy. "But we did hit a wall. The wall we hit was we just couldn't make the pelvis any bigger, so what we had to do is start giving birth to a more altricial infant."
Altricial means that the baby is essentially born helpless. Throughout early human history, brain development made fetal head size grow, but only to the point that it still had a chance to fit through the pelvis. The sorry truth is that babies' crania are actually so small as to be underdeveloped for our species, much more underdeveloped than those of other newborn primates. Human babies compensate by quadrupling brain size after birth. In contrast, most other primate offspring emerge with pretty well-developed brains, having only to double the cranium after birth.
Because human infants are born with their neural networks incomplete, leaving them writhing, helpless squawkers who need constant care during the first year of life, the baby's first three months outside the womb are a period of rapid growth, what many scientists refer to as a fourth "trimester" of development. Other scientists look at infant growth as a two-stage gestation: thirty-eight weeks, followed by thirty-eight weeks outside. Most infants begin to crawl at around nine months of age — the end of the theoretical second stage of gestation — a marker that brings their brains closer to the development level of a deer's when it is born. A deer can run shortly after birth. A baby ape can cling to its mother moments after coming out. But if a human was born with a cranium large enough to make it as developed as the brand-new deer or ape, its head would be too large to fit through the birth canal. For a human baby to emerge as developed as a newborn elephant — which has a 630-day gestation — the child would need to be born with a cranium the size of a one-year-old's, a physical impossibility. Instead, the baby comes out as immature as an infant opossum or kangaroo, which remain protected by a mother's pouch for a long while after birth. It's no wonder tiny babies are cranky. They're really not ready to live outside the womb.
(Continues…)
Excerpted from "Birth"
by .
Copyright © 2006 Tina Cassidy.
Excerpted by permission of Grove Atlantic, Inc..
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
