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Nature’s Contribution: The Biology of Emotions
There’s More to “Mothering” Than Meets the Eye, Scientists Discover
New York, New York. What happens when Mommy Rat runs away from home, leaving her litter of pups to fend for themselves? They get hungry—very hungry. No surprise there. But according to Columbia University professor Myron Hofer, there’s a lot more than that going wrong when Mom “turns tail” and runs. In fact, hunger is one of the least of the abandoned rat pups’ problems. Like a harp that stays silent without someone plucking at its strings, rat pups left without the cuddling, licking, and delicious smells and rhythms that constitute mothering in their world lack the ability to maintain many critical biological functions, the control of which is necessary for life itself. Their body temperatures drop, their heart rates increase, their breathing becomes erratic, their sleep-wake cycles are disrupted, their growth and stress hormones go haywire. In short, the result is true biological chaos, a level of disorganization that can kill.
Researchers studying human mothering say there’s an important lesson in all of this for us. Like the rat pup, the human infant may look like an independent little unit (especially in those identical little maternity ward cribs), but that’s a serious, even deadly, misperception. The newborn human baby is dependent on our tender loving care for much more than food and diaper changes. Just like rat pups, human babies require proximity to a warm body—one that breathes with regularity, strokes and cuddles, smiles and smells—to keep their biological systems in line. Or one could say, like the silent harp, human babies need their parents’ love to create the sweet, concordant rhythms that make for the beautiful music that is healthy life.
Biological Regulation: An Evolutionary Gamble
Myron Hofer’s work with rat pups is both exciting and exceedingly important. Instead of seeing motherhood through a veil of sentimentality, he has proved that what parents routinely do (or should do) with their babies is absolutely critical for their survival. There were earlier clues, of course, particularly in the many tragic cases of failure-to-thrive syndrome in orphanages, where food was plentiful, beds were clean, but anything approaching mothering was considered too expensive, too time-consuming, and totally unnecessary. These babies literally withered and died. And now we know why.
Both the problem and the strength of the human baby is that she is a work in progress. If human babies were prewired upon entry into the world, there would be no capacity to change, to adapt to different environments, to learn. In other words, if human babies were only a product of “nature” rather than equally dependent on “nurture,” human progress would have ground to a halt a long time ago. Instead, evolution took a chance, sending us newborn babies that are far from ready-wired, trusting that it could also nudge the big humans around these helpless creatures into providing them the attention needed to get their immature biological systems up and running in an organized, self-sufficient way.
Parents as the “Gelatin Molds” of Early Development
Human babies may arrive totally dependent on their parents to keep their biological rhythms working right, but they don’t stay that way. Over the first nine months of life, the infant gradually becomes able to exert his own control over his breathing, heart rate, sleep-wake cycles, stress reactions, growth hormones, and the like. But it doesn’t happen automatically. Again, this progress is not prewired. The active support parents provide the baby during those early months helps shape his own control mechanisms. Feeling the parent’s breath go in and out sets a pace for the baby’s breathing. Hearing the parent’s voice stimulates synchronized body movements. Being predictably roused from sleep and soothed back into it stabilizes sleep-wake cycles. The warmth of the parent’s body and stroking of the baby’s skin regulates his temperature. Touching the baby’s face stimulates sucking. On and on it goes. But if that parental support is itself erratic or disorganized, then the baby’s developing ability to regulate himself will be compromised accordingly.
When we explain the gradual development of biological regulation and the important role played by parents to our undergraduate students, we like to use the metaphor of the gelatin mold. The function of a gelatin mold is to contain the liquid gelatin until it slowly solidifies enough to hold its own shape once the mold is removed. Typically, the shape that results is a lovely, rippled mound with a flat spot on top for a dollop of whipped cream. But the shape the gelatin finally assumes won’t be so pretty if one or all of the following things go wrong: (a) the mold itself is bizarrely shaped, (b) the mold is removed before solidification is complete, or (c) the mold itself is too flexible to provide a consistent shape.
In this metaphor, babies, of course, are represented by the gelatin, with parental interactions, daily routines, and physical closeness acting as the mold that holds the gelatin together until it can solidify. Without the mold, the gelatin simply runs all over the place, achieving no coherent shape as it hardens, just as a baby’s biological rhythms disintegrate into chaos without the strength and warmth of a parent’s arms to hold them in place. That one person’s breathing, heartbeat, and nearness might exert such power over another person’s behavior may at first seem far-fetched—but notice what happens the next time you find yourself close to someone who yawns!
Individual Differences in the Gelatin
Children differ in many ways, including how much support they need early on to regulate their biological systems. Continuing the metaphor, they differ in how solid their gelatin is to start with. Although some babies seem to develop reasonable sleep-wake cycles within weeks, for other babies the process can take months. Similarly, some babies will be soothed quickly when upset, while others require rocking for what may seem like hours. And some babies can sleep through the sound of the vacuum cleaner, while other babies flinch at the sound of a car door closing outdoors. Such differences can be genetic in origin and can run in families. In other cases, particular characteristics of the prenatal environment (the amount of maternal stress, for example) may be playing a role. Whatever their source, these individual differences in the newborn baby’s gelatin contribute significantly to differences in infant temperament apparent from Day 1, the topic we turn to next.
Inborn Temperament: Variety Is the Spice of Life
What a boring world this would be if we were all alike, if we were all cut with the same cookie cutter. How would those of us who are shy be wooed into joining the action? How would those of us who jump in with both feet be persuaded to look before we leap? Fortunately, nature has guaranteed that we aren’t all alike, even at the very beginning.
Sudden Infant Death Syndrome (SIDS)
On a very serious note, there is good evidence that some babies need more help than others to keep their breathing regular, particularly when they are asleep. These babies, it is hypothesized, are the ones at most risk from dying of sudden infant death syndrome, or SIDS. As evidence, researchers note the young age at which most SIDS cases occur (before four months) and an impressively lower incidence of SIDS in cultures where baby and mother routinely sleep together, proximity that presumably provides the child with a stable breathing pattern and frequent arousal episodes.
There is a downside, however, to cosleeping. New research strongly suggests that the fewer items in the sleep environment that might accidentally cover the baby’s mouth and nose (pillows, crib bumpers, blankets, etc.), the lower the chance of SIDS. Many pediatricians worry that the parent’s body or bedclothes pose such dangers. As a compromise, some parents are using baby beds that attach directly to the side of their own bed, allowing easy access and close monitoring without the added worry of obstructing the baby’s breathing.
By far the most successful recommendation of all came in 1994 in the form of the “Back to Sleep” campaign launched by the American Academy of Pediatrics. The aim was to shift parents from routinely putting babies to sleep on their tummies to always putting them to sleep on their backs. As a result of these efforts, the incidence of SIDS in the United States is estimated to have declined by 40 percent.
The fact that babies differ from Day 1 is hardly a surprise to most parents—at least on an intellectual level. However, thanks to years and years of exposure to the well-behaved, cuddly babies popular among advertisers and greeting card designers, too many parents (particularly first-time parents) are indeed surprised at—and not fully prepared for—their baby’s unique personality. It’s as if they were expecting the perfect rose and received a happy-go-lucky sweet pea instead. It’s cute, all right, but why doesn’t it stand up tall and straight in the vase?
That’s why it’s so important for parents to know about the variations in what researchers call infant temperament. Once you know the wide variety from which the florist can pick, you’ll be better prepared to enjoy the surprise when your doorbell finally rings and your particular flower is delivered. “Oh, goody! A sweet pea!”
Cataloging Infant Temperaments
Carrying the metaphor a bit further, researchers tell us that there are four particularly popular flowers—or inborn temperaments—in the florist’s greenhouse (none of which, by the way, is the perfect rose). Before identifying these four, let’s first describe how this conclusion was reached. We have two pediatricians, Alexander Thomas and Stella Chess, to thank for the original, painstaking cataloging of infant temperament. Based on exhaustive interviews with parents of 136 children followed from age two to adulthood, they identified nine dimensions along which children reliably differ:
2.Adaptability (Are transitions hard?)
3.Willingness to approach new things
4.Tolerance for frustration
5.Intensity of emotions (both positive and negative)
7.Predominant mood (positive or negative)
8.Predictability of rhythms
9.Sensitivity to external events (stimuli)
Recognizing that some of these categories overlap, Chess and Thomas consolidated the groupings down to three: the “Easy” baby, the “Difficult” baby, and the “Slow-to-Warm” baby. As more and more researchers began viewing babies through these lenses, it gradually became apparent that Chess and Thomas’s divisions were not giving “activity level” a prominent enough place. The result, as Alicia Lieberman reports in her excellent book The Emotional Life of the Toddler, was a gradual consensus that a fourth category needed to be added: the “Active” baby.
As we discuss each of these in turn, it’s helpful to keep in mind that the four represent certain average profiles, or prototypes. In reality, of course, every baby’s personality reflects a unique blending of the nine variables just listed. As we’ll discuss later, it’s also crucial to keep in mind that “biology is not destiny”—that although nature is the starting point for personality, nurture’s forces (including you) have a huge role to play thereafter.
The Four Most Common Flowers
With all this as prelude, just what are the four most common flowers in the greenhouse and the inborn temperaments they represent? They include:
1.Baby Sunflower (aka the “Easy” baby)
2.Baby Holly (aka the “Difficult” baby)
3.Baby Orchid (aka the “Slow-to-Warm” baby)
4.Baby Dandelion (aka the “Active” baby)
We have chosen the plant analogy for several reasons. First, and most obviously, the specific plants and flowers really do seem to share characteristics with the babies they represent and, therefore, provide an easy way to remember the distinctions. The second reason is perhaps even more important. Although different from one another in many ways, each adds great beauty to the world—even the misunderstood dandelion, whose vivid yellow head creates golden meadows in the summer sun. Just as is true of every child on this earth, each of these plants adds greatly to the variety that is the spice of life. In addition, to grow tall and fine, all four plants require a specific blend of sun, soil, and water—just as each child, no matter what her inborn temperament, needs her parents’ uniquely suited tender loving care.
Parents are gardeners—planting the seeds of faith, truth, and love that develop into the fairest flowers of character, virtue, and happiness in the lives of their children.
—J. Harold Gwynne, author
Here are the four flowers in more detail.
Baby Sunflower: The “Easy” Child. What distinguishes a sunflower? First and foremost, it’s easy to grow. Look in almost any nursery school’s child-tended flower garden and you’ll find sunflowers for that very reason. Even four-year-olds can’t kill them! Second, they face the sky as if eager for each new day’s gift of sunlight. Third, they have an inborn tendency to grow straight and tall, inspired from birth to show off their warm and happy petals to any and all who pass by.
The “Easy” baby is like that too. She wakes up happy, her rhythms are fairly predictable, she adapts to change without undue protest, she’s open to new experiences but not impulsively so, she’s moderate in both her positive and negative expressions of emotions, and she’s fun to be around. In short, she’s got the sunny, easygoing disposition that all parents assume their baby will have. Fortunately, according to Chess and Thomas, 40 percent of parents are right.
Baby Holly: The “Difficult” Child. There’s beauty in the holly bush’s dark-green foliage and brilliant berries, but first one has to deal with the overall prickliness of the leaves. With tiny thorns at each of their six corners, these leaves are ready to scratch and poke at the least invasion of their territory, causing even the most skilled gardener to don sturdy gloves to prune and care for them.
Like the holly bush, the “Difficult” baby is by nature “prickly” and a challenge to nurture well. Constituting 10 percent of Chess and Thomas’s sample, these children are easily upset, irregular in their habits, react irritably to changes in routine, are emotionally intense, and are difficult to console. And yet, under this prickly veneer, there truly is a loving and lovable child whose fine points (and we don’t mean thorns) just need to be cultivated with care—and the proverbial kid gloves. One of our goals in Baby Hearts is specifically to help parents with their own versions of Baby Holly learn how to garden successfully.
Baby Orchid: The “Slow-to-Warm” Child. Think about a gardener with a passion for orchids and one typically imagines someone with great patience, someone willing to take the time and trouble to coax this beautiful flower out of the shade into the sun, all the time being careful not to let it get overwhelmed lest it quickly wilt and wither. And its beauty is delicate rather than robust, with petals that are easily bruised and colors that are subtle rather than brilliant.
“Slow-to-Warm” children (15 percent of Chess and Thomas’s sample), like the orchid, require great patience on the part of their caregivers. As the name implies, these children need time to adjust to new things, to observe from the sidelines before joining the action. They aren’t intense in their responses unless pushed too hard and too fast, at which point they bruise easily and withdraw fast. Their overall caution extends to their preferred forms of play—quieter activities like book-reading and puzzles rather than the rough-and-tumble play attractive to many of their peers.
Parents often worry that their Baby Orchid is too cautious and would benefit from being forced to confront fears and anxieties. Such a strategy usually backfires, however, leaving the child even more cautious and parents even more frustrated than before. The better strategy, says new research, is for parents to overcome their bias against their child’s caution and simply accept that they must be patient, always on the lookout for ways to gently encourage their “Orchid” to show off his delicate beauty to the rest of the world. (See Chapters 7 and 8 for additional research on cautious children.)
Baby Dandelion: The “Active” Child. Yes, dandelions are beautiful! Their bright, happy heads reach exuberantly to the sun, and, later, their wispy, white seedpods blow wildly in the wind. That’s all wonderful, of course. But when talk turns to dandelions, the characteristic most likely to be mentioned is the fact that they are incredibly hard to control. First they’re here, then they’re there, and then in the blink of an eye they are everywhere!
The “Colicky” Baby
“Poor Lisa and Jimmy. The baby has colic.” So goes the sympathetic lament when we hear about a baby who never seems to stop crying. But what is colic? Is it a disease? Are the children crying because they are in pain? And is a colicky baby simply a Baby Holly (irritable baby) by another name?
The truth is that scientists do not yet understand what causes colic. They can, however, describe it fairly accurately. Colic begins when a baby is about two weeks old, peaks at two months, and generally is gone by four months. Such a simple description, however, doesn’t begin to do justice to the misery experienced by baby and parent alike between the two end points.
The major symptom of colic is prolonged crying (and we mean hours!) generally starting in late afternoon and continuing through the evening. And nothing seems to work reliably to get the crying to stop. The baby looks like he’s in pain—with clenched fists, back arched, distended abdomen, legs bent over the tummy, and grimacing. However, less than 5 percent of cases are likely to be related to diagnosable organic problems like cow’s milk, lactose, or fructose intolerance.
The best guess at the moment is that colic is a “regulatory” problem, meaning that the baby’s nervous system just can’t stop once it gets set on a negative path. Colicky babies actually don’t cry any more often than non-colicky babies. It’s just that when a colicky baby starts crying, it’s like a freight train out of control going down a hill. There’s no braking mechanism strong enough to halt the momentum once it gets going.
It’s also important to note that colic is not a temperamental quality. A colicky baby is not simply a Baby Holly. Here’s the difference: Although crying episodes are longer than normal in both cases, irritable babies actually cry more often than either non-colicky or colicky babies (with their cries triggered by greater sensitivity to minor events) and don’t outgrow these tendencies at four months as colicky babies do.
So what’s our advice to poor Lisa and Jimmy? Simply to grin and bear it knowing it won’t last forever—and, in the meantime, to find as many folks to help them deal with the baby as they can.
So it is with “Active” children. Especially when they are too young to have developed any self-control, their exuberance makes them very challenging to parent. They are simply busy, busy, busy! They run rather than walk, climb obstacles rather than go around, and never look before they leap. Parents of these children face many challenges, particularly from other people. Strangers often are disturbed by the active child’s energy and impulsiveness and come too quickly to the conclusion that it’s the parent’s fault. “If that were my child . . .” frequently begins the whispered criticism behind the parent’s back. The truth is that parents of Baby Dandelions deserve a special award for hanging in there—and more than an occasional pat on the back rather than criticism behind it.
When my kids become wild and unruly, I use a nice safe playpen. When they’re finished, I climb out.
—Erma Bombeck, humorist
Where Do Temperaments Come From?
We’ve described these four different temperaments as inborn. By this we mean that they are apparent very early in a child’s life—at least by four months of age, when the newborn’s rhythms start to settle down. Contributing to this description is growing evidence suggesting a genetic base. In other words, at least to some extent, temperament is inherited. How do we know? From looking at twins. Comparisons of identical twins—twins who have identical genes—with each other yield greater similarities in temperament than comparisons of fraternal twins—twins who share no more genes than normal siblings. In other words, if one of your identical twins is a Baby Dandelion, hold on to your horses; the other one is likely to be one too.
There is even speculation that the nervous systems of these various groups have different set points in the oldest part of the brain (the brain stem at the top of the spinal cord) where automatic, unthinking reactions to events are triggered. These ancient systems are designed to react efficiently to sudden danger—producing the famous fight-or-flight responses via higher heart rates, faster respiration, disrupted digestion, increased muscle tension, and heightened perceptual awareness. Such responses enabled our reptilian ancestors, such as the crocodile, to quickly slip into the water with lightning speed if alerted to danger.
What is meant by the term “set point”? According to Washington University psychiatrist Robert Cloninger and his colleagues, if our set point on this continuum is high, it takes a relatively greater danger to trigger a reaction, whereas if our set point is low, it might take only a whisper of a threat to cause us to pull back in fear. Most of us, thankfully, are somewhere in the middle. Some individuals, however, quite likely including Baby Dandelion and Baby Orchid, must learn to deal with set points more toward the extremes.
Is Biology Destiny?
We just spoke about Baby Dandelion and Baby Orchid learning “to deal with” their more extreme set points. This is a critical statement that can be restated this way: Biology is not destiny! The advantage that humans have over our reptilian ancestors is that we can, in fact, learn to control our behaviors, if not our fundamental emotions. With careful and consistent support from caregivers, both Baby Dandelion (the “Active” child) and Baby Orchid (the “Slow-to-Warm” child) can learn to control their reactions to the wonders and worries of the world around them. Because such control depends a great deal on development of the highest and most sophisticated layer of the brain, the cerebral cortex, the development of the necessary self-control takes time. But, in keeping with the theme of nature and nurture as a partnership, without appropriate guidance from loving and patient adults, it’s not likely to develop at all.
Nature Meets Nurture: Learning to Manage Emotions
All this talk of self-control brings us to a third topic we want to address before jumping into the individual issues that form the heart of Baby Hearts, something researchers these days refer to as emotional self-regulation. That’s a very formal term for the simple idea that healthy emotional development involves gradually learning to manage (control) one’s own emotions. It’s just not a good idea, no matter what your age, to be so overcome with fear that you hide yourself away, or even so overcome with joy that you forget to look both ways before you cross the street. Like the discussions of biological regulation and temperament, the subject of emotional self-regulation is so fundamental to emotional development in general that at least a brief description is appropriate in this introductory chapter. Also like the discussion of biological regulation and infant temperament, it provides a great example of how nature and nurture interact to nudge children along their developmental journey.
How to Help Your Baby? “Know Thyself”
How can you, as a parent, prepare yourself to provide the kind of support your own particular “flower” child needs? One way is to assess what researchers call the goodness of fit between the two of you. What this boils down to is an assessment of your own temperamental qualities to see if they mesh easily with those of your child. For example, if you are a high-energy person with the emotional intensity and love of novelty characteristic of the “Active” child, then you and Baby Dandelion are likely to have an easier time relating to each other than you and Baby Orchid. The reverse is true too. A quiet, contemplative parent is likely to find a highly active or difficult baby a major challenge. Unless a parent is aware of his or her biases, temperamental mismatches can be challenging to the parent-child relationship. In such cases negative interactions and frustrations are likely to start the ball rolling in the wrong direction from very early on, making course corrections increasingly difficult as time goes by.
Here are a few questions to get you started thinking about your own temperament:
uDo you enjoy meeting new people (like Baby Sunflower and Baby Dandelion), or does the prospect make you nervous (like Baby Orchid)?
uDo you prefer to explore new places (like Baby Sunflower and Baby Dandelion), or do you return to the tried and true (like Baby Orchid and Baby Holly)?
uDo you worry when your day isn’t planned in advance (like Baby Orchid and Baby Holly), or do you welcome the unexpected (like Baby Dandelion)?
uDo you find it easy to sit still (like Baby Orchid and Baby Sunflower), or do you prefer to be on the go (like Baby Dandelion)?
That’s the idea. And don’t forget to consider the possibility of temperamental mismatches between your baby and other important caregivers too.
Step 1: From Biological Regulation to Emotional Regulation
Let’s start with “nature,” a reasonable choice given that’s where every baby starts. As we described, newborn babies are even more helpless than they look. Although they seem to be compact little units with a life unto themselves, in reality they depend on being “plugged into” good caregiving (“nurture”) in order to keep their biological systems functioning properly. What’s more, this outside support (remember the gelatin mold?) gradually enables them to take over the job themselves as their brains and bodies mature—a push toward greater sophistication fueled by “nature” but shaped by “nurture.”
At the very beginning, the helplessness of the child is so all-pervasive— involving everything from learning when to suck, to controlling body temperature, to being able to keep breathing regularly—that the issue is really total biological regulation. However, as the early months proceed and these vital biological systems gradually settle in, babies’ job of learning to regulate themselves starts to narrow down to the devilishly sticky problem of specifically keeping emotions under some kind of control.
Why is emotional regulation important for babies? If emotions were only a psychological phenomenon, the task would be significant enough. But emotions, especially for young children still limping along without the help of sophisticated brain centers (see the next section), are very much physical issues too. For example, if left unchecked, the emotion of distress that leads to crying will eventually unwind a baby’s whole body—causing symptoms as minor as hiccups, to catastrophes as serious as disruptions in breathing. And, even more critically, prolonged and frequent experiencing of highly stressful situations—and here we mean more than the frequent crying of the colicky baby—can permanently alter the chemistry of the brain through the release of large amounts of stress hormones like cortisol, resulting in problematic emotional patterns that become more and more difficult to change. Emotionally adverse environments can affect the brain even to the point of producing very substandard physical development (psychosocial dwarfism) and health (failure-to-thrive syndrome). (For more detail on the topic of the impact of severe stress on the developing brain, see Liu et al., 1997, and Perry et al., 1995.)
In other words, helping babies keep their emotions—especially the negative ones—within reasonable bounds is one of the most important responsibilities of a parent. Soothing a crying baby may seem like a good idea just from a noise perspective, but it’s even more important for the baby!
Step 2: From Emotional Regulation to Emotional Self-Regulation
As babies grow more complex and begin moving around the world on their own, relying on their parents to monitor and modulate their emotions becomes less and less practical. Fortunately, “nature” has thought of this and has managed to build in to human babies the desire to gradually take over the task of managing their own emotions. It’s this passing of the buck back to the child that scientists refer to as emotional self-regulation.
What does emotional self-regulation actually look like? We will be talking a good deal about the various forms it takes as we introduce specific topics in later chapters, but here are a few examples.
uWhen feeling bombarded by stimulation, babies learn to turn their heads away and may even start playing with their fingers to calm themselves down.
uWhen feeling anxious or upset, babies learn to comfort themselves by sucking on their thumb.
uWhen toddlers are in unfamiliar settings or with unfamiliar people, they learn the value of holding on tight to a favorite toy.
uWhen toddlers become anxious about new events or people, they learn to check out their parents’ faces for cues about what’s happening.
uWhen toddlers are required to wait, they learn to distract themselves by doing other things.
uFinally, once children can talk about emotions, they learn that doing so helps diffuse the intensity of their feelings.
Clearly, there’s a lot for babies to learn. And who will your own baby need to learn all this from? There’s no doubt that her teachers will include grandparents, siblings, babysitters, and peers—but Mom and Dad are definitely the most influential teachers of them all. Don’t worry, though; we plan to provide lots of lesson plans throughout the rest of the book.
The Brains Behind It All
No introduction to the biology of emotions would be complete without at least some discussion of the role played behind the scenes by the greatest of all evolutionary inventions: the human brain. “Behind the scenes” is an apt description, because we are rarely (if ever) aware of how much is going on up there when we experience even a fleeting emotion such as mild surprise, let alone a complex emotion such as love.
The love we feel for our children is magical, not mechanical. It seems to well up from deep inside of us, melting our hearts, making us smile, sometimes even bringing tears to our eyes. And when our children return this love, the magic is doubled. Love does indeed make our hearts sing.
But how does all this happen? What exactly is going on when we cuddle with our children, body to body and heart to heart? It may surprise you to learn that a large part of what is going on is actually brain to brain. What’s more, it’s not just two brains in sync with each other; it’s more like three brains each, for a total of six.
The Triple-Decker Brain
Thomas Lewis, Fari Amini, and Richard Lannon, three psychiatry professors at the University of California, San Francisco, School of Medicine, provide a wonderful description of the relation between our multiple brains and our experiences of love in their fascinating book A General Theory of Love. In it they explain how human emotions are really the result of incredibly rapid and complex cross-talk among three separate “mini-brains,” each one a separate product of evolution. Presented in the order in which they appeared over the eons, these three include the reptilian brain (the brain stem), the limbic or “emotional” brain (deep within our skulls), and the cerebral cortex or “thinking” brain (the wrinkled sheet of tightly packed nerve cells that covers it all).
From the Trade Paperback edition.