Excerpt from The Female Brain
Leila was always happy to see her cousin Joseph when he joined her on the playground, but her joy never lasted long. Joseph grabbed the blocks she and her friends were using to make a house. He wanted to build a rocket, and build it by himself. His pals would wreck anything that Leila and her friends had created. The boys pushed the girls around, refused to take turns, and would ignore a girl's request to stop or give the toy back. By the end of the morning, Leila had retreated to the other end of the play area with the girls. They wanted to play house quietly together.
Common sense tells us that boys and girls behave differently. We see it every day at home, on the playground, and in classrooms. But what the culture hasn't told us is that the brain dictates these divergent behaviors. The impulses of children are so innate that they kick in even if we adults try to nudge them in another direction. One of my patients gave her three-and-a-half-year-old daughter many unisex toys, including a bright red fire truck instead of a doll. She walked into her daughter's room one afternoon to find her cuddling the truck in a baby blanket, rocking it back and forth saying, "Don't worry, little truckie, everything will be all right."
This isn't socialization. This little girl didn't cuddle her "truckie" because her environment molded her unisex brain. There is no unisex brain. She was born with a female brain, which came complete with its own impulses. Girls arrive already wired as girls, and boys arrive already wired as boys. Their brains are different by the time they're born, and their brains are what drive their impulses, values, and their very reality.
If chemicals acting on the brain can create different realities, what happens when two brains have different structures? There's no question that their realities will be different. Brain damage, strokes, prefrontal lobotomies, and head injuries can change what's important to a person. They can even change one's personality from aggressive to meek or from kind to grumpy.
But it's not as if we all start out with the same brain structure. Males' and females' brains are different by nature. Think about this. What if the communication center is bigger in one brain than in the other? What if the emotional memory center is bigger in one than in the other? What if one brain develops a greater ability to read cues in people than does the other? In this case, you would have a person whose reality dictated that communication, connection, emotional sensitivity, and responsiveness were the primary values. This person would prize these qualities above all others and be baffled by a person with a brain that didn't grasp the importance of these qualities. In essence, you would have someone with a female brain.
We, meaning doctors and scientists, used to think that gender was culturally created for humans but not for animals. When I was in medical school in the 1970s and '80s, it had already been discovered that male and female animal brains started developing differently in utero, suggesting that impulses such as mating and bearing and rearing young are hardwired into the animal brain. But we were taught that for humans sex differences mostly came from how one's parents raised one as a boy or a girl. Now we know that's not completely true, and if we go back to where it all started, the picture becomes abundantly clear.
In the span of just thirty-eight weeks, we would see this girl grow from a group of cells that could fit on the head of a pin to an infant who weighs an average of seven and a half pounds and possesses the machinery she needs to live outside her mother's body. But the majority of the brain development that determines her sex-specific circuits happens during the first eighteen weeks of pregnancy.
Until eight weeks old, every fetal brain looks female—female is nature's default gender setting. If you were to watch a female and a male brain developing via time-lapse photography, you would see their circuit diagrams being laid down according to the blueprint drafted by both genes and sex hormones. A huge testosterone surge beginning in the eighth week will turn this unisex brain male by killing off some cells in the communication centers and growing more cells in the sex and aggression centers. If the testosterone surge doesn't happen, the female brain continues to grow unperturbed. The fetal girl's brain cells sprout more connections in the communication centers and areas that process emotion. How does this fetal fork in the road affect us? For one thing, because of her larger communication center, this girl will grow up to be more talkative than her brother. In most social contexts, she will use many more forms of communication than he will. For another, it defines our innate biological destiny, coloring the lens through which each of us views and engages the world.
I loved that this baby girl wanted to look at me, and I wished my son had been so interested in my face. He was just the opposite. He wanted to look at everything else—mobiles, lights, and doorknobs— but not me. Making eye contact was at the bottom of his list of interesting things to do. I was taught in medical school that all babies are born with the need for mutual gazing because it is the key to developing the mother-infant bond, and for months I thought something was terribly wrong with my son. They didn't know back then about the many sex-specific differences in the brain. All babies were thought to be hardwired to gaze at faces, but it turns out that theories of the earliest stages of child development were female-biased. Girls, not boys, come out wired for mutual gazing. Girls do not experience the testosterone surge in utero that shrinks the centers for communication, observation, and processing of emotion, so their potential to develop skills in these areas are better at birth than boys'. Over the first three months of life, a baby girl's skills in eye contact and mutual facial gazing will increase by over 400 percent, whereas facial gazing skills in a boy during this time will not increase at all.
Anyone who has raised boys and girls or watched them grow up can see that they develop differently, especially that baby girls will connect emotionally in ways that baby boys don't. But psychoanalytic theory misrepresented this sex difference and made the assumption that greater facial gazing and the impulse to connect meant that girls were more "needy" of symbiosis with their mothers. The greater facial gazing doesn't indicate a need; it indicates an innate skill in observation. It's a skill that comes with a brain that is more mature at birth than a boy's brain and develops faster, by one to two years.
These brief interactions show Leila picking up cues from her parents' faces that her cousin Joseph likely wouldn't have looked for. A Stanford University study of twelve-month-old girls and boys showed the difference in desire and ability to observe. In this case, the child and mother were brought into a room, left alone together, and instructed not to touch a toy cow. The mother stood off to the side. Every move, glance, and utterance was recorded. Very few of the girls touched the forbidden object, even though their mothers never explicitly told them not to. The girls looked back at their mothers' faces many more times than did the boys, checking for signs of approval or disapproval. The boys, by contrast, moved around the room and rarely glanced at their mothers' faces. They frequently touched the forbidden toy cow, even though their mothers shouted, "No!" The one-year-old boys, driven by their testosterone-formed male brains, are compelled to investigate their environment, even those elements of it they are forbidden to touch.
Because their brains did not undergo a testosterone marination in utero and their communication and emotion centers were left intact, girls also arrive in the world better at reading faces and hearing emotional vocal tones. Just as bats can hear sounds that even cats and dogs cannot, girls can hear a broader range of emotional tones in the human voice than can boys. Even as an infant, all a girl needs to hear is a slight tightening in her mother's voice to know she should not be opening the drawer with the fancy wrapping paper in it. But you will have to restrain the boy physically to keep him from destroying next Christmas's packages. It's not that he's ignoring his mother. He physically cannot hear the same tone of warning.
Whether or not she is being listened to will tell a young girl if others take her seriously, which in turn goes to the growth of her sense of a successful self. Even though her language skills aren't developed, she understands more than she expresses, and she knows—before you do—if your mind has wandered for an instant. She can tell if the adult understands her. If the adult gets on the same wavelength, it actually creates her sense of self as being successful or important. If she doesn't connect, her sense is of an unsuccessful self. Charles in particular was surprised by how much focus it took to keep up the relationship with his daughter. But he saw that, when he listened attentively, she began to develop more confidence.
Another study showed that typical female newborns less than twenty-four hours old respond more to the distressed cries of another baby—and to the human face—than male newborns do. Girls as young as a year old are more responsive to the distress of other people, especially those who look sad or hurt. I was feeling a little down one day and mentioned it to Cara. Leila, at eighteen months, picked up on my tone of voice. She climbed onto my lap and played with my earrings, hair, and glasses. She held my face in her hands, looked right into my eyes, and I felt better immediately. That little girl knew exactly what she was doing.
At this stage Leila was in the hormone phase of what is called infantile puberty, a period that lasts only nine months for boys, but is twenty-four months long for girls. During this time, the ovaries begin producing huge amounts of estrogen—comparable to the level of an adult female—that marinate the little girl's brain. Scientists believe these infantile estrogen surges are needed to prompt the development of the ovaries and brain for reproductive purposes. But this high quantity of estrogen also stimulates the brain circuits that are rapidly being built. It spurs the growth and development of neurons, further enhancing the female brain circuits and centers for observation, communication, gut feelings, even tending and caring. Estrogen is priming these innate female brain circuits so that this little girl can master her skills in social nuance and promote her fertility. That's why she was able to be so emotionally adept while still in diapers.
It was in this stressful environment that Jennifer spent her infancy. Jennifer became suspicious of everyone and by age six started telling her older sister that their kind and beloved new stepfather was certainly cheating on their mother. Jennifer was sure of it and repeated her suspicions frequently. Lisa, finally went to their mom and asked if it were true. Their new stepfather was one of those men who just didn't have it in him to cheat, and Sheila knew it. She couldn't figure out why her younger daughter had become so anxiously fixated on the imagined infidelity of her new husband. But Jennifer's nervous system had imprinted the unsafe perceptual reality of her earliest years, so even good people seemed unreliable and threatening. The two sisters were raised by the same mother but under different circumstances, so one daughter's brain circuits had incorporated a nurturing, safe mom and the other's a fearful, anxious one.
Neurological incorporation begins during pregnancy. Maternal stress during pregnancy has effects on the emotional and stress hormone reactions, particularly in female offspring. These effects were measured in goat kids. The stressed female kids ended up startling more easily and being less calm and more anxious than the male kids after birth. Furthermore, female kids who were stressed in utero showed a great deal more emotional distress than female kids who weren't. So if you're a girl about to enter the womb, plan to be born to an unstressed mom who has a calm, loving partner and family to support her. And if you are a mom-to-be carrying a female fetus, take it easy so that your daughter will be able to relax.
If you're a girl, you've been programmed to make sure you keep social harmony. This is a matter of life and death to the brain, even if it's not so important in the twenty-first century. We could see this in the behavior of three-and-a-half-year-old twin girls. Every morning the sisters climbed on each other's dressers to get to the clothes hanging in their closets. One girl had a pink two-piece outfit, and the other had a green two-piece outfit. Their mother giggled every time she'd see them switch the tops—pink pants with a green top and green pants with a pink top. The twins did it without a fight. "Can I borrow your pink top? I'll give it back later, and you can have my green top" was how the dialogue went. This would not be a likely scenario if one of the twins were a boy. A brother would have grabbed the shirt he wanted, and the sister would have tried to reason with him, though she would have ended up in tears because his language skills simply wouldn't have been as advanced as hers.
Typical non-testosteronized, estrogen-ruled girls are very invested in preserving harmonious relationships. From their earliest days, they live most comfortably and happily in the realm of peaceful interpersonal connections. They prefer to avoid conflict because discord puts them at odds with their urge to stay connected, to gain approval and nurture. The twenty-four-month estrogen bath of girls' infantile puberty reinforces the impulse to make social bonds based on communication and compromise. It happened with Leila and her new friends on the playground. Within a few minutes of meeting they were suggesting games, working together, and creating a little community. They found a common ground that led to shared play and possible friendship. And remember Joseph's noisy entrance? That usually wrecked the day and the harmony sought out by the girls' brains.
Boys know how to employ this affiliative speech style, too, but research shows they typically don't use it. Instead, they'll generally use language to command others, get things done, brag, threaten, ignore a partner's suggestion, and override each other's attempts to speak. It was never long after Joseph's arrival on the playground that Leila ended up in tears. At this age boys won't hesitate to take action or grab something they desire. Joseph took Leila's toys whenever he wanted and usually destroyed whatever Leila and the other girls were making. Boys will do this to one another—they are not concerned about the risk of conflict. Competition is part of their makeup. And they routinely ignore comments or commands given by girls.
The testosterone-formed boy brain simply doesn't look for social connection in the same way a girl brain does. In fact, disorders that inhibit people from picking up on social nuance—called autism spectrum disorders and Asperger's syndrome—are eight times more common in boys. Scientists now believe that the typical male brain, with only one dose of X chromosome (there are two X's in a girl), gets flooded with testosterone during development and somehow becomes more easily socially handicapped. Extra testosterone and the genes in people with these disorders may be killing off some of the brain's circuits for emotional and social sensitivity.
I met my first playmate, Mikey, when I was two and a half and he was almost three. My family had moved into a house next door to Mikey's on Quincy Street in Kansas City, and our backyards adjoined each other. The sandbox was in our yard, and the swing set straddled the invisible line that divided our properties.
Our mothers, who soon became friends, saw the advantage of their two kids playing with each other while they chatted or took turns watching us. According to my mother, almost every time Mikey and I played in the sandbox, she would have to rescue me because he would inevitably grab my toy shovel or pail while refusing to let me touch his. I would wail in protest, and Mikey would scream and hurl sand at us as his mother tried to pry my toys away from him.
Both our moms tried again and again, because they liked spending time together. But nothing Mikey's mother did—scolding him, reasoning with him about the merits of sharing, taking away privileges, imposing various punishments—could persuade him to change his behavior. My mother eventually had to look beyond our block to find me other playmates, girls who sometimes grabbed but always could be reasoned with, who might use words to be hurtful but never raised a hand to hit or punch. I had begun to dread the daily battles with Mikey, and I was happy about the change.
Studies show girls take turns twenty times more often than boys, and their pretend play is usually about interactions in nurturing or caregiving relationships. Typical female brain development underlies this behavior. Girls' social agenda, expressed in play and determined by their brain development, is to form close, one-on-one relationships. Boys' play, by contrast, is usually not about relationships—it's about the game or toy itself as well as social rank, power, defense of territory, and physical strength.
In a 2005 study done in England, little boys and girls were compared at four years of age on the quality of their social relationships. This comparison included a popularity scale on which they were judged by how many other children wanted to play with them. Little girls won hands down. These same four-year-old children had had their testosterone levels measured in utero between ages twelve and eighteen weeks, while their brains were developing into a male or a female design. Those with the lowest testosterone exposure had the highest quality social relationships at four years old. They were the girls.
Studies of nonhuman female primates also provide clues that these sex differences are innate and require the right hormone-priming actions. When researchers block estrogen in young female primates during infantile puberty, the females don't develop their usual interest in infants. Moreover, when researchers inject female primate fetuses with testosterone, the injected females end up liking more rough-and-tumble play than do average females. This is also true in humans. Though we have not performed experiments to block estrogen in little girls, or injected testosterone into human fetuses, we can see this brain effect of testosterone at work in the rare enzyme deficiency called congenital adrenal hyperplasia (CAH), which occurs in about one out of every ten thousand infants.
Most of the time, a girl like Emma would be the one in ten who is simply a tomboy. In this case, Emma had CAH. Congenital adrenal hyperplasia causes fetuses to produce large amounts of testosterone, the sex and aggression hormone, from their adrenal glands starting at about eight weeks after conception—the very moment their brains begin to take shape into the male or female design. If we look at genetic females whose brains are exposed to surges of testosterone during this period, we see that these girls' behavior and presumably brain structures are more similar to those of males than to those of females. I say "presumably" because a toddler's brain isn't so easy to study. Can you imagine a two-year-old sitting still for a couple of hours in an MRI scanner without being sedated? But we can deduce a lot from behavior.
The study of congenital adrenal hyperplasia provides evidence that testosterone erodes the normally robust brain structures in girls. At one year old, CAH girls make measurably less eye contact than other girls the same age. As these testosterone-exposed girls get older, they are far more inclined to scuffling, roughhousing, and fantasy play about monsters or action heroes than to pretending to take care of their dolls or dressing up in princess costumes. They also do better than other girls on spatial tests, scoring similarly to boys, while they do less well on tests that tap verbal behavior, empathy, nurturing, and intimacy—traits that are typically female. The implications are that the male and female brains' wiring for social connection is significantly affected not just by genes but by the amount of testosterone that gets into the fetal brain. Lynn was relieved to have a scientific reason for some of her daughter's behaviors, since no one had taken the time to explain to her what happens in the CAH brain.
As parents, we naturally respond to our children's preferences. We will repeat, sometimes ad nauseam, the activity—Mommy's smile or the noisy whistle of a wooden train—that makes our little one giggle or grin. This repetition strengthens those neurons and circuits in the baby's brain that process and respond to whatever initially captivated her or his attention. The cycle continues, and children thus learn the customs of their gender. Since a little girl responds so well to faces, chances are Mom and Dad will make a lot of faces and she'll get even better at responding. She'll be engaged in an activity that reinforces her face-studying skill, and her brain will assign more and more neurons to that activity. Gender education and biology collaborate to make us who we are.
Adult expectations for girls' and boys' behavior play an important role in shaping brain circuits, and Wendy could have blown it for her daughter Samantha if she had given in to her own preconceptions about girls being more fragile and less adventurous than boys. Wendy told me that the first time Samantha climbed the jungle gym ladder to go down the slide by herself, she immediately looked back at Wendy for permission. If she had sensed disapproval or fear in her mother's facial expression, she probably would have stopped, climbed back down, and asked for her mother's help—as would 90 percent of little girls. When Wendy's son was that age, he would never have bothered checking for her reaction, not caring if Wendy disapproved of this step of independence. Samantha obviously felt ready to take this "big girl" leap, so Wendy managed to squelch her fear and give her daughter the approval she needed. She says she wishes she had had a camera to record the moment Samantha landed with a bump at the bottom. Her face lit up with a grin that expressed her pride and excitement, and she immediately ran over to her mother and gave her a big hug.
The brain's first organizing principle is clearly genes plus hormones, but we can't ignore the further sculpting of the brain that results from our interactions with other people and with our environment. A parent's or caregiver's tone of voice, touch, and words help organize an infant's brain and influence a child's version of reality.
Scientists still don't know exactly how much reshaping can occur to the brain nature gave us. It runs against the grain of intuition, but some studies show that male and female brains may have different genetic susceptibility to environmental influences. Either way, we know enough to see that the fundamentally misconceived nature versus nurture debate should be abandoned: child development is inextricably both.
"Okay, Daddy, now the dollies are going to lunch, so we have to change their clothes," Leila said to her father, Charles, who dutifully changed the outfits—into party clothes. "Daddy! No," Leila screamed. "Not the party dress! The lunch outfits! And they don't talk like that. You're supposed to say what I told you to say. Now say it right."
"All right, Leila. I'll do it. But tell me, why do you like to play dolls with me instead of with Mommy?"
"Because, Daddy, you play the way I tell you to." Charles was a little thrown by this response. And he and Cara were taken aback by Leila's chutzpah.
Not all is perfectly calm during the juvenile pause. Little girls don't usually exhibit aggression via rough-and-tumble play, wrestling, and punching the way little boys do. Girls may have, on average, better social skills, empathy, and emotional intelligence than boys—but don't be fooled. This doesn't mean that girls' brains aren't wired to use everything in their power to get what they want, and they can turn into little tyrants to accomplish their goals. What are those goals as dictated by the little girl's brain? To forge connection, to create community, and to organize and orchestrate a girl's world so that she's at the center of it. This is where the female brain's aggression plays out—it protects what's important to it, which is always, inevitably, relationship. But aggression can push others away, and that would undermine the goal of the female brain. So a girl walks a fine line between making sure she's at the center of her world of relationships and risking pushing those relationships away.
Remember the wardrobe sharing twins? When one asked the other to borrow the pink shirt in trade for the green, she set it up so that if the other sister said "no" she'd be considered mean. Instead of grabbing the shirt, she used her best skill set—language—to get what she wanted. She was counting on her sister's not wanting to be seen as selfish, and indeed her sister gave up the pink shirt. She got what she wanted without sacrificing the relationship. This is aggression in pink. Aggression means survival for both sexes, and both sexes have brain circuits for it. It's just more subtle in girls, perhaps reflecting their unique brain circuitry.
Cara and Charles didn't know what to do about Leila's bossiness. It didn't end with telling her father how to play dolls. She screamed when her friend Susie painted a yellow clown instead of a blue one as she had ordered, and heaven forbid if a conversation at the dinner table didn't include Leila. Her female brain was demanding that she be part of whatever communication or connection was taking place in her presence. Being left out was more than her girl circuits could bear. To her Stone Age brain—and face it, we're all still cave people inside— being left out could mean death. I explained this to Cara and Charles, and they decided to wait out this phase instead of trying to change Leila's behavior—within reason, of course.
I didn't want to tell Cara and Charles that what Leila was putting them through was nothing. Her hormones were steady, they were at a low point, and her reality was fairly stable. When the hormones turn back on and the juvenile pause comes to an end, Cara and Charles won't have just Leila's bossy brain to deal with. Her risk-taking brain will have the stops pulled out. It will drive her to ignore her parents, entice a mate, leave home, and make something different out of herself. Teen girl reality will explode, and every trait established in the female brain during girlhood—communication, social connection, desire for approval, reading faces for cues as to what to think or feel—will intensify. This is the time when a girl becomes most communicative with her girlfriends and forms tightly knit social groups in order to feel safe and protected. But with this new estrogen-driven reality, aggression also plays a big role. The teen girl brain will make her feel powerful, always right, and blind to consequences. Without that drive, she'll never be able to grow up, but getting through it, especially for the teen girl, isn't easy. As she begins to experience her full "girl power," which includes premenstrual syndrome, sexual competition, and controlling girl groups, her brain states can often make her reality, well, a little hellish.
Dr. Oz reports on the differences between men and women.
Copyright © 2006 by Louann Brizendine
From the book The Female Brain by Louann Brizendine, published by Broadway Books, a division of Random House, Inc. Reprinted with permission.