The Female Brain (5 page)

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Because of her ability to observe and feel emotional cues, a girl actually incorporates her mother’s nervous system into her own. Sheila came to me wanting some help dealing with her kids. With her first husband she had two daughters, Lisa and Jennifer. When Lisa was born, Sheila was still happy and content in her first marriage. She was an able and highly nurturing mother. By the time Jennifer was born, eighteen months later, circumstances had changed considerably. Her husband had become a flagrant philanderer. Sheila was being harassed by the husband of the woman he was having an affair with. And things got worse. Sheila’s unfaithful husband had a powerful and rich father, who threatened to have the children kidnapped if she tried to leave the state to be with her own family for support.

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.

The “nervous system environment” a girl absorbs during her first two years becomes a view of reality that will affect her for the rest of her life. Studies in mammals now show that this early stress versus calm incorporation—called epigenetic imprinting—can be passed down through several generations. Research in mammals by Michael Meaney’s group has shown that female offspring are highly affected by how calm and nurturing their mothers are. This relation has also been shown in human females and nonhuman primates. Stressed mothers naturally become less nurturing, and their baby girls incorporate stressed nervous systems that change the girls’ perception of reality. This isn’t about what’s learned cognitively—it’s about what is absorbed by the cellular microcircuitry at the neurological level. This may explain why some sisters can have amazingly different outlooks. It appears that boys may not incorporate so much of their
mothers’
nervous system.

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.

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So why is a girl born with such a highly tuned machine for reading faces, hearing emotional tones in voices, and responding to unspoken cues in others? Think about it. A machine like that is built for connection. That’s the main job of the girl brain, and that’s what it drives a female to do from birth. This is the result of millennia of genetic and evolutionary hardwiring that once had—and probably still has—real consequences for survival. If you can read faces and voices, you can tell what an infant needs. You can predict what a bigger, more aggressive male is going to do. And since you’re smaller, you probably need to band with other females to fend off attacks from a ticked off caveman—or cavemen.

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.

It is the brain that sets up the speech differences—the genderlects—of small children, which Deborah Tannen has pointed out. She noted that in studies of the speech of two-to five-year-olds, girls usually make collaborative proposals by starting their sentences with “let’s”—as in “Let’s play house.” Girls, in fact, typically use language to get consensus, influencing others without telling them directly what to do. When Leila hit the playground, she said “Shopping” as a suggestion for how she and her companions might play together. She looked around and waited for a response instead of forging ahead. The same thing happened when another little girl said “Dolly.” As has been observed in studies, girls participate jointly in decision making, with minimal stress, conflict, or displays of status. They often express agreement with a partner’s suggestions. And when they have ideas of their own, they’ll put them in the form of questions, such as “I’ll be the teacher, okay?” Their genes and hormones have created a reality in their brains that tells them social connection is at the core of their being.

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.

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By age two and a half, infantile puberty ends and a girl enters the calmer pastures of the juvenile pause. The estrogen stream coming from the ovaries has been temporarily stopped; how, we don’t yet know. But we do know that the levels of estrogen and testosterone become very low during the childhood years in both boys and girls—although girls still have six to eight times more estrogen than boys. When women talk about “the girl they left behind,” this is the stage they are usually referring to. This is the quiet period before the full-volume rock ’n’ roll of puberty. It’s the time when a girl is devoted to her best friend, when she doesn’t usually enjoy playing with boys. Research shows that this is true for girls between the ages of two and six in every culture that’s been studied.

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.

The cause for this preference for same-sex playmates remains largely unknown, but scientists speculate that basic brain differences may be one reason. Girls’ social, verbal, and relationship skills develop years earlier than boys’. That their styles of communication and interaction are completely different is probably a result of these brain variations. Typical boys enjoy wrestling, mock fighting, and rough play with cars, trucks, swords, guns, and noisy—preferably explosive—toys. They also tend to threaten others and get into more conflict than girls beginning as early as age two, and they’re less likely to share toys and take turns than are female children. Typical girls, by contrast, don’t like rough play—if they get into too many tussles, they’ll just stop playing. According to Eleanor Maccoby, when girls get pushed around too much by boys their age—who are just having fun—they will retreat from the space and find another game to play, preferably one that doesn’t involve any high-spirited boys.

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.

Emma did not want to play with dolls. She liked trucks and jungle gyms and sets to build things with. If you asked her at two and a half years old if she was a boy or a girl, she’d tell you she was a boy and she’d punch you. She’d get a running start, and “the little linebacker,” as her mother called her, would knock over anyone who came into the room. She played catch with stuffed animals, though she threw them so hard it was tough to hang on to them. She was rough, and the girls at preschool didn’t want to play with her. She was also a little behind the other girls in language development. Yet Emma liked dresses and loved when her aunt styled her hair. Her mother, Lynn, an avid cyclist, athlete, and science teacher, wondered, when she brought Emma in to see me, if her being a jock had influenced her daughter’s behavior. 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.