About the Book
Did you know that every brain begins as a female brain and that it only becomes male eight weeks after conception? This is when excess testosterone shrinks the communication centre, reduces the hearing cortex and makes the part of the brain that processes sex twice as large.
In this groundbreaking book, Dr Louann Brizendine reveals how the uniquely flexible structure of the female brain determines not only how women think and what they value, but how they communicate and whom they will love. Based on decades of research, and complete with fascinating facts and case studies, this accessible guide also provides the neurological explanations behind why …
A woman remembers fights that a man insists never happened.
Thoughts about sex enter a woman’s brain perhaps once a day, but may enter a man’s brain about once every minute.
A woman over fifty is more likely to initiate divorce than a man.
A woman tends to know what people are feeling, while a man can’t seem to spot an emotion unless someone cries or threatens bodily harm.
With this accessible, fun guide, women will discover that they have a lean, mean communicating machine at their disposal – and men will find that they finally have a key to understanding their relations with women.
CONTENTS
Cover
About the Book
Title Page
Dedication
Acknowledgments
Introduction:
What Makes Us Women
ONE:
The Birth of the Female Brain
TWO:
Teen Girl Brain
THREE:
Love and Trust
FOUR:
Sex: The Brain Below the Belt
FIVE:
The Mommy Brain
SIX:
Emotion: The Feeling Brain
SEVEN:
The Mature Female Brain
Epilogue:
The Future of the Female Brain
Appendix One:
The Female Brain and Hormone Therapy
Appendix Two:
The Female Brain and Postpartum Depression
Appendix Three:
The Female Brain and Sexual Orientation
Notes
References
Index
Copyright
For my husband,
Samuel Barondes,
My son,
John Whitney Brizendine,
And in loving memory of
Louise Ann Brizendine
ACKNOWLEDGMENTS
THIS BOOK HAD its beginnings during my educational years at the University of California, Berkeley; Yale; Harvard; and University College, London, so I would like to thank the teachers and fellow students who most influenced my thinking during those years: Frank Beach, Mina Bissel, Henry Black, Bill Bynum, Dennis Charney, Marion Diamond, Marilyn Farquar, Carol Gilligan, Paul Greengard, Tom Guteil, Les Havens, Florence Haseltine, Marjorie Hayes, Peter Hornick, Stanley Jackson, Valerie Jacoby, Kathleen Kells, Kathy Kelly, Adrienne Larkin, Howard Levitin, Mel Lewis, Charlotte McKenzie, David Mann, Daniel Mazia, William Meissner, Jonathan Muller, Fred Naftolin, George Palade, Roy Porter, Sherry Ryan, Carl Salzman, Leon Shapiro, Rick Shelton, Gunter Stent, Frank Thomas, Janet Thompson, George Vaillant, Roger Wallace, Clyde Willson, Fred Wilt, and Richard Wollheim.
During my years on the faculty at Harvard and the University of California, San Francisco, my thinking has been influenced by Bruce Ames, Cori Bargmann, Regina Casper, Francis Crick, Mary Dallman, Herb Goldings, Deborah Grady, Joel Kramer, Fernand Labrie, Jeanne Leventhal, Sindy Mellon, Michael Merzenich, Joseph Morales, Eugene Roberts, Laurel Samuels, Carla Shatz, Stephen Stahl, Elaine Storm, Marc Tessier-Lavigne, Rebecca Turner, Victor Viau, Owen Wolkowitz, and Chuck Yingling.
My colleagues, staff, residents, medical students, and patients in the Women’s and Teen Girls’ Mood and Hormone Clinic have contributed in many ways to this work: Denise Albert, Raya Almufti, Amy Berlin, Cathy Christensen, Karen Cliffe, Allison Doupe, Judy Eastwood, Louise Forrest, Adrienne Fratini, Lyn Gracie, Marcie Hall-Mennes, Steve Hamilton, Caitlin Hasser, Dannah Hirsch, Susie Hobbins, Fatima Imara, Lori Lavinthal, Karen Leo, Shana Levy, Katherine Malouh, Faina Nosolovo, Sarah Prolifet, Jeanne St. Pierre, Veronica Saleh, Sharon Smart, Alla Spivak, Elizabeth Springer, Claire Wilcox, and Emily Wood.
I also thank my other colleagues, students, and staff at Langley Porter Psychiatric Institute and UCSF whose contributions I have appreciated: Alison Adcock, Regina Armas, Jim Asp, Renee Binder, Kathryn Bishop, Mike Bishop, Alla Borik, Carol Brodsky, Marie Caffey, Lin Cerles, Robin Cooper, Haile Debas, Andrea DiRocchi, Glenn Elliott, Stu Eisendrath, Leon Epstein, Laura Esserman, Ellen Haller, Dixie Horning, Marc Jacobs, Nancy Kaltreider, David Kessler, Michael Kirsch, Laurel Koepernick, Rick Lannon, Bev Lehr, Descartes Li, Jonathan Lichtmacher, Elaine Lonnergan, Alan Louie, Theresa McGinness, Robert Malenka, Charlie Marmar, Miriam Martinez, Craig Nelson, Kim Norman, Chad Peterson, Anne Poirier, Astrid Prackatzch, Victor Reus, John Rubenstein, Bryna Segal, Lynn Shroeder, John Sikorski, Susan Smiga, Anna Spielvogel, David Taylor, Larry Tecott, Renee Valdez, Craig Van Dyke, Mark Van Zastrow, Susan Voglmaier, John Young, and Leonard Zegans.
I am very grateful to those who have read and critiqued drafts of this book: Carolyn Balkenhol, Marcia Barinaga, Elizabeth Barondes, Diana Brizendine, Sue Carter, Sarah Cheyette, Diane Cirrincione, Theresa Crivello, Jennifer Cummings, Pat Dodson, Janet Durant, Jay Giedd, Mel Grumbach, Dannah Hirsch, Sarah Hrdy, Cynthia Kenyon, Adrienne Larkin, Jude Lange, Jim Leckman, Louisa Llanes, Rachel Llanes, Eleanor Maccoby, Judith Martin, Diane Middlebrook, Nancy Milliken, Cathy Olney, Linda Pastan, Liz Perle, Lisa Queen, Rachel Rokicki, Dana Slatkin, Millicent Tomkins, and Myrna Weissman.
The work presented here has particularly benefited from the research, writings, and advice of Marty Altemus, Arthur Aron, Simon Baron-Cohen, Jill Becker, Andreas Bartels, Lucy Brown, David Buss, Larry Cahill, Anne Campbell, Sue Carter, Lee Cohen, Susan Davis, Helen Fisher, Jay Giedd, Jill Goldstein, Mel Grumbach, Andy Guay, Melissa Hines, Nancy Hopkins, Sarah Hrdy, Tom Insel, Bob Jaffe, Martha McClintock, Erin McClure, Eleanor Maccoby, Bruce McEwen, Michael Meaney, Barbara Parry, Don Pfaff, Cathy Roca, David Rubinow, Robert Sapolsky, Peter Schmidt, Nirao Shah, Barbara Sherwin, Elizabeth Spelke, Shelley Taylor, Kristin Uvnäs-Moberg, Sandra Witelson, Sam Yen, Kimberly Yonkers, and Elizabeth Young.
I also thank supporters with whom I have had lively and influential conversations over the past few years about the female brain: Bruce Ames, Giovanna Ames, Elizabeth Barondes, Jessica Barondes, Lynne Krilich Benioff, Marc Benioff, ReVeta Bowers, Larry Ellison, Melanie Craft Ellison, Cathy Fink, Steve Fink, Milton Friedman, Hope Frye, Donna Furth, Alan Goldberg, Andy Grove, Eva Grove, Anne Hoops, Jerry Jampolsky, Laurene Powell Jobs, Tom Kornberg, Josh Lederberg, Marguerite Lederberg, Deborah Leff, Sharon Agopian Melodia, Shannon O’Rourke, Judy Rapoport, Jeanne Robertson, Sandy Robertson, Joan Ryan, Dagmar Searle, John Searle, Garen Staglin, Shari Staglin, Millicent Tomkins, Jim Watson, Meredith White, Barbara Willenborg, Marilyn Yalom, and Jody Kornberg Yeary.
I would also like to thank the individuals and private foundations that have supported my work: Lynne and Marc Benioff, the Lawrence Ellison Medical Foundation, National Center for Excellence in Women’s Health at UCSF, the Osher Foundation, the Salesforce.com Foundation, the Staglin Family Music Festival for Mental Health, the Stanley Foundation, and the UCSF Department of Psychiatry.
This book was initially developed through the skill and talent of Susan Wels, who helped me write the first draft and organize vast amounts of material. I owe her the greatest debt of gratitude.
I am very thankful to Liz Perle, who first persuaded me to write this book, and to the others who believed in it and worked hard to make it happen: Susan Brown, Rachel Lehmann-Haupt, Deborah Chiel, Marc Haeringer, and Rachel Rokicki. My agent, Lisa Queen of Queen Literary, has been a terrific supporter and has made many brilliant suggestions throughout this process.
I am especially grateful to Amy Hertz, vice president and publisher of Morgan Road Books, who had a vision for this project from the beginning and kept demanding excellence and crafting revisions to create a narrative in which the science comes alive.
I also want to thank my son, Whitney, who tolerated this long and demanding project with grace and made important contributions to the teen chapter.
Most of all I thank my husband and soul mate, Sam Barondes, for his wisdom, endless patience, editorial advice, scientific insight, love, and support.
THE FEMALE BRAIN
THE CAST OF
NEURO-HORMONE CHARACTERS
(in other words, how hormones affect a woman’s brain)
THE ONES YOUR doctor knows about
ESTROGEN—the queen: powerful, in control, all-consuming; sometimes all business, sometimes an aggressive seductress; friend of dopamine, serotonin, oxytocin, acetylcholine, and norepinephrine (the feel-good brain chemicals).
PROGESTERONE—in the background but a powerful sister to estrogen; intermittently appears and sometimes is a storm cloud reversing the effects of estrogen; other times is a mellowing agent; mother of allopregnenolone (the brain’s Valium, i.e., chill pill).
TESTOSTERONE—fast, assertive, focused, all-consuming, masculine; forceful seducer; aggressive, unfeeling; has no time for cuddling.
THE ONES YOUR doctor may not know about that also affect a woman’s brain
OXYTOCIN—fluffy, purring kitty; cuddly, nurturing, earth mother; the good witch Glinda in The Wizard of Oz; finds pleasure in helping and serving; sister to vasopressin (the male socializing hormone), sister to estrogen, friend of dopamine (another feel-good brain chemical).
CORTISOL—frizzled, frazzled, stressed out; highly sensitive, physically and emotionally.
VASOPRESSIN—secretive, in the background, subtle aggressive male energies; brother to testosterone, brother to oxytocin (makes you want to connect in an active, male way, as does oxytocin).
DHEA—reservoir of all the hormones; omnipresent, pervasive, sustaining mist of life; energizing; father and mother of testosterone and estrogen, nicknamed “the mother hormone,” the Zeus and Hera of hormones; robustly present in youth, wanes to nothing in old age.
ANDROSTENEDIONE—the mother of testosterone in the ovaries; supply of sassiness; high-spirited in youth, wanes at menopause, dies with the ovaries.
ALLOPREGNENOLONE—the luxurious, soothing, mellowing daughter of progesterone; without her, we are crabby; she is sedating, calming, easing; neutralizes any stress, but as soon as she leaves, all is irritable withdrawal; her sudden departure is the central story of PMS, the three or four days before a woman’s period starts.
PHASES OF
A FEMALE’S LIFE
HORMONES CAN DETERMINE what the brain is interested in doing. They help guide nurturing, social, sexual, and aggressive behaviors. They can affect being talkative, being flirtatious, giving or attending parties, writing thank-you notes, planning children’s play dates, cuddling, grooming, worrying about hurting the feelings of others, being competitive, masturbating and initiating sex.
INTRODUCTION
What Makes Us Women
MORE THAN 99 percent of male and female genetic coding is exactly the same. Out of the thirty thousand genes in the human genome, the less than one percent variation between the sexes is small. But that percentage difference influences every single cell in our bodies—from the nerves that register pleasure and pain to the neurons that transmit perception, thoughts, feelings, and emotions.1
To the observing eye, the brains of females and males are not the same. Male brains are larger by about 9 percent, even after correcting for body size. In the nineteenth century, scientists took this to mean that women had less mental capacity than men. Women and men, however, have the same number of brain cells. The cells are just packed more densely in women—cinched corsetlike into a smaller skull.
For much of the twentieth century, most scientists assumed that women were essentially small men, neurologically and in every other sense except for their reproductive functions. That assumption has been at the heart of enduring misunderstandings about female psychology and physiology. When you look a little deeper into the brain differences, they reveal what makes women women and men men.
Until the 1990s, researchers paid little attention to female physiology, neuroanatomy, or psychology separate from that of men. I saw this oversight firsthand during my undergraduate years in neurobiology at Berkeley in the 1970s, during my medical education at Yale, and during my training in psychiatry at the Massachusetts Mental Health Center at Harvard Medical School. While enrolled at each of these institutions, I learned little or nothing about female biological or neurological difference outside of pregnancy. When a professor presented a study about animal behavior one day at Yale, I raised my hand and asked what the research findings were for females in that study. The male professor dismissed my question, stating, “We never use females in these studies—their menstrual cycles would just mess up the data.”
The little research that was available, however, suggested that the brain differences, though subtle, were profound. As a resident in psychiatry, I became fascinated by the fact that there was a two-to-one ratio of depression in women compared with men.2 No one was offering any clear reasons for this discrepancy. Because I had gone to college at the peak of the feminist movement, my personal explanations ran toward the political and the psychological. I took the typical 1970s stance that the patriarchy of Western culture must have been the culprit. It must have kept women down and made them less functional than men. But that explanation alone didn’t seem to fit: new studies were uncovering the same depression ratio worldwide. I started to think that something bigger, more basic and biological, was going on.
One day it struck me that male versus female depression rates didn’t start to diverge until females turned twelve or thirteen— the age girls began menstruating. It appeared that the chemical changes at puberty did something in the brain to trigger more depression in women. Few scientists at the time were researching this link, and most psychiatrists, like me, had been trained in traditional psychoanalytic theory, which examined childhood experience but never considered that specific female brain chemistry might be involved. When I started taking a woman’s hormonal state into account as I evaluated her psychiatrically, I discovered the massive neurological effects her hormones have during different stages of life in shaping her desires, her values, and the very way she perceives reality.
My first epiphany about the different realities created by sex hormones came when I started treating women with what I call extreme premenstrual brain syndrome.3 In all menstruating women, the female brain changes a little every day. Some parts of the brain change up to 25 percent every month.4 Things get rocky at times, but for most women, the changes are manageable. Some of my patients, though, came to me feeling so jerked around by their hormones on some days that they couldn’t work or speak to anyone because they’d either burst into tears or bite someone’s head off.5 Most weeks of the month they were engaged, intelligent, productive, and optimistic, but a mere shift in the hormonal flood to their brains on certain days left them feeling that the future looked bleak, and that they hated themselves and their lives. These thoughts felt real and solid, and these women acted on them as though they were reality and would last forever—even though they arose solely from hormonal shifts in their brains. As soon as the tides changed, they were back to their best selves. This extreme form of PMS, which is present in only a few percent of women, introduced me to how the female brain’s reality can turn on a dime.
If a woman’s reality could change radically from week to week, the same would have to be true of the massive hormonal changes that occur throughout a woman’s life. I wanted the chance to find out more about these possibilities on a broader scale, and so, in 1994, I founded the Women’s Mood and Hormone Clinic in the Department of Psychiatry at the University of California, San Francisco. It was one of the first clinics in the country dedicated to looking at women’s brain states, and how neurochemistry and hormones affect their moods.
What we’ve found is that the female brain is so deeply affected by hormones that their influence can be said to create a woman’s reality. They can shape a woman’s values and desires, and tell her, day to day, what’s important. Their presence is felt at every stage of life, right from birth. Each hormone state—girlhood, the adolescent years, the dating years, motherhood, and menopause—acts as fertilizer for different neurological connections that are responsible for new thoughts, emotions, and interests. Because of the fluctuations that begin as early as three months old and last until after menopause, a woman’s neurological reality is not as constant as a man’s. His is like a mountain that is worn away imperceptibly over the millennia by glaciers, weather, and the deep tectonic movements of the earth. Hers is more like the weather itself—constantly changing and hard to predict.
NEW BRAIN SCIENCE has rapidly transformed our view of basic neurological differences between men and women. Earlier scientists could investigate these differences only by studying the brains of cadavers or the symptoms of individuals with brain damage. But thanks to advances in genetics and noninvasive brain-imaging technology, there’s been a complete revolution in neuroscientific research and theory. New tools, such as positron-emission tomography (PET) and functional magnetic resonance imaging (fMRI) scans, now allow us to see inside the human brain in real time, while it’s solving problems, producing words, retrieving memories, noticing facial expressions, establishing trust, falling in love, listening to babies cry, and feeling depression, fear, and anxiety.
As a result, scientists have documented an astonishing array of structural, chemical, genetic, hormonal, and functional brain differences between women and men. We’ve learned that men and women have different brain sensitivities to stress and conflict.6 They use different brain areas and circuits to solve problems, process language, experience and store the same strong emotion. Women may remember the smallest details of their first dates, and their biggest fights, while their husbands barely remember that these things happened. Brain structure and chemistry have everything to do with why this is so.
The female and male brains process stimuli, hear, see, “sense,” and gauge what others are feeling in different ways. Our distinct female and male brain operating systems are mostly compatible and adept, but they perform and accomplish the same goals and tasks using different circuits. In a German study, researchers conducted brain scans of men and women while they mentally rotated abstract, three-dimensional shapes. There were no performance differences between the men and women, but there were significant, sex-specific differences in the brain circuits they activated to complete the task.7 Women triggered brain pathways linked to visual identification and spent more time than men picturing the objects in their minds. This fact merely meant that it took women longer to get to the same answer. It also showed that females perform all the cognitive functions males perform—they just do so by using different brain circuits.8
Under a microscope or an fMRI scan, the differences between male and female brains are revealed to be complex and widespread. In the brain centers for language and hearing, for example, women have 11 percent more neurons than men.9 The principal hub of both emotion and memory formation—the hippocampus—is also larger in the female brain, as is the brain circuitry for language and observing emotions in others.10 This means that women are, on average, better at expressing emotions and remembering the details of emotional events. Men, by contrast, have two and a half times the brain space devoted to sexual drive as well as larger brain centers for action and aggression. Sexual thoughts float through a man’s brain many times each day on average, and through a woman’s only once a day. Perhaps three to four times on her hottest days.11
These basic structural variances could explain perceptive differences. One study scanned the brains of men and women observing a neutral scene of a man and a woman having a conversation. The male brains’ sexual areas immediately sparked—they saw it as a potential sexual rendezvous. The female brains did not have any activation in the sexual areas. The female brains saw the situation as just two people talking.12
Men also have larger processors in the core of the most primitive area of the brain, which registers fear and triggers aggression—the amygdala.13 This is why some men can go from zero to a fistfight in a matter of seconds, while many women will try anything to defuse conflict.14 But the psychological stress of conflict registers more deeply in areas of the female brain. Though we live in the modern urban world, we inhabit bodies built to live in the wild, and each female brain still carries within it the ancient circuitry of her strongest foremothers, engineered for genetic success but retaining the deeply wired instincts developed in response to stress experienced in the ancient wild.15 Our stress responses were designed to react to physical danger and life-threatening situations. Now couple that stress response with the modern challenges of juggling the demands of home, kids, and work without enough support, and we have a situation in which women can perceive a few unpaid bills as a stress that appears to be life-threatening. This response impels the female brain to react as though the family were endangered by impending catastrophe.16 The male brain will not have the same perception unless the threat is of immediate, physical danger. These basic, structural variances in their brains lay the groundwork for many everyday differences in the behavior and life experiences of men and women.
Biological instincts are the keys to understanding how we are wired, and they are the keys to our success today. If you’re aware of the fact that a biological brain state is guiding your impulses, you can choose not to act or to act differently than you might feel compelled. But first we have to learn to recognize how the female brain is genetically structured and shaped by evolution, biology, and culture. Without that recognition, biology becomes destiny and we will be helpless in the face of it.
Biology does represent the foundation of our personalities and behavioral tendencies. But if in the name of free will—and political correctness—we try to deny the influence of biology on the brain, we begin fighting our own nature. If we acknowledge that our biology is influenced by other factors, including our sex hormones and their flux, we can prevent it from creating a fixed reality by which we are ruled. The brain is nothing if not a talented learning machine. Nothing is completely fixed. Biology powerfully affects but does not lock in our reality. We can alter that reality and use our intelligence and determination both to celebrate and, when necessary, to change the effects of sex hormones on brain structure, behavior, reality, creativity—and destiny.
MALES AND FEMALES have the same average level of intelligence, but the female brain’s reality has often been misinterpreted to mean that it is less capable in certain areas, such as math and science.17 In January 2005, Lawrence Summers, then president of Harvard University, shocked and enraged his colleagues—and the public—when in a speech to the National Bureau of Economic Research he said: “It does appear that on many, many different human attributes—mathematical ability, scientific ability—there is relatively clear evidence that whatever the difference in means—which can be debated—there is a difference in the standard deviation, and variability of a male and a female population. And that is true with respect to attributes that are and are not plausibly, culturally determined.”18 The public surmised that he was saying that women are therefore innately less suited than men to be top-level mathematicians and scientists.
Judging from current research, Summers was and wasn’t right. We now know that when girls and boys first hit their teen years, the difference in their mathematical and scientific capacity is nonexistent.19 That’s where he was wrong. But as estrogen floods the female brain, females start to focus intensely on their emotions and on communication—talking on the phone and connecting with their girlfriends at the mall. At the same time, as testosterone takes over the male brain, boys grow less communicative and become obsessed about scoring—in games, and in the backseat of a car. At the point when boys and girls begin deciding the trajectories of their careers, girls start to lose interest in pursuits that require more solitary work and fewer interactions with others, while boys can easily retreat alone to their rooms for hours of computer time.20
From an early age, my patient Gina had an extraordinary aptitude for math. She became an engineer but at twenty-eight years old was struggling with her desire to be in a more people-oriented career and one that would allow her to have a family life, too. She relished the mental puzzles involved in solving engineering problems, but she missed daily contact with people, so she was considering a career change. This is not an unusual conflict for women. My friend the scientist Cori Bargmann told me that many of her smartest girlfriends dropped science to go into fields that they felt were more social. These are value decisions that are actually shaped by hormonal effects on the female brain compelling connection and communication. The fact that fewer women end up in science has nothing to do with female brain deficiencies in math and science. That’s where Summers really went wrong. He was right that there’s a dearth of women in top-level science and engineering positions but dead wrong in implying that women do not end up in these careers because of lack of aptitude.21
The female brain has tremendous unique aptitudes— outstanding verbal agility, the ability to connect deeply in friendship, a nearly psychic capacity to read faces and tone of voice for emotions and states of mind, and the ability to defuse conflict.22 All of this is hardwired into the brains of women. These are the talents women are born with that many men, frankly, are not. Men are born with other talents, shaped by their own hormonal reality. But that’s the subject of another book.
FOR TWENTY YEARS, I’ve eagerly awaited progress in knowledge of the female brain and behavior as I have been treating my women patients. It was only at the turn of the millennium that exciting research started to emerge revealing how the structure, function, and chemistry of a woman’s brain affect her mood, thought processes, energy, sexual drives, behavior, and well-being. This book is a user’s guide to new research about the female brain and the neurobehavioral systems that make us women. It draws on my twenty years of clinical experience as a neuropsychiatrist. It culls from spectacular advances in our understanding of genetics, molecular neuroscience, fetal and pediatric endocrinology, and neurohormonal development. It presents samplings from neuropsychology, cognitive neuroscience, child development, brain imaging, and psychoneuroendocrinology. It explores primatology, animal studies, and infant observation, seeking insights into how particular behaviors are programmed into the female brain by a combination of nature and nurture.
Because of this progress, we are entering an era, finally, when women can begin to understand their distinct biology and how it affects their lives. My personal mission has been to educate interested physicians, psychologists, teachers, nurses, pharmacists, and their trainees to benefit the women and teen girls they serve. I have taken every opportunity to educate women and girls directly about their unique brain-body-behavior system and help them to be their best at every age. It is my hope that this book will benefit many more women and girls than I can personally reach in the clinic. It is my hope that the female brain will be seen and understood as the finely tuned and talented instrument that it actually is.
ONE
The Birth of the Female Brain
LEILA WAS A busy little bee, flitting around the playground, connecting with the other children whether or not she knew them. On the verge of speaking in two- and three-word phrases, she mostly used her contagious smile and emphatic nods of her head to communicate, and communicate she did. So did the other little girls. “Dolly,” said one. “Shopping,” said another. There was a pint-size community forming, abuzz with chatter, games, and imaginary families.
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.
The brain shapes the way we see, hear, smell, and taste. Nerves run from our sense organs directly to the brain, and the brain does all the interpreting. A good conk on the head in the right place can mean that you won’t be able to smell or taste. But the brain does more than that. It profoundly affects how we conceptualize the world—whether we think a person is good or bad, if we like the weather today or it makes us unhappy, or whether we’re inclined to take care of the day’s business. You don’t have to be a neuroscientist to know this. If you’re feeling a little down and have a nice glass of wine or a lovely piece of chocolate, your attitude can shift. A gray, cloudy day can turn bright, or irritation with a loved one can evaporate because of the way the chemicals in those substances affect the brain. Your immediate reality can change in an instant.
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, pre-frontal 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.1 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.
Imagine for a moment that you are in a microcapsule speeding up the vaginal canal, hitting warp drive through the cervix ahead of the tsunami of sperm. Once inside the uterus, you’ll see a giant, undulating egg waiting for that lucky tadpole with enough moxie to penetrate the surface. Let’s say the sperm that led the charge carries an X and not a Y chromosome. Voilà, the fertilized egg is a girl.
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.2 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.3 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.4 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.5 For another, it defines our innate biological destiny, coloring the lens through which each of us views and engages the world.
READING EMOTION EQUALS READING REALITY
Just about the first thing the female brain compels a baby to do is study faces.6 Cara, a former student of mine, brought her baby Leila in to see us for regular visits. We loved watching how Leila changed as she grew up, and we saw her pretty much from birth through kindergarten. At a few weeks old, Leila was studying every face that appeared in front of her. My staff and I made plenty of eye contact, and soon she was smiling back at us. We mirrored each other’s faces and sounds, and it was fun bonding with her. I wanted to take her home with me, particularly because I hadn’t had the same experience with my son.
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.7 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.8
Baby girls are born interested in emotional expression. They take meaning about themselves from a look, a touch, every reaction from the people they come into contact with. From these cues they discover whether they are worthy, lovable, or annoying. But take away the signposts that an expressive face provides and you’ve taken away the female brain’s main touchstone for reality. Watch a little girl as she approaches a mime. She’ll try with everything she has to elicit an expression. Little girls do not tolerate flat faces. They interpret an emotionless face that’s turned toward them as a signal they are not doing something right. Like dogs chasing Frisbees, little girls will go after the face until they get a response. The girls will think that if they do it just right, they’ll get the reaction they expect. It’s the same kind of instinct that keeps a grown woman going after a narcissistic or otherwise emotionally unavailable man—“if I just do it right, he’ll love me.” You can imagine, then, the negative impact on a little girl’s developing sense of self of the unresponsive, flat face of a depressed mother—or even one that’s had too many Botox injections.9 The lack of facial expression is very confusing to a girl, and she may come to believe, because she can’t get the expected reaction to a plea for attention or a gesture of affection, that her mother doesn’t really like her. She will eventually turn her efforts to faces that are more responsive.
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.10 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.11
HEARING, APPROVAL AND BEING HEARD
Girls’ well-developed brain circuits for gathering meaning from faces and tone of voice also push them to comprehend the social approval of others very early.12 Cara was surprised that she was able to take Leila out into public. “It’s amazing. We can sit at a restaurant, and Leila knows, at eighteen months, that if I raise my hand she should stop reaching for my glass of wine. And I noticed that if her dad and I are arguing, she’ll eat with her fingers until one of us looks over at her. Then she’ll go back to struggling with a fork.”
These brief interactions show Leila picking up cues from her parents’ faces that her cousin Joseph likely wouldn’t have looked for. A University of Texas 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 an object. The mother stood off to the side. Every move, glance, and utterance was videotaped. 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 ten to twenty times more 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 object, 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.13
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 human vocal tones.14 Just as bats can hear sounds that even cats and dogs cannot, girls can hear a broader range of sound frequency and tones in the human voice than can boys.15 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.
A girl is also astute at reading from facial expression whether or not she’s being listened to. At eighteen months, Leila could not be kept quiet. We couldn’t understand anything she was trying to tell us, but she waddled up to each person in the office and unloosed a stream of words that seemed very important to her. She tested for agreement in each of us. If we appeared even the tiniest bit disinterested, or broke eye contact for a second, she put her hands on her hips, stomped her foot, and grunted in indignation. “Listen!” she yelled. No eye contact meant to her that we were not listening. Cara and her husband, Charles, were worried that Leila seemed to insist on being included in any conversation at home. She was so demanding that they thought they had spoiled her. But they hadn’t. It was just their daughter’s brain searching for a way to validate her sense of self.
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.
EMPATHY
This superior brain wiring for communication and emotional tones plays out early in a baby girl’s behavior.16 Years later Cara couldn’t understand why her son didn’t settle down as quickly when she picked him up as her daughter, Leila, had. She thought it was just temperament, a fussier personality. But likely it was also the sex difference in hardwiring in the brain for empathy. The baby girl is able to resonate more easily with her mother and respond quickly to soothing behavior, stopping her fussing and crying. Observations made during a study at Harvard Medical School found that baby girls do this better with their mothers than do boys.17
Another study showed that typical female newborns less than twentyfour hours old respond more to the distressed cries of another baby—and to the human face—than male newborns do.18 Girls as young as a year old are more responsive to the distress of other people, especially those who look sad or hurt.19 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.20 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.21 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.22 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.
INHERITING MORE THAN MOM’S GENES
Because of her ability to observe and feel emotional cues, a girl actually incorporates her mother’s nervous system into her own.23 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.24
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.25 This relation has also been shown in human females and nonhuman primates.26 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.27 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.28
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.29