Brain Rule #11
Male and female brains are different.
THE MAN WAS A HOT DOG. The woman was a bitch.
The results of the experiment could be summarized in those two sentences. Researchers had asked people to rate a fictional person’s job performance—an assistant vice president of an aircraft company. People were divided into four groups, each group with an equal number of men and women, for the experiment. The groups were given the vice president’s brief job description. But the first group also was told that the vice president was a man. Asked to rate both the competence and the likability of the candidate, this group gave a very flattering review, rating the man “very competent” and “likable.” The second group was told that the vice president was a woman. She was rated “likable” but “not very competent.” All other factors were equal. Only the perceived gender had changed.
The third group was told that the vice president was a male superstar, a stellar performer on the fast track at the company. The fourth group was told that the vice president was a female superstar, also on the express lane to the executive washroom. As before, the third group rated the man “very competent” and “likable.” The woman superstar also was rated “very competent.” But she was not rated “likable.” In fact, the group’s descriptions included words such as “hostile.” As I said, the man was a hot dog. The woman was a bitch.
The point is, gender biases hurt real people in real-world situations. As we hurtle headlong into the controversial world of gender differences, keeping these social effects in mind is excruciatingly important. There is a great deal of confusion regarding the way men and women relate to each other, and even more confusion about why they relate to each other differently. Terms are often confused as well, blurring the line between the concepts of “sex” and “gender.” In this chapter, sex will generally refer to biology and anatomy. Gender will refer mostly to social expectations. Sex is set into the concrete of DNA. Gender is not.
Differences between men’s and women’s brains can be viewed from several lenses: genetic, neuroanatomical, and behavioral. Scientists usually spend their whole careers exploring only one. So our tour of all three will be necessarily brief.
How we become male or female
The differences between men’s and women’s brains start with genes, which determine whether we become male or female in the first place. The road to sex assignment starts out with all the enthusiasm sex usually stimulates. Four hundred million sperm fall all over themselves attempting to find one egg during intercourse. The task is not all that difficult. In the microscopic world of human fertilization, the egg is the size of the Death Star, and the sperm are the size of X-wing starfighters.
X is the name of that very important chromosome that half of all sperm and all eggs carry. You recall chromosomes from biology class. They’re those writhing strings of DNA packed into the cell nucleus that contain the information necessary to make you. You can think of chromosomes as volumes in an encyclopedia. Creating you takes 46 of them. Twenty-three come from Mom, and 23 come from Dad. Two are sex chromosomes, either X or Y. At least one of your sex chromosomes has to be an X chromosome, or you will die. If you get two X chromosomes, you go into the ladies locker room all your life; an X and Y puts you forever in the men’s. The Y can be donated only by sperm—the egg never carries one—so sex assignment is controlled by the man. (Henry VIII’s wives wish that he had known that. He executed one of them, Anne Boleyn, for being unable to produce a son as heir to the throne, but it would have made more sense to execute himself.)
What the X and Y chromosomes do
One of the most interesting facts about the Y chromosome is that you don’t need most of it to make a male. All it takes to kick-start the male developmental program is a small snippet near the middle, carrying a gene called SRY.
David C. Page is the researcher who isolated SRY. Though in his 50s, Page looks to be about 28 years old. As director of the Whitehead Institute and a professor at MIT, he is a man of considerable intellect. He also is charming, with a refreshingly wicked sense of humor. Page is the world’s first molecular sex therapist. Or, better, sex broker. He discovered that you can destroy the SRY gene in a male embryo and get a female, or add SRY to a female embryo and turn her into a male (SR stands for “sex reversal”).
Why can you do this? In a fact troubling to anybody who believes males are biologically hardwired to dominate the planet, researchers discovered that the basic default setting of the mammalian embryo is to become female. Yet the male program is enthusiastic. The CIA estimates (though not everyone agrees) that 107 male babies are born for every 100 females worldwide. Because males die sooner, though, the adult ratio of men to women is about one to one.
There is terrible inequality between the two chromosomes. The X chromosome carries about 1,500 genes, which do most of the heavy lifting to develop an embryo. The little Y chromosome, by comparison, has been shedding its associated genes at a rate of about five every one million years. It’s now down to less than 100 genes.
With only a single X chromosome, males need every one of those 1,500 genes. With two X chromosomes, females have double the necessary amount. You can think of it like a cake recipe calling for only one cup of flour. If you decide to put in two, it will change the results in a most unpleasant fashion. The female embryo uses what may be the most time-honored weapon in the battle of the sexes to solve the problem of two Xs: She simply ignores one of them. This chromosomal silent treatment is known as X inactivation. One of the chromosomes is tagged with the molecular equivalent of a “Do Not Disturb” sign. Because males require all 1,500 X genes to survive, and they have only one X chromosome, X inactivation does not occur in guys. And because males must get their X from Mom, all men are literally, with respect to their X chromosome, Momma’s Boys—unisexed.
That’s very different from their sisters, who are more genetically complex. Since female embryos have two Xs from which to choose, Mom’s or Dad’s, researchers wanted to know who preferentially got the sign. The answer was completely unexpected: There were no preferences. Some cells in the developing little girl embryo hung their sign around Mom’s X. Neighboring cells hung their sign around Dad’s. At this point in research, there doesn’t appear to be any rhyme or reason, and it is considered a random event. This means that cells in the female embryo are a complex mosaic of both active and inactive mom-and-pop X genes. These bombshells describe our first truly genetic-based findings of potential differences between men’s and women’s brains.
What do many of the X’s 1,500 genes do? They govern how we think. In 2005 the human genome was sequenced, and a large percentage of the X chromosome genes were found to create proteins involved in brain manufacture. Some of these genes may be involved in establishing higher cognitive functions, from verbal skills and social behavior to certain types of intelligence. Researchers call the X chromosome a cognitive “hot spot.”
The purpose of genes is to create molecules that mediate the functions of the cells in which they reside. Collections of these cells create the large brain structures we’ve been talking about, like the cortex, the hippocampus, the thalamus and the amygdala. These make up the neuroanatomy of the brain, which we turn to next.
Differences in brain structure
When it comes to neuroanatomy, the real challenge is finding areas that aren’t affected by sex chromosomes. You can see differences in the cortex, the amygdala, even the biochemicals that brain cells use to communicate with each other.
The frontal and prefrontal cortex control much of our decision-making ability. Labs—headed by scientists of both sexes, I should perhaps point out—have found that certain parts of this cortex is fatter in women than in men.
The limbic system, home to the amygdala, controls not only the generation of emotions but also the ability to remember them. Running counter to current social prejudice, this region is much larger in men than it is in women. At rest, female amygdalas tend to talk mostly to the left hemisphere, while male amygdalas do most of their chatting with the right hemisphere.
Biochemicals have not escaped sex differences, either. Serotonin, key in regulating emotion and mood, is a particularly dramatic example. Males can synthesize serotonin about 52 percent faster than females. (Prozac works by altering the regulation of this neurotransmitter.)
What do these physical differences really mean? In animals, the size of structures is thought to reflect their relative importance to survival. Human examples at first blush seem to follow a similar pattern. We already have noticed that violinists have bigger areas of the brain devoted to controlling their left hand than their right. But neuroscientists nearly come to blows over how brain structure relates to function. We don’t yet know whether differences in the size of a brain region translate to anything substantial when it comes to behavior.
Differences in behavior
I didn’t really want to write about this. Characterizing gender-specific behaviors has a long and mostly troubled history. Institutions holding our best minds aren’t immune. Larry Summers was Harvard’s president, for Pete’s sake, when in 2005 he attributed girls’ lower math and science scores to behavioral genetics, comments that cost him his job. The battle of the sexes has existed for a very long time, illustrated by three quotes separated by centuries:
“The female is an impotent male, incapable of making semen because of the coldness of her nature. We therefore should look upon the female state as if it were a deformity, though one that occurs in the ordinary course of nature.”
Aristotle (384–332 BC)
“Girls begin to talk and to stand on their feet sooner than boys because weeds always grow up more quickly than good crops.”
Martin Luther (1483–1546)
“If they can put a man on the moon … why can’t they put them all there?”
Jill (graffiti I saw on a bathroom wall in 1985, in response to Luther’s quote scribbled there)
Almost 2,400 years of history separate Aristotle from Jill, yet we seem to have barely moved. Invoking planet metaphors like Venus and Mars, some purport to expand perceived differences into prescriptions for relationships. And this is the most scientifically progressive era in human history.
Mostly, I think, it comes down to statistics. When people hear about measurable differences, they often think scientists are talking about individuals, such as themselves. That’s a big mistake. When scientists look for behavioral trends, they do not look at individuals. They look at populations. Trends emerge, but the many variations and overlaps mean that statistics in these studies can never apply to individuals. There may very well be differences in the way men and women think about some things. But exactly how that relates to your behavior is a completely separate question.
Mental disorders
Brain pathologies represent one of the strongest pieces of evidence that sex chromosomes are involved in brain function and thus brain behavior. Mental retardation is more common in males than in females in the general population. Many of these pathologies are caused by mutations in any one of 24 genes in the X chromosome. As you know, males have no backup X. If their X gets damaged, they have to live with the consequences. If a female’s X is damaged, she can often ignore the consequences.
Mental-health professionals have known for years about sex-based differences in the type and severity of psychiatric disorders. Males are more severely afflicted by schizophrenia than females, for example. By more than two to one, women are more likely to get depressed than men, a figure that shows up just after puberty and remains stable for the next 50 years. Males have a greater tendency to be antisocial. Females have more anxiety. Most alcoholics and drug addicts are male. Most anorexics are female. Says Thomas Insel, from the National Institute of Mental Health, “It’s pretty difficult to find any single factor that’s more predictive for some of these disorders than gender.”
It’s a horrible slide show. In it, a little boy is run over by a car while walking with his parents. If you ever see that show, you will never forget it. But what if you could forget it? The brain’s amygdala aids in the creation of emotions and our ability to remember them. Suppose there was a magic elixir that could momentarily suppress it? Such an elixir does exist, and it was used to show that men and women process emotions differently.
You have probably heard the term left brain versus right brain. You may have heard that this underscores creative versus analytical people. That’s a folk tale, the equivalent of saying the left side of a luxury liner is responsible for keeping the ship afloat, and the right is responsible for making it move through the water. Both sides are involved in both processes. That doesn’t mean the hemispheres are equal, however. The right side of the brain tends to remember the gist of an experience, and the left brain tends to remember the details.
Researcher Larry Cahill eavesdropped on men’s and women’s brains under acute stress (he showed them slasher films), and what he found is this: Men handled the experience by firing up the amygdala in their brain’s right hemisphere. Their left was comparatively silent. Women handled the experience with the opposite hemisphere. Their left amygdala lit up, their right comparatively silent. If males are firing up the side in charge of gist, does that mean males remember more gist than detail of a given emotional experience related to stress? Conversely, do females remember more detail than gist? Cahill decided to find out.
That magic elixir of forgetting, a drug called propranolol, normally is used to regulate blood pressure. As a beta-blocker, it also inhibits the biochemistry that activates the amygdala during emotional experiences. The drug is being investigated as a potential treatment for combat-related disorders.
But Cahill gave it to his subjects before they watched a traumatic film. One week later, he tested their memories of it. Sure enough, the men lost the ability to recall the gist of the story, compared with men who didn’t take the drug. Women lost the ability to recall the details. One must be careful not to overinterpret these data. The results clearly define only emotional responses to stressful situations, not objective details and summaries. This is not a battle between the accountants and the visionaries.
Cahill’s results come on the heels of similar findings around the world. Other labs have extended his work, finding that women recall more emotional autobiographical events, more rapidly and with greater intensity, than men do. Women consistently report more vivid memories for emotionally important events such as a recent argument, a first date, or a vacation. Other studies show that, under stress, women tend to focus on nurturing their offspring, while men tend to withdraw. This tendency in females has sometimes been called “tend and befriend.” Is this caused by nature or nurture? As Stephen Jay Gould says, “It is logically, mathematically, and philosophically impossible to pull them apart.”
Verbal communication
Over the past several decades, behaviorist Deborah Tannen and others have done some fascinating work on how men and women communicate verbally. The CliffsNotes version of their findings: Women are better at it.
Women tend to use both hemispheres when speaking and processing verbal information. Men primarily use one. Women tend to have thick cables connecting their two hemispheres. Men’s are thinner. It’s as though females have a backup system that males don’t. Researchers think these neuroanatomical differences may explain why language and reading disorders occur approximately twice as often in little boys as in little girls. Women also recover from stroke-induced verbal impairment better than men.
Girls seem verbally more sophisticated than little boys as they go through the school system. They are better at verbal memory tasks, verbal fluency tasks, and speed of articulation. When these little girls grow up, they are still champions at processing verbal information. Real as these data seem, however, almost none of them can be divorced from a social context. That’s why Gould’s comment is so helpful.
Tannen spent years observing and videotaping how little girls and little boys interact, especially when talking to their best friends. If any detectable patterns emerged in children, she wanted to know if they also showed up in college students. The patterns she found were both predictable and stable. The conversational styles we develop as adults come directly from the same-sex interactions we solidified as children. Tannen’s findings center on how boys and girls cement relationships and negotiate status within same-sex groups, and then how these entrenched styles clash as men and women try to communicate with one another as adults.
Cementing relationships
When girl best friends communicate with each other, they lean in, maintain eye contact, and do a lot of talking. They use their sophisticated verbal talents to cement their relationships. Boys never do this. They rarely face each other directly, preferring either parallel or oblique angles. They make little eye contact, their gaze always casting about the room. They do not use verbal information to cement their relationships. Instead, commotion seems to be the central currency of a little boy’s social economy. Doing things physically together is the glue that cements their relationships.
My sons, Josh and Noah, have been playing a one-upmanship game since they were toddlers. A typical version might involve ball throwing. Josh would say, “I can throw this up to the ceiling,” and would promptly try. Then they would laugh. Noah would respond by grabbing and throwing the ball, saying, “Oh yeah? I can throw this up to the sky.” This ratcheting, with laughter, would continue until they reached the “galaxy” or the big prize, “God.”
Tannen consistently saw this style everywhere she looked—except when observing little girls. The female version goes something like this. One sister says, “I can take this ball and throw it to the ceiling,” and she does. Both laugh. The other sister grabs the ball, throws it up to the ceiling, and says, “I can, too!” Then they talk about how cool it is that they can both throw the ball. This style persists into adulthood for both sexes. Tannen’s data, unfortunately, have been misinterpreted as “Boys always compete, and girls always cooperate.” As this example shows, however, boys are being extremely cooperative. They are simply doing it through competition, deploying their favorite strategy of physical activity.
Negotiating status
By elementary school, boys finally start using their verbal skills for something: to negotiate their status in a large group. Tannen found that high-status males give orders to the rest of the group, verbally or even physically pushing the low-status boys around. The “leaders” maintain their fiefdoms not only by issuing orders but also by making sure the orders are carried out. Other strong members try to challenge them, so the guys at the top learn quickly to deflect challenges. Hierarchy is very evident with boys. It can be hard on them, too: The life of a low-status male is often miserable.
Tannen found that little girls have hierarchies of status, too. But they used strikingly different strategies to generate and maintain them. Verbal communication is so important that the type of talk determines the status of the relationship. Your “best friend” is the one to whom you tell secrets. The more secrets revealed, the more likely the girls are to identify each other as close. Girls tend to deemphasize the status between them in these situations. Using their sophisticated verbal ability, the girls tend not to give top-down imperial orders. If one of the girls tries issuing commands, the style is usually rejected: The girl is tagged as “bossy” and isolated socially. Not that decisions aren’t made. Various members of the group give suggestions, discuss alternatives, and come to a consensus.
The difference between girls’ and boys’ communication could be described as the addition of a single powerful word. Boys might say, “Do this.” Girls would say, “Let’s do this.”
Styles persist, then clash
Tannen found that, over time, these ways of using language become increasingly reinforced. By college age, most of these styles are deeply entrenched. And that’s when the problems between men and women become most noticeable.
Tannen tells the story of a woman driving with her husband. “Would you like to stop for a drink?” the wife asked. The husband wasn’t thirsty. “No,” he replied. The woman was annoyed because she had wanted to stop; the man was annoyed because she wasn’t direct. In her book You Just Don’t Understand, Tannen explains: “From her point of view, she had shown concern for her husband’s wishes, but he had shown no concern for hers.” How would this conversation likely go between two women? The thirsty woman would ask, “Are you thirsty?” With lifelong experience at verbal negotiation, her friend would know what she wanted and respond, “I don’t know. Are you thirsty?” Then a small discussion would ensue about whether they were both thirsty enough to stop the car and get water.
These differences in social sensitivity play out in the workforce just as easily as in marriage. At work, women who exert “male” leadership styles are in danger of being perceived as bossy and aggressive. Men who do the same thing are often praised as decisive and assertive. Tannen’s great contribution was to show that these stereotypes form very early in our social development, perhaps assisted by asymmetric verbal development. They transcend geography, age, and even time. Tannen, who was an English literature major, sees these tendencies in manuscripts that go back centuries.
Tannen’s findings are statistical patterns, not an all-or-none phenomenon. Many factors affect our language patterns, she found. Regional background, individual personality, profession, social class, age, ethnicity, and birth order all affect how we use language to negotiate our social ecologies. Boys and girls are treated differently socially the moment they are born, and they are often reared in societies filled with centuries of entrenched prejudice. It would be a miracle if we somehow transcended our experience and behaved in an egalitarian fashion.
Given the influence of culture on behavior, it is overly simplistic to invoke a purely biological explanation for Tannen’s observations. Given the great influence of brain biology on behavior, it is also simplistic to invoke a purely social explanation. The real answer to the nature-or-nurture question is “We don’t know.” That can be frustrating to hear. As scientists explore how genes and cells and behaviors connect, their findings give us not completed bridges but boards and nails. It’s dangerous to assume the bridges are complete. Just ask Larry Summers.
More ideas
Get the facts straight on emotions
Dealing with the emotional lives of men and women is a big part of the job for teachers and managers. They need to know:
1) Emotions are useful. They make the brain pay attention.
2) Men and women process certain emotions differently.
3) The differences are a product of complex interactions between nature and nurture.
Experiment with same-sex classrooms
My son’s third-grade teacher began seeing a stereotype that worsened as the year progressed. The girls were excelling in the language arts, and the boys were pulling ahead in math and science. This was only the third grade! The language-arts differences made some sense to her. But she knew there was no statistical support for the contention that men have a better aptitude for math and science than women. Why, for heaven’s sake, was she presiding over a stereotype? The teacher guessed that part of the answer lay in the students’ social participation during class. When the teacher asked a question of the class, who answered first turned out to be unbelievably important. In the language arts, the girls invariably answered first. Other girls reacted with that participatory “me too” instinct. The reaction on the part of the boys was hierarchical. The girls usually knew the answers, the boys usually did not, and the males responded by doing what low-status males tend to do: They withdrew. A performance gap quickly emerged.
In math and science, boys and girls were equally likely to answer a question first. But the boys used their familiar “top each other” conversational styles when they participated, attempting to establish a hierarchy based on who knew more. This included drubbing anyone who didn’t make the top, including the girls. Bewildered, the girls began withdrawing from participating in the subjects. Once again, a performance gap emerged.
The teacher called a meeting of the girls and verified her observations. Then she asked for a consensus about what they should do. The girls decided that they wanted to learn math and science separately from the boys. Previously a strong advocate for mixed-sex classes, the teacher wondered aloud if that made any sense. Yet if the girls started losing the math-and-science battle in the third grade, the teacher reasoned, they were not likely to excel in the coming years. She obliged. It took only two weeks to close the performance gap.
Can the teacher’s result be applied to classrooms all over the world? One classroom in a single school year does not make for a valid experiment. We need to test hundreds of classrooms and thousands of students from all walks of life, over a period of years.
Pair men and women in workplace teams
One day, I spoke about gender with a group of executives-in-training at the Boeing Leadership Center in St. Louis. After showing some of Larry Cahill’s data about gist and detail, I said, “Sometimes women are accused of being more emotional than men, from the home to the workplace. I think that women might not be any more emotional than anyone else.” I explained that because women perceive their emotional landscape with more data points (that’s the detail) and see it in greater resolution, women may simply have more information to which they are capable of reacting. If men perceived the same number of data points, they might have the same reactions. Two women in the back began crying softly. After the lecture, I asked them about it, fearing I may have offended them. What they said instead blew me away. “It was the first time in my professional life,” one of them said, “that I didn’t feel like I had to apologize for who I was.”
And that got me to thinking. In our evolutionary history, having a team that could understand both the gist and details of a given stressful situation helped us conquer the world. Why would the world of business be exempted from that advantage? Having an executive team or work group capable of simultaneously understanding both the emotional forests and the trees of a stressful project, such as a merger, might be a marriage made in business heaven. It could even affect the bottom line.
Companies often train managers by setting up simulations of various situations. They could take a mixed-sex team and a unisex team and have each work on the same project. Give another two teams the same project, but first teach them what we know about brain differences between the sexes. Would the mixed teams do better than the unisex teams? Would the groups prepped on how the brain works do better than the unprepped groups? You might find that management teams with a gist/detail balance create the best chance for productivity. At the very least, it means both men and women have an equal right to be at the decision-making table.
Imagine environments where gender differences are both noted and celebrated, as opposed to ignored and marginalized. We might have more women in science and engineering. We might shatter the archetypal glass ceiling. We might create better businesses. We might even create better marriages.
Brain Rule #11
Male and female brains are different.
• The X chromosome that males have one of and females have two of—though one acts as a backup—is a cognitive “hot spot,” carrying an unusually large percentage of genes involved in brain manufacture.
• Women are genetically more complex, because the active X chromosomes in their cells are a mix of Mom’s and Dad’s. Men’s X chromosomes all come from Mom, and their Y chromosome carries less than 100 genes, compared with about 1,500 for the X chromosome.
• Men’s and women’s brains are different structurally and biochemically—men have a bigger amygdala and produce serotonin faster, for example—but we don’t know if those differences have significance.
• Men and women respond differently to acute stress: Women activate the left hemisphere’s amygdala and remember the emotional details. Men activate the right hemisphere’s amygdala and get the gist.
