When I left Philadelphia to begin my residency in family practice, I threw out most of the papers I had accumulated during my six years at the University of Pennsylvania. Stacks of photocopied scientific papers had to go out in the trash. But there was one manila folder I didn't throw out, a folder containing a series of studies done by Professor John Corso at Penn State during the 1950s and 1960s, demonstrating that females hear better than males.*

* John Corso, "Age and Sex Differences in Thresholds," Journal of the Acoustical Society of America, 31:489-507, 1959; also John Corso, "Aging and Auditory Thresholds in Men and Women," Archives of Environmental Health, 6:350-356, 1963.

•

Not only do most of the books currently in print [2006] about girls and boys fail to state the basic facts about innate differences between the sexes, many of them promote a bizarre form of political correctness, suggesting that it is somehow chauvinistic even to hint that any innate differences exist between female and male. A tenured professor at Brown University recently published a book in which she claims that the division of the human race into two sexes, female and male, is an artificial invention of our culture. "Nature really offers us more than two sexes," she claims, adding, "Our current notions of masculinity and femininity are cultural conceits." The decision to "label" a child as a girl or a boy is "a social decision," according to this expert. We should not label any child as being either a girl or a boy, this professor proclaimed. "There is no either/or. Rather, there are shades of difference."* This book received courteous mention in the New York Times and the Washington Post. America's most prestigious medical journal, the New England Journal of Medicine, praised the author for her "careful and insightful" approach to gender.⁺

* Anne Fausto-Sterling, Sexing the Body: Gender Politics and the Construction of Sexuality (New York: Basic Books, 2000), pp.31, 3.
⁺ Claudia Dreifus, "Anne Fausto-Sterling: Exploring What Makes Us Male or Female," New York Times, January 2, 2001, p.F3. See also Courtney Weaver, "Birds Do It," Washington Post, March 26, 2000, p. X6; and Marc Breedlove, "Sexing the Body," New England Journal of Medicine, 343:668, 2000.

•

After waiting a few years for somebody else to write a book about girls and boys based on actual scientific research, I finally decided to write one myself. But I made myself a promise. Every time I make any statement about how girls and boys are different, I will also state the evidence on which my statement is based. Every statement I make about sex differences will be supported by good science published in peer-reviewed journals.

There is more at stake here than the old question of nature versus nurture. The failure to recognize and respect sex differences in child development has done substantial harm over the past thirty years — such will be my claim throughout this book....

•

According to the United States Department of Education, the average eleventh-grade American boy now writes at the same level as the average eighth-grade girl.*

* U.S. Department of Education, Educational Equity for Girls and Women (Washington, DC: U.S. Government Printing Office, 2000), p.18

Similar gender gaps have been documented in the United Kingdom, Australia, New Zealand, and Canada.*

* For more information about gender gaps in the United Kingdom, Australia, New Zealand, and Canada, please go to www.genderdifferences.org/gendergaps.htm

The U.S. Department of Education now projects that in the year 2011, there will be 140 women graduating from college for every 100 men — very nearly a 60/40 female-to-male ratio.*

* Department of Education, National Center for Education Statistics, Projection of Education Statistics To 2011, Chapter 4, "Earned Degrees Conferred." The department projects that in May-June 2011, 568,000 men will be awarded bachelor's degrees compared with 824,000 women. That works out to 59.2 percent of degrees being awarded to women. You can access this report online at http://nces.ed.gov/pubs2001/proj01/chapter4.asp.

Several major U.S. colleges and universities, such as New York University and the University of North Carolina, already report that their student body is more than 60 percent female.*

* These examples come from Michelle Conlin's cover story for Business Week magazine, May 26, 2003, "The New Gender Gap," pp.74-84.

I'm all in favor of women's colleges, but you have to ask the question: Why are nominally coed schools looking more and more like all women's colleges? The proportion of boys going on to college is dropping steadily, as is the proportion of young men who are sticking around long enough to graduate. The high school dropout rate in the United States is now close to 30 percent, and the great majority of dropouts are boys.* More and more boys, discouraged by years of failure in elementary school, middle school, and high school, are asking: "Why should I stick around for any more of this?"

* See the study conducted by the Center for Labor Market Studies at Northeastern University, "The Hidden Crisis in the High School Dropout Problems of Young Adults in the U.S.: Recent Trends in Overall School Dropout Rates and Gender Differences in Dropout Behaviour." The study can be downloaded at www.businessroundtable.org/document.cfm/914   [Link broken]. Recent reports have shown that some school districts "fudge" their graduation rates, for example, by coding dropouts as having transferred to other school districts or to a GED program. Such programs don't count as dropouts. The New York Times published a series of three articles in 2003 on this phenomenon. See Tamar Lewin and Jennifer Medina, "To Cut Failure Rate, Schools Shed Students," New York Times, July 31, 2003, p. A1; and also Tamar Lewin and Jennifer Medina, "High School Under Scrutiny for Giving Up on Its Students," New York Times, August 1, 2003; and also Tamar Lewin, "Education: The Pushouts," New York Times, August 3, 2003, sec.4, p.2. See also Diana Jean Schemo's article "Houston Punishes Former Principal in Undercount of Dropouts," New York Times, August 30, 2003 p. A11.

•

There is increasing evidence to suggest that the brain is a sexual organ, that brain sex [i.e. the sex of the brain] is paramount in determining human gender identity.

— pediatric endocrinologists Dr. Gaya Aranoff and Dr. Jennifer Bell, Columbia University, 2004*

* Gaya Aranoff and Jennifer Bell, "Endocrinology and Growth in Children and Adolescents," in Marianne Legato, ed., Principles of Gender-Specific Medicine (New York: Academic Press [Elsevier], 2004), p. 12. Dr. Aranoff directs endocrine testing for the Department of Pediatrics at Columbia University Medical Center. Dr. Bell is a lecturer in pediatric endocrinology at the Columbia College of Physicians and Surgeons.

•

Left Brain Verbal, Right Brain Spatial?
In the late 1800s, French neurologist Charles Edouard Brown-Séquard and British neurologist Henry Charlton Bastian independently discovered that the left side of the brain seems to be specialized for language. A man who suffers a stroke affecting the left side of the brain is much more likely to lose language functions than a man who suffers a stroke on the right side of the brain. The right side of a man's brain seems to be specialized for spatial functions such as navigation or mental imagery. But does this rule — left brain verbal, right brain spatial — apply to women as well as it applies to men?*

* Walter Riese, A History of Neurology (New York: MD Publications, 1959), chapter 4, "History of the Doctrine of Cerebral Localization," pp. 73-117.

The modern era of research in gender differences may be said to have begun in 1964, when Herbert Lansdell reported the existence of anatomical sex differences in the organization of female and male brains.*

* Herbert Lansdell, "Sex Differences in Hemispheric Asymmetries of the Human Brain," Nature, 203:550, 1964.

Over the next two decades, a series of studies demonstrated that while the left hemisphere of the brain is clearly specialized for language functions in men, that asymmetry is much less noticeable in women.*

* For a review of studies from the 1960s and 1970s demonstrating that the male brain is more asymmetric than the female brain, particularly with regard to language functions, see Jeannette McGlone's review, "Sex Differences in Human Brain Asymmetry: A Critical Survey," Behavioural and Brain Sciences, 3:215-263, 1980. For a more recent update using next-generation technology, see the paper by Ruben Gur, Bruce Turetsky, and associates, "Sex Differences in Brain Gray and White Matter in Healthy Young Adults: Correlations with Cognitive Performance," Journal of Neuroscience, 19:4065-4072, 1999, especially figure 3, p.4068.

Research with people who have suffered a stroke provided further support for the notion that male brains and female brains are organized differently, with functions more compartmentalized in male brains and more globally distributed in female brains. For example, men who suffer a stroke involving their brain's left hemisphere suffer a drop in verbal IQ of, on average, about 20 percent (from 111.5 to 88.7); men who suffer a stroke which affects their brain's right hemisphere suffer virtually no drop at all in their verbal IQ. If you damage a man's left hemisphere, he loses a big chunk of his language abilities; damage a mans right hemisphere, and his language ability is not affected. That sort of information provides strong evidence that the left hemisphere of a man's brain is very important for language, while the right hemisphere is not.

Women are different. Women who suffer a stroke affecting their brain's left hemisphere suffer a drop in their verbal IQ, on average, of about 9 percent (from 113.9 to 103.6); women who suffer a stroke affecting their brain's right hemisphere suffer a similar drop in verbal IQ, about 11 percent (from 113.9 to 101.0).* Women use both hemispheres of their brain for language. Men don't.

* These figures are drawn from Jeannette McGlone's review (see the previous note for the full reference), pp.218-19; see also Table 1, p.232 in the same citation.

•

Research in laboratory animals, for starters, has demonstrated large, innate, genetically determined sex differences in the brain. One striking illustration of this principle was published in 2004 by scientists at UCLA. They examined a bird that was a lateral gynandromorphic hermaphrodite: in other words, a bird that was half-female and half-male. Every cell on the right side of this bird's body was male; every cell on the left side of this bird's body was female. This bird had a testicle on the right and an ovary on the left. If you look at a picture of this bird[*], you will notice that it has male plumage on the right and female plumage on the left. This bird's blood contains a mix of female and male hormones: female hormones manufactured by the ovary and male hormones from the testicle.

[* Another study of lateral gynandromorphism here: http://www.biology.ed.ac.uk/people/homepage.php?id=hmcqueen ]

Now let's take a look at this bird's brain. If the theory popular in the 1970s and 1980s were correct [that hormones are responsible for sex differences in the brain], we shouldn't see big differences between the left and right sides of this bird's brain. The brain of this bird is nourished with blood that contains an equal mix of female and male hormones. So, if hormones are responsible for sexual differences of the brain, then the left and right sides of the brain should look the same.

But they don't. The left and right sides of this bird's brain are dramatically different. Scientists who have studied this bird have concluded that female brain tissue and male brain tissue are "intrinsically different,"* as a result of females and males having a different complement of sex chromosomes — and regardless of the mix of hormones in the blood.

* Arthur Arnold and Paul Burgoyne, "Are XX and XY Brain Cells Intrinsically Different?" Trends in Endocrinology and Metabolism, 15:6-11, 2004. For more about the hermaphrodite finch, see Robert Agate and associates, "Neural, Not Gonadal, Origin of Brain Sex Differences in a Gynandromorphic Finch," Proceedings of the National Academies of Science, 100:4873-78, 2003.

[ Arthur Arnold, images of a gynandromorphic finch's brain, Nature Reviews Neuroscience 5:701-708, 2004.
http://www.nature.com/nrn/journal/v5/n9/fig_tab/nrn1494_F4.html ]

[From above link: "Observations of a single gynandromorphic zebra finch lend credence to the view that adaptive sex differences can be caused by the direct action of sex chromosome genes in brain cells. a The zebra finch had male plumage (black breast stripes and bar, brown cheek patch) and a testis on the right side, and grey female plumage and an ovary on the left. Genetic tests showed that W-linked genes, normally only present in females, were higher on the left. b The song nucleus HVC, marked by in situ hybridization for androgen receptor, was larger on the right side than on the left. The lateral difference in brain sexual phenotype is attributed to genetic differences between the two sides. c In situ hybridization showed that the W-linked ASW gene (left), normally expressed only in the female brain, was expressed predominantly on the left half of the brain (dark areas). A sharp line in the middle divided the level of expression in the two halves of the brain. The Z-linked gene PKCIZ (right) was expressed more on the right than the left side of the brain, a difference normally found in ZZ males compared with ZW females." ]

Maybe that's true for birds, but what about humans? In fact, recent research suggests that female brain tissue is "intrinsically different" from male brain tissue in our species just as in other animals. In 2004 an all-star team of fourteen neuroscientists from the University of California, the University of Michigan, and Stanford University published their findings demonstrating a dramatically different expression of proteins derived from the X chromosome and the Y chromosome in human female and male brains. In men, many areas of the brain are rich in proteins that are coded directed by the Y chromosome. Conversely, women's brain tissue is rich in material coded directly by the X chromosome; these particular transcripts of the X chromosome are absent from men's brain tissue.*

* Marquis Vawter and associates, "Gender-Specific Gene Expression in Postmortem Human Brain: Localization to Sex Chromosomes," Neuropsychopharmacology, 29:373-84, 2004. If this topic interests you, you can learn more at http://www.genderdifferences.org/chromosomes.htm

These sex differences, then, are genetically programmed, not mediated by hormonal differences.

These scientists analyzed thirty samples of human brain tissue collected from different areas of the brain and different individuals. The scientists were not told the sex of the individuals from whom the specimens were taken. But just by analyzing the expression of two different genes in the brain tissue, they were able to corectly identify the sex of every one of the thirty specimens, female versus male. Female brain tissue and male brain tissue are intrinsically different.

Stop and think about this for a moment. This new research shows that females get more from their X chromosomes than males do,* and that the Y chromosome in men is directly responsible for differences in the brain. Differences. Not one better than the other. Not one worse than the other. Just different.

* Traditionally, molecular biologists have believed in the doctrine of "X-inactivation". According to that doctrine, one of the two X chromosomes in females in inactivated, so that females and males receive the same "dose" of X-chromosome genes. While that doctrine remains largely valid for organs such as the liver and spleen, there is now overwhelming evidence that the doctrine of X-inactivation is routinely violated in the brain. In other words, many X chromosome genes are transcribed in female brain tissue twice as much as in male brain tissue. The brain may well be the most sexually dimorphic organ after the gonads. For starters, see the paper by Jun Xu, Paul Burgoyne, and Arthur Arnold, "Sex Differences in Sex Chromosome Gene Expression in the Mouse Brain," Human Molecular Genetics, 11:1409-19, 2002.

Scientists continue to recognize that sex hormones do affect the brain. However, this recent research has also demonstrated that the direct effect of the sex chromosomes on brain tissue need not be mediated by hormones. It's genetically programmed. It's present at birth.

Sex differences in brain anatomy are all well and good, but do they matter? Do those sex differences in brain anatomy mean that there are sex differences in brain function? Are there significant differences in how girls and boys hear, or how they see, or how they learn? And if so, are those differences present at birth? Or not?

•

Lessons from the Nursery

... When any baby or child (or adult for that matter) hears a sound, there's an immediate reaction, called an acoustic brain response. Cone-Wesson and her colleagues decided to measure the acoustic brain response of more than sixty newborn girls and boys. For a 1,500Hz tone played to the right ear, they found that the average girl baby had an acoustic brain response about 80 percent greater than the response of the average baby boy.*

* My remarks in this paragraph are drawn from two studies. The first, chronologically, is: Barbara Cone-Wesson and Glendy Ramirez, "Hearing Sensitivity in Newborns Estimated from ABRs to Bone-Conducted Sounds," Journal of the American Academy of Audiology, 8:299-307, 1997. The second is: Yvonne Sininger, Barbara Cone-Wesson, and Carolina Abdala, "Gender Distinctions and Lateral Asymmetry in the Low-Level Auditory Brainstem Response of the Human Neonate," Hearing Research, 126:58-66, 1998. The fact that girl babies have a more sensitive threshold for very quiet sounds does not by itself prove that girls hear better than boys when the sound is louder; however, an earlier investigation by a European team found that girl babies do in fact have a brisker, faster acoustic brain response than boy babies do, for medium-amplitude sounds similar to normal conversation. See Giuseppe Chiarenza, Giulia D'Ambrosio, and Adriana Cazzullo, "Sex and Ear Differences of Brain-Stem Acoustic Evoked Potentials in a Sample of Normal Full-Term Newborns," Electroencephalography and Clinical Neurophysiology, 71:357-66, 1988.

(The range of sounds around 1,500 Hz is especially important, because that range of sound is critical for understanding speech.)*

* If you play a 4-kHz tone on a tone generator, you'll hear a very high pitch. Why are such high-frequency sounds so important for understanding speech? The answer is that distinguishing one consonant from another often involves that frequency range. For instance, consider the words "like" and "light". If you do spectral analysis of the sound energy when someone says those two words, you'll find that the difference in sound energy between "like" and "light" is almost entirely up in the 4-kHz range and higher.

This finding — that newborn baby girls hear differently than boys, especialy at higher frequencies — was recently confirmed by Jane Cassidy, a professor at Louisiana State University. Professor Cassidy used a different technique than Cone-Wesson, Sininger, and Ramirez had used to evaluate hearing in newborns: specifically, Professor Cassidy had used a technique known as transient evoked otoacoustic emissions.*

* We humans, like all mammals, hear because little "hairs" on cells in our inner ear are very sensitive to sound. Those "hair cells" wiggle when they detect a sound. That wiggling generates a subtle acoustic response, which is the transient evoked otoacoustic emission.

Professor Cassidy, studying 350 newborn baby girls and boys, found that the girls' hearing was substantially more sensitive than the boys', especially in the 1,000 to 4,000-Hz range, which is so important for speech discrimination.*

* Jane Cassidy and Karen Ditty, "Gender Differences among Newborns on a Transient Otoacoustic Emissions Test for Hearing," Journal of Music Therapy, 37:28-35, 2001.

Other studies have demonstrated that teenage girls (for example) do in fact hear better than boys do.*

* For more information about innate gender differences in hearing, please go to http://www.genderdifferences.org/hearing.htm

The female-male differences in hearing only gets bigger as kids get older.*

* Professor Corso's classic work (see note 3, ch. 1) demonstrated that the female superiority in hearing at frequencies above 2kHz gets larger as kids progress through adolescence and into adulthood and indeed throughout adult life.

•

The difference in how girls and boys hear also has major implications for how you should talk to your children. I can't count the number of times a father has told me, "My daughter says I yell at her. I've never yelled at her. I just speak to her in a normal tone of voice, and she says I'm yelling." If a forty-three-year-old man speaks in what he thinks is a "normal tone of voice" to a seventeen-year-old-girl, that girl is going to experience his voice as being about ten times louder than what the man is hearing.*

* Actually, the girl is going to experience her father's voice as being more than 100 times louder in amplitude than what the father himself is experiencing. Corso (1959) found that the threshold for a 3-kHz tone for a 43-year-old man was 30.5 decibels (dB), while the threshold for a 3-kHz tone for an 18-year-old-girl was 7.3 dB. That's a difference of 23.2 dB. A difference of 23.2 dB corresponds to more than a hundredfold difference in the amplitude of the sound. If you're a little rusty on this, recall the definition of decibels (dB):
 
Sound in dB = 10 log [amplitude/reference]
 
23.2 / 10 = 2.32, so a 30.5 dB sound has an amplitude that is 10^2.32 times louder or >100-fold louder, than a 7.3 dB sound.
 
[I've added this UNSW Physics page for reference: http://www.phys.unsw.edu.au/jw/dB.html#example —KJ. ]
 
What if the girl's 43-year-old mother spoke to her? In that case, the threshold for a 3-kHz tone for a 43-year-old woman is 13.7 dB, much closer to the girl's threshold. Result: middle-aged women are likely to speak in a more appropriate tone of voice to their daughters than are middle-aged men.

He is yelling at her, but he doesn't realize it. The father and his daughter are experiencing the same sound in two different ways.

•

The Eye of the Beholder

Most girls and women interpret facial expressions better than most boys and men can.*

* Many studies provide support for this statement. Start by reading Judith Hall's classsic and scholarly book Nonverbal Sex Differences (Baltimore: John Hopkins University Press, 1985). For a more recent review, see Erin McClure's authoritative article, "A Meta-Analytic Review of Sex Differences in Facial Expression Processing and Their Development in Infants, Children, and Adolescents," Psychological Bulletin, 126:424:53, 2000.

Researchers at Cambridge University wondered whether female superiority in understanding facial expressions was innate or whether it developed as a result of social factors such as parents encouraging girls to interact with other girls while the boys shoot each other with ray guns. These researchers decided to study newborn babies on the day they were born.

Their plan was to give babies a choice between looking at a simple danging mobile or at a young woman's face — more precisely, a live young woman, right there with the baby. The young woman smiled at the baby but didn't say anything. The mobile dangled and twisted but made no noise.

Was there a gender difference in what the babies preferred to look at? All 102 babies in the study were videotaped and their eye motions analyzed by researchers who didn't know the sex of the baby. The boy babies were much more interested in the mobile than in the young woman's face. The girl babies were more likely to look at the face. The differences were large: the boys were more than twice as likely to prefer the mobile. The researchers concluded that they had proven "beyond reasonable doubt" that sex differences in social interest "are, in part, biological in origin."*

* Jennifer Connellan, Simon Baron-Cohen, and associates, "Sex Differences in Human Neonatal Social Perception," Infant Behavior and Development, 23:113-18,2000. The quotation comes form page 114.

The results of this experiment suggest that girls are born prewired to be interested in faces while boys are prewired to be more interested in moving objects. The reason for that difference has to do with sex differences in the anatomy of the eye.

The retina is that part of the eye that converts light into a neurological signal. The retina is divided into layers. One layer contains the photoreceptors, the rods and the cones. Rods are sensitive to black and white. Rods are color-blind. Cones are sensitive to color.

The rods and cones send their signals to the next layer, the ganglion cells. Scientists have known for many decades that some ganglion cells are very large (magnocellular), while others are small (parvocellular). Most papers on this topic just refer to them as M and P ganglion cells.

P cells and M cells have very different jobs. M cells are wired primarily to rods, with little input from cones; they are essentially simple motion detectors. M cells are distributed all across the retina, so they can track objects anywhere in the visual field. You can think of the M cells as being wired to answer the question, "Where is it now and where is it going?" P cells are wired (in our species) to all threee varieties of cones, but have much less input from the rods. P cells are concentrated in and around the fovea, the center of the field of vision. You can think of the P cells as answering the question, "What is it?" P cells compile information about the texture and colour; M cells compile information about movement and direction.*

* Ehud Kaplan and Ethan Benardete, "The Dynamics of Primate Retinal Ganglion Cells," Progress in Brain Research, 134:17-34, 2001. See also Claire Meissirel and associates, "Early Divergence of Magnocellular and Parvocellular Functional Subsystems in the Embryonic Primate Visual System," Proceedings of the National Academy of Sciences, 94:5900-5905, 1997.

The P cells send information via their own special division of the thalamus to a particular region of the cerebral cortex that appears to be specialized for analysis of texture and color. The M cells send their information via a separate pathway to a different region of the cerebral cortex, a region that is specialized for analysis of spatial relationships and object motion. And guess what? Every step in each pathway, from the retina to the cerebral cortex, is different in females and males.*

* Tamas Horvath and K.C.Wikler, "Aromatase in Developing Sensory Systems of the Rat Brain," Journal of Neuroendocrinology, 11:77-84, 1999.

The real surprises have come from microscopic analyses of the eye performed in the past five years. Using recently developed techniques, scientists have found that the human retina is full of receptors for sex hormones.*

* See Alexandra Wickham and associates, "Identification of Androgen, Estrogen, and Progesterone Receptor mRNAs in the Eye," Acta Ophthalmologica Scandinavica, 78:146-53, 2000. See also Sandra Ogueta and associates, "Estrogen Receptor in the Human Eye: Influence of Gender and Age on Gene Expression," Investigative Ophthalmology and Visual Science, 40:1906-11,1999.

Anatomist Edwin Lephart and his associates have found that the male retina is substantially thicker than the female retina.*

* David Salyer, Edwin Lephart, and associates, "Sexual Dimorphism and Aromatase in the Rat Retina," Developmental Brain Research, 126:131-36, 2001.

That's because the male retina has mostly the larger, thicker M cells while the female retina has predominantly the smaller, thinner P ganglion cells.

We're not talking about small differences between the sexes, with lots of overlap. We're talking about large differences between the sexes, with no overlap at all. Every male animal had a thicker retina than any female retina, due to the males having more M cells.

Differences	P CELLS	M CELLS
Are wired predominantly to:	Cones	Rods
Are located mostly in:	The center of the retina (center of the field of vision)	All throughout the retina (entire field of vision, peripheral and central)
Are best adapted to detect:	Colour and texture	Location, direction, and speed
Answer the question:	"What is it?"	"Where is it now? Where is it going? How fast is it moving?
Ultimately project to:	Inferior temporal cortex	Posterior parietal cortex
Predominate in:	Females (more P cells than M cells)	Males (more M cells than P cells)

 

Girls Draw Nouns, Boys Draw Verbs

...Researchers who have studied the pictures drawn by young girls and young boys have found that girls typically draw pictures of people (or pets or flowers or trees), arranged more or less symmetrically, facing the viewer. Girls usually use ten or more colors in their pictures...and they are more likely to use the colors that Yasumasa Arai calls "warm" colors — red, green, beige, and brown.*

* Megumi Iijima, Osamu Arisaka, Fumie Minamoto, and Yasumasa Arai, "Sex Differences in Children's Free Drawings," Hormones and Behaviour, 40:99-104, 2001.

Boys typically draw action: a rocket hitting its target, an alien about to eat somebody, a car about to hit another car. Boys typically use at most six colors and they prefer what Yasumasa Arai calls "cold" colors such as blue, gray, silver, and black. Boys are also much more likely to employ a third-person perspective, looking at the action from a remote vantage point rather than from a perspective facing the vehicle or the animal actually doing the action.*

*Chris Boyatzis and Julie Eades, "Gender Differences in Preschoolers' and Kindergartners' Artistic Production and Preference," Sex Roles, 41:627-38, 1999. See also I. Kawecki, "Gender Differences in Young Children's Artwork," British Educational Research Journal, 20:485-90, 1994. See also the paper by Iijima et al., "Sex Differences," in the previous note.

Psychologist Donna Tuman summarizes the difference this way: girls draw nouns, boys draw verbs.*

* Donna Tuman, "Sing a Song of Sixpence: An Examination of Sex Differences in the Subject Preference of Children's Drawings", Visual Arts Research, 25:51-62, 1999.

...At least 95 percent of kindergarten teachers are women. Most are not aware of these differences...because nobody has ever told them. Instead, the teachers often act like Ms. Kanovsky, encouraging children to draw pictures of people, using lots of colors. Five-year-olds like Anita and Matthew quickly figure out that Anita is doing it "right" and Matthew is doing it "wrong"... Matthew will quickly decide that he's no good at art. Only five years old, Matthew has decided that "art is for girls."

•

Ask for directions?

Let's look another difference in how girls' and boys' brains work: geometry and navigation. Researchers have found that females and males use fundamentally different strategies for those tasks... Women typically navigate using landmarks that can be seen or heard or smelled. Men are more likely to use absolute direction such as north and south or absolute distance such as miles or city blocks.*

* The most definitive paper in this regard was published by Deborah Saucier and associates, "Are Sex Differences in Navigation Caused by Sexually Dimorphic Strategies or by Differences in the Ability to Use the Strategies?", Behavioral Neuroscience, 116:403-10, 2002. We will consider their paper at some length in chapter 5. See also N. Sandstrom, J. Kaufman, and S.A.Huettel, "Males and Females Use Different Distal Cues in a Virtual Environment Navigation Task," Brain Research: Cognitive Brain Research, 6:351-60, 1998.

A study published in 2003 demonstrated that this gender difference in navigation is well established by five years of age.*

* Jennifer Kersker, Melissa Epley, and Josephine Wilson, "Sex Differences in Landmark Learning by Children Aged 5 to 12 Years," Perceptual and Motor Skills, 96:329-38, 2003.

These different strategies correlate with different brain regions. Neuroscientists have found that young women and young men use different areas in the brain when they navigate: young women use the cerebral cortex while young men use the hippocampus, a nucleus deep inside the brain that is not activated in women's brains during navigational tasks.*

* Georg Grön, Mathias Riepe, and associates, "Brain Activation during Human Navigation: Gender-Different Neural Networks as Substrate of Performance," Nature Neuroscience, 3:404-8, 2000.

These differences may actually be more pronounced in children and adolescents than in adults.

•

Trucks, Rockets, Dolls, and Crayons

Child psychologist Lisa Serbin and associates at Concordia University studied 77 one-and-a-half-year-old toddlers, girls and boys. They found that these little children — boys especially — had not a clue which gender they belonged to, even when the psychologists used te simplest nonverbal prompts. Kids this age just cannot reliably assign themselves to the correct gender, and they score only slightly above chance in assigning other kids to the correct gender. Nevertheless, Serbin's group found that children's toy preferences are firmly in place by this age, especially among boys. When the experimenter offered a boy a truck or a doll, the boy chose the truck. In fact, the boys preferred trucks over dolls more strongly than girls preferred dolls over trucks.*

* Lisa Serbin and associates, "Gender Stereotyping in Infancy: Visual Preferences for and Knowledge of Gender-Stereotyped Toys in the Second Year," International Journal of Behavioral Development, 25:7-15, 2001.

...Another group, led by child psychologist Anne Campbell, looked at toddlers as young as nine months of age — and they found the same results. Nine-month-old boys strongly preferred "boy toys" such as balls, trains, and cars.*

* Anne Campbell and associates, "Infants' Visual Preference for Sex-Congruent Babies, Children, Toys and Activities: A Longitudinal Study," British Journal of Developmental Psychology, 18:479-98, 2000.

Nine-month-old girls preferred "girl toys" such as dolls and baby carriages, although the girls' preference was (again) not quite as strong as the boys' preference. Campbell's study is especially striking because she showed very clearly that kids this age have no clue what gender they belong to. Boys and girls show gender-typical toy preferences long before they understand gender. Dr. Campbell has recently said, politely, that "the impact of cognitive variables may have been overestimated."*

* Anne Campbell and associates, "Sex-Typed Preferences in Three Domains: Do Two-Year-Olds Need Cognitive Variables?" British Journal of Psychology, 93:203-17, 2002.

In other words, eighteen-month-old boys don't choose to play with trucks rather than dolls because they know they're "supposed" to. They choose trucks because they'd rather play with trucks.

...In fact, gender differences in play behaviour are present in just about every mammal that's been studied.*

* If you're interested in gender differences in play, please go to www.genderdifferences.org/playfighting.htm

More than twenty years ago, scientists knew that young male rats engage in much more rough-and-tumble play than do young female rats. In one study, scientists damaged the amygdala of young rats. (The amygdala, a small nucleus at the base of the brain, plays an important role in emotion and affect). That damage dramatically decreased rough-and-tumble play among the males but had no effect on females, suggesting that the gender differences in play behavior was due at least in part to sex differences in the amygdala.*

* Michael Meaney and William Beatty, "Sex Dependent Effects of Amygdalar Lesions on the Social Play of Prepubertal Rats," Physiology and Behavior, 26:467-72, 1981.

The fact that gender differences in play behavior are found in so many other species is another nail in the coffin for the idea that similar preferences in human children are entirely due to culture.

Today we know that innate differences between girls and boys are profound. Of course, not all girls are alike and not all boys are alike. But girls and boys do differ from one another in systematic ways that should be understood and made use of, not covered up or ignored.

Girls and boys play differently. They learn differently. They fight differently. They see the world differently. They hear differently. When I started graduate school in 1980, most psychologists were insisting that those differences came about because parents raised girls and boys in different ways. Today we know that the truth is the other way around: parents raise girls and boys differently because girls and boys are so different from birth. Girls and boys behave differently because their brains are wired differently.

•

For believe me! — the secret of realizing the greatest fruitfulness and the greatest enjoyment of existence is: to live dangerously! Build your cities on the slopes of Vesuvius! Send your ships out into uncharted seas!

— Friedrich Nietzsche, 1887 (The Gay Science)

Living dangerously

...Studies in the United States and around the world universally find that boys are more likely to engage in physically risky activities.*

* William Pickett and associates, "Multiple Risk Behavior and Injury: An International Analysis of Young People," Archives of Pediatrics and Adolescent Medicine, 156:786:93, 2002.

Boys are more likely than girls to be seriously injured or killed in accidents such as drowning, misuse of firearms, or head injury related to riding a bicycle.*

* Anna Waller, Susan Baker, and Andrew Szacka, "Childhood Injury Deaths: National Analysis and Geographic Variations," American Journal of Public Health, 79:310-15, 1989.

Psychologist Barbara Morrongiello interviewed children ages six through ten who had been injured or who had been in "close calls". She found that compared to the girls, the boys:

• were more likely to attribute their injuries erroneously to "bad luck" rather than to any lack of skill or foresight on their part;
• were less likely to tell their parents about the injury;
• were more likely to be around other boys at the time the injury occurred.*

* Barbara Morrongiello, "Children's Perspectives on Injury and Close-Call Experiences: Sex Differences in Injury-Outcome Processes," Journal of Pediatric Psychology, 22(4):499-512, 1997.

...Why are boys more likely to engage in risky and dangerous activities? One reason derives from gender differences in the autonomic nervous system, which we'll discuss at length in the next chapter. Risky and dangerous activities trigger a "fight or flight" response that gives a tingle, a charge, an excitement that many boys find irresistable.

...Lizette Peterson and her associates at the University of Missouri wanted to study sex differences in children's responses to risky situations. They set up a video game in which kids rode a stationary bicycle while watching an interactive video screen. The simulation was so realistic that when the bicycle on the screen went under the branch of a tree, some kids ducked their heads. Then the kids suddenly confronted a hazard: in some cases just a coiled garden hose blocking the path; in other cases, an extremely dangerous situation such as an oncoming car swerving suddenly from the opposing lane so that the car is about to hit the kid head-on. The bike was wired so that Peterson and her colleagues could measure how quickly the kids stepped on the brake to avoid a collision.

Let me tell you one thing: I wouldn't want to be sitting on the back of a bike if one of those boys was riding it. The boys were much slower to brake than the girls were. If the simulation had been real, many of the boys would have sustained life-threatening injuries. The boys were also more likely to report feeling exhilarated by the simulated collision, whereas girls were far more likely to report feeling fearful.*

* Lizette Peterson, Tammy Brazeal, Krista Oliver, and Cathy Bull, "Gender and Developmental Patterns of Affect, Belief, and Behavior in Simulated Injury Events," Journal of Applied Developmental Psychology, 18:531-46, 1997.

So: one reason many boys engage in physically dangerous activities may be that the danger itself gives the activity a pleasant tingle. That's a tough concept for some women to grasp. A mother who warns her son, "Don't ride your bike off the boardwalk. You might get hurt," has missed the point. Her son knows it's dangerous. He's riding his bike off the boardwalk because it's dangerous.

...a similar phenomenon — the male taking greater risks — has been observed in primates such as monkeys, baboons, and chimpanzees. Anthropologists Linda Marie Fedigan and Sandra Zohar wanted to find out why there are so many more adult female Japanese macaque monkeys than male monkeys. Although the ratio of female to male monkeys is roughly 1:1 at birth, by adulthood there are as many as five females for every one surviving male. What happens to all the other male monkeys? And why isn't a similarly imbalanced sex ratio seen in zoos? ... After carefully reviewing twenty-one years of data, Fedigan and Zohar found support only for the risk hypothesis. "Males are mainly lost to the population because of their risk-taking behaviors." Male monkeys do wild and crazy things, just like teenage boys. For example, these researchers found that male monkeys take stupid risks around highways: they try to scamper across a highway, only to be crushed by an oncoming truck. Female monkeys are much less likely to take the same risks. They tend to avoid highways.*

* Linda Marie Fedigan and Sandra Zohar, "Sex Differences in Mortality of Japanese Macaques: Twenty-One Years of Data from the Arashiyama West Population," American Journal of Physical Anthropology, 102(2):161-75, 1997.

Learned Helplessness
...Professor Babcock studied students graduating from Carnegie Mellon University with a master's degree in a business-related field. She found that the starting salaries of the men were about 8 percent higher on average than those of the women: the men were paid about $4,000 more. Babcock then looked to see who had asked for more money during the job-finding process. It turned out that only 7 percent of the female students had asked, compared with 57 percent of the men. Controlling for gender, Babcock found that students who asked for more money received a starting salary that was $4,053 higher on average than students who didn't ask. In other words, the gender gap could be explained by the fact that the women hadn't asked for more money.*

* Linda Babcock and Sara Laschever, Women Don't Ask: Negotation and the Gender Divide (Princeton: Princeton University Press, 2003).

To be successful, really successful in business or politics, you have to be willing to take those kinds of risks. You want your daughter to be able to do that. To take a risk when the moment is right. How can you empower her to have that kind of self-confidence?

...Moral of the story: if you have had plenty of experiences exploring new situations, facing your fears and mastering them, then you can face new challenges and conquer them as well [ed: unless you're a macaque monkey?]. If you don't have that experience of taking a risk and succeeding, then you won't be able to summon up your strength when it really counts.

...If a girl takes a risk and fails, she may end up being more risk-averse, not less. [Margrét Pála] Ólafsdóttir [educator in Iceland] acknowledges this hazard. "The feeling of weakness and inability and the tendency to low self-esteem are so integrated into girls' thinking, that [this risk-taking] training can be counter-productive if we do not know exactly what we are doing."* Start with something the girls know they can do, then gradually let them build up that wall, stretch their abilities to the limit.

* Margrét Pála Ólafsdóttir, "Kids are Both Girls and Boys in Iceland," Women's Studies International Forum, 19(4):357-69, 1996.

The Blessing of a Skinned Knee
...Child psychologist Wendy Mogel has written a charming book called The Blessing of a Skinned Knee. Without mentioning the theory of learned helplessness, she points out that shielding children from injury makes them more risk-averse. And, letting them explore their world — at the cost of a few scrapes and cuts — builds their character and gives them self-confidence, resilience, and self-reliance.*

* Wendy Mogel, The Blessing of a Skinned Knee (New York: Penguin, 2001).

"What doesn't kill me, makes me stronger," Nietzsche wrote.

I agree that a skinned knee can be a blessing. Girls in particular benefit from "dare training", to use Ólafsdóttir's term once more.... I'm not so sure when it comes to boys, though. Many boys are already prewired to take risks and enjoy taking risks.

...What about the boy who gets a thrill out of taking risks? He skateboards down a bannister. He rides his bike off a brick ledge onto the sidewalk... Each year he wants to do something even more hazardous. You have nightmares about spinal cord injuries. What to do?

[education]...Taking a lesson from an expert will keep your boy in touch with reality and give him a more accurate assessment of his skills.

[supervision]...your son is at much greater risk of injury in an unsupervised setting with other boys than in any setting where there's a responsible adult in charge.

[memory/stick to rules]...If you've told your boy that he's not allowed to ride his mountain bike without your permission, and he's broken that rule, don't tell him again. Don't ask him to "promise".

 

...Psychologist Janet lever spent a whole year at elementary school playgrounds watching girls and boys play. Boys fight a lot, she noticed: about twenty times as often as girls do. To her surprise, though, she found that boys who fight each other usually end up being better friends after the fight.*

* See two articles by Janet Lever: "Sex Differences in the Games Children PLay," Social Problems, 23:478-87, 1976, and "Sex Differences in the Complexity of Children's Games", American Sociological Review, 43:471-83, 1978.

...Girls seldom fight, but when they do — often with words rather than fists — the bad feelings last.

...Lever's reports are similar to what scientists have found with chimpanzees. Male chimpanzees are about twenty times as likely to fight as females are, but the fights don't last more than a few minutes and rarely result in major injury. Two male chimps who fight each other this morning may be grooming each other this afternoon. According to Frans de Waal, a primatologist at the Yerkes Primate Research Center in Atlanta, "Picking a fight can actually be a way for [male chimps] to relate to one another, check each other out, and take a first step toward friendship." Female chimps rarely fight, but when they do, their friendship is over. The hostility that results can last for years. Serious injury is also more likely to occur when female chimpanzees fight. Female chimps who have fought one another are "vindictive and irreconcilable" according to Dr. de Waal.*

* Quoted in Deborah Blum's book Sex on the Brain: The Biological Differences between Men and Women (New York: Penguin, 1998), pp.73-74.

In our species these differences are apparent as soon as children can talk. Boys as young as two years of age, given a choice between violent fairy tales and warm and fuzzy fairy tales, usually choose the violent stories. Girls as young as two years of age consistently choose the warm and fuzzy stories.*

* Tracy Collins-Stanley, Su-lin Gan, Jessy Hsin-Ju, and Dolf Zillman, "Choice of Romantic, Violent and Scary Fairy-Tale Books by Preschool Girls and Boys," Child Study Journal, 26(4):279-302, 1996.

In another study, psychologists found that five- and seven-year-old girls who prefer violent stories are more likely to have significant behavior problems than girls who prefer warm, nurturing stories. However, among boys, preference for violent stories is not an indicator of underlying psychiatric problems.*

* Kai Klitzing, Kimberly Kelsay, Robert Emde, JoAnn Robinson, and Stephanie Schmitz, "Gender-Specific Characteristics of 5-Year-Olds' Play Narratives and Associations with Behavior Ratings," Journal of the American Academy of Child and Adolescent Psychiatry, 39:1017-23, 2000.

...There's good evidence that at least some of these differences are biologically programmed. Some of that evidence comes from studies of girls with congenital adrenal hyperplasia (CAH). Owing to a genetic defect in the adrenal glands, the adrenal tissues of girls with CAH produce high levels of male hormone while the girl is still in the mother's womb. That male hormone partially masculinizes the girl's brain. [This is different to the brain of the gynandromorphic finch, in that the absence of hormonal effects on its brain was studied in adulthood. - KJ] When young girls who have CAH are offered a toy — given the choice of an airplan, a ball, military action figures, Barbie and Ken dolls, or Magic Markers — CAH girls are more likely to choose an airplane or a ball or the fighting action figures and less likely to choose the Barbie and Ken dolls or Magic Markers, compared with normal girls. When CAH girls are tested at age four, they are found to have story preferences about halfway between tose of normal girls and normal boys: CAH girls are more likely to choose violent stories than normal girls are, but less likely to choose violent stories than normal boys are.*

* See for example Sheri Berenbaum and Elizabeth Snyder, "Early Hormonal Influences on Childhood Sex-Typed Activity and Playmate Preferences," Developmental Psychology, 31(1):31-42, 1995. See also Sheri Berenbaum and Melissa Hines, "Early Androgens Are Related to Childhood Sex-Typed Toy Preferences," Psychological Science, 3:209-6, 1992.

In fact, the masculinity of a CAH girl's choice of toy is directly proportional to the severity of that girl's CAH. The more severe her CAH — that is, the more male hormone her brain was exposed to before birth — the more masculine her behavior and her toy preferences will be.* These researchers also found no evidence of parently influence on their child's play behavior. Parents who encouraged their daughters to play with more "feminine" toys had zero effect on their child's play behavior.

* Anna Servin, Anna Nordenström, Agne Larsson, and Gunilla Bohlin, "Prenatal Androgens and Gender-Typed Behavior: A Study of Girls with Mild and Severe Forms of Congenital Adrenal Hyperplasia," Developmental Psychology, 39:440-50, 2003.

...One essential premise of evolutionary biology is that if you find a behavior that is conserved across many different species within an order (in this case, the primate order), then that behavior probably serves some biologically useful purpose. It's not hard to see a biologically useful purpose for young female primates to feel drawn to caring for little babies. Formal studies have demonstrated that the more practice a young female monkey has taking care of a little baby, the better she will be at doing it.*

* Michael Meaney, Elizabeth Lozos, and Jane Stewart, "Infant Carrying by Nulliparous Female Vervet Monkeys," Journal of Comparative Psychology, 104:377-81, 1990.

But what about rough-and-tumble play? What evolutionary purpose is served when young males chase each other and wrestle, sometimes for hours on end? Primatologists have suggested two reasons why young males, and not young females, spend so much time engaged in rough-and-tumble play. One reason is that in many primate species — including our closest relative, the chimpanzee — the male is much more likely to pursue and kill moderate-sized prey. The adult male chimpanzee commonly hunts, kills, and eats medium-size animals such as monkeys while the adult female chimpanzee very rarely hunts such prey, instead preferring nuts, berries, and invertebrate species such as termites. Adolescent male chimpanzees often kill monkeys; adolescent female chimpanzees never do.*

* See for example the article by Jane Goodall and her associates in the American Journal of Physical Anthropology, "Patterns of Predation by Chimpanzees on Red Colobus Monkeys in Gombe National Park, 1982-1991," 94:213-28, 1994. They found that adolescent male and adult male chimps often kill colobus monkeys. The anthropologists never saw an adolescent female chimp kill a monkey, and even adult female chimps rarely killed monkeys. The anthropologists identified fifteen different male chimps each of whom killed three or more monkeys, and nine male chimps each of whom killed more than ten monkeys each. One male killed 76 monkeys. By contrast, only two female chimps killed more than two monkeys: one female killed four monkeys, and one (an infertile female who never mated) killed ten monkeys. See their Table 3, p.220. See also Michael Hopkin's article, "Girl Chimps Learn Faster than Boys," Nature, April 15, 2004, online at http://www.nature.com/nsu/040412/040412-6.html . In this article, primatologist Andrew Whiten is quoted as saying, "While termites are a valuable food for females, males often catch larger animals such as monkeys. Their rough-and-tumble play may be a way to hone their hunting skills."

...But there's another reason, primatologists say, why it's useful for young males to engage in play-fighting. Wrestling and fighting with other males teaches them the rules of the game. If young male primates are deprived of the opportunity to fight with other males, those males grow up to be more violent as adults, not less.*

* J. Dee Higley, "Aggression", in Dario Maestripieri, ed., Primate Psychology (Cambridge, Mass.: Harvard University Press, 2003), pp.17-40. See also the forthcoming paper by Christina Barr, Michelle Becker, and J. Dee Higley, "Early Life Events as Predictors of Aggression and Violence in the Adult."

They've never learned how to get along with other males in a playful, aggressive way. The rage seems to get bottled up inside until it explodes. And if it's true for our cousins, it may be true for us. In just a moment we'll discuss proposals offered by well-intentioned reformers to ban dodge-ball and even snowball-throwing on teh grounds that such activities are "violent" and "aggressive". The irony is that if our sons are anything like their primate cousins, such measures may not decrease the likeliood of serious violent acts: indeed, it may increase the likelihood of exactly the kind of violent outburst the reformers are trying to prevent.

 

Affirm the Knight

...Boys often employ aggressive behaviors playfully, as a way of making friends. Girls, especially young girls, very seldom do that. The proverbial boy pulling on a girl's pigtail is a boy who is trying to make friends with that girl. But his message is misunderstood.

...Differences between girls and boys are natural. Those differences should be acknowledged, accepted, and exploited for educational purposes. Instead, many educators today seek to eradicate gender-specific behaviors. In particular, they don't like "agressive" play.

...The solution to taming a boy's aggressive drive is NOT to squelch the drive every time it appears. Banning dodgeball from the schoolyard makes as much sense as Prohibition. Instead, you want to transform the boy's aggressive drive. Sublimate it into something constructive. Julie Collins, a counsellor at a high school I visited, explains it this way: "You can't turn a bully into a flower child. But you can turn a bully into a knight."

•

The PainStation

...Twenty years ago, psychologists knew that girls and women appeared to be more sensitive to pain than boys and men are. Back then, though, most psychologists believed that the apparently greater female sensitivity to pain was a product of social expectations. Men and boys claimed not to feel pain because they wanted to look tough, these psychologists thought. "We teach boys not to cry. We tell them it's not manly to show pain. So, of course, men are less willing to acknowledge pain than women are," these psychologists said. "They feel the pain just the same as women do. They're just less willing to admit it." Psychologists assumed that there were no fundamental sex differences in the perception of pain.

That assumption was wrong. In the past twenty years it's become clear that there are fundamental sex differences in the perception of pain: not just in humans, but in laboratory animals as well. The difference is especially large with regard to what scientists call stress-induced analgesia. Scientists have found that when you stress an animal in the laboratory — say, by immobilizing it — and then you subsequently test that animal's sensitivity to pain, you will find that the animal is much less sensitive. But that phenomenon is seen primarily in males. Females of all mammalian species studied so far show this effect to a much lesser extent. In some cases, exposure to stress actually makes females more sensitive to pain.*

* For a review of sex differences in stress-induced analgesia, see Wendy Sternberg and Melissa Wachterman, "Experimental Studies of Sex-Related Factors Influencing Nociceptive Responses: Nonhuman Animal Research", pp. 71-88, in the monograph Sex, Gender, and Pain, edited by Roger Fillingim, published by the International Association for the Study of Pain (Seattle, 2000).

Human females as well as female laboratory animals do demonstrate pregnancy-induced analgesia. If you test a woman's sensitivity to pain late in her pregnancy, you will find that she is significantly less sensitive to pain than when she is not pregnant. For example, a mild electrical shock that she might find very painful when she is not pregnant may be barely perceptible when she's in her third trimester.*

* To learn more about pregnancy-induced analgesia, start with the review by Alan Gintzler and Nai-Jiang Liu, "Ovarian Sex Steroids Activate Antinociceptive Systems and Reveal Gender-Specific Mechanisms," pp.89-108, in ibid.

That numbing of pain is nature's way of making pregnancy and the birthing process a little more bearable. And, it may explain the action of one pain medication — alphaxalone — which is "for women only". Alphaxalone is a non-narcotic pain reliever based on the female hormone progesterone. It's four times more effective in females than in males.*

* D. Sarkar and associates, "Sex Difference in Response to Alphaxalone Anaesthesia May be Oestrogen Dependent," Nature, 298:270-72, July 15, 1982.

In 2003, two different groups of researchers — one at the University of Texas at Austin, the other at the University of California at San Francisco — identified another factor underlying sex differences in pain perception: the cellular mechanism that mediates pain sensation is structurally different in males compared with females.*

* Igor Mitrovic and associates, "Contribution of GIRK2-Mediated Postsynaptic Signaling in Opiate and Alpha2-Adrenergic Analgesia and Analgesic Sex Differences," Proceedings of the National Academy of Sciences," 100(1):271-76, January 7, 2003. See also Y. A. Blednov and associates, "A Pervasive Mechanism for Analgesia: Activation of GIRK2 Channels," in ibid., p. 277-82.

Dr Igor Mitrovic, the lead author of one of the two studies, suggested that these sex differences may lead to the development of other pain releivers specifically for women.*

* See Alison McCook's article for Reuters, "Why a Man's 'Ouch' Is Different Than a Woman's", December 20, 2002.

These pills might have the potential to be more effective than current "one-pill-fits-both-sexes" pain medications.

The same jolt of electricity, the same blast of heat, will be experienced differently by girls and boys. The girl will experience more pain. This fundamental sex difference in sensory perception, mediated at the cellular level, may conceivably play some role in boys' greater willingness to risk pain. If you're a boy, the PainStation just isn't as painful.

•

Fight or Flight

Seventy years ago, physiologist Walter Cannon studied the hormonal response of animals to stress and confrontation. He didn't want to bother with the hormonal fluctuation of female estrus and menstrual cycles, so he studied only male animals. Cannon described the cascade of hormonal responses to stress: increased heart rate, dilated pupils, a surge of adrenaline in the blood, all mediated by that division of the autonomic nervous system known as the sympathetic nervous system. Because these responses prepare the animal to fight or run away, Cannon named this cascade the "fight or flight" response.

Incredibly, researchers who followed up on Cannon's work continued to study only male animals. UCLA professor Shelley Taylor has estimated that roughly 90 percent of all scholarly work on hormonal responses to stress has been done exclusively on male animals (including humans).*

* Shelley Taylor and associates, "Biobehavioral Responses to Stress in Females: Tend-and-Befriend, Not Fight-or-Flight," Psychological Review, 107:411-29, 2000. See also Dr. Taylor's book The Tending Instinct (New York: Henry Holt, 2002).

Scientists assumed that males and females were wired in the same way. It never occurred to those (male) scientists that females might be different. Nobody studied women.

We now know that females are wired to respond to stress in a different way than males are. Dozens of studies over the past twenty years have consistently shown dramatic sex differences in the biobehavioral response to stress. The female autonomic nervous system has been shown to be influenced more by the parasympathetic nervous system, which is energized by acetylcholine rather than adrenaline and which causes an unpleasant, nauseating feeling rather than the "thrill" of the sympathetic nervous system.*

* Many studies demonstrate that the female autonomic nervous system in humans is influenced more by the parasympathetic nervous system while the male autonomic nervous system is influenced more by the sympathetic nervous system. For a discussion and list of the relevant references, please go to www.genderdifferences.org/autonomic.htm

When most young boys are exposed to threat and confrontation, their senses sharpen and they feel an exciting tingle. (In chapter 9, we'll consider boys who are exceptions to this rule.) When most young girls are exposed to threat and confrontation, they feel dizzy and 'yucky'. They may have unaccustomed trouble expressing themselves with just the right words. They may experience nausea or an urge to use the bathroom.

Bottom line: many young boys get a thrill from violent or quasi-violent confrontation. Most young girls don't. Some ten-year-old boys will spend their last nickel to play video arcade games in which enemies are shooting at them. Few ten-year-old girls find simulated combat worth spending their last nickels on.

I'm not saying that girls are never violent, just that girls seldom enjoy physical violence the way boys do. Girls are violent in their own way. We'll get to that in a minute.

 

Fight Club

Across the United States the physical education curriculum is shifting away from traditional sports in favor of aerobic activities such as riding a stationary bicycle or jogging.*

*For one example, listen to the report that aired on NPR's Weekend Edition Sunday, May 23, 2004, entitled "New School Phys-Ed: Aerobics, No Sports," online at http://www.npr.org/templates/story/story.php?storyId=1907101

Advocates of this shift point out that competitive sports have winners and losers, and often involve an aggressive component. Nobody's a loser if you're just riding a stationary bike. But people who make that argument don't understand that many boys need the aggressive element found in sports such as basketball and soccer. The result of the shift away from competitive sports to aerobics is that boys who aren't athletic enough to make the team now have no socially acceptable outlet for their aggressive impulses.

 

Grand Theft Auto

What do you do if your son wants to energize his sympathetic nervous system, to get his fix of tingles, by playing a violent video game? Grand Theft Auto, referred to by teenage boys as GTA, is one of the most popular games in the ultraviolent genre. You play the part of an excon who has to reestablish his reputation as a tough guy. You steal cars, run over pedestrians, and kill people. You can have sex with a prostitute, then shoot her in the head and take your money back while blood oozes from her head and she moans in agony. Police officers are the enemy. The more police you kill, the better — if you can get away with it.

The most successful installment of GTA, entitled "Vice City," sold 1.4 million copies — at $50 each! — in its first week alone, and $400 million worth of product in its first year. That's roughly the same amount of money that the movie Titanic earned in its first year.

Do not buy this game for your son. Don't buy any video game that employs what I call a "moral inversion" — where good is bad and bad is good. Playing those games for hours on end can warp your mind. If your son absolutely has to play violent video games, choose something like SpyHunter instead. In SpyHunter, you're a James Bond sort of character, assigned missions such as escorting diplomats to embassies while various enemies try to shoot you and the diplomat you're escorting. In other missions, you're trying to destroy interballistic missiles in their silos or save a crowd at a stadium by disarming a hidden explosive device before it goes off — all while the bad guys are shooting at you and you're shooting back. You lose points if you kill or injure a civilian. You can't just fire your weapon blindly. You have to avoid the civilians (who become more numerous as you advance in the game) and make sure you're right on top of the bad guy before you fire. I've played both SpyHunter and GTA "Vice City" and I can tell you, those two games leave a very different residual in your head. After playing GTA "Vice City", when you see a real police car, you really do feel a momentary impulse to shoot or run away.

Stay involved. Your son needs to know that you're aware of every video game he's playing. Sit down and play with him. If the violence and gore turns your stomach, tell your son that you're going to toss that game in the garbage can.

Better yet, get your son away from video games altogether and toward real-life aggressive games such as football and ice hockey. Playing a violent sport like football or lacrosse can build many virtues in a boy: courage, physical endurance, and camaraderie, among others. No video game can do that.

 

Violence, Girl Style

...Provocation, leading to a violent response, followed by resolution. That's the pattern with many boys. But that simple pattern is rare among girls. "The surface of a girl fight can be silent and smooth as a marble," observes Rachel Simmons. Tension can arise so subtly that even the girls themselves sometimes can't honestly tell you how it happened.

...Tensions can simmer and build for weeks or months, corroding a friendship until there is no friendship left.

(Rachel) Simmons* uses the phrase "alternative aggression" to describe these ongoing wars among adolescent girls. It's a useful term because it reminds us that these ongoing tensions are a form of aggression. Parents sometimes don't recognize the damage that alternative aggression can cause. For one thing, the perpetrator is often a "good girl", polite to adults and clever at hiding her traces. A girl who victimizes other girls in this manner is often the most socially skilled and may even be one of the most popular girls — just the opposite of the typical boy bully.

* Rachel Simmons, Odd Girl Out: The Hidden Culture of Aggression in Girls (New York: Harcourt, 2002)

Girl bullies are different from boy bullies. Boys who bully are often pathetic characters themselves. The male bully may have few friends, may be socially inept, may not be doing well in school. He picks on his victim as a way of improving his own status, at least in his own eyes.... His bullying is motivated not so much by anything his victim has done or said, but by his own insecurities, his vague hope that he will feel better by making someone else miserable. He may also hope to ingratiate himself with other boys by picking on the victim. "When an unpopular kid is harrassed by someone from a popular crowd, wanna-bes and posers may take the incident as a signal that their own status can be improved by going after that victim," observes Professor John Bishop of Cornell University.*

* John Bishop, Matthew Bishop, Lara Gelbwasser, Shanna Green, and Andrew Zuckerman, "Nerds and Freaks: A Theory of Student Culture and Norms," in Brookings Papers on Education Policy, 2003, Diane Ravitch, ed. (Washington, DC: Brookings Institution Press, 2003), pp.141-213. The quote is from page 158.

The situation is almost completely reversed for girls. Whereas boys typically bully kids they barely know, girls almost always bully girls within their social group. These girls are intimate enemies. They know each other. They know where it hurts most.*

* See the review by Jon Sutton and colleagues, "Bullying and 'Theory of Mind': A Critique of the Social Skills Deficit View of Anti-Social Behavior," Social Development, 8:117-27, 1999. These authors observe that "the stereotype of a bully as a powerful but 'oafish' person with little understanding of others" may be a good description of the typical boy who bullies, but rarely describes the girl who bullies. Girls who bully "need good social cognition and theory of mind skills in order to manipulate and organize others, inflicting suffering in sublte and damaging ways while avoiding detection themselves."

 

Chapter 5: School

...Most girls will naturally seek to affiliate with the teacher. They expect the teacher to be on their side, to be their ally. Most girls won't hesitate to ask the teacher for help when they need it. Educational researchers have consistently found that girls are more concerned than boys are with pleasing the teacher and more likely than boys to follow the teacher's example.*

* See Tricia Valeski and Deborah Stipek, "Young Children's Feelings about School", Child Development, 72:1198-1213, 2001. See also Eva Pomerantz and Jill Saxon, "Conceptions of Ability as Stable and Self-Evaluative Processes: A Longitudinal Examination", Child Development, 72:152-73, 2001. See also Eva Pomerantz, Ellen Altermatt, and Jill Saxon, "Making the Grade but Feeling Distressed: Gender Differences in Academic Performance and Internal Distress," Journal of Educational Psychology, 94(2): 396-404, 2002.

Remarkably, a similar finding has recently been described in our closest genetic relative, the chimpanzee. In 2004, anthropologists who had spent three years observing chimpanzees in the wilds of Tanzania reported sex differences in learning similar to what we see in human children. Girl chimps follow their teacher's example — in this case, regarding the proper way to dig for termites — while boy chimps completely disregard the teacher, preferring to do it their own way — or they ignore the teacher's example altogether and go off to swing from a nearby tree or wrestle with another male chimp. The boy chimps are consequently much slower to master the task than the girls are.*

* Elizabeth Lonsdorf, Lynn Eberly, and Anne Pusey, "Sex Differences in Learning in Chimpanzees," Nature, 428:715-16, 2004.

Sex differences in how students relate to their teacher give rise to sex differences in motivation to study and in the weight that students give to their teacher's opinions. As a result, according to educational psychologist Eva Pomerantz, girls are at greater risk of being harmed by a negative assessment from a teacher:

Girls generalize the meaning of their failures because they interpret them as indicating they have disappointed adults, and thus they are of little worth. Boys, in contrast, appear to see their failures as relevant only to the specific subject area in which they have failed; this may be due to their relative lack of concern with pleasing adults.*

* Eva Pomerantz, Ellen Altermatt, and Jill Saxon, "Making the Grade but Feeling Distressed: Gender Differences in Academic Performance and Internal Distress," Journal of Educational Psychology, 94(2): 396-404, 2002. The quote is from page 402.

Girls are more likely to do their homework even if the particular assignment doesn't interest them. Girls want the teacher to think well of them. Boys on the other hand will be less motivated to study unless they find the material intrinsically interesting. Likewise, most boys will consult the teacher for help only as a last resort, after all other options have been exhausted.

 

Face-To-Face, Shoulder-To-Shoulder

Friendships between girls are different from friendships between boys. Girls' friendships are about being together, spending time together, talking together, going places together. Friendships between boys on the other hand usually develop out of a shared interest in a game or an activity. We might characterize the difference this way: girls' friendships are face-to-face, two or three girls talking with one another. Boys' friendships are shoulder-to-shoulder, a group of boys looking out at some common interest.*

* This observation — that girls' friendships are face-to-face, while boys' friendships are shoulder-to-shoulder — has been made by many scholars, most accessibly by Deborah Tannen, You Just Don't Understand: Women and Men in Conversation, rev. ed. (New York: HarperCollins, 2001); and by Helen Fisher, Why We Love: The Nature and Chemistry of Romantic Love (New York: Henry Holt, 2004).

Conversation is central to girls' friendships at every age. Girlfriends love to talk with each other. When they start having trouble talking, the friendship is in trouble. The mark of a truly close friendship between two girls or two women is that they tell each other secrets they don't tell anyone else. They confide in each other about their most personal doubts and difficulties. Self-disclosure is the most precious badge of friendship between females. When she tells you a secret she's never told anyone else, then you know that you are truly her dear friend.

Boys are different. Most boys don't really want to hear each other's innermost secrets.* With boys the focus is on the activity, not on the convesation. Four boys can spend hours playing a video game without exchanging a single complete sentence. You'll hear screams of agony and shouts of exultation, but you may not hear much that qualifies as conversation.

* See Kathryn Dindia and Mike Allen's review of 205 studies on this topic: "Sex Differences in Self-Disclosure: A Meta-Analysis", Psychological Bulletin, 112:106-24, 1992.

Girls' friendships then are more intimate and more personal than most boys' friendships. That has advantages and disadvantages. The advantage of course is that each girl derives strength from the intimacy of the relationship. When a girl is under stress, they want to be with their friends more. When boys are under stress, they usually just want to be left alone.* (May mothers don't know about these differences. When a mother sees that her son is under stress, she often tries to comfort him. Almost invariably she will be rebuffed.)

* See for example Deborah Belle's essay, "Gender Differences in Children's Social Networks and Supports," pp. 173-88, in the book edited, Children's Social Networks and Supports (New York: John Wiley, 1989).

Psychologist Shelley Taylor, who has specialized in the study of gender differences in the response to stress, summarizes her findings this way: "Women maintain more same-sex close relatioships than do men, they mobilize more social support in times of stress than do men, they turn to female friends more often, and they report more benefits from contact with their female friends and relatives."*

* Shelley Taylor and associates, "Biobehavioral Responses to Stress in Females: Tend-and-Befriend, Not Fight-or-Flight," Psychological Review, 107:411-29, 200. The quote is from page 418.

Girls' Friendships Have Distinct Values and Exhibit Different Dynamics Compared with Boys' Friendships

	Girls	Boys
Friendships form among...	Two or three girls	Two to twelve boys
Friendships focus on...	Each other	A shared interest in a game or activity
Games and sports are...	An excuse to get together	Central to the relationship
Conversation is...	Central to the relationship	Often unnecessary
Hierarchies...	Destroy the relationship	Build and organize camaraderie
Self-revelation is...	A precious badge of friendship	To be avoided if possible

...Girls are more likely to assume that the teacher is an ally and a friend. Boys are less likely to make that assumption. So, when encountering difficulties, girls are more likely to consult the teacher early. Boys, as I said a moment ago, usually consult the teacher as a last resort. And girls are much more likely than boys are to ask a teacher for advice about personal matters, totally unrelated to the academic material.

Continuing with our discussion of friendship: girls' friendships work best when the friendship is between equals. If you're a girl or a woman and you think your firend believes herself to be "better" than you, then your friendship with her is not likely to last. Boys on the other hand are comfortable in an unequal relationship, even if they are the lesser party.

...small group learning is a good teaching strategy for girls, but seldom for boys. How come?

First reason: Girls are more comfortable asking the teacher for help when they need it. If you give four girls a group assignment, you can be confident that if they get stuck, at least one of them will come to you for help.

Not so with boys. If four boys get stuck, there's no guarantee that any of them will ask the teacher for help, unless one of the boys is a geek, and even geeks know that asking the teacher for help lowers their status in the eyes of the other boys. If the boys get stuck, they must just throw spitballs and get rowdy instead of asking for help.

That leads us to a second reason why small-group self-directed learning works for girls but not for boys. Boys can raise their status in the eyes of other boys by disrupting the teacher's program. If the teacher breaks the class into small groups and two boys in a group of four start being disruptive, those boys raise their status in the eyes of at least some of the other boys in the room, no matter how puerile their behavior. (Incidentally, the word puerile is derived from the Latin word puer, meaning young boy. There is no pejorative word corresonding to the Latin puella, young girl.) That's what education writer Elinor Burkitt was trying to communicate when she wrote that "teen culture celebrates public displays of contempt for education and authority," which in unchecked will cause the class to disintegrate into "total anarchy."*

* Elinor Burkitt spent one year observing kids in a "good" public high school in a "nice" suburb. See her book Another Planet: A Year in the Life of a Suburban High School, (New York: HarperCollins, 2001). The quotation is from page 69. Burkitt mentions later in the same paragraph that "every once in a while, when the class deteriorated into total anarchy, some girl would take pity on [the teacher] and let loose a timid 'Come on, you guys.'" It is apparently usually a girl who seeks to come to the rescue of the beleaguered teacher.

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...Professor Tracy Shors and her colleagues at Rutgers, Princeton, and Rockefeller University have demonstrated that stress improves learning in males while it impairs learning in females.*

* See, for example, Gwendolyn Wood and Tracey Shors, "Stress Facilitates Classical Conditioning in Males, but Impairs Classical Conditioning in Females through Activational Effects of Ovarian Hormones," Proceedings of the National Academy of Sciences, 95:4066-71, 1998.

"Exposure to the stressor had diametrically opposed effects" on learning in females compared with males, Professor Shors has reported.*

* Tracy Shors and associates, "Sex Differences and Opposite Effects of Stress on Dendritic Spine Density in the Male Versus Female Hippocampus," Journal of Neuroscience, 21(16): 6292-97, 2001.

She has also shown that exposure to stress enhances the growth of neural connections in the male hippocampus while it inhibits growth of connections in the female hippocampus. Shors has conclusively demonstrated that the beneficial effect of stress on learning in males depends on prenatal masculinization of the male brain.*

* Professor Shors demonstrated this fact by injecting pregnant mothers with an antitestosterone drug that crosses the placenta. Male babies born to mothers injected with the drug showed no improvement, as adults, in their learning in response to stress. They lost that characteristic as a result of their mothers' being injected with the antitestosterone drug while they were in utero. Male babies castrated at birth did show the male-typical beneficial effect of stress on learning — despite the fact that they couldn't make testosterone after birth. See Tracey Shors and George Miesegaes, "Testosterone in Utero and at Birth Dictates How Stressful Experiences Will Affect Learning in Adulthood," Proceedings of the National Academy of Sciences, 99:13955-60, October 15, 2002.

...Rule of thumb: moderate stress improves boys' performance on tests — the boys do better than you might expect — whereas the same stress degrades young girls' performance on tests (this effect may be smaller in adult women than it is in school-age girls).*

* For an introduction to this topic, begin with the review by Lawrence Stricker, Donald Rock, and Nancy Burton, "Sex Differences in Predictions of College Grades from Scholastic Aptitude Test Scores," Journal of Educational Psychology, 85:710-18, 1993.

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A Different Sequence

...Girls and boys differ in their developmental timetables. Those differences in brain maturation are detectable while the baby is still in its mother's womb.*

* Reuwen Achiron, Shlomo Lipitz, and Anat Achiron, "Sex-Related Differences in the Development of the Human Fetal Corpus Callosum: In Utero Ultrasonographic Study," Prenatal Diagnosis, 21:116-20, 2001. This in utero study confirmed the findings of a previous anatomical study in which investigators examined the brains of babies who had died before birth. See M. de Lacoste and associates, "Sex Differences in the Fetal Human Corpus Callosum," Human Neurobiology, 5:93-96, 1986. These differences in the corpus callosum derive primarily from the fact that the female brain is more mature, further along in its development, than the male brain. In adults there are few significant differences in the corpus callosum between women and men.

These differences are larger and more complex than you might expect. Researchers at Virginia Tech examined brain activity in 508 normal children — 224 girls and 284 boys — ranging in age from two months to sixteen years. This study, the largest and most carefully executed of its type, demonstrated that various regions of the brain develop in a different sequence in girls compared with boys. It's not correct to say, "Boys develop along the same lines, only slower." The truth is more nuanced. These researchers found that while the areas of the brain involved in language and fine motor skills mature about six years earlier in girls than in boys, the areas of the brain involved in targeting and spatial memory mature about four years earlier in boys than in girls. These researchers concluded that the areas of the brain involved in language, in spatial memory, in motor coordination, and in getting along with other people develop in a "different order, time, and rate" in girls compared with boys.*

* Harriet Hanlon, Robert Thatcher, and Marvin Cline, "Gender Differences in the Development of EEG Coherence in Normal Children," Developmental Neuropsychology, 16(3):479-506, 1999. The quotation comes from page 502. Similar results were reported in a smaller study by A. P. Anokhin and associates, "Complexity of Electrocortical Dynamics in Children: Developmental Aspects," Developmental Psychology, 36:9-22, 2000.

...Sex differences in childhood are larger and more important than sex differences in adulthood. By thirty years of age, both males and females have reached full maturity of all areas of the brain. When people over thirty years of age think about their own experiences as adults, they may not see enormous sex differences in how women and men learn new material or master new tasks.

...many studies now have shown that when the main emphasis in kindergarten is on learning to read at the expense of other less structured and more developmentally appropriate activities, many boys tune out and turn off. Those boys develop negative feelings toward school that are likely to persist and color the child's entire academic career.*

* See Deborah Stipek and associates, "Good Beginnings: What Difference Does the Program Make in Preparing Young Children for School?" Journal of Applied Developmental Psychology, 19:41-66, 1998. See also D. Burts and associates, "Observed Activities and Stress Behaviors of Children in Developmentally Appropriate and Inappropriate Kindergarten Classrooms," Early Childhood Research Quarterly, 7:297-319, 1992.

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Recall our discussion of gender differences in how females and males give directions. In chapter 2 we learned that girls are more likely to use visible landmarks whereas boys are more likely to use compass directions north, south, east, west. Psychologist Deborah Saucier and her colleagues wanted to see whether females could use the male-typical strategy (compass directions), and whether males could use the female-typical strategy (landmarks). They recruited students and divided them randomly into two groups. Both groups had the same task: to find an unknown location on campus, using directions provided by Dr. Saucier. In one group, both the females and the males were given directions in terms of landmarks. "God straight down this road until you get to the small house with the green door. Then turn right and walk down the sidewalk until you get to College Avenue. Make a left onto College Avenue," and so forth. In the other group, both the women and the men were given compass directions: "Go north one block, then turn east and walk two blocks, then turn north," and so forth.

The results were dramatically different. When women and men were both required to use compass directions, the women made many more errors than the men did, and the women took substantially longer to get to the target than the men. But when the volunteers were given visible landmarks rather than compass directions, the women did much better: the women made fewer errors than the men did and reched the target faster. When the researchers assigned a similar task using a video game, the differences were even more dramatic: women did much better using landmarks rather than compass directions whereas men did better using compass directions instead of landmarks.*

* Deborah Saucier and associates, "Are Sex Differences in Navigation Caused by Sexually Dimorphic Strategies or by Differences in the Ability to Use the Strategies?" Behavioral Neuroscience, 116:403-10, 2002.

... Georg Grön and his colleagues at the University of Ulm in Germany rigged up a nifty video game apparatus... They created virtual reality goggles that allowed volunteers to play a video game while lying in an MRI brain scanner. In the video game the volunteer was trying to find a way out of a maze.

Males outperform females on spatial tasks when the task is framed in Euclidean terms (north, south, east, west); females outperform males when the task is geared to landmarks. Note the large differences between the sexes and the small variation within the sexes (from Saucier et al., 2002).

Their findings: females and males use completely different areas of the brain for the spatial task. Women use the cerebral cortex to solve the maze. You'll recall that the cerebral cortex is the most advanced area of the brain. We use our cerebral cortex for talking, for understanding, indeed for most of our interactions with the outside world. Men, on the other hand, do not use the cerebral cortex during the spatial task. Instead, they use the hippocampus, a phylogenetically primitive area of the brain that is prewired for spatial navigation.*

* Georg Grön, Matthias Riepe, and associates, "Brain Activation during Human Navigation: Gender-Different Neural Networks as Substrate of Performance," Nature neuroscience, 3:404-8, 2000.

The unique function of the hippocampus was first demonstrated in the 1970s by John O'Keefe and Lynn Nadel. These neuroscientists demonstrated that the hippocampus functions as a cognitive map.* They found they could map an animals' environment right onto the animal's hippocampus. When the animal moved in a straight line north to south across a room, the locus of activity in the hippocampus moved "north to south" as well, so to speak, tracking the animal's movement. Research over the subsequent three decades has confirmed O'Keefe and Nadel's hypothesis: The hippocampus is prewired to function as a dedicated microprocesor for spatial geometry, at least in males. O'Keefe and Nadel studied only male laboratory animals.

* John O'Keefe and Lynn Nadel, The Hippocampus as a Cognitive Map (London: Oxford University Press, 1978).

Remarkably, scientists have found sex differences in the performance of laboratory on spatial tasks that are similar to sex differences found in humans. Female laboratory animals use landmark cues while males use Euclidean cues ("compass directions").*

* See, for example, Robin Roof and Donald Stein, "Gender Differences in Morris Water Maze Performance Depend on Task Parameters," Physiology & Behavior, 68:81-86, 1999. See also Tara Perrot-Sinal and associates, "Sex Differences in Performance in the Morris Water Maze and the Effects of Initial NonStationary Hidden Platform Training," Behavioral Neuroscience, 110:1309-20, 1996.

Scientists have even proven that female laboratory animals use the cerebral cortex for spatial tasks while male laboratory animals use the hippocampus* — just as Dr. Grön's group showed to be the case in humans. Again, in view of the sex differences in how female and male laboratory animals navigate mazes, it's hard to argue that similar sex differences in humans are created by human culture. These differences are genetically programmed, not culturally constructed.

* Damage to the frontal cerebral cortex impairs spatial performance in females but not males, whereas damage to hippocampal circuits impairs spatial performance in males but not in females. See Robin Roof and associates, "Gender-Specific Impairment on Morris Water Maze Task after Entorhinal Cortex Lesion," Behavioral and Brain Research, 57:47-51, 1993; and Bryan Kolb and Jan Cioe, "Sex-Related Differences in Cortical Function after Medial Frontal Lesions in Rats," Behavioral Neuroscience, 110:1271-81, 1996.

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Facts, Fiction, and Feelings

In Chapter 2 we discussed brain imaging of emotion in girls and boys. We reviewed research done at Harvard University showing that activity in the brain of the teenage girl associated with negative emotion is localized to the cerebral cortex, the same part of the brain we use to comprehend and generate language. In teenage boys, brain activity associated with negative emotion is localized in the amygdala, a phylogeneticaly primitive nucleus at the base of the brain that makes few direct connections with the cerebral cortex.

That gender difference in brain organization has clear implications for education. In particular, questions of the form "How would you feel if..." don't work well for most boys. That question requires boys to link emotional information in the amygdala with language information in the cerebral cortex. It's like trying to recite poetry and juggle bowling pins at the same time. You have to use two different parts of the brain that don't normally work together. When most teenage boys experience intense feelings, they talk less.

...Most girls prefer fiction: short stories and novels. Boys are more likely to choose nonfiction: descriptions of real events — battles or adventures — or illustrated accounts of the way things work, like spaceships, bombs, or volcanoes.*

* See, for example, A. Simpson, "Fictions and Facts: An Investigation of the Reading Practices of Girls and Boys," English Education, 28:268-79, 1991. An extensive review of this topic may be found in the book edited by Myra Barrs and Sue Pidgeon, Reading the Difference: Gender and Reading in Elementary Classrooms (London: Centre for Language in Primary Education, 1994).

...Boys do like fiction, if it's the right kind of fiction: strong male characters doing unpredictable things. Hemingway, Dostoevsky, and Mark Twain, for starters. ... Critics object that this approach reinforces gender stereotypes. I respond that the most pernicious gender stereotype is the one that says boys don't like to read.

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Oxytocin, Testosterone, and Rape

What's the relation between love and sex? The neurochemical basis for both love and sex in females involves the hormone oxytocin, the same hormone released when a mother breast-feeds her newborn baby. "Oxytocin's effects on both [romantic] attachment and sexual behavior are estrogen dependent and gender specific," observes neuropsychologist Lisa Diamond, adding that there appear to be "more extensive oxytocin circuits in female than male brains."*

* Lisa Diamond, "What Does Sexual Orientation Orient? A Biobehavioral Model Distinguishing Romantic Love and Sexual Desire", Psychological Review, 110:173-92, 2003.

In males on the other hand the hormone underlying sexual attraction is not oxytocin but testosterone, the same hormone that mediates the aggressive drive.

The first brain-imaging study comparing brain areas activated in women and men during sexual arousal was published in 2002. Doctors found fundamental differences between females and males. The men showed lots of activation at the base of the brain, in the thalamus and especially the hypothalamus, while the women showed proportionally more activity up in the cerebral cortex.*

* Sherif Karama and associates, "Areas of Brain Activation in Males and Females during Viewing of Erotic Film Excerpts," Human Brain Mapping, 16:1-13, 2002.

Another study, published in 2004 by researchers at Emory University, showed that sexually aroused men show more activity in the base of the brain compared to women, even when the women report feeling more sexually aroused.*

* Stephan Hamann, Rebecca Herman, Carla Nolan, and Kim Wallen, "Men and Women Differ in Amydala Response to Visual Sexual Stimuli," Nature neuroscience, 7:411-16, 2004.

...it suggests that the sexual experience in women is "happening" more up in the cerebral cortex and is therefore more connected with the rest of what's going on in their mind. The sexual experience in men is less connected with the cortex, less connected with the outside world.

...[Anne] Peplau [UCLA psychologist studying the difference between female and male experiences of sexual desire] has concluded that "women's sexuality tends to be strongly linked to a close relationship. For women, an important goal of sex is intimacy; the best context for pleasurable sex is a committed relationship. This is less true for men."*

* Letitia Anne Peplau, "Human Sexuality: How Do Men and Women Differ?" Current Directions in Psychological Science, 12:37-44, 2003.

...For many boys, as for some men, the sexual urge is closely tied to aggression. That's not surprising when you remember that both the sexual urge and the aggressive urge, in males, are mediated by testosterone. In one carefully designed study, a surprisingly high percentage — 35 percent — of "normal" college men said that they not only fantasized about rape, they would actually rape a woman if they had the chance and they were sure they wouldn't be caught.*

* Neil Malamuth, "Rape Proclivity among Males," Journal of Social Issues, 37: 138-57, 1981.

In another study of "normal" college men, more than half of the men said they would actually rape a woman if they were assured of not being punished.*

* Neil Malamuth, "Testing Hypotheses Regarding Rape: Exposure to Sexual Violence, Sex Differences, and the 'Normality' of Rapists," Journal of Research in Personality, 14:121-37, 1980.

These men are not Neanderthal cavement. In fact, researchers have found no association between the liberality of a man's gender-role beliefs and the likelihood that he finds rape sexually appealing. Some men who are strongly in favor of equal rights for women, who approve of women in leadership roles, and so on also say that they would rape a woman if they had the opportunity. Nor is there any association, positive or negative, between a man's intelligence and the likelihood that he will be sexually aroused by depictions of rape.*

* Sarah Murnen, Carrie Wright, and Gretchen Kaluzny, "A Meta-Analytic Review of the Research that Relates Masculine Ideology to Sexual Aggression," Sex Roles, 46:359-75, 2002.

...As psychologist Roy Baumeister recently wrote, "Male desire aims at the sexual activity itself, whereas female desire aims beyond it toward other outcomes and consequences."*

* Roy Baumeister, "Gender Differences in Erotic Plasticity: The Female Sex Drive as Socially Flexible and Responsive," Psychological Bulletin, 126:247-74, 2000.

...In one major study, girls didn't even list sexual arousal as a reason for having sex.*

* Stephen Eyre and Susan Millstein, "What Leads to Sex? Adolescent Preferred Partners and Reasons for Sex," Journal of Research on Adolescence, 9:277-307, 1999.

Teenage girls have sex for other reasons. Girls may hope that having sex will earn them points in the popularity contest, or they may just want to please the boy they happen to be hooking up with ['hooking up with' in this book means, 'have oral sex with' rather than 'go on a date with' or even 'have penetrative sexual intercourse with'], or they may feel pressured either by the boy or by other girls who are having sex. Oprah Winfrey recently devoted a session of her talk show to this topic. She invited several teen girls on to the show to describe why they began having sex so young. One girl, Shana, began having sex at age thirteen. By age sixteen, when she appeared on the show, she had had intercourse with seven different boys.

Oprah Winfrey: When you started having sex, at 13, was it to fit in or was it just because you wanted to have sex?
Shana: It was definitely to fit in, because, I just figured, you know, this is what everyone's doing and I was getting ready to go into high school and I'm like, "this will make me popular".
Oprah: And has it?
Shana: No, it... I paid a big price for it. I paid a huge price.
Oprah: What is the huge price you've paid.
Shana: Just socially. Luckily, I didn't get pregnant or anything like that, but emotionally I have scars that are never going to go away. After he leaves, you know, you give him what he wants, then you feel, like, horrible.
Oprah: So if you do that a couple of times, and you know if you do it again, it's going to feel the same, why do you keep doing it?
Shana: I really can't answer that. Honestly, when I get an answer, I'll tell you.*

* The show was broadcast on October 2, 2003, rebroadcast on March 18, 2004. Transcript obtained through Lexis-Nexis.

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Hearing the Difference

Dennis McFadden and Edward Pasanen at the University of Texas at Austin studied the hearing of gay men, using the same technology Professor Cassidy used with newborn babies to demonstrate gender differences in hearing sensitivities. But McFadden and Pasanen did not find any evidence that gay men had better hearing than straight men. All the men — regardless of their sexual orientation — had less sensitive hearing than any of the women had.* In fact, the gay men actually had less sensitive hearing than the straight men!

* Dennis McFadden and Edward G. Pasanen, "Spontaneous Otoacoustic Emissions in Heterosexuals, Homosexuals, and Bisexuals," Journal of the Acoustic Society of America, 105:2403-13, 1999. See also an earlier article by McFadden and Pasanen: "Comparison of the Auditory Systems of Heterosexuals and Homosexuals: Click-Evoked Otoacoustic Emissions," Proceedings of the National Academy of Sciences, 95(5):2709-13, 1998.

Dennis McFadden has written recently about the apparent "hypermasculinization" of the hearing system in gay men.*

* Dennis McFadden, "Masculinization Effects in the Auditory System," Archives of Sexual Behavior, 31:99-111, 2002.

McFadden's team has repeatedly found that women have significantly better hearing than straight men, and straight men have somewhat better hearing than gay men. Far from being intermediate between straight men and straight women, gay men appear to be somewhat more "masculine" than straight men — at least as far as the auditory system is concerned. Hearing isn't the only realm where gay men appear to be "hypermasculine" compared with straight men. On certain skeletal measures, gay men appear to be hypermasculine compared with straight men.*

* S. J. Robinson and J. T. Manning, "The Ratio of 2nd to 4th Digit Length and Male Homosexuality," Evolution and Human Behavior, 21:333-45, 2000.

And on the most salient "anatomic measure" — whose penis is bigger? — gay men are hypermasculine. That's right: gay men have bigger penises, on average, than straight men do.*

* A. F. Bogaert and S. Hershberger, "The Relation between Sexual Orientation and Penile Size," Archives of Sexual Behavior, 28:213-21, 1999.

...William Masters and Virginia Johnston, in their exhaustive study of homosexuality, found that many gay men are "hypermasculine" in the sense that they often engage in sex for its own sake rather than in the context of a relationship.*

* William Masters and Virginia Johnston, Homosexuality in Perspective (Philadelphia: Lippincott, Williams & Wilkins, 1979).

Masters and Johnston interviewed hundreds of gay men over many years. Many gay men told them about having dozens or even hundreds of sex partners, sometimes more than one partner in a single evening. Many gay men described having anonymous sex with men they didn't even know. Lesbian women, by contrast almost never have sex with women they don't know.

...While there may be some correlation between gender-anomalous behavior and homosexuality, I suspect that the correlation is low. Many gay men are indistinguishable from straight men in all the dimensions we've discussed in the previous chapters: they like playing competitive sports, they don't listen very well, they're more interested in having sex than in talking about relationships, and so forth.

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Take a Walk on the Wild Side

...Dick Swaab, Frank Kruijver, and their associates at the Netherlands Institute for Brain Research studied the brains of transsexuals. They wanted to see whether men who felt that they were "really" women had brains that appeared in any respect to be like women's brains. In some of the most important areas of the brain, the areas that translate sexual feelings into endocrine responses, Swaab and his team found that the brain of a transsexual man resembles the brain of a woman, even if the man has not yet received any treatments with femininizing hormones.*

* Frank Kruijver, Dick Swaab, and associates, "Male-to-Female Transsexuals Have Female Neuron Numbers in a Limbic Nucleus," Journal of Clinical Endocrinology and Metabolism, 85:2034-41, 2000.

...Gay men are comfortable with their masculine identity....Transgender men — men who dress and act as females — are different. They are not comfortable with a masculine identity.

Lesbian: Born or Made?

...Debra Peters and Peggy Cantrell interviewed lesbian and heterosexual women, with special attention paid to sexual experiences in childhood and adolescence. Peters and Cantrell didn't find any difference between lesbian and straight women in terms of childhood or adolescent sexual experience. They concluded that female sexual orientation cannot be explained in terms of early sexual trauma or negative heterosexual experiences.*

* Debra Peters and Peggy Cantrell, "Factors Distinguishing Samples of Lesbian and Heterosexual Women," Journal of Homosexuality, 21:1-15, 1991.

...Most people, and even most psychologists, have assumed that romantic love usually arises in the context of sexual desire. In fact, for most of the twentieth century, psychologists beleved that romantic love was little more than a sublimation of the urge to have sex. But Diamond and many other psychologists, in the past fifteen years especially, have questioned that assumption. Recent work suggests that romantic love derives from different biobehavioral sources than sexual desire — especially in women. Psychologists have noticed that romantic love and long-term romantic relationships share many characteristics with the relationship between parent and child.*

* See, for example, Cindy Hazan and Phillip Shaver, "Romantic Love Conceptualized as an Attachment Process," Journal of Personality and Social Psychology, 52:511-24, 1987; and Cindy Hazan and Phillip Shaver, "Love and Work: An Attachment-Theoretical Perspective," Journal of Personality and Social Psychology, 59:270-80, 1990.

... "What does sexual orientation orient?" [Lisa] Diamond asks.* She suggests that maybe our rigid categories of gay versus straight get a little blurred when talking about women. Few straight men in our culture have close, physically intimate relationships with other men — although Diamond informs us that men in locales such as Melanesia, Guatemala, and Samoa often do. ... Perhaps what's genetically coded — in women — is the possibility, the willingness to engage in lesbian sexual activity, if the right woman comes along. The implication of Diamond's work is that many women who consider themselves heterosexual might actually be bisexual, if the right woman came into their lives. And for that matter, some women who consider themselves lesbian might also be bisexual, if the right man came along.

* Lisa Diamond, "Was It a Phase? Young Women's Relinquishment of Lesbian/Bisexual Identities over a 5-Year Period," Journal of Personality and Social Psychology, 84:352-64, 2003.

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The Anomalous Male

...There's growing evidence that a small subset of boys (and men) have female-typical physiology. Different researchers have used different terms for these boys, and different criteria to define them, so it's hard to consolidate the findings across the different studies. But there's reason to believe that these boys have a lot in common.

Harvard professor Jerome Kagan has spent many years studying these boys, whom I'll call "anomalous males".*

* Kagan calls these boys "highly reactive," but that term can be confusing because in some circumstances these boys are shy, passive, and withdrawn while other boys are outgoing and assertive.

Kagan began by analyzing baby boys who were only a few weeks old. He would simply touch the babies gently and see how they responded. Most baby boys don't mind being touched, but a few react intensely. When touched those boys begin crying and thrashing their arms and legs. Kagan followed these boys for years, from infancy through childhood and into adolescence (he's been doing this work for forty years now!). He found, first of all, that about half of these boys never outgrow their dislike of novelty. As teenagers, these boys shy away from strangers and new adventures, just as they did when they were babies.

Even more striking, Kagan found that these boys have other characteristics in common. Specifically, these "anomalous males" are:

• More likely to have allergies, asthma, or eczema than other boys;*

  * Jerome Kagan and associates, "Temperament and Allergic Symptoms," Psychosomatic Medicine, 53:332-40, 1991. See also Iris Bell, Mary Jasnoski, Jerome Kagan, and David King, "Is Allergic Rhinitis More Frequent in Young Adults with Extreme Shyness?" Psychosomatic Medicine, 52:517-25, 1990. See also Anne-Charlotte Lilljeqvist, Dag Smørvik, and Asbjørn Faleide, "Temperamental Differenes between Healthy, Asthmatic, and Allergic Children before Onset of Illnes," Journal of Genetic Psychology, 163:219-27, 2002.

• More likely to have a regular resting heart rate* whereas most boys have heart rates with lots of beat-to-beat variability: the heart speeds up when they breathe in and slows down when they breathe out;

  * Jerome Kagan, Galen's Prophecy: Temperament in Human Nature (New York: Basic Books, 1994), chapter 5, "The Physiology of Inhibited and Uninhibited Children," and chapter 7, "Infant Reactivity and Sympathetic Physiology".

• More likely to have a narrow face, a facial width-to-height ratio less than 0.55;*

  * Doreen Arcus and Jerome Kagan, "Temperament and Craniofacial Variation in the First Two Years," Child Development, 66:1529-40, 1995.

• Unwilling to engage in rough-and-tumble play.*

  * Jerome Kagan, Galen's Prophecy: Temperament in Human Nature (New York: Basic Books, 1994), especially chapter 6, "Early Predictors of the Two Types."

Sociologist Patricia Cayo Sexton also described such boys. She found other characteristics in addition to those identified by Kagan. Accordgin to Sexton, these boys also typically:

• are precocious, particularly with respect to language skills;
• are often loners with few close friends;
• may enjoy sports, but typically prefer noncontact sports such as tennis, track, bowling, and golf.*

* Patricia Cayo Sexton, The Femininized Male: Classrooms, White Collars, and the Decline of Manliness (New York: Random House, 1969).

...The "geek" becomes a loner, withdrawn and resentful, finding solace in his books and his fantasies.... Baby boys who are fearful and withdrawn become more so if their parents shield them from minor stresses and injuries.... If a boy is fearful and timid and "highly reactive" in early infancy but his parents believe in firm discipline, the odds are good that by two years of age the boy will have outgrown those tendencies. In fact, in Kagan's study, every single boy who did outgrow timid tendencies in infancy had a parent who believed in the importance of discipline. Conversely, in Kagan's study, if the parent of a timid child believed in "being sensitive to a child's needs" and did not place a high value on obedience, in every case the timid baby boy grew up to be a timid, fearful child.*

* Jerome Kagan, Galen's Prophecy: Temperament in Human Nature (New York: Basic Books, 1994), chapter 6, "Early Predictors of the Two Types," pp. 204-7.

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Differences [anomalous females]

...the most important contribution has been made by sociologist Patricia Cayo Sexton, who found that while the anomalous boys

...were noncompetitive, non-athletic, and fearful, the [anomalous] girls were fearless, independent, and competitive. Girls who were bold and daring from ages ten to fourteen became the most intellectual women as adults.... Among girls, strangely, high intelligence was associated with both greater masculinity and greater femininity. Bright girls were more likely than other girls to be dominant and striving and at the same time have more feminine qualities.*

* Sexton, The Femininized Male, p. 93.

...Anomalous girls have an advantage in school and in life; their social horizons are likely to be broader than those of other girls. Anomalous boys have an advantage in school but they pay a steep price for that advantage, and their social horizons are likely to be narrower than those of other boys.

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...Teachers at an all-boys elementary school in Chicago told me last month that the performance of their boys improved "500 percent" after teachers removed the chairs from the classroom. "Young boys just learn better when they stand up. When they sit down, their brains shut off," one teacher told me.