pressures." For more on cellular and genetic differences in the male and female brain, see Reinius 2008 and Arnold 2009b.
and the fix-it-fast emotional brain : Coates 2009 found that testosterone sets the male brain up for faster visuomotor scanning, faster physical reflexes, and more risky behavior.
Male and female brains : Penaloza 2009. The authors say, "Sex of the cell dictates its response." Malorni 2007 even found reduction-oxidation differences between male and female cells.
for later amplification by hormones : For more on sex hormones, genes, and the brain, see Arnold 2009c and Neufang 2009.
differences between women and men : For good reviews on sex differences in the brain, see Becker 2008b, McCarthy 2009, and Proverbio 2009.
role in shaping and reshaping our brains : It is important to note that biological predispositions can be shifted over time through experience and that existing dispositions can be mitigated or even overridden by situational demands in both men and women. For both males and females, upbringing, experience, and the environment can make long-lasting biological and behavioral impacts via epigenetic changes to our DNA. See Merzenich 1983 for early work on brain reorganization in response to changed circumstances. For more on changes in brain architecture with experience, see Kozorovitskiy 2005, and on environmental experience and epigenetic effects, see Meaney 2005, McCarthy 2009, and Murray 2009.
ONE: THE BOY BRAIN
wired into the male brain : Coates 2009 found prenatal androgens promote increased risky behavior, movement, and physical reflexes. For more on the male brain, see Arnold 2009c, Van Nas 2009, Chura, 2010, Wu 2009, Field 2008 and 1997, Baron-Cohen 2003 and 2009, Pfaff 2002, Holden 2004, Eme 2007, and Becker 2008b; see also De Vries 2008 and McCarthy 2009a. In humans and most other mammals, a gene on the Y chromosome, the SRY gene, confers maleness. Studies suggest that the SRY gene directly affects the biochemical properties of the dopaminergic neurons of the nigrostriatal system and the specific motor behaviors they control. This means that a direct male-specific effect on the brain is caused by a gene encoded only in the male genome.
their genes and sex hormones: Arnold 2009a.
on and off different genes: Arnold 2004 and Wu 2009. play at fighting off enemies : Auyeung 2009b says, "... our data are the first documentation that androgen exposure prenatally relates to sexually differentiated play behavior in boys and in girls." For more on genes and hormones in boys and girls, see Wu 2009 and Berenbaum 2008.
seemed to find them fascinating : Connellan 2000. For more on gender differences in newborns, see Ashwin 2009, Baron-Cohen 2009, Auyeung 2009, and Gilmore 2007.
stereotypical male behaviors like roughhousing: Wang P. 2009.
in different activities than girls: Maccoby 1998 and Byrd-Craven 2007.
they begin in the brain: Wu 2009 and Reinius 2008.
upset, they're harder to soothe: Weinberg 1999.
when she was a baby: Leeb 2004. without as much mutual gazing : Leeb 2004. For more on maternal attachment and bonding, see Young 2008, Baron-Cohen 2003, Carter 1998, Nichools 1996, and Bowlby 1980.
objects from the get-go: Connellan 2000. For more on sex differences, see Hampson 2008 and Quinn 2008. "contact much more than girls" : By six months old, boys gaze-avert more frequently than girls. Whether they are straining to look at something else that caught their eyes or away from the face is not entirely known. For further reading, see Byrd-Craven 2007, Knickmeyer 2006, Bayliss 2005, and Hittelman 1979. For more on autism and the male brain, see Baron-Cohen 2009, who says that his results suggest that prenatal exposure to high levels of testosterone influences some autistic traits and thus hormonal factors may be involved in vulnerability to autism. Ashwin 2006 says that, for still unknown reasons, Asperger's and autism affect four to ten times more boys than girls. Autism and Asperger's syndrome (AS) are genetic neurodevelopmental conditions characterized by social deficits, abnormal face processing, and amygdala dysfunction that are more common in boys.
"airplanes and other moving objects" : Moore 2008. For an overview of moving objects and movement in brain circuitry in boys and girls, see Hampson 2008 and Field 2008.
weeks after he was conceived : See Field 2008 for more on the development of sex differences in brain circuits for movement.
circuits that control male behaviors : For a review of the formation of male brain circuits, see Wu 2009, Gagnidze 2009, Becker 2008b, Eme 2007, Breedlove 1983, and Archer 2006. Note: a failure of masculinization is called pseudohermaphroditism. See Tsunematsu 2008 on vasopressin increasing locomotion in males.
make others wither and die : For more on hormones causing death or acting as growth factors, see Wu 2009 and Kimura 2008. For more on sex differences and brain development, see Penaloza 2009, Swaab 1985 and 2009, Ehrlich 2006, and Zuloaga 2008.
defeminized David's brain and body: Wang P. 2009. Wang and colleagues found that the foundations for the observed MIS-dependent increased movement and exploratory behavior in males is laid down in the brain circuits during fetal life. Wang P. 2005 found that in males, Mullerian inhibiting substance is secreted by the fetal testes and causes the death of the Mullerian ducts in order to prevent the growth and development of female reproductive organs in male bodies. Note: MIS is also called "anti-Mullerian substance."
off the female reproductive organs : Normal development of the male brain involves two distinct processes, masculinization and defeminization. They occur during critical periods of Masculinization allows behavior in adulthood, and defeminization eliminates or suppresses the expression of female sex behavior in adulthood. Once inside the fetal brain, much of the testosterone is actually converted by the enzyme aromatase into estrogen. Ironically, then, it is the estrogen that helps masculinize and defeminize the male brain, working in concert with MIS. For more on sex and the brain, see Wu 2009, Wang P. 2009, and Becker 2008b. brain sexual differentiation.
the expression of male sex spatial skills, and rough play : Wang P. 2009 found that male mice lacking MIS exhibit feminization of their spinal motor neurons and of their exploratory play behavior. They hypothesize that, along with testosterone, MIS may be a regulator of the sex-linked behavioral biases in the nervous system and brain toward more movement, pursuit, rough play, and exploration in males.
not develop male-typical exploratory behavior: For further reading, see Wang P. 2009. effects of testosterone or MIS : Fynn-Thompson 2003. MIS is not present in the female embryo but is induced in females only after birth. For a review of the association between testosterone and aggression that occurs in boys, but not girls, during childhood, see Becker 2008b, Eme 2009, and Archer 2006.
to appreciate her son's maleness : Diamond 2006 found that the boy's sense of masculinity early on is shaped by factors like the mother's recognition and affirmation of her son's maleness, the role of the involved or uninvolved father, and the nature of the parental relationship.
testosterone as in an adult man: For more on the infantile, or perinatal, masculinization of adult sex behavior, see Wu 2009, Wudy 1999, and Wright 2008.
exploratory behavior and rough play : Wang P. 2009 found that boys older than one year have very low levels of testosterone, but they continue to have high MIS until the onset of puberty.
when she's angry or afraid : Peltola 2009 found that an enhanced sensitivity to facial signals of threat emerges between five and seven months of age. This may reflect functional development of the brain mechanisms involved in processing of emotionally significant stimuli. Grossman 2007 found that seven-month-olds integrate emotional information across modalities and recognize common emotions in the face and voice. For more on brain processing of words, faces, and emotions, see Schacht 2009. For more on infant gazing at objects and adult emotional expressions, see Hoehl 2008.
and can easily ignore them : Rosen 1992. They found that by the age of twelve months, the intensity of the mothers' fear signals increased and were more intense toward boys, but boys ignored them more. For overview, see Maccoby 1
998, Mumme 1996, and Becker 2008b.
For girls, the opposite happens : Researchers find that by one year of age, girls are more socially oriented toward their mothers than are boys; see Wasserman 1985, Maccoby 1998, and Byrd-Craven 2007. They are more wary than boys, according to Jacklin 1983 and Gunnar 1984. Zahn-Waxler 1992 found that infant boys cry less than girls in response to hearing the distressed cries of another baby. By twelve to twenty months, boys are less interested in seeking out and inquiring about the distress of someone who is hurt; for overview see Byrd-Craven 2007 and Leppanen 2001. Even as children get older, studies show that what is important to girls and boys, and meaningful to pay attention to, is different in terms of nonverbal emotional communications. For overview of sex-difference brain research, see Becker 2008b.
of warning on Jessica's face: For boys ignoring their mothers more, see Rosen 1992 and Maccoby 1998. in the room with them : Rosen 1992 in "An experimental investigation of infant social referencing: Mothers' messages and gender differences." For more on gender differences in brain and behavior, see Maccoby 1998, Byrd-Craven 2007, Eme 2007, and Becker 2008b.
at the risk of punishment: Cialdini 1998a.
sons as to their daughters: Maccoby 1998. take risks and break rules : Maccoby 1998. For more on sex differences in play behavior, also see Minton 1971 and Berenbaum 2008.
many mothers wince, including me : A mother's reaction to a boy's genitals may have a bigger effect than is commonly acknowledged, even in other mammals. Wallen 2009 found that in primates, maternal increased responsiveness to boys is best accounted for by the mother's reactions to the penis of her offspring.
are "girl colors" like pink : Feiring 1987 and Fagot 1985. For overview of girls' and boys' toys, see Pasterski 2005 and Hassett 2008.
destroying, and seeking new thrills : Maccoby 1998. For more on the brain and boys' thrills, see Byrd-Craven 2007, Manson 2008, and Becker 2009.
more interested in cooperative games : Berenbaum 2008. McClure 2000 found that during the late preschool and early school years, girls tend increasingly to play in small, intimate groups, whereas boys more typically form large, hierarchically organized groups focused on competition. For overview of children's gender cultures, see Sheldon 1996 and Maccoby 1998. Charlesworth 1987 found that girls got greater access to the toys by verbal bargaining rather than through physical pushing like the boys.
while girls spend only 35 percent: Lever 1976.
twenty times more often than boys: Maccoby 1998.
to use as toy guns: Maccoby 1998.
and used beans as bullets: Sheldon 1996 and Maccoby 1998. is being called a girl : Blaise 2005 found that in early childhood classrooms, being called a "girl" is considered by boys to be one of the most shameful, polluting, and degrading insults of all.
like girls' games and toys: Feiring 1987 found that boys reject other boys who like girls' games and toys. and must therefore be avoided : Feiring 1987 says that even in the years before exclusionary same-sex play, groups evolved in several studies of children 24 to 36 months old, where boys were able to identify their own sex's toys and activities better than girls did. For more on self-imposed sex segregation, see Pasterski 2005 and Maccoby 1998.
doll and the wheeled toy: Hassett 2008.
toys more than other girls: Servin 2003. muscle groups when they play : Hassett 2008. Eaton 1986 says that boys' toys reflect their preference for using big muscle groups when they play, and sports reflect boys' preference for gross motor behavior and propulsion--of themselves and objects--from infancy onward. For overview of gendered play, see Berenbaum 2008.
like car and plane crashes: Iijima 2001 found that drawings by boys and girls showed clear sex differences. Girls tended to draw human figures, mainly girls and women, as well as flowers and butterflies. Girls used bright colors, such as red, orange, and yellow, and their subjects tend to be peaceful and arranged in a row on the ground. Boys, however, preferred to draw more technical objects, weapons, and fighting, and means of transport, such as cars, trains, and airplanes, in bird's-eye-view compositions and in dark, cool colors, such as blue. See also Tuman 1999 on children's gendered art.
is to determine social ranking: Archer 2006.
seen the humor in it: DiPietro 1981.
break his sense of self: Eaton 1986. "have their kind of fun": Maccoby 1998. form of a dopamine rush : Becker 2008b says that sex differences in the regulation of dopamine, DA, in the brain's ascending mesolimbic projections may underlie sex differences in motivation and result in the expression of differences in motivated behaviors between boys and girls, men and women.
and children self-impose sex segregation: Maccoby 1998. mock-fight frequently; girls do not : Maccoby 1998. Also see Eme 2007, Flanders 2009, and Becker 2008a on sex differences in motivation.
if they placed at all: Grant 1985.
the girls did not show: Feiring 1987.
establish physical and social dominance: Eme 2007 and Becker 2008b.
"most important thing to be good at": Boulton 1996.
of the six-month study: Edelman 1973 and Weisfeld 1987.
levels than did the other boys: Weisfeld 1987.
the hierarchy at age fifteen: Weisfeld 1987. of learning boys do differently : See Benenson 2003 and 2009 for more on boys' choosing to ally with stronger peers, and for more on girls' need to maintain conflict-free friendships.
Wii had become their favorite toy : Hoeft 2008 found that these gender differences may help explain why males are more attracted to and more likely to become hooked on video games than females. For more on computer game playing and improving spatial skills, see De Lisi 2002, Feng 2007, Ginn 2005, Olson 2007, Heil 2008, and Wolbers 2006.
brain linked to dopamine production : Hoeft 2008 found that males showed greater activation compared to females in the mesocorticolimbic areas--which may account reward prediction, learning reward values, and cognitive state during computer video games. For more on the male brain and dopamine, see Lavranos 2006 and Becker 2008b.
system--dopamine brain
for gender differences in
even if he isn't moving: Grafton 1997. control his own jumping muscles : Orzhekhovskaya 2005 found males have more activity in neurons in the motor areas of the brain. See Cherney 2008 on "Mom let me play more video games."
girls do in this way: For more on the gender difference in movement biology, see Field 2008. and express themselves as well : Ehrlich 2006 found that the boys frequently gestured about movement even when they did not talk about it; they found that gesture (but not talk) was associated with successful performance on spatial transformation tasks. Boys used their hands and body to convey an understanding of the spatial transformation task not found in their spoken explanations. And for more on girls catching up to boys on visuospatial tasks by practicing video games, see Feng 2007, who found that playing an action video game can virtually attention disparity in mental rotation ability. For more on sex differences in movement and the brain, see Field 2008, Hampson 2008, Spence 2009, and Becker 2009. eliminate the gender difference in spatial
and simultaneously decrease the gender the meaning of that word: For more on embodied cognition, see Siakaluk 2008, Thomas 2009, and DeCaro 2009. See Ullman 2008 for more on sex differences in the neurocognition of language.
their advantage at spatial manipulation: Keller 2009 found evidence for gender differences in the functional and structural organization of the right-hemisphere brain areas involved in mathematical cognition. Spence 2009 found that women can catch up to men on spatial skills by practicing single-shooter video games.
object in their mind's eyes : Hahn 2009. Also see Koscik 2009, Hampson 2008, Hugdahl 2006, and Clements-Stephens 2009 for more on mental rotation.
differences between boys and girls : Scientists agree that there are genuine between-sex differences in cerebral activation patterns during mental rotation activities even when performances are similar and that the sexes use different strategies in solving mental rotation tasks
. Clearly males and females can both generate male-and female-typical behaviors, but their brains use different strategies to do so. For structural differences in the brain related to visuospatial abilities and language, see Hanggi 2009, Shaywitz 1995, Jordan 2002, Piefke 2005, Neuhaus 2009, and Hampson 2008.
them to grasp its three-dimensionality : Scientists believe that sex effects reflect a difference in strategy, with females mentally rotating the polygons in an analytic, piecemeal fashion and males using a holistic mode of mental rotation. See Yu 2009, Heil 2008, Schoning 2009, and Hooven 2004 on testosterone and mental rotation.
explanation without using any words : Ehrlich 2006 found that before training, the response for the boys was to produce answers in movement and gesture on all eight problems; however, the response for the girls was to produce answers in movement and gesture on zero of the eight problems. After "gesture-training," the girls did much better. For further reading on gesturing and math teaching, see Goldin-Meadow 2009. For more on movement and math, see Broaders 2007, Terlecki 2008, Thomas 2009, Lorey 2009, Thakkar 2009, and Munzert 2009.
without intervention, use them differently : See Hampson 2008 for more on sex differences in visuospatial cognition and learning. For more studies that found sex differences in brain circuits used for mental rotation, see Nuttall 2005, Casey 2001, Jordan 2002, Peters 2006, Quaiser-Pohl 2002, and Parsons 2004.
amounts of the pheromone androstenedione : Hummel 2005. And see Larsen 2003 on the dramatic hormonal changes that begin before the body changes of puberty.