50 Psychology Classics by Tom Butler-Bowdon Page B

average every 52 seconds, while for women it is once a day. As the part of the brain where sexual thought and behavior is generated is two and a half times larger in the male, this is not surprising.
The baby female brain
    Until they are eight weeks old, the brains of male and female foetuses look the same—“female is nature’s default setting,” Brizendine observes. At about eight weeks, a male foetus’s brain is flooded with testosterone, which kills off the cells relating to communication and helps to grow cells relating to sex and aggression. Biochemically, the male brain is then significantly different from a female one, and by the time the first half of the pregnancy is over, the differences between male and female brains are mostly set.
    A female baby comes into the world wired to notice faces and hear vocal tones better. In the first three months of her life a baby girl’s abilities at “mutual gazing” and eye contact grow by 400 percent. In the same period, these abilities do not grow at all in boys.
    It is well known that girls usually begin speaking some time before boys, thanks to the better-developed language circuitry of their brains. This continues into adulthood, with women speaking on average 20,000 words a day and men averaging only around 7,000. (As Brizendine remarks, this higher ability “wasn’t always appreciated,” with some cultures locking up a woman or putting a clamp on her tongue to stop the chatter.)
    One other important difference in infancy is that baby girls are more sensitive to the state of their mother’s nervous system. It is important that infant girls do not have mothers who are stressed out, as when the girl grows up to have children of her own her ability to be nurturing will be reduced. However, armed with this knowledge, it is possible to break the cycle of mother–infant stress.
The teen girl’s brain
    At puberty, a girl’s thinking and behavior change according to the fluctuating levels of estrogen (one of the “feel-good” hormones), progesterone (“the brain’s valium”), and cortisol (the stress hormone) in her brain. Other important hormones produced are oxytocin (which makes us want to bond, love, and connect with others) and dopamine (which stimulates the brain’s pleasure centers).
    The effect of these chemicals is to give a teenage girl a great need for and pleasure in gossiping, shopping, exchanging secrets, and experimenting with clothing and hair styles—anything that involves connecting and communicating. Teenage girls are always on the phone because they actually
need
to communicate to reduce their stress levels. Their squeals of delight at seeing friends, and the corresponding panic at being grounded, are also part of these changes. The dopamine and oxytocin rush that girls experience is “the biggest, fattest neurological reward you can get outside of an orgasm,” Brizendine remarks.
    Why exactly does the loss of a friendship feel so catastrophic to a teen girl, and why is her social group so important to her? Physiologically she is reaching the optimum age for child rearing, and in evolutionary terms she knows that a close-knit group is good protection, since if she has a small child with her she is not able to attack or run away as a man can. (The concept of “flight or flight” in response to danger is an observation of men rather than women.) Close social bonds actually alter the female brain in a highly positive way, so that any loss of those relationships triggers a hormonal change that strengthens the feelings of abandonment or loss. The intensity of female pubescent friendships therefore also has a biochemical basis.
    The teenage girl’s confidence and ability to deal with stress also change according to the time of the month, and Brizendine has treated many “problem” girls who experience higher than average hormonal changes. The most brash