We all start out as female - at least our brains do. Then, just eight weeks after conception, the male foetus starts to experience a huge surge of testosterone. It gradually changes his brain, shrinking the communication centre, reducing the hearing cortex and growing more cells in the sex and aggression centres. So that's why men don't listen.
In terms of sheer size, the male brain is bigger. About 9 per cent bigger, even after correcting for body size. In the 19th century, scientists took this to mean that women had less mental capacity than men. But women and men have the same number of brain cells - they're just packed more densely into the skull. Neater, you see.
Such illuminating facts come thick and fast in neuro-psychiatrist Louann Brizendine's The Female Brain, the American bestseller that has now been published in the UK. It reveals how, almost from birth, girls are more interested in looking at faces than boys are. They are also more responsive to their mother's moods - especially to distress.
In fact, modern medical research appears to back up all the common notions about the differences between the sexes - that women talk more, have greater intuition, tend to avoid conflict and are more prone to depression - and to show they are based on physiological differences caused by hormones.
"The female brain," says Dr Brizendine, "is so deeply affected by hormones that their influence can be said to create a woman's reality." Dr Brizendine has wide knowledge and experience to draw on: she studied at Berkeley and Yale before undertaking research at University College London and Harvard and, in 1994, she set up the Women's Mood and Hormone Clinic at the San Francisco Medical School.
Her conclusions, based on insights from modern genetics and non-invasive brain-imaging technology, are illustrated by tales from her clinic. This is a scientific version of Men are from Mars, Women are from Venus, and equally entertaining.
Take her dramatic explanation of the reason why the good daughter suddenly turns into a moody, temperamental and resistant teenager: "Mom, I so totally can't go to school. I just found out Brian likes me and I have a huge zit and no concealer. OhmyGod! How can you even think I'll go?"
Her pituitary gland has "sprung to life as the chemical brakes are taken off her pulsing hypothalamic cells," writes Dr Brizendine. The teenage girl is obsessed with relationships, while her male counterpart worries about challenges to his authority.
Many women find biological comfort in one another's company, and language is the glue that connects them. When Dr Brizendine once asked a class of 15-year-olds what the boys would like to ask the girls, and vice versa, the boys asked: "Why do girls go to the bathroom together?" They assumed some sexual reason, but the girls replied: "It's the only private place at school we can go to talk." This sharing of secrets activates the pleasure centres in the female brain.
How should teachers deal with the effects of hormonal surges? On a day of pre-menstrual tension, a poor grade can produce what Dr Brizendine calls "meltdown".
Her advice to parents of teens is to stay calm and ignore much of what they say. As a teacher, presumably you just have to hope that not too many of your teenage girls reach the same point on the hormonal roller-coaster at once.
Does all this suggest that girls and boys are best educated separately, especially in their teenage years? Pat Langham, president of the Girls'
Schools Association, certainly thinks so. She says: "We specialise in girls. We know how their brains work, how to motivate them, how to support them. Now, to promote true gender equality in the classroom, teachers need to look at more boy-friendly education for boys. Their motivation is different; their concentration is different."
To discover the full extent and reasons for those differences, we will have to wait for Dr Brizendine's next blockbuster - about the male brain
The Female Brain by Louann Brizendine MD (Bantam Press, pound;10.99)
1 Anterior cingulate cortex (ACC): Weighs options, makes decisions. The worry centre - larger in women than men.
2 Prefrontal cortex (PFC): Queen of emotions. Puts the brakes on the amygdala (see below). Larger and matures one to two years earlier in women.
3 Insula: Centre that processes gut feelings. Larger and more active in women.
4 Hypothalamus: Conductor of hormonal symphony; kicks gonads into gear. Starts pumping earlier in life in women.
5 Amygdala: The wild beast within; the instinctual core, tamed only by the PFC. Larger in men.
6 Pituitary gland: Produces fertility hormones, milk and nurturing behaviour.
7 Hippocampus: The elephant that never forgets a fight, a romantic encounter, or a tender moment. Larger and more active in women.