Dr. Brizendine insists that despite the "hard wiring" of our brain chemistry, we do have free will. Clearly, not all women and men are the same. But for many the science is undeniable: powerful hormones and the complex circuitry of the brain do shape our behavior and, therefore, our destiny.
"It's biology, and it needs hands-on parenting,'" urged Dr. Brizendine. "It needs 'hands-on parenting.' That's why teens need a lot of wisdom and careful monitoring by adults in order to let the good connections grow strong and get rid of the bad connections."
And becoming a parent also sets in motion dramatic changes in the female mind.
During pregnancy, the biggest hormonal surge of a mother's life will send levels of estrogen and progesterone off the charts. It's something Sarah Cheyette, a pediatric neurologist and mother of three, knows all too well.
"If I'm crying hysterically about something during pregnancy, I feel, 'OK, it's the hormones and I'm not losing my mind entirely,'" said Cheyette.
"The progesterone level goes up -- way up," said Dr. Brizendine. "Thirty, 40 times what is normal… All of the surges and big changes that happen just wire you up for paying attention to that helpless little infant somehow."
During pregnancy, these powerful hormones literally hijack a mother's brain circuits. She first becomes sleepy, hungry and nauseous. Soon, the hormones oxytocin and prolactin intensely focus her maternal brain on the safety, and the needs of her child often to the detriment of everything else.
Scientists don't know why, but neuro-imaging studies show that pregnant women's brains actually shrink -- almost 8 percent -- during gestation. They return to their normal sizes six months after the mother gives birth, and then maternal aggression kicks in. Triggered by hormones, a mother's brain becomes a virtual GPS systems for tracking and protecting her young.
Studies have shown that, within about 48 hours or so, a mom can pick out the cry of her own baby above other babies. It could be that human evolution has been hard-wired in some ways to protect infants and propagate the species.
A similarly dramatic hormonal effect is experienced when mothers breastfeed. As she nurses, oxytocin, the feel-good hormone, marinates a mother's brain. Many women say they are awash in feelings of warmth and pleasure. According to Dr. Brizendine, "some women even say they almost have an orgasm while they're breast feeding -- that they can feel their uterus contracting."
Because of this, Dr. Brizendine suggests that it's no wonder that the mommy brain has little desire for sexual contact -- the baby is now her primary love interest, and the intense hormonal focus on her child leaves her satisfied, but exhausted.
"Having a baby definitely changes your sex life," said Cheyette. "The baby is taking up time and energy and brain space, and I think it's hard for a woman to get in the mood."
"The dad is there only in a supporting role now," adds Dr. Brizendine, "Whereas he's been used to being the main course, he's now like a side dish."
For many women, their child-centric behavior not only compromises their relationships, but also their jobs. Hormonally tethered to their child the interest of some mothers to return to work is often challenging.
"It's a struggle I live with everyday. Being at work, sometimes I feel guilty about being there. Sometimes being at home, I feel like I should be at work," said Cheyette. "And it's not just me, it's every mom that I know."
Balancing work, pregnancy and then family is a struggle for most women, and Dr. Brizendine hopes her book and research bring awareness about the difference between male and female brains.
Sarah Cheyette agrees: "For our children's sake, and for their children's sake, it would be best if people understood pregnant women, pregnancy and what being a mommy is about."