RH: So what about the political implications of putting a spotlight on gender differences?
BRIZENDINE: It's the way it is. Let's say someone were to say to you "Because you're a guy, you can't be a caring psychologist." Well, that's offensive, right? Well, there's nothing offensive about gender difference unless you say "Oh, because you're a male or female, you can't do a certain job." It's this next step that drives people nuts, and I don't take that step in my books. Saying that we're different doesn't mean that it's okay to discriminate against one gender or the other, or say that one's better than the other.
RH: How does what we're learning about the brain and development change the old nature vs. nurture debate?
BRIZENDINE: By now, most scientists agree that personality and temperament are about 50 percent due to what we're born with. But the other 50 percent is really big. So little boys like guns and like to pound each other with rough and tumble play. For little girls, it's the nurturing, verbal, eye-contact, relational play. You know, "You be the mommy, I'll be the daddy." Females all their life tend to cry about four times more than males do. Is that because we have larger tear ducts and more prolactin to make tears? That doesn't explain the whole story. So when people accuse me of being a biological determinist, I say no way. I believe that all of those things feed back to make us who we are. You can't escape the 50 percent that's the nature and the wiring and the hormones that you're born with. You also can't say that human nature is completely culturally created.
RH: So how does brain development fit into all this?
BRIZENDINE: Scientists now know that everything that happens—like trauma or growing up in a certain parenting environment or having your best friend move away in third grade or being sexually abused—all those things feed back on the brain to actually change some of the ways the genes are expressed. It's the whole area we now call the epigenetic forming of the brain. For example, none of us was born knowing how to play the piano, but practice and repetition can actually make the area of the brain related to piano playing grow six, seven, eight times larger than it would be otherwise. Just like pumping iron—by the time you end up bench-pressing 300 lbs., your biceps are pretty big.
RH: How might epigenetics impact relationships?
BRIZENDINE: For example, if you're born and raised in a really nurturing and supportive environment with parents who are life coaches on everything you do, versus one in which you're neglected, abused, and nobody can be trusted, that feeds back on the brain and changes the circuitry. So having the trusting environment that we'd like all people to grow up in reinforces a tendency to trust versus not trust.