Why have people been reluctant to accept the idea that so much of human behavior is programmed by gender?
Jo: The human race's arrogance about itself is why the book has caused so much controversy. We may be the dominant species on earth, but we are 99 percent identical with chimpanzees in terms of genes and proteins and DNA. Sex hormones operate on both our bodies and brains, just as they do in other species. Scientists are finding that hormones make for subtle and not so subtle differences in male and female brains.
How are they different?
Jo: According to some researchers, the left hemisphere in most women's brains develops the expression of language more fully early in life. At the-same time the right hemisphere of most men's brains develops more pronounced visual-spatial abilities. Women are more sensitive to touch, taste, smell and sound. Their fine motor control, affecting such things as finger dexterity, is better. They have significantly greater verbal abilities. Men, on the other hand, generally have better gross motor control, affecting such larger motions as throwing a ball, and better visual acuity. Because of these skills, by and large they are manipulators of their environment. Men are usually better at maps, mazes and math. Also scientists have found that there seems to be more connecting nerve fibers between the two hemispheres in women's brains than in men's. This may be why women are often better at skills that involve both hemispheres of the brain, like reading, which requires the ability to translate visual symbols into language. And it may be why men have more difficulty talking about their emotions.
Does this explain why males tend to be slow starters in school?
Diane: Men often have pronounced disabilities in the areas in which women are superior. Major learning disorders such as autism, hyperactivity and stuttering afflict males four or five times more often than they afflict females. Males suffer from birth defects much more than females do. They develop later and more slowly, and they only catch up at puberty when they get an increase of the male hormones.
Do feminists object to your conclusion that behavioral differences between men and women are both natural and inevitable?
Diane: Feminists have said that even if the differences we describe are true, they ought not to be true. Feminists aren't willing to look for the skills and abilities that have been selected for women by evolution, and then to compel men to acknowledge them. They still want to believe that men and women are the same.
Jo: What we can't understand is that feminists are the first to agree that when men have a learning problem it's probably genetic. But when women have a problem, they blame the environment. Certainly the environment has an effect, but our brains are made up before birth of chemicals and hormones. Our abilities and disabilities are rooted in these substances.
How do our sex hormones influence our brains?
Diane: Sex hormones are among the most powerful chemicals in nature. From conception through puberty they actually alter the genetic machinery in individual cells and switch them in a masculine or feminine direction. They do it all over the body—in the heart, lungs, muscles and in the brain.
How much of our behavior is instinctual?
Diane: No one really knows. But in evolution, new programs are built on old ones. We're all children of children of children, all the way back to the beginning of life. Look at the sense of smell. It's one of the oldest mechanisms. Females have a stronger sense of smell than males, and around the time of ovulation it's heightened. It may be one of the ways in which females discriminate among those with whom they will mate.
Jo: Scientists are just beginning to study the sense of smell and to find out that it is still a powerful, instinctual sense in humans. According to a study in Boston, women who lived together in the same dormitory, for instance, tended to have their menstrual cycles coincide. Scientists also found that women in a dormitory who dated frequently had shorter and more regular cycles than those who did not, and that women in the perfume industry who worked with musk, an animal hormone, had shorter and more regular cycles than those who did not. There is some evidence that an undefined male hormonal product is being passed by the sense of smell between men and women, and a female hormonal product is passing between women and women.
Are you implying that we have no control over our behavior?
Diane: Not at all. But the roots of behavior—sexual orientation, personality, skills, disabilities—are all developed to an extent before birth. There is evidence, for example, that a tendency toward homosexuality may be laid down in the brain prenatally. Also, schizophrenia, anorexia nervosa and autism may be based in the brain's chemical or hormonal predispositions. They aren't the fault of upbringing or environment, though they may be triggered by the environment. When a woman's hormone levels are altered, this may emerge in premenstrual tension or postpartum depression. When men have higher than normal levels of the sex hormone testosterone, this may emerge in violence. One way of treating men who are sexual deviants is by giving them a drug that depresses their level of testosterone. It not only decreases the undesirable behavior, it alters their sexual fantasies about it.
You mentioned homosexuality. Would you elaborate?
Jo: A number of scientists have found that if pregnant rats are subjected to stress, it lowers the level of testosterone available to the male fetuses. It can affect their eventual sexual orientation and create homosexual behavior. A scientist in East Germany, Gunter Dorner, has reasoned that this is because their brains have been feminized in part.
Diane: Dörner did a study of German males born before, during and after World War II. He felt that if his theory were true, there would be more homosexuals born during the last stressful years of the war than before or after. And he found that was so. Then he conducted extensive interviews with homosexuals born during the war, and with their mothers, about the stress level experienced while the child was in the womb. He found that it was considerable. The theory is controversial. We don't know all we would like to about these hormones, but Dörner's work fits in with the knowledge to date.
If hormones cause homosexuality, could they also cause a special susceptibility to AIDS?
Jo: Perhaps. AIDS is an immune-system malfunction, and males and females do have different immune systems. It can be argued that the process by which the male brain is developed in the womb through the agency of testosterone also works to make the immune system male. So the same thing that may partly feminize the brains of male homosexuals before birth may also alter the immune system, and this slightly different immune system may be providing a window for opportunistic diseases. This has not been talked about in public, but scientists are indeed investigating it.
Why do women live longer than men?
Jo: There seems to be only one population of men who live, on average, as long as women—castrated men who don't have so much testosterone available to them. So some researchers now argue that because women lack large amounts of testosterone, their life expectancy is increased. Their immune systems are more efficient, and they are less likely to have heart attacks. It's not that women's lives are less stressful.
Where is all this brain research going to take us?
Jo: The more scientists learn about the chemicals with which the brain communicates with itself, the more they can intervene in the processes that the brain controls: memory, learning, sensation, libido. Some of the drugs that result will be extremely valuable. The question is: How should their use be limited? For instance, as the numbers of the elderly increase, so will the problem of senility. If drugs are found to improve or restore memory, should their use be limited to those who really need them? Or should they also be made available to students? If drugs are found to restore normal sexual lives to people who have a loss of libido, should they be used by anyone who wants heightened sexual drive? If society wants to prevent male homosexuality, should doctors give testosterone to all pregnant women under stress who are carrying male fetuses?
Diane: Many people think we're a bit off the wall when we ask these questions, but the problem is that science usually leaps in and becomes a technology before anyone knows the whole story. And we're not going to know the whole story for years—whether, if you rewrite the genetic script for left-handedness, for instance, you might end up with fewer dyslexics—but also with fewer painters and mathematical geniuses. At this stage no one can say.
It shouldn 't come as news to anyone that there are profound physical differences between men and women. But whether these differences extend to behavior has been the subject of rancorous, if not explosive, debate. Enter the husband-and-wife team of Jo Durden-Smith, 41, and Diane De Simone, 34, authors of Sex and the Brain (Arbor House, $16.95), who maintain that not only do males and females think, act and express themselves differently, but also that in many respects they don't have much choice: Their brains simply aren't the same. Now living in Baltimore, the British-born, Oxford-educated Durden-Smith, and De Simone, a native New Yorker with an M.A. in psychology, spent three years reading research papers and interviewing more than 50 scientists in Britain, the U.S. and Canada. Though the book has been attacked by feminists and gays for downgrading environmental influences on behavior, it has been praised by some scientists as well-informed and enlightened. "The brain is who we are," declares De Simone. "It's what makes man man and woman woman." She and Durden-Smith discussed their findings with Molly McKaughan for PEOPLE.