Differences Between the Sexes, Part 3

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The Aggressive Sex

In every culture on this planet, boys are more aggressive than girls. That is the conclusion of researchers Eleanor Maccoby and Carol Jacklin.

In a study of elementary and junior high school classes, boys were found to be eight times more likely to call out answers than girls. In a three-year study, “Sexism in the Schoolroom of the 80’s,” it was found that boys participate and are called on in class more than girls — significantly more — and that the teachers didn’t realize it.

Teachers were shown a film of a classroom discussion. When it was over, they were asked who was talking more. Most of the teachers said the girls were. Then they went back through carefully coding and counting who was talking and they discovered that the boys were outtalking the girls at a ratio of three to one.

Boys get more attention in grade school. Maybe this explains why they do better on tests in high school. Why do they get more attention? Because they’re more aggressive — calling out answers, piping up with questions, etc. I’m using the term “aggressive” in the scientific sense. In everyday talk, we usually say someone is aggressive if they are hostile, selfish or picking a fight. But anything someone does that isn’t passive is aggressive. Saying “I love you” to someone is aggressive in the scientific sense. It is reaching, acting, approaching, initiating — trying to cause an effect. Interrupting someone who is talking is aggressive act of communication.

The opposite of aggression is being passive, receptive or responsive. A boy who has a crush on a girl is being aggressive if he asks her out on a date. He is being passive if he only fantasizes about it or tries to look attractive in the hopes she’ll ask him out.

Trini Johannesen, a teacher in Stockbridge, Michigan and vice president of the Michigan Education Association, took the advice of researchers and videotaped her own classroom to be able to observe dispassionately. Johannesen noticed girls take more time to think through their answers. Boys tended to simply shout out and appeared less concerned if their answer was right. She noticed some girls were having similar difficulties with classroom material as some boys, but the boys received more help because they were more noticeable. Says Johannesen, “The girls were simply less overt.”

Psychology professor Aletha Houston (University of Kansas in Lawrence) conducted experiments at several preschools and found girls more likely to do activities that were supervised by an adult. Boys were more likely to play independently.

Studies of young children show boys like hostile humor more than girls. Boys are more likely than girls to find aggressive cartoons funnier. Boys tend to initiate more aggression when playing. Part of the way aggression shows itself, and part of the cause of aggression is competition. There is a strong element of competition among men. We are, after all, larger than women, an indication that at some time in our past, there was competition between men for mates. In any species where an individual mates with several others of the opposite sex, there is competition, and the competing sex grows larger or more beautiful than the noncompeting sex. We must have taken the larger route.

Genes — acting on male brains with male hormones — make males bigger, more competitive and more aggressive. Boys tease more than girls and use forbidden words more often. As adults, polls have shown men far more likely than women to favor military intervention in other countries.

Animals exposed to testosterone in utero display markedly more aggression as adults.

Girls who were exposed to male hormones in the womb are found to be “tomboys” — they liked outdoor roughhousing and were more physically active. The parents weren’t trying to teach these girls to be more active. In fact, parents concerned about their daughter’s “boy-like” behavior is what brought them to the doctor. That’s how most of these accidental exposures to male hormones were discovered.

At one time, male hormones were given to pregnant mothers who had toxemia. The hormones made the mothers feel better, but those who were pregnant with daughters found the girls behaved like boys: not interested in playing with dolls, more active, enjoyed roughhousing, and more aggressive.

The researcher June Reinisch found the same thing at the Kinsey Institute for Research in Sex, Gender and Reproduction at Indiana University. The assessment of aggression was based on interviews with the girls’ mothers, questionnaires given to the girls themselves, and independent ratings by the girls’ teachers.

Reinisch gave multiple-choice tests to pairs of brothers and pairs of sisters (ages 6 to 18). The respondents were to answer how they would respond to different kinds of stressful situations. On average, the males gave more aggressive and belligerent answers than the girls did. But boys who were exposed to extra male hormones in the womb were even more aggressive than their unexposed brothers, and the girls exposed to extra male hormones were measurably more aggressive than their normal sisters.

Melissa Hines at UCLA and a colleague watched CAH girls, ranging from two and a half years old to eight years old, at play. CAH is a condition that produces an excessive amount of male hormones in girls (because of a lack of two key enzymes). Sometimes they are born with a clitoris so large they are thought to be boys. The researchers put the CAH girls in a room with toys of all kinds (kitchen supplies, books, dolls, board games, trucks, construction toys, etc.), and made careful notes of what they played with and for how long. They did the same thing with the girls’ brothers and sisters for comparison. The CAH girls played more with “masculine” toys than did their unaffected sisters. They played with the same toys as the boys did, played with them in the same ways, and spent the same amount of time playing with them, on average, as the boys.

A hormone is a powerful thing. It can not only change the way the body is built, but can also change what we’re interested in. Hines is perplexed by the findings. “Why,” she asks, “would you evolve to want to play with a truck?” There is good reason to expect that some of the CAH girls’ mothers would try to discourage “masculine” interests in their CAH daughters, or at least to not encourage it. But whether discouraged or not, the hormonally-influenced preferences persist.

Hormones affect us whether we want them to or not. We are animals, no matter how much you cover us with clothes and the trappings of modern civilization. A man’s beard grows faster when he is exposed to female pheromones (a particular molecule produced by certain glands in a woman).

When researchers sprayed male pheromones on half a doctor’s waiting-room seats, women sat in the sprayed seats, and men did not, even though when asked, none of them smelled anything or had any inkling their behavior was being influenced by anything but their own conscious decision. Pheromones have no odor. They effect special nerve endings in the nose that send messages to certain parts of the brain.

The testosterone levels of men rise and fall, not only in regular rhythms during the day, but in seasonal rhythms too. Levels of testosterone are highest during the months of the most sunlight — in summer and early fall. And since testosterone is responsible for sex-drives, the rate of intercourse frequency peaks in the month of July, during the longest and sunniest days of the year. Fertility rates, contraceptive sales and outbreaks of venereal disease all peak in summer and early fall. Is it a coincidence that in a more primitive setting, our young are more likely to survive when born in the spring? Keep in mind that the infant-mortality rate of all hunter-gather societies is very high. Any adaptations that improved the rate of infant survival have been genetically bequeathed to you and me.

Certain kinds of activities can raise a man’s testosterone level: Fighting, watching violence on TV, an intense emotional expression, winning or succeeding at something, and thinking about or engaging in sex.

Both men and women in positions of power have higher testosterone levels than people in lower ranks of a hierarchy. This is true for monkeys too. And when you give a small, weak male monkey at the bottom of the hierarchy a big dose of testosterone, he gets so aggressive, he’ll fight his way to the top of the hierarchy by sheer feistiness!

Testosterone makes animals more prone to extreme forms of aggression: violence. Men have 10 to 20 times more testosterone than women. The higher the testosterone level in humans, the more prone to antisocial behavior, fighting, arrests, drug use, and divorce. A study matching relationship histories and testosterone levels of over four thousand men showed that men with higher testosterone levels are less likely to marry and more likely to divorce.

In Europe, the reoffense rate for brutal rapists and child molesters is normally around 70 percent. But in some places they use an unusual method for handling them this problem: castration. And it works extremely well. It drops the reoffense rate from 70 percent down to 3 percent! They either do the castration surgically or they use drugs that neutralize the male hormones in the blood. Both methods work equally well.

In a placebo-controlled study by the National Institute of Mental Health, researchers found that anabolic steroids (artificial male hormones) caused anger, violent feelings, sexual arousal, a higher energy level and more self-confidence.

Could it be that 90% of the children diagnosed as hyperactive are boys because testosterone produces a high energy level and estrogen has a calming influence?

Rhesus monkeys have a nervous system similar to humans. The male monkeys play rougher and mount other monkeys more often than the females do. Yet when pregnant mothers are injected with male hormones, the female offspring behave like males. Depending on when the hormone is injected, they display specific male behaviors. Give the shot at a certain stage in the pregnancy for example, and the female will play rough, but not mount other monkeys. Give the shot at another time, and she will mount other monkeys but not play rough. The same has been found in experiments on rats. Apparently, the different parts of their brains (and ours) develop at different stages in the womb, and depending on the presence or absence of male hormones, those parts of the brain form a male design or a female design. Remember, the female design is what forms in the absence of male hormones.

At McGill University, a researcher by the name of Michael Meaney found that one of the male hormones (dihydrotestosterone) directly activates a brain structure (the amygdala) and produces play-fighting in juvenile male rodents.

You know they can teach rats to learn a maze by giving them a reward at the end, right? Well, they’ve found that male rats will learn the maze even if the only reward at the end is the opportunity to fight with another male rat.

In adult male mice, the more testosterone they have, the faster they will attack a strange male in their territory. Castrate them and they become less aggressive and less territorial.

In the hypothalamus, there is a small cluster of cells called the SDN (sexually dimorphic nucleus). We know that in animals, the SDN is responsible for mating behavior, sexual response, and territorial marking. In humans, the SDN is two and a half times bigger in men than in women.

In rats, the male SDN is also bigger than in females. But give a female a prolonged dose of male hormones in the womb and her SDN grows just as big as a male’s. Castrate a male just after birth and half his SDN neurons die within 24 hours.

The point is, different parts of the brain are different sizes in males and females, and that these different sizes are caused by different levels of hormones while the fetus is developing. And further, that these differences in brains show up as differences in interests and behavior. We may not like it, but that doesn’t mean it isn’t so. Men are more aggressive than women. That’s a fact. Testosterone makes men more aggressive, and estrogen makes women less aggressive.

I could go on and on. The amount of research on men’s aggression is even more extensive than research on women’s ability to communicate. Men are more aggressive than women.

To some people, this is a count against men. But aggression is only “bad” in certain contexts. And it is “good” (useful, advantageous, more effective) in others. It’s safe to say the human race would not exist today without a sizable aggressive capacity.

Aggression helps get things done. Sure, a lot of what gets accomplished is destructive. But that doesn’t mean aggression is bad. Aggression is only a power, like hydrogen. You can use hydrogen to get the space shuttle into orbit, or you can use it to make a hydrogen bomb. The power itself is not good or bad; it depends on what you do with it.

Aggression needs to be channeled into constructive, productive, life-enhancing projects. There is plenty that needs to be done on this Earth. Let’s harness the power of aggression and put it to work.

We've looked at trivial differences and important differences in the sexes and some of the evidence that shows these differences are not learned but inborn. In the final section (part four), we will explore what this all means and what we can do with this information.

go to part four 

This article was excerpted from the book, What Difference Does it Make? How the Sexes Differ and What You Can Do About It?

Adam Khan is the author of Principles For Personal Growth, Direct Your Mind, and co-author with Klassy Evans of How to Change the Way You Look at Things (in Plain English). Follow his podcast, The Adam Bomb.