Heroes, Rogues, & Lovers: Testosterone and Behavior (10 page)

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Authors: James McBride Dabbs,Mary Godwin Dabbs

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BOOK: Heroes, Rogues, & Lovers: Testosterone and Behavior
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behavior, and hormone levels. In the middle area, the limbic system, including the amygdala, is involved with memory, sex, aggression, and emotion and with assessing social and environmental factors. Recent discoveries of testosterone receptors among subcortical glial cells in primates suggest a pathway in the upper area of the human brain whereby testosterone might affect the cerebral cortex, which handles perception, voluntary movement, language, thought, planning, and other advanced intellectual processes.
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An important role of the upper centers of the brain is the civilizing control they exert over testosterone. These centers of the brain are where we store our knowledge of learning and culture. They restrain our animal impulses. They keep us from eating every time we are hungry, scratching every time we itch, and losing our temper every time we are frustrated. They make us accommodate to others in small and large ways. They remind us that, as Robert Frost said, "to be social is to be forgiving."
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They keep us from giving in to testosterone and seeking sex and power to the exclusion of everything else. At their best, these upper centers allow us to harness the strength of testosterone for positive social ends.
In discussing the brain we are quickly forced into guesswork, because we do not have a complete model of how it works. We know that signals go into the brain and thoughts come out. We are never exactly sure what happens in the middle. It is unclear how the activity of a few neurotransmitters can affect complex thinking and problem solving. We know that testosterone molecules signal some brain cells, which in turn signal other cells. One thing leads to another, and finally cascading patterns of nerve responses move us to think new thoughts and do new things. But we don't know all the details of this process, so it helps to have general models of the brain to guide us in our thinking about how the brain works.
A good model would summarize scientific knowledge about the brain into a metaphor that provides us with an image that goes beyond what is known precisely. The model may reflect our personal view of the world as well as objective reality. Today we compare the brain to a computer. We say people "process information" and have "memory banks." This sounds neat and orderly, but the idea that the brain functions like a computer is largely a modern fairy tale. Years ago, when peo-
 
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ple depended on steam for power, they used the steam engine as a model for the brain. When weaving was a major industry, they described the brain as "an enchanted loom where millions of flashing shuttles weave a dissolving pattern . . . "
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Where people once saw ideas weaving tapestries of thought, they now see electricity moving down the branches of neurons and jumping across switches to other neurons. But there is no electrical current in the brain, and there are no electrical switches. What moves along the neurons is a chemical change, and what crosses from one neuron to another is neurotransmitters. Modern computers provide us a handy metaphor, but they may not be much better than engines or looms as models in helping us understand what really goes on in the brain.
I think the brain is more like a soup than a computer. Its nerve cells float in a broth of supporting tissue, plasma, blood cells, nutrients, oxygen, hormones, neurotransmitters, and waste products. Its ingredients came, one at a time, from our ancestors and the world around us. It evolved over millions of years, stirred by many cooks struggling for survival and facing conflicting demands from the environment. Parts of the brain remain well suited to survival today. Other parts are random, left-over by-products of evolution, better suited to handling problems of the past. Some readers will find this view of the brain distasteful. The image of soup suggests an unseemly wetness about human nature. It is messy, organic, and subhuman. Surely, we think, people are better than that. But soup may be as useful a model as any for thinking about how the brain handles information.
Activity in the brain involves individual cells, and testosterone affects these cells. Regardless of the model we use, our practical concern is to discover the rules that link testosterone to our thoughts and actions.
Testosterone Is like the Weather
People differ in their testosterone levels, and testosterone is more important in some people than in others. For people near the middle of the range of testosterone, differences in testosterone do not matter much. These people are influenced more by other factors, and we would have to look at many such people to see the effects of testos-
 
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terone. But for people with very high or low levels, testosterone can make a big difference.
A testosterone measurement is like a weather prediction. It gives a general idea of what will happen, but it leaves much unspecified. For example, August is usually hot in Atlanta, but it is sometimes extremely hot and sometimes pleasantly mild. Late-afternoon showers are common, and occasionally there is the edge of a hurricane. The weather can be affected by vagaries of the jet stream, local winds, fast-moving fronts, and moisture from the Gulf of Mexico. Knowing it is August tells us to expect summer weather, but there's no way to be sure what the weather will be on any given August day. Testosterone is like this. We can count on it to affect behavior in the long run. In the short run, on any given occasion, its effects are likely to be relatively mild, one of many influences on our behavior.
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With salivary assays, we can collect enough data to see how small effects of testosterone add up to general patterns. My students and I have been doing this, exploring ways in which individuals with high or low levels of testosterone differ from each other. We have also been exploring social and environmental factors that interact with testosterone, sometimes beneficially and sometimes not. Evolution offers a theoretical framework to examine the hormone's role in the survival of males, females, and their offspring, which we will describe in the next chapter. In later chapters we will talk more about men, women, and the social effects of testosterone, and finally we will consider how social forces and human values can modify the effects of testosterone and even channel them in ways that lead to altruistic types of behavior.
 
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2
Two Sexes
Two Sexes and Testosterone
If a child asks us why there are two kinds of people, boys and girls, we are likely to say that is just the way it is, or God made us that way, or it is nice to have both kinds. These answers may miss the point of the child's question. Alun Anderson suggested in the journal
Science
that parents might try explaining why there are two sexes rather than a larger number or none at all. Two seems right to us, and we don't think about other possibilities, but in fact, there are a number of other possibilities. The prize goes to a lowly species of one-celled slime mold,
Plysarum polycephalum
, that has thirteen different sexes. A cell of one sex reproduces by joining with a cell of one of the twelve other sexes. This adds up to seventy-eight possible kinds of pairs, all different. For each pair there are rules as to what each party must do, including which one will pass on its mitochondria, the rod-shaped bodies that live within each cell and are essential to the host animal's metabolism. It is said that God must have loved beetles and other small bugs, or He would not have made so many of them. I think He may have picked the slime mold for special attention, or maybe experimentation, because he gave it such sexual variety. While variety could be the spice of slime mold life, thirteen sexes are an unnecessary complication in the wider evolutionary scheme, a complication that invites trouble. One problem involves the mitochondria. It is important that offspring inherit mitochondria from only one parent. If something goes wrong, and both parents pass along their mitochondria, the competing strains are likely to go to war, leaving the offspring
 
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with severely defective metabolism. In 1991, Shigeyuki Kawano of Tokyo University reported that aggressive mutant mitochondria were ignoring slime mold rules for mating. Competing mitochondria may be the beginning of the end for thirteen sexes.
1
Well before evolution got around to people, two sexes, male and female, had become the standard, with only the females passing along mitochondria. The answer as to why there are two kinds of people is that more than two sexes are vulnerable to problems with competing mitochondria, and fewer than two are vulnerable to other problems. Some species reproduce without sex, in which case each offspring has one parent and inherits a set of genes identical to those of the parent. In this asexual reproduction, the genetic variability that allows for change and adaptability in each new generation is absent. Two sexes bring two sets of genes, which mix and match to produce variety among offspring.
2
Among large animals, including people, two sexes bring diversity without undue complexity. Human females produce ova, which are large enough to contain twenty-two autosomes (chromosomes carrying nonsex linked characteristics), one X sex chromosome, and many mitochondria. Males produce sperm, which are much smaller than ova and too small to carry mitochondria. Sperm have just enough room for twenty-two autosomes and either an X or a Y sex chromosome. The fertilized ovum ends up with twenty-two pairs of autosomes and one pair of sex chromosomes, including an X chromosome from the mother and either an X or Y chromosome from the father, and the mother's mitochondria. A fertilized ovum with two X chromosomes will be female and develop ovaries, while a fertilized ovum with an X and a Y chromosome will be male and develop testes. Later on, unless there is a genetic or congenital error, the females will produce more estrogen than testosterone, and the males will produce more testosterone than estrogen.
Evolution
Two sexes and genetic diversity make evolution possible. Reproductive needs influence evolution's direction and partly explain human nature and the difference between the sexes. There are many places we can go to look for answers to questions about human nature. We can go to psy-
 
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chology, history, politics, religion, popular writing, our parents, or our friends. Most social scientists look to cultural history to explain human nature, but biology and evolution provide an equally useful way of thinking. Evolution molded us in the past and continues to mold us in the present. Life today can be understood in terms of its evolutionary past and offers clues about our evolutionary future. Examining the origins of human nature can make it clearer where the sexes are similar, where they are different, and what they have to disagree about.
Evolution is abstract, slow, and distant, with origins far into the past; it is one of many explanations for human nature, all of which may be true at once. Events have many causes. For example, a man may be alarmed when he meets a stranger on a dark street because of his earlier experiences, because of what others have told him, because of a release of neurotransmitters in his brain, and because evolution has shaped him to react that way. A boxer may fight because he has the ability and spirit of a fighter and because spectators pay to watch him fight. I exercise in a gym because it makes me feel good and constant messages from the fitness movement remind me that it's the thing to do. I eat a lot of rice, as do others from my home state, because rice once grew there and shaped the cuisine of the region. It is also true that my species evolved with muscles that need exercise and a stomach that digests rice.
People interested in evolution distinguish between "proximal" explanations, which are immediate and close at hand, and "distal" explanations, which are remote and far away. Evolution is a distal explanation. Long ago evolution shaped the structure of our bodies, brains, and behavior. It remains an invisible force, nudging us along and emerging at moments to arouse us or trip us up. Distal explanations are useful in understanding overall patterns. They allow us to put many facts into perspective and comprehend their significance.
We act as a result of immediate causes, while in the background other causes have led us to the moment. Evolution is in the background, and it influences us without our awareness. It works as in Lewis Thomas's description of a male moth flying toward pheromones released by a female miles away. The moth does not know why he flies. For all he knows, it is a good day for a flight and a pleasant direction in which to fly. If he does meet the female, then it's a nice surprise. In Lewis's words:
 
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The messages are urgent, but they may arrive, for all we know, in a fragrance of ambiguity. "At home, 4
P.M.
today," says the female moth, and releases a brief explosion of bombykol, a single molecule of which will tremble the hairs of any male within miles and send him driving upwind in a confusion of ardor. But it is doubtful if he has an awareness of being caught in an aerosol of chemical attractant. On the contrary, he probably finds suddenly that it has become an excellent day, the weather remarkably bracing, the time appropriate for a bit of exercise of the old wings, a brisk turn upwind. En route, traveling the gradient of bombykol, he notes the presence of other males, heading in the same direction, all in a good mood, inclined to race for the sheer sport of it. Then, when he reaches his destination, it may seem to him the most extraordinary of coincidences, the greatest piece of luck: "Bless my soul, what have we here!"
3
Like the moth, we are aware of only the more proximal reasons for our behavior. And, like the moth's pheromones, these reasons have the appealing fragrance of ambiguity. They obscure the importance of other reasons. Testosterone has distal origins. It is a legacy of evolution, and evolution stands in the background linking testosterone to our current interest in sex and power.
Simply put, evolution is a process whereby life adjusts to changing pressures and opportunities. New characteristics appear from time to time. Some are helpful, and others are detrimental. Characteristics that help survival increase in each new generation and become more prevalent. Characteristics that hinder survival diminish or disappear. Evolution involves two processes: natural selection and sexual selection. Natural selection explains how people as a species acquired the characteristics of human beings, which include having some amount of testosterone. Sexual selection explains how men and women became different, including being different in their testosterone levels.
Natural Selection
The principle of natural selection is simple. The world changes, and creatures change with it or disappear. A meteor impact wipes out a

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