Heroes, Rogues, & Lovers: Testosterone and Behavior (9 page)

Read Heroes, Rogues, & Lovers: Testosterone and Behavior Online

Authors: James McBride Dabbs,Mary Godwin Dabbs

Tags: #test

BOOK: Heroes, Rogues, & Lovers: Testosterone and Behavior
2.02Mb size Format: txt, pdf, ePub
 
Page 15
her to behave in a more masculine manner, which in turn made the other monkeys more cautious about biting her. Researchers have not studied how the sex of the fetus might affect a human mother, but some women report anecdotally that they can feel a difference emotionally between carrying a boy or a girl.
Adolescence and Adulthood
Effects of testosterone on a fetus are lasting, and they provide the background for further development. Receptors developed in the fetus allow the body to respond to testosterone later on. Further development comes in part from an unfolding of what was fixed before birth and in part from an increase in sex hormones during adolescence. Some effects of testosterone during adolescence are anabolic, a term derived from the Greek word for "building up," here meaning the building up of lean muscle tissue. Other effects are masculinizing, making organs more like those of a typical male. Testosterone and estrogen produce striking physical differences between males and females during adolescence, and these differences set the stage for differences in behavior.
Testosterone affects all parts of the body, especially the reproductive system, thyroid gland, blood, bones, skin, and brain.
20
It promotes faster, more intense action in males, in contrast with the slower, more durable action associated with estrogen in females.
21
Testosterone gives men more muscle, along with more red blood cells to carry oxygen to the muscle. Estrogen, on the other hand, gives women stronger immune systems and a greater ability to resist infection and disease.
22
Testosterone makes men store fat around their stomachs, where it can be easily burned off for energy in emergencies.
23
Estrogen makes women store fat on their hips, buttocks, and thighs, where it tends to stay unless needed to make up food shortages during pregnancy or breast-feeding.
24
Men have more body mass in their arms and legs, and women have more body mass in their torsos. Men, like other male mammals, have more development in their upper body areas, with stronger arms and shoulders, thicker skulls, and heads even larger than expected for their body size.
Figure 1.2 shows testosterone levels in both sexes across the life span. Boys have more testosterone than girls before birth. Boys also have
 
Page 16
a spike in testosterone in the first few months of life, when their levels rise briefly to the levels of adult females. From then until puberty, levels are low in both sexes. Testosterone increases in both sexes at puberty. By the end of puberty, males have levels eight to ten times as high as those of females, and then testosterone in both sexes begins a slow decline toward old age. The sexes become more alike as they grow older. Women begin to develop rougher skin and lower-pitched voices. This is because after menopause, women drop in estrogen more than they drop in testosterone, and it is the estrogen-testosterone ratio that matters.
Figure 1.2
Male and female testosterone levels across the life span. The two small peaks
among males occur around the midtrimester of pregnancy and a few months
after birth.
Our average testosterone level is inherited from our parents, but physical and social conditions produce changes around this average level. Testosterone falls with ill health and physical exhaustion. It rises when we win important contests and falls when we lose (as described in more detail in Chapter 4). It changes with our status in life (Chapter 5 describes changes when men marry, divorce, or become fathers).
 
Page 17
Changes in testosterone are usually temporary, riding along on top of a broad wave that rises and then declines across the life span.
25
Changes across the life span also differ among various populations around the world. Anthropologist Peter Ellison and his colleagues studied testosterone levels among Lese men in the Congo, Tamang men in Nepal, Ache men in Paraguay, and men in the United States from the Boston area.
26
Of the four groups, the Boston men dropped the most, going from highest in youth to lowest in old age. Figure 1.3 shows these findings.
Figure 1.3
Decline in male testosterone levels across the life span in different populations.
The graph represents men from Boston in the United States, the Lese of the
Democratic Republic of the Congo, the Tamang of Nepal, and the Ache of
Paraguay. The four sloping lines represent, from top to bottom, mean decline
across the life span in the four groups, respectively. Boston men have the
highest initial testosterone level and the steepest decline across the life span.
 
Page 18
Many substances from the environment can affect testosterone levels. Plants and animals use hormones and other chemicals to control each other; the study of these chemical relationships involving plants is called ''phytochemical ecology." Sometimes the chemicals are harmless, sometimes they benefit both parties, and sometimes they help one party and hurt the other. Testosterone and estrogen appear in animals, plants, and even bacteria. I discovered that cotton contains testosterone when I used cotton rolls to collect saliva. Suspecting that the cotton was affecting our test scores, I assayed cotton samples taken directly from a South Carolina cotton field. The cotton appeared to have testosterone levels about as high as those of adult women. I'm not sure what the testosterone in cotton does, but it could affect insects that eat the cotton. Alfalfa and clover produce estrogen. The estrogen helps the plants by acting as a birth-control substance, holding down the population of grazing animals. Alfalfa and clover produce enough estrogen to make sheep and cattle sterile. In Australia, a million sheep each year fail to have lambs because they eat too much clover.
27
Some creatures use the estrogen and other chemicals in plants to turn their reproductive cycles on and off.
28
Like sheep grazing on clover, people are affected by what they eat. A mother may absorb estrogens from plants she eats and pass them on to a fetus she is carrying or a baby she is nursing.
29
Testosterone levels are lower among vegetarians, perhaps because plant estrogens, including dadzein, enterolactone, and equol, bind with androgen as well as estrogen receptors and "decrease androgen production by interference with the pituitary testicular feedback mechanism."
30
Soybean products are high in estrogen, and they are used in infant formula, food supplements, and tofu. Maybe the saying "Real men don't eat quiche" should be "Real men don't eat tofu." But maybe not. I wouldn't want to tell a Sumo wrestler that he wasn't a real man. Tofu and other soy products are dietary staples in Japan and are credited by some nutritionists for the low rate of prostate cancer there.
31
Estrogen and estrogenlike chemicals, which are in our food, our water, and our cosmetic products, have become environmental pollutants. Estrogen from birth-control pills eventually passes into city water supplies, where it can affect people drinking the water,
32
and estrogens in hair care products may cause breast development in young girls.
33
 
Page 19
Sex-hormone molecules are busy chemical messengers. They hustle from place to place, like the Roman god Mercury, keeping their world in balance. They enable one organ or individual or species to affect another, and human beings are sometimes unwittingly caught up in the complex web of interactions. Recent reports of problems in male reproductive health, including an increased incidence of undescended testes, support this observation. In 1993, researchers reported a 50 percent drop in sperm counts over the past two generations, and they suggested that the drop may be caused by estrogenlike chemicals in the environment. More recent research indicates that the problem, while serious, may not be as extreme or as widespread as reported earlier.
34
It is clear that testosterone affects our bodies in many ways, but some people reject the idea that testosterone has important effects on how we think and act. This latter view arises in part from the political philosophy that all people are created equal, at least in the eyes of God and the law. If we are created equal, it is said, then important differences among us must come from education and experience. In this view, biology and testosterone do not matter much, and studying them will only distract us from more important issues of human justice. I have a different view. I agree that education and experience are important, but I think biology is important, too. It is obvious to me that we are biological creatures who live and die according to the rules of nature. Illness wears us down. Bad food shortens our lives. Genetic disorders cloud our judgment. Chemicals affect our moods. When people say testosterone is unimportant in the study of human affairs, I think they are speaking more from bias than from evidence.
The Brain and the Mind
A parent of a teenaged boy might say, "He's got sports cars on his brain," meaning "He's got sports cars on his mind." In everyday conversation, "brain" and ''mind" are often used interchangeably, but they are not the same. The brain is a complex organ with many parts and many functions. The mind is one of the functions of the brain, especially of the frontal lobes. It is influenced by experience as well as biology, and it encompasses awareness, emotion, problem solving, decision making, memory, and introspection. We think of the mind as conscious, but
 
Page 20
there is an unconscious part. That part can be called into consciousness, sometimes with a struggle. Dealing with the almost conscious parts of our mindsremembering where we put things, understanding why we distrust a person, or making sense of feelings of déjà vucan be frustrating. When we have brilliant insights, suffer emotional upsets, or make decisions, whether wise or foolish, both the conscious and the unconscious parts of our minds are working.
Testosterone acts on the brain and thereby influences the mind. When a man's testosterone binds with receptors in his brain and affects the way his mind works, especially when his thoughts seem to focus on inappropriate sexual conquests, we sometimes say, as many people said during President Bill Clinton's ordeal by sexual scandal, "He's thinking with his gonads." Testosterone works in tandem with the brain; it is produced by glands, but its production is controlled by the brain. Each testosterone molecule lasts at most only a few hours before being taken up by a target cell or broken down and discarded by the body. In the lower part of the brain, the hypothalamus works like a thermostat, monitoring how much testosterone is available and how much is needed. When the testosterone level in the bloodstream drops below a certain level called the set point, the hypothalamus signals the pituitary gland. In men, the pituitary signals the testes to produce testosterone, and about twenty minutes later the testosterone level begins to increase.
35
In men and women, the pituitary gland also produces a hormone called adrenocorticotropic hormone (ACTH), which signals the adrenal glands to produce testosterone. When the testosterone reaches the brain, the hypothalamus notes that the system is on track and stops further testosterone production until the level begins to drop again. While all this is going on, other parts of the brain can tell the hypothalamus to change its setting. For example, if a person is preparing for a fight, the brain will signal the hypothalamus to change its set point and increase the testosterone level.
This mechanical and regulatory activity is one aspect of the brain-testosterone relationship. Other aspects deal with thinking and feeling and the ways that the brain exerts control over the effects of testosterone. Testosterone is believed primarily to affect the lower and middle areas of the brain, including the hypothalamus and the limbic system. In the lower area, the hypothalamus regulates eating, drinking, sexual

Other books

Strike Dog by Joseph Heywood
Shallow Creek by Alistair McIntyre
The Quiet Heart by Susan Barrie
Dancing Aztecs by Donald E. Westlake
Accidental Creatures by Harris, Anne
Colouring In by Angela Huth
Waiting for Callback by Perdita Cargill