Heroes, Rogues, & Lovers: Testosterone and Behavior (8 page)

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the form of chromosomesdouble strands of long DNA moleculestells the cell what to do. Genes are sections on the DNA strands, and they contain information needed to build and maintain the body. Each cell has a complete set of genes, but it uses only a few of them. When a cell uses a gene, we say it "expresses" that gene. Gene expression begins when part of the double-stranded DNA unravels into a single strand, called RNA. The RNA moves out of the nucleus and into the main body of the cell, where it attracts small building-block molecules to form stable groups that make up new protein molecules. Creating the new protein is a step toward meeting the need of the moment, whether that need is to digest a meal, add a bit of muscle, attract a lover, or prepare for a fight.

Testosterone has many functions. Among other things, it signals cells to build muscle, make red blood cells, produce sperm, and release neurotransmitters in the brain. A testosterone molecule acts upon its target cell in one of two ways. It binds with a receptor at the membrane surrounding the cell and triggers action there, or it passes through the membrane to bind with a receptor inside the cell and triggers the expression of a gene. Action at the membrane can be completed within seconds. Action inside the cell takes minutes or hours.
⁹Action inside the cell is complicated by the fact that testosterone, after binding with a testosterone receptor, is often transformed into estrogen (by aromatase) before triggering gene expression. Thus we have the interesting situation in which men, whose primary sex hormone is testosterone, convert their testosterone into estrogen before using it.

Testosterone is a sex hormone, and I think it is the most social of hormones. Other hormones indirectly affect the brain and mental function by affecting other organs of the body first. Testosterone makes direct contact with many cells in the brain. It stimulates activity in those cells, and that activity goes on to affect thinking. The major social effect of testosterone is to orient us toward issues of sex and power. This provides a background against which we act, encouraging some behaviors and discouraging others. It affects how we treat other people and how we react to the way they treat us. It makes us impatient with dull and boring aspects of school, but if we manage to sit through school and listen to our elders, the lessons we learn restrain and guide the effects of testosterone.

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Testosterone has two different, but coordinated, effects on the mind and body. It is involved in both design and function. It first helps organize and develop the body and brain, beginning before birth and continuing through adolescence. It then helps direct activities in the body and brain throughout life. It is like a young automotive engineer who designs a fast, powerful car and then races it. The engineer designs a car with the capacity for power and speed, and then later he uses that capacity to race. Testosterone designs a fetus with the potential for power and speed, and when the fetus grows into an adult, testoterone encourages the adult to use this potential.

The Fetus

Testosterone first appears
in utero
, where its job is to turn a neutral fetus into a male. Sex is determined by the X and Y chromosomes; females have two X's and males have an X and a Y. There is one gene, lying along the Y chromosome of every male, that determines his development as a male. The presence of this gene, like the flip of a switch, sets the stage for all that follows. The fetus starts off as a single cell, without a brain or body. Testosterone appears in the middle third of pregnancy, and it transforms the developing fetus into a male. When the gonads first appear, they are undifferentiatedneither ovaries nor testes. Left alone, they will become ovaries. Fallopian tubes will grow out of ducts in their sides, and a female reproductive system will grow out of the fallopian tubes. If the fetus is to be male, however, the gene on the Y chromosome will act to close these ducts and develop cells that produce testosterone and later produce sperm. Males and females are built from the same basic body parts. Organs that appear to be found only in one sex are in fact present in rudimentary or modified form in the other sex. Thus, in females, the gonads remain inside the body and develop into ovaries, and in males, they descend below the body and develop into testes. Dihydrotestosterone, a potent form of testosterone, causes external genitalia in males to develop into a penis and scrotum. Otherwise the same organs develop into a clitoris and the folds around the vagina in females.

Testosterone goes beyond determining the difference between males and females. The amount of testosterone affects the degree of

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masculinity within each sex. Regardless of whether people are male or female, they vary in how masculine they are. There are many examples, from animals and people, of how testosterone increases masculinity. Female hyenas are tougher than males because testosterone from their mothers affects them as fetuses.
¹⁰Canary mothers put a little extra testosterone into the last few eggs they lay in each clutch. All the eggs hatch at the same time, and testosterone gives chicks from the last few eggs an extra toughness to compete with their "older" brothers and sisters.
¹¹

Hormonelike substances from the environment can sometimes affect the fetus. In the 1950s and 1960s, physicians prescribed diethylstilbestrol, or DES, to prevent miscarriages. DES is a synthetic estrogenlike hormone, but
in utero
it has some testosteronelike effects. The daughters of women who took DES were more masculine than other girls. They played with boys' toys and engaged in more rough-and-tumble "tomboyish" play. My wife's cousin took DES when she was pregnant, and she had a hyperactive, hard-to-handle baby girl, who grew up to be a supersalesperson in the cellular phone business. Unfortunately, the DES also caused reproductive disorders in many of the children of mothers who took it.

Pregnant women no longer take DES by prescription, but they can get it and similar chemicals from the environment. These chemicals are called "estrogenic," because they work like estrogen. Farmers give DES to cattle to promote growth, and some is passed on to people who eat meat from the cattle. A pregnant woman who encounters these substances can pass them on through her bloodstream to the fetus she is carrying. Later on, she can pass them on to her infant through her milk. Among some reptiles, birds, and fish, environmental pesticides and pollutants can feminize males. In 1980, there was a large pesticide spill in Florida's Lake Apopka. Following the spill, zoologists examined young male alligators from the lake and found they had low testosterone levels, high estrogen levels, and exceptionally small penises.
¹²

Testosterone from human mothers affects their offspring. A recent study examined the daughters of mothers who were low or high in testosterone.
¹³High-testosterone mothers tended to have high-testosterone daughters, and when the daughters grew up they were more

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masculine in their manner. Because testosterone exerts many of its effects after it is converted into estrogen, one might expect that estrogen from the mother would also masculinize the fetus. This does not happen, perhaps because female fetuses are protected by a substance called alpha-fetoprotein, which blocks the potential masculinizing effect of the mother's estrogen.

Testosterone that influences the fetus can come from another fetus sharing the same pregnancy. Among people, girls with boy cotwins are more tomboyish than girls with girl co-twins. This is partly due to the girls' experiences of growing up with twin brothers, but it is also biological. I once had a bold and forward female student assistant, an expert softball pitcher who married a football player, wanted to learn to box, and enjoyed going to prisons with me to collect testosterone measurements from inmates. She told me she was different from her sisters, who were more feminine, and she wondered why. When I told her about twin brothers, her mouth fell open. She said she had a twin brother who died at birth. He had not been around to affect her while she was growing up, but his testosterone could have affected her before she was born. We measured her testosterone level, and it was above the female average. When they share the womb with male siblings, females can get enough extra prenatal testosterone to masculinize them to varying degrees. The extra prenatal testosterone can increase the number of their testosterone receptors and make them more sensitive to testosterone in later life.

Testosterone from one fetus affecting another
in utero
has been studied more in animals than in people. Farmers have long known that when a cow has male and female twin calves, the female will be sterile. Such a calf is called a "freemartin," and the effect is presumably due to the testosterone she gets from her cotwin. In other animals, females born with males are not sterile, but testosterone from the males still affects them. During gestation, gerbil fetuses are lined up in the uterus in a row, like peas in a pod. A female gerbil situated between two males in the uterus will grow up to be more masculine than one between two females, and she will have more male offspring.
¹⁴Among human beings, women who are more dominant are reported to have more sons. How this could happen is unclear, because it is the father's sperm rather than the mother's egg that determines whether conception will produce a

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male or a female. However, genetic factors or local chemical and physiological factors might affect a woman's reproductive tract so as to affect differentially the viability of x- and y-bearing sperm before conception, or the viability of male and female zygotes after conception.
¹⁵The human studies have not measured the mothers' testosterone levels, though I suspect more dominant mothers are higher in testosterone. Some informal studies suggest that this may be the case.

A student at Georgia State University, Jonathan Bassett, has been exploring this area. Research shows that testosterone differs among occupations, so Jonathan used occupation as an indicator of testosterone level, in lieu of actually measuring it. He thought that women trial lawyers, known to be a high-testosterone group,
^*would have more sons than daughters. He read the biographical sketches of the women trial lawyers listed in Who's Who and found that 58 percent of their children were boys. Findings from waist-to-hip-ratio research
¹⁶suggested to Jonathan that curvaceous figures might be correlated with lower testosterone levels and thus that beauty queens, generally a curvaceous bunch, might be significantly different from trial lawyers in the sex ratio of their children. He read the biographical sketches posted at the Miss America Internet site,
www.missamerica.com
, to see if former Miss Americas had more daughters than sons. They did. They had twice as many.
¹⁷

Extra
, a syndicated television magazine show, ran a story about Jonathan's findings.
Extra
did some research, too. They thought the women working in the high-pressure atmosphere of the newsroom at
Extra
would be high in testosterone and, if Jonathan's hypothesis was right, they would have more boys than girls. Of the eleven women who had children, eight had boys, and three had girls.
¹⁸

Researchers have paid more attention to how testosterone affects babies
in utero
, but there is some research concerning the effect of testosterone from the fetus on the pregnant mother. Gene Sackett, who studies monkeys, found that other monkeys bit pregnant monkeys less often when the pregnant monkeys were carrying males than when they were carrying females.
¹⁹Sackett suspects that hormones from the male fetus passed into the bloodstream of the mother and led


^*Chapter 6 provides details on testosterone levels in different kinds of lawyers.

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