Woman

by Natalie Angier

  The female brain, by contrast, is the steady-state brain, the default brain, the plan we go with unless otherwise signaled. The female brain is not exposed to a burst of testosterone prenatally, because the female has no testes to release testosterone. The characteristic circuitry of the female brain is established by absence rather than presence. On reaching puberty and feeling the surge of estrogen and progesterone, that circuitry is activated in its female-specific conformation, forthwith to counsel behaviors like ... well, it's hard to say, and naturally it differs from individual to individual, but in essence, all things muzzled—not quite as aggressive as the male, not quite as ambitious, not quite as obnoxious, not as obsessed with sex. That, at least, is the persistent presumption of the standard organizational/activational theory of the sexing of the brain—that the female brain is comparatively less primed to aggressive, dominant behavior and all accessories and permutations of such.

  Now we can consider the blemishes and qualifications of the O/A hypothesis. First, testosterone as such may not be what matters during the prenatal imprinting. The thinking among many researchers is that much of the testosterone that reaches the fetal brain is promptly converted by the neurons to estrogen, and only as estrogen does it affect the sexual architecture of the brain. Yes, only as a "female" hormone can the male hormone masculinize the brain. Which means that estrogen is what counts for the sexing of the brain and the dispensation of aggressive, dominant, or satyric behavior. Females know from estrogen. In this hormone, we can't exactly be ranked as deprived. Still, one can preserve the O/A hypothesis by insisting that what counts is not estrogen versus testosterone but the quantity of steroid hormone to which the fetal brain is exposed. Supposedly, estrogen in a fetus's blood, whether from the mother or from the fetal ovaries, gets bound up by a fetal protein called alpha-fetoprotein and is unable to penetrate the brain. Supposedly, testosterone from a boy fetus's testes doesn't get bound up by this fetal protein, so it can reach the brain. If it is then converted to estrogen before influencing brain architecture, so what? It is nonetheless cortically present and accounted for, and a girl's estrogen is not. The great steroid surge remains the ken of the male fetus. The female brain keeps its hormonal virginity.

  Except that it doesn't. Most of the experiments suggesting that it did were performed in rodents, where alpha-fetoprotein is adept at waylaying blood estrogen. In humans, the protein doesn't distract estrogen from reaching the brain. And so estrogen from the mother is free to affect a girl baby's brain, and estrogen from the girl's ovaries may do the same. A drizzle of estrogen plies the female brain throughout gestation, and who can say how much is flowing or what its impact on the neuronal conduits may be? Scientists assume that the dose is still relatively low compared to the hormonal swell that reaches a male fetus's brain from his testes, and that, to put it schematically, low estrogen feminizes a brain while high estrogen masculinizes a brain, and high estrogen comes from prenatal ejaculates of androgen which are converted to estrogen in the brain. Yet there is no proof for this assertion. Even in rodents, the tidy dichotomous model doesn't pan out. Take female mice that have been genetically altered so they lack estrogen receptor-alpha and therefore have one less way of responding to estrogen than a normal mouse does. If a brain that is spared the impact of estrogen during development is slated for femininity, these mice should be the murine equivalent of the goo-girls on television commercials, superfemmes. But they're not. On the contrary, they're unusually aggressive. Some are infanticidal. They see another female's pups, and they attack. The receptor-deficient females are more aggressive than the male mice that lack estrogen receptors. Those males appear somewhat feminized. They don't like to venture across open spaces, as male mice usually do. They mount females, but then they don't ejaculate. Their brains were also deprived of the developmental persuasions of estrogen; their testes made testosterone, but the testosterone couldn't exert its organizing influence on the brain because the hormone had to do its deed as estrogen, and the estrogen receptors weren't listening.

  What, then, is the moral of our story? That if you're a chromosomal gal and you can't respond to estrogen in utero, you turn guyesque? But if you're a guy and you can't respond to estrogen, you turn gal? Or something like that, or something else altogether? Or is the moral that the old stories won't do, and that the female brain is made, not defaulted, and that if brain development in either sex is perturbed by a genetic anomaly, the resulting animal will defy expectations and laugh in all the wrong places?

  Women have testosterone, but it's nothing to hang a helmet on. We can't count on testosterone, and there's a good chance we don't need to.

  The studies that link testosterone to aggressive or dominant behavior in men are not pretty. They are a mess. Some studies have found that among male prisoners, the more violent the offense committed, the higher the man's testosterone level. Other studies have failed to find such a correlation. Among young adolescents, boys rated as "tough leaders" by their peers have been shown to have high levels of testosterone; yet one boy's "tough" is another boy's "tough luck," for the same study showed that those boys who had spent their childhoods getting into fights and trouble had fairly depressed levels of testosterone on reaching puberty. As a rule of thumb, a man's testosterone will rise right before a challenge, like a football game or a chess tournament, and if the man triumphs, his testosterone stays high for a time, but if he loses, it drops, and it has difficulty getting up again. Testosterone will rise when a man receives a medical degree or a professional honor. It will climb when he is awarded a cash prize for winning a tennis match, but not if he wins the same amount in a lottery and can't feel the peacock for it. The testosterone levels of male trial lawyers—who must get up in court and shake their verbal scimitars and slash at any who doubt them—are higher, on average, than the testosterone concentrations of tax lawyers, who do most of their work in the privacy of their office and may even keep an orchid plant on the desk.

  But gearing up for a challenge does not always elicit a testosterone spike. Young men competing in a video game tournament show no detectable testosterone shift, neither beforehand nor in the wake of virtually exterminating their opponents. Before a male parachutist leaps from a plane, his testosterone drops; it sees what's coming, we can suppose, and swoons at the thought. A man's testosterone concentration also falls when he has fallen in love to the point where he is committed to the woman, and it falls when he is on the verge of fatherhood. Some scientists interpret these results to mean that men in a monogamous relationship don't need their testosterone. They don't want their testosterone. It does them no good if they're going to stay put and be a loyal lover and a devoted father. They don't need as much testosterone as they did when they were on the hunt and might be forced to rattle their chain mail at a rival en route. There are alternate storylines, though. Testosterone can fall when a man is under stress; that's presumably part of the reason why it dips with a drop in social status, or with the loss of a chess game. Is commitment not stressful? Is commitment not a match for the scream that precedes a parachute jump? And impending and new fatherhood—are they stressful? If you have to ask, you are inert, and need neither testosterone nor oxygen.

  We don't know the meaning of testosterone fluctuations in men. They rise and fall every day, throughout the day, peaking in the morning, subsiding by late afternoon, and rising again before bed. If you cut off the major source of a man's testosterone, his testicles, he may or may not become less aggressive than he was before. Some men who have been chemically castrated for the treatment of prostate cancer report extreme mood changes, usually in a more passive and depressed direction; but they have cancer, for Thor's sake, and why expect them to be out there pretending they are jujitsu masters? Men who were castrated to guard a sultan's harem were not unaggressive. They could be pissy. That's why they were good watchdogs. In ancient China, court eunuchs could be notoriously bloodthirsty, arranging assassinations of emperors and enthroning chosen successors; some were milit
ary strategists, others fought as foot soldiers. In this country, surgical or chemical castration sometimes is used as a treatment for sex offenders, particularly child molesters. The therapy has its detractors, and rightfully so. Not only does the punishment smack of barbarism and anticonstitutionalism, but it can have tragic results. Some child molesters who were castrated have ended up killing their young victims rather than stopping at molestation. The loss of testicular androgen dampened their sex drive and made erections difficult, but their aggression was unslaked, and, furious with their failure to perform, they lashed out at the unfortunate objects of their pathological urges.

  Men who are hypogonadal—whose testosterone levels have, for a variety of clinical reasons, dived into the subnormal range—say they feel more aggressive and angrier than they did before, not less, and when their androgen levels return to normal they feel calmer, happier, at ease with themselves once again. So it is with all our hormones—thyroid, sex steroids, Cortisol. Too much or too little, it doesn't matter. We feel dis-eased, out of sorts, crotchety, aggressive.

  If the link between testosterone and aggressive or dominant behavior in men is a mess, that for women is the floor under your refrigerator: you don't want to think about it. Female athletes don't have a testosterone spike before a competition, and they don't have a spike if they win a competition. Female trial lawyers are hardly more blessed with testosterone, on average, than female tax attorneys are. In one study, researchers sought to determine if the aggressiveness of a woman might track the rise and fall of her testosterone levels throughout the menstrual cycle, peaking at the phase when the egg is ripening and when androgen output is highest. Two dozen women were subjected to multiple rounds of a fast-paced game called the "Point Subtraction Aggression Paradigm," in which a person is given the option of either pressing a bar one hundred times to raise her score by one point, worth ten cents, or pressing another bar ten times to knock a point off the score of an unseen (and fictitious) opponent. The player is then provoked by the periodic subtraction of a point from her score, which is attributed to the hostility of her imaginary opponent. The researchers found no correlation between a woman's relative testosterone concentration and the chance that she would greet the provocation tit-for-tat, pouncing irately on her subtraction bar rather than staying focused on raising her own tally. What the researchers did find, however, is that women who reported suffering from premenstrual syndrome were generally more bellicose throughout the month, and more likely to press the "get that sucker" bar, than the women without PMS were—their testosterone levels notwithstanding.

  Testosterone is lawless, unmanageable. In one study, the higher a female prisoner's testosterone level was, the more likely she was to have committed a violent crime like murder than a nonphysical offense like embezzlement. In another study, the correlation did not hold. Investigators have found that female inmates with high testosterone display more domineering and intimidating behavior than low-T prisoners do, and, conversely, that the low-Ts are "sneaky," "manipulative," and "conniving," acting like "snakes in the grass," according to the assessments of the prison staff. But let's bring some perspective to this study, a little aggressive extending of our cat's claws. The high-T women in the sample population were also younger, on average, than the lower-T women. Youth has its perquisites. When you're young, you have quite a bit of muscle tissue. You still think death is exciting and provisional. As a rule, people in prison have a history of bad habits—too much smoking, too much drinking, too many drugs in too many corrosive combinations—and so the older you are, the weaker, sadder, and more shopworn you are likely to be. Better to connive in the grass than to confront in the flesh.

  Testosterone is oversold. We think too much of it. It is not what we need or want in attempting to understand the roots of a woman's aggressiveness. I don't know if testosterone is meaningful to a man's behavior, or if a man can feed off a testosterone high that comes in the wake of a personal victory and take the high and catapult from there to greater achievement. Men have a lot of testosterone, and they probably put some of it to behavioral use. The body does that: it takes what's available and plays with it, though the use will be deeply influenced, and often overruled, by experience, history, social constraints, and the placebo effect of a brain that wants to believe. But the fact that men have more testosterone than women and may use that hormone, unconsciously or even consciously, to exaggerate and prolong a response and sensation—just as some women can play the strings of their sexuality and orgasmic capacity when estrogen peaks at midcycle—doesn't much matter to the outcome. There are other ways to ascend to a throne of our specifications, or to grasp at liberation and transcendence. We must shake off the yoke of testosterone and the feeling that we can't keep up without it, that men have the monopoly on the designated hormone of libido and hormone of aggression and hormone of heroes. It is not that. There is nothing to fear from testosterone.

  Let us think about some of our phylogenetic sisters and what they have to say about the roots of female aggressiveness. The spotted hyena is one of my favorite examples. The spotted hyena, Crocuta crocuta, is an African carnivore that some people say is ugly, but they are wrong. The spotted hyena doesn't look like any other mammal. Its rear legs are shorter than its front legs, the better to run long distances. Its neck is mammoth, a redwood trunk of muscle, which powers its jaw and allows it to pulverize every bit of its prey, meat, skin, bones. The spotted hyena mashes bone to powder; its scats look like chalk. The face of the spotted hyena is a blend of felid, canid, ursid, and pinniped. The hyena soul is pure fury. A lion cub is born helpless, blind and toothless. A hyena pup emerges with its eyes open and its canines fully erupted, and it strains toward the throats of its siblings. Often one newborn pup will kill another. After the initial bloodletting ceremony, the survivor settles down and, in the universal spirit of the young, turns playful.

  What makes the spotted hyena truly unusual, though, is its sexual appearance and behavior. As I mentioned earlier, the external genitals of males and females look alike. Each seems to have a penis and scrotum. But where the male's genitals are indeed a penis and scrotum, the female's apparent phallus is a combination of her vagina and clitoris, while her faux scrotum is fused labia. The female does everything through her phallus—urinates, copulates, and gives birth. Her first birth, through that slender tunnel, is agonizing. She is ripped apart by the descending pup. Many female hyenas die during first parturition. For those who survive, subsequent births are much easier—a fact that even a human mother can understand. The first is the worst.

  The spotted hyena's exceptional genitalia have misled naturalists from Aristotle through Ernest Hemingway, who thought the animals were hermaphrodites. Even after realizing that there were two sexes, per usual, scientists were stumped by the hyena's behavior and social organization. Males and females are roughly the same size, yet the females invariably rule. They are the dominant sex. An older, larger male will capitulate to a younger, smaller female. Where does female preeminence come from in this species? On first pass, the answer appears to be ... testosterone. Male and female cubs are exposed in the uterus to extremely high doses of testosterone, which is why the females emerge from the womb with masculinized genitals. The source of the testosterone is the mother's unusual placenta. In most mammals the placenta is rich in aromatase, which converts maternal androgens to estrogens, and low in the enzymes that transform precursor molecules into testosterone. The ratio of conversion enzymes in the hyena placenta is just the opposite: high in the enzyme that turns precursor steroids into testosterone, low in the aromatase that would make testosterone into estrogen. Thus the bloodstream of a fetal hyena flows thickly with testosterone, and testosterone, more than estrogen, has access to the hyena brain, where it again may be converted to estrogen, but in any event it's there, so it could be what makes for hyena scald, and why a pup snaps its canines viciously the moment it rips its way free of its mother's phallic vagina. And as the testosterone levels in the pups
' blood fall in the weeks after birth, the pups become more manageable and playful, all in keeping with the hormone's reputation.

  Yet the ways and means of our dominant female elude us. The testosterone levels of hyena pups drop in both sexes postnatally, and still the juvenile female remains more aggressive than the male. In adolescence and adulthood, the testosterone levels of the male climb considerably above those of the female hyena, as happens with sexual maturity in a male mammal, and still the female hyena refuses to budge. If there is a zebra femur under dispute, she wins. She ladies it over him. It's become a habit. But wherefore this habit, this taste for preeminence? Testosterone is not the whole story. Scientists who study spotted hyenas have looked at hyena brains with an understandable expectation that the prenatal exposure of all hyena brains to high doses of testosterone would masculinize all brains and that they would find very few if any differences between the brains of male and female hyenas. In fact, the areas of the brain that are larger in males than they are in females of many mammalian species are also larger in male hyenas, including regions that control sexual behavior. Female hyenas have "feminine" brains, and still theirs is a jabberwockying, osteophagous matriarchy.

  One interesting observation that has emerged from hyena studies is the importance of a steroid hormone called androstenedione (spoken in good, firm ladylike lilt, andro-steen-DIE-own). It is classified as an androgen—the same chemical category as testosterone—but it has never been viewed as an especially manly or exciting androgen. To the contrary. For years researchers dismissed androstenedione as a dull intermediary that signified nothing until its conversion into either testosterone or estrogen. It was assumed to be a product largely of the adrenal glands rather than of the gonads, and adrenal hormones have never seemed as sexy as ovarian or testicular hormones, because the adrenal glands of males and females just aren't different enough for those of us in thrall to sexual apartheid. Hyenas showed just what could be done with androstenedione. An adult female may not have as much testosterone as a male does, but she makes up for it with a profusion of androstenedione. The bulk of the hormone comes not from her adrenal glands but from her ovaries. For unknown reasons, a female hyena's gonads generate huge amounts of androstenedione. During pregnancy, the hormone is metamorphosed by the hyena's placenta into testosterone, which then infiltrates the bloodstream of the fetuses she bears. Yet even when the female isn't pregnant, her ovaries supply a steady current of androstenedione, and it could be this hormone that helps stoke her aggressive hauteur. Maybe, or maybe not. We don't know. What we can say is that androstenedione merits more attention than it has received heretofore. Feed, groom, and collar it, and you have a hormonal mascot of the furious female. In one study, aggressive teenage girls were found to have high levels of androstenedione in their blood. The researchers initially assumed that the findings were irrelevant, the result of the girls' being under stress and their adrenal glands' being hyperexcited, secreting excessive quantities of a number of adrenal steroids, including androstenedione. Now the researchers wonder if their subjects were really so stressed and adrenalized after all, or whether their ovaries were responsible for the androstenedione storm, with possible behavioral consequences or cadences—for instance, a brash, demonstrative, in-your-face style. Relative aggressiveness scores notwithstanding, women have much more androstenedione than testosterone in their blood plasma—four or five times the amount—and a greater percentage of that androstenedione is free—that is, unbound by blood proteins and so theoretically more accessible to the brain. A woman's androstenedione level equals that of a man. Here she is not muted. Here she has clay to play with.