Woman

by Natalie Angier

  The rat work has yielded a wealth of detail and gives a sense of how nuanced the conversation between ovary and society can be. As a rule, female rats in a group strive to ovulate and conceive within a week or two of one another. They keep in reasonably close gestational step so that when all is done, they can breastfeed together, in a squirming, squealing mass. They're not sweet little communists. They're Norway rats, the kind of surly, toothy scavengers you find in dumpsters and sewers. But it turns out that by pooling pups and breastfeeding duties, each female benefits. She spends less time and energy lactating than she would if she had to attend to her offspring solo, and her pups are comparatively fatter and healthier at weaning. Synchrony, then, is the optimal state. And if a female for some reason miscarries or loses her litter soon after birth, she will do what rats hate to do, which is to hold back before breeding again. She awaits signals from her lactating sister rats. She wants to reset her clock so that it synchronizes once again with theirs.

  There is more to the rats' tale of how society shapes biology. If a female for some reason falls out of sync with the group and conceives pups anyway, her sense of her own procreational asynchrony has a profound effect. She ends up giving birth to a litter composed largely of daughters rather than the standard half male, half female brood of the harmonious rat. Here is what happens. The new mother rat is going to be living and breastfeeding around other females, who are on a different bioclock from hers and who are thus likely to have pups that are much older than the newborn litter. Older pups are notorious milk hounds, and no milk is sweeter and more nutritious than the milk of a freshly lactating breast. They will steal much of the new mother's milk, and she can do little to prevent their nips. Therefore, many of her own helpless offspring will die of starvation. If only one or two of her pups are going to make it, it's best that they be females. Among rats (and many other species), daughters are the safe sex, sons the high-risk sex. Daughters are government bonds; sons are junk bonds. A male rat might copulate widely and madly and make scores of babies and make his mother a triumphant, wealthy grandmother, but he might fail completely and inseminate nobody and make nothing of himself or his bloodline. By contrast, it is a very rare female rat who does not breed at all. She can have only so many pups in her lifetime, but she will have some. When times are hard and prospects grim, then, invest in daughters. They will keep the lineage alive. We see here an extraordinary example of the outside elbowing its way into the deepest chambers, into the womb. The pregnant female rat senses her asynchrony, and the status of her social group and of the communal breast, and somehow she translates that sensory information into a bias against male fetuses, resorbing them into her body before they cost her a drachma of possibly fruitless care. Feeling at risk, her body seeks guarantees. It gives her girls.

  In 1998, the McClintock team again published a major report in the journal Nature, confirming that we have a bit of the rat in us and that our ovaries too are susceptible to the sway of the Weltanschauung of the group. The scientists showed that if they took swabs from the armpits of women at different points in their ovulatory cycle and applied the swabs to the upper lips of other women, the donor secretions could act as pheromones, as odorless chemical signals. The secretions either hastened or prolonged the cycles of many, though not all, of the women exposed to them. Armpit swabs taken from women early in their cycle, in the follicular phase, before ovulation, had the effect of shortening the cycles of the recipient women—that is, the beneficiaries ovulated several days earlier than predicted from prior records of their cycles. If, in contrast, the underarm swabs were taken later in the month, around the time when the donors were ovulating, the pheromones extended the cycles of the women given an upper-lip treatment—the recipients ovulated several days later than predicted from their ordinary cycle span. Pheromone samples taken later still, after the donors had ovulated—during the luteal phase of the cycle, which precedes menstruation—had no impact on the recipients one way or another.

  Not all of the women were influenced by the pheromones, but enough of them were to elevate the findings to robust statistical significance and to demonstrate with fair firmness that human pheromones exist. What we see in this carefully controlled experiment is that women can push and women can pull, and they can respond to other women in varying ways, all unconsciously, without knowing why, without the benefit even of olfaction, for the women in the study said they smelled nothing when the swab was applied under their nose, save for the scent of rubbing alcohol used as a prep in the experiment. The results also explain why studies of menstrual synchrony have wandered all over the place, sometimes coming up positive and sometimes negative: because the pheromonal signals can either bring women's cycles together or push them apart, depending on when in the month the signals are produced, studies that just searched for total synchrony missed the equally important asynchronous patterns that emerged.

  But what is the good of this social control of ovulation? What is the good of trying to bring other women into concert with you or trying to throw other women out of reproductive joint? We don't know. We can only speculate. We must expand our imaginations, backward, forward, and outward. We must think beyond lunar phases and simple ovulation and menstruation and take into account the months that women spend being pregnant, and the months or years they breastfeed, and the smells and cues they might emit during those protracted states. We must think as well of our emotional and political relationship to our cohabitants and the degree to which we feel camaraderie with them, or competition, or utter disinterest. If we are very comfortable with the women in our intimate domain, then menstrual synchrony might more easily emerge. To feel safe is to feel willing to risk impregnation. It is easier to conceive when ovulation is regular, and one way to entrain the cycle, to stabilize it, is to attend to the resonant frequency of those around you.

  If, though, we feel at odds with our den mates, then why expect ovarian collusion, or any sort of stabilizing influence from them at all? Subordinate cotton-top monkeys will not ovulate when they are around the ruling female. The alpha female doesn't hound them. She doesn't beat them or steal food from them. Mostly she ignores them. Yet the smell or sight or aura of her muffles the subordinates' neural oscillator, and they don't ovulate. Might a woman also recoil in the presence of a threatening or irritating female? If that rival is nursing a newborn, might the woman choose to delay her own ovulation a bit—unconsciously choose, of course—so that when she conceives and must meet the demands of pregnancy, she will not face the additional burden of competing for resources against a hostile lactator? The social control of ovulation could be used cooperatively, then, to harmonize cycles, or it could be used defensively, to avoid conflict, or it could be used offensively, to destabilize a competitor's cycle, to attempt to undermine her fertility, if need be.

  "Information is the key. It is always the key," says McClintock. "The more information one has, the better. The woman who is able to regulate and optimize her fertility, to ensure that she is fertile at the best possible time in terms of both her physical and her social environment, will be more successful than the woman who hasn't a clue." Pheromones are only one source of information, McClintock says. They are not the sole source, or even necessarily a central source, of information about where you stand and whether it's time to make your move. Pheromones simply add to the mix, and sometimes they're worth attending to and sometimes they're not—and so it was that some of the women in McClintock's study were susceptible to them and some were not.

  We are submerged in a sea of sensory advice. Our sexual partners exert influences of their own on our brains and baskets. Women who live with men tend to cycle in a more predictable fashion than women who live alone, and regular cycling augments the chance of conception. A woman might again be responding to pheromones, secreted by the man's armpit, his groin, or the back of his neck, at just the spot where she feels compelled to nuzzle. But why stop at the nose? Your whole body can serve as a busybody. As we saw earlier, a woma
n is likelier to become pregnant from sex with an adulterous lover than she is from sex with her husband. The data are under dispute and could be explained by something as mundane as the fact that a woman may be unwilling to take birth control to an assignation for fear of discovery. Alternatively, as we have seen, the discrepancy could be the result of orgasm's pulling desired sperm in, as a form of last-ditch female choice. Yet another possibility is that pleasure, like the presence of other females, can have congress with the ovaries and sway the timing of ovulation, perhaps by triggering the LH surge that liberates an egg from its cell. I strongly suspect that climax counts, and that anything capable of causing the uterus to shudder so insistently must impress the neighboring pods and their seeds as well. Maybe a follicle, on feeling the temblor, will quicken its pace of maturation and tell the brain, Hurry up, please, it's time, and the brain will respond with an LH surge, the ovum's hymn of freedom.

  Admittedly, I have been seduced by experience, my personal encounter with the fertility spirits. My husband and I had been trying for years to become pregnant. I cycled like a metronome, every twenty-eight days. And for a while our sex became metronomic too, concentrated furiously around midmonth, when I thought I was likeliest to conceive. We tried all the suggested positions. Sometimes I'd have an orgasm during sex; sometimes I consciously refrained. Who knew whether a pulsing cervix would pull in the sperm or spit it out? Best to be catholic in every detail. I would lie afterward immobilized, with buttocks elevated. I used ovulation predictor kits to detect my LH surge. For several months we abided by the thin blue line. Nothing happened, nothing, nothing, nothing.

  In November of 1995, my little predictor sticks failed to detect evidence of an LH surge. I was terribly glum about that: an anovulatory cycle, I thought, and there I was, thirty-seven years old, running out of time. But in December I found out that I was pregnant—that I had conceived the month before, when I was certain all lay fallow. I reviewed the sequence of events, and I knew what had happened. Early in my cycle, days before I thought conception was possible, my husband and I had done what we managed so rarely in those times of procreation fixation and had sex for the pure love and pleasure of it. That act, I am sure, that pointless, magic squander, pumped up my cycle as smartly as Jan Ullrich jazzing through the Tour de France. My climax quickened the hatching of an avid egg. It provoked an LH surge, and the surge spurred a follicle, and the egg broke free and dove down a tube, and the sperm from the precipitating event was there to greet it. And everything fell into place so swiftly that by the time I started the usual midmonth screening for an LH surge, I had missed the excitement. I thought I lay fallow, but in truth I already was in clover.

  I have no proof of any of this, of course. All I have is my child. A rat's distress will give her daughters. I got mine from joy.

  10. GREASING THE WHEELS

  A BRIEF HISTORY OF HORMONES

  EVERY MORNING I take a little pill that contains thyroxine, a hormone produced by the moth-shaped thyroid gland in the middle of the neck. When I was in my twenties I had Graves' disease, an autoimmune disorder in which the thyroid becomes hyperactive and generates too much thyroxine. I hate going to doctors, and it went undiagnosed for months. I was jittery, anxious, an emotional hacksaw. My heart raced at 120 beats a minute, nearly twice my normal pulse, even when I lay in bed. I had been an athletic woman, but suddenly I lost all my strength and could not walk up a flight of stairs without stopping for a break midway. I ate ravenously and still lost weight, but I looked too sick to elicit compliments on my slimmer figure. My eyes bulged out slightly and lent me the appearance of a tree frog, a symptom that I now recognize in the faces of other Graves' alumnae, like the former first lady Barbara Bush.

  I was treated with radioactive iodine, which homed in on the diseased thyroid gland and destroyed much of it. Now I am hypothyroid, making less thyroxine than I need, and so I will have to swallow one of these supplements every day for the rest of my life. It's a dull business. It doesn't change anything about my mood or personality. It doesn't even offer the mild refreshment of other daily rituals, like the brushing of the teeth or the washing of the face.

  Yet if I were to stop taking thyroxine, my life would change for the worse. Gradually, over days or weeks, I'd become irritable, depressed, lethargic, and stupid. I'd gain weight, feel cold most of the time, and lose my libido. My heart rate would become slow and irregular, and my blood pressure would rise. Again I'd be sick and at risk of early death; again I'd be crushed by my chemistry.

  Thyroxine is not a sexy hormone. It is not what we mean when we talk of being "flooded with hormones" or "high on hormones," as teenagers and lovers are said to be. The hormone family of chemicals is a vast kindred that includes such familiar bio-actors as the sex hormones—the estrogens and the androgens—and the stress hormones, our private hair-trigger sentries that counsel panic whether it's a lion or a landlord snorting at the door. It includes a host of backstage technicians that tell us we need salt, food, or water, and it includes compounds that we don't normally think of as hormones at all, like serotonin, the famed target of Prozac, Zoloft, and the other perimillennial mood brighteners.

  Through my years of dependency on hormones, I became curious about their contours, their edges and their limitations. I wondered why something like thyroxine, which could be so brutal and upheaving when generated in excessive or insufficient quantities, was otherwise so unremarkable, so unilluminating. In taking the right amount of thyroxine, I returned to the status quo of myself, the stable instability that I have known since the onset of sentience, but nothing more. The best I could do was to keep the old version operating. Thyroxine, then, was at once global and narrow. No tissue, not even my brain, was spared from an abnormality of its production, yet it was not me, not the flesh of self or of consciousness. What was going on, then? Hormones have effects, they have failings, they have meanings. Hormones are far more important than most of us realize, but not in the ways that most of us think.

  Lately there has been a hormone renaissance, a renewed fascination with these chemical messengers and what they can do for us, say about us, solve about us. Part of the interest is rhetorical fashion. It is fashionable now to ascribe such supposedly male traits as the tendency to swagger, posture, interrupt, and belch in public to testosterone. Men in groups are said to "reek of testosterone," to be "poisoned by testosterone," to be "caldrons of testosterone." It sounds cute, it sounds clever, and because yes, men do have a fair amount of testosterone, it sounds accurate as well. Hormone humor does not spare women, though, and so gals on a shopping expedition or sharing a cappuccino become "estrogen sinks" or waft "billows of estrogen." It is also fashionable to talk of love hormones, mommy hormones, and even crime hormones. We want to explain ourselves to ourselves, and hormones look like a clean and quantifiable way to do so, to distinguish male from female, competitor from cooperator, domesticated from feral. We are incorrigible categorizers.

  Popular interest in hormones also reflects a revival of interest among the high priests of organizing principles, scientists. There has been an explosion of hormone research unmatched in ferocity since the first hormones were isolated and synthesized more than seventy years ago. Comforting analogies no longer apply. In the past, hormones were talked of as keys, each designed to fit into a specific receptor—the metaphorical lock—located on different tissues of the body and brain. In so fitting, a hormone would swing wide the door to a defined suite of behaviors and reactions. Now the metaphor has rusted. It turns out that the body offers up multiple locks to the pryings of any given hormone, and sometimes the hormones exert their might without the need for any lock at all. Instead they can ramrod their way through from blood into tissue, or slip in between the cracks, leaving us agog once more at how potent, how exquisite, and how crude these chemical emissaries can be.

  Hormones have a music to them, a molecular lyricism that explains why they are potent and ancient: why they work well enough to have merited retention in one
form or another through hundreds of millions of years of evolution. Certain hormones are among the things that make us women, and these are the hormones that I will focus on. They are the fashionable hormones: estrogen, progesterone, testosterone, oxytocin, and serotonin. But the hormones are not slaves to fashion. They don't conform to expectations. They hate clichés.

  Hormone comes from the Greek horman, which means to arouse, to excite, to urge. This is what a hormone does. It excites. It urges, though sometimes what the hormone urges is a sense of calm, a call to rest. By the classic definition, a hormone is a substance secreted by one tissue that travels through blood or another body fluid to another tissue, whereupon the hormone arouses the encountered tissue to a new state of activity. The thyroid gland secretes thyroxine, which stimulates the heart, the muscles, and the intestines. A follicle on the ovary bursts open and releases a draft of progesterone, which cues the endometrium to fatten. The classicists thought that hormones differ from neurotransmitters, the quick-snapping chemicals such as norepinephrine and acetylcholine that allow brain cells to communicate; but that distinction has begun to disintegrate as researchers have learned that hormones, like neurotransmitters, can alter the texture and disposition of brain cells, making them more likely to fire. Brain cells talk to one another in a rat-a-tat-tat of electrical impulses. And so, while it wouldn't be quite proper to call estrogen a neurotransmitter, it would be proper to call it and the neurotransmitters members of a large chemical family of neuromodulators—brain inflectors. This reclassification is more than a semantic issue. It affects how we think about our thinking and feeling and being. It also brings the body and brain into synchrony rather than continuing the old distinction that said en-docrinologists get the chemistry from the neck down, while the neurobiologists claim the domain of the brain.