Life on a caribbean island isn’t all fun and games. By measuring stress hormones in Dominican children, anthropologist Mark Flinn is showing where the tension lies.
Loping through the village of Bwa Mawego, on the Caribbean island of Dominica, Mark Flinn looks and acts like a slimmer, bespectacled Al Gore stumping on the campaign trail. He stops at each house to chat. He shakes hands, touches shoulders. He asks parents about their children in lilting Creole and talks of his own three young boys back home. At the University of Missouri, where Flinn teaches anthropology, he is an admittedly aloof and distant colleague. But here in Bwa Mawego, everyone knows everything about everybody— "If you talk about someone and you don't see them soon," one villager says, "they are either in jail or in the cemetery"— and that suits Flinn just fine. In fact, his research depends on it. As Flinn makes his way up the crest of a ravine on a winding dirt road, he runs into two boys, aged 10 and 7, on their way to school. The boys have on the requisite brown shorts and pale yellow shirts and carry book bags. "Have time to spit?" Flinn asks
Flinn gives each boy a stick of Wrigley’s spearmint gum, and they chew and spit into plastic cups. Next, an elderly matriarch named Evelyn comes up the road and lends a hand. Moving like a veteran lab assistant, she takes a plastic pipette, deftly sucks up five milliliters of saliva from one of the boys’ cups, and transfers the saliva to a labeled tube. Finally, Flinn turns to the boys and asks them how things are at home. “When did you get up? Did anybody fall this morning? Did you sleep at your grandmother’s or at home?”
Two Schoolboys stop to give Mark Flinn saliva samples for his stress research. The gum Flinn gives them is God’s gift to endocrinologists, since it doesn’t react with stress hormones.
The whole sequence, described in that way, sounds faintly absurd. Yet every action here has a reasonable purpose, and Flinn’s lines are hardly non sequiturs. He is studying the relationship between stress and health in children, and two of the best ways to gauge stress are by asking personal questions and by measuring a hormone called cortisol, found in saliva. Since 1988, Flinn has collected more than 25,000 saliva samples from 287 children in this village—an average of 96 samples per child. He has tracked the children’s growth and measured their immunoglobulin levels to see if their immune systems are healthy.
He has checked their health records and sent out an assistant to see who’s sick. Perhaps most important, he has watched, listened, and asked questions. The result is a year-by-year, day-by-day, and sometimes even hour-by-hour glimpse of these children’s lives. It’s also a compelling rebuttal to one of the most widely publicized new theories in developmental psychology.
According to that theory, propounded by psychologist Judith Harris in her controversial 1998 book The Nurture Assumption, parents have relatively little power to shape a child’s character. Studies of identical twins raised apart since birth have proved “beyond a shadow of a doubt that heredity is responsible for a sizable portion of the variations in people’s personalities,” Harris writes. At the same time, she points to a number of studies that seemed to suggest that the rest of a child’s personality is shaped more by peers than by parents. How else—to take one example—could the children of non-English-speaking immigrants speak perfect English?
After generations of child-centered parenting books, Harris’s argument immediately captured the media spotlight, perhaps mostly because it lets parents off the hook. If The Nurture Assumption is right, parents can all relax, put their kids in day care, and stop worrying that a little scolding will damage them for life. As an article in The New Yorker put it: “In some key sense, parents don’t much matter.”
Flinn’s work makes an altogether different point—one as unfashionable as it is reasonable. His thousands of data points can be grouped into any number of constellations, but one pattern shines through all the others: Families matter more than anything else in a child’s life. When a family has problems, it sends stress hormones coursing through a child’s system. When family members get along, or have numerous relatives to call on, they can shelter a child from the worst social upheavals in the outside world. Emotionally and physiologically, family life is ground zero for a child’s health.
The payoff for Flinn’s 13-year study is a startlingly intimate view of childhood and its discontents
Bwa Mawego is the perfect setting for such research. (For the sake of privacy, the names of the village and all villagers have been changed.) Life is lived in the open here, making it far easier to meet people and follow them around, and many incidental sources of stress are naturally filtered out. There is no traffic, no rat race, no threat of war. The forest is fragrant with bay leaf bushes, the winding paths littered with ripe mangoes, the houses clustered in picturesque hamlets overlooking the sea. Of course, poverty, poor roads, and exposure to the elements take their own toll, but local people—some 700 of them, all of mixed African, Carib, and European descent—are unlikely to blame their stress on their surroundings.
Take Kristen, a 4-year-old in town. Every morning she wakes up to a billion-dollar view: Her house is built on stilts, on a volcanic cliff overlooking the Atlantic. In the front yard, clean laundry hangs on the trees that dot the hard-packed mud, chickens run about, and a soft Caribbean breeze wafts the smell of roasting coffee beans across the porch. With her large brown eyes, sweet smile, and quiet manner, Kristen is a child anyone would want to hug, and lots of people do—her mother, grandparents, and a multitude of relatives all live within walking distance.
Yet Kristen’s life has its share of stress. Before she was born, her mother, Julianne, was single and going to high school in the city. When Julianne became pregnant, she had to move back home and hasn’t worked since. Although Robbie, a nice guy and an old friend of Julianne’s, has since become a kind of stepfather to Kristen, Julianne still worries about the opportunities she missed by not getting an education. In Bwa Mawego, as in most places, life can be tough for a single mother. And today Kristen has a cold.
Children at home tend to have higher cortisol levels than children at school, one british study has shown. It seems that Life at home is far more unpredictable, and so more stressful.
Flinn sees no coincidence there. “In the village, illness among children increases more than twofold following significant stress,” he says. “About 30 percent of the children in the village have the current cold, even though most of them have been exposed to the pathogen. So why are only certain ones sick? In the West we think it is mostly contact—send your child to preschool and expect them to get sick. But I am convinced that resistance is more important than contact frequency.”
The reason is as complex biologically as it is emotionally. When a person is in trouble, Flinn explains, the brain automatically sends signals to the sympathetic nervous system, initiating a “fight or flight” response. First adrenaline and then cortisol are secreted by the adrenal glands, revving up the body and then sustaining the energy flow to different systems. The lungs pump faster and the heart starts to race; blood pressure rises, charging up the muscles and sharpening the mind; the stomach gets jumpy and the rush of endorphins numbs the body. At the same time, the appetite, libido, and immune system shut down, and the energy they would normally consume is diverted to muscles that will help the body fight the immediate threat.
This is all well and good—unless the perceived threat persists. In that case, adrenaline washes out of the body quickly, but cortisol may linger for days, weeks, or even years, keeping the immune system and other important functions depressed. Children are especially vulnerable to stress. Their bodies are “nothing other than a long-term building project,” says Robert Sapolsky, a stress researcher at Stanford University. Yet chronic stress is “constantly telling them, ‘Don’t fix stuff now, do it tomorrow, do it tomorrow.’” In the long term, too much cortisol can slow down a child’s growth, brain development, and sexual maturation. In the short term, it can make a child prone to upper-respiratory infections and diarrhea, diseases that are often fatal at that age.
Stress can make you sick.
Thanks to cortisol, measuring stress is as easy as a lab test or two. But only patient, detailed, long-term work like Flinn’s can untangle its myriad causes. Hormone levels differ from child to child, Flinn says, and they fluctuate naturally over the course of a day. “The old dogma was that if you got a sample once a day, collected between 8 and 10 a.m., that was enough. But I’ve found that controlling for time of day is not enough. If you have a tough kid who is habituated to the mundane, giving a saliva sample in a lab would be a bore. You need to know what happened to this kid the day before: Is he burned out? What are his reserves? What’s the context?”
The National Institute of Mental Health offers more about the effects of stress on developing brains: www.nimh.nih.gov/publicat/develop.cfm