Anxiety: Inherited Through Genetics?

Robin Marantz Henig took a close look at a long-running study out of Harvard that tried to figure out why certain people are wired to worry. The work belonged to Jerome Kagan, who in 1989 was a Harvard psychology professor deep into tracking temperament and how it plays out across a lifetime. Temperament, as Kagan saw it, has many layers. So he narrowed his attention to a single thread: how easily a baby became upset when something new entered its world. That one trait was pickable for study because you could actually measure it, and because it seemed to account for a good chunk of ordinary differences between people. An earlier project of his on toddlers had already hinted that the jumpiest infants tended to become shy, held-back, anxious kids.

Kagan went back through the videotapes of his first study babies, hunting for the kind of jittery response he would eventually label high-reactive. The first eighteen gave him nothing. They watched unfamiliar things with a sort of calm. Then came the nineteenth. New sounds, new voices, new toys, new smells, all of it threw her. She kicked her legs, arched her back, cried. This was exactly the reaction Kagan had hoped to find without being certain it existed: an infant who came undone at the first taste of the unfamiliar. He kept following her.

Baby 19, it turned out, grew up more or less as her infant self predicted. By the time the study reached her at fifteen, she was an unremarkable-looking teenager who kept her face half-hidden behind long dark hair. Every fifteen-year-old in the study sat for the same interview, which opened with questions about school. In a quiet voice she mentioned she didn't do much outside of class, though she liked writing and the violin. She couldn't sit still. She twirled her hair, tugged at an ear, bounced a knee. Kagan read that restlessness as the spillover of her high-reactive makeup.

Asked what she worried about, she stalled. A long pause, hair twirling faster, hands going to her face and knee. A small smile, a shrug, another pause. And then it came out in a rush. Not knowing what she was supposed to do, especially when everyone around her seemed to. The constant inner questioning: should I go here, should I go there, am I in the way. Deadlines and whether she'd finish. Crowds, and the dread of what she might say and what others might say back. By then she was wringing her hands. How she would handle adulthood, whether she'd ever do anything that counted for something. She wanted to matter, she said, and couldn't be sure she would. "I can't stop thinking about that."

Grown now, she could name the things that frightened her, which she did, at length. She remains anxious about nearly everything. There are people who, no matter how secure the finances or how healthy the kids, are quietly bracing for catastrophe. Kagan put Baby 19 squarely in that camp. Born worriers, their brains permanently listening for the next shoe to fall. For roughly twenty years he and his colleagues tracked hundreds of people like her from infancy forward, watching what became of children who seemed primed to fret. With those infants now young adults, the research was starting to reveal something about how the anxious brain actually works.

The notion that temperament is something you're born with has long had traction among psychologists. We can, in other words, come into the world tilted toward anxiety. By this point four major long-term studies were running: the two Kagan launched at Harvard, plus two at the University of Maryland led by Nathan Fox, one of his former graduate students. Their findings mostly line up. Babies arrive with differing temperaments. Somewhere between fifteen and twenty percent will respond intensely to unfamiliar people or situations. And those strongly reactive babies carry a higher chance of becoming anxious adults.

One of the larger things Kagan drew from all this: the temperament sticks around, but the behavior attached to it does not always follow. He broke an emotion into three parts, the physiological state of the brain, how a person puts the feeling into words, and what the person then does. A given brain state, he noted, doesn't guarantee a given experience of it. One person reads a revved-up brain as tense or anxious; another likes the buzz and calls it feeling alert. Nor does the same brain state produce the same actions. Some bury the unpleasant feeling and carry on looking fine; others pull back. For Kagan, the behavior and the conscious sense of anxiety can often be steered. The underlying physiology usually cannot. He named that gap the long shadow of temperament.

The oldest high-reactive subjects, Baby 19 among them, had reached their twenties. They were still anxious, still on guard, still wrestling with focus and an inability to settle. Anxiety, in Kagan's framing, is fear that has slipped its leash. It starts in the head and then drives a physical reaction. Thoughts the brain generates can send the amygdala into overdrive. In his high-reactive subjects, Kagan found exactly that, an amygdala firing like a motion-sensor light that flicks on when nothing's out there but the rain.

Other physical signs showed up in children of this type, many of them tied to that same amygdala overactivity. They leaned toward more activity in the right hemisphere, the side linked with low mood and anxiety. Their heart rate and pupils responded more sharply to stress. At times their stress hormones, cortisol and norepinephrine, ran higher.

As for Baby 19, she had not broken from her type, and probably never would. Kagan said she was doing fine in college, yet her temperament still showed through. He described her as dour and melancholy. A worrier, as she likely always will be.

A reader named Kim B. pushed back. In her view anxiety owes more to environment than to genes, a position she drew from her own life and from watching other people rather than from any formal study. She didn't deny that genetics shapes every part of how a person develops. She simply put environment on equal footing with it. Genes shouldn't be waved off, and belong in the research alongside everything else about our physical and mental makeup; they often set us up for certain physical traits or diseases. But environment, she argued, does as much to shape who we grow into and how we come to understand ourselves.

Take a child adopted and raised apart from the biological family. That child picks up most of their behavior and beliefs from the people closest to them, the adoptive parents. The body is a different matter. The child might still carry the same cancer, diabetes, or even mental disorder that ran in the biological line. When the biological parents were never present to exert any influence, DNA is about the only explanation left for a disease or disorder surfacing in the child. There have also been well-known studies on touch and the withholding of it from infants, and what that does to how both groups develop. People need the touch and nearness of others, and that example rests entirely on environment.

Studies of how peers affect one another point the same direction, Kim wrote. The young especially hunger for acceptance. They'll bend who they are and what they believe to get it, and in bending they stunt their own growth. That alone breeds anxiety, a kind that flares from a clash within a person's own sense of identity.