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partly because his “nurturist” reputation was so strong.
If anyone could help me untangle the nature-nurture question, I
hoped, it was Jerry Kagan.
Kagan ushers me inside his office in Harvard’s William James Hall,
surveying me unblinkingly as I sit down: not unkind, but definitely
discerning. I had imagined him as a gentle, white-lab-coated scientist in
a cartoon, pouring chemicals from one test tube to another until—
poof!
Now, Susan, you know exactly who you are
. But this isn’t the mild-
mannered old professor I’d imagined. Ironically for a scientist whose
books are infused with humanism and who describes himself as having
been an anxious, easily frightened boy, I find him downright
intimidating. I kick off our interview by asking a background question
whose premise he disagrees with. “No, no, no!” he thunders, as if I
weren’t sitting just across from him.
The high-reactive side of my personality kicks into full gear. I’m
always soft-spoken, but now I have to force my voice to come out louder
than a whisper (on the tape recording of our conversation, Kagan’s voice
sounds booming and declamatory, mine much quieter). I’m aware that
I’m holding my torso tensely, one of the telltale signs of the high-
reactive. It feels strange to know that Kagan must be observing this too
—he says as much, nodding at me as he notes that many high-reactives
become writers or pick other intellectual vocations where “you’re in
charge: you close the door, pull down the shades and do your work.
You’re protected from encountering unexpected things.” (Those from less
educated backgrounds tend to become file clerks and truck drivers, he
says, for the same reasons.)
I mention a little girl I know who is “slow to warm up.” She studies
new people rather than greeting them; her family goes to the beach
every weekend, but it takes her ages to dip a toe into the surf. A classic
high-reactive, I remark.
“No!” Kagan exclaims. “Every behavior has more than one cause.
Don’t ever forget that! For every child who’s slow to warm up, yes, there
will be statistically more high-reactives, but you can be slow to warm up
because of how you spent the first three and a half years of your life!
When writers and journalists talk, they want to see a one-to-one
relationship—one behavior, one cause. But it’s really important that you
see, for behaviors like slow-to-warm-up, shyness, impulsivity, there are
many routes to that.”
He reels off examples of environmental factors that could produce an
introverted personality independently of, or in concert with, a reactive
nervous system: A child might enjoy having new ideas about the world,
say, so she spends a lot of time inside her head. Or health problems
might direct a child inward, to what’s going on inside his body.
My fear of public speaking might be equally complex. Do I dread it
because I’m a high-reactive introvert? Maybe not. Some high-reactives
love public speaking and performing, and plenty of extroverts have stage
fright; public speaking is the number-one fear in America, far more
common than the fear of death. Public speaking phobia has many
causes, including early childhood setbacks, that have to do with our
unique personal histories, not inborn temperament.
In fact, public speaking anxiety may be primal and quintessentially
human, not limited to those of us born with a high-reactive nervous
system. One theory, based on the writings of the sociobiologist E. O.
Wilson, holds that when our ancestors lived on the savannah, being
watched intently meant only one thing: a wild animal was stalking us.
And when we think we’re about to be eaten, do we stand tall and hold
forth confidently? No. We run. In other words, hundreds of thousands of
years of evolution urge us to get the hell off the stage, where we can
mistake the gaze of the spectators for the glint in a predator’s eye. Yet
the audience expects not only that we’ll stay put, but that we’ll act
relaxed and assured. This conflict between biology and protocol is one
reason that speechmaking can be so fraught. It’s also why exhortations
to imagine the audience in the nude don’t help nervous speakers; naked
lions are just as dangerous as elegantly dressed ones.
But even though all human beings may be prone to mistaking
audience members for predators, each of us has a different threshold for
triggering the fight-or-flight response. How threateningly must the eyes
of the audience members narrow before you feel they’re about to
pounce? Does it happen before you’ve even stepped onstage, or does it
take a few really good hecklers to trigger that adrenaline rush? You can
see how a highly sensitive amygdala would make you more susceptible
to frowns and bored sighs and people who check their BlackBerrys while
you’re in mid-sentence. And indeed, studies do show that introverts are
significantly more likely than extroverts to fear public speaking.
Kagan tells me about the time he watched a fellow scientist give a
wonderful talk at a conference. Afterward, the speaker asked if they
could have lunch. Kagan agreed, and the scientist proceeded to tell him
that he gives lectures every month and, despite his capable stage
persona, is terrified each time. Reading Kagan’s work had had a big
impact on him, however.
“You changed my life,” he told Kagan. “All this time I’ve been blaming
my mother, but now I think I’m a high-reactive.”
So am I introverted because I inherited my parents’ high reactivity,
copied their behaviors, or both? Remember that the heritability statistics
derived from twin studies show that introversion-extroversion is only 40
to 50 percent heritable. This means that, in a group of people, on
average half of the variability in introversion-extroversion is caused by
genetic factors. To make things even more complex, there are probably
many genes at work, and Kagan’s framework of high reactivity is likely
one of many physiological routes to introversion. Also, averages are
tricky. A heritability rate of 50 percent doesn’t necessarily mean that my
introversion is 50 percent inherited from my parents, or that half of the
difference in extroversion between my best friend and me is genetic. One
hundred percent of my introversion might come from genes, or none at
all—or more likely some unfathomable combination of genes and
experience. To ask whether it’s nature or nurture, says Kagan, is like
asking whether a blizzard is caused by temperature or humidity. It’s the
intricate interaction between the two that makes us who we are.
So perhaps I’ve been asking the wrong question. Maybe the mystery of
what percent of personality is nature and what percent nurture is less
important than the question of
how
your inborn temperament interacts
with the environment and with your own free will. To what degree is
temperament destiny?
On the one hand, according to the theory of gene-environment
interaction, people who inherit certain traits tend to seek out life
experiences that reinforce those characteristics. The most low-reactive
kids, for example, court danger from the time they’re toddlers, so that by
the time they grow up they don’t bat an eye at grown-up-sized risks.
They “climb a few fences, become desensitized, and climb up on the
roof,” the late psychologist David Lykken once explained in an
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