EVOLUTION

My husband and I were a classic introvert-extrovert pair. Then we switched

Obsession
Life as Laboratory
Obsession
Life as Laboratory

When I met the man who would become my husband nearly 20 years ago, we were a study in contrasts. I was drawn to Erik’s studious silence. He liked to spend his free time reading, hiking, and meditating. Meanwhile, I was boisterous and prone to hyperbole. My little day planner was so crowded with events that you could barely see the white.

I often cajoled Erik into attending parties and invited our friends along on couples’ activities. “Don’t you ever need downtime?” he’d ask me after a busy weekend, dragging a hand heavily down his face.

I thought I understood our dynamic: We were a classic introvert-extrovert pair. But over years of marriage, our social preferences began to shift. I found myself opting to stay home in the evenings and write, while my husband was the one to ask about our New Year’s Eve plans or invite friends over for a barbecue. Once, at our son’s third birthday party, I’d found Erik hiding from the crowd alone in a dark garage. Now he happily volunteered to take our kid bowling with a dozen of his classmates—and I couldn’t wait to get some time alone.

In an era when Myers-Briggs tests and BuzzFeed personality quizzes dominate the web, it’s popular to divide ourselves along clean lines of personality. According to the terms coined by Swiss psychiatrist Carl Jung, either you’re an introvert who feels drained after too much social time, or you’re an extrovert who’s energized by parties and meeting new people. But a closer look at the research on introversion and extroversion suggests these traits aren’t as fixed as they seem. As my marriage would prove, it may be possible for both types to change their spots.

Unfixed personalities

Science can offer some insights into the biological underpinnings of introversion and extroversion. Through fMRI imaging, a Harvard neuroscientist showed that introverts have thicker gray matter in their prefrontal cortexes—the part of the brain linked to rumination and deep thought. Introverts’ nervous systems also tend to have a greater level of “arousal”—that is, they respond more intensely to stimulus. This means they are more likely to feel overwhelmed by stimulus ranging from noise to light to social activity.

Extroverts’ nervous systems are also less easily aroused—which might explain their tendency to seek outside stimulation in the form of a busy social schedule. You might even liken the extrovert’s tendency toward greater activity to an addict pursuing a high.

The measurable neurological differences in brain imaging don’t explain why introverts and extroverts sometimes act out of character. But what we can say, as Cambridge University personality psychologist Brian Little explains, that there is a definitive “biogenic” component to personality.

Of course, personality isn’t solely determined by biology. Our personalities are also formed by “sociogenic” factors—the early childhood experiences and cultural norms that shape the people we become.

 I exuded a social brightness so that people would never look too closely. Growing up, for example, my husband often sought out solitude in order to avoid other people’s demands. My friendly personality, meanwhile, was motivated by my desire to be a people-pleaser. I exuded a social brightness so that people would never look too closely and uncover the shame I’d felt growing up in a family darkened by addiction.

But as our circumstances change, so can our social preferences. As I’ve become more stable and secure, I’ve found that I don’t need the distraction of constant social activity. And once my husband became a psychologist, he realized that his job was to meet others’ needs head-on. So he developed a skill set that would allow him to sustain energy in the midst of a lot of social interaction.

My research into the way our social preferences can evolve led me to the burgeoning field of personality psychology known as “free trait theory,” which holds that under the right circumstances, a person can transcend their fixed personality style to act “out of character.” The man behind this theory is Brian Little.

 Under the right circumstances, a person can transcend their fixed personality style to act “out of character.”  Little explains that in addition to the “biogenic” and “sociogenic” factors that shape personality, there’s an “idiogenic” component as well. Depending on the circumstances and our own desires, we can consciously choose to behave a certain way—at least for a period of time. Introvert expert Susan Cain summarizes the idea in her book Quiet: The Power of Introverts in a World That Can’t Stop Talking: “Free trait theory explains why an introvert might throw his extroverted wife a surprise party or join the PTA at his daughter’s school.”

I stopped short at that particular example. Two Augusts ago, my husband threw me a large surprise 40th birthday party, months in the planning. “The secret to his surprise,” one friend said later, “was that a party like this is the last thing Erik would ever want you to do for him.”

“I wanted your party to be massive,” he told me later, sounding disappointed. “Hundreds, a sea of faces to blow you away.”

Growing into ourselves

To some extent, then, we can choose how introverted or extroverted we want to be in a given situation. But is it also possible that introverted and extroverted brains can change—or are they set from birth?

Our brains exhibit remarkable levels of plasticity, particularly when we challenge ourselves to learn new skills or pursue new activities. Research shows that meditation, for instance, when done consistently, can have a dramatic, measurable effect on the thickness of the prefrontal cortex, as can yoga. A 2014 study (PDF) found that students taking drawing and painting classes experienced changes in their prefrontal white matter that were linked to increased creativity. So it’s possible that an introvert motivated to take on extroverted activities could potentially reshape their introversion, and vice versa.

There’s another major factor that can influence the way our personalities develop over time: aging. By midlife, we “become better at being who we are,” according to Dawn Carr, a social science researcher at Stanford University. As we gain practice exhibiting the traits of our personalities, we perform less, choosing our activities and friends based on our deeper values rather than our need to be liked or accepted.

 As we gain practice exhibiting the traits of our personalities, we perform less, choosing our activities and friends based on our deeper values. We also become more selective as we get older about how to spend our time, and with whom. Speaking from personal experience, in my younger days I was happy to socialize constantly, even with distant acquaintances. But as I began to raise a child and devote myself to my career, I became more judicious, reserving my energy for the people closest to me.

As I write this piece, my introverted husband is out at dinner on a weeknight, with a leadership group he joined in order to meet new people. Meanwhile, I’m in bed, relishing the quiet after my child has gone to sleep.

Neither of us are quite the people we were when we married. But as a recent episode of the NPR podcast “Invisibilia” highlighted, personality can be a pretty fluid thing. We’ve each become a little more like the other—domestic chimeras, no less loved for our complexities.

Follow Jordan Rosenfeld on Twitter @JordanRosenfeld. We welcome your comments at ideas@qz.com.

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