[BACKGROUND CHATTER] CHRIS EGUSA: When my sister Kelly was around 15 or 16, she got invited to her very first high school party.

JOHANNA MAYER: Producer Chris Egusa, back this week.

CHRIS EGUSA: It was at Ally's house, the most popular girl in her class. There were over 50 people coming, a live band. It was a classic coming of age moment.

KELLY EGUSA: I picked out an outfit, wanted it to look cool, but not like I was trying too hard.

CHRIS EGUSA: This was her chance to break into the popular group, shake up the social ladder a little bit.

KELLY EGUSA: I was expecting to just do what they do in the movies. You make friends, you see people you know, you hang out, you have a good time.

CHRIS EGUSA: But as she settled in--

KELLY EGUSA: I was just like, wow, I don't want to be here. And I hated every moment of it.

CHRIS EGUSA: She wasn't super close with anyone there. And she ended up doing that thing where you shuffle around the outside of conversations, unsure of how to jump in.

KELLY EGUSA: And I was waiting all night to go home.

CHRIS EGUSA: As she counted down the excruciating minutes until she could leave, she developed a little party hack, one that she still uses to this day.

KELLY EGUSA: Find the snack table. Then you can make small talk around food, which is super awesome. And you just can like, oh, this dip is amazing. And I just hung out by the snack table and ate chips for two hours.

CHRIS EGUSA: See, the thing about Kelly is she's an introvert, and not just slightly introverted. When she took an introversion test back in high school, she got the highest score possible. As a refresher, here's the popular definition of an introvert, someone who is quiet, generally prefers one-on-one interaction to things like parties, and who enjoys solitary activities. Its opposite is an extrovert, someone who just can't get enough of people.

And I should say Kelly has a ton of friends. But growing up, she definitely had a hard time with some social situations. Even ordering at restaurants was draining. For Kelly, self-serve is basically a dream come true.

KELLY EGUSA: Oh, my gosh, yes, buffets, all that stuff. No human interaction is the ideal.

JOHANNA MAYER: Classic introvert story. But how much do labels like introvert or extrovert really matter? And why do we find it so very satisfying to slot ourselves into these personality buckets?

Taken to its extremes, it can all feel like a very 21st century, internet-era phenomenon. But it's actually a story that goes back a hundred years to a time when a famous psychiatrist fell out with his friend and just tried to make sense of where they went wrong. From Science Friday, this is Science Diction. I'm Johanna Mayer.

CHRIS EGUSA: And I'm Chris Egusa. Today, we're talking about the word "introvert."

[MUSIC PLAYING]

JOHANNA MAYER: The two toured conferences together-- in February of 1907, two men met in a richly-decorated apartment in Vienna, both giants of the psychology world, Carl Jung and Sigmund Freud. At that point, Freud was well-known as the founder of psychoanalysis. Intensely ambitious and often controversial, he introduced the world to ideas like repressed trauma and the ego. But he had yet to find a contemporary who he felt was at his level.

Enter Carl Jung. Nearly 20 years younger than Freud, Jung was obsessed with dreams and spirituality. When they met that first time in Vienna, they talked for 13 straight hours about theory and practice and the extramarital affair that Jung was having. This cemented an intense relationship which often walked the line between friendship and rivalry.

The two toured conferences together, wrote each other letters. And after only a month of knowing each other, Freud was ready to appoint Jung as the heir apparent to the psychoanalytic movement. And at one point, Jung wrote to Freud to confess that he had what he called a religious crush on him.

Yeah, I am not entirely sure what that means. But nevertheless, Freud had found a younger protege to take under his wing whose ideas and intellectual curiosity rivaled his own. And Jung had found a mentor, colleague, and as time went on, even a father figure.

CHRIS EGUSA: But soon, as often is the case with intense relationships, cracks began to surface. Professionally, their critiques of each other's work intensified and often got personal. Jung felt that Freud placed far too much importance on feelings of sexual repression while Freud looked at many of Jung's ideas as pure mysticism.

Finally, the two had a blowout fight. In 1913, only six years after their first meeting, Freud wrote a letter to Jung in which he suggested that they "abandon our personal relations entirely. I shall lose nothing by it, for my only emotional tie with you has been a long, thin thread, the lingering effect of past disappointments." And that was the end. They never saw each other again.

It was devastating for Jung. And in the midst of the fallout, this one question kept bothering him. How could two people look at the same set of facts and come up with completely different conclusions? Here's Jung much later in life talking about his impressions of Freud.

CARL JUNG: Well, he was a complicated nature, you know. I liked him very much. But I soon discovered that when he had thought something, then it was settled, while I was doubting all along the line. So from the very beginning, there was a discrepancy.

CHRIS EGUSA: The more he thought about this, the more he decided that there must be something innate within people that makes us who we are, something that makes us fundamentally different from each other, different types of people who approach the world in radically different ways. He put his ideas down on paper, and in 1921 published a book called Psychological Types. In it, he lays out several distinct personality types. And it was in this book that Jung popularized the words "introvert" and "extrovert."

JOHANNA MAYER: "Introvert" is taken from Latin. "Intro" means "inward" or "to the inside" and "vertere" means "to turn." So together, they mean "to turn inward." And "extrovert," of course, means "to turn outward."

For Jung, it was a matter of energy, where it's directed and where it comes from. And according to Jung, introverts are attuned to the internal world of thoughts, ideas, and feelings. This internal world is also the source of their, quote, "psychic energy."

And extroverts, of course, are just the opposite. Their energy comes from the world around them. He also thought that both sides had a tendency to misunderstand each other. The extroverts could see the introverts as aloof, dull, and self-centered while the introverts often see extroverts as superficial and insincere.

CHRIS EGUSA: And for the record, Jung thought of himself as an introvert and Freud as an extrovert. Ultimately, Freud's ideas about psychoanalysis propelled him to greater fame maybe because he was, well, more outward-facing. But also, a lot of Jung's ideas were pretty out there.

He had an ongoing fascination with the occult, and he would frequently attend seances. He believed that all people share a collective unconscious that we inherit from our ancestors. And in his later years, he wrote an entire book about the psychological implications of UFO sightings.

But UFOs and seances aside, many came to see his theories about the unconscious as ahead of their time. And his ideas about introverted and extroverted types really caught on. And a hundred years later, we're still calling ourselves introverts and extroverts.

JOHANNA MAYER: And we cling to these identities. I remember taking one of those personality tests in elementary school and trying to fudge my answers so I'd be classified as an extrovert. Because the extroverts were the popular, funny kids.

SLOANE PETERSON: What do you think Ferris is gonna do?

[MUSIC - THE BEATLES, "TWIST AND SHOUT"]

JOHANNA MAYER: Remember that scene in Ferris Bueller? He jumps on a float in a parade and lip syncs to "Twist and Shout."

[MUSIC - THE BEATLES, "TWIST AND SHOUT"]

THE BEATLES: (SINGING) Well, shake it up, baby, now. Shake it up, baby. Twist and shout. Twist and shout.

JOHANNA MAYER: Walker-bys break into choreographed routines. A baby waves excitedly. A businessman in an office overlooking the parade busts some moves. Ferris is charming, loved. And he is definitely an extrovert.

And while he's dancing up on that float, his best friend Cameron Frye, depressed, a hypochondriac-- Cameron just watches on. He didn't even want to leave the house until Ferris made him. Life's hard for Cameron. I mean, it's Ferris Bueller's day off, not Cameron Frye's.

[MUSIC - THE BEATLES, "TWIST AND SHOUT"]

THE BEATLES: (SINGING) C'mon, c'mon, c'mon, c'mon baby, now. Come on, baby. Come on and work it on out. Work it on out. You know you twist your little girl.

JOHANNA MAYER: For a long time, it really was an extrovert's world out there, at least in America. In her book Quiet, author Susan Cain lays out a theory about the extroverting of American society. Before the 20th century, most people tended to live in smaller towns, more rural areas. Everyone knew everyone. So people valued good character above all, traits like trustworthiness and loyalty.

But at the turn of the 20th century, urbanization would change all of that. As people began migrating to big cities and corporations employed more and more people, Cain argues that the rules for success changed. It wasn't about good character anymore. Now, traits that allowed you to make good first impressions and connect with new people quickly were at a premium, things like charisma.

Books were published with titles like How to Win Friends and Influence People. And the prevailing attitude became, to make it in this world, you need to be a go-getter. Cain calls this the rise of the extrovert ideal.

Its legacy can be seen in all parts of our society, from the multibillion-dollar self-help industry to our total obsession with personal branding. It can be seen in our schools and workplaces. Classrooms prioritize class discussion and group work. Companies emphasize collaboration. And not so long ago, most of us office types worked in open floor plans where we could freely exchange ideas and viruses.

There just isn't the same emphasis on solitary thinking time, quiet reflection. It's not a world set up for introverts. Quiet was published in 2012, and it was a smash success, selling over 2 million copies. Cain's TED Talk has been viewed over 27 million times.

SUSAN CAIN: So I wish you the best of all possible journeys and the courage to speak softly. Thank you very much.

[APPLAUSE]

Thank you. Thank you.

JOHANNA MAYER: This was our moment. Introverts were taking back the silence. I distinctly remember this shift. By my early 20s, we introverts were proud, a little smug, even.

My group of friends mostly identified as introverts. We would humor the occasional extrovert interloper, but only if guaranteed a recovery period afterwards. We'd enthusiastically leave events early, declaring ourselves ready to head home to nurture our delicate, introspective souls.

CHRIS EGUSA: But in the background of all the popular curiosity surrounding these personality types, science was chugging along on an entirely different track. The big question was, what makes people behave the way they do? And it turns out that's a really hard question to answer, because in science, you need something to test. And the problem with personality traits is that while they may seem pretty self-evident to us, they aren't directly measurable. There's no machine that measures how determined someone is or how kind. You have to rely on how people describe themselves.

In 1936, about 15 years after Jung published his book on psychological types, a psychologist named Gordon Allport had an idea about how to solve this conundrum. It had to do with something called the lexical hypothesis. The lexical hypothesis had been around since 1884.

And it basically says that if a certain personality trait is important enough, it will eventually become embedded in the very language people use, that is, we'll create a word for it. Just like "tree," "fire," or the color "blue," if something is worth communicating, it will eventually get turned into a word. And so, Allport figured, the best place to start looking for the key ingredients that make up a personality would be the dictionary. He and a colleague read through Webster's, all 400,000 words of it, and picked out every word they could find that could be used to describe personality or behavior.

They published a paper called "Trait Names-- A Psycho-Lexical Study." And reading through it is pretty remarkable. The first few dozen pages are standard stuff, introduction, methods, analysis. And then it's just page after page, top to bottom words. It goes on for 130 pages, about 18,000 words altogether, terms like "baffled," "deliberative," and "mordacious."

Of those, they identified a few thousand as being prime candidates for further study. And in the next decades, this list got condensed further and further and confirmed across several languages and cultures until a group of researchers in the 1980s found that all these words could be captured in just five basic factors. They called them the Big Five. The five ingredients that make up a person are conscientiousness, openness to experience, agreeableness, neuroticism, and extroversion.

Their goal was not to oversimplify the nuances of human personality, but to make it scientifically manageable. One researcher noted that these broad domains incorporate hundreds if not thousands of traits. And today, scientists don't use the terms introversion and extroversion the way Jung did, or the way most people do for that matter.

DAN MCADAMS: Personality doesn't come in types. It's a romantic ideal.

CHRIS EGUSA: This is Dan McAdams, a professor of psychology at Northwestern University. He studies personality.

DAN MCADAMS: A lot of people find it very compelling to think of themselves as being of a certain type. But it's really not like that. It's more about traits rather than types. And traits are linear continua.

CHRIS EGUSA: By that, he means that these traits are on a spectrum, and you can fall anywhere between the two extremes. And in fact, most people are somewhere in the middle.

DAN MCADAMS: So let's think of height as a trait. Some people are taller than others. But types, basically, are like saying, OK, we got two kinds of people out there, tall people and short people, and that's it.

CHRIS EGUSA: Calling some people introverts and the rest extroverts is oversimplifying.

DAN MCADAMS: You lose all kinds of precision if you say, well, everybody from 50th percentile over to the left is an introvert and everybody from 50th percentile over to the right is an extrovert, especially since most people find themselves somewhere in the middle of this distribution.

CHRIS EGUSA: McAdams cautions against even using the words "introvert" and "extrovert" because they reinforce this idea of types. Probably more accurate to say "person lower on the introversion-extroversion spectrum." But we won't subject you to that in this episode. So if people don't really fall into these strict categories, why have these labels of introvert and extrovert become so core to some people's identities?

DAN MCADAMS: People love to be categorized. We just love labels. It's need for closure, I guess. We want to have it all figured out.

And so like, oh, wow, now I get it, I'm an introvert. Done. Right? I'm labeled. I'm contained.

CHRIS EGUSA: Labels are validating, like the fact that I'd rather chill at home and cook dinner than go out for happy hour. There's nothing wrong with me. That's just the type of person I am.

I think it also has to do with finding your tribe. If there's a whole group of people out there who would rather cook at home than go to happy hour, then having that shared experience can be comforting. Dan says the second issue with the popular idea of introversion is that people think being introverted comes with certain special abilities.

DAN MCADAMS: Kind of like Jung suggested. They might be more in touch with their inner desires and needs. They might be more introspective.

Well, there's just no evidence for that. Sure, there are some people who are very introverted who have that introspective quality and are very creative. But there are just as many people on the extroverted end of the continuum who are also introspective and creative and so on.

JOHANNA MAYER: If at this point you're like me and you're wondering what this whole introversion-extroversion thing even is, like, what is actually happening in our brains, McAdams says that the latest research shows it really comes down to one thing.

DAN MCADAMS: It turns out to be mainly that extroversion is about reward-seeking and it's about gregariousness and enthusiasm and positive emotion. And some people just have a lot of that going.

JOHANNA MAYER: And when McAdams talks about rewards, social rewards are at the top of the list, things like warmth, affection, praise, status.

DAN MCADAMS: On the other end of the continuum, people who don't have that, they're more towards the introverted end. So they're more reticent. They are likely to be somewhat less seeking of rewards.

JOHANNA MAYER: So it's likely that sociability is actually a byproduct of how sensitive we are to rewards in our environment. And what's behind this is a neurotransmitter in the brain, dopamine.

DAN MCADAMS: The activity of dopamine in the brain seems to go into overdrive for extroverts when they are pursuing something that they really want.

JOHANNA MAYER: Dopamine is often called the chemical of pleasure, but that's not really accurate. It would be better described as the chemical of desire. Dopamine motivates us to pursue things like money, sex, social status, or food. And when we anticipate these rewards, dopamine floods the brain, which causes us to become more alert and motivated to take risks. This is true for both introverts and extroverts, but especially for extroverts.

And these neurochemical differences show up in real life outcomes, too. One study found that people who scored high on extroversion were also likely to have higher salaries, be promoted quicker, and have more job satisfaction. At the same time, people high in extroversion are also more likely to engage in risky behavior and suffer substance abuse issues and gambling addiction. On the opposite end, highly introverted people are more likely to suffer from mood disorders like depression, but they're also less likely to take big risks, which obviously has its benefits.

But there is one interesting finding that came to the forefront recently. Extroverted people tend to be happier. It's not that introverted people have more negative emotions. It's just that their positive feelings are more muted. So where an extroverted person might feel happy or elated, an introverted person might just feel satisfied.

And what's more, a 2019 study found that when introverted people force themselves to act more extroverted, they reported feeling happier, as well. And this caught a lot of people's attention because it goes completely against Susan Cain's message that people should embrace their inner introvert.

CHRIS EGUSA: It also goes against something my sister told me, which I've seen echoed in countless other stories. The more she tried being something she wasn't, the worse she felt. And in fact, what that study likely didn't capture is the potential cost of acting in a way that's contrary to your nature. A similar study found the opposite, that when introverts forced themselves to act extroverted, they felt worse. Makes you think that maybe long term, pretending to be something you're just not could lead to feeling burnt out.

And all of this brought up another question for me. Can you change your fundamental personality? Can a person switch from being introverted to extroverted or vice versa?

WIEBKE BLEIDORN: Yeah, hello. My name is Wiebke Bleidorn. I am a professor of psychology at the University of California Davis. And I study personality traits and personality change across the lifespan.

CHRIS EGUSA: Wiebke says that while some traits can change considerably--

WIEBKE BLEIDORN: Extroversion is really stable, remarkably stable.

CHRIS EGUSA: It's basically hardwired in. In fact, it's so innate, we pick up on it incredibly quickly when meeting another person.

WIEBKE BLEIDORN: Research shows that it doesn't take much for people to judge others' extroversion or introversion.

CHRIS EGUSA: I was curious how she would assess me after only speaking for five minutes.

WIEBKE BLEIDORN: Ah, you're more introverted.

CHRIS EGUSA: And here I thought I was doing my best extrovert impression. Some research even shows that we can detect whether someone is introverted or extroverted just from a photo.

WIEBKE BLEIDORN: So looking at someone's Facebook or Tinder profiles might already give you a good idea of their introversion.

CHRIS EGUSA: It comes down to how much information is encoded in just a snapshot of a person, like extroverts tend to smile more.

WIEBKE BLEIDORN: People who smile more also have different faces. So you can see that people who are very smiley, you have different wrinkles, for example, have different configuration of facial features.

CHRIS EGUSA: The clues come from a person's environment, too.

WIEBKE BLEIDORN: Well, I see your room in the background. And I see you don't have many pictures hanging of other people. People who are extroverted tend to have plenty of pictures of other people, often including themselves, big face selfie.

CHRIS EGUSA: From an evolutionary standpoint, Wiebke says it makes sense for people to exist on both sides of this spectrum. Diversity helps a population adapt to different environments. And in some environments, being more extroverted is helpful. In other environments, it's better to be introverted.

And the way I see it, both sides of the spectrum need each other. Without the caution of the more introverted among us, extroverted people might constantly be off doing risky things. And without the drive of extroverts, introverts might never leave their comfy rooms and good books. My sister says she now uses her extrovert friends to her advantage.

KELLY EGUSA: They just bring a lot of energy to a social situation. I can feed off of that a little bit.

CHRIS EGUSA: And just because labels like introvert or extrovert can be overly broad doesn't mean they don't have value. When a friend gave her a book about introverts--

KELLY EGUSA: --and basically told me, I'm OK, this is normal, this is how I'm supposed to be, that basically changed the game for me.

CHRIS EGUSA: Now when she gets a party invite, she has more than just the snack table trick up her sleeve. She makes sure that she's had some time to herself recently and doesn't force herself to stay longer than she wants.

KELLY EGUSA: If I'm ready to go home, then I'll go home.

CHRIS EGUSA: But the biggest change is just accepting who she is.

KELLY EGUSA: I do enjoy going to parties now. But I know that I enjoy being at home or being with just like close friends even more.

CHRIS EGUSA: And she's fine with that. She no longer feels like she has anything to prove to the extroverts of the world.

JOHANNA MAYER: When Carl Jung coined the words "introvert" and "extrovert," he was doing what many of us do, attempting to make sense of his behavior and feelings and the relationships in his life. For Jung, this journey led him to create one of the most enduring ideas about personality. And in doing so, he created a tool for future generations to have a little bit more insight into their own minds. Because one thing research has shown us is that regardless of introversion or extroversion, one of the most important predictors of well-being is accurate self-knowledge, which is to say knowing who you are. And so it would seem that there is some truth to his words when Jung said, "Who looks outside, dreams; who looks inside, awakes."

[MUSIC PLAYING]

This episode of Science Diction was written and produced by Chris Egusa, along with the Elah Feder and me, Johanna Mayer. Elah is our editor and senior producer. Daniel Peterschmidt sound designed this episode and composed all our music except the Timbo March, which is by Tim Garland from the Audio Network.

We had fact-checking from Robin Palmer. Nadja Oertelt is our chief content officer, and she recently told me my interviews just needed a little spicing up, little special sauce. So she had some advice.

KELLY EGUSA: Find the snack table. And you can make small talk around food, which is super awesome. And you just can like, oh, this dip is amazing.

JOHANNA MAYER: This is our last episode of the season, but we will be back in just a couple weeks. In the meantime, I have a really fun newsletter recommendation for you. It's chock full of science history from Science Friday. It's got stories and audio bites from our archives. The most recent issue is about how NASA's Mars Rover program began.

I am obsessed with it. And if you like Science Diction, I'm willing to bet you'll like this newsletter, too. Find it at ScienceFriday.com/Rewind.