I am the first-born child of two introverted Thinker-Judgers. Our summer vacations were planned in detail months in advance, right down to what time we’d leave the house. And I was right there in the thick of it, making packing lists and choosing activities that I’d write down in a spiral-bound notebook.

My younger brother likes to think he’s more spontaneous, but he’s as much of an ISTJ as my parents and I are. Typology definitely runs in our family. The question is whether it’s nature, nurture, or coincidence.

I’ve basically ruled out coincidence at this point. I’ve seen how my friends’ personalities resemble those of their parents and siblings — and in some cases, their children.

The question is, how much of our personality do we inherit and how much do we develop as a response to our environment? Does it really “run in the family,” or do we just learn it by spending so much time around our parents?

It’s a tough question to answer. One way we can learn is by looking at genetic relatives who don’t grow up together.

Nature and Nurture Face Off

Some of the strongest information we have on personality and heredity comes from the famous “twin studies,” which came out of the University of Minnesota between 1979 and 1999. In that time, researchers followed more than 350 pairs of twins, some raised in the same household and others raised apart.

Theoretically, if personality is innate rather than developed, twin pairs would be similar whether they grew up together or not. But if environment matters more than genetics, the twins raised apart would have more variance in personality.

The result? Growing up separately didn’t seem to make twins diverge in terms of personality. If anything, twins raised apart were more similar. Researchers think this might happen because twins in the same household often emphasize their differences. In separate households, personality genes are free to express themselves without the person’s interference.

Overall though, there’s no clear winner in the nature vs. nurture debate. Between 40% and 60% of personality differences seem to be genetically based, but it’s a sliding scale, and it’s hard to tease out one from the other.

It Depends on the Trait

Some personality dimensions seem to run in families more than others. Take Extraversion vs Introversion, for example.

Extraverts direct their energy outward and gain more energy from being around others. Introverts tend to process things internally and feel drained quickly without enough alone time. According to genetic modeling, about 60% of the differences in Introversion vs Extraversion seems to come from genetics.

The same is true for differences in Thinking and Feeling. Thinkers lead with logic, using facts rather than feelings to make decisions. Feelers decide based on their values and how their actions would make others feel. If your parents are Thinkers, you’re more likely to be a Thinker, too. (Thanks, Mom and Dad.)

Environment has more of an influence on Sensing vs Intuition, which indicates how you collect and process information. Some people are Sensors, relying on tangible data and past experiences. Others are Intuitives and rely more on instinct. Up to 40% of where you fall on that spectrum comes from your genes.

Judgment vs Perception is similar. Judgers structure their lives carefully and make plans before acting, while Perceivers are more spontaneous. Like Sensing and Intuition, this tends to depend slightly more on the environment.

Beyond Genetics

When we talk about something “running in families,” we usually assume DNA drives the bus. It’s clear that genes play a role, but what about environmental influences?

For most of us, it’s difficult to tease out heredity from how we were raised. I’ll never know if I’m an introvert because I’m genetically wired to be one, or because my parents avoided crowds and encouraged my need for alone time.

Children come into the world with certain temperaments. Some are fussy; others are more easygoing. Some are shy, while others seek out social interactions. Parenting can either affirm these tendencies or offer alternatives.

A friend of mine was born an introvert. Her parents, however, were community organizers who ran large events and hosted people from out of town frequently. Her parents wanted their kids to participate in these visits, so her Extraverted tendencies got plenty of reinforcement.

My friend is now a town selectperson and head of the recycling committee for her child’s school. She’s become much more of an ambivert (the popular term given to those who fall closer to the middle of the introvert-extrovert spectrum). She’s not a full-on Extravert, but she can handle plenty of social time.

Parents can’t “teach” a solidly Thinker child to become a Feeler, but they can help their child develop emotional intelligence. In time, that child will learn to consider emotions and values as well as facts when making decisions.

Family Dynamics and Personality

There’s no doubt that family influences your personality, and it’s not just parents who play roles in the process. A family is a multifaceted unit, and everything about it affects who you turn out to be. That includes whether you’re the oldest, youngest, or somewhere in the middle.

At Truity, we did an in-house study to look at the influence of birth order on personality. We found that someone’s place in the family significantly affects their Myers-Briggs type.

First-born children were significantly more likely to self-identify as Thinker-Judgers. (Well, I feel seen.) Middle children were the Feelers and more likely to be Extraverts. The babies of the family are also Extraverts and Perceivers. It makes sense. Perceivers are more adaptable, and youngest kids have to do a lot of adapting.

It’s not really an argument for personality type running in families, but it does show that the family environment plays a pretty big role. And who knows? Maybe that firstborn-child tendency toward logic and organization is stronger if parents encourage those traits.

Six of One, Half a Dozen of the Other

All of this information leads us to a pretty straightforward conclusion. Personality type is part nature, part nurture. Not only that, but nurture affects how our nature expresses itself.

We’re a product of our genetic families and the people who raised us, whether or not those are the same people. We’re also the product of our school and community environments, not to mention a variety of other factors we haven’t identified yet.

What about you? Do you see your own personality type in your family members? In what way? Let us know in the comments below. And don’t hesitate to share your best “oh no, I’m becoming my mother/father” stories. We love those!

Laura DeCesare
Laura is a freelance writer and ghostwriter focused mainly on mental health, wellness, and self-care. She received her master's degree in Expressive Therapies from Lesley University but discovered she is far too much a Thinker and Judger to be a therapist. She now uses her knowledge of psychology and human behavior to connect with people via words. Her Introvert self is much happier with this arrangement.