Studies Say Birth Order Doesn’t Affect Your Personality, But As The Eldest I Say These Are Lies

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I usually love science. It has provided me with a legitimate excuse to buy more workout clothes and it has made me feel better about the fact that I’m currently single. But today is the day that science has gone too far, suggesting that birth order has virtually no impact on your adult personality. Have the memes been lying to me this whole time? I’m being dramatic, of course (typical eldest child), but according to The Washington Post, several studies suggest that birth order personalities aren’t a thing. This is both a topic I care passionately about and one that I have not spent more than five minutes thinking about before today.

I called my mother to set the record straight. Have I just been imagining that my siblings and I fit neatly into the stereotypical categorization of birth order personalities? “I always have said I have three only children,” she said. “You were each five years apart so I had time alone with each of you during your formative younger years.” (I think that was her diplomatic way of telling me that we were all spoiled; further, she failed to confirm my long-standing belief that I am her favorite child.)

My mother agrees that my siblings and I fit into our respective stereotypes: I, the eldest, am neurotic and a rule-follower; my sister, the middle child, wants attention; my brother, the youngest, exhibits more characteristics of an elder child but is most certainly the baby of the family—my parents are so lenient with him I simply cannot. (Yes, distain for my younger brother’s ability to get away with almost anything is stereotypical behavior as the eldest child, and that’s the point.)

Now, let’s take a look at the science. The most recent study, published last week, looked at whether birth order might have an effect on risk-taking behaviors. Stereotypically, younger siblings are prone to risky behavior because, and I’m paraphrasing here, they want so much attention. Researchers reviewed the birth order of explorers and revolutionaries. They surveyed 11,000 German households and assessed the findings of the Basel-Berlin Risk Study, for which 1,500 people spent a day undergoing 40 psychological tests on the likelihood of engaging in risky behavior. Birth order, researchers concluded, was not a good indicator of whether or not one might engage in risky behavior.

Fine, science, you’ve got me there. I’d say this tracks, given my very limited and anecdotal experience. My sister is a risk-taker, and she’s the middle child. But my brother, the youngest, is even less of a risk-taker than I am—and I’m the kind of person who refuses to cross the street if the signal doesn’t tell me it’s okay, so that’s really saying something.

A study conducted in 2015 found that birth order did not influence any of the five major personality traits (openness, conscientiousness, extroversion, agreeableness, and neuroticism), known as the Big Five. Another study from 2015, analyzing 370,000 high school students, reached the same conclusion. There is no correlation between birth order and personality traits. You know what these studies did find, though? That the eldest children tend to have IQs one or two points higher than their younger siblings.

In the spirit of journalistic integrity and impartiality, it’s my duty to share with you this follow-up passage from the Washington Post article: “[B]efore all you firstborns lord your enhanced brains over your siblings, beware: The typical intelligence bonus from birth order is so small that ‘at an individual level it’ll never make a difference in your life.’”

Okay, first of all, calm down. Second of all, that’s exactly what I’m going to do.

You know you’re curious—here’s how to find out where you rank on each of the Big Five personality traits (plus what that means for you). And here’s how to pick the best plant for your personality.

Here’s How Birth Order Shapes The INFJ Personality

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an INFJ personality with her siblings in birth order
Firstborns are commanding, middles are mediators, and last-borns are the life of the party. We all have our stereotypes when it comes to birth order. But are those stereotypes true?To find out, we surveyed 5,747 people who took our personality assessment, the TypeFinder, to find out where they sat in their family tree. We analyzed their responses, along with their personality test results, to see how birth order might impact personality type.

Our number-crunching revealed that there is a connection between birth order and personality type — in some cases, a big one. Some types are much more likely to be only children, or eldests, or middles. Other types are rarely found in a particular branch of the family tree. And oddly enough, INFJs showed some of the most interesting results.

If you’re curious how your birth order may have shaped you as an INFJ, read on to discover how your own experience might fit with our findings. And if you’d like to learn more about how birth order affects all types, you can read the full analysis here.

Middle Children Are More Likely to Be Feelers

Our analysis showed that middle children are much more likely to be Feelers (+6.93%) and much less likely to be Thinkers (-7.23%) than if personality had no relationship with birth order. What’s more, INFJs were markedly overrepresented among middle kids (+8%). These findings support the stereotype of middles as compassionate, friendship-oriented, and people-pleasing — traits which are associated with a Feeling preference, according to Isabel Briggs Myers’ personality theory.

Is there something about growing up as middle kids that forces people to become more sympathetic and conciliatory than they might otherwise be? Our INFJ readers had some theories. “I am the peacemaker in my family and the person everyone confides in,” said one 41-year-old middle child, “and I believe this shaped me into an INFJ.”

A 54-year-old INFJ agrees. “I think when you have other siblings, and you’re taught you be conscientious, caring of others, that becomes part of your personality,” she said. “You care deeply for others.”

Firstborns Are More Likely to Be Introverts

Firstborns are more likely to be introverts (+2.37%) according to our data, and the effect is especially pronounced when combined with Thinking (+3.04%) and Judging (+4.41%) traits. INFJs are 4% more likely to be eldest children than we would expect to see if personality and birth order occurred entirely by chance.

At the opposite end of the scale, ESTPs and ESFPs are much less likely to have grown up as the oldest child. It’s not easy being a free-wheeling Extraverted Perceiver when your parents are watching your every move!

As to why firstborns may develop the specific trait of introversion, some respondents felt their duty to take care of younger siblings played a part. “I learnt to sit back and observe, listen more and be supportive of others because of my birth order,” said one 52-year-old female. “I would have developed into a more outgoing personality if I hadn’t had siblings.”

This 31-year-old eldest child felt she had to be “reserved” as the oldest and an “advocate” for her younger siblings. “I feel introversion is higher for elder children because they tend to have their shine dulled a bit caring for younger siblings,” she said.

INFJs Are More Likely to Have Siblings

According to our research, onlies are much more likely to be Thinkers (+8.23%) rather than Feelers (-7.8%), and much more likely to be Perceivers (+6.91%) rather than Judgers (-8.3%). INTPs were 32% more likely to be only children than if personality had no connection with birth order. INFJs, by contrast, were 34 percent less likely to have grown up as only children than we would expect to see by chance — one of the most striking data points we found in the entire study.

So what’s going on here? Could having siblings push someone in the INFJ direction?

Our respondents seemed to think so. Overwhelmingly, they reported that having siblings was pivotal in developing the conscientious (Judging) and nurturing (Feeling) aspects of their personalities. In the words of one 20-year-old respondent: “INFJs, despite being introverts, love people and human interaction and highly value it … Growing up with siblings is the perfect fostering ground for an INFJ.”

This 41-year-old echoes the sentiment: “INFJs are very people focused…particularly when it comes to the emotions. I believe that an only child would not be exposed enough to others’ emotions and perhaps this would shape them into another personality type.”

Growing up with siblings is unlikely to change your personality drastically. However, our research indicates that having to get along with brothers and sisters throughout childhood could provide an extra “nudge” towards an empathetic, agreeable style of relating to others.

The Rare INFJ Only Child

INFJs are less likely to be only children — but that doesn’t mean INFJ only children don’t exist! Some of our respondents were shocked to learn just how rare INFJ onlies are. Many were passionate about INFJ being the archetype of the only-child personality. Here’s what this 49-year-old male only child had to say:

“I believe that growing up as an only child allowed me to cultivate a strong relationship with my own inner world. I had the time and freedom, and the need, to develop my imagination and process my experiences in my own way. People I know who have siblings seem to be far more inclined to be extroverted and to have a greater need to conform to what others expect rather than being inwardly motivated.”

This 47-year-old female only agrees, “As the only child of two academics, I spent a lot of time either alone or with adults, listening to their conversation and ideas, and reading. This seemed to foster my introspective, old soul nature early on, and for as long as I can remember, I felt very at home being alone….Perhaps because I had no siblings, I longed [for] meaningful relationships all the more. …I always surmised that my INFJ status was strongly correlated with being an only child, for [these] reasons.”

Did Your Birth Order Make You an INFJ?

If you believe that parents, siblings, and family dynamics can shape personality, then it’s difficult to ignore birth-order theory. It can lend some fascinating insights into why you are different than your siblings, despite having the same parents, similar genetics, and the same family environment.


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Of course, this research does not take into account other factors that are known to influence personality: genetics, health, education, socio-economic status, and gender have all been demonstrated by extensive research to influence personality development, and many of these factors almost certainly have a much greater impact than birth order.

Ultimately, your personality developed from a complex mix of nature and nurture — of which birth order may be a small but significant part. Understanding the impact of birth order may shine a light on why we are the way we are — but it’s just one small part of a much bigger puzzle