Does Your Birth Order Affect Your Personality?

Let’s dig into the science.


You’re such an only child, might be a simple observation, or a blatant insult. Swap in middle child or baby of the family or firstborn and everyone’s offended. Birth order theory has the capacity to insult and captivate in equal measure. Psychologists have been talking about it for over a century; supporting studies have been all over the map.

The theory of birth order was first proposed in the early 1900s by psychotherapist Alfred Adler, a disciple of Freud. Adler believed his theory answered the question of why siblings (who might share both nature and nurture, to some extent) are so different. While the relevance and application of its principles inspires a bit of debate, the core tenet of birth-order theory — that family position influences one’s personality — is hard to contest. So, what exactly does birth order theory say about you?


The firstborn, sometimes called The Achiever, is reliable, conscientious and controlling. “If you are a firstborn, you are probably a high achiever who seeks approval, dominates and is that perfectionist who uses up all of the oxygen in the room,” says Dr. Gail Gross, a human behavior and parenting expert. “The eldest child will probably have more in common with other firstborns than their own brothers and sisters.”

Dr. Kevin Leman, who’s been studying birth order since 1967 and wrote The Birth Order Book: Why You Are the Way You Are, says, “The one thing you can bet your paycheck on is the firstborn and second-born in any given family are going to be different.”


Middle children, sometimes called The Peacemakers, are social people-pleasers with rebellious streaks. “If you are a middle child,” says Dr. Gross, “you are probably understanding, cooperative and flexible, yet competitive. You are concerned with fairness.” You’re also more likely to have an intimate circle of friends that act like family.

“These kids are the most difficult to pin down,” says Dr. Leman. “They are guaranteed to be opposite of their older sibling, but that difference can manifest in a variety of ways.” He says if firstborns are CEOs, middle children are entrepreneurs.


The baby of the family, which Dr. Gross calls “the life of the party,” is fun-loving, uncomplicated and manipulative. “As the youngest child, you have more freedom than the other siblings and, in a sense, are more independent,” says Dr. Gross. “Your range of influence extends throughout your family, which supports you both emotionally and physically.” She says youngest children, for that reason, experience a sense of security that their siblings might not.

As the baby of my family, I will hold my offense until the end.


Only children are said to be mature and diligent perfectionists, not so different from firstborns, but have no one to compete with for attention. “If you’re an only child, you grow up surrounded by adults, and therefore are more verbal,” says Dr. Gross. “This allows for gains in intelligence that exceed other birth order differences. Having spent so much time alone, you are resourceful, creative and confident in your independence.”

These are extreme characterizations and they beg the question: How could birth order possibly have this much impact? Or rather, why do so many experts believe it does? “Some of it has to do with the way the parent relates to the child in his spot, and some of it actually happens because of the spot itself. Each spot has unique challenges,” says Meri Wallace, child and family therapist and author of Birth Order Blues.

New parents’ cautiousness and attentiveness with firstborns, for example, may make the child more concerned with being perfect. Second and middle children, by contrast, may not receive the same level of obsession, making them more likely to vie for attention through people-pleasing. Last-borns benefit from the least amount of discipline and plenty of coddling, and may turn out more free-spirited. (I’m paraphrasing; you can see examples broken down here.)

There are plenty of situations for which these explanations won’t apply. Kids’ natural temperaments hugely influence personality, as does sex and gender. (Some say that a second-born of a different gender is like another firstborn.) Also, physicality matters — a smaller eldest and a larger youngest might change their dynamic — as do things like age spacing (of the kids and the parents), twins, adoption and blended step- and half-siblings.  There are millions of caveats, which is exactly why birth order theory is so hard to prove.

“Psychology goes through periods of alternatively accepting and rejecting these myths,” says Dr. Susan Whitbourne in Psychology Today. “Although various theories abound, when you come right down to it, the matter is one that requires the right research approach. Methods are everything in studies of birth order and personality.”

A lot of early studies have proven ill-constructed. There was the 1972 study that found a disproportionate number of firstborns in Congress, for example. Or the one in 2010 that said 21 out of 23 astronauts were elder siblings. But Dr. Joshua Hartshorn, psychological research and language expert, calls these findings inherently flawed.

Take, for instance, family size. Dr. Hartshorn points out there are many reasons that family size could affect our predilections and personalities. More children mean that parental resources (money, time and attention) have to be spread more thinly. Perhaps more telling, family size is associated with many important social factors, such as ethnicity, education and wealth. For example, studies have shown that wealthier, higher-educated parents typically have fewer children, meaning kids who grow up in lower-stress environments are more likely to be firstborn (think of a two-kid home versus a five-kid home: in the former, a kid has a 50% of being firstborn; in the latter, a kid has a 20% chance of being firstborn) Maybe, then, you could reason that astronauts are more likely to be firstborn simply because they came from wealthier, more comfortable upbringings. There’s a bias there.

“Of the some 65,000 scholarly articles about birth order indexed by Google Scholar,” writes Dr. Hartshorn in Scientific American, “the vast majority suffer from this problem, making the research difficult to interpret.” Most of the data just doesn’t hold up.

Alan Stewart, a psychologist interested in making sense of all this, wrote, “what is perhaps the definitive recent work (2012) on the theory and research on birth order,” according to Psychology Today. Stewart’s most critical breakthrough was distinguishing between “actual” birth order (ABO) and “psychological” birth order (PBO), the latter of which is self-perceived. Your PBO is just whichever type you most identify with. This was later realized in a test developed to measure whether people are a psychological match for their biological rank. It’s called the White-Campbell Psychological Birth Order Inventory. Surprisingly, only 23% of women and 15% of men identify with their actual position.

That casts a serious shadow of doubt on the initial approach to birth order. There have been some recent studies, however, that have held up under scrutiny and which do support the biological theory. There was a 2007 study in Norway that showed firstborns had IQs two to three points higher than the next child, for example. And a study in 2009 — of which Dr. Hartshorn was a part — that proved, “birth order influences whom we choose as friends and spouses. Firstborns are more likely to associate with firstborns, middle-borns with middle-borns, last-borns with last-borns, and only children with only children.” That, of course, means there are personality factors at play.

Despite being around for a while, birth order theory is clearly still in its infancy. Validity notwithstanding, I see the appeal. I, too, want to latch on. Personalities are shifty, nebulous puzzles, and there’s something satisfying about diagnosing them, even if the implications are a little affronting. Middle child or youngest child, Type A or Type B, creative or logical, ENTJ or ISFP. Labeling can be the perfect antidote to feeling like a contradictory, gaseous cloud.

As I was researching this story, I kept applying the baby, middle and firstborn characteristics to myself and my two siblings. It’s hard to know whether I found them to be true — I am charming, TYSM, but am I irresponsible?! — or whether I’d fallen victim to the Forer effect. Have you heard of it? It’s the psychological phenomenon, “whereby individuals will give high accuracy ratings to descriptions of their personality that supposedly are tailored specifically to them but that are, in fact, vague and general enough to apply to a wide range of people.”

It’s the same reason, in my opinion, why horoscopes feel true. (Sorry, Amelia.) The thing is — and this may be the case with astrology, too — it didn’t ultimately matter if the theory was accurate to a T, because it offered an interest framing through which to observe my sibling dynamic.

Do you believe in birth order theory?

Illustrations by Amber Vittoria; follow her on Instagram @amber_vittoria.

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  • Holly Laine Mascaro

    I SO believe in birth order theory, it’s obvious for both myself and for my boyfriend, who I harangue often because it’s so obvious he was the baby of the family (and I’m the oldest/was only child for a while).

  • Alice

    I think it has some influence but it’s not a big piece in our personality puzzle. Of course everyone likes to believe they’re intelligent, so myself as an only child like the characteristics from this article. Usually people just assume I’m selfish (I’m not! Just ask me before you touch or borrow my things).

    • Adrianna

      The best roommate I ever had was an only child. I’m the youngest, and still get very triggered if somebody eats my food.

      • Alice

        I’ve never lived with roommates, but when I’m counting on food being there and my mother has gotten there first I get very sad.

        • Adrianna

          This was a big issue for me when I first lived in college. I wasn’t from the same kind of economic background as my three roommates, and I also didn’t have the overpriced dorm meal plan. So when someone ate my food, they ate the only food I had.

          • Alice

            I hope you now have a fridge full of food that isn’t touched by rude roommates. I would flip at them if I was in your situation.

  • Adrianna

    I’m the youngest out of two, and we are 4.5 years apart. (four grade levels apart)

    People who didn’t know about my personal life have assumed that I had younger siblings. People have also thought I was the oldest when my sister’s friends met me when I was 15-22 years old.

    Some of these cliche dynamics were true in our household. I’m what you would call “a strong personality.” (INFJ here.) I was in fact, always the more independent one. One of the last conversations I’ve had with my sister was when she was in her late twenties, and quietly told me that she always envied that I was so self-possessed.

    I always sensed that my mother had a deeper attachment to my sister, despite the fact that I’m a physical carbon copy of my mother and we have similar personalities. Things got deeply complicated in my household after my older sister’s bipolar disorder and drug use started unraveling. I frequently wondered if there would be less enabling and co-dependence if she wasn’t the oldest

  • Officially, I don’t believe in horoscopes and birth orders. 🙂
    And yet … I will make conclusions based on both of them.

  • Rae

    My family is so complicated because there are large age gaps – I’m 10 years older than my younger brother. So I was effectively a youngest child for the first ten years of my life, but also acted kind of as an oldest after my older brothers had left & it was just my little brother and me. I will say that my oldest brother definitely does not fit the profile of an eldest child – he’s so laid back and easy-going, although very intelligent. However, he and my second-oldest are polar opposites, so I laughed at that line! Regardless of whether I think they’re true or not, I find the theories fascinating!

    Extremely well-written and interesting article Haley!

  • Teresa

    Coming from a large family, not only do I believe in birth order theory but I realize none of my closest friends are only children. Having siblings definitely impacts your social interactions. I wonder if only children also gravitate towards friends who grew up in similar households.

    • Sheila T.

      That is so interesting! I don’t think any of my closest friends are only children, either.

      • Teresa

        It is definitely one of those things you don’t notice until you do! The first time I consciously thought about it was when I was looking for a roommate in college and realized I would be most compatible with someone who also had a lot of siblings and shared a room her entire life. The thoughtless lack of boundaries on both of our parts actually meant we were more compatible and better friends.

    • Ariane

      I realised recently that a lot of my close friends have been only children, including my current boyfriend. He is in his thirties and I can absolutely see how he was once an eccentric and even spoiled child who didn’t have to learn to share. I only have one sibling but my family is noticeably louder than his all the time, and he is totally confused by the fact that my brother and I, two adults, will completely regress to children when we argue and generally be horrible to each other.
      People say only children are “weird”, and this is true of all the only children friends I have had, and I love it about them.

      • Jen

        Why are they “weird?”

        • Ariane

          a kinder word would be “quirky”, I’m just repurposing the negative word that I’ve heard others use. But all my only child friends (and boyfriend) have had unique habits and views on the world, and are generally very individual in a way I admire and find cool. They’ve all been music lovers or enthusiastic readers within specific, even niche genres that they like. They’ve seemed like people who have their own “bubble” where they like to spend time, and I like people who don’t cave to popular opinion.
          (Obviously I can’t actually speak for all only children, I hope my former comment didn’t come off as rude!)

          • Jen

            I appreciate the explanation! Not offended at all, I’m just kind of tired of the offhand way a lot of people kind of stereotype and/or marginalize people that are different than them in some way—in the sense that only children are not the norm.

    • Hayley

      I am an only child and I am now realizing that a majority of my friends (and my husband) come from larger families. Hmm.

    • Jen

      I don’t entirely agree with that. I have no other friends who are only children, yet I am an only child myself. I don’t know if it “definitely impacts your social interactions,” and, if so, in what way?

    • Hailie Durrett

      Interesting! Growing up I had three very close friends – one was an oldest, one was a middle, one was a youngest, and I am an only. We all fit into our stereotypes within our family and within our friend group. As an adult, I have gravitated towards oldest children as my closest friends…and primarily those with a large age gap or those who aren’t as close with their younger siblings.

  • Sheila T.

    The “second child of a different gender” applies to me a little, as the third child out of four but the first girl (I have a little sister). I definitely identify with both the “firstborn” and “middle child” categories. In the larger group, I’m cooperative and diplomatic, but I boss my sister around (“direct her”) all the time too. Interestingly, people I have met in college and after have told me that I strike them as an only child and are surprised that I have three siblings!

  • I come from a very large complicated family (step siblings, half siblings) but I grew up mostly as a middle child of three girls – and I strongly relate to all middle child theories! Being the same gender, quite close in age (2.5 and 4.5 years apart), and with similar interests means it’s very easy to compare us and see in what ways we differ… I think we all pretty much adhere to the birth order stereotypes!

  • KK

    As a youngest, I feel I was always able to have more of an “adult” relationship with my parents. I once dated an oldest child and his parents were def still very in “parent mode” and treated him like a child. I guess maybe mine were almost done with the raising and therefore more relaxed about everything.

    • Mary Kate Kloeblen

      I’m a youngest as well (have 3 older siblings) and feel the exact same way! I feel like I have always been able to have more of a mature relationship with my parents and was given more responsibilities and space than others I know who were oldest or middle children. I think being the youngest also allowed me to come into my “own” a bit more easily than my siblings. My parents were more relaxed with me so I never really felt like my life choices (school, career, relationships, etc) were “letting them down” whereas I feel like even my own two sisters have felt that pressure moreso.

      • meme

        I second the more mature relationship, but maybe because of that, my parents never really saw me as the baby that needed attention and they still baby my brother and my sister much more than me.

        • Mary Kate Kloeblen

          Yes! That makes a lot of sense and I feel like my parents are the same way with older siblings – especially my brother (he’s the only boy, so maybe that’s why?). Regardless, I’m not sure if you feel the same way but I feel like my older siblings actually tend to come to me for advice/guidance on situations (potentially as a result of obtaining this more self-reliant behavior??)

          • meme

            Yes! All the time. People actually assume that I’m older than my sister because of how we interact, her looking for my approval, me telling her not to do whatever because I am a wiseass sometimes. And my brother also calls me whenever he has conflict with someone else in the family. In fact, everyone (my parents included) assumes I will take care of it when there’s a problem.

  • beccamu

    Love personality theories! I wonder: can siblings swap roles? I am the second-oldest in a family of 4 but play the role of first-born. My older sister (the actual oldest) adopted a middle child personality. When we were kids she bucked her role as first born and left it up to me.
    The rest of my family follows the framework: youngest brother is a charming, laid-back guy, and my fellow middle-kid can’t handle conflict to save his life. How’d I end up an over-achieving perfectionist when I could’ve been a fun, rebellious, social butterfly!?

    • grace

      this is me exactly, too! i’m the second of six and i 100% feel like an oldest child. i think it’s because for me i had a lot of the “firsts” (e.g., first to drive, first to go out of state for college, first to move out, etc.). i feel like i bore the burden of figuring out those big life changes with my parents as a young adult and now i totally identify as an oldest child. when people ask about my birth order, i’ll actually say “well second of six, but i’m pretty much the oldest.”

      • beccamu

        hahaha that’s exactly what i say too!

  • Rheanonn Perez

    it might be just a stereotype, but i fit it so well!!!! i grew up an only child so i have no problem spending a lot of time by myself or doing things (traveling, going out to eat, going to concerts) by myself. people tell me i’m mature for my age. at 4/5 of my retail jobs i was promoted or approached for promotions, i wonder if my only child-ness played a part in that.

    whenever people ask me for a bite of food i pretty much always share but sometimes in my head i’m like “UGH CAN U NOT” lol. OH i’m also very particular about my things & am semi-germaphobic! i wonder if that’s from not always having to share my belongings growing up // not having to deal with another kid’s snot as a kid lol

    the birth order theory might be weak but it’s fun to think about!

  • Meg S

    I come from an upper middle class 2 child family. I’m the youngest, and the epitome of everything described above. The apron strings will never be cut at any age, though my sister doesn’t get these benefits. She’s also married, has children and moved out of state, so my parents focus has turned solely to me.

    My sister used to dance for me while my mom played the piano. She would hold me and carry me around when we were younger. Everything was about making me smile and laugh for the first 3-4 years of my life. I was the center of the universe in our house, and part of that has led me to believe that I’m still the center of the universe. For everyone. I generally stomp this belief down because it’s not true and it’s unrealistic to believe that it is.

    But I’m still the life of the party, and I do what I want. If I want to go travel somewhere, I’ll save up the money and go. Luckily I have a best friend who loves to travel, or I’d be doing all this on my own. I’ve always been a free spirit because I was raised that way. Still, no matter what I do, I’ll always be able to run back to my parents. The apron strings will likely never be cut, and the bank of mom & dad will probably never close.

    I’m incredibly lucky to have this kind of life, but there were some unrealistic expectations and lots of pressure from attending a school starting at age 12 that was all about getting me into college. I took the PSATs the first time when I was 13. I took them every year until I took the SATs. I had an overachieving older sister who got A’s seemingly without trying (we went to the same school). It was a lot to live up to, for fear of being a disappointment. It’s a fear I live with to this day, because the last thing I want to be is a disappointment to anyone.

  • Ariane

    I am a HUGE believer in this, in part because I am one of 6 firstborns in my family who are ALSO all female and I think we share a lot of traits.
    I also think it’s significant that when you’re the eldest, you spend your earliest years interacting primarily with juts two adults, whereas younger siblings are born into a GROUP. My little brother has always been the social butterfly who is VERY tight with his huge group of friends. I am not so at ease as him, socially, but I am definitely more independent minded and less driven to conform. (Obviously my family could be full of coincidental stereotypes)

  • Lanatria Brackett Ellis

    Wow the facts!! lol I am a middle child..rebellious streak , on the road to entrepreneurship, small circle of “framily” , peacemaker all the damn time, and ready to scream for fairness at any given time.

    • Celina Ann Chan

      I’m also a middle child, and the rebellious streak, framily, and peacemaker things are all true. And only now am I realizing that I have closer friendships with other middle children, too. Haha.

    • Veronica Lodge

      Don’t you hate the people-pleasing side? I wouldn’t mind it if it didn’t make me be attracted to needy people or guys who take advantage of my ability/propensity to please. I wanna have some of my niceness given back!

  • meme

    I was coming here to say I don’t think they apply to my siblings and me. Then I opened the link you shared where it said “Some babies resent not being taken seriously. They might become very responsible, like the oldest, or social, like the middle.” And now I feel very small like we do when you find that you are in fact a living breathing archetype and also slighlty vindicated in that this baby is the most responsible of all 3 of us so stop with the baby gets all the attention jokes. 😛

  • Riley W

    I definitely see some truths. But, my parents are pretty hardcore about all of us being independent, so even though I’m the oldest of three, I think I may have been babied less than the other two.

    For instance, when my baby sisters was in kindergarten her teacher had to tell us to stop putting on her shoes for her because she was the only 5 year old who couldn’t put on her own shoes. She just got everything done for her because it was easy and there were so many of us to help.

  • gamingnails

    I don’t subscribe to these broad portraits but think parenting style plays a larger role; how parents treat their children varies a lot. As the eldest I will *never* do well enough in the eyes of (mum), whereas my younger siblings will be applauded for the achievement of picking the correct bus. So it’s not so much my perfectionism or their whimsical nature that “grades” us but our parents attitude and reactions.

    • Valerie

      lol same! It would make me slightly upset that my parents were never really impressed with any of my achievements and always seemed to expect more (whether it be school, sports, career, etc) but they would praise my younger sister for the most basic decent enough thing she’d do! They are also over protective of me (at the tender age of 27) but are very leaned back with my sister.

  • Anonymous

    I’ve been told sooooooo many times that I seem like an only child whereas in reality, I’m the eldest of three. everytime someone tells me this, i feel offended but am unsure as to why

  • Julia

    I can see how this theory can apply to my family, and I feel that me and my 3 siblings seem to have switched roles along the way due to large age gaps between us. I was the baby for 6 years, the middle one for 5 more and, once both my brothers left home, became the ‘firstborn’…I don’t know which order won.

  • Jessica TeBeest

    omg am I the only one who thought the title said “Does Your Birth Control Affect Your Personality?” wow. very interesting article even though it was NOT what I thought it was going to be about at all!

    • Krusty the Kat

      Totally read it that same way.

  • Car

    Not sure how I feel about the specifics of this, but when I was growing up, my four best friends and I were all first-born with one sibling around the same age and I definitely felt some kind of bond over that. My boyfriend now is the same and we do approach a lot of things in a similar way, we’re both also the same Meyers Briggs type.
    On the other hand, my parents both come from huge families though and are middle-ish children and I never really pinned down any traits in that. Maybe it loses some of it’s accuracy after three kids!

  • Yep, these descriptions are pretty close to some of the major differences in me (middle child) and my 2 brothers. And my favourite cousin (out of 13) is a middle child too. And I definitely believe it has an influence on our personalities, just like everything else in our environment.

  • I think there’s truth to it. There are always exceptions, but I’ve seen pretty spot-on examples. I’m a baby but my sister didn’t spend a lot of time at home as a teenager and moved out when I was 12 so I spent my teenage years like an only child. I think my personality has traits of both. My boyfriend is the oldest of 3 brothers and in with his siblings it’s pretty accurate too. But none of my close friends are the youngest siblings.

  • tiabarbara

    I’m from one of those “blended/step” families so the dynamics within my family are very interesting.. I am the middle child within my household, and I identify rather closely with the description up there.. my older brother is definitely controlling and conscientious, but my younger sister is my step-sister (having been born from my step-dad’s previous marriage) and she exhibits a lot of the traits of a firstborn! I would even go so far as to say that my sister and I both embody traits of the youngest sibling as well, given how our family eventually came together.

  • Shinkajo .

    Great science. Well not really. I’m becoming more and more convinced that psychologist don’t know wtf they are talking about really and are just guessing most of the time. I am the eldest and am much more like the “youngest” and my little brother is more like “the firstborn”. I have friends from all kinds of positions. You are an idiot if you let cultural norms dictate who your are. Also your parents probably suck.

    • Veronica Lodge

      I think you hit that on the head…the parents suck if the kid is a conformist lol but seriously, the parenting style (& numbers of kids & “parents” which are involved) is more important than anything, imo.

  • David Wright

    It’s a shame that Haley has ignored the main reputable study of this subject, Born to Rebel: Birth Order, Family Dynamics, and Creative Lives, by Frank J. Sulloway.

  • Injie Anis

    I don’t quite know whether I am a middle-born or the youngest of my family. I only have one older brother. Plus, people tend to write younger children off as less successful and more irresponsible and spoilt. So I’m kind of stuck.

    • abby

      your obviously the youngest, there has to be 3 for you to be middle. I have 3 siblings (at the house i live in) and i’m the 2nd oldest. but, only oneof them are biological so i dont really know. although ive grown up with them so maybe that had some effect. i dont really know what to label myself as, but i have to know for an 8th grade assignment

      • Veronica Lodge

        I wonder if the biological thing plays into it all. It sounds like your family is similar to mine. I have two older brothers from my dad’s first marriage but rarely saw them, one older brother born to my mother and adopted by my dad then they had me together. Then my dad married another female but didn’t have any biological kids but I did live with them for four years with a younger step-sister & one who was basically a step-twin as we were both born in 1977 & in the same grade. I am so confused, and I just turned 40. Maybe that is why I am confused lol too many kids & too many marriages, etc., so I still don’t know where I fit in! 😉 Good luck with your project, I hope you get an A!!!

  • Marie-Eve

    I’m the oldest (with quite a bit of age difference), and I just realized that the vast majority of my friends are oldest children. I think they all have very different personalities, but still, the coincidence is striking.

  • Mar

    “If you are a firstborn, you are probably a high achiever who seeks approval, dominates and is that perfectionist who uses up all of the oxygen in the room,”

    Yep, that’s totally me.

  • Veronica Lodge

    What about all the three marriages my father had? Two boys in the first, adopted my older brother who was MY mother’s by another man she was not married to, then came me – so there were two kids between MY two parents…then he married another female which gained him technically two step-children. Go eff yourself, Dad. 😉

  • Catherine Stanley

    I don’t believe in birth order because I have an older half brother and me and my twin sister are the second borns of my mom and the first borns of my dad. Of course my younger brother is the youngest for both my mom and dad. But my half brother has an older half brother and two younger half brothers that he barely knows. The birth order theory doesn’t take half siblings into account or adopted siblings or blended families. My 5 nieces are all half siblings, some of my nieces I’ve never seen and some I rarely see. So my nieces have sisters they’ve never meet or they know exist but rarely see and they also have older half and whole siblings they live with a majority of the time. This theory really doesn’t work for the modern world.