Does Your Birth Order Affect Your Personality?

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.

Haley Nahman

Haley Nahman

Haley Nahman is the Features Director at Man Repeller.

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