Does birth order affect personality? Here’s what the latest research says

Chloe Schneider
Chloe Schneider
Chloe is a writer and content strategist with bylines in mindbodygreen, Mashable, Ageless by Rescu, and more. She's a mum to one-year-old Felix, and believes that you can have it all, you just can't have it all at once
Created on Jun 05, 2024 · 4 mins read

At the park recently, I met a couple with a toddler my son’s age and we got to talking about whether or not we’ll expand our families. Like so many parents before us, we worried aloud whether our decisions around adding siblings would change our kids' personality or life trajectory.

It’s a conversation I’ve had before and I’ll likely have again — birth order stereotypes are everywhere. We love to pigeonhole But how much truth is there to them? 

And how much of our personality can we actually tie up in it?

The history of birth order theory

In the early 1900s, a psychoanalyst named Alfred Adler explored the idea that birth order could determine personality traits. 

Adler believed that firstborns were neurotic because they were held to a higher standard by parents with more time, and they resented sharing their parents when a secondborn came along. Middle children were said to be the most emotionally stable and optimally positioned, while the youngest children were rebellious and independent. 

No prizes for guessing, Adler was a middle child. 

Since then, there has been much debate about whether birth order influences what psychologists call the ‘Big Five’ personality traits. 

These are:

  • Openness
  • Conscientiousness
  • Extraversion
  • Agreeableness
  • Neuroticism 

Theories around birth order affecting the Big Five were popularised in part because, on the surface, they just make sense! 

Parents are likely to treat kids differently based on birth order — there’s more time and attention for a first child, and it’s natural to feel more cautious. Things relax a little with middle children when parents have less time and feel more comfortable in the role. By the time the youngest comes along, parents are comparatively laissez-faire in their approach.

At the same time, children might form behaviours and habits in response to their place in the family. For example, firstborns might go on to become perfectionists because they have all their parent’s focus in their early years and more is expected of them as the eldest sibling. Youngest children, with fewer rules to abide by and a whole family of people to compete with, might be more fun-loving and attention-seeking.

What does the latest research say?

While some studies support these early theories, they are largely flawed by modern standards simply because there are too many variables to contend with. 

For example, one team of researchers hypothesised that families of lower socioeconomic class tend to have more children, and therefore studies that were conducted on families of varying sizes were unreliable.  

Since then, some controlled studies have shown differences in personality as a result of birth order — but the differences are so minor they really just point to birth order being one, tiny contributing factor in a greater web of things that play a role in personality formation.

For example, a 2015 study including 377,000 high school students showed that firstborns tended to be more conscientious, extraverted, and willing to lead. All in line with Adler’s original theory. But they also found that firstborns were more tolerant and emotionally stable, which is in contest to Adler’s theory. 

In both cases, the differences were extremely minor with an average absolute correlation of .02. As a result, the researchers, “concluded that the importance that is generally attached to sibling position in shaping one’s character is exaggerated.” 

This same study examined intelligence and the conclusion was much the same — while the older children in families did show slightly higher intelligence, the absolute correlation was only 0.4. In other words, barely there.

So how is our personality formed?

If not birth order, then what? 

Personality development happens over time and it’s far more complicated than our place in a family. Things like our natural temperament, genes, environmental conditions, social experiences, and our parent’s approach to raising children all play a role. 

More recent research has shown that our temperament, in other words, the way we react to the world around us, is present from birth. While the two things are not the same, temperament does influence how our personalities develop.

For example, a firstborn with a highly adaptable temperament would react very differently to a sibling coming along compared to a firstborn who needs more time to transition to new situations. The difference in this reaction to the new sibling could mean one firstborn is more neurotic, and another is more open. 

There is a huge range of temperament traits including things like activity level, distractibility, intensity, and sensitivity — and each of these changes the way we react to other people and the situations we’re in. As we age, these reactions are part of what shapes our personality. 

Parenting a personality

Stereotypes around birth order can be a bit of fun, just like stereotypes around astrological signs. But it’s important not to get too hung up on them or make decisions based on them. 

The science says that birth order only plays a minor role in determining personality. Plus, while temperament remains fixed, our personality continues to evolve, even as adults. 

In saying that – I’ll still be accusing people of middle-child syndrome.

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