For decades, families and psychologists alike have puzzled over a curious question: Does your position in the family—firstborn, middle child, youngest, or only child—shape your personality?
As the eldest of two daughters, I’ve often found myself fitting the classic firstborn mold: responsible, rule-following, a bit of a perfectionist. My mother, also a firstborn daughter, shares many of these traits. Meanwhile, my younger sister, though raised in the same home with the same parents, is far more relaxed and carefree.
So I began to wonder: Could our birth order really explain our differences—or is this just another pop psychology myth?
The Century-Long Debate
Birth order theory has intrigued scientists and the public for over 100 years—but despite all the attention, there’s still no scientific consensus.
Why? For starters, it’s a tough thing to measure. Many early studies were small, and personality tests often rely on self-reporting, which can be biased. Rodica Damian, a psychology professor at the University of Houston, notes that other variables—like the number of siblings or socioeconomic status—can complicate the picture.
In other words, being the firstborn in a two-child family may be a completely different experience than being the firstborn in a family of six. Add in the family’s financial situation, cultural background, and gender roles, and the idea of a universal “birth order effect” becomes much harder to prove.
Not One-Size-Fits-All
Despite popular beliefs about “eldest daughter syndrome” or the rebellious youngest child, researchers like Julia Rohrer, a personality psychologist at Leipzig University, argue that there’s no strong evidence linking birth order to major personality traits—at least not in a consistent, global way.
Rohrer and her colleagues analyzed massive data sets from the US, UK, and Germany. Their conclusion? Birth order does not have a lasting impact on broad personality traits. However, they did find one area where it seems to matter: intelligence.
Why Firstborns May Appear Smarter
Across various studies, firstborns consistently scored slightly higher on IQ tests. But this doesn’t mean they’re naturally more intelligent.
Damian explains that it may come down to environmental factors, like being exposed to more adult speech in early childhood or having undivided parental attention before younger siblings arrive. In larger families, these cognitive advantages might be diluted as parents juggle more children.
Interestingly, this pattern doesn’t hold true everywhere. In some developing countries, later-born children sometimes have more access to education than their older siblings, especially when family finances improve over time.
Beyond Personality: Does Birth Order Shape Careers?
Historically, scientists speculated that firstborns might lean toward analytical careers, while later-borns might be more creative. But in a rare longitudinal study spanning 60 years, Damian found the opposite: firstborns were more likely to choose creative careers.
When it comes to career success, birth order appears to have only minor or negligible effects overall.
What About Only Children?
Only children often get a bad rap—spoiled, selfish, attention-seeking. But modern research has found that these stereotypes don’t hold up. In fact, the social behaviors and personalities of only children are largely comparable to those of kids with siblings—and any small differences fade with age.
One 2025 study by Canadian psychologists Michael Ashton and Kibeom Lee examined personality across more than 700,000 adults. They found that middle-born and last-born siblings scored slightly higher in traits like Honesty-Humility and Agreeableness compared to firstborns. However, these differences were tiny—especially among people from families of the same size. Much bigger personality differences were found between people from single-child families versus very large families.
So… Does Birth Order Really Matter?
Maybe—but not in the way pop culture tells us. The effects of birth order are subtle, often tangled up with cultural expectations, family dynamics, and the natural differences that come with age and maturity.
For example, older siblings might seem more “responsible” simply because they’re older—and developmental changes, not birth order, may explain the gap. A moody 14-year-old is naturally more anxious and self-aware than their happy-go-lucky 10-year-old sibling.
And yet, these narratives persist because they feel true to many of us. As Rohrer puts it, while birth order may not define your personality, sharing a birth order with others can give you a sense of identity or community. It’s fine to relate to terms like “eldest daughter syndrome”—as long as you remember it’s not a universal rule.
Final Thoughts
So, is birth order a dead-end theory? Not quite. It’s just more complicated than it first appears. As researchers refine their methods and study more diverse populations, we may one day understand the true (if modest) influence of birth order.
In the meantime, I’ll keep letting my younger sister believe I’m inherently smarter than her. After all—science says I might be, just a little.
By BBC
