What Your Sibling Birth Order Reveals About Your Personality Traits (Even If You’re an Only Child)

When it comes to birth order, think about where you fall into place. Did you grow up as an only child where your immediate family consisted of just you and your parents? Or was your situation the complete opposite and instead, you had lots of siblings to play with under your roof?

No matter what your circumstance is, psychologists believe that the order in which you were born influences your overall personality. In fact, being the oldest child, middle child, the youngest child and the only child actually all have specific birth order traits that go along with them—many of which you’ve probably heard before. For instance, the oldest child is usually known to be more mature, while the youngest is known to be able to pretty much get away with anything.

But is the belief that your birth order can affect your personality traits actually true? Experts say yes—here’s why.

What is sibling birth order?

When you hear someone mention birth order, they’re talking to the order in which a person is born compared to their siblings:

  • If you’re the firstborn child, your birth order would be referred to as the oldest child.
  • If you’re the second born, you’re a middle child—however, there can be multiple middle kids in a family.
  • If you’re the last sibling to be born, you’re the youngest child or the baby of the bunch.
  • If you have no siblings at all, you’re an only child.

How does sibling birth order affect personality?

Your personality is shaped by a combination of your genetics and your environment, and since parents sometimes treat children differently based on their birth position (and a slew of other factors, like the child’s age, etc.), some personality traits become more common in oldest, middle, youngest and only children as a result.

This concept of how sibling birth order affects personality was first introduced by psychologist Frank Sulloway. “Sulloway’s niche differentiation theory of birth order effects suggests that successive children are most different from the sibling preceding them in an attempt to be unique, obtain attention, resources. etc. From this perspective, personality is a strategy that shapes how you interact with the world around you,” explains Dr. Catherine Salmon, professor of psychology at the University of Redlands and co-author of The Secret Power of Middle Children. “Birth order differences are thus shaped by differences in parental investment and the effects of sibling competition.”

According to marriage and family counselor Sarah Smelser, LPC, an easy way to understand this is to look at the relational interactions among family members. “For example, let’s say new parents bring home their firstborn from the hospital and have a desire to do everything just right (i.e. sanitizing the pacifier every time it falls on the floor or attending to each whimper in the crib). The parents’ level of anxiety and internal expectations of themselves is communicated and reinforced through repeated behaviors and interactions with the child over time. As the parents become more comfortable attending to the needs of a child their anxiety decreases and their expectations become more in-sync with what is actually possible. ” Makes sense, right?

But things get tricky when another sibling is added to the equation. Building on the above example, Smelser says, “When the middle child arrives, parents may not sanitize the pacifier every time it falls and remark ‘A little dirt won’t hurt’ or let the child whimper a bit in the crib to learn how to self-soothe.” Essentially, now that parents have done the drill the first time around, it’s common for them to be slightly more lax about their next child.

When it’s three or more siblings, a new twist is added to the dynamics. Smelser explains, “As the parents adjust to having two, then comes the youngest child. The older children are now a part of attending to the needs of the youngest (i.e. play, attention, entertainment).” And, since there is a combination of nature and nurture involved in the development of an individual’s personality, these subtle environmental differences can play a role in how each sibling’s personality evolves.

Oldest Child Birth Order Traits (Firstborn)

“Firstborn children can be goal-oriented, outspoken, stubborn, independent, and perfectionistic,” Smelser says, and when you look at the way firstborns are nurtured, it starts to make sense why. “These traits are often reinforced by parents through their interactions with the child,” she says.

Firstborn children are unique from other children because their parents are new to the job—they’re learning how to do everything as they go. Therefore, they tend to be more strict, have higher expectations, and be more anxious with their oldest child than they would be with any other children they may have down the road.

As other siblings are added into the mix, the oldest child tends to take on a bit of a second parent role to their younger sister or brother. “Firstborns tend to score high on conscientiousness,” Dr, Salmon explains, “due to their surrogate parent role in the family and the responsibilities that go with that.” They end up helping out with things like feeding them bottles, playing with them and will even feel protective over them, which makes them someone their sibling looks up to and admires.

“They also score high on the aspect of extraversion known as dominance,” Dr. Salmon says, which is where the strong leader stereotype comes from—but it makes sense: “One can see how these traits would make for people inclined to be leaders in various settings,” she says. “Their privileged status as first child and the fact that it’s in their best interests to continue to curry parental favor also plays a role,” in how their personality evolves.

Key birth order traits of firstborn children:

  • Go-getter
  • Responsible
  • Role model
  • Determined
  • Rule follower
  • Hard worker
  • Cautious
  • Bossy
  • Timely

Middle Child Birth Order Traits

“Middle children tend to stand out somewhat on agreeableness and openness to experience,” Dr. Salmon says, and she would know! Her book is all about the behaviors and personality traits of middle children.

“They are highly invested in getting on well with others—they have experience negotiating for what they need within the family and always have to share divided parental investment.” From the moment the second child is born, they share everything with their older sibling, so they never know what it’s like to have 100% of their parent’s attention.

This can influence the development of their inherent personality traits, says Smelser. “Middle children can be diplomatic, nurturing, introspective, tentative, and have a tendency towards keeping the peace.” If these traits are already inherent, being a middle child can make them develop even more, since “these traits are often reinforced by parents and siblings through familial interaction,” Smelser says.

As a second-born’s family expands and that child becomes an older sibling, their role in the family changes as they officially become the middle child. Sometimes this causes what’s known as “middle child syndrome.” If this occurs, it can lead them to rebel or try to find a way to get people’s attention, such as by being funny.

But, claiming that middle child spot also has quite a few advantages, too. Being a middle child in your sibling’s birth order means you’re likely more creative since you’ve had to teach yourself how to combat boredom, and that you’re likely super-flexible and can adapt to changing situations.

Key birth order traits of middle children:

  • Adaptable
  • Social butterfly
  • Dreamer
  • Generous
  • Creative
  • Rebellious
  • Competitive
  • Funny
  • Great negotiator

Youngest Child Birth Order Traits

Parents with multiple kids are more laid-back and lenient when it comes to raising their youngest child—the so-called “baby” of the family. This is why youngest children usually end up having a more happy-go-lucky personality. And since the youngest born’s other siblings are older and becoming less reliant on their parents, the baby of the family is also given extra attention—which can sometimes keep them from becoming super-independent.

“In general, high agreeableness, extraversion (the social dimension) and openness are associated with youngest children,” Dr. Salmon says, “and sometimes low conscientiousness due to lack of responsibilities and parental indulgence over expectations. As a result, they tend to excel in areas involving a social dimension but may always be seen (or see themselves) as the ‘baby.’”

Smelser adds: “Youngest children can be charismatic, creative, mischievous, boisterous, and dependent on others—traits that, if inherent to the child, are often reinforced through the family’s communication and behavior.” Because no matter how old the youngest child turns, they will always fill one role: being the baby of the family. That’s where the spoiled, can-do-no-wrong youngest child stereotype comes from.

Key birth order traits of youngest children:

  • Risk-taker
  • Outgoing
  • Dependent
  • Persistent
  • Fun-loving
  • Charming
  • Easy-going
  • Free-spirited
  • Spoiled

Only Child Birth Order Traits

“Only children have different influences, no sibling competition, and are the sole focus of parental investment,” Dr. Salmon says. “As a result, parental expectations and pressure can be high, driving them toward traits shared with firstborns.” Smelser says some of these include being ambitious, independent, bossy, and strong-willed.

However, because only children don’t have other siblings to play with or compete against growing up, they may be less competitive. But on the flip side, only children can be independent and mature, since they are often around more adults than kids.

Key birth order traits of only children:

  • Mature
  • Loyal
  • Independent
  • Confident
  • Leader
  • Cautious
  • Curious
  • Sensitive