Birth order theory, developed by psychoanalyst Alfred Adler in the 1920s, posits that children’s hierarchy within a family influences their personality.
Adler believed that family dynamics, parental attention, and sibling role differentiation shape personality traits and life trajectories. This theory has become mainstream.
“Over time, birth order theory gained popularity in cultural psychology and parenting literature, but its scientific status has been debated for decades,” Dr. Patel says.
Most experts agree that birth order is one of many factors that contribute to personality, but here’s what theory suggests about its influence.
Personality traits of the firstborn
Birth order theory traditionally associates firstborns with specific attributes, such as:
- Excellent grades
- competitiveness
- perfectionist
- person in charge
- with confidence
- leader
- bossy
- stubborn
For firstborns, an important life event is the birth of a sibling, at which the caregiver’s attention shifts dramatically, says Dr. Stefan Schmukl, a professor of psychology at the University of Leipzig in Germany who has published research on birth order theory and related topics.
“According to Adler, the firstborn is ‘dethroned’ upon the birth of a second child, and this loss of perceived privilege and superiority can have a lasting impact on the firstborn,” Dr. Szumkul explains.
Still, receiving special parental attention early in life may help firstborns develop intellectually. Some studies have shown that this group typically scores higher on intelligence tests than their younger siblings.
Personality traits of the middle child
Being born between an older and younger sibling is commonly associated with “peacemaker” type traits, including:
- intermediary
- I can agree
- diplomacy
- independent
- realistic
“Middle children are usually more outgoing. Sometimes they can feel like the forgotten child and be more independent or more team players,” says Dr. Gabriel Shapiro, a general, child, and adolescent psychiatrist and professor at the Icahn School of Medicine at Mount Sinai in New York City.
With this in mind, cooperative traits may be especially true for middle children, who by default are part of families with at least three children. “We suspect that growing up with more siblings may promote cooperation, leading to a more reserved and cooperative personality,” Dr. Lee says.
Personality traits of the youngest child
The youngest child, known as the “baby” of the family, is often portrayed as:
- free thinking
- rebellious
- extroverted
- Outgoing
- attract attention
- socializing
According to this theory, these extraversion-related traits associated with last-born children may be due to parents becoming more relaxed in their approach by the time their youngest child is born.
“Younger siblings may imitate older siblings’ behavior or benefit from a more relaxed parenting environment, which may shape social behavior without reflecting innate personality differences,” Patel says.
Personality characteristics of only children
Similar to firstborn children, only children are classified within birth order theory as:
- mature
- perfectionist
- with confidence
- self-entertainment
- Detail-oriented
According to Adler’s theory, only children are more comfortable interacting with adults, given the time and attention of a full-time caregiver, and some may perceive that only children are less cooperative in social situations, such as the workplace. But it all depends on the environment they grew up in, Dr. Shapiro says.
Despite anecdotal theories that not having to share resources may only give children an advantage in some areas, available research generally indicates more similarities than differences in cognitive and social behavioral development between these and other sibling types.
For example, a UK-based cohort analysis that looked at groups of children over several decades (those born in 1946, 1958, 1970, and 2000 to 2002) found that only children had cognitive abilities comparable to children in families with two siblings and tended to have higher cognitive scores than children in families with two or more siblings. However, the so-called only-child advantage appears to diminish for more recent generations (those born in 2001). The researchers suggest that family background factors, rather than birth order, are likely to explain the difference in ranking between only children and other siblings.
“Outcomes depend more on the quality of parenting, peer involvement, and social opportunities than on the absence of siblings,” Patel added.
