Birth order theory suggests that birth order changes the way a family perceives and treats a child, which in turn affects their personality development.

The Austrian psychotherapist Alfred Adler first introduced the birth order theory.

This article looks at the ideas of birth order theory and how it may influence personality.

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Birth order theory suggests that the order in which children are born affects their personalities.

Whether a child is the firstborn, a middle child, the youngest, or an only child may affect how their family treats them, how much attention they receive, and how they may compete for their parents’ attention.

These factors may affect a person’s personality. Below are some possible characteristics of people of various birth orders.

As a firstborn, the oldest child may receive the most undivided attention from their parents, and parents may impart their beliefs and rules predominantly onto this child.

Having younger siblings may cause an eldest child to take on more leadership and responsibility.

This child may:

  • display self-reliance
  • have a serious attitude
  • behave conventionally to keep the attention of their parents
  • be a high achiever
  • abide by rules
  • be responsible
  • be a perfectionist
  • trust their capabilities
  • uphold family traditions and morals
  • imitate the behavior of their parents in looking after younger siblings

The oldest child may take on a teaching role for their younger siblings, which may reinforce their own learning and increase their intellectual abilities.

The youngest child may look for ways to stand out from their older siblings and create their own unique position in the family.

They may try to gain attention in different ways than their sibling or siblings and may become sociable, extroverted, and fun-loving in order to assert their uniqueness.

A youngest child may feel they have to compete or catch up to older siblings and may feel less capable or at a disadvantage.

They may develop an outgoing personality, humor, and social intelligence to elevate themselves in the family dynamic.

Birth order theory suggests that first- and last-born children have a unique position in the family, while middle children do not.

Research suggests that middle-born children may believe that they have less emotional and financial support from their parents than their siblings do.

As a result, middle children may have lower self-esteem or greater insecurity than their siblings. However, this may not be the case if the middle child is a different gender than all of their siblings or if there is only a small age gap between siblings.

Middle children may focus more on building strong relationships outside their family, such as through friendships or romantic partnerships.

Middle children may be:

  • the most independent of the siblings
  • ambitious
  • thoughtful
  • sociable

Only children may receive more attention from their parents and will not experience conflict or competition with siblings. Growing up as an only child may result in characteristics such as:

  • maturity
  • creativity
  • intelligence
  • an easier transition into adulthood

Research suggests that only children may be high achievers, complete more years of education, and have secure, higher-status jobs.

An only child may also feel greater responsibility and expectations from parents and may feel more intertwined with their parents’ lives.

Many factors may influence personality traits, including the following.

Sibling age gaps

According to a 2018 review, the age gap between children may influence birth order personality.

A smaller age gap between a firstborn and a middle child may mean that the firstborn feels less unique, and the two children may receive more equal attention from parents.

Similarly, the presence of twins in a family may affect sibling and family dynamics. The twins may receive equal attention from their parents and may have to share and spend more time together. As a result, they may develop similar personality traits and a strong bond with each other.


Gender may also affect birth order personality. Research suggests that a middle-born male with all-female siblings may have higher self-esteem than is typical for a middle-born child.

If a child is a different gender from all of their siblings, they may receive different treatment or feel more unique.

Genetics and environment

Research on twins suggests that genetic factors account for around 50% of personality traits, while the other half may be due to environmental factors.

Environmental factors that may influence personality include:

  • the socioeconomic status of parents
  • parenting styles or practices
  • peer relationships
  • romantic relationships
  • work experiences

Culture can also influence how a person feels, thinks, and behaves, although researchers are still discussing how culture affects personality.

Other factors may also affect birth order, such as adoption or the death of a sibling, although there is little scientific research around this.

This section answers some frequently asked questions about birth order theory.

Is birth order theory scientifically proven?

There is a lack of conclusive evidence around birth order theory.

According to an older 2015 article, scientific evidence suggests there is little or no substantial link between birth order and personality and that birth order may have a very small link to intelligence. While birth order theory may help explain differences between siblings, but there is not enough evidence to suggest that it is scientific fact.

What is the birth order theory of gender?

The birth order theory of gender suggests that gender may change the way a family perceives children. This may subvert birth order theory.

For example, being the only male or only female sibling may change how a family perceives a child and may alter typical characteristics of birth order. Research suggests that middle-born males with all-female siblings may have higher self-esteem than a middle child otherwise might.

Birth order theory suggests that the order in which a child is born influences their personality.

Although the theory may resonate with typical experiences, there is little scientific evidence to suggest a significant link between birth order and personality.