Does Birth Order Influence Sibling Personality?

Does birth order influence sibling personality? Let's see what science has to say!

For years, the scientific community has been interested in the relationship between personality traits and birth order. Could birth order condition sibling personality?

The first studies focused on the relationship between birth order and certain physical traits, including vulnerability to certain diseases. The results of these early studies were, for the most part, inconclusive. Around 1930, concern about physical characteristics gave way to an interest in the degree of adaptation, with equally confusing results.

Thus, in 1983, Ernst and Angst reviewed 1500 articles on birth order and personality characteristics. The authors concluded that reports of the effects of birth order have been greatly exaggerated so far.

Physical and social differences

There seems to be evidence of some physical differences right before and after birth:

• Firstborn children tend to weigh less at birth.
• Firstborn children are more likely to die in the womb after 20 weeks.
• Also, they’re at a greater risk of intracranial and spinal birth injuries.
• Likewise, they’re at a higher risk of dying at birth and soon after birth.

In addition, they have some socialization differences in relation to second-born children:

• Parents are more demanding with firstborn children and pay more attention to them when they’re infants. This attention diminishes with the second child.
• Firstborn children are described as more likely to communicate with their parents.
• In small families, firstborn children are described as more willing to accept their parents’ authority.

Also, there are very modest differences in educational and occupational achievement. Firstborn children in small families, and younger children in general, tend to achieve higher education and higher occupational status than middle children.

However, Ernst and Angst argue that, when the right controls are applied, birth order isn’t related to IQ, school performance, mental illness, anxiety, and dependence on these characteristics.

This is how authors Ernst and Angst (1983) questioned the relationship between birth order and personality traits. However, somewhat later, in 1996, the author Frank J. Sulloway published the book Born to Rebel: Birth Order, Family Dynamics, and Creative Lives. In it, the author proposes that the effects of birth order stem from a competition between siblings as they struggle to find their place in the family.

Sulloway and sibling competition

According to this author, the firstborn has the first choice of their place in the family. Therefore, they try to please their parents in the traditional way through school success and responsible behaviors. But, as other siblings arrive, firstborn children must deal with threats to their natural priority in the sibling status hierarchy.

As a result, in adulthood, they tend to be conscientious and conservative. Thus, those born later must resist the higher status of the firstborn, while seeking alternative ways to distinguish themselves in their parents’ eyes.

Consequently, they develop a character in adulthood that’s marked by an empathic interpersonal style, a struggle for uniqueness, and political views that are both egalitarian and anti-authoritarian.

Sulloway focused his investigations on the subject by taking into account the five-factor model (Goldberg, 1990). On this foundation, authors such as Paulhus, Trapnell, and Chen (1999) investigated the effects of birth order. In their study, they concluded that:

• Firstborn children tend to be the most successful and conscientious. Also, they score higher on neuroticism and extraversion and lower on friendliness and openness.
• Secondborn children tend to be more rebellious, liberal, and pleasant.

Personality characteristics in cases of three siblings

In 2003, authors Saroglou and Fiasse conducted another study in this field. In their study, the authors analyzed 122 young adults from families with three siblings. The results of this study were related to the order of the siblings and their personalities. They found that:

• The middle siblings seemed to be the “rebellious” siblings from birth. Compared to their siblings, they were less conscientious, less religious, and had a lower school performance. Also, they were more impulsive and open to fantasy.
• The younger siblings were the most pleasant and warmest.
• The firstborn children were more conscientious and higher-achieving.
• The last ones to be born were more pleasant, liberal, and rebellious.

In conclusion, it seems that birth order might have something to do with sibling personality. All the studies on the subject show that more research is needed in this field. Future research should take into account factors and variables that weren’t taken into account or that couldn’t be controlled in previous studies. This could lead to clearer results on the subject.