Does Birth Order Play a Role in Personality?

Abstract

The objective of this paper is to review the age old debate: does birth order effect personality? In this study, we reviewed three fairly recent peer-reviewed articles--one overview and two case studies. Daniel Eckstein and Jason Kaufmann provide an overview of the debate, including history and case studies accounting for both sides. They concluded that there is some evidence to support birth order's effects in personality, but additional research is needed. In the first case study, Ashta Kaul and Anupama Srivastava tested 100 adult Indians, half firstborns and the other half being last-borns, for personality differences. They concluded no significant differences. Lastly, Ben Cotterill conducted a 2022 study which yielded significant personality differences for introvertedness in only-children and middle-children.

Background Information of the Argument
The concept of birth order relating to personality goes back to Austrian doctor and founder of individual psychology, Alfred Adler. In 1937, Adler claimed that each child in a family is treated "uniquely" in accordance with their birth order (Cotterill 2022). Adler believed that each child in accordance to their birth order possess unique characteristics and traits (Kaul & Srivastava 2018). An example of a unique characteristic, according to Eckstein and Kaufman (2012), was second-born children being the best "counselors". Adler himself engaged in sibling rivalry throughout his childhood with his older brother, Sigmund. He believed Sigmund was the favored child in his family.

According to Kaul & Srivastava (2018), American psychologist and Harvard graduate Frank J. Sulloway proposed his "Family Niche Theory" of the effects of birth order. He believed that birth order is responsible for various inequalities experienced by all siblings and must be accounted for in order for each sibling to understand their "niche" in the family system. His theory proposes that first-born children are more dominant and less cooperative with their younger siblings. The younger siblings, in return, turn to "social support" to find other ways to "assert" themselves. This naturally makes younger siblings more extraverted.

In 2001, American psychologist Joseph Lee Rodgers dwelled on the significant cultural context behind the debate (Eckstein & Kaufman, 2012). Parents may introduce their children by their birth order ("my youngest is...") and the youngest in the family may forever be labeled as the "baby of the family", despite reaching old age. For most first-born children, their status as the "first born" will forever remain and will always be the "casual explanation" for any sort of abnormal behavior. Even parents are responsible for reinforcing these stereotypes, as Rodgers claims that parents will usually dismiss certain behaviors exhibited by their children as "they are just like that".

Support for the Argument
As common as the debate is, there are scientific evidences and significant trends amongst siblings to support the notion that birth order does relate to personality.

Adler's "theory of sibling rivalry", competition between siblings, was the source of Swiss researchers' Jules Angst & Cécile Ernst stereotypes for firstborns and later-born persons. They stated that firstborns are stereotyped to be "adult-oriented", "conservative", "creative" and are more likely to "become leaders", while later-born persons are stereotyped to be "ambitious", "popular" and "extroverted". This is also echoed by Kaul & Srivastava (2018). Although these are stereotypes, these are being regarded as evidence that birth role has a significant effect on behavior as, according to Eckstein and Kaufman (2012), research has found that stereotypes influence peoples' behaviors. This was concluded in a 1968 study on "self-fulfilling prophecies" done by American researchers Robert Rosenthal and Lenore Jacobson (Eckstein and Kaufman (2012)).

According to Cotterill (2022), there is evidence to support that firstborns are more intellectually sound than their younger siblings. This is shown in firstborns achieving higher IQ scores and completing additional years in advanced education. American social psychologist Robert Zajonc theorized that firstborns have more exposure to adults and their ways of interactions. He also believed that firstborns are more supervised and protected than the younger siblings, which is why they are self-disciplined. Firstborns being stereotyped as "leaders" holds significant truth to it, as a 2001 study done by McGill university professor Blema Steinberg found that firstborns were "overrepresented" in various political posts (members of US congress, US governors, Australian prime ministers, etc.) (Eckstein & Kaufman, 2012). It was reasoned that parents value their firstborns, therefore they are more likely to become political leaders.

On the other hand, second-born children are regarded as "rebellious" (Cotterill 2022). This is because they must "equal" their elder sibling in achievements. If they cannot equal their elder sibling in a certain field, they will seek a different field to complete their mission. Youngest-borns have a higher tendency to achieve "lower IQ scores", divorce, and drink excessively during college (Cotterill 2022). A 2006 study found that youngest borns are more likely to engage in risky behaviors, such as substance abuse and careless sexual activity, than their elder siblings (Eckstein & Kaufman, 2012).

Middle-born children are regarded as "sociable", "least likely to act out" and "less bold" (Cotterill 2022; Eckstein & Kaufman, 2012).

Only children have a likelihood of being more "self-centered" and mature at a faster pace as they are around adults more often than children with siblings (Cotterill 2022).

Opposition Against the Argument
Although a correlation is observed, it is crucial to investigate whether birth order is the cause of these trends.

Kaul & Srivastava (2018) conducted a study in India with 100 adults, half of them being firstborns and the other half are last-borns. The study was done in order to observe any differences between the firstborns and the last-borns in personality differences. Personality was tested by a shorten version of the NEO personality inventory, termed the NEO-FFI Adult form. The NEO-FFI Adult form was administered as a self-survey, where participants had to rate traits under the following categories from a scale of 1 to 5 (strongly disagree to strongly agree): Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness. The scientists concluded that there were no significant differences between the personalities of the firstborns and last-borns. This result went against Sulloway's "Family Niche" theory. which was mentioned in their introduction.

Zajonc argued that birth order effects do not appear until after the age of 11. This was derived from the confluence model, which justified significant intelligence changes at different ages. Zajonc explained that the "mental maturity" of children developing under the same household "flow together" over time, thereby effecting each other. The model predicts that birth order has no effect, thereby predicting lower IQ scores for higher ranked birth orders. Zajonc's findings proved to be the opposite, where a 1951-1983 Iowa cohort of schoochildren displayed significant IQ test score increases after the age of 11. Eckstein and Kaufman (2012) both concluded that some empirical findings support the notion that birth order does affect personality, but more research needs to be done (including more longitudinal studies).

Conclusion
Although the significant stereotypes and cultural influence do seem to suggest that birth order plays a role, it seems that it doesn't have a direct role and that the correlations that exist do not equal causation. Kaul and Srivastava conducted a study which proved to be in opposition to the argument while Eckstein and Kaufman believed that although there was decent empirical evidence in support of the argument, they suggest more research was needed--including a longitudinal study. Cotterrill echoes this sentiment, stating that research should be done focusing on the effects of birth order on self identity. Further research should be employed in this field, including longitudinal tests and more studies relating to identity rather than personality.