WikiJournal Preprints/Birth Order and Personality

Background


Birth order is defined as the "ordinal position of a child in the family".

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" and possessed unique characteristics and traits in accordance with their birth order (Cotterill 2022; Kaul & Srivastava 2018), Adler believed that it was a "fallacy" that every child in a family is raised in the same manner, as he attributed differences in the "psychic" of each sibling to the order of their birth (Mariet, pg. 96). Examples of unique characteristics tied with birth orders are that second-born children are regarded as the best "counselors" and first-born children are held to be the "decision-makers" of the family. Adler, a second-born of six children, engaged in sibling rivalry throughout his childhood with his older brother, Sigmund, as he viewed Sigmund was the favored child.

In 1996, American psychologist and Harvard graduate Frank J. Sulloway proposed his "Family Niche Theory" of the effects of birth order in his book, Born to Rebel. He asserted that birth order is responsible for various inequalities experienced by all siblings and must be accounted for so that each sibling is able to understand their "niche" in the family system. His theory proposed that first-born children are more dominant, stubborn in regards to their viewpoints, and less cooperative with their younger siblings. The younger siblings, in return, turned to "social support" to find other ways to "assert" themselves. This naturally makes younger siblings more extroverted. He even claimed that birth order is a better measure of social development than race, gender, or working class. With such outstanding claims, Sulloway's "Family Niche Theory" was met with heavy criticism. In modern times, the attitude towards the effects of birth order on personality have shifted towards it having an almost nill effect on personality. Causes for this change may come from confounding variables on different study designs. Rodica Ioana Damian & Brent W. Roberts of the University of Illinois theorize Sulloway's "Family Niche Theory" are heavily based off of the evolution model, where siblings are naturally wired to compete against one another to gain maximum parental attention - thereby failling into certain "niches" within their own family complex.

In 2001, American psychologist Joseph Lee Rodgers discussed the significant cultural context surrounding birth order (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 "firstborn" will forever remain and will always be the "casual explanation" for any sort of abnormal behavior. Parents are responsible for reinforcing these stereotypes, as, according to Rodgers, parents will usually dismiss certain behaviors exhibited by their children as "they are just like that" - referencing their birth order.

Support
As common as the debate is, it is appearant that a correlation does exist between birth order and certain personality traits.

Adler's theory of sibling rivalry was the source of Swiss researchers' Jules Angst & Cécile Ernst stereotypes for firstborns and later-born persons. They believed that firstborns are stereotyped to be "adult-oriented", "conservative", "creative", "persistent" and are more likely to "become leaders", while later-born persons are stereotyped to be "ambitious", "popular" and "extroverted". Stereotypes are being mentioned because research has shown that stereotypes influence peoples' behaviors, as concluded in a 1968 study by American researchers Robert Rosenthal and Lenore Jacobson.

There is evidence to support that firstborns are intellectually more sound than their younger siblings. Firstborns are more likely to achieve higher IQ scores and complete additional years in advanced education. The idea of firstborns being the most intelligent siblings originates from British polymath Sir Francis Galton, who found that most established British scientists were firstborn. He attributes primogenitures and "family environmental influences", such as firstborns baring more responsibility than their younger siblings, as causes for this phenomenon. Saher et al., (2022) explained that firstborns feel a pressure of being a "perfect" role model for their younger siblings, so they are more likely to take up roles that require increased responsibility.

A 2001 study conducted 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.). For example, 25 out of the 46 (>50%) US presidents are firstborns. Steinberg reasoned that because parents value their firstborns, they are more likely to become political leaders. On the other hand, second-borns are theorized to have an inner desire to "equal" their elder sibling in achievements. Therefore, second-born children are described as "rebellious" (Cotterill 2022). 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). American social psychologist Robert Zajonc theorized that firstborns have more exposure to adults and their ways of communications, hence their niche as the "adult-oriented" sibling. He also believed that firstborns are more supervised and protected than the younger siblings, which is why they are self-disciplined. Zajonc argued that birth order effects do not appear until after the age of 11. Zajonc explained that the "mental maturity" of children developing under the same household "flow together" over time, thereby affecting each other at latter stages of the siblings' lives. His findings done on a 1951-1983 Iowa cohort of schoolchildren found that the schoolchildren significantly improved in IQ test scores after the age of 11. In their overview, 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).

Middle-born children are regarded as "sociable", "least likely to act out" and "less bold" (Cotterill 2022; Eckstein & Kaufman, 2012), while only children have a likelihood of being more "self-centered" and have a tendency to mature at a faster pace due to their increased exposure to adults (Cotterill 2022). The latter correlates with Zajonc's "confluence model", which states that the number of children in a household and overall intellectual environment have a negative correlation between each other. Adler also believed that only-children are "friendly" and "engaging".

Opposition
Although a correlation is observed, it is crucial to investigate whether birth order is the direct cause of these trends. As mentioned earlier, the modern attitude towards this discussion is birth order has little to no effect on personality. With conflicting results over the last 50 years or so concerning this topic, it is difficult to discern the line between birth order and personality. Damian & Roberts explain that confounding variables and underpowered studies are the issues preventing scientists from truly seeing the effects of birth order on personality.

Sample Size
They suggest that studies on personality (between-family) need to be done with a large sample size, specifically a sample size of 15,455, a correlation of r=.02 with 80% power (80/100) at p<.05.

Kaul & Srivastava
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.

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.

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