Oldest siblings are overachieving leaders, youngest are the rebellious attention seekers, and the middle children are the forgotten diplomats. Are the stereotypes true? Research shows mixed evidence on whether birth order impacts personality.
Despite genetic similarities, some scientists believe the differences between siblings arise from their birth order. The concept of sibling order has been around since the 19th century when psychotherapist Alfred Adler suggested that first born children are “neurotic” because they do not share their parents for the early part of their life whereas youngest children are supposedly the most ambitious, and middle children are known for their emotional stability. Psychologist Frank J. Sulloway believed that each child occupied a specific niche in their family and developed their own strategies to succeed. For example, younger children are typically unsure of their parents’ views and choose alternate paths, unlike older siblings who follow their parents.
Early studies conducted to test the impact of sibling order were hard to carry out because personality is difficult to quantify. A 1980 study by Edgar Howarth found that firstborn children displayed lower anxiety, greater ego, and higher persistence. However, it should be noted that this study was conducted via personality questionnaires (Howarth Personality Questionnaire) and all data was self-reported. Additionally, the study did not evaluate the children over time and only reflected a snapshot of their personalities. .
“Research shows mixed evidence on whether birth order impacts personality.”
Newer studies, such as one by Joseph Doyle in 2020 at MIT, studied quantifiable data: delinquency rates between firstborn and secondborn boys. Researchers compared populations in Denmark and Florida and found consistent evidence that secondborn boys are 20-40% more likely to be disciplined and enter the criminal justice system. The data here is somewhat more plausible because comparing siblings within the same family negates the effect of family environment. NPR’s Social Science Correspondent Shankar Vedantam suggests that the reason for this stark difference is likely that younger siblings often compete for parents’ time and resources. The second born children also have an additional role model in their slightly older siblings, rather than only their parents.
However, numerous studies found negligible personality differences between siblings. A 2015 study led by Julia M. Rohrer at the University of Leipzig examined a data set of over 20,000 participants from the United States, Germany, and Great Britain. Comparing sibling profiles within individual families and between strangers, they found no substantial differences between traits like extraversion, emotional stability, agreeableness, or imagination. Although, they did find an intellectual difference, where intellect increased alongside birth order position. In other words, older siblings were found to be smarter.
The conflicting evidence and the difficulty of measuring personality leads scientists to make the general claim that birth order can shape personality, but not systematically. Frank Spinath, a psychologist at Saarland University in Germany, suggests that there are many factors contributing to personality that sibling order does not account for. The environment, social circle, and innate temperament can all affect the way parents raise their children and consequently their children’s personality. Sex, age difference, and siblings with disabilities also play a large role.
While the stereotypes of birth order exist, and are often intuitive, it is likely that these conclusions are only valid on a broad, general scale. Every family is different and any impact of sibling order is only a small part of a person’s complex personality.
