A new study published in the Proceedings of the National Academy of Sciences (PNAS) reveals that middle children exhibit higher levels of honesty and agreeableness compared to their siblings. Conducted by Canadian scientists Michael Ashton of Brock University and Kibeom Lee of the University of Calgary, the research analyzed data from over 700,000 adults to assess whether personality trait levels could be linked to birth order and sibling number, according to The Independent.
The study found that middle-born individuals tend to score higher on traits associated with cooperation, such as agreeableness and honesty-humility. "Honesty-Humility and Agreeableness both showed the highest means for middle-borns, followed in order by last-borns (youngests), firstborns (oldests), and only children," the researchers wrote, as reported by The Independent. This suggests that being a middle child may be associated with the development of stronger cooperative traits.
Michael Ashton and Kibeom Lee noted that individuals with more siblings were more likely to develop cooperative personalities. "A commonsense possibility is that when one has more siblings, one must more frequently cooperate rather than act on selfish preferences. This ongoing situation might then promote the development of cooperative tendencies generally," the researchers stated, according to Live Science. The study assessed the number of siblings in a sample of over 70,000 adults and replicated the same results, as reported by The Independent.
Participants were asked about the household in which they grew up and provided information on their birth order and the number of siblings. The researchers used data from hexaco.org, where individuals can take a personality test, providing a large and diverse data set, according to Live Science.
The researchers controlled for religiosity because religious families tend to have more children, according to Live Science. While religion explained about 25% of the differences in personality traits, birth order and family size explained the rest. The differences between siblings in these traits were found to be small but consistent.
The study considered previous theories on birth order and personality. Austrian psychologist Alfred Adler had claimed that firstborns are responsible, the youngest are continuously pampered, and middle children often feel overlooked, developing certain traits in response. The new research provides empirical evidence that supports some aspects of these theories, according to Yahoo News.
Previous research has found some evidence that firstborns average slightly higher than later-borns in intellect-related traits, reported The Independent. However, studies on personality differences have been inconclusive. A 2015 study, for instance, found no strong relationship between birth order and personality traits measured by the Big Five personality dimensions, according to Live Science.
The new study used the HEXACO model, which includes six personality traits: honesty-humility, emotionality, extraversion, agreeableness, conscientiousness, and openness to experience. This differs from the Big Five model, with the inclusion of honesty-humility as a separate trait, reported Live Science. Despite the small differences found, the authors suggest that the development of cooperative tendencies in middle and last-born children may be due to the dynamics of larger families.
These findings are not likely to be the last word in birth order research. Other studies have found no significant differences in personality traits among siblings of different birth orders. For instance, a 2020 study found no differences in narcissism between only children and children with siblings, and a 2019 study using HEXACO found only minimal differences between only children and people with siblings, reported Live Science.
The article was written with the assistance of a news analysis system.