Whether the number of siblings and the position in the sibling sequence has an influence on character has so far been controversial. Now a large psychological study confirms that there is indeed a connection with various personality traits. Adults with siblings, for example, are more cooperative than people who grew up without siblings. Middle children develop into particularly cooperative adults, followed by last- and first-borns as well as only children. But only children also differ in other characteristics: they develop into more open people than siblings and are at the same time more introverted.
The birth order of siblings influences the character of children and the adults they grow into, numerous studies seem to show. Firstborns therefore develop different personality traits than “middle children” and lastborns. However, the differences discovered so far are rather weak. In some cases, the study results contradict each other or are not meaningful due to insufficient data. To date, there has been little research into whether and to what extent the personalities of people who grew up with siblings or as an only child differ.
Siblings make you more cooperative
Psychologists Michael Ashton from Brock University and Kibeom Lee from the University of Calgary have now examined this question in detail in a larger sample. To do this, they evaluated information from around 711,000 adults who answered a comprehensive online questionnaire on the most important personality traits. These are divided into five dimensions: Honesty-Humility, Emotionality, Extraversion, Agreeableness (as opposed to Anger), Conscientiousness and Openness to Experience. The respondents came from different, predominantly English-speaking countries. Ashton and Lee looked for differences in the responses based on birth order and number of siblings.
The analysis showed that some personality traits actually vary depending on position in the sibling sequence and family size. Accordingly, middle-born participants show the highest willingness to cooperate – measured by the associated characteristics of honesty, modesty and agreeableness. These characteristics are second most pronounced in the last-born, followed by the first-born and the only children, as psychologists report. Middle children are therefore the most cooperative, followed by the youngest and oldest siblings. Only children develop the least willingness to cooperate.
The number of siblings also plays a role: the two character traits of honesty-modesty and agreeableness are therefore more pronounced in people with a larger number of siblings than in people with few siblings. Among the participants with the same number of siblings, these characteristics were somewhat less pronounced in the first-born than in the middle-born and last-born, as the analysis showed. Ashton and Lee suspect that people with more siblings need to cooperate more often instead of acting selfishly. “This ongoing situation could then promote the development of cooperative tendencies in general,” say the psychologists.
Only children are more open and introverted
For another personality trait, however, the picture was the opposite. Openness was weaker among adults with siblings; The psychologists found this characteristic to a greater extent in people without siblings. Anyone who grew up as an only child develops into a more open adult. But people with only one sister or brother and first-borns, i.e. the eldest, were also more open as adults than middle- and last-borns. The character trait of extraversion showed a different distribution: the oldest and middle siblings and people with many siblings were the most extroverted, while the youngest in a family, people with a few siblings and only children were more introverted.
Ashton and Lee conclude from the findings that there is a clear connection between growing up with many children as siblings and the development of a cooperative, open and extroverted personality. They didn’t differentiate whether they were biological siblings or a patchwork family. “We refer to children in a household as siblings without distinguishing between full and half siblings, between biological, adoptive, step and foster siblings and without distinguishing between siblings and other child relatives such as cousins,” explain the psychologists.
Source: Michael Ashton (Brock University) et al.; Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2416709121