How Birth Order Affects Social Relationships

by Amanda Ng (’18)

birth order
Fig. 1: Research shows that birth order can affect how we deal with social relationships.

Although much research has been done on birth-order and its affects on relationships, it has mostly focused on theories such as the “middle-child syndrome” and how birth order can affect siblings’ relationships. However, what has not been studied is the idea that a person’s birth order may also affect their prosociality, which is the degree to which a person acts in the interests or benefits of others.

Dr. Catherine Salmon of the University of Redlands in California recently tested this idea. The study involved 220 female undergraduates, 48.6% of which were firstborns, 17.7% were middleborns, and 33.6% were lastborns. The participants completed a series of questionnaires that measured traits such as competitiveness, self-perceived competence, executive function, and emotional control, which indicated their level of prosociality. Better behavioral regulation, higher emotional intelligence, and personality as a general factor were all positively correlated with prosociality. When using a regression model to predict prosociality based on birth order, it was found that later birth order increased prosociality, with the largest difference between the first and second-born child. It is hypothesized that this difference occurs because later born children are less focused on family and parental authority. As a result, the children become more extroverted and in tune with others in order to create connections with individuals outside of the family to set themselves apart from their older siblings.

In the future, research in this field will focus on whether birth intervals or the size of the family affects a child’s sense of prosociality and competence in society.



  1. Salmon et al., The relationship between birth order and prosociality: An evolutionary perspective. Personality and Individual Differences 96, 18-22 (2016). doi:10.1016/j.paid.2016.02.066
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