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The Effect of Birth Order on the Level of Intelligence

Different scholars have studied the influence of birth order on cognitive ability, including academic achievement, verbal articulation, and the desire to achieve. A great deal of the studies agrees that there is a positive relationship between birth order and the level of intelligence. First-born children in a family possess certain characteristics including being more active, articulate, better performers in school, and are likely to proceed to college. In addition, children born alone in a family tend to score higher on aptitude tests and standardized tests than those born further down in the birth order. This discussion investigates how birth order does affect intelligence.

According to the confluence theory developed by Zajonc and Markus in 1975, siblings’ intelligence is positively related to family size. Intelligence, according to the confluence model, decreases as the number of children increases in a family (Zajonc & Sulloway, 2007). The only exception to this model is when there is one child in a family because he or she does not have an older sibling to act as a teacher. The confluence model is also based on the idea that the intellectual growth of family members depends on others in the family. The confluence theory is further supported by the dilution model that asserts that there is a positive relationship between the number of parental resources and the level of intelligence. Given that resources are often limited, the value of parental resources allocated to each child decreases with the birth of a new child. This implies that child welfare decreases with an increase in the number of children.

In another interesting study, every birth order within the family tends to have unique characteristics. First-born children are hard-working and grow to be more competitive than other siblings (Barclay, 2018). Further to this, they exhibit higher academic and career ambitions. In a family of more than one child, firstborns can be described as high achievers, pace-setters, perfectionists, highly determined, responsible, and success-oriented. Similarly, children born alone have characteristics similar to firstborns. Middle children in the birth order, on the other hand, have greater cooperation skills and are good mediators (Barclay, 2018). Due to their superior negotiation abilities, they often become good leaders and managers. They can be described as peacemakers, competitive, flexible, diplomatic, and social beings. The lastborns are found to be great motivators and highly outgoing. They also tend to be too affectionate and often make good salespeople. They are described as humorous, risk-takers, and creative.

Parental intelligence coupled with child-rearing attitudes plays a critical role in a child’s intellectual development. Children born in large families tend to develop slowly and therefore attain a lower intelligence quotient than children born in small families (Barclay, 2018). The smaller the family size, the more parental contact. In addition, firstborns always have to explain things and answer questions to the younger siblings. Through teaching and tutoring the younger siblings, firstborns develop cognitively and process information faster. As they teach others, firstborns also develop their verbal skills, so they are more articulate. On the contrary, younger siblings rarely get an opportunity to teach anyone, which results in lower intelligence and cognitive abilities.

Gender and age also play an important role as far as determining the level of intelligence is concerned. For instance, a youngest-born boy can serve as a firstborn given that he is the firstborn male child. As such, he may exhibit both the characteristics of a firstborn and those of the youngest sibling in a family. The age spacing also affects the level of intelligence because as the family expands, the intellectual environment reduces (Rauf, 2015). Depending on age spacing, children who come further down in the birth order are raised in a less stimulating environment than those born earlier in the birth order.

Overall, it can be observed that birth order does influence the level of intelligence. As demonstrated by the different models, including confluence theory and dilution model, birth order determines intelligence. Parental intelligence, age spacing, and gender are other key factors that affect the level of intelligence in children.


Barclay, K. J. (2018). The birth order paradox: sibling differences in educational attainment. Research in Social Stratification and Mobility54, 56-65.

Rauf, K. (2015). Effect of Birth Order and Gender on Emotional Intelligence of Adolescents. Bahria journal of professional psychology14(1).

Zajonc, R. B., & Sulloway, F. J. (2007). The confluence model: birth order as a within-family or between-family dynamic?. Personality and Social Psychology Bulletin33(9), 1187-1194.


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