The Psychology of Birth Order and Personality

This article is an excerpt from the Shortform book guide to "Originals" by Adam Grant. Shortform has the world's best summaries and analyses of books you should be reading.

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Does birth order affect the psychological make-up of a child? What are some ways firstborn children differ from lastborn?

Birth order has a very strong effect on a child’s psychology. Firstborns tend to be more dominant and conscientious, while lastborns— more unconventional and rebellious.

Keep reading to learn about birth order psychology.

What Is the Birth Order Effect?

Birth order psychology has a very strong effect—firstborn children tend to be conscientious and dominant, showing achievement along classical lines—income, academic achievement, Nobel Prize winning (but apparently only until age 30, when the differences even out). Lastborn children are more likely to be risk-seeking, rebellious, and unconventional. (Middle children tend to be more diplomatic, having to negotiate between the extreme members of the sibling group.) This tends to be true regardless of child gender.

Suggestive observational studies on the psychology of birth order:

in baseball, stealing bases is a very risky, not necessarily optimal play. Younger brothers are 10.6x more likely than older siblings to steal a base.
laterborn children are more likely to adopt revolutionary scientific ideas like Copernican astronomy and Darwinian evolution, even controlling for the mentally calcifying effects of age
rebels were twice as likely to be lastborn as firstborn
of a list of the top 100 comedians, 83% were more likely to be lastborn than chance would predict. (why is this relevant? not only is comedy an unconventional career, it requires humor, explained below)
riskier jobs tend to be taken up by lastborn

Why Birth Order Affects Originality

A few models try to explain this pattern. First is niche picking. Like animal species in ecology, children try to find a niche to thrive in, avoiding direct competition with their siblings when there’s little hope of outshining them. Free of competition, the firstborn child models after the parents, based on rules and authority. This child performs well in school and traditional structure. When a new child arrives, the older child, risking being dethroned, emulate their parents, enforcing rules and authority over the younger sibling. The younger child, seeking an identity, finds it difficult to compete with the firstborn child and attract commensurate attention. Thus the younger child seeks niches like humor and rebellion to attract attention, and this becomes ingrained in identity.

(The effect seems to be strongest in a middle range of age distance. If separated by just a year, the younger child can hold her own; if separated by 10 years, the firstborn’s niche is open again.)

Another explanation comes from caretaker effects. The firstborn is usually cared for strongly by parents, who have the anxiety of firsttime parents as well as the energy of youth. As the parents have more children, they relax due to more experience and declining energy with age. The older children also then take up a greater share of the care, but they enforce fewer rules than parents would. Finally, older children become more responsible and capable of handling chores, leaving the youngest kids free to roam. For all these reasons, the lastborn thus experiences relatively more freedom.

These are general trends, because most parents probably react to birth order predictably in the ways stated above. But some unique situations may contravene this trend – for instance, if the parents exert even more pressure on laterborn children.

Andre Agassi was the last of 4 children of a father who wished to raise a tennis superstar. When the first 3 children failed to show promise, the father exerted considerable pressure on Andre. In response, Andre became rebellious, but also obviously fulfilled his father’s desires.

The Psychology of Birth Order and Personality