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Family Dynamics

Does Birth Order Affect Personality?

Which child will be more agreeable: Your oldest, middle, youngest or only child?

Tetiana Iatsenko/Shutterstock
Source: Tetiana Iatsenko/Shutterstock

Not too long ago I explained why people still “feel sorry” for only children. Negative thoughts and myths about them have swirled for centuries. And in spite of a steady spike in the only-child population in the U.S. and most developed countries, children without siblings are still singled out for intense scrutiny.

Here we go again: A new study published in the journal Brain Imaging and Behavior—“Only-child and Non-only-child Exhibit Differences in Creativity and Agreeableness: Evidence from Behavioral and Anatomical Structural Studies"—claims that only children are more creative, yet less agreeable.

To investigate and reach their conclusion, Junyi Yang and a team of researchers in China studied the brain’s structural development in only children and in children with siblings. Their results revealed that “only-children exhibited higher flexibility scores (a dimension of creativity) and lower agreeableness scores (a dimension of personality traits) than non-only-children.”

The study included 303 participants—126 only children and 177 children with siblings. When discussing their findings, the researchers qualify their results: The study was small, conducted in China, a country with a very different culture than in the US, and looked at brain structure (the structural differences in grey matter) rather than behavior. The researchers point out that their sample centered largely on “highly educated young adults” and that further studies exploring specific differences between adolescents or younger children could reach different conclusions.

“Only Child” Is a Birth Order

We can draw some conclusions about only children and agreeableness from large studies of siblings. In 2015 Julia Rohrer and her colleagues examined the effects of birth order on personality. Although only children were excluded from the study, its large scope and methodology bring into question the issue of “agreeableness” raised in the China study.

Siblings from three countries—the U.S. (5,240), Germany (10,457) and England (4,489)—were measured to find birth-order effects on personality. The researchers concluded, as have others, “that birth order does not have a lasting effect on broad personality traits outside of the intellectual domain.” They “consistently found no birth-order effects on extraversion, emotional stability, agreeableness, conscientiousness, or imagination.”

Rodica Ioana Damian and Brent W. Roberts, psychologists at the Universities of Houston and Illinois respectively, explained why Rohrer’s investigation is so valid for assessing personality traits. In their commentary on the subject at the Proceedings of the National Academy of Sciences—"Settling the Debate on Birth Order and Personality"—they write:

“We commend Rohrer et al. for conducting the most thorough and methodologically sophisticated examination of the relation between birth order and personality to date. [It] clearly laid to rest as a viable explanation for the fascinating differences we see across people and siblings in the typical ways in which they feel, think, and behave.”

Being an only child is a birth order and thus it seems that Damian and Roberts’s conclusion and their own investigation of 377,000 students—“The Associations of Birth Order with Personality and Intelligence in a Representative Sample of U.S. High School Students”—apply to only children as well: “Scientific evidence strongly suggests that birth order has little or no substantive relation to personality trait development.”

The Problems with Pigeonholing

Given that Yang’s Chinese team tested a sample size of only 303 students, to accept that only children are not as agreeable as children with siblings is a reach. Many parents of only children don’t agree. They are quick to tell me, “Maybe some children are just more agreeable than others, regardless of their family constellations. Our personalities are impacted by so much more than that.” Indeed, myriad factors influence any given individual’s personality, over the course of a lifetime.

We need to make sure “not agreeable” doesn’t get tagged on to a long list of stereotypes about only children. More than 10 years after his book Born to Rebel: Birth Order Family Dynamics, and Creative Lives, Frank Sulloway, a strong proponent of birth order effects, softened his position and told a USA Today reporter, "People love to pigeonhole individuals by birth order. These are modest differences. It's important to understand that there are a lot of exceptions to these generalizations."



Damian, R.I. and Roberts, B.W. “Settling the debate on birth order and personality.” Proceedings of the National Academy of Sciences. October, 2015. doi:10.1073/pnas.151906411

Damian, R.I. and Roberts, B.W. “The Associations of Birth Order with Personality and Intelligence in a Representative Sample of U.S. High School Students.” Journal of Research in Personality: Volume 58, October 2015, Pages 96–105.

Rohrer, Julia, Boris Egloff and Stefan C Schmukle, “Examining the effects of birth order on personality.” Proceedings of the National Academy of Sciences: October 2015. DOI: 10.1073/pnas.1506451112

Sulloway Frank J. Born to Rebel: Birth Order, Family Dynamics, and Creative Lives. New York: Pantheon, 1996.

Yang, Junyi, Xin Hou, Dongtao Wei, Kangcheng Wang, Yadan Li and Jiang Qiu. “Only-child and non-only-child exhibit differences in creativity and agreeableness: evidence from behavioral and anatomical structural studies.” Brain Imaging and Behavior. March, 2016. DOI: 10.1007/s11682-016-9530-9

Copyright @2017, 2018 by Susan Newman