More than Just Stereotypes, "Only" Children Have Different Brain Structures

If you’re an only child, you know all of the stereotypes: you’re spoiled and stubborn, have to get your way, and don’t like to share. But you’re also independent, self-reliant, and good at keeping yourself busy and entertained. Anecdotally, these are all true to varying degrees, while it’s also true that someone who grew up with siblings is perfectly capable of being spoiled and selfish, and those of us who didn’t have to share with siblings when we were kids can still develop the skill later in life.

But new research shows the differences between people who grew with and without siblings goes deeper than we previously knew, and that the stereotypes might have some real truth to them. A new study, published in Brain Imaging and Behavior in April, looked at brain scans of people who had grown up with and without siblings, and discovered real, physical differences. The study was conducted in China, where the country’s “one-child policy” has led to a higher than usual rate of only children, so there’s particular interest in studying the potential psychological impacts of growing up sibling-less.

Researcher Junyi Yang and his colleagues scanned the brains of hundreds of students, about half of whom were only children, using voxel-based morphometry (VBM) to measure structural differences of gray matter volume (GMV) between only children and people with siblings. The researchers also used verbal tests and questionaires to quantify subjects’ overall intelligence and creativity.

The behavioral tests showed that only children exhibited more creativity and less agreeableness (just like the stereotypes say). Even more interestingly, the brain scans showed differences in gray matter volume in the areas of the brain that correlate with creativity and agreeableness – that means it’s not just habit or behavior patterns that are shaped by our early lives and whether or not we have siblings, but the actual physical structure of our brains.

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The only children in the study, on average, scored lower on the agreeable section of the personality questionnaire—meaning they showed less warmth and concern for others than their counterparts. The brain scans showed a corollary proportion of grey matter in the medial prefrontal cortex of the brain. The part of the brain that controls concern for others is literally less developed in only children—and it makes sense, if you spend less time during your developing years having to measure your own desires against the competing desires of a sibling, the part of your brain that allows you to do so will be weaker.

On the other hand, the only children in the study showed a more developed supramarginal gyrus area of the brain, which correlates to mental flexibility and imagination. These findings also correlated with the creativity test—where participants were asked to come up with unusual uses for a cardboard box and describe consequences for imaginary scenarios. The only children in the study, who scored higher on the creativity test, had more grey matter, on average, in this area of their brains than the subjects with siblings even after factoring in other differences like family income and parents’ education.

So, only children of the world, the next time some tries to give you a hard time about how you never learned to share as a kid, just let them know that all that time you spent playing alone made you more mentally flexible and creative—and that you have the increased grey matter in your supramarginal gyrus to prove it. (But also, maybe, try to learn how to share.)

Top photo by Pixabay, CC0

Lilly Dancyger is Deputy Editor of Narratively, and a freelance journalist based in New York City.

More than Just Stereotypes, “Only” Children Have Different Brain Structures