Conventional wisdom has it that only children are smarter and less sociable. Parents, freed from the shackles of constantly settling sibling disputes, devote more time and money to the singleton, exposing them to a greater variety of higher-level activities (there’s a term for what happens when you spread that time and money over more kids: resource dilution). Conversely, since those only children never have to share a toy, a bedroom, or a parent’s attention, it is assumed they miss out on that critical life skill of forever-having-to-get-along.

But are their actual brains different?

Jiang Qiu, a professor of psychology at Southwest University in Chongqing, China and director of the Key Laboratory of Cognition and Personality in the ministry of education, led a team of Chinese researchers that sought to answer this question with more than 250 college-aged Chinese students. They used standard tests of intelligence, creativity, and personality type to measure their creativity, IQ, and agreeableness. They also studied their brains, to see if growing up as an only child affects the structure of them. It did.

On the behavioral tests, only children displayed no differences in terms of IQ, but higher levels of flexibility—one measure of creativity—and lower levels of agreeableness than kids with siblings.

The brain scans then confirmed these findings, showing significant differences between only children and non-only children in the brain regions associated with flexibility, imagination, and planning (supramarginal gyrus) and with agreeableness and emotional regulation (medial prefrontal cortex). The scans also revealed differences in the parahippocampal gyrus, which helps manage emotional and mood regulation.

The study concluded that the family size we choose, or end up with, affects not only the environment in which children grow up, but also the architecture of their brains. The research was published in Brain Imaging and Behavior.

The idea that only children are somehow deficient was started 125 years ago by Granville Stanley Hall, a leader in the child-study movement, writes Lauren Sandler, author of One and Only: The Freedom of Having an Only Child, and the Joys of Being One. Having worked on the 1896 study “Of Peculiar and Exceptional Children,” Hall cast only children as “oddballs” as “permanent misfits,” descriptions that have stuck over the years with remarkable persistence. “Being an only child is a disease in itself,” he claimed.

There is ample evidence suggesting the stereotypes of the “lonely only” are wrong. Toni Falbo, a professor of educational psychology at the University of Texas at Austin and research methodologist Denise Polit undertook a meta-study looking at only children and intelligence and personality. They found that only children, along with firstborns and people who have only one sibling, score higher IQ marks and achieve more, but aren’t markedly different personality-wise (context matters: an only child in an unhappy household may be disagreeable; so might a child with five siblings in a poor family).

Jiang and his co-authors hypothesized a few reasons for their findings. Creativity —defined as having original ideas that have value—is strongly influenced by everything from family structure and parental views, to interactions and expectations (one older study showed that children were more likely to excel if they had a mother whose abilities matched her expectations). Parents of only children may interact more with their children, and seek out more opportunities to extend their children’s creativity. A parent might also have higher expectations of an only child, or they might give the child more independence, and some studies have shown that independence fosters creativity.

Mark Runco, editor of the Creativity Research Journal and a distinguished research fellow of the American Institute for Behavioral Research & Technology, applauded the study but with a few caveats. He noted that the authors focused on flexibility, which is just one of three measures of creativity assessed by the verbally administered Torrance test; the other two are originality (the number of unique or original new ideas a person has) and fluency (how easily a person can move between them).

“Flexibility is important but it’s not as important for creativity as originality,” he said. There were no significant differences in originality scores.

He also noted that just like IQ tests, creativity tests are not perfect measures of the thing they are measuring. “You are looking at performance on a test and it’s not perfectly indicative of what a person can or will do,” in real life, he said. Creativity involves spontaneity and intrinsic motivation—things which are a bit hard to assess on a test.