A study in China claims that growing up without siblings can lead to a different brain structure than those who do. They found that only children tended to be more creative and less sociable.

Previous studies have focused on the difference in behaviors, cognitive function, and personality traits between only children and those with siblings. After all, it’s common sense that those without siblings don’t have to share their parents’ attention, and so likely get more encouragement, but miss out on the early experience of sharing, or competing.

This new study, by the Southwest University in Chongqing, and published in Brain Imaging and Behavior, wanted to find out if the difference in behaviors had a neural basis. It also examined if different family environments actually affected children’s brain structural development.

China operated a one-child policy from 1979 to 2015 in an attempt at population control, resulting in a large increase in only children.

The researchers studied 250 university students, a somewhat small sample, around half of which were only children. They scanned their brains while also testing their personality, creativity, and intelligence using already established methods.

Corroborating previous findings, the tests showed that only children outperformed those with siblings on creativity, but consistently scored lower on agreeable personality traits. The scans demonstrated that the parts of the brain associated with the development of these were indeed structurally different in the two.

The only children who performed higher on creativity showed a higher volume of gray matter in the parietal lobe, a part of the brain associated with mental flexibility and imagination. The scans of those only children who showed less agreeable traits showed less gray matter in the medial prefrontal cortex, a part of the brain known to be involved in thinking about the self in relation to others.

The researchers claim this shows that different family environments do affect children’s structural brain development, and the kind of upbringing we have shapes the kind of people we become on a neurological basis. 

They point out that other studies have already shown that only children tend to exhibit more positive developmental outcomes, such as higher intelligence and creativity, often demonstrated in achievements at school.

However, the sole attention of parents, and grandparents to an extent, can result in what they call “undesirable” personality traits: dependency, selfishness, and social ineptitude. Only children miss out on early opportunities to develop and practice social skills, emotional support, and empathy.