By Christian Jarrett

There are some common-sense reasons for thinking that being raised without siblings will have meaningful psychological consequences – after all, “only children” are likely to get more attention from their parents than kids with sibs, but at the same time they miss out on the social experience that comes from sharing, playing and competing with brothers or sisters.

The latest study to look into this, published recently in Brain Imaging and Behavior, comes from China where the government’s one-child family planning programme has led to a huge increase in the numbers of only children. Junyi Yang and his colleagues scanned the brains of hundreds university students, about half of whom were only children and also tested their personality, creativity and intelligence. The only children outperformed the participants with siblings on creativity, but they scored lower on trait agreeableness – psychological differences that appeared to coincide with relevant structural differences in their brains.

The test of creativity – the verbal part of the Torrance Test – was fairly comprehensive and involved the participants doing things like coming up with unusual uses for cardboard boxes, improving a toy elephant and thinking about the consequences of an imaginary scenario. Personality was assessed using a fairly standard self-report questionnaire. And the brain imaging scan was used to look for group differences in grey matter volume in specific brain areas that the researchers thought might be relevant based on past research.

The only children’s superior performance on the creativity tasks tied in with their having more grey matter, on average, in the supramarginal gyrus of their brains than the participants with siblings (even after factoring out group differences in family income and parents’ education). This is a region in the parietal lobe that Yang and his team said has previously linked with mental flexibility and imagination; also in this study, across all participants, grey matter volume in this brain region correlated with creativity scores. The researchers speculated only children’s apparent superior creativity may be related to the greater contact they’d had with their parents, and perhaps their parents’ having heightened expectations for them.

Meanwhile, the only children also scored lower on agreeableness – a trait that’s associated with warmth and concern for others. This seemed to tie in with their having less grey matter in the medial prefrontal cortex (and across the sample, more grey matter here correlated with trait agreeability) – a region at the front of the brain that’s known to be involved in thinking about the self in relation to others. The researchers speculated this could be explained by only children receiving excessive attention and praise from parents and other family members, and having a lack of social practice with siblings.

It’s always interesting when data comes in that speaks to some of our folk assumptions about human psychology – in this case, how the kind of upbringing we have shapes the kind of people we become. But it’s worth treating these new findings with some caution, especially given the recent, rigorous studies that have suggested birth order is not linked to personality.

Apart from the snapshot nature of the new findings, with measures only taken at one time point, and the lack of diversity in the current sample – highly educated young people in China – being an only child is also heavily confounded with other factors like parents’ social and educational background and genes inherited from parents (although the researchers made some effort to account for some of this). Also, it’s always risky trying to interpret the meaning of structural brain differences. Still, the new results give us something to work with and could help direct the course of future research on the topic.

—Only-child and non-only-child exhibit differences in creativity and agreeableness: evidence from behavioral and anatomical structural studies

Christian Jarrett (@Psych_Writer) is Editor of BPS Research Digest