London - Children without siblings are often said to be spoiled brats compared with their peers who have brothers and sisters.
Now MRI scans suggest there may be truth to those claims, because of changes to the structure of the brain that result from growing up alone.
Only children have brains which make them more creative – and more selfish – than those with siblings, according to a Chinese study.
While they have extra grey matter in the part of the brain thought to help people come up with new ideas and think outside of the box, researchers found there was less in the region thought to govern how cooperative an individual is.
Scientists from Southwest University examined 270 college students by scanning their brains and giving them personality tests. Half of those tested had no siblings.
They found there was a clear rise in creativity – as well as a corresponding fall in agreeableness – among those who grew up alone.
Writing in the journal Brain Imaging and Behaviour, the authors from Southwest University in Chongqing, China, said: "Only children might have more opportunities for independent activity, and independence is strongly related to creative thinking."
However, the study said children who grew up in a single-child household had a diminished ability to properly process social information compared to those with siblings, meaning they were less empathetic.
"Only children usually miss out on important opportunities to rehearse some of the more complicated aspects of relationships," the researchers said.
They also warned that "receiving excessive attention" from parents and grandparents also negatively impacted their social skills.