Researchers, at the Pennsylvania State University, the University of Hawaii at Manoa and Purdue University, interviewed children and their parents to assess their personalities.

They also took saliva samples to measure testosterone levels and asked the children to keep a diary of their activities outside school.

The study – published in the journal Child Development – found personality traits developed differently in first and second-born children.

‘Second-born children showed increases in traits like adventurousness and independence across adolescence, whereas in first-borns, these traits did not change much over time,’ a spokesman for the researchers said.