Personality types are linked with structural differences in the brain - which could explain why one child grows up to be impulsive and outgoing while another becomes diligent and introspective.
If the findings are confirmed by other scientists, they suggest that children are not only born with a given personality type, but they develop anatomically different brains as a result of being that sort of person. It raises the prospect of being able to test a young child's future personality by viewing the anatomy of their brain with a hospital scanner.
"If you are looking at volume, you are quantifying the tissue that is there. What we found was not just speculative. There is quite a bit of difference between people with different personality traits," said Professor Venneri.
The study is to be published in the journal Brain Research Bulletin.
Of course, within the constraints of their hard-coded personalities, people clearly exercise free will.