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.
Anatomical differences between the brains of 85 people have been measured and linked with the four main categories of personality types as defined by psychiatrists using a clinically recognised system of character evaluation.
The researchers said the brain differences are structural and can be measured as variations in the size of specific regions of the brain that appear to be linked with each of the four personality types.
Brain scans that measure differences in volume down to an accuracy of less than one cubic millimetre found, for instance, that people defined as novelty-seeking personalities had a structurally bigger area of the brain above the eye sockets, known as the inferior part of the frontal lobe.
People with smaller volumes of tissue in this region displayed higher levels of timidity, approval-seeking behaviours and a greater tendency to seek gratification from external sources such as food or drugs, said Professor Annalena Venneri of the University of Hull.
People with "harm-avoidance" personalities had significantly smaller volumes of tissue in brain regions called the orbito-frontal area and the posterior occipital region, compared with other personality types.
"Reward-dependence" personalities stood out for having smaller volumes of tissue in the fronto-striatal and limbic areas of the brain.
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.
"This study shows that personality traits are something you are born with, but their full expression can be modulated during development with the right approach," said Professor Venneri, who carried out the study with colleagues from the University of Parma in Italy and Washington University in St Louis.
The four personality types were classified as "novelty seeking" - characterised by impulsive actions; "harm avoidance" - marked by pessimism and shyness; "reward dependence" - with an addictive personality; and "persistence" - who are people who tend to be industrious, hard-working and perfectionist.
"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 fact that traits are reflected in specific anatomical differences is useful to know, for instance when it comes to understanding a child's behaviour and choosing the right approach so that somebody who is, for example, particularly timid might be helped through education and development.
"There is no point shouting at a child who is very shy and telling them off, because it does not come naturally to them to put themselves forward. But actually knowing there is a biological basis for this helps educators or parents to use the right approach to help a child to compensate."
People who have a "reward dependence" personality could, for example, be helped at an early age because they are at risk of turning to drink, drugs or food if they do not get the family support and encouragement they need, Professor Venneri said.
"If you know it's not something you do but something you are, you can alter the environment to minimise the risk. Knowing that someone has such a predisposition could help them adopt preventive strategies and avoid situations where they might seek rewards which could be potentially harmful."
The study is to be published in the journal Brain Research Bulletin.