Scans have shown that paedophilia may be the result of faulty connections in the brain.
Paedophile brain: Red areas show where white matter content is down
Researchers used sophisticated MRI scans to compare the brains of paedophiles and non-sexual criminals.
Paedophiles had significantly less of a substance called "white matter", responsible for wiring the different parts of the brain together.
The study, by the Centre for Addiction and Mental Health in Toronto, appears in the Journal of Psychiatry Research.
The study follows work by Yale University which uncovered differences in the thought patterns of paedophiles.
They team found activity in parts of paedophiles' brains were lower than in other volunteers when shown adult, erotic material.
It had been widely thought that paedophilia was triggered by childhood trauma or abuse.
However, the condition has also been linked to low IQ, suggesting a possible link to brain development. Paedophiles are also three times more likely to be left-handed.
Lead researcher Dr James Cantor said the latest study found a signficant lack of white matter connecting six different areas of the brain all known to play a role in sexual arousal.
His theory is that the lack of adequate wiring between the different centres results in paedophiles not being able to differentiate between appropriate and inappropriate sexual objects.
However, Dr Cantor stressed the latest study did not suggest that paedophiles could not be held criminally responsible for their actions.
He said: "Not being able to choose your sexual interests doesn't mean you can't choose what you do."
Dr Narender Ramnani, an expert in cognitive neuroscience at Royal Holloway University of London, was surprised by the results.
He said: "Environmental factors cause changes in the structure of the brain, so it is not clear whether these differences occur because of environmental factors, or whether these are in fact innate developmental traits that make people susceptable to such traits."
A total of 127 men participated in the study; approximately equal numbers of paedophiles and non-sexual offenders.