AFP

PARIS

Is a violent criminal born that way, or shaped by childhood experiences and circumstances?

Delving into one of oldest questions in psychology, some scientists have suggested genes may contribute to roughly half of the influence — by affecting complex brain chemistry, for instance.

But, until now, DNA clues to support this have been sketchy.

Scientists in Europe and the United States on Tuesday fingered two genes which in a mutated form are found in a “substantially higher frequency” in violent offenders.

A study of nearly 800 Finns jailed for both violent and non-violent crimes, and compared to the general population, found variants of two genes, called MAOA and CDH13, to be “associated with extremely violent behaviour”.

“No substantial signal was observed for either MAOA or CDH13 among non-violent offenders, indicating that findings were specific for violent offending,” said the study, published in the journal Molecular Psychiatry. The scientists took into account environmental factors — whether or not people had a history of substance abuse, antisocial personality disorders or childhood maltreatment.

But this did not alter the outcome.

The study was not designed to explain the impact of genetic variants and the authors believe there could be many other genes which play a role, directly or indirectly, in the molecular cascade.

And, they note, the two mutated gene versions or genotypes are “rather common.” As many as one in five people have them, of whom the vast majority never commit rape, assault or murder.