Over many years British neuroscientist Prof Adrian Raine and his team scanned the brains
of numerous murderers; nearly all showed similar brain changes. There
was reduced activity in the pre-frontal cortex, the area of the brain
which controls emotional impulses, and over activation of the amygdala,
the area which generates our emotions. So it seems that murderers have brains that make them more
prone to rage and anger, while at the same time making them less able to
control themselves.
Raine's studies suggest that part of the reason may be childhood
abuse, which can cause physical damage to the brain.
The pre-frontal cortex is especially vulnerable. But only a small proportion of those who have a terrible
childhood grow up to become murderers.
A breakthrough came in 1993 with a family in the Netherlands where
all the men had a history of violence. Fifteen years of painstaking
research revealed that they all lacked the same gene - one which produces an enzyme called MAOA, which regulates the
levels of neurotransmitters involved in impulse control. It turns out
that if you lack the MAOA gene or have the low-activity variant you are
predisposed to violence. This variant became known as the warrior gene.
About 30% of men have this so-called warrior gene, but
whether the gene is triggered or not depends crucially on what happens
to you in childhood. Jim Fallon, professor of psychiatry at the University of
California, has a particularly personal interest in this research. After
discovering a surprisingly large number of murderers in his family tree
he had himself genetically tested and discovered he had an awful lot of
genes that have been linked to violent psychopathic behaviour. But Jim isn't a murderer - he's a respected professor.
His explanation is that he was protected from a potentially violent
legacy by a happy childhood. "If you've the high-risk form of the gene
and you were abused early on in life, your chances of a life of crime
are much higher. If you have the high-risk gene but you weren't abused,
then there really wasn't much risk. So just a gene by itself, the
variant doesn't really dramatically affect behaviour, but under certain
environmental conditions there is a big difference".
So it seems that a genetic tendency towards violence, together with
an abusive childhood, are literally a killer combination - murderers are
both born and made. Research is focusing on ways to reduce violent behaviour and
there is good evidence that teaching families who are at risk positive
parenting skills is effective at improving impulse control. The hope is that now we know so much more about the causes of
murderous behaviour we can spot the early warning signs and intervene
before it's too late.
BBC Horizon programmes Are you good or evil? and The mystery of murder, 9 March 2015 and article by Dr Michael Mosley on BBC website http://www.bbc.co.uk/news/magazine-31714853
