Posts Tagged ‘violence genes’

“Free will” is further circumscribed as two genes associated with violence are identified

October 29, 2014

The range of application of human “free will” is increasingly being circumscribed as we identify genes which are associated with specific behavioural characteristics. This is not to say that any gene or set of genes makes certain specific behaviour inevitable – but it does say that that particular behaviour is more probable for that individual. Perhaps it is more accurate to say that an individual’s gene set defines (and therefore constrains) the envelope of possible behaviour. But that itself means that he can only exercise “free will” within the envelope of possible behaviour that is available to him.

A new study from Finland has identified two genes associated with violent crime. The study of 900 Finnish criminals is published in Molecular Psychiatry.


Variants in two genes were significantly more common in Finnish criminals convicted of multiple violent crimes compared with the general population, researchers said.

Statistical analysis indicated that 5% to 10% of all severe violent crime in Finland could be attributed to these variants, affecting the genes for monoamine oxidase A (MAOA) and CDH13, a neuronal membrane adhesion molecule, according to Jari Tiihonen, MD, PhD, of the Karolinska Institute in Stockholm, and colleagues.

Offenders who had committed 10 or more serious violent crimes were significantly more like to carry one of several loss-of-function variants in the MAOA gene (odds ratio 2.66, 95% CI 1.60-4.42) or the so-called rs11649622 variant in the CDH13 gene (OR 2.72, 95% CI 1.77-4.15), versus participants in population-based survey studies in Finland who were considered representative of the general population.

Criminal offenders with no violent crime convictions showed no increases in risk of carrying the flagged MAOA/CDH13, with an OR of 1.12-1.13 relative to the population-based sample, which did not approach statistical significance.

In their report published online in Molecular Psychiatry, they acknowledged that crime “is a complex phenomenon, and the outcome is shaped by both genetic and environmental factors.”

But that doesn’t mean that genetic contributors cannot be identified, they argued. “It is plausible that while research of the genetic background of criminal or violent behavior is hampered by many confounding factors, focusing on extreme phenotypes might yield more robust results,” Tiihonen and colleagues wrote.

J Tiihonen et al, Genetic background of extreme violent behavior, Molecular Psychiatry , (28 October 2014), doi:10.1038/mp.2014.130

This may not have much practical application yet, and there are certainly many more genes which also predispose to violence and a genetic screening for “violent” tendencies is not coming any time soon. Violent tendencies are also certainly not only due to genes and nurture surely has a very significant part to play.

AbstractIn developed countries, the majority of all violent crime is committed by a small group of antisocial recidivistic offenders, but no genes have been shown to contribute to recidivistic violent offending or severe violent behavior, such as homicide. Our results, from two independent cohorts of Finnish prisoners, revealed that a monoamine oxidase A (MAOA) low-activity genotype (contributing to low dopamine turnover rate) as well as the CDH13 gene (coding for neuronal membrane adhesion protein) are associated with extremely violent behavior (at least 10 committed homicides, attempted homicides or batteries). No substantial signal was observed for either MAOA or CDH13 among non-violent offenders, indicating that findings were specific for violent offending, and not largely attributable to substance abuse or antisocial personality disorder. These results indicate both low monoamine metabolism and neuronal membrane dysfunction as plausible factors in the etiology of extreme criminal violent behavior, and imply that at least about 5–10% of all severe violent crime in Finland is attributable to the aforementioned MAOA and CDH13 genotypes.

I conceive an individual’s genes as defining the range of behaviour available to a human and his “nurture” as then determining his actual behaviour by the exercise of what we call “free will”. What is becoming increasingly obvious though, is that any individual’s “free will” is severely circumscribed. The application of “free will” is restricted to be within the envelope of behaviour that the genes allow.

Behaviour envelopes

I envision an individual whose limits are set by his genes. He cannot think faster or run faster or behave differently to what his genes allow. Thus no amount of “free will” (or nurture) could get an individual to behave outside the envelope of his possible behaviour as set by his individual set of genes.


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