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Killer Genes: Genetic Determinism and Criminal Liability

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About The Author

Rowan Clapp (Former Public Law & Human Rights Editor)

Rowan graduated from Durham University in 2013 with a First Class degree in Philosophy and Theology. He completed the GDL at BPP University on a Lord Haldane Scholarship and Hardwicke Entrance Award from Lincoln’s Inn. He is currently undertaking an LLM at University College London and working as a volunteer caseworker at Reprieve.

Image © Caroline Davis

Bradley Waldroup brutally murdered his wife in a premeditated flurry of butchery inside his trailer in Kimsey Mountain, Tennessee. He was not sufficiently intoxicated to avoid forming the mens rea for murder and was mentally fit to stand trial. His defence was utterly unique and he avoided the death penalty. Simply, his genes saved his life.

It is often thought that there are two prevailing, diametrically opposed bodies of opinion: either people who commit atrocious crimes are born to do so, or the tragic circumstances of their lives drive them to crime.

However, this recent BBC article on Dr. Cesare Lombroso suggests that both views may be correct. The middle road essentially boils down to this: ‘criminals are not born, but the odds at the moment of birth of becoming one are not even’. It seems that some people are born significantly more genetically predisposed to committing certain types of crime.

Biological Background

Monoamine Oxidase A is an enzyme that breaks down neurotransmitters such as dopamine, norepinephrine and serotonin in the brain. The enzyme is regulated by the monamine oxidase A gene (MAOA). Naturally, people have various forms of the gene and some produce less of the enzyme, this is the ‘low activity form’ (MAOA-L). Conversely, those with the high activity form (MAOA-H) produce more. As a consequence, MAOA-L individuals will have higher adrenaline, dopamine and serotonin levels. For those interested, a more detailed discussion of MAOA genes can be found in “The Extreme Warrior Gene: a reality check?”

The discovery of an extremely violent family in the Netherlands drew the scientific community’s attention to the correlation between the expression of the gene and antisocial behavioral traits such as extreme violence. The medical history of the male side of the family revealed that aggressive behaviour and some degree of mental deficit was traceable as far back as 1870. Of the living members of the family, two were convicted arsonists, one had run over an employer, one had raped his sister and another had assaulted someone with a pitchfork. All male members of the family were MAOA-L individuals. A relatively recent study by Rose McDermott of Brown University has built on this initial discovery and confirmed a ‘clear demonstration of the relationship between MAOA-L and behavioral aggression’. Crucially, the violent effects of the gene are expressed in individuals with a history of childhood abuse. 

The problem of forming a genetic defence

Up to 40% of the population may possess the MAOA-L gene. As 40% of us are not criminals with a proclivity for extreme violence, this causes problems for those who affirm the role of genetics in criminal behaviour. Yet I suggest all that need be proven for us to consider alternative punitive measures for those with MAOA-L is that they are genuinely significantly more likely to commit violent crimes, not that all MAOA-L individuals do so. To this extent, the legal argument is not dependent on a hard, scientific calculation as long as there is a substantiated general suggestion of increased risk. This level of support does seem to be stacking up. A Finnish study suggested that 5-10% of all violent crime can be linked to genetic factors, and offenders who had committed ten or more serious violent crimes were 2.66 times more likely to be MAOA-L individuals. 

Substantiating the impact of MAOA-L

This broad data is supported by the ‘hot sauce’ experiment conducted by McDermott. In a controlled game in which hot sauce could be administered to punish opponents who the participants believed had stolen money from them, MAOA-L individuals were ‘more likely to be aggressive and/or […] punish severely as a form of revenge out of ‘spite’. As a consequence, McDermott’s findings were that the gene ‘predicts behavioral aggression’ and ‘significantly predicts such behaviour in a high pressure situation’. As such, since 2004, MAOA has been labeled ‘The warrior gene’ by scientists, criminologists and even Dr. Phil.

The increased propensity for MAOA-L individuals to become violent when subject to abuse as children raises many interesting questions for jurists. Of particular importance is the question of moral culpability and punishment. Punishing someone who has a propensity to commit a crime with the same force as someone who freely chose to commit the same crime seems intuitively wrong. Should MAOA-L individuals be punished in the same way as ‘normal’ people? Forensic Psychiatrist William Bernet does not think so, on the basis that the ‘combination of the high risk gene and child abuse increases one’s chances of being convicted of a violent offence by more than 400%.’

Criticisms of Evolutionary Biology

It is immediately obvious that Bernet’s figure of 400% is speculative. Our understanding of genetics is nowhere near sufficient for a claim like this to have much force in a legal context. Similarly, skeptics argue that the warrior gene is not a wholly scientific concept, viewing it as a kind of ‘junk-science’. Instead, they say, the gene ‘might be called […] the gambling gene, the depression gene, the irritability gene’ because it is also linked with these behaviours.

This seems a fair criticism. It must also be noted that the accompanying history of child abuse muddies the waters. It is difficult to say which factor, the genetic makeup or the history of abuse contributes decisively to the behaviour of the defendant. Steven Erickson, a forensic and legal scholar agrees, noting:

the law is not interested in brain [or genetic] abnormalities. The law is interested in whether or not someone at the time that the criminal act occurred understood the difference between right and wrong

I suggest that this superficial conception of legal culpability should be mediated to accommodate MAOA-L individuals who have been subject to abuse as children. I see the merit in the skeptic’s position: there simply is not enough data to mount a meaningful separate ‘genetic defence’ to murder at present. However, this is not simply ‘junk science’; the cumulative effect of research on the warrior gene suggests that there is more than some force to the argument that if present, the MAOA-L gene significantly increases an individual’s propensity to violent crime given the right (or rather the wrong) environmental stimuli. Indeed, despite the lack of precision in ‘warrior gene’ research 'it’s pretty clear that something really does seem to be going on with that gene variant that is (or can be) in some way related to bad behaviour.’

I would argue that these are sufficient grounds to begin discussing ways in which genetic research could be factored into a defendant’s defence to murder. Support for the suggestion that a genetic predisposition to certain types of crime should be a mitigating circumstance in sentencing is offered by a relatively recent American murder case.

The example of Bradley Waldroup

So what of Bradley Waldroup and his defence? In 2009, during a 'bloody rampage' he shot his wife’s friend eight times and attacked his wife with a machete. His attack was gruesomely premeditated. He told his children to bid their mother goodbye whilst armed with both a gun and a machete. Waldroup had been drinking and retained the key from his wife’s van to prevent any chance of her escape. Prosecutor Cynthia Lecroy-Schemel offers a snapshot of the brutality that ensued, noting:

[t]here are murders and then there are … hacking to death, trails of blood […] I have not seen one like this. And I have done a lot.

Waldroup was charged with felony murder. The death penalty was available and seemed a near formality relative to the gravity of his crimes. Yet the jury convicted him of voluntary manslaughter and attempted second-degree murder. He escaped the death penalty and was given 32 years in prison. Why? Because jurors were persuaded by a combination of the ‘warrior gene’ in conjunction with a history of violent abuse. As one juror notes, ‘A diagnosis is a diagnosis, it’s there. A bad gene is a bad gene’. Prosecutors were mystified, and deemed the deployment of expert testimony by Bernet as a smoke and mirrors technique to confuse the jury.

The future of the genetic defence

It seems clear, on surveying the relevant material, that ‘until there is significant agreement […] we should not rely heavily on such evidences for sentencing such major criminal acts’. The scientific community is not close to agreeing on the impact of the ‘warrior gene’ or its role in criminal responsibility. But how might a defence operate in the UK legal system?

It seems fitting that genetic predispositions could feature as a specific defence to murder, namely as an addition to the defence of diminished responsibility under s2(3) Homicide Act 1957. This allows for a partial defence to murder where an abnormality of mental functioning arising from a recognised medical condition substantially impairs the defendant’s ability to understand the nature of his conduct, to form a rational judgement or to exercise self control.

The cumulative effect of MAOA-L and childhood abuse is not strictly a recognised abnormality of mental functioning (AMF); genetic predispositions to violence are not included in the DSM. However, the ‘warrior gene’ seems to have almost exactly the same effect. If, following R v Byrne (1960) 2 QB 396 an AMF is ‘a state of mind so different from that of ordinary human beings that the reasonable man would term it abnormal’ then it is difficult to disagree with the assertion that MAOA-L individuals are suffering from AMF. If it were to be classified as such, then those with the ‘warrior gene’ and a history of abuse could make use of this defence because it is obvious that the condition impacts on an individual’s ability to exercise self control and to form rational judgement (s2(1A)(b-c) Homicide Act 1957). Thus, the second part of the defence would be easily satisfied. Even a brief overview of diminished responsibility suggests that it would only be a minor matter of classification to extend the defence to MAOA-L individuals. I suggest that the ease with which the defence may be extended as such reflects that it is designed to cover exactly the kind of situation that the MAOA-L individual finds himself in.

Recognition and awareness of the impact that the ‘warrior gene’ has on an individual’s legal responsibility for his crimes could equally give rise to a stand alone defence. One obvious drawback of this is the calculation of the extent to which an individual’s genetic makeup contributed to his decision making at the time that the crime was committed. There is no need to deny that this is a difficult exercise that would require careful mitigation by defence counsel and likely long deliberation. However, what is becoming clear is that added consideration should be afforded to those who, through no fault of their own, are more likely to commit impulsive and violent crimes.

It might also be suggested that the defence of insanity might better accommodate ‘warrior gene’ individuals. However this is problematic. Once labeled insane at the time of committing the crime it will be difficult to substantiate any claim that the MAOA-L is not insane at any later stage. The factors which lead to the deficit in mental change are historical, environmental ones, which cannot be changed, and equally immutable genetic ones. Will this recognition in mind, I suggest that the diminished responsibility analysis explained above is preferable if only purely for the flexibility in classification that it provides.  

It is by no means suggested that evolutionary biology can provide an accurate map of one’s criminal inclinations. What I have established, however, is the growing support for the view that certain genetic malformations make some people inherently more likely to commit the crimes that we punish most harshly. With this in mind, I have suggested just one of a number of possible ways to accommodate this apparent imbalance.

In practice, a superior understanding of the connection between environmental stimuli and genetics could facilitate medical intervention before any criminal activity. This kind of approach begins to sound a bit like The Minority Report, yet it seems clear that understanding that MAOA-L individuals are not truly autonomous in the classic sense may be a step towards a more sympathetic and informed understanding of the punishment for and prevention of crime.

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Tagged: Criminal Law, Medical Law & Ethics

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