Abstract
In this thesis, I will focus on one important piece of genetic evidence, concerning the Monoamine Oxidas Acid A (MAOA) gene, unscientifically known as the ‘warrior’ gene. In 2002, a famous study by Caspi and his colleagues suggested that individuals who have one variation of MAOA, and were severely maltreated during childhood, have a greater predisposition to antisocial behaviour compared to other groups in the study. It was the first study to measure the effect of the combination of genetic and environmental factors (GxE) on the further development of antisocial behaviour. I will refer to this discovery as GxE evidence.
A fundamental dispute, influenced by scientific advances such as the discovery of GxE, is the age-old philosophical schism between free will and determinism. It has been suggested that science will be able to indicate that agents’ actions are determined by their genes and the notion of free will is an illusion. That claim has alarming implications for the criminal law. The fundamental premise of criminal law is that people are responsible for the outcome of their conduct. That responsibility depends on the extent to which agents knowingly and voluntarily choose the outcome of their conduct. If science can indicate that human’s conduct, far from being knowingly and voluntarily chosen, is predetermined genetically, then considering any role for criminal responsibility must be controversial. A part of this thesis will consider the legal response to the free will/determinism debate.
Setting aside the imperious challenges of science, and the free will/determinism debate, I will look at other scientific challenges which are relevant to the present categories of criminal responsibility and which can improve, but not dictate, the criminal law. Specifically, I will focus on the issue of loss of self-control. That issue has been chosen because scientific researchers have indicated that individuals’ ability to exercise their self-control is affected to some degree by GxE. There are other advances in science which trigger the issue of loss of self-control but I am looking at only GxE evidence. Loss of self-control can be considered as the basis for two defences.
Firstly, loss of self-control can take the form of a claim of complete inability to control impulses. In some jurisdictions the total inability to control impulses is recognised as a full defence, called volitional insanity (V-insanity). In those jurisdictions, if an individual is unable to completely control his/her impulses, he/she is not considered criminally responsible. In stark contrast, neither New Zealand nor English law – the focus of this thesis – recognises V-insanity; they recognise cognitive insanity (C-insanity) only. C-insanity is only a defence where a person is unable to appreciate the nature – factual or moral – of his/her conduct. As a result of the non-recognition of V-insanity, if an individual is not able to control his/her impulses, and if he/she cannot establish any other defences, the person will be treated as fully criminally responsible. For the first time in New Zealand law, I will develop an argument in favour of the introduction of V-insanity as a defence.
The second form of the claim of loss of self-control, which is relevant to GxE evidence, is the claim of significant impairment in controlling impulses. This is the basis for the defence of diminished responsibility (DR) as it is recognised under some common law jurisdictions such as English law. The difference between DR and V-insanity is that for V-insanity it is impossible for a person to control his/her impulses but in the case of DR it is not totally impossible for a person to control them. Instead, in the case of DR, it is seriously difficult for a person to control his/her impulses. Under English law DR, which is available only for murder charges, is a partial defence. It reduces, but does not totally exempt, a person’s criminal responsibility. However, DR is not accepted under New Zealand law and a person who has significant difficulties in controlling his/her impulses, is considered fully criminally responsible. In this thesis, building on the academic literature, I will argue that New Zealand should adopt the DR defence.
Having argued that New Zealand should adopt the defence of V-insanity and DR, I will analyse GxE evidence as the basis for those defences. To date, there has been no such discussion in the scholarly discourse. It is not my aim to definitely determine whether GxE evidence as the basis for the two defences should be accepted or not. Rather, my goal is to highlight legal requirements for establishing those defences where GxE is concerned. The legal prerequisites I propose are not just applicable to the assessment of GxE as a basis for the aforementioned defences, but also to any form of genetic defence.