The notion of a 'crime gene' has attracted the attention of the general public and legal practitioners. In this book, McCay paints a picture of influences on criminal conduct that, instead of simply resulting from a 'crime gene', result from the interplay of biological and social factors. Such a view of moral agency has implications for sentencing, and courts are now or will soon be asked to consider the mitigating effect of this interplay. The work contends that from the perspective of a retributivist, there may be ethical merit to a behavioural genetics based plea in mitigation. Furthermore, there may be ways of making such a plea that are consistent with existing lines of authority. In short there may be ethical and legal merit to such a plea.However, common law sentencing regimes generally pay attention to both retributive considerations and issues of community protection. The book argues that behavioural genetics based pleas in mitigation may make it more difficult to reconcile the retributive and community protection orientated aims of sentencing. It may thus raise ethical and legal difficulties for the many jurisdictions that attempt to balance these aims. In an area of law which lacks a body of precedent, this book benefits from insights from judges obtained through interviews.