Bioethics is concerned with the moral aspects of biology and medicine. The bioethical relevance of aggression and violence is clear, as very different moral and legal responsibilities may apply depending on whether aggression and violence are forms of behaviour that are innate or acquired, deliberate or automatic or not, or understandable and justifiable based on causes. Biological research and natural science theories are a basic ingredient for reflections, arguments and decisions on such matters. This study presents the problem of the causes of aggressive behaviour, the evolutionary understanding and definition of aggressive behaviour, the biological basis for this behaviour and the link between emotions and aggression. A growing body of evidence suggests that innate factors of behaviour (be they genetic or neurobiological) do not by themselves define behaviour and nor do acquired factors such as learning, cultural norms or worldviews. Both types of factor interact from the outset to shape a development process that mutually interacts to define beliefs or behaviour.