Biological theories of crime assume a person’s biological characteristics influence criminal behaviour. These theories include physiognomy, physiology, genetics, and, more recently, neurology. They are all subtypes of positivism, a philosophical system recognising only that which can be scientifically verified. Positivism initially evolved as a response to the perceived harshness of classical theories, claiming that human behaviour was the result of free will and rational thought. In other words, a person could choose any course of action that suited them. In this context, it was believed that individuals would largely focus on pleasurable behaviours, avoiding those that were not—especially if that behaviour resulted in punishment or pain. It was from this premise that the belief that punishment would deter someone from committing a criminal act emerged. In contrast, positivism adopted a more scientific approach to test the theories and advocated rehabilitative treatment instead of punishment.