The study also found an increased likelihood for the twins to exhibit similar specific external behaviors, such as alcoholism or drug addiction. That is, where both twins exhibited antisocial behaviors, they also tended to exhibit the same antisocial behaviors. Unable to establish a genetic link, however, the study concluded, "environmental factors such as peer pressure may influence the way in which a genetic vulnerability to externalizing behaviors is expressed" (Hick, Krueger, Iacono, McGue & Patrick 1). Thus, the study concluded that while there may be a genetically transmitted vulnerability to externalizing antisocial behaviors, the manner in which this vulnerability is expressed - the particular antisocial behaviors expressed - must be the result of environmental factors. Thus, according to this study, while Kyle and Stan might share a genetic tendency to act antisocially, whether and how they act so is likely based on environmental factors.

Nonetheless, critics argue that there is, in fact, no way to identify specifically a genetic trait that controls external behaviors such as thes

For the most part, the criminal justice system determines punishment for an offense based on a non-deterministic "free will" model (Littman 1). In other words, the criminal justice system presumes that people know right from wrong and possess the free will to choose between the two (Littman 1). The system, therefore, views the commission of a crime as based on a rational choice for which the criminal must be punished. This view, of course, is based on the classical free will theories of social contract and rational choice, both of which view the commission of a crime as a violation of the social contract necessary for an orderly and civilized society. Generally, punishment under a system based on theories of free will is based on the belief that swift, severe and certain punishment is the best method of controlling deviant human behavior (Littman 1). The goals of such punishment are to ensure that the criminal is accountable to society for his violation of the contract and to deter future crime (Littman 1).

Still, evidence from the Minnesota twin study and others forces one to consider a genetic basis for antisocial behavior. This information is of particular interests to determinists, or theorists who believe that a person's actions are essentially pre-determined by genetic, environmental and other factors outside their control. Proponents of determinism argue that human beings do not act based on free will, but rather that their actions are determined by often uncontrollable factors that make people who they are.