Theories of causation Few modern criminologists would claim that any single theory constitutes a universal explanation of criminality or a valid predictor of future criminal behaviour in a particular population. A more common view is that many of the different theories offered may help to explain particular aspects of criminality and that different types of explanation may all contribute to the understanding of the problem of crime. Biological theories Some theories attribute the tendency toward criminality to innate biological factors. The most famous of these is probably that of the Italian Cesare Lombroso (1835-1909), one of the first scientific criminologists, whose theories were related to Darwinian theories of evolution. His investigations of the skulls and facial features of robbers led him to the hypothesis that serious or persistent criminality was associated with atavism, or the reversion to a primitive stage of human development. Another biological theory related criminality to body types, suggesting that it was more common among muscular, athletic persons (mesomorphs) than among tall, thin persons (ectomorphs) or soft, rounded individuals (endomorphs). These theories have little support today, but there is some interest in the idea that criminality may be related to chromosomal abnormalities--in particular, the idea that so-called XYY males (characterized by the presence of a surplus Y chromosome) may be more likely to be involved in criminal behaviour than the general population. Some criminologists have endeavoured to answer the question of whether biological factors are more important than social factors in criminal behaviour by studying the behaviour of twins. Various studies have shown that twins are more likely to exhibit similar tendencies toward criminality if they are identical (monozygotic) than if they are fraternal (dizygotic). The suggestion of genetic influences in criminal behaviour is supported by studies of adopted children carried out to determine the influence of the biological parent on criminality. One such study showed that the rate of criminality was higher among those adopted children who had one biological parent who was criminal than among those who had one adoptive parent who was criminal but whose biological parents were not. The highest rates of criminality were found among those children who had both biological parents and adoptive parents who were criminal.
Sociologists have proposed a variety of theories that explain criminal behaviour as a normal adaptation to the offender's social environment. One such theory, known as differential association, proposed that all criminal behaviour is learned behaviour and that the process of learning criminal behaviour depends on the extent of the individual's contact with other persons whose behaviour reflects varying standards of legality and morality. The more the individual is exposed to contact with persons whose own behaviour is unlawful, the more likely he is to learn and adopt their values as the basis for his own behaviour. The theory of anomie, proposed by the American Robert K. Merton, suggested that criminality is a result of the offender's inability to attain by socially acceptable means the goals that society expects of him; faced with this inability, the individual is likely to turn to other, not necessarily socially acceptable, objectives or to pursue the original objectives by unacceptable means. A development from this theory is the concept of the subculture--an alternative set of moral values and conventional expectations to which the person can turn if he cannot find acceptable routes to the objectives held out for him by the broader society. This theory, developed particularly with reference to delinquent gangs in U.S. cities, has been disputed by other sociologists who deny the existence of any subculture of delinquency among the lower classes of society; the behaviour of gangs is for these latter sociologists an expression of widespread lower-class values emphasizing toughness and excitement.
A further group of sociological theories denies the existence of subcultural value systems and portrays the delinquent as an individual who subscribes generally to the morals of society but who is able to justify to himself particular forms of delinquent behaviour by a process of "neutralization," in which the behaviour is redefined in moral terms to make it acceptable. Control theory emphasizes the links between the offender and his social group--the individual's bond to society. According to this theory, the ability of the individual to resist the inclination to commit crime--which may be an easy way to satisfy a particular desire--depends on the strength of his attachment to parents, his involvement with conventional activities and avenues of progress, and his commitment to orthodox moral values that prohibit the conduct in question. Labeling theory, by contrast, portrays criminality as a product of the reaction of society to the individual, rather than of his own inclinations and personality. It assumes that the criminal is not substantially different from any other individual, except that he has become involved in the processes of the criminal justice system and has acquired a "criminal" identity. Through a process of rejection by law-abiding persons and acceptance by other delinquents, which is a consequence of the criminal identity conferred on him by the courts, the offender becomes more and more socialized into criminal behaviour patterns and estranged from law-abiding behaviour. Eventually he comes to see himself cast by society into the role of a criminal, and he acts out society's expectations. Each time he passes through the court system, the process is extended to form a process described as "amplification of deviance." Radical criminologists change the focus of inquiry, looking for the causes of delinquency not in the individual but in the structure of society, in particular its political and legal systems. The criminal law is seen as an instrument by which the powerful and affluent maintain their position and coerce the poor into patterns of behaviour that preserve the status quo.
Psychologists have approached the task of explaining delinquent behaviour by examining in particular the processes by which behaviour and restraints on behaviour are learned. Psychoanalytical theories emphasize the instinctual drives for gratification and the control exercised through the more rational aspect of personality, the superego. Criminality is seen to result from the failure of the superego, as a consequence either of its incomplete development or of unusually strong instinctual drives. The empirical basis for such a theory is necessarily thin. Behaviour theory views all behaviour--criminal and otherwise--as learned and thus manipulable by the use of reinforcement and punishment. Social learning theory examines the manner in which behaviour is learned from contacts within the family and other intimate groups, from social contacts outside the family, particularly from peer groups, and from exposure to models of behaviour in the media, particularly television.
Mental illness is the cause of a relatively small proportion of crimes, but its importance as a causative factor may be exaggerated by the seriousness of some of the crimes committed by persons with mental disorders. Severe depression or psychopathy (sometimes described as sociopathy or personality disorder) may lead to grave offenses of violence. On a less serious level, depression may lead to theft or other uncharacteristic behaviour.
A non-Western perspective: China The Chinese have in general adopted a Marxist interpretation of the causes of crime. Crime is viewed as a product of class society, of exploitative systems founded upon the institution of private property. Because the socialist system is considered by its proponents as incapable of producing crime, official theory has always looked outside of post-1949 Chinese society to find the causes of contemporary crime. A number of specific sources of criminal activity have been suggested: (1) external enemies and remnants of the overthrown reactionary classes (the latter referring to the government of the Republic of China in Taiwan) who infiltrate the country with spies and conduct sabotage; (2) remains of the old (pre-1949) society, such as gangsters and hooligans, who refuse to reform; (3) lingering aspects of bourgeois ideology that prize profit, cunning, selfishness, and decadence and thus encourage crime; and (4) the poverty and cultural backwardness that is seen as the legacy of the old society. The Cultural Revolution (1966-76) has also been cited as a cause of crime; it is said to have confused notions of right and wrong and to have destroyed respect for authority. While Chinese criminology thus adopts a social explanation of crime in capitalist society, it has little sympathy for the view that society is to blame for crime in contemporary China. The two main causes are seen to be backward thinking and ignorance. For this reason, crime is ideally to be fought, and ultimately eliminated, by thought reform and by education.
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In most countries the detection of crime is the responsibility of the police, although special law enforcement agencies may be responsible for the discovery of particular types of crime (customs departments, for instance, may be responsible for the detection of smuggling and related offenses). Crime detection falls into three distinguishable phases: the discovery that a crime has been committed, the identification of a suspect, and the collection of sufficient evidence to indict the suspect before the court. Criminologists have shown that a high proportion of crimes are discovered and reported by persons other than the police (such as victims or witnesses), but certain types--in particular crimes that may involve a subject's assent, such as dealing in drugs or prostitution, or those in which there may be no identifiable victim, such as obscenity--are often not discovered unless the police take active steps to determine whether these crimes are being committed. This may require controversial methods, such as surveillance, interception of communications, infiltration of gangs, and entrapment (e.g., by making a purchase from a suspected drug dealer). Once the commission of a crime has been discovered, the identification of the suspect becomes essential.