Psychologists throughout the years have come up with many different theories about crime, and why criminals commit illegal acts. Many different aspects are looked at, covering a lot of the different approaches to psychology, and looking at different explanations. The main theories include Physiological theories, psychoanalytical theories, learning theories and social theories.

Within the physiological theories, psychologists have taken into account genetic factors.Lombroso was the first to suggest this idea back in the 19th century, claiming that criminals had different genetic make-ups and that they had certain qualities including body types and facial characteristic. Upon his research of convicted criminals, he concluded that approximately one-third of criminality was inherited. Problems arose from Lombroso's research, as there was no control group, only convicted criminals.

Despite this, from here Schafer (1976) decided he could build upon Lombroso's research, claiming it was just the beginning of criminology.Family studies were carried out, which indicated that criminality ran in the family. Osborn and West (1979) looked at the sons of criminals and found that 40% of them were also criminals compared to the 13% whose parents were no criminals. People have questioned this however, saying that the problem lies with the fact that sons spend a lot of time and share their environment with their fathers, linking more closely to the social learning theory (covered later).

This comes back to the nature/nurture debate, and it cannot be claimed from these studies and results that genes contribute more to criminal activity than the environment does.Other studies, which have looked at genetic influences, have included twin studies, which assess the concordance rate between twins on their particular characteristics. Identical twins (MZ) share 100% of their genes whilst non-identical twins (DZ) share 50% of their genes. This results in higher concordance rates between MZ twins, implying that there could be genetic components to criminality.

Hollin (1989) carried out a study to look at criminality between MZ and DZ twins, and found that there was a concordance rate of 48% between MZ twins, but only 20% between DZ twins.This has also posed problems however, as deciding between MZ and DZ twins was based solely on their appearance, whereas recent studies have suggested many pairs of twins could have been wrongly diagnosed. Another problem is that even though MZ twins and DZ twins share same home environments, studies have shown that other people, due to their likeness in appearance, treat MZ twins more similarly. This again raises the issue of the nature/nurture debate as stated earlier, and whether one is more important than the other.Another way of looking at genetic composition for criminality was to look at adopted children. The idea behind this was that the adopted child experiences the environment of the adopted parents, rather than that of the natural parents.

This could be used to cancel out the issue of the nature/nurture debate, putting any correlation that arose down to genetics and not environment. Mednick et al. (1983) studied 14,500 adopted children and found that an adopted boy with a biological parent who is a criminal was also much more likely to commit a crime.Similarly, Crowe (1974) found that 50% of adopted children whose natural mothers had a criminal record had themselves committed a crime by the age of 18, whereas the control group he used showed that out of those whose mothers where not criminals, only 5% were likely to commit crimes.

Many adoption studies show that response bias plays a vital role, as the adopting family often try to show the criminality of the biological parent against their law-abiding nature. As data is often collected via interviews, this means findings can be distorted.There was also a myth that criminals were so because of an extra chromosome in their genetic make-up. During the beginning of the 1960s, it was not as widely known as it is today that people can have what is known as XXY syndrome. In 1961, Sandberg et al. found that 5% of their convicted criminal participants had an additional X chromosome, and so this was thought to contribute to their likeliness of being a criminal.

This idea was well publicised, but it was less known that people from all walks of life could have this disorder.Owen (1972) at the time looked into these findings and found that those with the XXY disorder were more likely to commit sexual offences rather than violent ones, which was more widely recognised as being true. Another idea about physiological approach to theories of criminology came from the work of Sheldon (1942) in which he looked at 1800 research participants and their 'body shapes'. He argued there were three main body types - ectomorphs, who are thin and bony; mesomorphs, who are broad and muscular; and endomorphs, who are large and heavy.Sheldon argued that these body types linked to particular personalities.

Ectomorphs tend to be introverted, mesomorphs are adventurous, and endomorphs sociable. In a follow-up study, Sheldon found that the majority of 400 participants in a rehabilitation centre were mesomorphs. The major flaw with Sheldon's work was that his conclusions were not backed up by empirical evidence. Similarly, it is likely that the majority of those in rehab would be mesomorphs, as they spend a lot of time in confinement 'working-out' in the gyms and facilities their, as there is little else to do.

Other flaws, as with many studies about criminology, is that the study does not account for women. Despite this, body build may have some involvement in crime in some way, as mesomorphs may be 'recruited' into crime by other people to help them, more so than with ectomorphs. Feldman (1977) in his study also found that certain body builds led to more arrests, possibly as it could fit with the police conception of a 'typical criminal'. Goldstein et al. (1984) found that stereotyping in this way led to more arrests.

From statistics, we have also been able to see that men are more likely to commit crimes than women. In Britain, 1 in 3 men will have a criminal conviction before 35, compared to 1 in 13 women (home office statistics, 1992). Hogan et al. (1979) showed girls are socialised to be more conforming, are more strictly supervised by parents and are shown greater disapproval if they break societies rules. Heidersohn (1996) suggested early socialisation effects carried on through life with women having part-time and low paid jobs, which they are reluctant to risk by taking part in criminal activity.The second group of theories of crime are the Psychoanalytical theories.

They emphasise inner forces as causing criminal behaviour more than social and environmental factors, though these are sometimes taken into account. According to this theory, inner dynamic forces cause crime. One of the most important features is the emphasis it places on childhood experiences. Aichorn (1955) argues that environmental factors could not by wholly responsible for crime.

Some delinquent tendencies could be innate, however early emotional experience could also be an important factor.Unfavourable early emotional experiences could cause latent delinquency. If the process of socialisation was to go wrong then latent delinquency could become to dominant state, described by Aichorn as 'dissocial'. Healy and Bronner also found in 1936 from their study that emotionally disturbed children were more likely to commit criminal offences. This was seen as evidence linking delinquency to sublimation, which is the process by which unacceptable impulses are channelled into other thoughts and behaviours, leading to criminality.

Another aspect of the psychoanalytical approach is that criminal behaviour can result from over-permissive parenting. If parents are too permissive, the superego may not develop fully, and antisocial impulses can become poorly controlled. As this theory links directly to the psychodynamic approach, many of the flaws with that approach apply to this theory, mainly that there is a lack of evidence to support this view, as well as problems with research methods. In contrast to the psychoanalytical approach, learning theorists look to the environment as the main contributor to someone committing a crime.Firstly, there is operant conditioning, which focuses on the rewards as being positive enforcement for someone committing a crime, for example during burglary or fraud.

Deterrents may often not work simply because they are not strong enough to overcome the rewards and/or satisfaction someone gets from committing crime. This theory can easily be supported with evidence, and studies can be carried out quite simply that will show criminals have done so for the rewards. The social learning theory looks at how external reinforcement can be an important factor into why people carry out illegal acts.A second factor is vicarious learning, which is learning from observing and consequences, as well as self-reinforcement, which involves someone's personal gain. Bandura, Ross and Ross used their study of the Bobo doll to study aggression amongst children when subject to various environments. Bandura's experiment however did have several problems despite the results and conclusions he drew.

As it focuses on environmental factors being the sole cause of crime, it takes away emphasis of the individual's free will; therefore people cannot be blamed for their actions.A further criticism of the theory is that the thought of imprisonment should reduce criminal activity as criminals are cut off from environmental factors that would influence them, however this is not so. Another theory associated with the learning approach is the Differential Association Theory proposed by Sutherland in 1939. It states that: * Criminal behaviour is learned, not inherited; * Learning takes place via association, mainly in close social groups; * Criminal techniques, motives and opportunities are learnt, and so are rationalisations; Learning involves social norms (Differential associations = where social norms --> law breaking--> delinquency; social norms --> law abiding --> no delinquency) different social groups have differential associations.

* Although social learning explains criminality as a means to supplying needs/wants, it doesn't explain why all people aren't criminals. As with all the other theories, the differential association theory has several evaluation points. The theory does not explain why others, given the same examples, do not learn to commit crime.Also, association as an explanation for criminal behaviour ignores mediating cognitive factors, which do seem to play a part in explaining criminal behaviour as well as certain other factors that are dealt within the social learning theory.

The final theory of crime involves the social theories, which looks at social factors for explaining criminal behaviour, one of the most well known of these theories is the labelling theory. It draws on social psychological mechanisms, such as the self-fulfilling prophecy, which shows how people can live up to negative expectations.It states that what is criminal is decided by the authorities, such as police, teachers, judges etc...

and this means that it is the disadvantaged of society who are most likely to receive the label. Along with the different theories of crime, there is a variety of different views on what crime is, and these influence the different theorists and their conclusions. The Consensus view uses the functionalist approach - looking at societies functioning within its accepted framework. Crime is simply a violation of the law, and goes against the general consensus of what is right.The second view is the conflict view. It states that society is seen as being made up of conflicting groups.

Some are poor and dissatisfied, and this dissatisfaction leads to conflict, and this conflict helps provoke crime. The final of these views on crime is the interactionist view. This view is the idea that we can understand social behaviour in terms of the roles and role-behaviours which people adopt in day-to-day living. It says that behaviour is guided by interpretation of events in our lives, and the act itself is not criminal (actus reus), but is the meaning behind it (mens rea).