By the twenty-first century criminologists looked to a wide range of factors to explain why a person would commit crimes. These included biological, psychological, social, and economic factors. Usually a combination of these factors is behind a person who commits a crime. Reasons for committing a crime include greed, anger, jealously, revenge, or pride.
Criminologists focused on the physical characteristics and sanity of an individual. They believed it was "predetermined" or that people had no control over whether they would lead a life of crime. For example, criminologists believed people with smaller heads, sloping foreheads, large jaws and ears, and certain heights and weights had a greater chance to be criminals.
As late as the 1950s researchers continued to investigate the relationship of body types to crime. Aside from biological traits indicating a natural tendency toward criminal activity by some individuals, Lombroso and other early twentieth century researchers also reasoned that criminal behavior could be a direct result of psychological disorders. They believed these mental disorders could be diagnosed and possibly cured. If this was true, then criminal activity could be considered a disease and the offender could be "cured" through psychiatric treatment.
In addition to studying the biological and psychological causes of criminal behavior, others looked toward society in general for possible causes. In the early 1900s researchers believed social changes occurring in the United States, such as an industrial economy replacing the earlier agricultural economy and the growth of cities, as well as the steady flow of immigrants from eastern Europe affected crime levels.
In the 1990s a new idea spread through the criminal justice field concerning the influence of a person's