There are many different theories on what causes a person to perform deviant behavior, including biological explanations, psychological explanations, and sociological explanations. Biological theories of deviance see crime and deviant behavior as a form of illness caused by pathological factors that are specific to certain types of individuals. They assume that some people are "born criminals" who are biologically different than non-criminals. The underlying logic is that these individuals have a mental and physical inferiority, which causes an inability to learn and follow the rules. This in turn leads to criminal behavior. Three major biological theories of deviant behavior include Lombroso's Theory, Sheldon's Theory of Body Types, and the Y Chromosome Theory. It should be noted that since their inception, all of these theories have been discredited. Read more about each of them and how they explain deviance and crime.