Biological theories of crime state that the biological nature of human beings determines whether they commit criminal acts or not.
On the basis of physical or at least purely biological characteristics, a typology of criminals and non-criminals could be established according to which criminals are to be distinguished from non-criminals with regard to their genetics, neurology or physical constitution. Biological theories of crime therefore clearly distinguish themselves from those (e.g. sociological) theories which address external factors to which the individual is exposed in their approaches. However, many of the (above all modern) biological theories also include contextual and environmental conditions in their considerations. Some of these theories are therefore also called biosocial theories.
The history of biological criminology is in many cases congruent with the history of criminology in general, so that anthropological and physiological theories have been predominant or at least in their main features always the subject of criminological discussion for many decades before being overtaken in recent times by sociological, socio-psychological and economic approaches.
Criminals differ from non-criminals by a number of biological and psychological characteristics. More modern theories are based on the interplay of biological and social factors that cause crime – biosocial theories.
Forensic biology first appeared as a separate and independent science in Italy in the 19th century. Cesare Lombroso developed the concept of the born atavistic criminal under the influence of the then emerging phrenology (craniology) in medicine, but above all also following Darwin’s theory of evolution. The idea of being able to distinguish criminals from non-criminals on the basis of their physical characteristics was a conscious departure from classical criminology and led to the first scientific attempts to find out the cause of criminal behaviour. He was thus the first criminologist to devote himself to direct observation and measurement of the individual case in order to trace the origin of the crime. For many criminologists, he is therefore regarded as the founder of their science.
Positivism, however, was not only – as with Lombroso – purely biologically offender oriented.
Especially in the French-speaking world, there were already early considerations as to which external, social influencing factors could cause or promote crime. In addition to Gabriel Tarde and Lombroso critic Alexandre Lacassagne, the so-called crime statisticians were in charge here: André-Michel Guerry and Adolphe Quetelet recorded the number and distribution of crimes by collecting and reviewing statistical data, thereby producing astonishing regularities with regard to age, gender, social origin, etc.
Lombroso was influenced by these statistics and the assumption that crime was the result of environmental and social factors. His students Raffaele Garofalo and Enrico Ferri, however, represented even more sociological, psychological and multifactorial approaches than purely biological-anthropological ones.
The German criminal law expert Franz von Liszt finally developed the “Anlage-Umwelt-Formel” (nature vs. nurture), which is based on individual and personal factors on the one hand and on countless social factors on the other hand as additive conditions for criminal behaviour. Gustav Aschaffenburg argues similarly in his so-called Vereinigungstheorie (Vereinigung refers here to an argumentative solidarity of the Italian anthropological and the French sociological schools).
Nevertheless, Lombrosian crime theory enjoyed a large following, especially in German-speaking countries. Emil Kraeplin and others represented the so-called degeneration thesis, according to which criminals were pathological and hereditary deviators of the regular type, although they no longer represented their own anthropological type. This genetic “type primitif” could also only be identified by psychological, but not by physical, characteristics à la Lombroso.
In the Weimar Republic and in the Third Reich both the atavistic and the degeneration thesis were very often received and adapted and abused with regard to racial hygiene projects. Thus many ethnic and other minorities were branded by the National Socialists as genetically criminal and thus incorrigible. They were perceived as inferior pests, to whom every right could and must be denied. Representatives of this view were, for example, Franz Exner, Edmund Mezger and many others. Scientific justifications were drawn from Johannes Lange’s twin research, Friedrich Stumpfl’s genealogical research and comparable studies, which took the view that criminal patterns of action could only be explained by human genetic predispositions.
However, this National Socialist thought drew its strength not only from the genetic theories mentioned above, but also from purely physiological theories such as Ernst Kretschmer’s theory of constitution. Such approaches pursued the aim of associating criminal behaviour only with physical abnormalities or to explain crime through psychopathological research.
Anomalies in the structure of the body and its constitutional composition, but also abnormalities in the brain or the skull were regarded as reliable criteria for distinguishing between inevitable delinquency on the one hand and equally determined righteousness on the other.
Although criminologists such as Hans von Hentig and Max Flesch rejected political-racist criminology, they also assumed genetic or physiological causes of crime.
Biological theories of cime also lost more and more of their scientific significance after the Second World War due to the biologically reduced image of man and its fatal consequences in the Nazi regime. Apart from a few exceptions, modern biological theories are also multifactorial concepts or at least concepts that unite nature and nurture – entirely according to the ideas of Franz von Liszt and Gustav Aschaffenburg. Most criminal biologists and pathologists have completely abandoned the idea that delinquency can be explained solely by biological deviations in the offender and prefer so-called biosocial concepts. Terrie Moffit’s Two-Path theory is one example.
Since the Second World War, biological theories have also been expanded to include other aspects: In addition to genetic and physiological investigations, biochemical and extensive neurological research in criminology has become increasingly important in recent decades. In the foreground were investigations of the prefrontal cortex, the central nervous system, neurotransmitters (e.g. serotonin) that may influence crime, and certain hormones (e.g. testosterone). William Sheldon, in his theory of body types, has investigated a potential connection between physiology and crime à la Kretschmer. The latter is related to the research of the couple Glueck & Glueck, and the genetic questions on crime have repeatedly found supporters: In addition to more recent twin and adoption studies, there was a rumour in the 1960s, for example, that a number of criminals were born with an additional Y chromosome, according to which the latter theory was almost completely refuted, but in terms of biological theories in general it remains to be said that, despite their history, they are still topical and, above all, as biosocial hybrids, can make a valuable contribution to criminal causal research.