Biological Theories of Crime

Key Takeaways

  • Biological theories of crime, which encompass a lineage of thinking dating to the 19th century, argue that whether or not people commit crimes depends on their biological nature.
  • Some individuals are predisposed to crime because of genetic, hormonal, or neurological factors that may be inherited (present at birth) or acquired (through accident or illness).
  • No one can be a ‘born criminal’ because crime is socially defined. A link has to be made from some more general factor like aggression, impulsivity, risk-taking etc.
  • Early biological theories of crime drew influence from Darwin’s theory of evolution and natural selection. Theories such as degeneration theory posited that people who used certain poisons — such as alcohol and opium — acquired morally degenerate traits, and these traits could be passed on biologically and socially to their offspring.
  • Historically, biological theories of crime — in particular, the work of Lombroso and B.A Morel — have been used as justification for eugenic programs such as those carried out by the Third Reich.
  • The formulation of neuroscience in the latter half of the 20th century brought genetic studies of crime to light. These studies investigate how certain neurotransmitters, or chemicals in the brain, interact with a number of environmental behaviors to produce criminal behavior. One common methodology for this is twin adoption studies.

History and Overview

Biological theories of crimes state that whether or not people commit crimes depends on their biological nature. The biological characteristics that biological theories of crime claim are associated with criminality could include factors such as genetics, neurology, or physical constitution.

Although many modern biological theories of crime consider the effect of contextual and environmental conditions (what criminologists call biosocial theories), biological theories of crime distinguish themselves from sociological theories in their focus on internal factors.

Biological theories of crime developed in parallel to their sociological counterparts.

Forensic biolog y first became a science in itself in Italy in the 19th century, with Cesare Lombroso as its founding father. Lombroso developed the concept of the “born criminal” under the influence of both phrenology (a now-defunct study of the features of the skull as indicative of mental capacity and character traits) and Darwin’s theory of evolution.

Although criminologists often paint biological theories of crime in opposition to sociological ones, Lombroso was influenced by the work of French crime statisticians such as André-Michel Guerry and Adolphe Quetelet.

These crime statisticians recorded the number and distribution of crimes by collecting and analyzing statistical data, producing connections between age, gender, social origin, and crime.

These statistics pointed to the hypothesis that crime was the result of environmental and social factors as well as biological ones. His students would lean more heavily into this hypothesis, producing integrated biosocial theories of crime.

Lombroso’s criminal theory developed a large following in the German-speaking world. One remnant of this following was the so-called degeneration thesis, promoted by the criminologist Emil Kraeplin. According to the degeneration thesis, criminals pathologically and hereditary deviated from a regular genetic type. However, this genetic type could only be identified by psychological, rather than physical, characteristics.

Both the Weimar Republic and the Third Reich would use the atavistic and degeneration theses as justification for so-called “racial hygiene” projects. Thus, the Third Reich branded many ethnic minorities as genetically criminal and inferior; people to whom every right could and must be denied.

Representatives such as Franz Exner and Edmund Mezger drew scientific justifications from the twin studies of Johannes Lange, Friedrich Stumpfl’s genealogical research, and other studies that argued that criminality could only be explained by human genetic predisposition.

The Nation Socialists (that is, the Nazi Party), also drew influence from purely physiological theories of crime, such as Ernst Kretchmer’s theory of consitituion. The physiological abnormalities leading to crime, according to Kretschmer, could be in the brain or skull as well as in the structure of the body.

Because of their fatal consequences in the Nazi regime, biological theories of crime largely lost their scientific significance after the Second World War.

Most criminal biologists have abandoned the idea that delinquency can be explained only by biological deviations in the offender, preferring approaches that combine biology and sociology. Terrie Moffit’s Two-Path theory is such an example.

Degeneration Theory (1857)

Degeneracy Theory, an offshoot of 19th-century research into biological theories of crime, argues that certain (lower) social classes and races were predisposed to neurological and mental illnesses by inheritance, making them more likely to commit crimes.

Those of low social standing, such as prostitutes, criminals, the poor, and those with mental illnesses, were morally defective and represented a regression in human evolution.

B.A. Morel (1857) proposed the first theory of progressive degeneracy in his book, Traits des Dégénérescences Physiques, Intellectuelles et Morales de l’Espèce Humaine.

Morel believed that the use of specific substances such as hashish, alcohol, and opium resulted in progressive physical and moral deterioration that would get passed on from one generation to the next, resulting in a society with both a worsened intellectual and moral character as well as certain physical characteristics.

This theory would come to influence Cesare Lombroso’s biological theory of crime.

Another key aspect of degeneration theory is the idea that moral degeneracy is heritable. Degeneration theorists widely believed that the moral and physical pathologies leading to low social status would persist and proliferate from generation to generation biologically and socially.

Thus degeneration theorists believed that the so-called “miscegenation” between morally-defective people should be regulated by eugenics and moral hygiene for the good of society.

Atavistic Theory of Crime (1876)

Cesare Lombroso (1876) was most famous for developing the avastic theory of crime in his book, The Criminal Man . In this book, Lombroso argued that there is a distinct biological class of people prone to criminality.

Lombroso’s (1876) theory of criminology suggests that criminality is inherited and that someone “born criminal”” could be identified by the way they look.

He suggested that there was a distinct biological class of people that were prone to criminality. These people exhibited ‘atavistic’ (i.e. primitive) features.
Lombroso suggested that they were ‘throwbacks’ who had biological characteristics from an earlier stage of human development that manifested as a tendency to commit crimes.

Connected to the idea of atavistic characteristics is the idea of degeneration. According to Lombroso, offenders have certain physical and mental characteristics of primitive humans, and they commit crime because of these biological abnormalities.

Credit: Wellcome Library, London. Wellcome Images Six figures illustrating types of criminals Printed text L’Homme Criminel Lombroso, Cesar Published: 1888

Lombroso claimed that criminal types were distinguishable from the general population because they looked different.

These people have atavistic, or primitive, features.

Thieves had expressive faces, manual dexterity, and small, wandering eyes; murderers had cold, glassy stares, bloodshot eyes, and hawk-like noses; sex offenders carried thick lips and protruding ears; and female criminals were shorter, more wrinkly, had darker hair and smaller crimes than normal women.

This meant, Lombroso argued, that criminals were at a more primitive stage of evolution than non-offenders, making them unable to fit into contemporary society and thus prone to committing crime. This came with the implication that criminality was heritable.

Sheldon Somotypes Theory (1942)

William Sheldon (1942) proposed a strong correlation between personality and somatotype (i.e., physique).

From a study of several hundred male physiques, he derived three made body types:

  1. The ectomorph, characterized by a thin, wiry frame.
  2. The endomorph, heavy and rounded.
  3. The mesomorph, with a solid, muscular frame.

Human body types. Three figures. Forms: ectomorph, mesomorph and endomorph.

Each body type was associated with a particular personality:

  1. Ectomorph = introvert, quiet, fragile, sensitive
  2. Endomorph = relaxed, sociable, tolerant, peaceful
  3. Mesomorph = aggressive, assertive, and adventurous.

Sheldon noted that the vast majority of criminals were mesomorphs. One explanation for this is that a solid muscular person becomes involved in crime at an early age due to their intimidating appearance.

This biological theory may seem implausible, but people often stereotype others on characteristics such as their appearance.

Certain individuals (e.g. the police) may make “snapshot” judgments about people, which may have implications for criminal behavior.

Terrie Moffit’s Two-Path Theory (1993)

Terrrie Moffit’s Two-Path theory is a biosocial theory of crime. Moffit (1993) proposes that there are two groups of people who commit crimes: life-course-persistent offenders, whose anti-social, criminal behavior begins in childhood and continues to worsen thereafter, and adolescence-limited offenders, whose antisocial behavior begins in adolescence but ends in young adulthood.

While life-course-persistent offenders are rare but pathological in nature, adolescent-limited offenders are relatively common, temporary, and near the normal.

Moffit’s two-path theory has had important implications for criminal policy, as one of the most widely received modern criminological theories.

Notably, those who follow Moffit’s theory believe that about 5% of the population could be life-course-persistent offenders. The government of Hamburg, Germany, in response to this theory, has screened primary-school age children in an attempt to provide social therapeutic measures that could possibly compensate for poor parental support.

Modern Biological Theories of Crime

Modern biological theories of crime focus specifically on how different regions of the brain are responsible for thoughts, emotions, and behaviors, and how the dysfunction of these regions can cause criminality (Raine, 2008; Viding et al., 2005; Newsome, 2014).

Neurological Theories of Crime

Neural explanations look at the structure and functioning of the central nervous system.

There are several regions of the brain that criminologists and neurologists have focused on in modern biological studies of crime.

The cerebral cortex makes up the outer part of the brain, and is divided into left and right hemispheres. Each hemisphere has four lobes.

Criminologists have focused on the frontal lobe in their biological theories of crime because the region is involved in abstract thought, planning, goal formation, sustaining attention and concentration, self-monitoring, and behavioral inhibition (Moffit, 1990; Ishikawa and Raine, 2003).

Raine et al. (1997) carried out a study of 41 violent murderers and found reduced activity in the prefrontal cortex and the limbic system of these offenders compared with control non-criminals.

Individuals with Antisocial Personality Disorder (psychopathy) display a decrease in emotional response and lack of empathy with others. These symptoms have been found in many offenders.

Brain imaging studies have found reduced activity in the prefrontal cortex of individuals with APD. Additionally, Raine et al. (2000) found a reduced volume of grey matter in this region in the brain of these individuals.

Neuroscientists also study how chemicals in the brain known as neurotransmitters can work to influence thought, emotion, and behavior. For example, some studies have shown that excessive levels of dopamine may be related to aggressive and criminal behaviors, and antipsychotic drugs that reduce dopamine may also be used to reduce aggression.

Similarly, scientists have found that increased levels of norepinephrine can result in aggressive behavior, and reduced levels can lead to antisocial behavior. These results suggest that both high and low levels of norepinephrine can result in behavioral problems.

Another neurotransmitter of interest to biological theories of crime is serotonin, an inhibitory neurotransmitter used throughout the brain, including in the limbic system and frontal cortex.

Researchers have determined that reduced levels of serotonin are linked to criminal behavior, and that the neurotransmitter manages impulsivity (Brizer, 1988; Raine, 2008).

Genetic Explanations

Genetic explanations of crime propose that genetic factors could predispose individuals to commit crimes because genes code for physiological factors such as the structure and functioning of the nervous system and neurochemistry.

As in early biological theories of crime, criminologists have used family, adoption, and twin studies in estimating the extent to which certain traits are heritable (Plomin, 2004). In these studies, if the behavior of an individual is more similar to those of their biological relatives than their adopted ones, then this indicates that a trait is more influenced genetically than environments.

In one such study by Mednick, Gabrielli, and Hutchings (1984), criminologists examined 14,427 adoptees and their biological and adoptive families to determine genetic and environmental influences on criminal behavior.

The study’s results indicated that 13.5% of adoptees for whom neither adoptive or biological parents had been convicted of a crime were convicted. 14.7% of those for whom only their adoptive parents had been convicted became convicts.

These numbers spiked when the biological parents were convicted of a crime. 20% of those whose biological parents had been convicted became convicted, and 25% of those for whom both biological and adoptive parents had become convicted became convicted (Mednick, Gabrielli, and Hutchings, 1984).

These results suggest that the traits that lead to criminality are somewhat heritable, but those who are reared in an environment where they are exposed to criminal behavior are even more likely to engage in it themselves (Newsome, 2014).

More recent criminality adoption studies have supported these findings.

Rhee and Waldman (2002) conducted a review of twin and adoption studies and found that there are substantial genetic and environmental influences on antisocial behavior.

Specifically, the researchers found that about 32% of the variation in antisocial behavior is due to additive genetic effects, 9% due to nonadditive genetic effects, 16% due to environmental influences shared by the twins, and 43% due to unique environmental influences not shared by the twins.

After Rhee and Waldman, Moffitt (2005) conducted a review that concluded that about 50% of the population’s variation in antisocial behavior was due to genetic influence.

Gene-Environment Interactions

Those with dissimilar genes are likely to act differently in the same environment. Those who have genetic predispositions towards criminality are more likely to engage in criminal behaviors if they are exposed to environments conducive to criminality.

In contrast, those that do not have criminal dispositions are unlikely to engage in criminal behavior, even when they are in a criminogenic environment. Scientists such as Caspi et al. (2002) have found evidence for how criminological genes themselves interact with the environment.

Caspi et al.’s study revealed that genetic variants of a gene that produced an enzyme that breaks down neurotransmitters such as serotonin and dopamine did not have a direct effect on behavior normally.

However, boys who experienced maltreatment as children as well as having a gene that codes for low enzyme production were more likely to have antisocial behavior problems than those who did not have this gene (Kim-Cohen et al., 2006; Caspi et al., 2002).

Critical Evaluation

Genetic studies are limited because they cannot determine which specific genetic factors lead to behavioral differences. Many genes can disrupt normal development, resulting in abnormal behavior. To find out which genes could be related to antisocial and criminal behavior, scientists have conducted molecular genetic studies.

Criminologists have been interested in two types of genes: the genes that control dopamine and those that control serotonin. The varying levels of dopamine in the brain can result in a wide range of behaviors, and variants in the genes that control dopamine can lead to serious and violent antisocial behavior (Comings et al., 2000).

There are also a number of genes that code for the production, detection, and removal of serotonin in the brain, and research has indicated that low levels of serotonin is associated with increases in antisocial behavior (Raine, 2008).

The biological approach is socially sensitive as it has consequences for the legal system and society as a whole. If offending is genetic then people should not be considered responsible for their crimes, however this then leaves an important decision to be made as to what is to be done with these dangerous offenders.

Based on this theory, crime prevention measures could include genetic testing of the public but once individuals carrying genes predisposing to crime what do we do with these individuals?


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Saul Mcleod, PhD

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Educator, Researcher

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.

Charlotte Nickerson

Research Assistant at Harvard University

Undergraduate at Harvard University

Charlotte Nickerson is a student at Harvard University obsessed with the intersection of mental health, productivity, and design.