Biological Explanations and Eysenck's Personality Theory
Biological Explanations of Criminality: Eysenck’s Personality Theory
Not every explanation of crime focuses on what a person learns from others. Hans Eysenck (1964) argued that criminality has a biological basis, rooted in personality traits that a person is born with. Unlike learning theories, which focus on upbringing and role models, Eysenck’s approach looks inward, at the nervous system itself, to explain why some people are more likely to offend.
Eysenck argued that personality has a physical, biological basis in the nervous system. He identified three dimensions — extraversion, neuroticism and psychoticism — that can be measured using personality questionnaires and linked to criminal behaviour.
Eysenck’s Three Personality Dimensions
Eysenck argued personality has a biological basis, not just one shaped by upbringing. The dimension of extraversion describes people who are outgoing, sociable and crave excitement, while its opposite, introversion, describes people who are quiet, cautious and prefer calm surroundings. The key difference between the two lies in cortical arousal — the resting activity level of the brain.
The second dimension, neuroticism, describes how anxious, moody or emotionally unstable a person is. Its opposite is stability — being calm and even-tempered. Neuroticism is linked to how reactive a person’s nervous system is to stress.
Eysenck later added a third dimension, psychoticism. This describes people who are aggressive, cold, egocentric and lacking in empathy for others. High psychoticism is not the same as having a psychotic illness — it is simply the far end of this personality dimension.
Extraverts are thought to have naturally low cortical arousal. Their brains are under-stimulated at rest, so they seek out excitement, noise and risk to bring their arousal up to a comfortable level. This can make them impulsive and more willing to take risks, including breaking rules.
People high in neuroticism have a highly reactive autonomic nervous system. They respond to stressful situations quickly and strongly, which can make them prone to overreacting under pressure — including lashing out impulsively when they feel threatened or provoked.
Psychoticism has been linked to higher levels of testosterone and lower activity in brain areas involved in empathy. This can make a person more aggressive, less troubled by guilt afterwards, and less sensitive to the threat of punishment.
The ‘Criminal Personality’
Eysenck argued that a person who scores highly on all three dimensions — extraversion, neuroticism and psychoticism — has what he called the criminal personality. He suggested this combination makes a person poorly suited to learning right from wrong as a child, because conditioning — the process by which children learn to feel guilt and anxiety when they do something wrong — works best on people with average arousal and average reactivity.
The ‘criminal personality’ combines high extraversion, high neuroticism and high psychoticism. Eysenck believed this combination makes conditioning of conscience less effective, so the person is less restrained by guilt or fear of punishment.
According to Eysenck, three features work together to raise the risk of offending:
- Under-arousal (high extraversion) drives a need for stimulation, which can be satisfied through risk-taking or rule-breaking.
- High reactivity (high neuroticism) makes the person quick to act impulsively under stress or provocation.
- Aggression and low empathy (high psychoticism) reduce the person’s concern for the harm caused to victims.
Researchers have tested Eysenck’s theory using personality questionnaires, such as the Eysenck Personality Questionnaire (EPQ), given to samples of convicted offenders and compared with non-offenders. These studies have often found that offender groups score higher, on average, on neuroticism and psychoticism than non-offender groups, which is used as evidence to support the biological explanation.
Evaluating Eysenck’s Theory
Strength: The theory can be tested objectively. Eysenck developed a personality questionnaire so that scores on each dimension can be measured and compared between offender and non-offender groups, giving the theory a scientific, falsifiable basis rather than relying on guesswork.
Weakness: The theory is reductionist — it reduces a complex behaviour like offending to biological personality traits and largely ignores situational and environmental factors, such as poverty, peer influence or upbringing, which learning theories suggest also play a major role.
When evaluating this theory, it helps to think about validity, reliability and generalisability. Personality questionnaires rely on self-report, so answers can be affected by social desirability bias. Not every offender scores highly on all three dimensions, and some people with this profile never offend, which questions how far the theory can predict criminal behaviour on its own.