Science for Everybody

Mark value: 2 marks

AO focus: AO1

Bullet-point answer points

• A gene selected for study because researchers have a reason to believe it may contribute to a particular trait or behaviour.
• It represents a possible risk factor or association, not a gene that directly and inevitably causes the behaviour.

Full model answer

A candidate gene is a gene chosen for investigation because researchers think variation in that gene may contribute to a particular behaviour or trait. In offending research, a candidate gene may be associated with increased risk, but it does not directly determine that a person will offend.

Common pitfalls and how to avoid them

Do not write that a candidate gene is a “criminal gene”. Use probabilistic language such as “may contribute to” or “may increase risk”.

Mark value: 4 marks

AO focus: AO1

Bullet-point answer points

• Lange (1930) compared MZ and DZ male twin pairs where at least one twin had been imprisoned.
• The sample included 13 MZ pairs and 17 DZ pairs.
• In 10 of the 13 MZ pairs the co-twin had also been imprisoned, compared with 2 of 17 DZ pairs.
• The higher MZ concordance suggested a genetic contribution to offending behaviour.

Full model answer

Lange (1930) investigated male twin pairs in which at least one twin had been imprisoned. He compared 13 monozygotic twin pairs with 17 dizygotic twin pairs. In 10 of the 13 MZ pairs, the other twin had also been imprisoned, whereas this was true for only 2 of the 17 DZ pairs. Because MZ twins share more genes than DZ twins, Lange concluded that inherited factors may contribute to criminal behaviour.

Common pitfalls and how to avoid them

Do not confuse MZ and DZ twins or reverse the findings. Also avoid claiming that Lange proved a genetic cause; the study only showed higher concordance.

Mark value: 4 marks

AO focus: AO2, with AO1

Bullet-point answer points

• The diathesis is a possible inherited vulnerability associated with her biological family history.
• A vulnerability does not guarantee offending.
• Her stable adoptive environment may have reduced stress and provided protective factors such as consistent parenting and prosocial modelling.
• Therefore, the biological risk may never have translated into offending behaviour.

Full model answer

The diathesis-stress model suggests that a biological vulnerability increases risk only when it combines with relevant environmental stress. Nadia may have inherited some vulnerability associated with impulsivity or antisocial behaviour from her biological father. However, her stable adoptive home may have provided protective experiences, such as consistent boundaries and prosocial role models. Because the environmental stress needed to activate or amplify the vulnerability was limited, Nadia did not develop offending behaviour. This shows why biological risk is not the same as biological destiny.

Common pitfalls and how to avoid them

Apply both parts of the model to Nadia. Do not simply say that “good parenting stopped the gene”; explain that protective environmental factors can reduce the expression of a vulnerability.

Mark value: 6 marks

AO focus: AO1 and AO3 comparison

Bullet-point answer points

• Both are biological explanations and treat offending risk as partly rooted in bodily processes.
• Genetic explanations focus on inherited variation, for example MAOA and CDH13, while neural explanations focus on brain structure, brain activity and neurotransmitters.
• The two explanations can overlap because genes influence neural development and neurotransmitter systems.
• Both use objective scientific methods such as genetic analysis, twin/adoption designs and brain imaging.
• Both risk biological reductionism and determinism if researchers ignore environmental and social influences.
• An interactionist account can integrate both with environmental stressors.

Full model answer

Genetic and neural explanations are similar because both locate part of the risk for offending in biological processes. Genetic explanations focus on inherited variation. For example, variants involving MAOA and CDH13 have been investigated in relation to severe violent offending. Neural explanations instead focus on brain systems, such as reduced prefrontal functioning, and on neurotransmitters such as serotonin.

However, the explanations are not fully separate because genes help shape neural development and neurotransmitter regulation. Both approaches can use objective scientific methods, including genetic analysis and brain imaging, which makes their predictions testable.

In contrast, both can become reductionist if they explain complex offending mainly through biology and overlook learning, poverty, peer influence or trauma. Therefore, the most complete account combines biological factors with environmental risk in an interactionist model.

Common pitfalls and how to avoid them

A comparison needs direct similarities and differences. Do not write two separate mini-essays with no linking words. Use phrases such as both, whereas, in contrast and the two overlap because.

Mark value: 8 marks

AO focus: AO2 and AO3, with supporting AO1

Bullet-point answer points

• Neural explanations link reduced prefrontal functioning with weaker inhibition, planning and emotional control.
• Raine et al. (1997) found reduced prefrontal activity in 41 murderers compared with matched controls.
• The article makes a causal claim that the evidence cannot support because neuroimaging findings are usually correlational.
• Brain differences may result from head injury, substance misuse, stress or other experiences.
• Group-level differences do not accurately predict what any one individual will do.
• Samples often focus on severe male offenders, limiting generalisability to other forms of offending.
• Neural explanations are scientifically testable, but an interactionist interpretation is more defensible than determinism.

Full model answer

Neural explanations suggest that differences in brain systems involved in behavioural control may increase the risk of offending. The prefrontal cortex is especially important because it supports inhibition, planning and the evaluation of consequences.

Raine et al. (1997) used PET scans with 41 murderers and 41 matched controls and found lower prefrontal activity in the murderer group. This supports an association between reduced executive control and serious violence.

However, the news article goes beyond the evidence when it claims that low prefrontal activity proves a person will become violent. Raine’s research was correlational, so it cannot show that reduced activity caused the offending. Other factors, such as head injury, substance misuse, chronic stress or medication, could affect brain functioning.

In addition, the research identifies average differences between groups. It does not allow psychologists to predict an individual’s future behaviour with certainty. Many studies also use unusual samples such as male violent offenders, so findings may not generalise to women or to non-violent crime.

A strength of the neural approach is that brain imaging provides objective, testable data and links offending risk to specific psychological functions. Nevertheless, the most defensible conclusion is that neural differences may contribute to vulnerability alongside environmental and psychological factors rather than determining criminal behaviour.

Common pitfalls and how to avoid them

Do not treat a brain scan as proof of causation. Apply the scenario by challenging the word “proves” and the claim about individual prediction. Balance criticism with at least one strength.

Mark value: 16 marks

AO focus: AO1 and AO3

Bullet-point answer points

• Genetic explanations: higher MZ than DZ concordance; adoption evidence; candidate genes such as MAOA and CDH13; polygenic and probabilistic interpretation.
• Lange (1930): 10/13 MZ co-twins versus 2/17 DZ co-twins also imprisoned.
• Mednick et al. (1984): biological and adoptive parental convictions both related to adoptee convictions, with highest risk when both were present.
• Tiihonen et al. (2014): MAOA and CDH13 variants were overrepresented in the most violent Finnish offenders.
• Neural explanations: prefrontal cortex, executive control, emotional regulation and serotonin.
• Raine et al. (1997): reduced prefrontal activity in the murderer group compared with controls.
• Strength: converging evidence from different scientific methods supports a biological contribution.
• Strength: mechanisms are testable and can inform prevention and rehabilitation.
• Weakness: twin/adoption designs contain environmental confounds and selective placement issues.
• Weakness: candidate-gene associations may have small effects and limited replication or cultural generalisability.
• Weakness: neuroimaging is correlational, so cause and effect remain unclear.
• Weakness: biological reductionism, determinism, sample bias and ethical risks of labelling.
• Overall judgement: biology contributes to vulnerability, but interactionist explanations provide the most complete account.

Full model answer

Biological explanations of offending behaviour argue that inherited characteristics and neural functioning can increase a person’s vulnerability to crime. Genetic explanations receive support from twin and adoption studies. Lange (1930), for example, studied male twin pairs in which one twin had been imprisoned. In 10 of 13 monozygotic pairs the co-twin had also been imprisoned, compared with only 2 of 17 dizygotic pairs. Because MZ twins share more genetic material, this higher concordance suggests a genetic contribution.

Adoption research reaches a similar conclusion. Mednick et al. (1984) studied more than 14,000 Danish adoptees and found that convictions were more common when biological parents had convictions, but the rate was highest when both biological and adoptive parents had convictions. This supports an interaction between inherited vulnerability and environmental risk rather than a purely genetic explanation.

Molecular genetics has also identified candidate genes. Tiihonen et al. (2014) analysed almost 900 Finnish offenders and reported that variants involving MAOA and CDH13 were overrepresented among the most violent offenders. MAOA is relevant because it affects the breakdown of monoamine neurotransmitters, including serotonin and dopamine. However, modern genetic explanations do not propose a single “criminal gene”. Offending is complex and likely polygenic, with many small genetic effects interacting with experience.

Neural explanations focus on brain systems involved in inhibition, planning and emotional control. The prefrontal cortex is important because it helps people suppress impulses and consider consequences. Raine et al. (1997) compared PET scans from 41 murderers who had pleaded not guilty by reason of insanity with 41 matched controls. The murderer group showed reduced prefrontal activity and atypical activity in other emotion-related regions. Low serotonergic functioning has also been associated with impulsive aggression, which provides a second possible neural pathway.

One strength of biological explanations is that several different methods produce converging evidence. Twin studies, adoption studies, genetic analysis and brain imaging all suggest that biology contributes to at least some forms of offending. This improves credibility because the evidence does not depend on one method.

Biological mechanisms are also testable. Researchers can measure genotype, neurotransmitter function and brain activity, which allows more precise hypotheses than broad social descriptions. Such research may eventually help rehabilitation by identifying difficulties with impulse control, emotional regulation or neurodevelopment that can become targets for support.

However, twin studies cannot cleanly separate genes from shared environment. MZ twins often experience more similar treatment than DZ twins, and early studies such as Lange used small samples and old methods. Adoption studies also contain confounds because selective placement, prenatal influences and contact with biological relatives can blur the distinction between heredity and environment. Therefore, these methods estimate genetic influence rather than proving it.

Candidate-gene research has further limitations. Complex behaviours such as violent offending are unlikely to result from one or two variants, and some candidate-gene findings have not replicated consistently. Tiihonen’s Finnish sample may also limit cultural generalisability because genetic frequencies and social conditions vary between populations. A gene may therefore alter risk without having the same effect in every cultural or environmental context.

Neural evidence also raises a cause-and-effect problem. Raine et al. found an association between reduced prefrontal activity and murder, but the study cannot show whether brain differences existed before the offending. Substance misuse, head injury, chronic stress or other experiences could change brain functioning. Many neural studies also use male, violent or psychiatric samples, creating sample bias and making it difficult to generalise to the full range of offenders.

Finally, biological explanations can become reductionist and deterministic. Explaining offending through genes or brain regions may underplay poverty, social learning, peers, trauma and opportunity. Deterministic claims may also stigmatise people by suggesting that they are biologically destined to offend, and this creates ethical and legal problems around responsibility.

The evidence is better interpreted probabilistically. Overall, biological factors appear to contribute to vulnerability, but the most convincing explanation is interactionist: genes and neural systems influence risk while environmental experiences shape whether that risk develops into offending behaviour.

Common pitfalls and how to avoid them

Do not spend the whole answer describing studies. Keep AO1 concise, then develop AO3 with explained strengths and weaknesses. Avoid deterministic wording. Make an overall judgement that weighs biological evidence against interaction with the environment.