What you'll learn

• How genotype, phenotype and evolution explain genetic influences on behaviour.
• How brain structures, the nervous system and neurochemistry affect thoughts, emotions and actions.
• What cognitive neuroscience is and how it studies mental processes biologically.
• How to evaluate the biological approach for AO3: evidence, applications, reductionism, determinism and ethics.

The big idea: behaviour has biological roots

The biological approach assumes that what you think, feel and do is linked to the body. For example, anxiety might be explained through inherited vulnerability, activity in the amygdala, and neurotransmitters such as serotonin.

The diagram below shows how the main parts of the biological approach fit together.

The genetic basis of behaviour

Genes, genotype and phenotype

A gene is a section of DNA inherited from biological parents. Genes help build proteins, which influence the development and functioning of the body, including the brain.

A person may inherit a genetic vulnerability for a behaviour, but whether that vulnerability becomes visible depends on environmental factors such as upbringing, stress, education, relationships and culture.

A useful term here is polygenic, meaning that most psychological characteristics are influenced by many genes, not one single “behaviour gene”.

Evidence and evaluation of genetic explanations

Twin, family and adoption studies are often used to estimate genetic influence. For example, Gottesman (1991) found higher concordance for schizophrenia in identical twins than non-identical twins, supporting a genetic role. Caspi et al. (2003) found that a version of the 5-HTT serotonin transporter gene was linked to depression mainly when people had also experienced stressful life events — a clear gene-environment interaction.

These studies strengthen the biological approach because they show that behaviour has measurable biological influences. However, twin studies can be criticised because identical twins may be treated more similarly than non-identical twins, so higher concordance might partly reflect environment, not just genes.

Ethically, genetic research is sensitive. Researchers need informed consent, minimal deception, a clear right to withdraw, protection from distress or stigma, confidentiality of genetic data, and a debrief explaining what the findings can and cannot show.

Evolution and behaviour

The evolutionary explanation says some behaviours exist because they were adaptive for ancestors. For example, fear responses may have helped humans avoid danger, and attachment behaviours may have kept infants close to caregivers, increasing survival. Bowlby (1969) used an evolutionary argument when explaining attachment as an adaptive system.

Evolutionary explanations usually follow this logic:

1. There is genetic variation in a population.
2. Some traits are better suited to the environment.
3. Individuals with those traits are more likely to survive and reproduce.
4. Their genes become more common in future generations.

AO3 point: evolutionary explanations can be useful because they explain why some behaviours appear widespread across cultures. However, they are often difficult to test directly because ancestral environments cannot be recreated. This means some evolutionary explanations risk becoming “just-so stories” — plausible after the event, but hard to falsify.

Biological structures and behaviour

Biological structures are physical parts of the body that influence behaviour. In psychology, the main focus is usually the brain and nervous system.

The central nervous system is the brain and spinal cord. The brain contains specialised areas linked to different functions. Localisation of function means that particular brain areas are associated with particular behaviours or mental processes.

Examples include:

• The amygdala, linked with fear and emotional processing.
• The hippocampus, linked with memory and spatial navigation.
• The prefrontal cortex, linked with planning, decision-making and impulse control.
• Broca’s area, linked with speech production.
• Wernicke’s area, linked with language comprehension.

Maguire et al. (2000) used MRI scans and found that London taxi drivers had larger posterior hippocampi than controls, supporting a link between brain structure and spatial memory. Raine et al. (1997) used PET scans and found differences in prefrontal and limbic activity in murderers pleading not guilty by reason of insanity compared with controls, suggesting possible biological links with aggression and impulse control.

Scanning studies provide objective, scientific evidence, which is a strength. However, they can be correlational and may oversimplify behaviour by focusing on one brain area when real behaviour involves networks of regions working together.

Ethically, brain-scanning and forensic research require informed consent, the right to withdraw, confidentiality, protection from harm such as anxiety in scanners, careful debriefing, and caution about socially sensitive conclusions — especially if findings could stigmatise people as “biologically criminal”.

Neurochemistry: chemical messages in the brain

Neurochemistry refers to the role of chemical substances in the nervous system. The key idea is that neurons communicate using neurotransmitters.

The synapse is the tiny gap between neurons. Neurotransmitters can make the next neuron more likely to fire, called excitation, or less likely to fire, called inhibition.

Examples include:

• Dopamine, linked with reward, motivation and movement.
• Serotonin, linked with mood regulation.
• Adrenaline, a hormone involved in arousal and the fight-or-flight response.
• Cortisol, a hormone involved in stress.

Drug therapies are a major real-world application of the biological approach. Antidepressants and antipsychotics are based on changing neurotransmitter activity. This supports the value of biological explanations.

However, not everyone responds to drug treatment, and side effects can be significant. Also, if a drug changes behaviour, that does not automatically prove the original cause was purely chemical.

Cognitive neuroscience

“Cognitive” means mental processes; “neuroscience” means the study of the nervous system. Cognitive neuroscience combines cognitive psychology with biological methods.

Common methods include:

• fMRI, which detects changes in blood flow linked to brain activity. It has good spatial resolution but is expensive and can lack ecological validity.
• EEG, which records electrical activity from the scalp. It has excellent temporal resolution but weaker spatial resolution.
• ERPs, which are averaged EEG responses to specific stimuli, useful for studying attention and perception.
• PET, which uses radioactive tracers to measure brain activity, but is more invasive.
• Lesion studies, which study behavioural changes after brain damage.

Cognitive neuroscience has helped map functions such as memory, language and emotion, and has applications in neurosurgery, brain-injury rehabilitation and understanding disorders.

Overall evaluation of the biological approach

A major strength is that the biological approach is scientific. It often uses objective methods such as scans, genetic testing and controlled drug trials. This improves reliability and makes psychology closer to the natural sciences.

Another strength is practical application. Biological explanations have led to drug treatments, brain-imaging techniques and better understanding of neurological conditions.

A key limitation is biological reductionism, which means explaining complex behaviour at a lower biological level while ignoring thoughts, emotions, learning and culture. For example, explaining aggression only through genes or brain activity may miss social learning, cognition and situational triggers.

The approach can also be deterministic if it suggests people have little control over behaviour because of biology. A more balanced view is interactionist: biology creates possibilities and constraints, while experience shapes how they develop.