Part 1 — Assumptions of the Biological Approach

The biological approach rests on one foundational claim: everything psychological is first biological. All thoughts, emotions, and behaviours ultimately have a physical basis in the body. From this perspective, the mind lives in the brain — it is not a separate, non-physical entity. This stands in direct contrast to the cognitive approach, which treats mental processes as distinct from the physical hardware of the brain.

Because the mind is rooted in biology, psychologists working within this approach focus on three key influences on behaviour:

1. Genes — inherited instructions encoded in DNA that shape both physical and psychological characteristics.
2. Biological structures — the organisation of the brain and nervous system, including specific brain regions associated with particular functions.
3. Neurochemistry — the action of chemical messengers (neurotransmitters and hormones) that regulate thought, mood, and behaviour.

Understanding how these three levels interact is, for biological psychologists, the key to explaining why people behave the way they do. For instance, imbalances in neurochemistry have been linked to mental disorders — low levels of the neurotransmitter serotonin are associated with obsessive-compulsive disorder (OCD), while overproduction of dopamine has been implicated in schizophrenia.

Part 2 — Genotype, Phenotype, and the Genetic Basis of Behaviour

A person's genotype is fixed at conception — it is the complete set of genetic instructions they inherit. However, genes do not operate in isolation. The phenotype is the way those genes are actually expressed, and this expression is shaped by environmental factors. Two people can share the same genotype yet display different phenotypes. Identical (monozygotic) twins are the clearest example: they share 100% of their DNA, yet they may differ in weight, personality traits, or susceptibility to mental illness because their environments — diet, stress levels, life experiences — are never perfectly identical.

A striking illustration of the genotype-phenotype distinction is phenylketonuria (PKU), a rare genetic disorder. Individuals with the PKU genotype lack the enzyme needed to metabolise the amino acid phenylalanine. If left untreated, a build-up of phenylalanine causes severe learning difficulties. However, if the condition is detected early (via a heel prick test at birth) and the child is placed on a restricted diet, they develop normally. The genotype is the same in both cases — it is the environment (the dietary intervention) that changes the phenotype.

This distinction matters because it shows that genes are not destiny. The biological approach acknowledges that behaviour results from an interaction between inherited factors (nature) and the environment (nurture), though the emphasis remains firmly on biological mechanisms.

The genetic basis of behaviour

Psychologists investigate whether psychological characteristics have a genetic basis using twin studies. The logic is straightforward: if a characteristic is strongly influenced by genes, identical (MZ) twins — who share 100% of their genes — should show higher concordance rates than non-identical (DZ) twins, who share approximately 50%. Concordance rate refers to the likelihood that if one twin has a certain trait, the other twin has it too.

For example, research into depression has found concordance rates of approximately 49% for MZ twins compared to 17% for DZ twins. This large difference suggests a substantial genetic contribution. However, the fact that concordance for MZ twins is not 100% tells us that genes alone do not determine whether someone develops depression — environmental factors must also play a role.

The role of the environment in shaping phenotype is also crucial. Environmental factors such as diet, stress, upbringing, and life experiences can affect how inherited tendencies are expressed. This helps explain why people with the same genotype — including identical twins — can still differ in behaviour, health, and psychological characteristics.

Part 3 — Evolution and Behaviour

Charles Darwin's theory of natural selection, first set out in On the Origin of Species (1859), provides the framework for understanding how behaviour evolves. The core principle is simple: individuals within a species vary in their traits, some of which are genetically determined. If a particular trait gives an individual a survival or reproductive advantage, that individual is more likely to live long enough to reproduce and pass the advantageous gene to offspring. Over many generations, the trait becomes increasingly common in the population.

Consider the classic example of the giraffe. Darwin argued that within ancestral giraffe populations, individuals varied in neck length. Those with slightly longer necks could reach food that shorter-necked rivals could not — a clear survival advantage. Longer-necked giraffes were more likely to survive, reproduce, and pass on their genes. Over millions of years, natural selection progressively favoured longer necks.

Psychologists are especially interested in the evolution of behaviour. If a behaviour has a genetic basis and provides a survival or reproductive advantage, natural selection can act on it just as it acts on physical traits. Several examples are relevant to AQA Psychology:

• Attachment — John Bowlby argued that infant attachment to a primary caregiver is an evolved, adaptive behaviour. Infants who form strong attachments are more likely to be protected, fed, and cared for, increasing their survival chances.
• Fight-or-flight response — The stress response evolved because it prepared early humans to respond quickly to threats, increasing survival in dangerous environments.
• Biological preparedness for phobias — Seligman (1971) proposed that humans are biologically prepared to fear stimuli that posed genuine threats to our ancestors, such as snakes, spiders, and heights. This preparedness would have conferred a survival advantage, explaining why these phobias are far more common than fears of modern dangers like cars or electrical sockets.

It is important to note that evolution operates over vast timescales. The behaviours that were adaptive for our ancestors may not always be adaptive in the modern world — the stress response, for example, evolved for immediate physical threats, but in modern life it is more often triggered by non-life-threatening situations such as exams or work pressure.

Evaluation Bank (AO3)

The following evaluation paragraphs are exam-ready. Each follows the PEEL structure (Point, Evidence, Explain, Link) and could be used directly in a 16-mark essay on the biological approach.

Strength: The biological approach has significant real-world application, particularly in the development of drug therapies for mental disorders. Increased understanding of neurochemical processes in the brain has led to the creation of psychoactive medications — for example, antidepressants such as SSRIs work by increasing levels of serotonin at synapses, and antipsychotics such as chlorpromazine reduce dopamine activity to manage symptoms of schizophrenia. These treatments have enabled many individuals to manage their conditions and live independently rather than requiring hospitalisation. However, the effectiveness of drug treatments is not universal — Cipriani et al. (2018), in a large-scale meta-analysis comparing 21 antidepressant drugs, found that while most were more effective than placebos, the overall effects were described as "mainly modest." This suggests that neurochemistry alone may not fully account for disorders like depression, and that the biological approach's practical contribution, while valuable, has clear limitations. This relates to the reductionism debate: reducing complex conditions to neurochemical imbalances may oversimplify disorders that also involve cognitive, social, and environmental factors.

Limitation: The biological approach is criticised for being biologically determinist — it suggests that behaviour is governed by internal biological forces (genes, neurochemistry, brain structures) over which the individual has no control. This has potentially troubling implications. If behaviour is entirely determined by biology, then individuals cannot be held morally responsible for their actions — a violent offender might claim their behaviour was caused by a "crime gene." The legal system, however, is built on the assumption that people exercise free will and are accountable for their choices. Furthermore, if genetic information about predispositions to conditions such as schizophrenia or criminal behaviour were made publicly available, individuals could face discrimination in employment or insurance. The genotype-phenotype distinction demonstrates that biological determinism is overly simplistic: identical twins share 100% of their genes yet do not show 100% concordance for any psychological characteristic, meaning environmental factors always play a mediating role. This connects to the free will versus determinism debate, suggesting that a strict biological determinist position underestimates the role of personal choice and environmental influence in shaping behaviour.

Limitation: A further limitation concerns the validity of twin studies, which are a key research method within the biological approach. The standard logic of twin studies assumes that if MZ twins show higher concordance rates than DZ twins, this difference must be due to their greater genetic similarity (100% versus approximately 50% shared genes). However, this reasoning relies on the equal environments assumption — the assumption that MZ and DZ twins experience equally similar environments. In practice, MZ twins are more likely to be treated similarly by parents, share the same friendship groups, and be exposed to comparable life experiences, precisely because they look alike and are often perceived as interchangeable. This means that higher concordance rates in MZ twins could be partly explained by their more similar environments rather than solely by genetic factors. This criticism does not mean that genes are irrelevant to behaviour, but it does suggest that twin studies may overestimate the genetic contribution. This relates to the nature-nurture debate: an interactionist approach, acknowledging that behaviour arises from the interaction between genes and the environment, provides a more complete account than a purely biological explanation.