IB DP Psychology Core: The Biological Approach to Understanding Behaviour

Course note (legacy syllabus): This resource describes IB DP Psychology for first assessment 2019, now in its final teaching cycle (last examination session November 2026). A replacement course (first assessment 2027) reworks the approaches into content areas applied across four contexts, integrated with six named concepts – a rescoping this file has not undergone. A companion resource for the 2027 course does not yet exist on this site.

This guide covers the Biological Approach to Understanding Behaviour, one of three compulsory core approaches for IB Diploma Programme Psychology, first assessment 2019. The full syllabus guide confirms all three core approaches — biological, cognitive, sociocultural — are compulsory for every DP Psychology student, tested on Paper 1.

Where this fits in the syllabus

The syllabus deliberately revisits shared topics across more than one approach: memory, for example, can be examined biologically (through brain structures such as the hippocampus), cognitively (through information-processing models), and socioculturally (through the influence of schema and culture on recall). Revising the biological approach in complete isolation from the cognitive and sociocultural approaches misses this deliberate overlap — for any topic studied biologically, check whether it also appears under the other two approaches, and be able to compare what each approach adds.

Syllabus coverage

IB DP PSYCHOLOGY — CORE: BIOLOGICAL APPROACH TO UNDERSTANDING BEHAVIOUR

The IB Psychology guide (first assessment 2019) sets out the biological approach as four topics, and this resource is organised under the guide’s own headings:

• The relationship between the brain and behaviour (SL and HL) — how brain structures and neural processes contribute to behaviour, for example the role of specific brain regions in memory, emotion or decision-making, studied using techniques such as brain imaging. This resource also revises neurotransmitters here, as the chemical messengers that carry signals between neurons.
• Hormones and pheromones and their effects on behaviour (SL and HL) — hormones are chemical messengers released by endocrine glands into the bloodstream that act on target cells elsewhere in the body; pheromones are chemical signals released by one individual that affect the behaviour or physiology of another member of the same species.
• The relationship between genetics and behaviour (SL and HL) — how inherited factors contribute to behaviour, including twin and adoption studies used to separate genetic from environmental influence.
• The role of animal research in understanding human behaviour (HL only) — why researchers study animals to understand human behaviour, and how far such findings can be applied to humans.

The guide also names the contribution of research methods used in the biological approach as relevant to all of these topics. Underlying all four is the assumption that behaviour and mental processes can be at least partly explained by biological structures and processes, without the approach claiming to be a complete explanation on its own.

How to approach it

The relationship between the brain and behaviour

Be able to name at least one specific brain structure or system relevant to a behaviour studied, and describe the evidence (often from a named study) linking that structure to that behaviour, rather than describing brain function in general terms only. A well-established example: Maguire et al. (2000) used structural MRI to compare the hippocampi of licensed London taxi drivers, who must memorise the city’s complex street layout, with non-taxi-driving controls. Taxi drivers had significantly larger posterior hippocampal volume, and hippocampal volume correlated with years spent driving a taxi, supporting the hippocampus’s role in spatial memory and demonstrating neuroplasticity (structural brain change in response to experience). Evaluative point: the design is correlational (drivers were not randomly assigned to their profession), so it cannot fully rule out that people with naturally larger posterior hippocampi are more likely to become, and remain, taxi drivers, rather than the driving experience alone causing the enlargement. For neurotransmitters, revise each explanation as a two-part claim — what the chemical does physiologically, and what specific behaviour that mechanism is proposed to explain — rather than naming a neurotransmitter as an isolated fact.

Hormones and pheromones and their effects on behaviour

Revise hormones with the same two-part structure: what the hormone does in the body, and which behaviour it is proposed to influence. Cortisol, for example, is released by the adrenal glands as part of the body’s response to stress, which makes it a natural starting point for explaining stress-related behaviour; oxytocin and testosterone are other hormones widely studied in relation to social behaviour. Keep the two terms distinct: a hormone acts within the body that produced it, while a pheromone acts between individuals of the same species. Pheromones are well established in other animals (the first to be chemically identified was bombykol, the sex attractant of the female silkworm moth), but whether humans produce pheromones that affect behaviour is contested: candidate chemicals such as androstadienone have been studied, yet no human pheromone has been conclusively identified. That uncertainty is itself an evaluative point — be ready to explain why human pheromone research is hard to interpret: human behaviour is also shaped by cognitive and social factors, and it is difficult to show that a single chemical, rather than expectation or context, produced an effect.

The relationship between genetics and behaviour

Understand the logic of twin and adoption study designs specifically: twin studies compare concordance rates between identical (monozygotic) and non-identical (dizygotic) twins to estimate a genetic contribution, while adoption studies compare adopted individuals to both their biological and adoptive relatives to help separate genetic from environmental influence — explaining why these designs are used, not just that they exist, is what distinguishes a strong evaluative answer from a descriptive one.

The role of animal research in understanding human behaviour (HL only)

Researchers study animals when a procedure would be unethical or impractical in humans (for example, directly manipulating brain structures, hormone levels or genes), when they need close control over genes and environment, or when a species’ short lifespan lets effects be observed across generations. Revise both sides of the question this topic poses. On the side of its value: animal studies allow controlled experimental tests that human research often cannot, and many biological systems, such as neurotransmitter and hormone systems, are shared across mammals. On the side of its limits: findings may not generalise to humans because of species differences, especially for behaviour shaped by human cognition and culture, and the research raises ethical questions about harm to animals — many research frameworks apply the “3Rs” principle (replacement, reduction and refinement) when judging whether animal research is justified. For any animal study you use, be ready to argue how far it contributes to understanding human behaviour, not just what it found in animals.

Across all the topics

Paper 1’s essay question specifically rewards evaluation, not just accurate description of what a study found, so for every biological study or theory learned, build the habit of recording at least one genuine strength and one genuine limitation.

Worked example: building a two-part biological explanation

A question asks about the role of a neurotransmitter in a named behaviour. The strong answer below draws on two topics at once: brain chemistry (revised in this resource under brain and behaviour) and a gene-environment interaction (genetics and behaviour).

Weak (fact only):     "Low serotonin levels are linked to
                       depression."

Strong (mechanism +   "Serotonin is a neurotransmitter involved in
behaviour, evaluated): regulating mood; Caspi et al. (2003) found
                       that individuals with one or two copies of a
                       "short" variant of the 5-HTT gene (which
                       affects serotonin transporter activity) were
                       more likely to develop depression, but only
                       when they had also experienced stressful life
                       events -- a gene-environment (diathesis-stress)
                       interaction rather than the gene or serotonin
                       activity alone causing depression. This
                       finding is itself contested: several later,
                       larger studies and meta-analyses (e.g. Risch et
                       al., 2009) failed to replicate the same
                       interaction, so it should be presented as an
                       influential but disputed finding, not settled
                       fact."

The strong version states the mechanism, links it explicitly to the named behaviour, cites named evidence, and evaluates that evidence’s limitations (a gene-environment interaction rather than a simple cause, and a contested replication record) — this is the structure Paper 1’s essay question rewards over a single unevaluated fact.

Connecting to the internal assessment

Approaches to researching behaviour, taught alongside all three core approaches, is directly relevant to your own experimental study write-up. Many biological-approach studies use experimental or quasi-experimental designs (as opposed to purely qualitative sociocultural research), so understanding how biological psychologists justify their experimental designs and address ethical considerations – such as informed consent for physiological measures, or managing the invasiveness of a procedure like a brain scan – is useful preparation that pays off directly in your own IA write-up, not just in exam answers about published studies. A student who can explain why a biological researcher chose a particular experimental control, or how they addressed a specific ethical concern, is demonstrating exactly the kind of methodological reasoning the IA rewards.

Common mistakes

Naming a neurotransmitter, hormone, brain structure, or genetic study design without explaining the specific mechanism or behaviour it is meant to explain. Describing a study’s finding without evaluating it — stating a genuine strength and limitation is expected, not optional, for Paper 1’s essay question. Treating the biological approach as a complete, standalone explanation rather than one of three complementary lenses the syllabus expects to be compared against the cognitive and sociocultural approaches. Revising twin and adoption studies as facts to recall rather than understanding the logic of why each design helps separate genetic from environmental influence. Confusing hormones (which act within the body that produced them) with pheromones (which act between members of the same species), or presenting effects of human pheromones as settled. At HL, describing an animal study without discussing how far its findings can be applied to human behaviour.

Quick revision checklist

• For each biological study or theory, record at least one named strength and one named limitation.
• Know the guide’s four topic headings: brain and behaviour, hormones and pheromones, and genetics and behaviour (SL and HL), plus the role of animal research in understanding human behaviour (HL only).
• Practise the two-part explanation structure for neurotransmitters and hormones: chemical mechanism, then the specific behaviour it explains.
• Be able to explain the difference between a hormone and a pheromone, and why evidence for human pheromones is contested.
• HL: prepare an argument on how far animal research contributes to understanding human behaviour, including generalisation and ethics.
• Understand why twin and adoption study designs are used, not just that they exist.
• For any topic studied biologically, check whether it also appears under the cognitive or sociocultural approach, and prepare a comparison.
• Connect biological-approach research design and ethics (such as informed consent for physiological measures) to your own internal assessment write-up.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief – Individuals and Societies: Psychology, first assessment 2019, © 2018 – the same source already cited by the full syllabus guide, which first identified the biological approach as one of the three compulsory core approaches. Verified 2026-09-06. The four topic headings above were checked against the IB Psychology guide (first assessment 2019), p. 23, on 2026-09-16.