# Biological reductionism

> IB Psychology · IB Psychology 2027 First Assessment
> Source: https://www.owlsprep.com/study/ib-psychology-bio-biological-reductionism/

The strengths and limitations of a reductionist approach to the study of behaviour.

## Learning objectives

- The strengths and limitations of a reductionist approach to the study of behaviour.

## Core concept

Biological reductionism explains a behaviour by breaking it down to its simplest biological parts — a gene, a neurotransmitter, a brain area — rather than the whole person in context. Its strength is that these parts can be isolated, measured and tested in controlled studies, giving clear cause–effect claims and biological treatments. Its limitation is that stripping away cognition, emotion and social context can oversimplify: a single gene or chemical rarely explains a complex behaviour on its own.

## Key studies

IB Psychology answers must be supported by named studies. Learn these to cite as evidence:

**Sullivan, Neale & Kendler (2000)** — Twin meta-analysis estimated the heritability of depression at about 37%. — *A reductionist-style single-factor estimate — and the ~63% it leaves to non-genetic factors is exactly where reducing to genes alone falls short.*

**Caspi et al. (2003)** — Depressive response to stressful life events depended on 5-HTT genotype; the gene alone did not predict depression. — *Shows why strong reductionism fails — the biological factor mattered only in interaction with the environment.*

## Evaluation (AO3)

**Strength — testable and useful** — Isolating one variable is how controlled science works, and it yields concrete biological treatments (e.g. drugs).

**Limitation — necessary but not sufficient** — A low-level cause is usually one part of the story; interactionist (gene × environment) models fit the data better.

## Scope

> **note**
>
> This is a conceptual/evaluative point applied across the approach. The specific gene, neurotransmitter and structure studies live in BIO_4, BIO_6, BIO_7, BIO_9.

## Common pitfalls

- **Wrong:** 'Reductionism' is a lazy or automatically bad explanation.
  - Why it fails: A frequently penalised misconception in IB Psychology exams.
  - Correct: Reductionism is a necessary step in controlled science (isolate one variable). The valid criticism is OVER-reduction — treating one part as the whole.

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