Genetic inheritance
IB Psychology· Biological approach· 14 min read
1. Core concept
This concept asks how far behaviour is inherited. Researchers estimate heritability using twin studies (comparing identical vs fraternal twins), plus family and adoption studies. A heritability figure — say ~37% for depression — is a population estimate of how much of the variation is linked to genes, not a claim that an individual is 37% 'destined'. Genes set predispositions that then interact with the environment, and can be switched on and off by it (epigenetics).
2. Key studies
IB Psychology answers must be supported by named studies. Learn these to cite as evidence:
Sullivan, Neale & Kendler (2000)
Twin meta-analysis put the heritability of depression at about 37%. — Quantifies the genetic contribution — and, by leaving ~63%, the environmental one.
Kendler et al. (2006)
In Swedish twins, heritability of major depression was higher in women (42%) than men (29%). — Shows heritability is not a fixed constant — it varies by group.
3. Evaluation (AO3)
Strength — separates genes from environment — Twin and adoption designs let researchers estimate the genetic share of variation that ordinary family studies confound.
Limitation — the equal-environments assumption — Twin studies assume identical and fraternal twins share environments equally, which may inflate heritability; the figure is population-specific, not individual.
4. Scope
5. Common Pitfalls
Wrong move:
'Heritability of 37%' means 37% of my depression is genetic.
Why:
A frequently penalised misconception in IB Psychology exams.
Correct move:
Heritability describes variation across a population, not a proportion within one person, and it says nothing about how changeable the trait is.
Going deeper
- Diathesis–stress modelinherited predisposition is the diathesis in diathesis–stress (BIO_5).
- Biological reductionismreading a heritability figure as the whole cause is over-reduction (BIO_2).