IB Psychology Biological Explanations Notes

Biological explanations attribute psychological disorders to genetic, neurochemical, and brain structural factors that interact with environmental stressors.

What are biological explanations?

1. Biological explanations propose that psychological disorders result from genetic inheritance, neurotransmitter imbalances, and brain structural or functional abnormalities.
2. Biological factors do not act alone; they interact with environmental stressors through the diathesis-stress model, which explains how genes and environment combine to produce disorder.

Genetic contributions

1. Genetic predisposition refers to inherited genetic variations that increase vulnerability to developing a disorder, though they do not guarantee its development.
2. Twin studies measure heritability by comparing concordance rates (the probability both twins develop the same disorder) between monozygotic (identical) and dizygotic (fraternal) twins.
3. Higher concordance in identical twins (who share 100% DNA) versus fraternal twins (who share 50%) suggests genetic influence.
4. For example, schizophrenia shows 45% concordance in identical twins versus 15% in fraternal twins, indicating substantial genetic influence.

Gottesman's twin research

1. Irving Gottesman (2001) reviewed twin studies across multiple disorders and calculated heritability estimates.
2. His findings: schizophrenia (83% heritability), bipolar disorder (80%), depression (38%), showing that different disorders have different genetic bases.
3. Even highly heritable disorders remain influenced by environment; heritability describes population variation, not individual causation.
4. Family studies show relatives of affected individuals have elevated risk even when raised apart, supporting genetic influence.

Neurochemical mechanisms

1. Neurotransmitters are chemical messengers that carry signals between neurons; imbalances correlate with many psychological disorders.