Assumptions of the biological approach

The biological approach in psychology focuses on how physical and biological factors influence behaviour and mental processes. It assumes that these factors provide a comprehensive explanation for human actions.

Core assumptions

• Biological factors as explanations - Behaviour results from elements like hormones, genetics, evolution, and the nervous system.
• Potential for biological treatments - If all behaviour stems from biological causes, undesirable behaviours could be altered or eliminated through interventions such as drugs for mental disorders.
• Animal research applicability - Studies on animals can reveal insights into human behaviour due to shared biological features.

Basic genetic knowledge and evolutionary concepts

Genetics play a fundamental role in shaping both physical characteristics and behaviour, starting from the moment of conception. Evolutionary theory further explains how certain behaviours have developed over time to aid survival.

Fundamentals of genetics

• At fertilisation, the combination of egg and sperm results in 46 chromosomes.
• Chromosomes consist of DNA, which contains numerous genes.
• Genes determine unique physical traits, such as hair, skin, and eye colour.
• Genes contribute to brain development, influencing behaviour patterns.

Principles of evolution

• According to Darwin's theory, individuals with genes that enhance adaptation to their surroundings are more likely to survive, reproduce, and transmit those genes.
• Less adaptive individuals have a lower chance of passing on their genes.
• Natural selection gradually removes less beneficial genes from a species' gene pool.
• Early humans evolved adaptations that improved survival in their environments.
• Behaviours like fearing dangerous predators or exhibiting defensive reactions likely evolved due to the survival benefits they provided.

Key genetic terminology

Important genetic terms

• Genotype - Refers to an individual's specific set of genes.
• Phenotype - Describes the observable characteristics produced by those genes, such as hair or eye colour.
• Heritability - Measures the extent to which genetic factors explain variations in traits, scored from 0 (no genetic influence) to 1 (entirely genetic). For instance, major depressive disorder has a heritability estimate of around 0.3 to 0.5.

Genetics and psychological traits

Biological psychologists explore how genetics underpin various psychological aspects, using specific research methods to investigate these links.

Role of genetics in traits and disorders

• Certain defective genes cause conditions with psychological impacts, such as Huntington's disease, which leads to cognitive decline.
• Genetics may explain psychological traits including gender-related behaviours, intelligence, personality, and sexual orientation.
• Research examines genes that increase susceptibility to mental disorders or addictions.
• Twin studies and adoption studies help disentangle genetic from environmental influences.

Genetic basis of schizophrenia

Schizophrenia is a severe mental disorder characterised by distorted thinking and perceptions. Research suggests a genetic component, evidenced by studies comparing relatives with varying genetic similarities.

Types of twins in genetic research

• Identical twins (monozygotic) share all their genes, so if schizophrenia were purely genetic, both would always develop it if one does.
• Non-identical twins (dizygotic) share half their genes, so concordance rates should be lower.

Gottesman (1991) - A meta-analysis of twin studies

• Method - Analysed data from approximately 40 twin studies on schizophrenia.
• Results - Identical twins showed about a 48% concordance rate for schizophrenia, compared to about 17% for non-identical twins.
• Conclusion - These findings indicate a substantial genetic influence on schizophrenia.
• Evaluation:
  • The studies analysed were conducted in real-world settings, enhancing ecological validity.
  • However, since identical twins only showed concordance in about half the cases despite sharing all genes, environmental factors must also contribute.
  • Additionally, identical twins often experience more similar upbringings than non-identical twins, which could confound genetic interpretations.

Heston (1966) - An adoption study of schizophrenia

• Method - Examined 47 adoptees whose birth mothers had schizophrenia, compared to a control group of 50 adoptees whose birth mothers did not. Participants were assessed in adulthood via interviews, intelligence tests, and personality assessments.
• Results - In the experimental group, 5 out of 47 developed schizophrenia, and 4 showed borderline symptoms; none in the control group developed the disorder.
• Conclusion - The higher incidence in the experimental group supports a genetic link to schizophrenia.
• Evaluation - Interviews may be prone to biases like social desirability, but they capture natural behaviours effectively. A limitation is that control group participants might develop symptoms later in life, as schizophrenia can emerge at varying ages.