The biological approach: the influence of genes, biological structures and neurochemistry on behaviour. Genotype and phenotype, genetic basis of behaviour, evolution and behaviour.
The biological approach proposes that our behaviour and actions are determined by our genes and physiology. Specifically it focused on the roles of genetics, neurochemistry, brain structure and infection. Research methods within this approach often include laboratory studies (with physiological tests) and animal studies. Animals are often used in drugs testing and to determine genetic inheritance; for example mice breed very quickly, so multiple generations can be studied.
Besides animal studies, there are 3 main ways psychologists study the role of genes in behaviour.
- Family studies
- Adoption studies
- Twin studies
The prevalence rates of a trait or disorder within a family can be compared to the genetic similarity between relatives. If a trait/disorder has a genetic basis, then we would expect closer relatives to be more similar in terms of the trait than distant relatives. The main problem with such data is that close relatives are more likely to share the same environment though (nurture), so any similarities may not be solely due to genes (nature).
Adoption studies are useful in studying whether nature (genes) or nurture (environment) are more important in determining certain behaviours or traits. If a child has been adopted, then we can see if they show more similarities to their adopted parents (nurture) or biological parents (nature). Adoption studies have shown that both schizophrenia and IQ have strong genetic elements, as adopted children are more similar to their biological, rather than adopted, parents in both cases.
Twin studies are the most common way to study genetic influences. Monozygotic (identical) and dizygotic (non-identical) twins are compared. MZ twins share 100% of their genetics and DZ twins share 50% of their genetics. Both types of twin are likely to have been raised in shared environments, however, so the only (hypothetical) difference between them is their 50% genetics. If a disorder/trait is purely genetic we would expect MZ twins to have a concordance rate of 100% and DZ to have a concordance rate of 50% (if we only looked at concordance rates for MZ twins, any similarities may be due to their shared environment; thus comparing concordance rates to DZ twins is critical to determine genetic influence).
Neurotransmitter transmit messages between the synapses in your brain. Imbalances in these levels of neurotransmitters can affect your mood, behaviour and even lead to symptoms of mental disorders. Whilst neurotransmitters have complex interactions with one another, some are seen to have main roles in the brain. For example:
It is difficult to study neurotransmitter levels in live patients, so autopsies are usually conducted after death. One way is to use brain activity scans (i.e. PET scans or fMRI), although these only show activity levels in parts of the brain over time; not the total levels. Another way is via lumbar puncture (ouch!). Metabolite levels (waste products from the breakdown of neurotransmitters) can give an indirect measure of neurotransmitter levels.