The Biological Theory of Addiction (AQA GCSE Psychology)

• Biological explanations of addiction take the ‘nature’ side of the nature/nurture debate which assumes that human behaviour is the result of inherited traits
• A genetic explanation of addiction assumes that the genes a person inherits are responsible for their addiction (hereditary)
  • Variations or adaptations in some genes may affect the likelihood of someone becoming addicted to a substance i.e. there is no ‘one gene’ that codes for addiction
  • If someone inherits a combination of genes that make them more susceptible to addiction then - given certain conditions - addiction may follow
  • A genetic vulnerability increases a person’s risk of developing addiction as explained in the diathesis-stress model
• Twin studies have been used to determine the likelihood of one person developing an addiction to a substance if their twin is also addicted 
• As monozygotic (MZ) twins have identical DNA they are often used for research into genetic vulnerability
  • MZ twins are compared to dizygotic twins (DZ) who share 50% of their DNA to measure the extent to which particular traits/behaviours may be inherited
  • If there is a high concordance rate for the specific behaviour (e.g. addiction) between the MZ twins then this is used as evidence for a biological basis to behaviour

• Kaij (1960) was one of the first researchers to investigate whether the addiction of alcohol was the result of genes or environment (i.e. nature or nurture)
• The following study (the first of its kind to use twins to study addiction) is as follows:
• Aim: Is there a genetic vulnerability for alcoholism (alcohol addiction) i.e. is alcoholism inherited?
• Sample: 
  • 384 male twins who had been identified as having issues with alcohol (at least one of the twins was known to have alcoholism)
  • 48 of the twins were MZ; 126 of the twins were DZ

• Procedure: 
  • Interviews were conducted with the participants and with their close relatives by the Kaij to ascertain the following:
    • The twins’ drinking habits
    • Whether the twins were MZ or DZ (there was no way of testing the DNA in the 1960s to determine zygosity)

• Results: 61% of the MZ twins shared an addiction to alcohol; this dropped to 39% for the DZ twins
• Conclusion: Addiction to alcohol may be hereditary: a genetic vulnerability to alcohol may be triggered by social problems (the twins in the study with problematic social issues were more likely to have alcoholism)

Evaluation of Kaij’s twin study of alcohol abuse

Strengths

• Kaij’s findings have been supported by subsequent research in the field, for example:
• Heath (1995) conducted a systematic review of twin studies which had investigated alcoholism
• The evidence from the reviewed research suggested that alcoholism has a strong genetic component
• This finding (that there may be a genetic vulnerability to alcoholism) was consistent across many different research methods and studies
• The fact that this was the first study of its kind to identify alcoholism as potentially inherited takes away some of the stigma from the disease i.e. people do not necessarily ‘choose’ to become addicted to alcohol

Weaknesses

• The fact that the researchers could not be 100% sure of each twin pair’s zygosity means that not all of the MZ twins may have been identical i.e. they could have looked very similar but not have had identical DNA
• MZ twins share an environment as well as the same DNA which means that environment cannot be ruled out as a contributing factor to alcoholism which reduces the validity of the findings