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Addiction » Genetic Explanation of Addiction

What you'll learn this session

Study time: 30 minutes

AQA spec: 3.2.4.7

The biological explanation of addiction: hereditary factors and genetic vulnerability
Why genes make addiction more likely but do not cause it on their own
How family, twin and adoption studies test the role of genes, including concordance
Strengths and weaknesses of the explanation, and why it is reductionist

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Does addiction run in families?

Some people can drink alcohol or try a drug and walk away. Others get hooked. Why? One answer comes from the biological explanation, which is about the influence of nature: the idea that our biology, especially the genes we inherit from our parents, affects how we behave.

Doctors and researchers have noticed that addiction often seems to run in families. A child with a parent or a brother or sister who is addicted is more likely to have a problem themselves than a child with no addicted relatives. This is the starting point for the genetic explanation.

Key terms:

Hereditary factors: features that are passed down from parents to children through genes.
Genes: the instructions in our cells that we inherit from our parents. They help to shape our body and brain.
Genetic vulnerability: inheriting genes that make a person more likely to develop a problem. It is a higher risk, not a certainty.
Identical twins: twins who share all (100%) of their genes.
Non-identical twins: twins who share about half (50%) of their genes, the same as any brother or sister.
Concordance: how often both twins in a pair have the same condition. High concordance means they are alike.

The genetic explanation

🧬 Hereditary factors

Genes are passed from parents to children. The explanation says that a person can inherit genes that make addiction more likely, which would help to explain why it runs in families.

💊 Genetic vulnerability

Genes may make some people more vulnerable. For example, genes might change how a substance affects a person's body and brain, so that one person feels more reward from it, or finds it harder to stop, than another person.

Key point

There is no single gene that makes someone an addict. Genes make addiction more likely. They do not decide it. Many people with a family history of addiction never become addicted, and many people with no family history do.

How do psychologists test it?

It is hard to separate genes from upbringing, because family members share both. So psychologists use three kinds of study to try to tell them apart.

👪 Family studies

Researchers check whether addiction is more common in the relatives of someone who is addicted. If it is, genes may play a part. But relatives also share a home, so this cannot prove it is genes.

👥 Twin studies

Researchers compare identical twins with non-identical twins. Identical twins share all their genes. Non-identical twins share about half. Both types usually grow up together, so they share a similar environment.

👶 Adoption studies

Researchers look at children who were adopted. They ask whether the child is more like their biological parents (who gave them their genes) or their adoptive parents (who gave them their upbringing).

Reading twin studies

Twin studies use concordance. Suppose one twin is addicted. The researcher asks: is the other twin addicted too?

If identical twins are more concordant than non-identical twins, this supports a genetic explanation. The big difference between the two types is how many genes they share.
If both types are equally concordant, genes are probably not the main cause.

In adoption studies, if adopted children are more like their biological parents than their adoptive parents, this also supports genes. The next lesson looks at one named twin study of alcohol abuse in detail.

Worked example: reading some made-up results

A researcher studies 50 pairs of identical twins and 50 pairs of non-identical twins. In each pair, one twin has an alcohol problem. In 30 of the identical pairs the other twin also has a problem. In 15 of the non-identical pairs the other twin also has a problem.

Reasoning:

Identical concordance: 30 out of 50, which is 60%.
Non-identical concordance: 15 out of 50, which is 30%.
Identical twins are more alike. Since they share more genes, this supports the idea that genes play a part.
It is not 100%, so genes cannot be the whole story. Some identical twins are not alike.

Evaluating the genetic explanation

✅ Strengths

Family, twin and adoption studies all point to a hereditary link, so there is evidence from more than one kind of study.
It explains why addiction runs in families and why some people are more at risk than others.
It can help to show who may be more at risk.

❌ Weaknesses

Concordance in identical twins is not 100%, so genes are not the only cause. Environment must matter too.
Twins and families share an environment as well as genes, so it is hard to be sure which one caused the addiction.

Reductionism

Reductionist, as in Biological Explanation of Depression: it explains addiction by genes alone and ignores other things such as stress and how easy a substance is to get. A more complete view says addiction comes from nature and nurture together.

Common mistakes

Saying genes cause addiction. Genes only make a person more vulnerable.
Writing "there is an addiction gene". The idea is that inherited genes raise the risk.
Mixing up identical twins (100% of genes shared) and non-identical twins (about 50%).
Forgetting that concordance means how alike the twins are, not how many twins there are.
Saying the explanation is wrong because identical twins are not 100% concordant. This shows genes are not the only factor, which is a limit rather than a failure.

Exam-style question

Dan is 17 and has an alcohol problem. His father also has an alcohol problem.

(a) Explain how the biological explanation could account for Dan's alcohol problem. [2 marks]

(b) A twin study found that identical twins were more concordant for addiction than non-identical twins. Explain what this suggests about addiction. [2 marks]

Model answer

(a) Dan may have inherited genes from his father that make him more vulnerable to alcohol (1), for example genes that affect how alcohol acts on his body and brain, which made addiction more likely (1).

(b) Identical twins share all of their genes, but non-identical twins share only about half (1), so if identical twins are more alike, it suggests that genes play a part in addiction (1).

(c) Identical twins are not 100% concordant (1), so genes cannot be the only cause, and the explanation is reductionist because it ignores the influence of the environment (1). Any other valid weakness is accepted, for example that twins share an environment as well as genes.

Exam tip

For a 2-mark explain question, make a point and then add a reason or link. In (a), name "genes" or "vulnerability" first, then link it to Dan and his father.

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