Explaining Addiction: Genes and Learning Theory
Explaining Addiction: Genes and Learning Theory
Why does one person become addicted to a substance while another person who tries the exact same drug does not? Edexcel’s specification sets out two competing explanations for addiction. The genetic explanation points to nature — the idea that addiction is inherited. Learning theory points to nurture — the idea that addiction is learned through the consequences of behaviour. Both explanations appear in extended exam answers, so you need to know their evidence, and their strengths and weaknesses, in detail.
The genetic explanation views addiction as inherited (nature). Learning theory views addiction as learned through reinforcement (nurture). Both explanations have strengths and weaknesses that can be evaluated using validity, reliability and objectivity.
The Genetic Explanation of Addiction
The genetic explanation argues that addiction sometimes runs in families because of inherited biological factors, not only because family members share a home and habits. Simply showing that addiction clusters in families is not strong evidence on its own, because families also share their environment. Psychologists therefore turn to twin studies for stronger evidence. They compare the concordance rate of identical (monozygotic, or MZ) twins, who share 100% of their genes, with the concordance rate of non-identical (dizygotic, or DZ) twins, who share only around 50% of their genes. If MZ twins are more often concordant for addiction than DZ twins, this is taken as evidence that genes contribute to addiction risk, because the two twin types differ in genetic similarity but are assumed to share similarly close environments.
Twin research on alcohol dependence has found that when one identical twin has a history of alcohol abuse, the other identical twin is more likely to also be affected than chance would predict, and more likely than for non-identical twin pairs. A higher concordance rate for MZ twins than for DZ twins is used as evidence that genetic vulnerability plays a part in addiction.
This evidence has limits. Twin studies are correlational, so they cannot prove that genes cause addiction. Identical twins may also share a more similar environment than non-identical twins — they are often treated more alike by parents, dress similarly and spend more time together — so some of the higher concordance could be explained by environment rather than genes alone.
Strength: twin studies showing higher concordance in MZ than DZ twins support a genetic contribution to addiction. Weakness: the explanation is deterministic, and twin studies cannot rule out the effect of a shared environment.
Learning Theory Explanation of Addiction
Learning theory explains addiction as a learned behaviour rather than an inherited trait. It draws on operant conditioning, developed by Skinner, which explains behaviour through its consequences: reinforcement makes a behaviour more likely to happen again, while punishment makes it less likely. According to this view, substance use continues because it is repeatedly reinforced — the immediate consequences of taking the substance make the behaviour more likely to be repeated, regardless of the long-term harm it causes.
Positive reinforcement occurs when the substance produces a pleasurable effect, such as the rush of pleasure from a drug stimulating the brain’s reward system. Because this feels rewarding, the person is more likely to use the substance again.
Negative reinforcement occurs when the substance removes an unpleasant state, such as withdrawal symptoms, stress or low mood. Because using the substance stops these unpleasant feelings, the person is more likely to use it again to avoid feeling that way. Many addictions are maintained by negative reinforcement long after the original pleasurable effects of a substance have faded.
A primary reinforcer is naturally rewarding, such as the direct physical effect a drug has on the brain and body. A secondary reinforcer becomes rewarding through learned association — for example, money to buy the substance, or the approval of a peer group who use it too.
Learning theory is useful because it explains why addictive behaviour can be so hard to stop: every time the substance removes an unpleasant feeling or produces a pleasant one, the behaviour is reinforced again. However, it struggles to explain individual differences — many people are exposed to the same reinforcing effects of a substance but do not go on to develop an addiction, which suggests other factors, such as genetic vulnerability, must also be involved.
Strength: learning theory explains why addictive behaviour is so persistent — it is repeatedly reinforced. Weakness: it cannot fully explain why some people exposed to the same reinforcement do not become addicted.
The Nature-Nurture Debate
Addiction is a good example of the nature-nurture debate in psychology. The genetic explanation sits on the nature side of the debate; learning theory sits on the nurture side. In reality, most psychologists now accept that genes and environment interact rather than working separately. A person might inherit a genetic vulnerability to addiction, but whether that vulnerability develops into an addiction can depend on their environment and the pattern of reinforcement they experience — for example, whether they are exposed to substances, and whether using them relieves stress or produces pleasure. When you answer exam questions on this debate, use evidence from both explanations and explain how they interact, rather than treating the question as if only one explanation can be correct.