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Genetic explanations of depression and addiction
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Do mental health problems run in families? Genetic explanations say some people inherit a greater risk.
Genes and depression
Family and twin studies: depression is more common in close relatives of people with depression. Identical (MZ) twins share all their genes and are more likely to both have depression than non-identical (DZ) twins.
The 5-HTT gene: this gene affects how serotonin, a neurotransmitter linked to mood, is transported in the brain. People with one or two short versions (alleles) of the gene may have less efficient serotonin activity.
Caspi et al. (2003) found people with short alleles were more likely to become depressed after stressful life events.
The 5-HTT gene: this gene affects how serotonin, a neurotransmitter linked to mood, is transported in the brain. People with one or two short versions (alleles) of the gene may have less efficient serotonin activity.
Caspi et al. (2003) found people with short alleles were more likely to become depressed after stressful life events.
Genes and addiction
Twin and adoption studies suggest addiction risk is partly inherited, as MZ twins are more similar than DZ twins.
The DRD2 gene: affects dopamine receptors, part of the brain's reward system. One version of this gene has been linked to alcohol addiction. People with fewer dopamine receptors may get less pleasure from everyday rewards and seek out substances that give a stronger reward.
Genes may explain why only some people who try a drug become addicted.
The DRD2 gene: affects dopamine receptors, part of the brain's reward system. One version of this gene has been linked to alcohol addiction. People with fewer dopamine receptors may get less pleasure from everyday rewards and seek out substances that give a stronger reward.
Genes may explain why only some people who try a drug become addicted.
Strengths and weaknesses
Strengths: supported by research evidence, such as twin studies and Caspi et al. It can explain why some people are more vulnerable than others. It is scientific, using biological evidence.
Weaknesses: MZ twins do not always both develop the problem, so genes cannot be the whole explanation; environment matters too. Genes seem to raise risk rather than cause a problem directly (a diathesis-stress view: a vulnerability plus a stressful trigger). It can be deterministic, suggesting people have no control, and it does not directly provide a treatment.
Weaknesses: MZ twins do not always both develop the problem, so genes cannot be the whole explanation; environment matters too. Genes seem to raise risk rather than cause a problem directly (a diathesis-stress view: a vulnerability plus a stressful trigger). It can be deterministic, suggesting people have no control, and it does not directly provide a treatment.
If depression were caused only by genes, what would we expect in identical twins? What do studies actually show?
- Identical twins share 100% of their genes.
- If only genes mattered, both twins would always have depression if one did.
- Studies show this is not always the case.
Answer: We would expect 100% concordance, but studies show it is lower, so environment also plays a part.
Genetic explanations say people inherit risk. For depression, twin studies and the 5-HTT gene (short alleles) are evidence; for addiction, twin studies and the DRD2 dopamine gene. Genes cannot be the whole story, because identical twins are not always both affected.
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