Major Depressive Disorder (MDD) is characterized by persistent low mood, loss of interest in activities, significant changes in sleep and appetite, low energy, and feelings of worthlessness. These symptoms impair daily functioning and social/occupational performance.
Biological Approach – Genes:
The biological explanation emphasizes that genetic factors contribute to the etiology of MDD. Research in this area typically uses methods such as twin studies and gene–environment interaction studies to assess heritability and identify specific genetic influences (e.g., polymorphisms in the 5-HTT gene). Both the diathesis-stress model and heritability estimates indicate that while genetics play a significant role, environmental triggers are essential for the disorder’s manifestation.
Strengths:
Empirical Support:
Twin studies (Kendler et al., 2006) provide strong evidence for genetic influence, showing higher concordance rates for MDD in monozygotic twins.
Caspi et al. (2003) supports the diathesis-stress model, showing how genetic predisposition interacts with environmental stressors.
Biological Credibility:
Advances in neuroscience and genetics support the role of serotonin and genetic markers (e.g., 5-HTT gene) in depression.
Consistent findings across genetic and neurochemical studies strengthen the theory.
Limitations:
Reductionist:
Overemphasizes genetic influence while neglecting cognitive (negative thinking patterns) and sociocultural (life stress, trauma) factors.
MDD is complex and likely results from multiple interacting factors beyond genetics.
Lack of Predictive Power:
Genetic predisposition does not guarantee that someone will develop MDD.
The theory cannot explain why some individuals with high genetic risk never experience depression, highlighting the importance of environmental triggers.
