Diathesis-Stress Model in Human Development
Diathesis-Stress Model in Human Development
The diathesis-stress model has particular relevance to human development, where it helps explain why individuals with similar genetic or biological backgrounds develop along different psychological trajectories depending on their developmental environments.
In a developmental context, diatheses may include genetic vulnerabilities inherited at conception, prenatal exposures (e.g., maternal stress, alcohol, or infections), temperamental factors such as high emotional reactivity or low impulse control, or early attachment experiences. These vulnerabilities do not produce disorders on their own. It is the interaction with stressful developmental environments — including childhood adversity, trauma, family dysfunction, or peer victimisation — that translates vulnerability into disorder.
Real-World Application: Case Example
Real-World Application: Case Example
Imagine two children raised in the same household, both with a family history of depression. The first child faces peer rejection at school (a stressor) and develops clinical depression by age 14. The second child, whose social environment remained supportive, develops no disorder. The diathesis-stress model explains this clearly: the diathesis was present in both children, but only the first encountered a significant stressor. Genetic risk alone is not sufficient — disorder emerges when vulnerability and stress combine.
The Vulnerability Threshold
The Vulnerability Threshold
A key concept within this model is the idea of a threshold — the level of stress required to activate a given vulnerability. Individuals with high biological sensitivity (such as a highly reactive temperament) have a lower threshold, meaning even relatively minor stressors can trigger a disorder. Those with lower biological sensitivity require considerably more stress before a disorder emerges.
Crucially, this threshold is not fixed. Early positive experiences — such as secure attachment, consistent caregiving, or a supportive school environment — can raise the threshold over time, building resilience. This is one of the strongest arguments for early intervention: it does not change a child’s genetic makeup, but it can meaningfully reduce the chance that their vulnerability is ever activated.
Belsky's Differential Susceptibility
Belsky’s Differential Susceptibility
The traditional diathesis-stress model focuses primarily on negative outcomes, treating biological sensitivity as a liability. Belsky’s differential susceptibility hypothesis challenges this by arguing that sensitivity is essentially neutral — it amplifies both bad and good environmental effects.
Evidence for this comes from research on the serotonin transporter gene (5-HTT). Caspi et al. (2003) found that individuals carrying the short allele of this gene were more likely to develop depression following stressful life events. Critically, follow-up research found that these same individuals, when placed in nurturing, low-stress environments, showed better mental health outcomes than those without the short allele. The gene did not predispose them to depression — it made them more responsive to their environment in general.
The practical implication for child development is significant: highly sensitive children should not be viewed as inherently “at risk,” but as “high-responders” who stand to gain the most from positive environments and the most to lose from negative ones. This reframing has real consequences for how parents, teachers, and clinicians approach sensitive children.
Epigenetic Mechanisms
Epigenetic Mechanisms
Epigenetics adds a biological layer to the diathesis-stress model by explaining precisely how environmental stress becomes physically embedded in the body. Three mechanisms are worth understanding:
- DNA methylation: the most studied epigenetic process. When a stressful experience occurs — such as childhood abuse or chronic neglect — methyl groups attach to certain gene promoter regions, effectively silencing those genes. Research has shown that abuse survivors show methylation of glucocorticoid receptor genes, which regulate the body’s stress response via the HPA axis (hypothalamic-pituitary-adrenal axis).
- Histone modification: DNA is wound around proteins called histones. Stress can alter how tightly the DNA is wound — tighter winding silences gene expression, looser winding activates it. Like methylation, these modifications can persist long after the original stressor has passed.
- Transgenerational epigenetics: studies on the descendants of Holocaust survivors and populations who experienced severe famine suggest that some epigenetic modifications may be passed to the next generation. This remains an active area of research and is more firmly established in animal models than in humans.
For evaluation purposes, students should note that while epigenetic research is compelling, establishing direct causal links in humans is methodologically difficult. Many key findings come from rodent studies, and the degree to which human epigenetic modifications are reversible or heritable remains an open question.
Practice Question
Question 3.3 — Structured Analysis
“Arjun grew up in a household with a history of anxiety disorders. As a child he was described as highly emotionally reactive. At age 12, his family relocated internationally, and he struggled to adapt to his new school environment, where cultural expectations and social norms were very different from those he had grown up with. By age 15, he had developed significant generalised anxiety and social withdrawal. His younger sister, raised in the same household but who did not relocate, shows no signs of anxiety disorder.”
(a) Using the diathesis-stress model, explain why Arjun developed an anxiety disorder while his sister did not.
(b) Identify one epigenetic mechanism that could explain how Arjun’s early stressors may have become embedded in his biology.
(c) Belsky’s differential susceptibility hypothesis offers an alternative interpretation of Arjun’s situation. Outline what this hypothesis would predict about Arjun in a different developmental environment. [4 marks]