Recent studies have suggested that the Differential Susceptibility Hypothesis (DSH) is more consistent with current evidence than the Diathesis-Stress Model, which has dominated the views on the causes of psychological disorders for over 30 years.
What is Differential Susceptibility
Differential susceptibility to environmental influences summarizes the observations that some individuals are disproportionately more susceptible to both negative and positive environmental conditions. It explains why people react different to apparently same environment1.
Individuals with heightened susceptibility are more plastic or malleable. They are more sensitive to both adverse and beneficial experiences. This enhanced sensitivity to environmental influences can result in enduring developmental changes2.
Susceptibility to environmental influences is rooted in the biology of the nervous system. But besides neurobiology, experiences during the early years also play a role in determining individual differences in susceptibility3.
Diathesis Stress Model vs Differential Susceptibility Hypothesis
The Differential Susceptibility Hypothesis differs from the Dual-Risk Model in how some susceptible individuals are not just more vulnerable to negative conditions, but they are more plastic to both positive and negative environments.
Decades of research demonstrate that exposure to environmental adversity places children at elevated risk for developing cognitive, social, emotional, and health problems4.
However, it is still striking that some children would not develop psychological or physical disorders despite being exposed to high levels of adversities. The Diathesis-Stress Model, first proposed in the 1970s, serves to explain why some people are more vulnerable than others to the negative effects of adversity5.
In the Diathesis-Stress Model, children with ‘difficult’ temperaments, or who carry certain ‘risk alleles,’ are more likely to sustain maladaptive development when facing stressful life events. The interaction of their predisposition and environmental stress can result in psychological disorders such as depression or schizophrenia.
This is a dual-risk model because those with such vulnerability (first risk) are disproportionately or even exclusively likely to be affected negatively by environmental stressors (second risk). The stressors may be child maltreatment, insensitive parenting, or negative life events6.
In DSH, sensitive people are more susceptible to both positive and negative conditions, for better and for worse. Hence, the susceptible characteristics are not liabilities, but plasticity traits. Given a supportive and enriching environment, these people can reap the most benefit.
The Origin of Developmental Theories
In recent years, two different hypotheses have emerged on why there are variations in individual susceptibility to the environment.
The evolutionary perspective contends that both adverse and supportive environments have been part of human experience throughout our history, and that development and psychopathology shaped by natural selection respond adaptively to both kinds of contexts.
- Differential-Susceptibility Theory (DST) by Belsky
DST suggests that developmental plasticity is based on evolutionary biology and natural selection. If an effect of parenting is proven counterproductive, the less susceptible children will be less affected. On the other hand, if a parenting style is proven beneficial, the more malleable offspring will benefit more. The genetic variation allows the genes adaptable to the environment to pass on. This is why humans, unlike other animals, can adapt to drastically different climates all across the world7,8.
- Biological Sensitivity to Context Thesis (BSCT) by Boyce and Ellis
BSCT suggests that natural selection has favored developmental mechanisms that can detect specific features of the childhood environment and adjust levels of biological sensitivity to match the environment9.
While DST addresses the role of nature in natural selection, BSCT addresses the role of nurture as follows. These two theories converge on the fact that susceptibility to rearing influence is an evolutionary neurodevelopmental phenomenon in human development.
Stressful environments do not so much disturb child development as regulate it toward strategies that are adaptive under adverse conditions at that moment, even if those strategies will be harmful in terms of the long-term welfare of the individual or society as a whole in normal conditions. The adaptation “makes the best of a bad situation”10.
In positive environments, adjusting development to optimize reproductively relevant processes and behaviors such as growth, status, fertility, and offspring quality is emphasized.
Besides nature or nurture, another perspective of diverse plasticity is that the differential effects are in the gene environment interaction, denoted as GxE, e.g. Temperament x Parenting, Stress Reactivity x Family Stress, etc.
Differential Susceptibility to Parenting
Differential susceptibility hypothesis has shed immense light on why children react different to apparently same environment.
Researchers have identified several potential differential susceptibility factors, called plasticity markers. Here are some example of plasticity markers.
Every parent dreams of having a baby with easy temperament. These babies sleep better, eat better, tantrum less, and listen more. While having a difficult temperament predicts worse outcomes if the child is exposed to bad parenting11, it also predicts more positive outcomes if the child is raise with good parenting practice12.
A study found that highly impulsive children resulted in the least depressive symptoms when their mothers provided consistent discipline but the most when discipline proved highly inconsistent13.
This parenting–depression relation was the strongest for the most impulsive, weakest for those least impulsive, and intermediate for those in between.
Toddlers who are more prone to get angry are more likely to show behavior problems at age 5 if their parents used ineffective parenting practice. On the flip side, they are also less likely to show behavior problems if they had experienced effective parenting14.
Final Thoughts on Differential Susceptibility
It is tempting to say that the solution to differential susceptibility is to make your sensitive child more “hearty” or “tough“. But the discovery of neurobiologically susceptibility has provided a different perspective. While we cannot change our genetic makeup, we can make social environments safe and supportive for even the most sensitive people so that we can make the world better for our children and all people.
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