Differential susceptibility to the environment.

Ellis, B. J., Boyce, W. T., Belsky, J., Bakermans-Kranenburg, M. J., & Van Ijzendoorn, M. H. (2011). Differential susceptibility to the environment: An evolutionary- neurodevelopmental theory. Development and Psychopathology, 23(1), 7–28. https://doi.org/10.1017/S0954579410000611

Summary

Ellis et al. (2011) proposed an evolutionary-neurodevelopmental theory of variations in adaptive development (based upon evolutionary models), which differed from the dominant “Diathesis-Stress/Dual Risk” paradigm of adaptation.

The authors proposed 7 defining characteristics of individual differences in susceptibility to the environment:

1. Increased sensitivity to both negative and positive environments.
2. Increased likelihood for persistent change in development in reaction to the environment.
3. Neurobiological basis for differential susceptibility.
4. Prior developmental experiences interact with heritable polygenic variations to determine neurobiological susceptibility.
5. Neurobiological susceptibility may vary across the life span.
6. Neurobiological susceptibility are evolutionarily adaptive interactions with historical, social and physical contexts across time.
7. Different patterns of human development across time are regulated and facilitated through variations in Neurobiological susceptibility to the environment.

Diathesis-Stress/Dual Risk paradigm of adaptation: variations in personal characteristics contribute most towards environmental conditions. This led to the focus on studying the absence and presence of negative environments instead of investigating all ranges of environments to form a more complete understanding of adaptation.

Evolutionary Models of Adaptive Development: natural selection over time shaped development to respond adaptively to all types of contexts – stressful and supportive, termed conditional adaptation. Such models assert that environments (positive and negative) interact with individual neurobiological systems to “direct or regulate it (people) towards strategies that are adaptive under stressful conditions, even if those strategies are currently harmful in terms of long-term welfare of the individual or society as a whole.” (p. 8)

Implications of adopting an evolutionary model:

1. Behaviors are understood within contexts.
2. Focus on how individuals respond as context changes.

Background :

Ellis et al. (2011) presented two recent theories: Biological Sensitivity to Context Theory (BSCT) and the Differential Susceptibility Theory (DST).

Both theories are based on evolutionary perspective, focus on individual and environmental interactions, individual characteristics that are neurobiologically based, moderate both stressful and supportive environmental conditions. Both models define change experienced by susceptible individuals to be more enduring. It is not clear how neurobiological susceptibility interacts over time.

The models differ in predictions on “development and distributions of susceptible phenotypes across ecological and social contexts” (p.17). BSCT predicts increase survival under dangerous environments through conditional adaptation, while DST predicts genetic survival through unpredictable future environments through offspring diversity (bet-hedging) which ensures different phenotypes have different optimal adaptation conditions.

BSCT (Boyce & Ellis, 2005): evolution has maintained developmental variations in biological sensitivity to context through natural selection.

1) “Stress response” systems are dual function(central neural and peripheral neuroendocrine responses to survival) and should be conceptualized as “biological sensitivity to context” (p.11).

2) Biological stress response variations within individuals regulate responses to environmental influences ranging from harmful to protective.

3) Relationship between levels of early support and biological response dispositions is hypothesized to be a U-shaped linear curve. Early extreme environments increase biological sensitivity and reactivity to context.

DST (Belsky, 1997): focused on within-family variations in susceptibility of siblings to the parenting environment. Differential susceptibility to environments is evolutionarily advantageous due to future uncertainty.

DST supports or explains the following data:

1) Modest impacts on the environment within families.

2) Across studies data show variable effects of rearing environments that are modest (masking effect between high and low susceptible individuals within and across studies.