Why and how does early adversity influence development? Toward an integrated model of dimensions of environmental experience

Abstract

Two extant frameworks – the harshness-unpredictability model and the threat-deprivation model – attempt to explain which dimensions of adversity have distinct influences on development. These models address, respectively, why, based on a history of natural selection, development operates the way it does across a range of environmental contexts, and how the neural mechanisms that underlie plasticity and learning in response to environmental experiences influence brain development. Building on these frameworks, we advance an integrated model of dimensions of environmental experience, focusing on threat-based forms of harshness, deprivation-based forms of harshness, and environmental unpredictability. This integrated model makes clear that the why and the how of development are inextricable and, together, essential to understanding which dimensions of the environment matter. Core integrative concepts include the directedness of learning, multiple levels of developmental adaptation to the environment, and tradeoffs between adaptive and maladaptive developmental responses to adversity. The integrated model proposes that proximal and distal cues to threat-based and deprivation-based forms of harshness, as well as unpredictability in those cues, calibrate development to both immediate rearing environments and broader ecological contexts, current and future. We highlight actionable directions for research needed to investigate the integrated model and advance understanding of dimensions of environmental experience.

Testing the empirical integration of threat-deprivation and harshness-unpredictability dimensional models of adversity

“…Important to appreciate is that the slow life history may also be induced by conditions of resource scarcity, that is, deprivation (Ellis et al, 2022). When energetic resources (e.g., nutrition) are limited, the developing organism privileges survival and maintenance rather than development, according to life history theory.…”

“…This should result in slower growth, smaller body size, later sexual maturation and constrained reproductive potential (Ellis et al, 2009). Related to the threat-deprivation model is the fact that conservation of energetic resources may come at a cost of neurobiological complexity and maintenance of physical fitness (Ellis et al, 2022).…”

“…At the same time, it reveals no evidence of irrevocable contradictions that would preclude their integration. (For more extensive discussion of the models and this point, see Ellis et al, 2022).…”

“…Environmental harshness represents external conditions associated with increased risk of morbidity and mortality, which may be conveyed via cues of resource scarcity, conspecific violence, and population-level epidemiological indicators of risk to safety and survival that evolution has sensitized the developing individual to detect (e.g., crime rate; Brumbach et al, 2009;Ellis et al, 2009). To this extent, dimensions of deprivation and threat identified under the harshness-unpredictability framework map on to the conceptually broader components of environmental harshness (Ellis et al, 2022). Indeed, whereas in the threat-deprivation view, poor caregiving quality and/or absence of a caregiver largely accounts for the absence of experience-expectant environmental input, the harshness-unpredictability framework considers the critical role of material resources, such as nutrition, shelter, and basic safety, in terms of survival and eventual reproductive success (Ellis & Del Giudice, 2019;Ellis et al, 2009).…”

“…These effects on the brain lead to deficits in cognitive control and executive functions, such as working memory, cognitive flexibility and cognitive inhibition, which collectively can manifest as cognitive and language delays as well as developmental disabilities (Lambert et al, 2017;Miller et al, 2018;Rosen et al, 2020). Considered within the evolutionary-developmental perspective, cognitive outcomes may be a marker of low embodied capital, shaping development of a slow life history (see Ellis et al, 2022), rather than as evidence of dysfunction or disorder (see Ellis et al, 2022).…”