Models of Adaptation:
What Different Frameworks Explain

01Start with the question

A model selects relationships to explain. A useful comparison asks what it treats as the system, what changes, what it predicts and which observations could challenge it. The frameworks below overlap, but they are not interchangeable tests or a ranked list of theories.

02Sterling: preparing for demand

Sterling’s 2012 account emphasizes anticipation, coordinated resource allocation and learning. It gives TAP a reason to include events before a challenge and behavior that changes exposure.^[1]

The argument is theory-led. Presenting it fairly includes identifying its assumptions, rather than announcing that homeostasis or feedback has been disproved. A compelling physiological example is not validation of every extension of the theory.

03Allostatic load: the costs of adaptation

McEwen and Stellar connect stress and individual differences with cumulative physiological costs. This perspective directs attention to repeated or persistent adaptation across time.^[2]

It asks a different question from whether one response returns quickly. Neither fatigue nor the shaded area under an illustrative curve establishes a person’s allostatic load.

04Reactive Scope: ranges matter

Romero and colleagues distinguish mediator ranges supporting predictable and unexpected demands from overload and failure. Their graphical account considers how history and context can change those ranges.^[3]

A response range is defined for a mediator and an organism. Converting the drawing into universal human thresholds, or calling its width a measured reserve score, would require separate justification.

05NIH: define the system and follow its response

The NIH framework organizes resilience around a system, a challenge and the response over time. It includes resistance, adaptation, recovery and growth.^[4]

Its practical contribution is a research question: which function, following which challenge, over which interval? Citing this framework does not mean NIH has endorsed a TAP model or an intervention.

06A newer proposal: allostasis and active inference

Harrison and colleagues propose a theoretical connection between allostasis, active inference and resilience phenotypes, including actions that shape the environment.^[5]

Published as Hypothesis and Theory in 2025, it is an important comparison for new frameworks. Its four phenotypes should not be presented as established diagnostic categories. Linking allostasis to resilience is already part of the literature, not a new discovery by TAP.

07Where TAP’s synthesis begins

TAP uses these traditions to organize three questions: what demands arise, how the system regulates, and what happens to specified functions over time. Physiological reserve is a potential contributor to a response, not the same thing as the trajectory observed after a challenge.^[6]

The proposed contribution is an explicit map between explanations, assumptions and possible measurements. Its value can be assessed by whether it prevents conceptual errors and supports better testable questions. The synthesis itself has not been empirically validated.