Models of Adaptation:
What Different Frameworks Explain

01Start with the question

Each model selects relationships to explain. Compare how it defines a system, which quantities change, what it predicts and which observations can test it. The following sections use these questions to examine the frameworks.

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]

Sterling’s argument emphasizes anticipatory regulation; its theoretical assumptions and physiological examples should be read separately. Comparison with modern homeostatic accounts clarifies how each handles prediction, feedback and coordination.

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]

It leads to a practical question: after which challenge, over what period, and for which function? These questions provide a concrete starting point for selecting a design and interpreting trajectories.

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]

This 2025 Hypothesis and Theory paper proposes four resilience phenotypes as theoretical categories to be tested. It offers another route for connecting allostasis with resilience and warrants comparison with other frameworks.

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.