In APS, developmental stability does not mean the absence of change, flexibility, or responsiveness.
A developmental process or outcome can remain relatively stable despite variation in some of the conditions under which development proceeds. Where such stability occurs, explaining it requires identifying the processes and dependencies responsible for maintaining the relevant developmental feature or trajectory.
Regulation, compensation, redundancy, feedback, or other processes may contribute to developmental stability in particular cases. Their presence and explanatory importance must be established rather than inferred from stability itself.
Developmental stability should also be distinguished from robustness, resilience, plasticity, and adaptation. These concepts can be related in particular biological systems, but they identify different explanatory relations. A stable developmental outcome need not exhibit all of them, and their occurrence does not make them constituents of developmental stability.
Nor does stability require complete resistance to change. Developmental processes may undergo substantial adjustment or reorganisation while some feature, relation, or outcome remains stable. Conversely, flexibility or compensation may alter a developmental trajectory rather than restore or preserve an earlier state.
Developmental stability therefore concerns the relative maintenance of a specified developmental feature, relation, trajectory, or outcome under the conditions relevant to the case. Whether that stability contributes to viability, organised persistence, resilience, adaptation, or some other biological outcome is a further explanatory question.
Key point: developmental stability is not rigidity. Stability can coexist with change and regulation, but the processes responsible for it and its biological consequences must be established for the developmental target concerned.