Introduction
Living systems persist in a changing world.
Conditions fluctuate, internal states vary, and environments shift continuously. Despite this, living systems maintain their biological organisation over time. They do not remain fixed — they remain coherent.
This form of persistence cannot be understood as the maintenance of a constant state. It requires a different concept: homeorhesis.
Homeorhesis in APS is the regulation of viability-oriented, constraint-closed biological organisation as a trajectory through which persistence is enacted under changing conditions.
Beyond Homeostasis
Biological regulation is often described in terms of homeostasis: the maintenance of variables within stable ranges.
Homeostasis is an important part of biological biological organisation. It explains how systems stabilise temperature, chemical concentrations, or pressure within limits that support viability.
However, living systems do not persist by holding everything constant. They grow, develop, adapt, and change.
To understand this, we need a concept that captures the regulation of change itself.
Homeorhesis as Regulation of Trajectory
Homeorhesis describes the regulation of biological organisation as a trajectory rather than a fixed state.
In APS, it refers to the regulation of viability-oriented, constraint-closed biological organisation through ongoing reorganisation under changing conditions. What is maintained is not a particular value, but a viable trajectory of biological organisation across time.
This allows systems to preserve viable trajectories of biological organisation across time, even as specific states fluctuate.
Homeorhesis therefore explains how persistence is enacted through change rather than despite it.
Trajectory, Not State
The key distinction is simple but fundamental:
- Homeostasis stabilises variables
- Homeorhesis stabilises trajectories
A plant maintaining internal water pressure exhibits homeostasis. The same plant maintaining a growth trajectory toward light exhibits homeorhesis.
In the first case, stability is defined by constancy. In the second, stability is defined by direction and biological organisation across time.
Living systems depend on both, but homeorhesis captures what homeostasis cannot: persistence as organised change.
Homeorhesis and Constraint Closure
Homeorhesis is grounded in constraint-closed biological organisation.
Living systems maintain networks of mutually sustaining constraints. As conditions change, these networks must be continuously reshaped to remain viable.
Homeorhetic regulation consists in this ongoing reorganisation. It preserves the biological organisation by modifying the relations that sustain it.
This makes homeorhesis an intrinsic feature of living systems, not an external description.
Homeorhesis and Agency
Homeorhesis is enacted through biological biological agency.
Living systems do not passively follow trajectories — they actively maintain them. Through biological agency, systems regulate their own biological organisation in relation to viability.
Homeorhesis therefore describes the temporal mode through which biological agency sustains coherent biological organisation across change.
It explains how systems reorganise without losing their identity.
Homeorhesis and Adaptation
Homeorhesis provides the temporal mode within which adaptation occurs: adaptation reorganises the system, while homeorhesis maintains the viability of its trajectory.
Adaptation describes the reorganisation of living systems under changing conditions. Homeorhesis describes how this reorganisation preserves viable trajectories.
Together, they explain how systems maintain continuity while remaining responsive to change.
Homeorhesis ensures that adaptation does not lead to disintegration but to sustained biological organisation.
Homeorhesis and Persistence
Persistence in living systems is not the maintenance of a fixed condition. It is the maintenance of an organised trajectory.
Homeorhesis is therefore the temporal mode of persistence. It describes how systems remain viable by continuously reorganising themselves.
Without homeorhesis, persistence would require stasis. With it, persistence becomes compatible with change.
Why Homeorhesis Matters
Clarifying homeorhesis helps resolve several key issues:
- Why living systems cannot be understood as static equilibria
- How stability and change are integrated in biology
- Why adaptation preserves biological organisation rather than disrupting it
- How persistence can be maintained across shifting conditions
By distinguishing trajectory from state, homeorhesis provides a more accurate account of how living systems endure.
Conclusion
Living systems persist not by remaining the same, but by remaining organised through change.
Homeorhesis defines this form of persistence: the maintenance of viable trajectories through ongoing reorganisation.
In APS, homeorhesis is the temporal mode of persistence — the way life sustains itself as conditions change.