Levels vs Scale — Why Biological Organisation Is Not Hierarchical

Abstract

Traditional biology explains living systems using hierarchical levels, from molecules to ecosystems. APS replaces this framework with scale: a relational account of organisation across space and time. This article clarifies why levels fail and how scale provides a more accurate explanatory grammar for biological systems.

The Limits of Hierarchical Thinking

Biology has long been organised around the concept of hierarchical levels: molecules, cells, tissues, organisms, populations, ecosystems. This framework suggests that living systems are composed of nested layers, each building upon the one below.

While this representation can be heuristically useful, it introduces significant distortions. It treats biological organisation as:

a stack of discrete entities
ordered from lower to higher
connected by largely unidirectional causation

In doing so, it obscures the actual organisation of living systems.

APS rejects hierarchy as an explanatory framework, not because biological systems lack structure, but because that structure is not hierarchical.

Why Levels Fail

The concept of levels fails for three reasons.

First, levels imply ontological separation. Molecular, cellular, and organismal processes are treated as distinct domains, when in fact they are inseparable aspects of a single organisation.

Second, levels suggest directional causation—from lower to higher or vice versa. Biological systems do not operate in this way. Causation is reciprocal and distributed across scales.

Third, levels treat organisation as static. They describe where things are located in a hierarchy, not how they are coordinated over time.

As a result, hierarchical models capture classification, but not organisation.

Scale as Relational Organisation

APS replaces levels with scale.

Scale is not a position in a hierarchy. It is a way of describing how processes are organised across space and time.

To describe a system in terms of scale is to specify:

the spatial extent of its processes
the temporal duration of its organisation
the relations that coordinate activity across these dimensions

Scale is therefore relational. It does not divide the world into layers. It describes how different processes are integrated within a single system.

Cross-Scale Causation

In a scale-based framework, causation is inherently cross-scale.

molecular processes influence organismal behaviour
organismal activity reshapes molecular conditions
environmental interactions reorganise internal processes

These are not interactions between levels. They are expressions of a single, integrated organisation operating across different scales.

Causation is therefore:

reciprocal rather than unidirectional
distributed rather than localised
continuous rather than segmented

This reflects the reality of living systems more accurately than hierarchical models.

Time as a Dimension of Scale

Scale is not only spatial. It is also temporal.

Biological organisation unfolds across multiple timescales:

rapid physiological regulation
developmental trajectories
evolutionary transformation

These are often treated as separate domains, but in APS they are understood as coordinated aspects of the same system.

Time is therefore not an external parameter. It is intrinsic to biological organisation.

To understand a living system is to understand how it sustains itself across time.

From Structure to Process

Hierarchical models emphasise structure: where components are located within a system.

Scale-based models emphasise process: how activity is coordinated across space and time.

This shift changes the explanatory focus:

from parts → to organisation
from position → to relation
from static arrangement → to dynamic integration

Biological systems are not stacks of components. They are processes organised across scales.

The Organism as Cross-Scale Organisation

The organism exemplifies scale-based organisation.

It integrates:

molecular activity
cellular processes
physiological regulation
environmental interaction

into a single, viability-oriented system.

These are not levels within the organism. They are coordinated aspects of its organisation across scales.

Understanding the organism therefore requires abandoning hierarchical thinking in favour of relational integration.

Scale and Biological Explanation

Replacing levels with scale has direct consequences for explanation.

It allows biology to:

account for reciprocal causation
integrate development, physiology, and evolution
avoid reduction to any single domain

Explanation becomes a matter of tracing how organisation is maintained and transformed across scales.

This aligns with APS’s broader explanatory grammar, in which agency, process, and scale are inseparable aspects of living systems.

Levels Replaced, Not Rejected

APS does not deny that hierarchical descriptions can be useful. It reinterprets them.

What are called “levels” are better understood as:

coarse descriptions of processes at different scales
heuristic simplifications of relational organisation

They are not fundamental features of biological reality.

Scale Reframed

Scale provides a more accurate account of biological organisation.

It captures:

integration without hierarchy
causation without directionality
persistence without static structure

By replacing levels with scale, APS offers a framework in which biological systems can be understood as dynamically organised processes across space and time.

Key Point. Biological organisation is not hierarchical but scale-dependent: a continuous integration of processes across space and time through which living systems sustain and transform themselves.