Biology rests on a quiet but unresolved tension: living systems are organised in ways that sustain themselves in the present, yet they are also products of historical evolutionary processes. How these two dimensions fit together remains one of the central conceptual challenges of the life sciences.
The conceptual development of biology has long been shaped by two foundational insights concerning living systems. Aristotle’s biological writings articulated the first systematic account of organisms as intrinsically organised systems whose structures and activities contribute to maintaining the living individual. Darwin’s theory of natural selection provided a second foundational insight by explaining how such organised systems change historically through evolutionary processes.
These insights address complementary aspects of biological explanation. Aristotle’s biology focused on the organisation of living systems and the coordination of their parts and processes in sustaining persistence. Darwin’s theory explained the historical transformation of such organisation through variation, inheritance, and differential persistence across generations.
In compressed form, this relationship can be expressed simply:
Aristotle clarified how living systems sustain themselves as organised entities; Darwin explained how such organisation changes across time; contemporary theoretical biology seeks to understand how these dimensions are intrinsically related.
The Darwinian Reinterpretation of Purpose
One of Darwin’s most influential conceptual moves was to reinterpret biological purposiveness. Classical biological thought explained functional organisation by appealing to intrinsic purpose: organs and behaviours exist because they contribute to the maintenance of the organism. Darwin showed that adaptive organisation can arise historically through natural selection acting on heritable variation.
As a result, evolutionary theory often adopted the formulation that natural selection explains the appearance of purpose in living systems. Structures appear organised for particular functions not because they were intentionally produced for those ends, but because selection has historically preserved variants that enhance persistence and reproduction.
This interpretation successfully removed the need for external design in explaining biological adaptation. However, it also encouraged a tendency to treat purposive language as merely heuristic or metaphorical.
In recent decades, theoretical biology has increasingly recognised that this interpretation leaves an essential feature of living systems underarticulated. Evolution explains how adaptive organisation arises historically, but living systems must also continuously maintain and regulate their organisation in the present. Metabolism, regulation, development, and ecological interaction together sustain organised persistence despite continual material turnover and environmental change.
From this perspective, natural selection does not simply explain the appearance of purpose. Rather, evolutionary processes shape the organisational architectures through which living systems sustain their own persistence.
Why Teleology Disappeared from Biology
The relative disappearance of teleological language from biology during the late nineteenth and early twentieth centuries did not result primarily from Darwin’s theory itself. Rather, it reflected the broader influence of mechanistic explanatory ideals in the natural sciences.
Successful physical theories emphasised efficient causation, mathematical description, and reductionist analysis. Teleological language was therefore often regarded as metaphysical or unscientific. Many biologists consequently replaced purposive terminology with concepts such as function, adaptation, regulation, and control.
Despite this linguistic shift, the underlying phenomena never disappeared. Physiological regulation, homeostasis, development, and ecological interaction continued to reveal the distinctive organisation of living systems. Contemporary theoretical biology increasingly recognises that explaining these phenomena requires understanding how living systems actively sustain the conditions of their own persistence.
Agency as Persistence-Sustaining Organisation
The unresolved tension between historical explanation and present-tense organisation points to a deeper issue: biology lacks a clear account of how living systems actively maintain themselves while also undergoing evolutionary change.
Within the Agency–Process–Scale (APS) framework, this organisational capacity is described as biological agency. Agency refers not to intention or consciousness but to the viability-oriented organisation through which living systems sustain, regulate, and recreate the conditions required for their continued existence.
In this sense, purposive organisation is not merely an appearance generated by evolutionary history. It is an operational feature of living systems themselves: organisms continuously modulate internal and external conditions in ways that maintain their persistence as organised entities.
Evolutionary processes act on these persistence-sustaining systems, gradually transforming the organisational architectures through which agency is realised.
A Structural Symmetry in the Foundations of Biology
Seen in this light, the development of biological theory reveals a conceptual symmetry.
Aristotle’s biology investigated how living systems maintain their organised existence in the present. Darwin’s theory explained how such systems change historically. Contemporary theoretical biology seeks to integrate these perspectives by clarifying how persistence-sustaining organisation and evolutionary transformation are related across time.
This integration is captured in the explanatory grammar of APS:
| Historical perspective | APS dimension | Explanatory focus |
|---|---|---|
| Aristotelian biology | Agency | organisation that sustains persistence |
| Darwinian evolution | Process | historical transformation of organisation |
| Contemporary theory | Scale | coordination across spatial and temporal extent |
These are not separate domains but analytically distinct aspects of a single biological reality: living systems sustain themselves, change through time, and do so across interacting spatial and temporal scales.
Reintegrating Organisation and Evolution
From this perspective, organisation and evolution are not competing explanatory frameworks but complementary aspects of a unified theoretical architecture. Evolution explains how persistence-sustaining organisation is transformed, while the organised activity of living systems provides the conditions under which evolutionary processes occur.
The Agency–Process–Scale framework makes this relationship explicit by interpreting agency as viability-oriented organisation, process as the transformation of that organisation across time, and scale as the domain across which these dynamics unfold.
The historical trajectory of biology can therefore be understood as an ongoing effort to integrate two foundational insights: how living systems sustain themselves, and how such systems change.
Key Point
Biological explanation integrates two inseparable dimensions: the organisation through which living systems sustain themselves and the processes through which this organisation is transformed across time.