Where this article fits: This article examines a historical problem that precedes APS: how biology came to use multiple successful forms of explanation, and how the relationships among those explanations became a question in their own right. It does not argue that biological explanation has failed, that explanatory plurality requires unification, or that this history establishes APS. Instead, it asks how mechanistic, evolutionary, molecular, organisational, systems, and other biological explanations came to coexist while addressing different questions about living systems. The article ends with an open question: can the relationships among biology’s heterogeneous explanations themselves be investigated systematically without erasing their differences? The next stage of the General Biological Explanation sequence asks whether a general explanatory framework for biology is possible, and what such a framework could and could not legitimately claim.

Introduction

Biology has never explained living systems in only one way. Biologists explain how structures work, how organisms develop, how physiological processes are regulated, how traits evolved, how populations change, how organisms interact with their environments, and how molecular processes contribute to these phenomena. These explanations can be extraordinarily successful without all answering the same question.

That diversity has a history. At different times, biological explanation has been organised around form and function, mechanical causation, evolutionary history, molecular mechanisms, organisation, systems dynamics, ecology, and other explanatory approaches. New approaches have repeatedly transformed what could be explained, but they have rarely made all earlier biological questions disappear.

This history matters because it changes what it could mean to seek a general explanation in biology. The problem is no longer simply to find one principle that distinguishes living from non-living matter. It is also to understand whether the many successful explanations used across biology are related, and, if so, what kind of relationship they have.

Biology Has Never Had Only One Kind of Explanation

It is tempting to describe the history of biology as a succession of explanatory systems. One view is displaced by another: organism gives way to mechanism, vitalism to materialism, natural history to evolutionary theory, organismal biology to molecular biology, and component-based explanation to systems biology.

The actual history is less orderly.

Biological explanations have accumulated as well as changed. Evolutionary explanations did not make physiological explanations unnecessary. Molecular mechanisms did not eliminate development. Ecology did not replace organismal biology. Systems approaches did not make molecular mechanisms obsolete. Instead, different investigative traditions developed explanatory resources appropriate to different biological questions.

This does not mean that all biological explanations are independent or equally useful for every purpose. Molecular events can matter to development; development can alter evolutionary possibilities; physiology can constrain behaviour; ecological conditions can influence selection. But establishing such relationships is itself explanatory work. The fact that two phenomena belong to the same living system does not by itself tell us how their explanations should be connected.

The history of biological explanation is therefore not simply a history of competing answers. It is also a history of changing questions about what requires explanation.

Organisms Before Mechanisms

Long before modern experimental biology, living things were investigated as organised beings whose parts, activities, development, and ways of life could be considered together.

Aristotle’s biological works are an important early example. In his investigations of animals, material constitution, form, and what bodily parts do are considered within the same biological inquiry. Structures are examined not only in terms of what they are made of, but also in relation to their activities and contributions to the life of the organism.

Much of Aristotle’s natural philosophy was subsequently abandoned or transformed. Modern biology does not depend on Aristotelian physics or metaphysics. The historical importance of this earlier explanatory setting lies elsewhere: biological investigation began with several explanatory questions already intertwined. What is an organism made of? How is it organised? How does it develop? Why does a structure have the form it has? What contribution does that structure make to the organism’s activities?

Later biology would answer such questions very differently. It would also increasingly separate them.

Could Life Be Explained Mechanically?

The rise of mechanical and experimental approaches to nature transformed the study of living systems. Processes that had once been described primarily through the activities of organisms could increasingly be investigated in terms of matter, motion, physical structure, chemical transformation, and experimentally accessible causal processes.

This was a decisive achievement. Biological phenomena did not need to be insulated from the material sciences in order to be investigated as biological phenomena.

Yet the historical opposition between mechanism and vitalism is easily oversimplified. There was no single mechanical doctrine that remained unchanged across the history of biology, and positions concerning life were not divided neatly between mechanists on one side and defenders of a mysterious vital force on the other. Physiologists and naturalists developed intermediate and changing positions as experimental knowledge expanded.

Vitalist proposals themselves varied. Many expressed dissatisfaction with the claim that the organisation and activities of living systems had already been exhaustively explained by the physical and chemical resources then available. Some responses invoked special principles or forces associated with life. Those proposals ultimately failed to secure a place in modern biological explanation.

But the rejection of vital forces did not make the phenomena that had motivated the debate disappear.

Organisms still regulate their internal conditions. Their parts operate in coordinated ways. They develop characteristic forms. Structures make different contributions to continued functioning. Living systems repair themselves, reproduce, respond to changing conditions, and maintain organised activity despite continual material turnover.

Removing a proposed vital substance or force was therefore not the same thing as removing organisation, regulation, function, or apparent purposiveness from the explanatory agenda of biology.

Organisation Without Vital Forces

During the twentieth century, organisation became one way of addressing these problems without returning to vitalism.

Organismic and organicist approaches differed substantially from one another, but they shared resistance to the idea that understanding isolated components must always be sufficient for understanding the living system in which those components operate. Relations among parts, patterns of organisation, development, regulation, and the properties of organised wholes became explicit subjects of biological and theoretical investigation.

This was not a rejection of material explanation. Nor did it establish that biological organisation constituted an independent non-material cause. The important shift was methodological and explanatory: material components could be indispensable while their organisation and relations also remained relevant to what a biological explanation needed to specify.

These concerns did not simply disappear with the later growth of molecular biology. Questions about organisation continued in changing forms in subsequent biological and theoretical research, although the concepts, methods, and empirical resources used to investigate them changed substantially.

The persistence of these questions should not be mistaken for evidence that one particular organisational framework is correct. Historically, it shows something more limited but important: eliminating vital forces did not eliminate the scientific problem of explaining organised living activity.

Evolution Changes What Biological Explanation Can Mean

Evolutionary theory transformed biological explanation in a different way. Darwinian explanation made the historical transformation of populations, adaptation, and diversification central to understanding living forms. Later evolutionary theory greatly extended the precision and scope of those explanations.

A biological feature could now be explained not only by describing how it works in an organism, but by asking how populations possessing different heritable variants changed over generations. Historical processes became indispensable to explaining why biological forms have the distributions and characteristics they do.

This introduced an extraordinarily powerful form of explanatory generality into biology. Yet evolutionary explanation did not make every biological question an evolutionary question.

Knowing how a trait evolved is not identical to knowing how it develops in an individual. Explaining the selective history of a physiological capacity is not the same as identifying the mechanisms that produce that capacity. Explaining changes in populations does not replace explaining metabolic pathways, cellular regulation, developmental interactions, or ecological processes.

These explanations can interact. Development can affect evolutionary possibilities; physiology can affect fitness; ecology can alter selection; evolutionary history can help explain features of mechanisms and developmental systems. But such connections have to be specified rather than assumed.

Evolution therefore enlarged biological explanation without reducing biology to a single explanandum.

The Molecular Revolution

The rise of molecular biology produced another major expansion of explanatory power. Genes, proteins, nucleic acids, regulatory interactions, biochemical pathways, and cellular mechanisms became accessible to increasingly precise experimental investigation.

This changed biology profoundly. Processes previously described at the level of tissues, organisms, or inheritance could increasingly be connected to molecular components and interactions. Mechanistic explanation acquired unprecedented experimental detail.

It would nevertheless be misleading to equate this success with the reduction of all biological explanation to molecular description.

Reduction can mean several different things: identifying a phenomenon with its molecular basis, deriving one theory from another, decomposing a mechanism into components, or showing how higher-level behaviour depends on lower-level processes. Success in one of these senses does not automatically establish the others.

Contemporary mechanistic biology also bears little resemblance to a crude picture of organisms as simple machines assembled from independently acting parts. Biological mechanisms may be cyclic, dynamically organised, regulated, nested, and dependent on interactions across levels of organisation. Mechanistic explanation can therefore incorporate organisation rather than standing in opposition to it.

The molecular revolution demonstrated how much explanatory power can come from identifying components and their organised activities. It did not establish that every biological explanandum is exhausted by the same level or form of mechanistic description.

From Components to Systems

As molecular knowledge expanded, another problem became increasingly visible: knowing more components did not automatically show how their collective behaviour should be understood.

Systems biology developed in part around this challenge. Networks, feedback, dynamics, robustness, modelling, large-scale data, and the integration of experimental and computational approaches became increasingly important. Instead of asking only what individual components do, researchers could investigate how patterns of interaction generate and stabilise system behaviour.

This did not amount to abandoning molecular biology. Systems approaches frequently depend on molecular data and mechanistic knowledge. Their contribution lies partly in asking questions for which interaction structure, dynamics, or system-level behaviour is itself explanatorily relevant.

Nor did systems biology establish one new universal form of biological explanation. Systems research uses different models and explanatory strategies for different purposes. Some explanations remain strongly mechanistic; others emphasise dynamics, network organisation, robustness, mathematical structure, or integration across investigative levels.

The result was therefore another enlargement of biology’s explanatory repertoire rather than its collapse into a single explanatory method.

This is historically significant. As biology acquired more detailed knowledge of components, the problem of relating components, interactions, dynamics, and larger-scale behaviour became more explicit. Integration itself became something that required scientific work.

Why Successful Biology Still Has an Explanatory Problem

Modern biology is not short of explanations.

It possesses evolutionary explanations of historical change, mechanistic explanations of organised causal processes, molecular explanations of cellular activity, developmental explanations of organismal formation, physiological explanations of regulation and function, ecological explanations of interactions among organisms and environments, and systems approaches to networks and dynamics. Other explanatory practices add still further resources.

The existence of this plurality need not indicate theoretical disorder. Different explanations can be successful because they answer different questions.

The difficulty begins when we ask how those explanations relate.

Sometimes one explanation supplies a mechanism required by another. Sometimes explanations concern different temporal or spatial extents. Sometimes one describes the historical origin of a feature while another explains its present operation. Sometimes explanatory models deliberately omit detail that is essential for a different question. Sometimes two approaches genuinely compete because they address the same explanandum differently.

These relationships cannot be inferred merely from the fact that all the explanations concern biology.

This creates a distinctive explanatory problem. Biology’s success has generated an increasingly rich set of explanatory practices, but the relations among those practices are not automatically given by the practices themselves. Determining whether two explanations compete, complement one another, operate at different scales, identify different dependencies, or address different explananda requires further analysis.

Pluralism, in this sense, is not the opposite of successful science. It is partly a consequence of successful investigation into a complex subject matter.

What Would “General” Mean Now?

Against this historical background, the idea of a general biological explanation becomes ambiguous.

One possibility is a general theory: a theory, law, mechanism, or principle intended to explain a very wide range of biological phenomena. Biology has repeatedly developed explanatory ideas of enormous scope, most notably evolutionary theory, without thereby turning every biological question into the same kind of question.

A different possibility is a general explanatory framework.

Such a framework would not necessarily provide one mechanism or theory from which biological explanations could be derived. Its possible role would instead concern the relationships among different explanations: when they address the same target, when they address different targets, when one depends on another, when they can be integrated, and when their differences should be preserved.

That possibility should not be assumed merely because contemporary biology is explanatorily diverse. Diversity alone does not demonstrate that biology needs an overarching framework, that its explanations can be systematically integrated, or that one framework could relate them without distortion.

The historical problem therefore ends with an open question rather than a general solution:

Can the relationships among biology’s heterogeneous explanations themselves be investigated systematically without erasing the differences among their targets, mechanisms, histories, scales, and evidential requirements?