Biology is commonly divided into domains such as development, physiology, ecology, cognition, and evolution. These distinctions are valuable because they identify different explanatory questions and different aspects of living organisation. Each domain highlights particular patterns of organisation, persistence, and transformation that would be difficult to study simultaneously.
In APS, domain status is therefore determined by explanatory function rather than by website classification or terminology alone. A substantive domain is warranted where a sufficiently coherent family of biological explananda, explanatory dependencies, and research questions can be investigated together. Not every concept or research category is therefore a biological domain: foundational commitments concerning viability and organised persistence, and the cross-cutting analytic projections of Agency, Process, and Scale, can contribute across multiple domains without constituting additional peer domains themselves.
Problems arise when these domains are treated as separate levels of reality. Development is not a developmental level, ecology is not an ecological level, and evolution is not an evolutionary level. These domains distinguish explanatory questions and the biological organisation relevant to answering them. They can concern the same organism or overlapping biological organisation without thereby constituting separate ontological layers.
The same organism can be investigated developmentally, physiologically, ecologically, cognitively, and evolutionarily, but this does not mean that only the explanatory perspective changes while the explanandum remains identical. Different domains can address genuinely different explananda, materially relevant relations, and spatial or temporal extents. Their explanations can nevertheless overlap because the biological organisation to which they refer can itself overlap.
APS therefore treats organisational domains as distinctions within biological explanation rather than as distinct ontological levels. Their explanatory diversity reflects differences in the questions being asked and in the organisation relevant to those questions. Neither their plurality nor their overlap implies separate levels within nature.
Key Point. Organisational domains distinguish bounded families of explanatory questions, explananda, and materially relevant relations. Their boundaries are determined by explanatory function rather than terminology or website classification. Domains may overlap without constituting distinct ontological levels, while foundational commitments and cross-cutting APS resources can operate across domains without themselves becoming peer biological domains.