Abstract
Function is a central yet contentious concept for understanding biological traits. Contemporary approaches primarily fall into two categories: fitness-based theories, which appeal to the efficiency of organism-environment interactions, and causal analysis approaches, which rely on internal causal descriptions. In this paper, I argue that both paradigms face difficulties in grounding functional attribution. Specifically, I show that fitness-based theories are overly sensitive to environmental changes, making it difficult for them to distinguish between a temporary functional malfunction and a genuine functional loss in the Cavefish case. Conversely, the causal analysis approach suffers from a normative deficit: as illustrated by the Alien case, it struggles to explain the non-accidental suitability between a trait’s physical characteristics and its function. To address these difficulties, I defend a shift toward Systemic Teleology (or the Organizational Account). On this view, biological function is grounded in constraint closure, through which an organism produces and maintains the conditions of its own existence. By applying this framework to the Cavefish and Alien cases, I show that adequate functional attribution cannot rely solely on external fitness or internal causal description. It must also attend to the constitutive requirements of the organisation of constraints in which the trait exists.
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Nanay explicitly distinguishes his modal theory from Bigelow and Pargetter’s propensity view, partly because he takes the latter to remain vulnerable to the trait-type individuation problem. I group these views together here only for the limited dialectical purpose of this section: both determine function by reference to fitness-relevant contributions in non-historical, forward-looking or counterfactual terms, rather than by appeal to past selection.
In the broader organisational literature, closure of constraints is sometimes treated as a specific organisational pattern that may be relevant to the demarcation between living organisms and non-living systems (Mossio & Bich 2017). I set this demarcation issue aside here. My concern is narrower: when closure of constraints is realised in biological organisms, it provides the basis for functional attribution.
The reciprocal dependence involved in closure should be distinguished from the trait-individuation circularity discussed in §2.1. The former is a circularity in the organisation being described: it belongs to the biological system's own structure of constraint-dependence. It is not an explanatory defect because it does not generate an explanatory regress. Closure is an organisational property that can be characterised independently, in terms of the structure of constraint-dependence relations among the system’s constitutive components, and the account then appeals to this property to ground functional attribution without presupposing the functional relations it aims to explain. The circularity belongs to the object of explanation, not to the explanation itself. The latter, by contrast, is a potential circularity in explanation. Although the organisational framework may have resources for developing a non-circular account of trait individuation, doing so would require a separate argument, and I do not pursue it here. For present purposes, I only rely on the narrower point that organisational integration can guide the distinction developed in the Cavefish discussion without first settling the individuation of the relevant trait type.
Corti (2023) raises an important challenge to the Organisational Account, arguing that the counterfactual claim that a system would cease to exist unless certain conditions were satisfied does not by itself justify a transition from organisational facts to normative claims. Although his critique is directed at the OA, it reflects a broader pressure on naturalistic attempts to ground functional normativity in factual conditions of biological persistence. I do not settle this general meta-normative issue here. My claim is only that the Cavefish and Alien cases require attention to the constitutive requirements of the organism’s organisation of constraints.
Judgments about minimal physical requirements are grounded in our understanding of the laws of nature within specific physical environments. If alien organisms used electromagnetic force to pump blood, the relevant minimal physical requirements might include conductive or coil-like structures, or some biological analogue of them. However, this does not undermine the argument; rather, it reinforces it. Whatever the mechanistic details, the activity through which a trait performs its function must be physically realisable. The adequacy of a functional explanation depends on correctly identifying the constraint-dependence relations through which a trait’s activity contributes to the maintenance of O. If the environment or physical mechanisms undergo fundamental changes, the criteria for the physical realisation of the relevant function will change accordingly. This illustrates the explanatory flexibility of systemic teleology.
This does not imply that we have, to some extent, accepted defining traits and functions on the basis of physical characteristics. Function remains determined by the closure requirements of the system as a whole. The satisfaction of basic physical necessary conditions merely serves as evidence that the trait is produced and maintained by O as the bearer of the pumping function. More fundamentally, the trait has the pumping function because other processes and constraints within O, such as oxygen exchange in the lungs and nutrient delivery to tissue cells, depend on circulation for their own maintenance, and O produces and maintains the relevant trait in a way that can realise this contribution.
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Xing, Y. The systemic teleological turn in biological function: the alien and cavefish cases. Euro Jnl Phil Sci 16, 89 (2026). https://doi.org/10.1007/s13194-026-00803-3
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DOI: https://doi.org/10.1007/s13194-026-00803-3