Life is a particular *shape*, not a special substance: a system that keeps rebuilding itself while energy keeps flowing through it. Two things have to be true at once. Life is the case where both hold together (a configuration that uses the energy passing through it to keep producing itself) and once that shape first appears, evolution follows from it.

> [!definition]
> **Life** · *Definition*
>
> A closed self-producing recursion coupled to sustained energy throughput.

This account follows the living process as a configuration that maintains itself, without yet taking up its own self-modeling. That question belongs to Chapter 8.

The earlier chapters establish the conditions: §§1–2 work out what Reality must provide to be Reality at all, and §[§7.1](<7.1 Convergence of Method.md>)–7.7 follow what those conditions make possible once they run: gradients, dissipation, and cycles that elaborate into things able to hold themselves together. Nature now reaches the threshold where it produces living things: configurations that maintain themselves.

Both conditions (closure and throughput) matter, and neither alone suffices.

A configuration that is closed but does not import energy is a *clock.* A reversible chemical cycle that returns to its starting state, again and again, dissipating nothing and producing nothing, is geometry, not life. The cycle has shape but no work.

A configuration that imports energy but is not closed is a *flame.* A candle dissipates a gradient (chemical bonds released as heat and light) but the flame does not produce its own wax. It eats what was already there, until the supply ends, and the structure was never doing anything to keep the supply coming. A *battery* is the same structural shape in a different mode: a stored electrochemical gradient that discharges through a circuit, doing real work but never rebuilding its own electrodes or replenishing its own electrolyte. Hurricanes, Bénard cells, Belousov–Zhabotinsky reactions: every dissipative structure that channels energy without enrolling that energy in its own continuation belongs here. They have throughput but not closure.

*Life is the intersection.* The configuration closes on itself to produce its own conditions of continuation, and remains coupled to a sustained energy gradient that it dissipates through itself in order to keep producing itself. Closure plus throughput. Said as one sentence: *energy held in a self-producing recursion that keeps absorbing more.*

*Autonomy is organized dependence.* A living system remains itself not by closing itself off from its environment but by regulating what crosses its boundary and using that exchange to reproduce the organization that maintains the boundary. It is materially open and organizationally closed. Its autonomy therefore consists in actively organizing its dependence on surrounding conditions into continued self-production. The material components can change while the living identity persists, because what persists is primarily the organization being reproduced rather than an unchanging inventory of matter. Self-production is therefore not self-subsistence. A living configuration makes itself, but it does not stand on its own: it produces its own conditions of continuation only by continuously drawing on an energy gradient it cannot guarantee, which is why every such configuration is finite where Nature, requiring nothing outside itself, is not.

*Life introduces an immanent better-or-worse gradient.* Once a process produces the conditions of its own continuation, environmental and internal states are no longer neutral relative to it. Some sustain closure, some impair it, some restore it, and some terminate it. This is biological normativity: a condition can be good or bad for a living being according to whether it sustains or degrades that being's continued self-production. It is not yet moral obligation, conscious preference, or a command issued by Nature. It is the factual relation from which drive and valence can later develop when the living process becomes capable of registering the difference from within.

*Minimal agency begins as regulation.* To maintain closure, a living system must respond differently to conditions that sustain it and conditions that threaten it. At its thinnest, agency is this state-sensitive self-regulation: detecting a departure from viable conditions and acting in ways that tend to restore them. No reflective intention is required at this level. But once continued action depends on registration, error becomes possible: the system can respond to conditions as though they were sustaining when they are not, or fail to register a threat that is present. This is the biological root of the later distinction between a representation and what it tracks. Chapter 8 takes up what regulation becomes when the living system's representations include itself and a range of alternatives.

*What three traditions were each tracking.* This is the structural form Schrödinger -(Schrödinger, E., 1944) reached for in *What is Life?*, life "feeds on negative entropy" (extracts order from the environment by exporting disorder), and that Prigogine elaborated into the chemistry of *dissipative structures* (configurations that maintain themselves far from equilibrium by channeling energy through themselves; Nicolis and Prigogine -(Prigogine, I., and G. Nicolis, 1977)), and that Maturana and Varela -(Humberto R. Maturana, Francisco J. Varela, 1980) named *autopoiesis* (self-production through the same molecules the configuration uses to maintain itself) in the closure dimension. Each tradition was tracking part of the same fact. The framework here unifies them: closure names the production side, throughput names the energetic side, and life is the moment both are present at once, in a configuration that uses the energy passing through it to keep itself producing itself.

*The NASA definition and what the account adds.* The most widely cited working definition of life in astrobiology, Joyce -(Joyce, G. F., 1994), adopted by NASA, defines life as a self-sustaining chemical system capable of Darwinian evolution. The definition correctly picks out process rather than chemistry, which allows it to cover life that might be nothing like Earth life. The account here is compatible with it and clarifies the relationship between its two components. *Self-sustaining* names the closure condition, and the word carries the closure sense fixed above rather than the energy-independence it can suggest: it is the recursion sustaining its own self-production while drawing on a gradient it cannot guarantee, self-producing but not self-subsistent. *Darwinian evolution* names what happens to populations of self-producing recursions over time: a recursion that copies itself will make errors; errors that improve self-maintenance persist; the population drifts toward better closures. Evolution is downstream of closure, not a separate requirement alongside it. The two criteria are tightly coupled: closure with heritable variation drifts strongly toward evolution, and the absence of evolution over sufficient time and population size is structurally surprising for something that has genuinely closed. The coupling is convergence-strong rather than strictly modal: what closure plus heritable variation does over time, on the reading developed here, is evolve.

*Cleland and the anti-definitional challenge.* Carol Cleland -(Carol E. Cleland, 2012); -(Carol E. Cleland, 2019) argues that the project of defining life is methodologically misguided: science needs a theory of living things (analogous to the molecular theory that replaced pre-scientific definitions of 'water') not a definition that adjudicates borderline cases from the armchair. Definitions, on Cleland's view, substitute conceptual analysis for the empirically grounded theoretical unification that would actually advance the science. The definition invites this challenge directly, and the first move is to concede its form: closure-plus-throughput is a definition in form (a short necessary-and-sufficient statement, set in a definition box) so the reply cannot be that it is not a definition. The reply is rather about the *source of its warrant*: closure-plus-throughput is offered as a *structural characterization*, naming what the living configuration *is* modally, the structural shape any configuration instantiating life must exhibit, derived from what the cosmic-evolutionary trajectory ([§7.7](<7.7 Cosmic History.md>)) must deliver, rather than as a stipulative-conceptual definition that settles whether viruses, prions, or fire are alive by armchair necessary-and-sufficient-condition matching. This is closer to Cleland's own preferred mode (a theoretical characterization grounded in what the phenomenon structurally requires) than to the definitional projects she criticizes. The definition does not claim to resolve the borderline cases; it claims that whatever is alive has the closure-plus-throughput structure, and that this structural characterization is derivable from what the cosmic-evolutionary trajectory ([§7.7](<7.7 Cosmic History.md>)) must deliver for the biological trajectory to begin. Cleland's epistemological complaint (we should not define life before we have the theory) and the present metaphysical claim (life has this structural shape) are therefore orthogonal: her critique targets the substitution of definition for theory, and the present account makes the theoretical claim, not the definitional substitution.

*Kauffman and self-organizing criticality.* Stuart Kauffman's autocatalytic-sets program -(Stuart A. Kauffman, 1993); -(Stuart A. Kauffman, 1995); -(Stuart A. Kauffman, 2008) locates the emergence of life in networks of catalytic polymers that collectively catalyze each other's production, reaching a phase-transition threshold at which the autocatalytic set becomes collectively self-sustaining. Kauffman foregrounds the network-level phase transition rather than the closure of any individual configuration. The structural account takes closure-plus-throughput as the characterization of the configuration once the transition has occurred; Kauffman's autocatalytic-set dynamics describe the mechanism by which the first closure is reached: the *how* of origin, where the definition names the *what* of the result. The accounts are complementary rather than competitive: closure-plus-throughput names the structural shape the self-organizing network instantiates at the phase transition, and Kauffman's dynamics describe the path to that threshold. Where Kauffman would press that edge-of-chaos criticality is itself constitutive of life rather than merely the path to it, the reply is that the criticality is what sustains the throughput (the self-organizing network maintains its closure precisely by operating at the critical regime) so the structural characterization absorbs rather than excludes Kauffman's insight.

*The design inference, and what the account does and does not lean on.* Because these are generative claims (that undirected dissipative and autocatalytic dynamics can produce, and not merely redescribe, the specified molecular architecture of the first closure), they meet the design inference head-on: Behe's irreducible complexity and edge-of-evolution limits -(Michael J. Behe, 1996); -(Michael J. Behe, 2007) press that observable mechanisms can describe such architecture without being able to build it. Two things keep the definitional claim clear of that dispute. First, the generative supports invoked here, England's thermodynamic favoring of self-replication and Kauffman's autocatalytic criticality, are live and contested results rather than settled ones; the structural characterization of life (closure plus throughput) names what the living configuration *is*, and does not stand or fall with either mechanism for how the first one formed. Second, the design inference proper, whether specified complexity licenses an inference to a designer, is adjudicated directly at [§5.1.6](<5.1.6 Intelligent Design.md>) (its cosmological-scale counterpart, the fine-tuning argument, at [§5.1.5](<5.1.5 Fine-Tuning Argument.md>)), and it is that treatment, not an appeal to 'emergence,' that governs the verdict; what [§5.1.6](<5.1.6 Intelligent Design.md>) defers back to Chapter 7 is precisely the generative half, how the immanent operators of change, composition, and constraint produce form rather than presuppose it. What would bear on the generative question empirically is not a gap to be plugged by stipulation but the integrated-abiogenesis frontier of [§7.8.4](<7.8.4 What is Confirmed.md>): whether geochemistry, protometabolism, polymerization, compartmentalization, and replication can be run together in one sustained system.

*Jablonka-Lamb and the extended evolutionary synthesis.* Eva Jablonka and Marion Lamb -(Eva Jablonka, Marion J. Lamb, 2005) and the extended evolutionary synthesis (Massimo Pigliucci, Gerd B. Müller (eds.), 2010) broaden the heritable variation driving Darwinian evolution beyond strictly genetic inheritance to epigenetic, behavioral, and symbolic dimensions: chromatin-state transmission, learned behaviors passed across generations, symbolic systems as inheritance channels. The section's claim that Darwinian evolution is downstream of closure-plus-heritable-variation needs to absorb this extension: if heritable variation encompasses epigenetic marks, learned behaviors, and symbolic transmission, then the coupling from closure to evolution covers all four of Jablonka and Lamb's dimensions, not only the genetic one. The reply is available and structural: closure-plus-throughput generates a self-producing recursion that encodes its own state; any encoding mechanism (genetic, epigenetic, behavioral, or symbolic) that preserves variation across reproduction counts as heritable variation in the relevant sense. Evolution under the extended synthesis is still downstream of closure; what the extension shows is that the heritable-variation channel is broader than the genetic channel alone, which the structural account accommodates by treating heritable variation as any encoding of the recursion's state that persists across reproduction events.

*The first closure.* The first time this happened in the universe (wherever and however it happened) was the moment life began. It was not a new substance. The molecules involved were already there, doing their dissipative work. What was new was a *shape*: the closure of a recursion that, once closed, stayed open to energy. Whether the first instance was at a deep-sea hydrothermal vent, in an alkaline pond, on a tidal mineral surface, or somewhere else entirely is an empirical question; what *kind* of event it was is the constitutive one. And one constitutive feature of the kind is forced by what the moment is: the first life cannot have been heterotrophic, since there was no prior life to consume, so its energy source must have been non-biological. Photosynthesis as we know it is ruled out: it requires sophisticated molecular machinery (chlorophyll, photosystems, electron-transport chains) that is itself a downstream evolutionary product. The same constraint rules out simpler photon-harvesting: any chromophore-based photochemistry requires evolved molecules to convert photon energy into directed chemical work. Solar-thermal driving (wet-dry cycles, surface-pond convection) is real but is a form of chemical and thermal disequilibrium, not a separate energy class. What remains is chemistry: redox gradients between reduced and oxidized species, available wherever sustained geochemical disequilibrium persists.

The first closure was therefore structurally favored to be chemoautotrophic: the alternatives the literature has surveyed all require evolved molecular machinery the first closure could not have inherited. The structurally favored sites, alkaline hydrothermal vents (Martin, W., and M. J. Russell, 2003); (Lane, N., 2015), surface ponds with wet-dry cycles (Matthew W. Powner, Béatrice Gerland, John D. Sutherland, 2009); (Damer, B., and D. Deamer, 2020), mineral-surface catalysis, and other redox-disequilibrium environments, are where the empirical literature has independently converged. The framework is neutral on which specific site hosted the first closure; it requires only sustained chemical disequilibrium of the kind chemoautotrophy can metabolize.

Life has retained the chemiosmotic shape ever since: every cell pumps protons across its membrane to build a charge-difference, then lets that gradient discharge through the molecular machinery that synthesizes the cell's own components: the cell powers its own production by routing a gradient through itself (Mitchell, P., 1961). The first closure inherited a gradient that geology already maintained; subsequent depths learned to build and maintain their own. It was the first time the universe contained a closure that maintained itself by routing energy through itself.

*Life as evolutionary trajectory.* What the first closure inaugurates is an *evolutionary trajectory*: a directional, asymmetrical sequence of states unfolding under temporal asymmetry, energetic constraint, and the openness [§7.7](<7.7 Cosmic History.md>) names. Cosmic evolution is one such trajectory, traced in [§7.7](<7.7 Cosmic History.md>): the dissipation of cosmic-scale gradients across one turn of the cycle, delivering the chemoautotrophic threshold this section picks up at. Biological evolution is another, given by what closure-plus-throughput configurations do once they appear. They are not produced by a single additional engine. They instantiate the same structural conditions at different scales: the cosmic trajectory is what dissipation looks like across the universe as a whole; the biological trajectory is what dissipation looks like across configurations that have closed into self-production.

That first closure already had what subsequent depths elaborate further. To maintain itself, a self-producing recursion must track its own state; the tracking is what the maintenance, at any depth of recursion, already *is*. What deepens across four billion years (bacteria, archaea, eukaryotes, multicellularity, nervous systems, brains, recursive self-modeling that includes itself) is the same recursion deepening into itself further and further, shaped by ecosystem-level constraint, selection, feedback, and coevolutionary depth. This configuration is *life*. What the recursion's self-modeling amounts to is the next question, and it should arrive only after this account has done its work.

The dialectical engagement with consciousness (zombie conceivability, the knowledge argument, the explanatory gap, eliminativism, illusionism, cosmopsychism) is at the [§4.3](<4.3 Physics and Mind.md>) cluster (§[§4.3.1](<4.3.1 The Hard Problem of Consciousness.md>)–4.3.5) and in Chapter 8's structural defense of the inside.


- [7.8.1 What is Disputed](<7.8.1 What is Disputed.md>)
- [7.8.2 What is Required](<7.8.2 What is Required.md>)
- [7.8.3 What is Predicted](<7.8.3 What is Predicted.md>)
- [7.8.4 What is Confirmed](<7.8.4 What is Confirmed.md>)
- [7.8.5 What is Concluded](<7.8.5 What is Concluded.md>)


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← [7.7.5 What is Concluded](<7.7.5 What is Concluded.md>) | [7.8.1 What is Disputed](<7.8.1 What is Disputed.md>) →
