Chapter 2 What Is Life?
2.1 Chapter Overview
Before asking whether consciousness preceded life or emerged from it, we need a working definition of life. This is harder than it first appears. Life seems obvious when we point to a tree, an animal, a bacterium, or a human being. Yet the boundary becomes less clear when we consider viruses, prions, self-replicating molecules, synthetic cells, artificial life, or possible life on other planets.
This chapter surveys several major ways of defining life: biological, thermodynamic, informational, autopoietic, functional, and ontological. Each definition highlights something important, but each also leaves something unresolved. More importantly, each definition shapes how we understand the relationship between life and consciousness.
If life is mainly chemistry, then consciousness may appear as a later biological achievement. If life is information processing, then the distance between life and mind becomes smaller. If life is self-production and self-maintenance, then something like minimal cognition may be present from the beginning.
The question “What is life?” is therefore not only biological. It is also philosophical, physical, informational, and perhaps even experiential.
2.2 Why Defining Life Is Hard
Life is one of the most familiar realities we encounter, yet it remains surprisingly difficult to define. We recognize living beings around us, but recognition is not the same as definition. A bird, a mushroom, a bacterium, and a human being are all alive, but they differ enormously in structure, behaviour, complexity, and form of existence.
The difficulty becomes clearer at the edges. Viruses reproduce and evolve, but they cannot reproduce independently outside host cells. Prions can transmit biological effects without containing DNA or RNA. Self-replicating molecules may copy themselves but may not metabolize or maintain a boundary. Synthetic biological systems may be engineered to perform life-like functions, raising the question of whether they are alive, artificial, or something in between.
These edge cases matter because they reveal that life is not defined by a single feature. No one property seems sufficient on its own. Reproduction is important, but sterile organisms are still alive. Metabolism is important, but some dormant organisms can suspend metabolism for long periods. Genetic information is important, but information alone does not make something alive. Cellular structure is important, but viruses challenge the boundary between living and non-living systems.
The problem is not simply that we lack a good definition. The deeper problem is that life may not be a single thing in the ordinary sense. It may be a process, a pattern, a form of organization, or a cluster of related properties. Depending on which feature we emphasize, we arrive at a different answer.
This matters for the central question of this book. If life is defined narrowly as cellular chemistry, then consciousness appears to be a separate and later problem. If life is defined as adaptive information processing, then the roots of consciousness may already be near the roots of life. If life is defined as self-producing organization, then the gap between life and cognition becomes less clear.
The definition of life is therefore not neutral. It shapes the entire discussion that follows.
2.3 Biological Definitions
Biological definitions often begin with the observable features of living systems. Living beings grow, reproduce, metabolize, respond to stimuli, maintain internal organization, and evolve. These features are useful because they describe what living organisms actually do. They also provide practical criteria for distinguishing living systems from non-living matter.
One influential working definition, often associated with NASA astrobiology, describes life as a self-sustaining chemical system capable of Darwinian evolution. This definition is powerful because it combines chemistry, self-maintenance, and evolution. It is especially useful in the search for life beyond Earth because it does not depend on the details of Earth biology alone. It allows scientists to ask whether another system, perhaps based on different molecules, could sustain itself and evolve.
Yet even this definition has limitations. It emphasizes evolution, but not every individual living being evolves. Populations evolve; individuals live. It emphasizes chemistry, but it does not fully explain why some chemical systems become living systems while others do not. It also leaves open the question of whether a system must be conscious, cognitive, or responsive in any meaningful sense to count as alive.
Metabolic definitions place more emphasis on organized chemistry. From this perspective, life is a network of chemical reactions that extracts energy and matter from the environment in order to maintain itself. A living system is not merely a collection of molecules. It is a dynamic process that continually rebuilds itself.
Genetic definitions emphasize replication and heredity. Life depends on information that can be copied, modified, and transmitted across generations. DNA and RNA are central in known life because they store and transmit biological information. This perspective makes evolution possible because variation in hereditary information can be acted upon by selection.
Cellular definitions emphasize bounded organization. Life, as we know it, is cellular. Cells create boundaries between inside and outside. They regulate what enters and leaves. They maintain internal conditions. They coordinate chemical reactions within a protected space. From this view, life begins not only when molecules replicate, but when they become organized within a boundary that can sustain a self-maintaining process.
Each biological definition captures part of the truth. Life is chemical, metabolic, genetic, cellular, and evolutionary. But none of these alone fully explains why living systems seem different from ordinary matter. Life is not only made of molecules; it is made of molecules organized in a particular way.
That organization becomes central when we turn to physics and thermodynamics.
2.4 Thermodynamic and Physical Definitions
From a physical perspective, life is not separate from matter and energy. Living systems obey the laws of physics. They require energy, produce waste, maintain structure, and exist far from thermodynamic equilibrium.
Erwin Schrödinger famously described life in relation to “negative entropy.” He was not suggesting that life violates the second law of thermodynamics. Rather, living systems maintain internal order by drawing energy and matter from their environments. A living organism can remain highly organized only because it exchanges energy with the world around it.
This perspective is important because living systems are not static objects. They are dynamic processes. A living body is not like a stone. It must continually maintain itself. Its order is not permanent; it is actively produced. The organism survives by resisting decay, repairing damage, regulating internal states, and transforming energy into organized activity.
Ilya Prigogine’s work on dissipative structures further developed this idea. A dissipative structure is an ordered pattern that arises in a system far from equilibrium through the flow of energy. Examples include whirlpools, convection cells, and certain chemical oscillations. These systems show that order can emerge spontaneously under the right physical conditions.
Life can be understood as a highly complex form of organized energy flow. It is not merely a structure, but a structure that persists through activity. It survives by dissipating energy, maintaining boundaries, and creating internal order through external exchange.
This view narrows the distance between life and other forms of self-organization in nature. It suggests that life may be part of a broader physical tendency for complex systems to arise under certain conditions. However, life is not just any dissipative structure. A flame also consumes energy and maintains a dynamic form, but we do not usually call it alive.
So something else is needed. Living systems do not merely process energy. They also store, transmit, and use information.
2.5 Informational Definitions
Information is central to life. DNA stores hereditary information. RNA participates in information transfer and regulation. Cells process signals from their environments. Organisms use information to maintain themselves, respond to change, and reproduce.
From an informational perspective, life is not only chemistry, but chemistry organized by information. A living system does not simply react. It interprets molecular signals in context. The same molecule can have different effects depending on where it appears, when it appears, and what state the cell is in. Biological information is therefore not only stored in genes; it is distributed across networks, structures, interactions, and regulatory processes.
This makes information a bridge between physics and biology. Physical systems involve matter and energy. Biological systems also involve matter and energy, but they add layers of coding, regulation, memory, and control. The living cell is not only a chemical factory. It is also an informational system.
Hereditary information is especially important because it allows continuity across generations. Life persists not only by surviving in the present but by transmitting patterns into the future. Mutation, variation, and selection operate on these patterns. Evolution is therefore both a material and informational process.
Some theorists argue that the origin of life should be understood as a transition in informational architecture. In this view, life begins when information gains causal power over matter: when stored patterns do not merely describe a system, but help organize and maintain it. The genome is not alive by itself, but in a cellular context it participates in the ongoing production of the organism.
This approach brings life closer to cognition and consciousness. If life is fundamentally about information processing, then the difference between life and mind may be a matter of degree, organization, and complexity rather than an absolute divide.
However, information alone is not enough. A book contains information, but it is not alive. A computer processes information, but whether it is alive or conscious remains contested. Biological information is embedded in self-maintaining processes. It is not detached from the organism. It matters because it participates in the ongoing production of life.
This leads to a deeper definition: life as self-production.
2.6 Autopoietic Definitions
The theory of autopoiesis, developed by Humberto Maturana and Francisco Varela, defines living systems as self-producing systems. The term “autopoiesis” literally means self-making or self-production. A living system is one that continuously produces and maintains the components that make the system possible.
A cell is the classic example. It produces molecules that maintain its membrane, enzymes that support its metabolism, and internal structures that allow it to continue operating as a cell. The cell is not assembled once and then left alone. It is constantly remaking itself.
Autopoiesis emphasizes operational closure. This does not mean that the organism is closed off from the environment. Living systems are materially and energetically open; they exchange matter and energy with their surroundings. But they are organizationally closed in the sense that their internal processes form a network that sustains the system’s own identity.
A living system is also structurally coupled to its environment. It does not merely exist in the world; it changes in relation to the world. The organism and environment shape each other through ongoing interaction. The organism responds to environmental changes according to its own structure, needs, and possibilities.
This is where autopoiesis becomes important for the question of consciousness. Maturana and Varela argued that cognition is not something added to life later; rather, living itself is already a form of cognition. To live is to enact a world of relevance. A living system distinguishes, through its own organization, what matters for its continuation.
This does not mean that all living systems are conscious in the human sense. A bacterium does not reflect on its existence. A cell does not have language or self-awareness. But autopoiesis suggests that the roots of cognition may be present wherever there is self-maintaining, world-directed organization.
If this is true, then cognition is not a late addition to life. It is built into the structure of living systems from the beginning. Consciousness may still emerge later, but it emerges from a field already shaped by responsiveness, self-maintenance, and meaning for the organism.
This view will become important in later chapters on self-organization, minimal cognition, and the possible continuity between life and mind.
2.7 Functional vs Ontological Definitions
Definitions of life can be divided into two broad types: functional and ontological.
Functional definitions ask what life does. A system may be considered alive if it metabolizes, grows, reproduces, evolves, responds to stimuli, maintains homeostasis, and processes information. This approach is practical because it gives us a list of observable features. It is especially useful in biology, astrobiology, and synthetic biology.
The weakness of functional definitions is that no single function is decisive. Some non-living systems perform life-like functions. Fire grows and consumes energy. Crystals grow and replicate patterns. Computer viruses reproduce in a digital environment. Artificial systems can process information, adapt, and respond. Yet we hesitate to call all of these alive.
Ontological definitions ask what life is. They treat life not only as a list of functions but as a distinctive mode of being or process. From this perspective, life is not just replication, metabolism, or responsiveness. It is a self-maintaining, self-producing, historically continuous process that creates and preserves its own organization.
The distinction matters because something might appear functionally life-like without being fully alive. A simulation of a cell may reproduce some biological dynamics, but it may not be materially self-producing. A robot may respond to stimuli, but it may not have metabolism or biological self-maintenance. A virus may evolve, but it depends on host cells for reproduction.
This raises a difficult question: can something be functionally alive but not really alive?
The answer depends on what we mean by “really.” If life is defined by functions, then sufficiently life-like systems may count as life. If life is defined by material self-production, then simulations and machines may not qualify. If life is defined more broadly as adaptive organization, then artificial life may occupy a middle category.
This debate foreshadows later questions about artificial consciousness. A machine may behave intelligently, but is it conscious? A system may simulate life, but is it alive? In both cases, we face the same challenge: whether function is enough, or whether there is something deeper about the organization, embodiment, or existence of the system.
2.8 Implications for the Central Question
The way we define life has direct consequences for the central question of this book.
If life is defined primarily as chemistry, then consciousness appears as a separate problem. Life begins with chemical systems capable of metabolism, replication, and evolution. Consciousness emerges much later, perhaps only with nervous systems and brains. This view supports the standard scientific sequence: matter first, life second, consciousness third.
If life is defined as information processing, the distance between life and consciousness becomes smaller. Living systems are not only chemical systems; they are systems that store, interpret, regulate, and respond to information. Since consciousness is also often associated with information processing, integration, attention, and responsiveness, the roots of consciousness may be closer to the roots of life.
If life is defined through autopoiesis, then cognition may be built into life from the beginning. A living system does not merely exist; it maintains itself, distinguishes itself from its environment, and responds to the world in ways that matter for its continuation. This suggests that the earliest forms of life may already contain the foundations of sense-making, even if not consciousness in a rich experiential sense.
If life is defined thermodynamically, then both life and consciousness may be viewed as forms of organized process. Life maintains order through energy flow. Consciousness may depend on patterns of organization within living systems. This view encourages us to ask whether consciousness is related to the same principles of self-organization that make life possible.
None of these definitions proves that consciousness existed before life. None proves that consciousness emerged only after life. But each definition changes the shape of the question.
A narrow chemical definition creates a larger gap between life and consciousness. An informational definition creates a possible bridge. An autopoietic definition places cognition close to the foundation of life. A thermodynamic definition situates life within broader principles of organization and energy flow.
The central question therefore cannot be answered without first deciding what kind of phenomenon life is.
2.9 How This Chapter Changes the Central Question
This chapter changes the central question by showing that consciousness is not a single simple concept. It may refer to subjective experience, access to information, self-awareness, sentience, reflective thought, or a fundamental field-like reality.
The question therefore cannot be answered until we are clear about which meaning of consciousness is being discussed. If consciousness means reportable awareness, it may appear late in evolution. If it means sentience, it may appear earlier. If it means a fundamental reality, it may not emerge from life at all.
2.10 Chapter Summary
This chapter examined several major approaches to defining life.
Biological definitions emphasize chemistry, metabolism, heredity, cellular organization, and evolution. Thermodynamic definitions emphasize energy flow, order, and far-from-equilibrium organization. Informational definitions emphasize coding, regulation, memory, and causal control. Autopoietic definitions emphasize self-production, operational closure, and structural coupling. Functional definitions focus on what life does, while ontological definitions ask what kind of process life is.
No single definition resolves all difficulties. Edge cases such as viruses, prions, self-replicating molecules, synthetic cells, and artificial life show that life exists near conceptual boundaries. These boundaries matter because they shape how we understand the relationship between life and consciousness.
If life is only chemistry, consciousness may seem like a later addition. If life is information processing, consciousness may appear as a more complex form of a process already present in living systems. If life is autopoiesis, then minimal cognition may be inseparable from life itself.
The open question is therefore:
Does every viable definition of life already smuggle in some form of cognition?