The Concept of Life
The concept of life is notoriously hard to define. The OED makes a decent stab at it with the following: “The condition that distinguishes animals and plants from inorganic matter, including the capacity for growth, functional activity, and continual change preceding death”. The first part of this is blatantly circular, since “inorganic matter” just means “lifeless matter”, so we are being told that life is the opposite of non-life. All we can gain from this is that “life” is a contrastive term, distinguishing animals and plants from such things as rocks and water. But the rest of the definition gives us more to chew on: life involves growth, activity with a function, and continual change, culminating in death. I would emphasize that life involves birth, youth, maturity, old age, and death: developmental stages in which there is growth, relative stasis, and decline. This growth is not purely a matter of increasing size, since organisms can grow in their complexity and sophistication (the brain is the obvious example). We speak of the mind growing, reaching maturity, and then declining, thus conceiving it as part of life—as a living thing. We also refer to our “inner life” or “mental life”. The dictionary does not stipulate such properties as homeostasis or reproduction or metabolism or DNA; no doubt these characterize life on earth, but they don’t belong in a definition, because they are too parochial. They provide neither necessary nor sufficient conditions for the concept of life as such. For example, crystals reproduce (replicate) but they are not living, and we do not withhold the concept from animals that are unable to reproduce. Our concept of a living thing does not require these conditions to be met, though they are certainly typical of actual living things, as we know them. The concept is neither a family resemblance concept nor a primitive concept nor a concept rigorously definable by means of necessary and sufficient conditions; it is a concept that can be roughly glossed in terms of such features as growth, functional (goal-directed) activity, and change unto death. We might call it a “typical features concept”.
Does the concept apply to anything other than whole organisms? Does it apply to the parts of whole organisms? It would be wrong to say that the molecules that compose an organism are living things (certainly not the atomic constituents of such molecules), but it isn’t a stretch to say that the gross organs that compose a body are themselves living things. The heart is a living thing and it fits the dictionary definition: it grows, actively functions, and changes till death stops it—and similarly for the other bodily organs. Also, it seems right to say that cells are living things, because they too fit the definition—they grow, act functionally, and eventually die off. Even outside the context of an organism these entities count as living things. Bacteria do too—though viruses are not clearly living things (they can’t survive without a host cell and lack the kind of development characteristic of life forms). They are more like tiny robots that invade an organism, replicating but not really living. They disappear or disintegrate, but they don’t really die; they don’t have a childhood, a middle age, and an old age followed by death—they don’t change form in these ways. In any case, the definition applies to bodily organs as well as whole organisms. The tougher question is whether the organs of the mind qualify as living things. The eyes are living things, but is vision a living thing? Is memory a living thing? Is language a living thing? Is the rational faculty a living thing? We certainly think that persons are living things—and they clearly fit the definition—but do the mental faculties characteristic of persons also qualify? If so, that would make psychology into a branch of biology by definition—and philosophy too, if it deals with such faculties. I shall suggest that they do so qualify: so mental organs are as much living things as bodily organs.
The obvious point is that the faculties in question bear the marks of life as specified in the dictionary definition: growth, change, and functional activity. Memory, intelligence, the senses, language ability, consciousness, and the emotions all develop and grow during ontogenesis, display functional characteristics, and suffer decline in their later stages, eventually ceasing to exist with death. They may be healthy or diseased, effective or defective, and they are bound up with the survival of the organism. They are not extraneous to the life of the organism but integral to it. No doubt they have an innate component as well as acquiring features as they mature. They are adapted to the organism’s environment–part of the equipment the organism brings to its life. So the components of mind are as much living things as the components of the body. The study of the mind is thus a study of an aspect of life, hence a part of biology. This kind of perspective is not entirely alien to the analytical tradition in philosophy—there is Wittgenstein’s “form of life” and Husserl’s lebenswelt (life-world), for example—but it is not taken as a clear truth and generally acknowledged. The categories of Mind and Matter are standard philosophical categories, but we don’t hear much about the third category of Life. Nor is it that this category has suffered any demotion in intellectual history comparable to the travails of the concept of matter: it isn’t as if Darwin destroyed the notion of life as Newton destroyed the notion of matter by introducing the “occult” force of gravity. It is true that the conception of life as an expression of the “vital spirit” has fallen into disrepute, but that is not to say that the concept of life itself has fallen upon hard times. So there is nothing suspect about using the concept of life to describe the faculties of mind and body as well as complete organisms. There is nothing “non-natural” afoot here, or conceptually bankrupt. We are simply resisting the tendency to take the mind to belong to some sort of supernatural realm by insisting that it belongs to biology—not because of any reductive urge but because mind is an evolved and functional trait of organisms. Growth, maturity, and decline are aspects of its natural history, setting it apart from inanimate matter, which neither matures nor ages nor acts functionally.
Are there any other living things that are not conventionally described as such? How far can the concept be legitimately extended? Rocks, planets, and electrons are clearly not living things, but what about numbers or geometric forms? I think not: they don’t display the sort of developmental arc characteristic of life, and they don’t die or contract diseases or suffer injuries. Is God a living thing (as God is traditionally conceived)? Jesus certainly was, being part man, but what about God the Father? There is no birth or death in his case, to be sure, but there is purpose and activity, not stasis and aimlessness. Perhaps God is partly a living thing—a quasi-organism (blasphemous as that may sound). The concept is perhaps not clear enough to yield a determinate answer. Hair and fingernails also hover on the border, exhibiting both growth and functionality, but lacking in feeling and organic substance (they are made of keratin and consist of dead cells). What about human productions like artifacts and systems of belief? Artifacts have functions and something close to birth and death, but they lack self-directedness and adaptability; thus they can give an appearance of life while lacking the key ingredients of life (robots, in particular). Fire too can look like a living thing, but it has no functional properties: it grows and changes and dies out, but it never does anything directed towards a goal. What about physics or religion? We might describe them as having a birth and undergoing growth, possibly entering a mature phase, conceivably dying a death; but this seems metaphorical in the absence of active self-propelled survival tactics. Physics and religion don’t strive to stay alive by exploiting the environment functionally. Particular natural languages are similar: we speak of “dead” languages like Latin, but there is no active self-preservation on the part of Latin. The idea of a meme might seem more promising: memes replicate and proliferate, following Darwinian logic, but they don’t engage in functional activity (certainly no metabolism or functional organization)—they lack a physiology. Perhaps surprisingly, genes are dubious candidates for life too: genes are not themselves living things despite their role in the life of living things. Genes (bits of DNA) don’t grow and mature or purposefully act to preserve themselves—they are not like mini organisms. The double helix is not an animal or a plant, however microscopic: it is a chemical, and chemicals are not alive. No one has ever seen a strand of DNA scavenging for food or trying to find a mate or running for its life or growing protective spikes. Genes lack the chief characteristics of life: they cause life but they are not alive. Cells yes, genes no. Are beliefs alive? That sounds odd, and not without reason: beliefs are states of living things but are not themselves living things, since they lack the features of growth, self-directed functional activity, and eventual death. It is a category mistake to say that beliefs can be healthy or unhealthy, alive or dead, though they may make the organism that has them to be so describable. In general, states and properties of organisms are not themselves living things: being hairy or strong is not a living thing, merely a property of a living thing. Is the unconscious mind a living thing? As conceived by Freud, it may qualify, as it is self-like in its organization, like a second buried person: it has a natural history, it is functionally active, and it keeps changing till death puts a stop to its machinations. The brain certainly is a living thing and presumably the unconscious occupies a part of the brain (the occipital lobe is a living thing). Are art and music living things? They mimic life to some degree—they originate, mature, and expire like life—but again they lack autonomous functional activity. Is the earth a living thing? Some have supposed so and one can understand why, but again the suggestion seems metaphorical given that the earth itself lacks goals and goal-directed activity. The universe looks to have a birth (the big bang), a mature period, and then an end (the big crunch), but to call it living is stretching the concept given that it lacks goal-directed activity. It is perhaps an epistemic possibility that it has goals we know nothing of, and might even be one of a multitude of other goal-directed universes, in which case it is one exceedingly large organism; but that is not our usual conception of the universe, so as far as we know it is not alive. The concept of life may not be precisely defined but it is quite restrictive. It is important to get right what it does apply to and what it does not apply to.
 A note about the connection between consciousness and life: the former is neither necessary nor sufficient for the latter. Not necessary because many living things are not conscious (plants obviously), and not sufficient because we can conceive of non-living robots that are conscious. In the case of conscious robots we have a curious hybrid in that while their bodies may not be living things their minds may be: the body may lack organic development (being born as “adults”) but they could be designed so as to develop and grow mentally. They would thus be physically lifeless but mentally alive. Isn’t this just how some fictional robots appear?