Classical Definition = Life, or Something Else?

A nudibranch and a sea squirt, both classically alive

More precisely, does the classical definition define all forms of life?

"The unexamined life is not worth living for a human being" (ho de anexetastos bios ou biôtos anthrôpôi — ὁ δὲ ἀνεξέταστος βίος οὐ βιωτὸς ἀνθρώπῳ), said Socrates, according to Plato in The Apology. Among the many reasons to live an examined life is that the greatest revelations usually await us in the things we take for granted, the things we do not examine.

Chief among those overconfident blind spots is our habit of framing the bounds of discussion and then letting that frame go unquestioned. This discussion of whether VISTA is a living system hinges on our definition of life, so let's put the spotlight on that.

Sure, VISTA may not fully fit the classical definition of life, but does that definition actually define life? Most biologists agree it does, more or less, but what does that really mean? It means it defines something they equate with life, but that's not the same as saying it actually defines life.

Could this definition be defining something else, something other than life per se? If so, what is it? What is so close to life that biologists would nearly universally confuse it with life?

The wording of the definition - especially certain clauses - gives it away. What is made of cells, metabolizes food into energy, and reproduces? The definition even answers the question for us by using the answer as a synonym for life: an organism. This definition equates life with an organism. It cannnot conceive of non-organismic life, because it has bundled together multiple characteristics - some of which are different in kind from one another - into a single definition and then made an implicit assertion about the subject of the definition.

This definition has begged the question of what is life by offering a definition that only claims to define life. We can all see it defines an organism, and we assume a priori that an organism is the only form life can take.

Is it?

About the Photo

A nudibranch (Nembrotha lineolata, right) lays eggs in a spiral pattern on a sea squirt (Polycarpa aurata).

Nudibranchs are a kind of sea slug, marine gastropod mollusks in the family Polyceridae and class Gastropoda (which includes sea slugs, slugs, and snails). They are often spectacularly colorful, and their external gills rise from their backs like floral plumes.

Sea squirts are a kind of tunicate, immobile filter-feeding marine animals found in shallow waters throughout the world’s oceans. Tunicates preserve the original form and life-patterns of the earliest chordates; all vertebrates—including Homo sapiens—are descended from creatures much like tunicates. In their larval form, tunicates have a notochord, a stiff, spine-like rod that is the ancient predecessor of the spine. Tunicates lose their notochord by the time they reach adulthood, so we evolved from animals like them via neoteny—the retention of juvenile characteristics into adulthood.

Photo: Nick Hobgood
Source: Wikipedia