One of the (many and oft-debated) aspects of life is that via homeostasis it maintains a negative entropy gradient. That is, over time, it will coalesce more "order" within itself than the 2nd Law of Thermodynamics says should normally happen -- more than if it were merely a random bag of chemicals.
I like this definition, because it implies some kind of "trying" -- life must "try" to keep some balance that continues its existence.
(a) Viruses (and certain bacteria) confound this approach because they can indefinitely continue (and even evolve) their existence without actively maintaining or improving any kind of this "balance"; they rely on their host to provide the balance, or at least some critical parts of it (if by definition, they cannot exist outside a host).
(b) Does this make them life? Unclear, maybe.
(c) Could such an organism evolve to no longer depend on a host? Yes, conceivable.
(d) Would this organism that maintains homeostasis on its own be considered life? I would venture to say yes.
So at what point during the evolution from (a) to (d) did this organism become "life"? It seems like it is just semantics at that point. Pick your criterion, call it life.
I think a virus has much lower entropy than a cell. It's tightly packed, ordered and semi-crystal-like. Viruses make more viruses. I think they may be winning if you measure them by creating pockets of deceased entropy!
I like this definition, because it implies some kind of "trying" -- life must "try" to keep some balance that continues its existence.
(a) Viruses (and certain bacteria) confound this approach because they can indefinitely continue (and even evolve) their existence without actively maintaining or improving any kind of this "balance"; they rely on their host to provide the balance, or at least some critical parts of it (if by definition, they cannot exist outside a host).
(b) Does this make them life? Unclear, maybe.
(c) Could such an organism evolve to no longer depend on a host? Yes, conceivable.
(d) Would this organism that maintains homeostasis on its own be considered life? I would venture to say yes.
So at what point during the evolution from (a) to (d) did this organism become "life"? It seems like it is just semantics at that point. Pick your criterion, call it life.