I think it’s not that hard to make a definition of life that includes everything most people consider alive and excludes everything else. You could just call life anything that stores instructions for making more copies of itself on nucleic acids. Maybe I’m being too glib, I dunno. But the better definitions of life don’t really seem to be trying to determine whether edge cases should count as alive or not, which as you note is not really a pressing question.
It’s more a matter of saying, “This thing we call life is interesting. What are the characteristics that make it so interesting?” and coming up with things like self-replication, homeostasis, metabolism, that stuff.
I agree that it isn’t that hard. But your definition doesn’t quite do it. As written, your definition includes things that have died and things that aren’t yet alive.
Dead plants and animals still have usable DNA for a while after death. If the tissues are preserved, sometimes it’s a long while. And mostly, we don’t think of spores or viruses as living things, but they certainly have DNA.
I would supplement your definition by saying that we refer to an organism as alive when its pieces are functioning in a coherent and mutually-dependent way to keep the organism as a whole alive. (Some fuzziness creeps in when you try to distinguish a composite organism from a collection of separate components...but I don’t think that causes problems in practice.)
Oh yeah, good call, dead things. You know, the more I think about it, the more I think the concept of “dead” might be even more fraught with vitalism than “alive” is.
The point was to make a clearly after-the-fact definition that works, but doesn’t say anything interesting. There may not be any exocritters that use some other macromolecule for their genetic material. If not, it would be a non-issue, right?
If you try to make a definition that says something interesting, I think it’s got to be a whole checklist of interesting characteristics of life in order to exclude things most people wouldn’t consider alive. Then you get people looking at objects that exhibit some, but not all of the characteristics and wringing their hands over whether or not it’s really alive, as if that’s a thing. Which I still don’t think it is. I think what we’re looking at here is lingering vitalism.
Life is just matter with interesting characteristics. We can talk about why it’s interesting, but we can’t explain why it’s totally different from all the other matter, because it isn’t.
The point was to make a clearly after-the-fact definition that works, but doesn’t say anything interesting. There may not be any exocritters that use some other macromolecule for their genetic material. If not, it would be a non-issue, right?
It would still be an issue if we started making synthetic life. A good definition ought to cause as little inconvenience as possible. I agree that life isn’t fundamentally different from all other matter, but the reason we have the word at all is because it’s handy to be able to encapsulate it as a reference class. Individuals with a solid grounding in natural sciences may at least be at a state of “I know what I mean when I talk about it,” but if we are going to define it at all rather than simply taking the Justice Stewart approach, the definition should encapsulate what we actually mean.
I agree that life isn’t fundamentally different from all other matter, but the reason we have the word at all is because it’s handy to be able to encapsulate it as a reference class.
I think the reason we have the word is more to do with historical vitalism than with carving reality at its joints. These days it’s most often, or at least most rigorously, used to indicate “that thing biologists study, with all the membranes and nucleotides and amino acids.” If you want to be more abstract than that, I don’t think trying to define “alive” is really a good approach at all, because it means too many different things. But you can certainly look at all the interesting things it can mean and figure out which one you’re currently talking about. You might want to give it a new name, though.
I think it’s not that hard to make a definition of life that includes everything most people consider alive and excludes everything else. You could just call life anything that stores instructions for making more copies of itself on nucleic acids. Maybe I’m being too glib, I dunno. But the better definitions of life don’t really seem to be trying to determine whether edge cases should count as alive or not, which as you note is not really a pressing question.
It’s more a matter of saying, “This thing we call life is interesting. What are the characteristics that make it so interesting?” and coming up with things like self-replication, homeostasis, metabolism, that stuff.
I agree that it isn’t that hard. But your definition doesn’t quite do it. As written, your definition includes things that have died and things that aren’t yet alive.
Dead plants and animals still have usable DNA for a while after death. If the tissues are preserved, sometimes it’s a long while. And mostly, we don’t think of spores or viruses as living things, but they certainly have DNA.
I would supplement your definition by saying that we refer to an organism as alive when its pieces are functioning in a coherent and mutually-dependent way to keep the organism as a whole alive. (Some fuzziness creeps in when you try to distinguish a composite organism from a collection of separate components...but I don’t think that causes problems in practice.)
Oh yeah, good call, dead things. You know, the more I think about it, the more I think the concept of “dead” might be even more fraught with vitalism than “alive” is.
We could, for all the good it would do if we encounter organisms on other planets that store reproductive information on something else.
The point was to make a clearly after-the-fact definition that works, but doesn’t say anything interesting. There may not be any exocritters that use some other macromolecule for their genetic material. If not, it would be a non-issue, right?
If you try to make a definition that says something interesting, I think it’s got to be a whole checklist of interesting characteristics of life in order to exclude things most people wouldn’t consider alive. Then you get people looking at objects that exhibit some, but not all of the characteristics and wringing their hands over whether or not it’s really alive, as if that’s a thing. Which I still don’t think it is. I think what we’re looking at here is lingering vitalism.
Life is just matter with interesting characteristics. We can talk about why it’s interesting, but we can’t explain why it’s totally different from all the other matter, because it isn’t.
It would still be an issue if we started making synthetic life. A good definition ought to cause as little inconvenience as possible. I agree that life isn’t fundamentally different from all other matter, but the reason we have the word at all is because it’s handy to be able to encapsulate it as a reference class. Individuals with a solid grounding in natural sciences may at least be at a state of “I know what I mean when I talk about it,” but if we are going to define it at all rather than simply taking the Justice Stewart approach, the definition should encapsulate what we actually mean.
I think the reason we have the word is more to do with historical vitalism than with carving reality at its joints. These days it’s most often, or at least most rigorously, used to indicate “that thing biologists study, with all the membranes and nucleotides and amino acids.” If you want to be more abstract than that, I don’t think trying to define “alive” is really a good approach at all, because it means too many different things. But you can certainly look at all the interesting things it can mean and figure out which one you’re currently talking about. You might want to give it a new name, though.