Question
Are all living things just some complex chemical macro-molecules?
Answer
Try Gregory Chaitin, "Towards a Mathematical Definition of Life" as a starting point.
http://citeseerx.ist.psu.edu/vie...
Self-replication is correlated with, but neither necessary, nor sufficient for "life." John von Neumann's classic work on "universal constructor" cellular automata, and the work inspired by that on an idea called "clanking replicator" show that self-replication is a simpler idea than people think. Hod Lipson's group at Cornell has in fact created limited forms of robotic self-replication.
There are some interesting fundamental theoretical issues there though, that are relevant, including the minimum information-theoretic complexity of a self-replicator.
Response to stimuli is also obviously not a particularly useful criteria, since it can created at even simpler levels than self-replication. A thermostat responds to stimuli in a life-like way, and it is not clear what meaningful thresholds of complexity make the responsiveness "life like."
So given all this, I don't pay attention to any of the superficial "correlates of life." The only useful approach I have found is Chaitin's based on Kolmogorov-Chaitin (or Algorithmic) complexity, a cousin of the NP-completeness variety.
Since this is a very computational approach to defining life, an implication is that the "hardware" could conceptually be something other than carbon-based biochemistry.
I am not sure I am comfortable accepting this conclusion, so I personally leave it as an unanswered mystery, whether or not the specifics of DNA-based biochemistry have something fundamental to do with "life" that is NOT captured in computational models. The ability of the substrate to allow consciousness to emerge is an important criterion for me. I don't yet know whether silicon-based computing hardware that is computationally equivalent to "life" would be conscious. If not, I don't know whether the substrate would have anything to do with it. Maybe if consciousness is a property of space/time like I believe, carbon is just a more conscious kind of matter than silicon.
May sound like a stupid thought, but the point I am making is that there's a mystery there.
http://citeseerx.ist.psu.edu/vie...
Self-replication is correlated with, but neither necessary, nor sufficient for "life." John von Neumann's classic work on "universal constructor" cellular automata, and the work inspired by that on an idea called "clanking replicator" show that self-replication is a simpler idea than people think. Hod Lipson's group at Cornell has in fact created limited forms of robotic self-replication.
There are some interesting fundamental theoretical issues there though, that are relevant, including the minimum information-theoretic complexity of a self-replicator.
Response to stimuli is also obviously not a particularly useful criteria, since it can created at even simpler levels than self-replication. A thermostat responds to stimuli in a life-like way, and it is not clear what meaningful thresholds of complexity make the responsiveness "life like."
So given all this, I don't pay attention to any of the superficial "correlates of life." The only useful approach I have found is Chaitin's based on Kolmogorov-Chaitin (or Algorithmic) complexity, a cousin of the NP-completeness variety.
Since this is a very computational approach to defining life, an implication is that the "hardware" could conceptually be something other than carbon-based biochemistry.
I am not sure I am comfortable accepting this conclusion, so I personally leave it as an unanswered mystery, whether or not the specifics of DNA-based biochemistry have something fundamental to do with "life" that is NOT captured in computational models. The ability of the substrate to allow consciousness to emerge is an important criterion for me. I don't yet know whether silicon-based computing hardware that is computationally equivalent to "life" would be conscious. If not, I don't know whether the substrate would have anything to do with it. Maybe if consciousness is a property of space/time like I believe, carbon is just a more conscious kind of matter than silicon.
May sound like a stupid thought, but the point I am making is that there's a mystery there.