Self Replication

SelfReplication [moved from DefinitionOfLife]

Over at DefinitionOfLife, we're trying to find a good definition of life that covers the common-sense idea of "alive". One candidate was something like "If it can replicate, it is alive".

This led to some general discussion of replication.

Since the topic changed to replication in general, DavidCary decided we needed a new page for it. It seems related to ReplicatorTechnology and SelfReplicatingMemeSystems.

SelfReplication can be argued to be *more* on-topic for C2 than DefinitionOfLife, because the idea of "closure" is so important to programming languages. Any programming language that does not have closure is seen as "incomplete", because it (by definition) doesn't have enough features to make it possible to write a compiler for that language in that language. (In one twisted point of view, the compiler is using the source code to replicate itself).

(EditHint: Perhaps some of this text needs to be moved back to DefinitionOfLife.) (EditHint: SelfReproducingProgram SelfAssembly MetaProgramming seem related ... )

Discussion on replication / reproduction...

So people who for some reason can't have children aren't alive???

This is the only stumbling block I've come across for this definition. We could say that the person is still alive to some degree since:

1. Their cells are still dividing, just not their sexual cells.
2. It is theoretically possible to clone them.

Also keep in mind that in terms of evolutionary history, it is not the person that is important, but their genes. A person may be considered alive if it is possible for them to influence the survival of their genes (e.g. help raise parent's children, etc.) -- RobHarwood

According to Dawkins (paraphrased), the unit of life is the gene, bodies are just the machines the genes use to get around and do stuff. Some people think this definition is too centred on natural life, and so the above definition includes things like ArtificialLife and GeneticAlgorithms, but excludes things like fire and simple crystals.

Oops, I forgot to say that the differences are inheritable (amended above). -- RobHarwood

This is sophistry. If your definition is correct and only the cells are dividing then the cells are alive and the person is not, despite being composed of stuff which is alive. Clearly the definition is absurd from this consideration alone. It's even worse if you only consider genes to be alive because this contradicts the fact that most people do not consider genes to be alive. And if you were to argue that the ability of cells to divide confers life on an animal then you would be saddled with the unpleasant conclusion that the ability of animals to replicate confers life on species. -- RichardKulisz

"This is sophistry." Care to back up your claim with facts or proof?

If a person is sterile then by your definition they are dead. If their cells are still reproducing then it is merely those cells which are alive. The person still remains dead by your definition. Your claim to the contrary is sophistry.

"Clearly the definition is absurd from this consideration alone." Read TheSelfishGene by RichardDawkins. Dawkins is an actual scientist (and well respected), unlike some trolls I know.

I would be very, very surprised if Dawkins considers human beings to not be alive. If he does, I'll call him a cretin and a fool as much as I have you. Happy?

"... unpleasant conclusion ..." regarding species. Unpleasant how, exactly?

Because species are not single entities and so cannot be conceived of as alive, only as collections of things which are themselves alive. Being 'alive' is not a property the whole acquires from its parts but from the relationship of these parts to each other. If you cut up a human being with an axe then they are quite dead despite the fact that their constituent parts will not die for some time. If this were not the case then organ transplants could never be ethical.

If this were not the case, then perhaps organ transplants would be ethically mandatory. Many people, including myself, feel we have special ethical obligations towards things that are "alive" -- but there seems to be a huge variation in what obligations each person feels, not to mention this seems to be drifting off-topic ... -- DavidCary

An interesting conclusion from the "If it can replicate, it is alive" definition:

"DNA ... Each copy is alive (it can reproduce itself) ... No other tissue in our body is alive." -- http://www.onelife.com/onelife2.html

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discussion on importance of the cause for replication...

Another thing to consider, btw, is who is responsible for the reproduction. Bacteria do most of the work themselves, people (needing all sorts of premixed chemicals) a lot less so, viruses less so, prions less so, memes less so, record remixes not very much at all. -JoshuaGrosse

Interesting, I never considered songs before. However, I don't consider this a problem with the definition. Call me weird, but to me the most important thing that characterizes living things is their EvolutionByNaturalSelection. If other things happen to exhibit this same behaviour without typically being called 'alive' by the general populace, then I say include them, dammit! Excluding them to satisfy 'common sense' reduces the usefulness of the definition to characterize life.

The obvious problem is that most people do not consider evolution by natural selection to be the most important characteristic of life. In fact, many people legitimately consider it to be trivial and unimportant. For example: fans of the Gaia theory never gave a damn that the biosphere is incapable of reproducing itself, and people suspicious of GeneticProgramming & Memetics (see MemesShmemes) aren't likely to care about natural selection. - and note even proponents of such things don't necessarily consider them alive, just evolving.

Life is an already established concept. You are not trying to formulate a correct definition of this concept. Rather, you are trying to replace it with a completely different concept, one whose usefulness is highly questionable and controversial. Your definition is motivated by ideology, not reality. People are wise to be leery of your antics. -- RichardKulisz

According to the definition, and I stand by it, it is irrelevant 'who is responsible' for the reproduction. Who is responsible for reproduction in humans? The brain? The body? The cell? The enzymes? The RNA? The DNA? It's impossible to say, and in the end it doesn't make any difference at all. All cases of reproduction can be reduced to interaction with the environment. If the environment happens to be the inside of a cell, or inside someone's mind, or inside a CD burner, it is completely irrelevant. The important part is that the thing exhibit the complex characteristics of EvolutionByNaturalSelection.

I don't think you understand what I mean by who is responsible. Your brain, body, cells, enzymes, and nucleic acids are all part of you. To a very large extent, people copy themselves. On the other hand, to get copied a record should sound good. Records are, to a very large extent, copied by their environment. It's not that they aren't normally considered alive, rather that you are doing all the work for them, that makes records dead. But, of course, viruses and prions are a gray area.

Who am I but a bunch of molecules? I don't think you understand how fundamental the concept of 'interaction with environment' is to the concept that NaturalSearchIsaDefinitionOfLife. If I'm floating in the vacuum of outer space, I won't get much chance to reproduce. I need to be in my cozy space shuttle. Me = virus. Vacuum = extracellular environment. Shuttle = cell. No double standards, I say! If I am alive, then I must apply the same standards to any other thing that could be alive. Sure, a virus needs to interact with its environment (inside a cell) to reproduce. But you know what? So do humans (need to interact with their environment). And only certain environments will do, in both cases. And in both cases, the role of responsibility is an illusion (see CardForceTrick?). What am I doing but interacting with my environment? If I were in a tub of hydrochloric acid, I sure wouldn't be typing this right now. When you say, "But the virus isn't doing anything, the cell's doing all the work," I say, "Look who's talking." Besides, the requirement of responsibility does not add power or usefulness to the definition, it only forces it to conform to the social norm. In NaturalSelection, who's responsibility is it to do the selecting?

Did you even listen to me? As a stated, there's a spectrum. Near one end are cases where most of the information is present in the object, and it can be said to be replicating itself; near the other most of the info is present in the system, which is replicating the object. No, this isn't a hard and clean distinction; you can have degrees either way (viruses for instance have slightly more system-info then people but less than records) - but that doesn't make it any less important.

Otherwise almost anything I please is alive. Letters are alive, for instance, because if I like the way they look I will copy them out and sometimes make mistakes, that make them look better or worse - hence natural selection. That's as much a mistake as fire and crystals, believe you me.

And, as a side note, no-one is responsible for the selecting: the whole point is better replicators naturally dominate. But that doesn't change that someone must be responsible for the replicating, in this sense (and this isn't a CardTrick): the structure which causes the replication to happen must reside somewhere between the object and the system. Reading GEB never hurts.

Btw, by this standard genetic algorithms are not alive. The physics does the reproduction for the bit-strings, which are more or less inert. The information contained in them has nothing to do with reproduction; you could never have one that wouldn't reproduce unless outcompeted. Evolution still takes place, but it's close-ended ArtificialSelection? rather than open-ended NaturalSelection.

An example of open-ended selection was Tierra, which was a simulation of evolving self-replicating programs with a mortality queue (to ensure they had to try and copy or maintain themselves). Here the programs did all the work themselves, and evolved only according to what was better at copying itself and dodging mortality...one saw all sorts of innovations like parasites and immune systems appear. This is the sort of A-life that might be considered living.

Basically, the above DefinitionOfLife gives the necessary and sufficient conditions for EvolutionByNaturalSelection without actually needing to go into immense detail. The definition fits precisely because it is the most compact specification for life (that I've seen so far, anyway). It includes anything that could reasonably be considered alive, and excludes anything that could not. Think of it like a class Life, and you can sub-class it into NaturalLife?, Memes, Language, or whatever categorizations turn out to be useful. The question is (or should be) What does all life exhibit?, not just What does natural life exhibit?. -- RobHarwood

As stated, this was not at all my complaint. I have no problem with A-life, anyway, but I've pretty much summed up what's relevant. And it's important, because without a concept of self-reproduction or self-homeostasis or so forth it's just life in a universe with a different set of physics. But when your rules become so complicated as "after WWII people became disillusioned with the contemporary cultures and so more radical things become viable", it becomes more questionable whether or not the replicators aren't really just inert. This, btw, is touched on in GoedelEscherBach, which is why I felt it might be a fair reference.

I haven't read that one, so I'll have to remain ignorant.

Well, no...Hofstadter's presentation is a bit better, and it's something you should read you can never have an exclusive definition of life.