[Ericson2314]

Considering that the first proto-computers were not programmable, I can't help but be skeptical that the first life needed genetic material.

Certainly there were lipid membranes. Maybe there were spontaneous proteins, maybe there was purely-catalytic RNA.

I guess it's also a matter of line drawing. I'm OK with calling crystals life, for example. One should feel bad about breaking up big ones the same as one should feel bad about killing 150 year old lobsters.

[cossatot]

The crystal thing is throwing me (a geologist) off. Basically all Earth materials are crystalline. So rocks are alive (colonial organisms I guess since they are aggregates of crystalline minerals) but the magma that they crystallize from is not alive? Or is magma alive too? What about obsidian, which is glass but compositionally identical to a crystalline igneous rock. No crystals! The Earth's crust and mantle: Crystalline. Alive. The Earth's outer core: liquid iron and nickel. Non-living. The inner core: crystalline iron and nickel. Alive.

Crystallization is reversible in a thermodynamic sense. You take some granite, melt it, and then cool it (slowly, under pressure), and you have granite again. Is this a phoenix/Jesus-like life and death cycle? Or does life only change forms?

I agree with you generally that 'life' may be gradational. However I think calling crystals 'life' actually removes any meaning whatsoever from the term. If the line isn't somewhere in the neighborhood of viruses and prions then it kinda has to expand to include anything made of matter (and then energy etc.).

While we don't (and don't have to) have a precise definition of 'life', the 'life' gradation needs to branch like a Bezier curve off the x axis at some point for it to be a functional term.

[andrewflnr]

Playing devil's advocate: "crystalline" in bulk is different from "a crystal". I think the idea is that individual crystals are "alive" in that sense, and the bulk is maybe a colonial organism. Maybe quartz crystals forming in a chunk of what will soon be granite are only "alive" in the brief period where they are still growing. When the rock solidifies, the crystal "starves" and "dies", leaving only a corpse. Melting and refreezing granite would basically be composting, using formerly alive material to foster new life.

On a similar note, a dead human is "compositionally identical" to a living one, at least for a little while, so I think that's entirely a red herring. :)

[BlueTemplar]

Interesting parallel, after all crystals release energy in the form of heat while forming!

Edit : forgot about crystals that absorb energy while forming:

https://news.ycombinator.com/item?id=25516072

[BlueTemplar]

> the 'life' gradation needs to branch like a Bezier curve off the x axis at some point for it to be a functional term.

What do you mean? Bezier curves are 2d parametric curves, the x and y axes are completely arbitrary...

[6510]

As the ancients knew: All facts require an observer so life is what can be convincingly be identified as life by a human being.

[narag]

Is key word "alive" or is it "conscious"? Or at least "sentient"?

[whatshisface]

Crystals are mostly not sentient, except for quartz. The high prevalence of quartz in the Earth's crust can be explained by the anthropic principle.

[angst_ridden]

I think you've got a minority opinion calling crystals "alive," although it does jibe with one definition of life that I heard: "any self-sustaining system that reduces internal entropy."

[DanBC]

Dawkins doesn't call crystal structures alive, but he does mention them as a potential hypothetical source for life.

http://www.bbc.co.uk/earth/story/20160823-the-idea-that-life...

> Cairns-Smith found a more eager audience in science journalists and the popular press. Other scientists showed interest, too: the evolutionary biologist and writer Richard Dawkins discussed the crystals-as-genes hypothesis in his 1986 book The Blind Watchmaker.

[...]

> His aim was to find a system much simpler than modern life, but which had some of the crucial properties of a living system. He found an answer in an unlikely place: clays.

[api]

My favorite version of this classifies life as an exotic phase of matter in the sense of other exotic phases like Bose-Einstein condensates, etc.

Life is a phase of matter in which the dynamics of information and Turing-complete computation overcome the ordinary dynamics of matter and energy. I am not aware of who originated this idea, but I heard it from Christoph Adami (a researcher in evolutionary information theory). I also recall someone at a conference proposing the term "Turium," for "Turing-complete phase of matter."

Earth just happens to have an environment that contains a large abundance of this phase of matter, much like how stars are full of plasma etc.

[kubanczyk]

How is this model useful? It certainly moves away from our domain knowledge and paints a new picture that is considerably more fuzzy than the old one. What do you gain by considering life in such way?

Side note: computation seems like a wrong term, because it's not about counting/calculating/determining any abstract value, is it? A Turing-complete mechanism maybe?

[api]

I find the idea of it as a phase of matter very conceptually elegant in that it neatly classifies life as a unique but still physical phenomenon. Nevertheless I agree with you that the details of the definition are hard to pin down.

Of course I have yet to see an attempted definition of life that isn’t a little squirrely or that isn’t just a list of criteria taken from the one example we have.

[adrian_b]

While obviously crystals are not alive, they satisfy more careless definitions of life that were sometimes encountered, i.e., when put in a "nutritive" solution, they are able to grow and reproduce themselves.

[dekhn]

This is just wrong (as you say, careless). The criteria is "metabolism", not growth and reproduction. Similarly, viruses are not alive although they can reproduce. Interestingly, there are some highly parasitic organisms with limited ability to metabolize, that is, they have lost their genes and instead depend on their host organism (but I think all those examples still have some level of metabolic capability).

[Ericson2314]

I don't really know what "metabolism" means, abstractly. I am deader than a virus without chloroplasts existing elsewhere. Viruses need a host for the productive bit, I had food for the non-reproductive bit. Viruses don't break down fast enough compared to their abundance to cause extinction, so why fault them for optimizing?

People commonly theorize that virus came from rump parasitic cells. I wouldn't be surprised if at some point a huge virus with a membrane accidentally picked up enough stuff to become a cell again. To go back to chloroplasts again, it would be like how brown algae is an ex-heterotroph.

[bonzini]

There used to be a hypothesis that DNA originated in viruses and that the three branches of life (archea, bacteria and eukaryota) evolved when three different DNA viruses encountered preexisting RNA-based cells. (https://www.pnas.org/content/103/10/3669)

Nowadays however it is more widely believed that eukaryota descend from archea, but anyway it's pretty much a given that viruses are not and have never been alive. And while the opposite has happened, gene transfer usually goes from viruses to cells, endowing them with new abilities, more than the opposite direction.

[geomark]

Metabolism has two parts: Catabolism breaks down complex molecules into smaller building block molecules - think proteins -> amino acids. Then anabolism uses those building blocks to build up larger molecules for growth and maintenance. Crystals don't do the catabolism part.

[kubanczyk]

Nah, this seems more like an implementation detail than an actual core of life's "functionality".

[webmaven]

> People commonly theorize that virus came from rump parasitic cells.

I have an alternate theory, that I've never seen articulated elsewhere: Viruses might be inter-microbial biochemical warfare gone wild; Among primitive and not-particularly robust cells, one competitive strategy might be to package toxins or other disruptive molecules into capsids that cleverly get past the 'enemy' cell membrane, perhaps aimed simply at disrupting the initially brittle reproductive process. Packaging random genes in with these capsids would be the beginning of the Horizontal Gene Transfer function that viruses perform in the ecosystem. A refinement would be to add in the specific genes for producing capsids as a deliverable so a subverted 'enemy' then takes out several neighbors (but 2nd gen capsids don't have to necessarily contain the same genes in order to accomplish their 'mission', or even be entirely identical to the 1st gen, as long as they work). A further refinement would be increasing fidelity, and packaging the responsible genes into the 2nd gen capsids produced by subverted cells so the 'weapon' can spread exponentially.

And voila, the 'weapon' has now escaped the originating organism and can evolve independently parasitizing the target. Each incremental step can at least hypothetically provide an evolutionary advantage so the whole thing doesn't have to spring forth fully formed.

Depending on how widespread variants of the original strategy were, viruses might have independently emerged more than once.

If I'm right, we ought to still be able to find cells that attack or suppress competitors with capsid-like molecules that don't particularly resemble existing virus lineages, possibly containing non-genetic payloads of various sorts.

We might also find bacteriophage endoviruses that as their 2nd stage only produce capsids sans-genes or that otherwise aren't identical to the endovirus, or ones that aren't very good at packaging up the correct genes, or that are much better at disrupting cell reproduction than hijacking it, or that the subsequent copies are only low-fidelity ones that can similarly penetrate the host but not spread any further; basically any indicators that the mechanisms for penetration of the membrane, attacking the cell, and even for making poor 2nd gen copies, have been evolving longer than capabilities only needed for indefinitely repeated copying, retransmission, and reinfection.

I suspect though that the oldest reconstructible endoviruses will no longer be capable of penetrating current members of their host cohort, which tells us little about the virus itself, but may offer clues about whatever ancestral cells were still prone to infection were like.

[pmayrgundter]

Neato!

[sterlind]

Viruses need a host environment to replicate. Fish need water and plant life or other fish to replicate. Algae needs nutrients to replicate. Every lifeform can only exist in some host environment. Viruses simply happen to have biological host environments, right?

[bufferoverflow]

You're equivocating environments and hosts.

Hosts do the replication for the viruses.

Environments do NOT do the replication for the fish.

[tw25508394]

Single-cell organisms replicate.

Single cells of multi-cellular organisms replicate.

Shoot me in the head and all my cells will eventually stop replicating.

To a cell in my body, is the body a host or an environment? Is the distinction useful?

[jacquesm]

In fact, for quite a few fish they do, ditto amphibians and insects too.

Mammals are the exception here, there the environment for replication is an integral part of the body of the parent. But in all those other cases, including, technically, marsupials it isn't.

[Ericson2314]

We are all just environments for ribosomes.

[plutonorm]

You've not understood the depth of the original comment's thinking.

[dekhn]

this is certainly not the mainstream way of thinking; it's certainly not specific enough.

[beowulfey]

I think even under that definition they don't truly reproduce and still aren't really life -- they don't create the same material they arise from for example (so not allowing for additional crystals to form). A non-renewing source of the material has a maximum amount of crystal that can grow, I would imagine. This is different than something like a virus, which carries the instructs to replicate itself and the ability to travel to new hosts to create more of itself (and still isn't really considered alive).

[Ericson2314]

> A non-renewing source of the material has a maximum amount of crystal that can grow

So any biosphere that fails to escape its looming red giant was never alive?

I'm not a "all abstractions leak" type of person, so I will choose my definitions very carefully, with funny choices about clays, crystals, virus, etc. as an acceptable causality.

[Igelau]

> obviously crystals are not alive

Very few things are obvious. Is this?

[snowwrestler]

Crystals don’t reduce their internal entropy. They grow only on the interface with the media, and the portions of the crystal that become internal during this process do not change after crystallization if kept at constant temp and pressure.

In contrast, if you put a plant and its media (soil, air, water) into constant temp and pressure, the plant will continue to grow and change until it exhausts the media. (assuming the temp and pressure are conducive to life) Ultimately plants become their own media by decomposing into soil.

[BlueTemplar]

If an external disturbance scatters the atoms inside the crystal, they will snap back to the lattice again. In a way similar (up to a point) to "normal" living organism's homeostasis.

[Razengan]

> "any self-sustaining system that reduces internal entropy."

Planet Earth would/should definitely count as alive, especially if it "reproduces" via us terraforming other planets to become like Earth.

[whimsicalism]

Ultimately, this is a semantic debate trying to apply human linguistic constructions to physical processes.

[dilawar]

Good plot for Rick and Morty. Wait, they already did it.

[tw25508394]

Amen! This is about as useful as debating whether Pluto is a planet.

[snowwrestler]

By this argument houses would also count as alive because they “reproduce” via humans building more houses.

(When you feel compelled to “air quote” a key term in your argument, that’s a clue you probably don’t have a good argument.)

[Razengan]

You know that kind of reduction isn't the same thing.

Earth+Life is a different entity than Earth on its own, or any other planet.

Earth allows and protects life, and life in turn influences Earth. That kind of symbiosis on such a scale is in a class of its own, with no other equivalent or analogy that we know of. It deserves a special classification.

[angst_ridden]

There are plenty of conceptualizations of planet-as-organism, e.g., Gaia Hypothesis.

[SuoDuanDao]

It seems nonsensical in any case to claim something that contains life among its constituent parts is not itself alive. Plenty of organisms have 'dead' tissue as part of their gestalt and no one thinks of them as 'mostly' alive.

[Supermancho]

> It seems nonsensical in any case to claim something that contains life among its constituent parts is not itself alive.

Parts of yogurt are alive. Yogurt is not alive. I have no problem with this.

[cossatot]

Life isn't a constituent part of the Earth. It's a coating.

[Razengan]

That statement is such a gross oversimplification of a tiny fraction of the whole picture.

Life permeates deep into Earth and even influences its geology:

https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole#Resear...

https://en.wikipedia.org/wiki/Petroleum

[kevmo]

That's one place where my "What is Life?" college class landed.

[marcosdumay]

I think it's likely that the first life like our kind was only composed of genetic material.

RNA and DNA are prone to replicating themselves (with many errors and not efficiently) in a wide variety of situations. It's way more likely that evolution selected those molecules for efficiency than that some complex life appeared without some transferable data storage.

[adrian_b]

No they are not able to replicate themselves, in any circumstances.

Obviously, any RNA or DNA molecule can serve as a template for the polymerization of another nucleic acid molecule.

However the polymerization cannot proceed spontaneously. The nucleotides polymerize by condensation, i.e. by releasing water.

It should be obvious that such a reaction cannot be spontaneous when the molecules are already surrounded by water. You need some molecule able to extract the water from the nucleotides, for example an acid anhydride, like ATP.

That anhydride must have also been produced by water extraction and in the water environment you need an energy source for that.

So if you will complete the analysis you will reach the conclusion that you need an existing living being for the replication, no replication can occur otherwise.

Obviously, in a lab you can yourself substitute the role of that living being, by providing adequate supplies of monomers and of energy sources, so you can replicate nucleic acids in abiotic conditions. Nevertheless, that could not happen in natural conditions.

[marcosdumay]

You seem to want life to appear in a likely condition, without some external power source.

Whatever condition there was, it could as well be some extremely rare one, and I really can't imagine how some molecules could start to reproduce without their environment being constantly changed by some external energy flux.

Besides, I'm no expert, but I don't think there were huge amounts of pure water running around on the early Earth. There were so much more stuff to use those hydrogen and oxygen atoms, and Earth's water wasn't all here since the beginning.

[adrian_b]

It is pretty certain that the first life did not use any kind of genetic material, because that is impossible.

When RNA or any other kind of genetic material first appeared, the first thing that must have been possible to do with it was to copy it, a.k.a. to replicate it.

If the genetic material was used first to do anything useful, e.g. to control protein synthesis or to catalyze directly any useful reaction, that genetic material would have disappeared immediately, because it could not be replicated.

So the first genetic material must have been able of being replicated without doing any useful function, therefore is was actually an RNA virus.

The useful functions must have appeared later and then the genetic material was integrated as an essential part of the living beings, allowing a much faster evolution towards levels of complexity that would have been impossible to reach without having a genetic material.

To be able to replicate the first genetic material, there must have already existed some life forms able to exploit an energy source to reproduce themselves.

You have noticed a correct analogy, exactly like the control automaton of a CPU, which can be either hard-wired, having a dedicated structure that cannot be easily changed to perform other functions, or it can be microprogrammed, using a control memory, whose content can be easily rewritten to implement a very different CPU, a self-reproducing living being can use genetic material, in which case it can easily evolve into a different living being, or it may use no genetic material, but consist, like how it seems to be said in Gánti's work, of which I was not aware until now, by a cycle of reactions, where in each reaction some cell component assembles another cell component, until the last component, which assembles the first component.

Such a living being, without a genetic material, could not evolve easily, because almost any change would have damaged the cycle of reactions, most likely stopping the reproduction.

Regarding RNA, before the first RNA molecule was ever assembled, the existing life forms must have been using ATP and the other nucleotides as dehydrating agents able to condense smaller molecules into larger molecules, e.g. for creating peptide bonds.

Therefore ATP (with some of it current uses) is certainly older than RNA.

The polymerization of nucleotides into RNA must have been initially an undesirable side reaction consuming the useful nucleotides.

[Ericson2314]

Have you seen the research of Ribosomes being quine-like? (the structural nucleic acids and genes for the protein parts are related).

[adrian_b]

While that is an interesting fact about the evolution of ribosomes, no kind of ribosome could have ever appeared, except after the process of RNA replication was already a perfected process.

Otherwise the first ribosome would have disappeared soon after it was first assembled, without leaving any descendants.

The first ribosome was probably made only of RNA, as there were no other ribosomes to assemble the ribosomal proteins, so it is not surprising that at some point some of the ribosomal RNA segments were replaced by proteins transcripted also from some ribosomal RNA segments, if that happened to improve the ribosome structure.

[jacquesm]

Many statements made with certainty about an era about which we know absolutely nothing for sure.

[adrian_b]

While there are many things that we do not know about that era, there are also many other things about which we are completely sure.

For example we know for sure that all the chemical reactions required to assemble the components of a living being required the same amount of energy then as they require now, so either there was a source of energy large enough to enable them, or they were impossible.

Other things may not be completely certain, but they are overwhelmingly plausible, for example if we know that the transition from a more primitive structure to a more complex structure required 5 improbable mutations, we can be pretty sure that there is no chance that all those changes happened simultaneously, but they must have happened in a certain sequence, one by one.

If moreover, there are some causal links between those events, so that some of them cannot happen unless others already happened, then we may be able to determine which was the sequence of those 5 events, with considerable certainty.

While we are unable yet to estimate confidently which of many possible things really happened in the distant past, we can actually exclude with great certainty many other things, about which we can say for sure that they did not happen, because they contradict fundamental laws, like the conservation of energy.

Among these things that certainly did not happen are some previously popular theories about the origin of life, whose authors did not attempt to analyze them in enough detail to see if they are compatible with the known chemistry and physics, e.g. the ancient theory of the "organic soup" or the more recent theory of the "RNA world".

[kubanczyk]

It's good to make bold statements, because if anything it enables clear and convincing counter-arguments to show up.

[alextheparrot]

Couldn’t one take the view point that the formation of a transient ribosome could have created the conditions to solve replication?

This route would be much more of a dance than what you’ve implied. A transient ribosome makes a protein-based RNA replicase, replicase copies all local the RNAs including the RNA ribosomes. This process would eventually result in a large number of ribosome RNAs and replicase proteins without the need to have a “perfected process” prior to either step.

The whole process would be much messier than what we see today after millions of years of refinement, of course. The stability of an arbitrary RNA polymer is also increased by the presumed lack of RNases as well.

It has been a few years since I took a grad course covering the ribosome, so excuse my lack of currentness if new research has discounted this.

[davidhowlett]

I haven't seen that research but I find the idea fascinating. Where can I read more about this?

[proc0]

How would you define genetic material? I think some kind of movement and a metabolism can already be called alive. It's not so much about the material but rather the interaction between the materials that gives rise to behavior and then natural selection.

[adrian_b]

"Genetic material" is memory. Therefore it must have the following properties:

1. It must be able to store any random sequence of symbols belonging to a certain set (e.g. any possible sequence of bases in the case of nucleic acids).

2. There must be a way to make identical copies of it (e.g. nucleic acid replication).

(the previous 2 properties are true both for its own genetic material and for a foreign virus that does not have any use for a living being)

3. There must be a way to use the stored sequence of symbols to direct some process that is useful for a living being.

(for nucleic acids, the better known useful processes are protein synthesis and the synthesis of certain kinds of useful by itself RNA, but there are also some other poorly understood functions of most of the "junk" DNA)

[randallsquared]

I'm not sure defining requirements by analogy is a valid process.

[adrian_b]

I do not understand what you have meant by "analogy".

The 3 requirements that I have listed do not contain any analogy, they just give a precise expression of the conventional meaning of the words "genetic material" as applied to a component of the living beings, now known to consist of nucleic acids for the life on Earth.

While not all biologists would be able to define precisely what they mean by "genetic material", the listed requirements correspond to the actual use of the word, in the most general sense.

[randallsquared]

The actual requirements you listed were beyond my point. You said:

> "Genetic material" is memory. Therefore it must have the following properties:

A more precise wording of my understanding of this line would be:

> "Genetic material" is loosely analogous to memory. Therefore, we can derive what properties it has in physical reality by declaring what properties memory must logically have.

This makes it clearer what I was disagreeing with, I hope.

[a9h74j]

I am not sure we have colonized the minerals, but I am pretty sure we have been relying on fossil fuels as so-called "energy slaves."