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The big question isn't how simple molecules (building blocks) come about. The big question is how these building blocks organized themselves into the complex st
by sthnblllII 6y ago
The big question isn't how simple molecules (building blocks) come about. The big question is how these building blocks organized themselves into the complex structure of even the most primitive microbes.
Every new form of life tends to fill successively smaller niches. There are more prokaryotes than eucaryotes, more singe celled than multi celled etc. but there is nothing in between the primordial chemical soup and the simplest life forms. I would expect a huge mass of simple RNA based life forms simpler than prokaryotes.
- paulryanrogers 6y agoIt's possible there was once an abundance of such life and they were too simple to be preserved in the fossil record. And now that life has leveled up and conditions have changed such forms are rare or non-existent today.
- vmception 6y agonot simple, just not fossilized. complex things would not have been fossilized if they were not in an area conducive to fossilization. natural selection assumes rapid iteration, so for every evolution tree, you have to imagine thousands of more variants at each step, not shown and not fossilized.
- paulryanrogers 6y agoYeah I was thinking I should've written 'fragile'. And many environments aren't suited to preserving evidence for billions of years.
- sthnblllII 6y agoSomething like that yea. But what could have changed so radically that it would kill every trace of those simpler life forms? Anaerobic bacteria thrive despite the oxygen rich atmosphere. One would expect at least a trace of these simpler life form if not an abundance. What environment existed 4 billion years ago that is totally gone today? Thats the more interesting question to me.
- stormbrew 6y ago> What environment existed 4 billion years ago that is totally gone today? One with no complex lifeforms but sufficient resources to support life seems like the obvious answer. Also, you can't really ignore the transformative effect that life has had on all environments (underwater and on land) in terms of chemical composition. Less water, less oxygen, etc. Presumably the evolution of cellular life was synergistic with the evolution of the environments on the planet?
- alextheparrot 6y agoA pet theory of mine is that they simply were out-competed. If these processes require chemical concentration 100X over timespan 100X to form de-novo, but a basic prokaryotic structure may only require concentration 1X over timespan 1X, that could make de-novo synthesis entirely unfavorable. Once those prokaryotic structures propagate enough, it could be reasonable that the conditions for de-novo genesis would no longer be routine enough that it would play an observable role today. This also helps make sense of why more complex organisms would form de-novo - they would be entropically more stable ("Filling a niche").
- klmr 6y ago> A pet theory of mine is that they simply were out-competed. This is the (by far!) most prevalent expert opinion.
- thegabriele 6y agoVery nice question. Perhaps this could hint towards primordial life structure to be from outside our planet?
- throwaway_pdp09 6y agoIf those simpler life forms existed it's almost certain we've loads of traces, it's just we can't distinguish them from noise because they've degenerated so far. It's like looking for fossil structures in crude oil - crude oil is remnants of life but is mainly long carbon chains. Very little if any structure remains. Analogy #2: your great-great-...-great grandparents of 10,000 years ago unquestionably existed, but show me any direct evidence they did. You can't. All signal is gone.
- asplake 6y agoInteresting read around that question: Stuart Kauffman’s At Home in the Universe: The Search for the Laws of Self-Organization and Complexity
- vmception 6y agoThere is also too many unknowns and assumptions about the goal. From what I can tell, the best science right now is that if you simply put enough neurons in the same place, they'll start questioning the universe. Why do these building blocks in some circumstances do anything? Why do they make life, or sentience, or even something to reproduce when the building blocks don't need to reproduce at all - nothing new is created or destroyed just the same building blocks being recycled in different configurations. Why would the building blocks go beyond the mere reproducing-life to something that thinks unnecessarily? All an accident that we can appreciate?
- fwip 6y agoFrom one point of view, nothing is necessary. Life is not necessary, planets are not necessary, matter is not necessary. From another, thinking is as necessary as anything can be. We observe thinking, therefore it exists. Anthropic principle.
- R0b0t1 6y agoOne interpretation is entropy increases at the maximum rate although such an assumption cant be derived. More complex life is more anthropic than simple life and is then an eventuality.
- folli 6y agoThat's pretty much the premise of the RNA world. I assume your actual question is why we don't observe RNA based lifeforms anymore. And the most likely explanation is that this type of life form has a massive evolutionary disadvantage to currently existing life forms in terms of competing over resources and is extinct as the huge majority of all once existing species have gone extinct in the course of this planet's history.
- sthnblllII 6y agoGood point. See my reply to paulryanrogers
- folli 6y agoTo add on to that (sorry, I think it's a very exciting topic): it's hypothesized that virions (a virus-like 'thing' that infects plants) are descendants of such RNA life that evolved to be parasitic.
- netcan 6y agoInteresting. That still doesn't give us any nonparasitic or non-symbiotic survivors. Merge with it, feed on it or go extinct.
- ufo 6y agoAnother thing is that the current world is more hostile to RNA. Anyone who has ever worked with RNA will tell you that you need to be very careful during the preparation to avoid contamination with ribonuclease enzymes that degrade RNA. We're covered in them.
- tachyonbeam 6y agoIt might just be that DNA has a better sweet-spot in terms of mutation probability, useful for evolution, and robustness, important for survival and transmission of useful genetic information.
- jonplackett 6y ago
- divbzero 6y ago> There are more prokaryotes than eucaryotes, more singe celled than multi celled etc. but there is nothing in between the primordial chemical soup and the simplest life forms. I would expect a huge mass of simple RNA based life forms simpler than prokaryotes. This is an interesting perspective. Following this line of reasoning, prokaryotes must be close to the simplest unit that can self-replicate and grow to fill the planet. The simpler “proto-life” forms before that built up complex molecules by chance but could never quite achieve a replicative cycle. Perhaps the closest to a huge mass of simple RNA based life forms that still exist today are viruses.
- pfdietz 6y agoViruses depend on the existence of complex structures (the machinery in cells) to replicate themselves, so I don't think it's valid to point to one as an organism in the same sense as a prokaryote.
- pishpash 6y agoProkaryotes depend on the existence of complex structures (the world outside) to replicate themselves. Yours is not a good example. That aside, people have argued that the viral particle is like a gamete, which is also an incomplete stage of life unable to replicate itself. It would be like calling a sperm a human and saying humans are therefore parasitic and not living. A virus's primary life stage is lived within the environment of the cell which it commandeers, and from where it sends its progeny. The whole commandeered cell is the viral organism, and very much living.
- pfdietz 6y agoInvalid argument. Bacteria exist that can grow in very simple media with low structure. Viruses canmot. They absolutely depend on the existence of a very complex replication machinery.
- reubenswartz 6y agoThey must have achieved many replication cycles, but presumably proto-prokaryotes were much more efficient replicators and outcompeted their ancestors.
- mentos 6y agoIsn’t the big question how matter exists at all? My outlook is that things just exist in some higher dimension but because we perceive things in 3D we wrongfully assume there needs to be a start/end. Look inside a box of mirrors at the infinitely repeating pattern and ask yourself where it begins/ends? Curious to hear how other people rationalize the irrational.
- jakear 6y agoThis has been bugging me quite a bit recently. The model I keep coming back to is some giant cellular automata embedded in a some sort of higher dimensional compute structure —- perhaps what we call the “big bang” was the randomly initialized start state, and everything since has been its update algorithm ticking along with an encoding of what we call “physics”. This plays interestingly with things like quantum mechanics - perhaps they’re the underlying implementation of “Math.random()” and things like entanglement are implementation details leaking through. Similarly, perhaps wave/particle duality is the result of some sort of legacy code built to deal with light as particles that got shoehorned into the current implementation’s wave-based approach (easer to simulate at-scale), and it only gets activated when the results are under observation! It, like every proposed answer to the existential question, is both unverifiable and unrefutable, making pondering it somewhat pointless. Though it is good to know even our proposed higher-dimensional overlords haven’t solved the problem of leaky abstractions!
- Darkphibre 6y agoI had a pet theory that Plank Time is the clock-step (or mantissa precission) of our simulation. :)
- amelius 6y agoA global clock can't exist. https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://en.wikipedia.org/wiki/Relativity_of_simultaneity
- 6y ago
- rriepe 6y agoYou're right but the thing you're talking about isn't life. It's a precursor to life. Life would stick around but the precursor wouldn't. It's like a hot flash in a pan starting a more sustainable housefire. The flash is gone by the time the fire is raging.
- coliveira 6y agoRNA life forms do still exist: they're inside more complex cells. These simpler life forms just came together into cells in a stable arrangement that was able to replicate itself, and evolution took care of spreading them over.
- patcon 6y ago> The big question isn't how simple molecules (building blocks) come about. [...] but there is nothing in between the primordial chemical soup and the simplest life forms. There's a view that the early evolution of "life" involved metabolic cycles that were not yet bounded in cells, but perhaps in increasingly constrained geological boundaries. So for example, early precursors to the Krebs Cycle may have started within oceans, or perhaps some arrangement of pools and geysers or other geological features. So in essence, early life was bounded not in membranes, but within the flows of rock and air and heat of the atmosphere itself. For more citable references to this stuff, this podcast episode from the Santa Fe Institute touches on it: https://complexity.simplecast.com/episodes/40 https://complexity.simplecast.com/episodes/40
- pfdietz 6y agoThere's a lot of vague handwaving like that. But that's really all it is.
- yes_man 6y agoConway's game of life shows how small building blocks randomly create giant crazy complicated formations that have the capability to do astonishing things, like replicate themselves in an organized way. Kind of implying that logically functional structures arise from randomness given enough time. The rules in Conway's game of life are simpler than real world physics, but it is enough to convince me that in a reasonable time frame (Earth's timeline), given enough building blocks and iterations, there's not really any reason to not assume the chemical building blocks of life happened to create all sorts of complicated structures that constantly failed to replicate or survive. On Earth, there was a lot of primordial soup, and there were a lot of chemical reactions. On a span of millions of years, complex data structures (such as RNA) may have occurred constantly somewhere on the planet. Every now and then, a cell randomly formed. Sometimes prokaryotes with RNA formed, like weird things in Conway's game of life. And then maybe once upon a time, a cell with just the right RNA to make it be able to reproduce in the ooze formed. That or life on Earth is panspermic and we have skipped the pre-prokaryotic evolution altogether
- dvt 6y ago> The rules in Conway's game of life are simpler than real world physics This is tricky. Conway's rules are "simpler" but far more rigid (e.g. tractable/computable). In real life, we deal with not just plain ol' turbulence (Navier–Stokes three-dimensional existence is yet to be proved), but also quantum effects (some of which might also not be computable, such as entropy in a Hamiltonian system).
- fullstackchris 6y agoI'd say it's ultimately hard to argue if these more random constraints (compared to Conway's game of life) are more _helpful_ or _harmful_ towards the ability to produce life or life-like structures.
- dvt 6y ago> ...more random constraints Want to point out that this is much more than simply "random" constraints (the universe isn't merely a probabilistic machine). These are not (or at least might not be) computable constraints; any comparison with Conway's Game of Life stops right there.
- jonplackett 6y agoI remember reading about what it’s actually like inside a cell - that it’s not the smooth and organised world you see in biology animations. It’s a mess of molecules moving around at hundreds of miles an hour. That’s what life is inside all our cells. Just a bunch of molecules bashing around randomly but because it’s all the right ingredients in there, the right things find each other and fit together and somehow it still works.
- alistairw 6y agoYes I remember one of the most interesting examples I saw of this was with how actin and myosin gain motion in cells, there's enough stuff bashing around everywhere that the right chemical reactions cause them to take each step.
- jonplackett 6y agoIt kinda makes it more amazing doesn't it? Before I read that i just had this totally false view of tiny-biology as this cold, organised place. But I really like the truth that it's chaotic and messy and powerful.
- laurent92 6y agoSilly question, but could that explain bad health? People who don’t enough sports don’t shake their cells enough, so they aren’t as functional? I know the usual explanation is blood circulation and organ maintenance, but did we think of looking intra-cell?
- Jabbles 6y agoThere may well be subcellular problems that cause all kinds of bad-health, but not being well-mixed is not one of them. Movement at the level of sports won't cause well-mixed cells - their fundamental frequencies are too different.
- lovehashbrowns 6y agoThat would make people who ride older rail trains (like Chicago's trains) regularly super healthy. People who ride horses would be super healthy, too. Train conductors. Anyone who does a lot of off-roading. Etc. Oh actually, people who have shaky legs would have disproportionately healthier legs than the rest of their body. But actually moving around a lot wouldn't make a difference if the bits in your cells are moving around at hundreds of miles per hour.
- AareyBaba 6y agoWhich evolved first cellular metabolism or replication ? Without replication you can't have evolution. Without metabolism you don't have a system to support replication. (What Is Life? by Erwin Schrödinger 1944)
- thegabriele 6y agoCould someone point out a good eli5, recent book about this topic? From building blocks and their physics to membrane/rna/dna and so on? Thank you.
- forgotpwagain 6y agoThe Vital Question, by Nick Lane is a pretty good book that takes a thermodynamics first approach to this question.
- adrian_b 6y agoThis is a very good recommendation. There are several other publications on this subject by Nick Lane, which can be easily googled, and all of them are good. They are somewhat incomplete, because there are parts that are not covered, especially about what is known on the metallic catalysts that were required for the emergence of life, but overall, the Nick Lane publications are the best from what I have seen.
- thegabriele 6y agoThank you!
- learnstats2 6y ago>I would expect a huge mass of simple RNA based life forms simpler than prokaryotes. There is such a mass: viruses. As such, we know that cellular life has evolved multiple mechanisms to efficiently kill external RNA. If cellular life can efficiently outcompete non-cellular life for resources (and perhaps for RNA itself), then this outcome is not unreasonable at all. Counter-example: There are (far) more Homo sapiens on the planet than other primates in total.