Did Life Begin in an RNA World?
quantamagazine.org
quantamagazine.org
RNA gets made from pure, energy-rich molecules that themselves are quite complex. This soup of pure monomers isn't something that just arises naturally in the absence of life. Prebiotic chemistry produces a random soup of a wide variety of chemical species, with the abundance of each declining exponentially in its size and complexity.
You see this issue all the time in origin of life claims. For example, that recent result of "all the bases of RNA and DNA were found on this asteroid by the Japanese" tended to slide over the fact that they were there at extremely low levels, mixed with huge numbers of other non-biological organic molecules.
Trying to replicate RNA in a mix of random crap will just give you polymers of crap, if it gave you anything at all.
OoL needs an idea that will work in a soup of junk, not in massively artificial pure soup on a lab bench.
The research does something like this. You run an experiment and show some chemicals are present in low concentration. You say "ah ha, we've shown one step". Those chemicals are now taken off the shelf in high concentration and used in the next experiment, which makes slightly more complex chemicals in low concentration. Repeat this multiple times until done.
Lampooning this, the fictional OoL researcher in the book also demonstrates that monkeys can type out "To be or not to be, that is the question" on a typewriter. He arranges the typewriter with an automatic right margin and lets them type away until he gets a line starting with "T". First letter demonstrated! Now he rereun the experiment, but now with paper the "T" in the first column and margins set to the second column. Repeat this with subsequent letters until the entire sentence is produced. Of course, the monkeys didn't type the sentence, the researcher did.
Getting around the exponential complexity barrier is the whole goddamn point, it's not something to just wave away with a "we don't know" comment.
IMO some fundamentally new idea is needed for OoL.
But the researcher is performing the selection process for the purposes of the experiment, to speed things up. Evolution functions via natural selection. That's what makes it different from the pure random chance processes.
Biochemist and OoL enthusiast here. This is very not true. Evolution happens in even the simplest complex systems. It's very likely a process of matter.
Look up the work of Dr Michael Levin. He shares on YouTube many of his convos with leading thinkers. He's quite prolific lately.
So I strongly dispute your assertion there.
Similarly, when creating single-crystal metal parts (turbine blades) a handful of growing crystals is put through a maze, with only one surviving to continue out into the bulk of the part. One is selected and thrives, the others stop growing after being out-competed for resources/space. It looks and sounds like life but... crystals are a special case imho.
And "it's not exponential, therefore it's not possible" is?
The general problem here is that handwaving ignores the issue I raised, and those making OoL theories have to address these issues, not require skeptics to disprove their handwaving. Requiring the skeptical to disprove such things is classic crank behavior.
They certainly warrant discussion and investigation.
Handwaving away the possibly infinite nature of the available experimentation space and the anthropic principle is the same failing you're widely accusing others of.
You, elsewhere in the thread: "I expect people to not make declarations about things we don't know."
How do we know that? When did we confirm what came before the Big Bang? How do we know this isn't the sixty trillionth iteration of a 15 billion year process that only just now resulted in life on one of untold trillions of planets to pay notice to it?
Please don't say death implies life. By death you should infer removal from category a la RNA depolymerization, or lipid membrane lysis.
Of course I don't know what the pre-life entities are. But they were surely selected for.
what does accurate mean
> there's no plausible way proposed that can occur without life already existing
Why do you say that. RNA can replicate by templating. obviously replicators came to exist from non replicators. and life from nonlife. what claim are you making? that that isn't selection because you have a definition of selection that excludes that process?
Life has very complicated mechanisms for ensuring very accurate replication of DNA, but of course these mechanisms would not have been available at OoL.
You cannot point out exact steps how we evolved till now yet here we are. "We don't know" is a perfectly fine answer even if it somehow triggers you. Universe is not arranged around such folks, universe doesn't care about some tantrums, universe just is, in ways we still don't fully understand and thats fine.
Who, specifically, is doing this in this thread? People are very clearly discussing hypotheses, possibilities/probabilities, and outstanding questions. No one's claiming "here's the answer".
Not the best analogy.
Lets say you are looking for 'any sentence'. What if you never get the T, you get a G. The sentence is what your looking for, not a specific one. It could be another sentence, but a sentence none the less. Then you can ask, how many typewriters did it take to get the first letter, then how many for the next, (not infinite). Now how likely would this sentence appear in nature if a bunch of chimps were let loose in a typewriter store.
Its funny you are using this as an argument against. When it is actually is the process in Assembly Theory.
"Life As No One Knows It: The Physics of Life's Emergence ". Assembly Theory: A centerpiece of the book is Assembly Theory, which Walker co-developed (with Lee Cronin and collaborators). Assembly theory measures the "assembly index" of an object—quantifying the minimum number of steps and building blocks required to construct it.
Ever since I first learned about it, it seems to me a much more likely origin of life hypothesis, as it doesn't require something to catalyze itself, which causes inevitable problems with mutation causing loss of catalytic efficiency.
Also, it is not incompatible with RNA being one of the early building blocks. It just doesn't require RNA to be where everything started.
I don't think you can say this with certainty. It is assumed that life and evolution go hand-in-hand from the beginning but it is not proven to be the case.
Evolution is actually the accumulation of errors that happen to have a beneficial effect. But that does not say anything about how it all began, that's just what we are seeing now. So there are two options: evolution was there from the beginning and is a requirement for the kind of life that came into being or it was an upgrade that came a little later.
This is where the hard part of the field is currently: finding chemistry that can support accurate RNA copying that is also both sufficiently high yielding and also compatible with these reactions being inside protocells (fatty acids for example). An RNA genome only really has value when it can be selfish and keep any innovations it makes to itself inside a protocell!
I work in Origins Research - if you have questions please ask and ill try to answer with the current opinions of the field!
PS most asteroids that hit earth hit with such an angle and speed that pretty much nothing survives! When you read articles about finding building blocks of life on steroids it doesn't matter as they wont survive impact with a planet - its mostly just interesting that the chemistry is general enough to work in space and on earth!
†one note about my em dashes: I am a real person who thinks evolution AND em dashes are cool and for a total aside: it’s such a bummer people think I’m a bot just because I like tinkering w/ f* punctuation marks.
Good source that develops on this?
https://en.wikipedia.org/wiki/Ribosomal_RNA#Sequence_conserv...
It may just be that the life that ended up thriving on Earth isn't objectively the best for the environment but it just happens to be what won out by being at the right place at the right time and the better chemistry or body plan was at the wrong place at the wrong time and got hit by a meteor or some massive gas burst from the interior of the earth that wiped them out.
In that context it's neat to think about alternate biochemical systems that could be available to us provided that we can figure them out and that would have tremendous economic potential.
We have a lot of conserved RNA sequences because it has done a good enough job since LUCA (Last Universal Common Ancestor - 4.2 billion years ago!) and its been trapped epistatically ever since! Things like the ribosome (an RNA based machine that makes all our proteins) for example is very conserved across all domains of life from us to sharks and trees and bacteria!
I would recommend reading the primary literature and asking AI to help you fill in context that authors leave out!
Evolutionary theory: https://www.nature.com/articles/227520a0
Origins research: https://www.nature.com/articles/35053176 https://www.science.org/doi/abs/10.1126/sciadv.aax3419
About that, not that long ago I was entertaining the idea of what environments can be completely devoid of life. I was thinking about examples like a volcano Cauldron, a nuclear reactor or the insides of a particle accelerator.
Of course, the are too many limitations for evolving into some more complex, but they can self-replicate and they can infect other organisms. If we could give them an oceanic soup of PrPC and enough time, who knows?
Isn't the building block that a prion requires to create a copy of itself essentially a chemically almost-identical protein that is just folded differently?
How about an alternative analogy of the prion folding pattern spreading through chemically-similar molecules like a meme through a population of similarly conditioned brains?
https://www.youtube.com/watch?v=K0K-pMPFzGY
I like your analogy memes and prions need an already existing condition and then twist them into something else. If we are allowed to enter the philosophical domain, it's like the devil's work twisting the mind of the righteous or the Sith turning the force-sensitive beings :-)
Sorry, I went off the rails.
Most mutations are negative dead-ends, not unlikely DNA now where most pregnancies spontaneously abort due to errors. But life has many, many chances — especially at the molecular scale. So what’s the actual problem?
Similarly, if you have a soup of 10-15 nucleotide sequences, what are the odds actually that they’d link into larger segments?
Let’s suppose that density is a million times lower than blood, so you have one picogram per gram of water. There are 10^24 grams of water on Earth’s surface and 10 base pairs weighs 10^-20 grams, giving us approximately 10^32 segments of that length.
Feel free to play with my numbers, but I’m supposed to believe that with ~10^30 pieces, we can’t have ten of them form the right sequence?
A combinatorial explosion. To have mutations you need to have replication first. If a smallest viable self-replicator is, say, 100 nucleotides long, and there's not many other such replicators of the same length, the improbability of its spontaneous formation (~4^-100) dwarfs any amount of material available on Earth.
The researchers have found QT45 replicator. But it replicates other RNA strands, that is it needs another replicator nearby to replicate itself, which brings the probability down to 4^-90 range.
And it's not clear from the article whether QT45 is a viable replicator. That is whether it is stable enough and replicates other RNA strands correctly enough to sustain exponential growth instead of petering out due to filling its surroundings with broken copies that don't perform replication before decaying itself.
What's the probability of spontaneous formation across an infinite universe?
Let's say that you have some RNA soup with some ribozymes some of which weakly encourage some reaction involving other RNA molecules. The occurrence of a cycle of reinforcing reactions might be sufficient to build a crude evolutionary ratchet.
In fact the "cycle of reactions" perspective feels a bit more robust to me since it allows for the proto-replication process to take place over a longer period of time and over larger areas.
Core wars (1984) strongly favored short replicators, so at least in some possible universes complexity growth is not a given.
Imagine you have molecules that can form spontaneously, like gliders in Conway's Game of Life. You may have several different molecules that are capable of helping to create one another -- an autocatalytic set.
Eventually this could result in more complex chains, and eventually a self replicating molecule can arise.
Imagine slamming a bunch of gliders together to make a machine that replicates more gliders. It's possible! Not likely, but there are so many variables that can influence the environment substantially. It's not like there was a giant homogeneous soup. Parts from over here and over there would form differently and when they meet, amazing things can happen.
In the Game of Life, this spontaneous event is extremely unlikely, astronomically unlikely.
Unlike Game of Life, the real world has a few advantages that improve performance. For one, it's less fragile. Bonds are much stronger and collisions don't cause everything to break. Another advantage is that bonds are attractive: molecules can rotate and turn to snap together strongly. Gliders just explode violently. And finally, the real world is very dense. We're talking trillions of molecules mixing around millions of times per second per microdroplet. Compound that with a few hundred million years... it certainly doesn't feel as surprising as you might expect.
If there were a highly advanced alien race watching earth over a long period of time, it might be interesting, but not unexpected, that suddenly an Eiffel tower springs forth from the surface of the planet, erected by intelligent organisms.
"Life's first molecule." Take your favorite quantum field theory and consider how it draws a line between a molecule and not a molecule. Consider how it draws a line between life or not. That'd be cool. Consider that it doesn't give a shit who did what first.
"given any word, there's no such thing"
Interestingly we now are thinking about ways to use mutations in other ways, youve spent a lot of energy making these polymers, so it would be a shame to waste that right? We think that they can be used to assemble larger functional pieces as mutations are mostly deterministic meaning you'll get the same kinds of errors - so why not put them to use!
Early on that may have been a feature though, isn't it?
What strikes me as the most interesting thing about life is that almost immediately (on geological time scales) after Earth had developed an environment where life in theory could exist it came to be. That suggests strongly that the mechanism to do so was relatively simple. Then again, the Earth was a vast laboratory and it only has to happen once.
aside: you have the most interesting job!
Yes it is remarkable how seemingly quickly life started however most productive chemical reactions occurr on the order of hours and days so a couple of million years is still a long time to explore chemical space!