On the Origin of Life and Falsifiability

Hi, Genomicus.

Genomicus writes: See Mautner 2002 and Mautner et al. 1997, and other work along these lines, for observations that meteorite material can sustain growth and metabolism of prokaryotic organisms.

I don't think those papers are as relevant as you think they are. Here's an excerpt from the methodology on the first paper:

quote:

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All plant cultures were grown for 20 days in closed microfuge tubes in standard tissue culture growth chambers under illumination by cool white fluorescent lights with an incident light flux on the samples of 80 μEm−2 s−1 using 16-h light–8-h dark
photocycles. Algal cultures were grown in similar growth chambers in vials with a punctured cap that allowed air exchange. The algal cultures were contained in glass jars saturated with water vapor to allow full light exposure but prevent evaporation.

---

In a nutshell, they grew plants and algae on meteorite-based soil under Earth-like* conditions. I don't think that does very much to advance a panspermia argument.

*I had to google "μEm−2 s−1": it's micro-Einsteins per square meter per second. An Einstein is a mole of photons. So, using this conversion table, 80 μEm−2 s−1 for a cool white fluorescent light is about 6000 lux. Full daylight is 10,000 lux, and interior lighting is usually around 50-100 lux. They don't mention temperature, so I assume they used ambient temperatures, with this light as the only additional heat source. That's probably going to be a rather warm growth chamber.

Genomicus writes: Most published papers on lithopanspermia AFAIK are based on the premise that prokaryotes will continue to metabolize during the voyage through space.

I'm not very familiar with the panspermia literature, so I guess I can't argue with you. But, I was always under the (apparently unjustified) assumption that panspermia generally assumes microbial spores, rather than active organisms. Having the microbes active during transit really complicates the issue of evolutionary adaptation before, during and after transit, though.

Genomicus writes: My discussion so far has been mainly focused on lithopanspermia because I don't find the cometary model as convincing...

Well, then I think you need recognize that your falsification would only apply to that specific type of panspermia, and not to the overall Panspermia Hypothesis as a whole. The main reason why I disagree with your claim that Panspermia is falsifiable is because your proposed falsification is much narrower in scope the overall concept. And, I believe that this will be true of any proposed falsification. There will always be possibilities for panspermia that are not easily falsifiable.

Genomicus writes: ...nonetheless, survival of prokaryotes in the icy interior of a comet would require its own set of proteins for (1) protection from cold temperatures, and (2) mechanisms allowing for activating a dormant state among these prokaryotes, as they would not exposed to the kind of organic molecules (for metabolism) found in meteorites.

A comet would not be any more frozen than a meteorite or any other space object, so these same restrictions should apply to any panspermia model.

Unfortunately, there are a lot of anti-freeze proteins (AFPs) in life on Earth. Freeze tolerance is apparently possible with a very small suite of semi-specialized AFPs, and many different clades of organisms have independently evolved (and lost) novel types of AFP, so it's much harder to wield the power of phylogenetics against this one.

Genomicus writes: Well, a planet with a surface temperature of several thousand degrees Celsius isn't exactly going to be friendly to prokaryotic life.

What about a meteorite at deep-space temperatures?

Genomicus writes: ...my concern is when abiogenesis models are patently shown to face chemical difficulties -- but these can always be cavalierly tossed aside with the riposte, "Well, we don't really know how early Earth was like, so maybe the conditions were just right to make this particular chemical scenario plausible." So, in a way, an appeal to ignorance is made in an effort to keep the hypothesis alive -- but at the expense of falsifiability IMHO.

And I completely agree with you on this. My whole argument is that Panspermia is no different from the other models in this regard: there are always going to be a whole lot of messy contingencies that can't be easily dismissed, so we'll have to continue considering alternative panspermia models for a very long time after these phylogenetic have ostensibly "falsified" panspermia. To me, that means it isn't really a falsification at all.

Genomicus writes: Moreover, assuming your scenario was plausible, my falsification model for lithopanspermia would still hold: the FUCA --> LUCA scenario you propose involves the elimination of functional analogs of ABC transporters + the innovation of ABC transporters. Yet since the function of ABC transporters is so important to prokaryotic life, it is exceedingly difficult to imagine an evolutionary scenario wherein prokaryotic life would ever exist without the functional equivalent of ABC transporters...

I think I made a mistake somewhere. I latched onto ABC transporters as my example because they were one of the few proteins you mentioned that I actually knew a little about. But, they don't seem to be on the list of proteins Cavalier-Smith suggested were absent from LUCA, so I guess they aren't an example of what I thought. Sorry about that.

My general point is that you're trying to have it both ways: you're trying to claim that a gene can be both essential to an organism's survival, and possibly absent from LUCA.

If a certain genomic feature is legitimately essential, then all organisms should have it, and the LUCA~FUCA assumption is appropriate. But, such a genomic feature would be useless for your phylogenetic falsification, because it can't be missing from any organism.

On the other hand, if the genomic feature is not essential, then it is useful for your falsification, because it could hypothetically be lacking in some organisms. But the LUCA~FUCA assumption is no longer appropriate, because such a genomic feature could believably be lost between FUCA and LUCA.

Sorry for the big delay.

This sort of comment might get a layperson thinking that the dozens and dozens of scientific papers published on molecular clock analyses of prokaryotic phylogeny is little more than evolutionary biologists dreaming stuff up. I find this argument suspect as it seems to imply that the aforementioned problem has not been tackled by those in the field, when in fact the paper I cited -- and many others -- understood the nature of the problem and properly addressed it with the appropriate methodology.

There are much smarter and more educated people than me working on this. Of course they've thought of the problem and tried to deal with it. And some have concluded that the variation in subsitition rates between different bacterial groups and lack of clear calibration means that estimates of deep divergences are still highly problematic.

I lack the expertise to talk about your different points, but I did want to ask if you could expand on:

(2) The use of node age constraints as calibration points, thereby providing information as to the minimum absolute ages of the nodes in the tree (which can be pretty easily done with Bayesian software like MrBayes).

as I don't really understand what you mean.

A further problem which occured to me as I was thinking about what you wrote is that calibration points are only of limited value given that we do not actually possess a consensus phylogeny of bacteria. If chlorobactane is a clear biomarker for Chlorobi that's all well and good, but what does that actually mean if we don't know where they fit in a bacterial phylogeny?

Since Cavalier-Smith's (arguably weak) transition analyses can't be used to establish absolute dates of origin, his figure in the paper (from which I believe you got the 850 million years) cannot be taken to be any sort of evidence for absolute ages.

I got the date of 850 million years by reading the words that he wrote, here and elsewhere, rather than looking at a figure. The idea comes from his belief that eukaryotes and archaea are nested deeply with bacteria due to the plausibility of different evolutionary steps.

Now, I don't think that his argument is very convincing, and is even less so now than ten years ago, as it requires dismissing an enormous number of putative eukaryotic fossils from far too early. My point was simply that an argument which relies on divergence dates between archaea and bacteria may be premature when the estimates for this in the literature span an order of magnitude.

More importantly though, I don't see how it helps. You note that:

(2) Molecular clock analyses based on (a) multiple protein sequences from multiple prokaryotic taxa, and (b) different molecular clock approaches with a variety of calibration points in each study all converge on a more-or-less unanimous conclusion: that prokaryotes are more than 4 billion years old, and less than 4.5 billion years old. (3) This is complete accordance with lithopanspermia(..)

But it is also in complete accordance with life evolving here, on earth. Panspermia adds an additional step while explaining nothing more.

And not one Wallis is making per se. He proposes the following two scenarios as possible explanations for the geologic distribution of Aib peptides: (1) that fungi from space landed on Earth, and that the genomes of these fungi encoded genes for Aib polypeptides, or (2) an unknown kind of microbial organism landed on Earth, equipped with genes for Aib polypeptides; these genes were subsequently transferred to fungal genomes. Your attempt to refute (1) by pointing to the long branches of fungi in eukaryote phylogenies fails to consider that it's hypothetically possible for fungi-like organisms to land on Earth with that lineage going extinct -- but not before some of their genes were laterally transferred to other fungi clades and certain prokaryotes.

So you mean that he's using fungi as description of a type of organism, rather than as a clade? That's slightly more plausible, but it does mean that we're talking about a constant stream of DNA-based life flying through the cosmos, rather than a one-off event four billion years. What I don't see is any evidence that this is the case.

Anyways, what's your explanation for the particular distribution of Aib in the K/T transition?

What particular distribution? All he mentions in the article is two sites associated with the Chicxulub impact which contain the amino acid Aib. He also points out that that same amino acid was found in a meteorite that fell in historical times. If I had to make an explanation it would be that it's a compound sometimes found in meteorites. I don't know why, but I don't see any reason to invoke space organisms.

The thing is that amino acids are falling out of the sky all the time, unaccompanied by alien space fungi. Consider, for example, the Murchison meteorite. It fell in 1969; analysis showed that it contained numerous amino acids --- including aminoisobutyric acid. The amino acids were racemic and have all been produced in the laboratory by Miller-Urey type setups.

Nonprotein Amino Acids in the Murchison Meteorite

Nonprotein Amino Acids from Spark Discharges and Their Comparison with the Murchison Meteorite Amino Acids

Edited by Dr Adequate, : No reason given.

Just FYI, I haven't abandoned this thread and will be responding shortly.

Genomicus writes: (1) Such a scenario has never occurred on Earth. Despite a truly enormous variety of environments and ecological niches on Earth, no prokaryotic population has ever been discovered that has completely re-invented entire suites of core molecular machines (ATP synthases, transcription machinery, ABC transporters, etc.). That this has not occurred suggests that the core molecular machinery of biological life is not so easily replaced by evolutionary processes, regardless of the environment.

Once one type of prokaryotic population became dominate, wouldn't it wipe out less competitive alternatives, and subsequently soak up all primitive organic molecules from which primitive life develops?

(2) The scenario would not be believable from a molecular evolutionary perspective. If the hypothetical FUCA -- containing a wide range of radically different core protein sets -- could survive on Earth upon landing, then these protein sets would most likely be tinkered with and gradually co-opted and improved upon, instead of massive deletions taking place along with massive molecular innovations.

Wouldn't they be treated as food?

(3) A large number of these core proteins function in an information processing context and so are not immediately affected by the external environment. E.g., polymerases are involved with nucleic acid polymers and do not interact with the external environment, so postulating a radically different external environment for the "source planet" would not require a radically different set of information processing proteins. These proteins would arguably retain their basic tertiary and quaternary structure regardless of the external environment.

Wouldn't polymerases be digested as food instead of incorporated into existing life?

(1) Molecular clock analyses. If the core protein machinery of prokaryotic life was the product of radical evolutionary innovation, then molecular clock analyses should place the time of origin of core protein machines at around 3.5 Ga, in concordance with paleontological evidence for when membrane-bound prokaryotes emerged on Earth. This is not the case, however, so this conjecture is not consistent with molecular phylogenetic evidence.

Do you have references showing that "molecular clock analyses should place the time of origin of core protein machines at around 3.5 Ga?" And since one of the most common headlines in anthropology, paleontology and abiogenesis research is, "Scientists push back earliest date of <fill-in-the-blank>," that we've found nothing before 3.5 Ga isn't particularly meaningful.

--Percy

Sorry for the big delay.

Back at you!

This sort of comment might get a layperson thinking that the dozens and dozens of scientific papers published on molecular clock analyses of prokaryotic phylogeny is little more than evolutionary biologists dreaming stuff up. I find this argument suspect as it seems to imply that the aforementioned problem has not been tackled by those in the field, when in fact the paper I cited -- and many others -- understood the nature of the problem and properly addressed it with the appropriate methodology. There are much smarter and more educated people than me working on this. Of course they've thought of the problem and tried to deal with it. And some have concluded that the variation in subsitition rates between different bacterial groups and lack of clear calibration means that estimates of deep divergences are still highly problematic.

From the paper you linked to:

"By examining the evolution of 16S rRNA gene in obligate endosymbionts, which can be calibrated by the fossil record of their hosts, we found that the rates are consistent within a clade but varied widely across different bacterial lineages. Genome-wide estimates of nonsynonymous and synonymous substitutions suggest that these two measures are highly variable in their rates across bacterial taxa. Genetic drift plays a fundamental role in determining the accumulation of substitutions in 16S rRNA genes and at nonsynonymous sites. Moreover, divergence estimates based on a set of universally conserved protein-coding genes also exhibit low correspondence to those based on 16S rRNA genes."

The variation in substitution rates between different bacterial groups is a well-known phenomenon in molecular evolution research, and tools have been created to ameliorate the problems that may arise for a given gene or protein sequence set. E.g., see relative rate test and likelihood ratio test for tests to determine if a sequence set resolves to a constant molecular clock. For sequence sets that do not adhere to a constant clock, local clock approaches can be used.

I lack the expertise to talk about your different points, but I did want to ask if you could expand on: (2) The use of node age constraints as calibration points, thereby providing information as to the minimum absolute ages of the nodes in the tree (which can be pretty easily done with Bayesian software like MrBayes). as I don't really understand what you mean.

Node age constraints are constraints on the molecular clock nodes based on external paleontological or geological information. See here for a discussion on this technique. Here's a quote from that paper discussing node age constraints based on paleontology and geology:

"(1) Fossil. The earliest known fossil assigned to a lineage provides a minimum age constraint on the divergence event (i.e., internal node) at the base of its clade (Donoghue and Benton, 2007). Depending on the quality of the fossil record, the probability that the actual divergence falls around the fossil date may be expressed as a parametric distribution between minimum and maximum bounds (i.e., soft bounds; Yang and Rannala, 2006). (2) Geological event. Geological calibrations are assigned to internal nodes based on the assumption that phylogenetic divergence was caused by vicariance. Examples include the appearance of land bridges generating barriers to gene flow in aquatic organisms (minimum age constraint), or the emergence of an island on which a clade is inferred to have diversified (maximum age constraint) (Ho et al., 2011). As with fossils, the degree of uncertainty surrounding correspondence between the geological event and date of divergence may be expressed probabilistically."

Hope that helps!

A further problem which occured to me as I was thinking about what you wrote is that calibration points are only of limited value given that we do not actually possess a consensus phylogeny of bacteria. If chlorobactane is a clear biomarker for Chlorobi that's all well and good, but what does that actually mean if we don't know where they fit in a bacterial phylogeny?

We do not possess a consensus phylogeny of bacteria phyla. The internal branching order of many bacteria is well-established. Chlorobactane is a good biomarker for Chlorobi, and we can establish an approximate age of origin for Chlorobi through this biomarker's presence in the geologic record. This, in turn, allows us to calibrate a molecular clock of protein sequences. So if we have a given protein phylogeny, we can determine the divergence dates of the various sequences of those proteins. That protein phylogeny may not be reflective of actual bacterial phylogeny, but they do tell us information regarding the particular phylogeny and divergence dates of that kind of protein. Just because it might not wholly reflect bacterial phylogeny doesn't somehow skew the molecular clock estimates mapped onto that phylogeny.

(2) Molecular clock analyses based on (a) multiple protein sequences from multiple prokaryotic taxa, and (b) different molecular clock approaches with a variety of calibration points in each study all converge on a more-or-less unanimous conclusion: that prokaryotes are more than 4 billion years old, and less than 4.5 billion years old. (3) This is complete accordance with lithopanspermia(..) But it is also in complete accordance with life evolving here, on earth. Panspermia adds an additional step while explaining nothing more.

Well, it's not all that in agreement with life arising on Earth, because there's very little convincing biomarkers for full-fledged prokaryotic organisms existing on Earth 4 billion years ago, but the molecular clocks suggest otherwise. This observation is explained by lithopanspermia, in a single stroke, by positing that life is older than the time at which Earth became habitable -- and this ancient age of fully-fledged prokarya is reflected in protein molecular clocks. In other words, if life arose elsewhere and evolved for several hundreds of millions of years before being transported to Earth, these molecular clock observations would be immediately explained.

Edited by Genomicus, : No reason given.

I've been letting this simmer in the back of my mind. A number of criticisms were levied against my OP, the most challenging of which have come from Blue Jay and Dr Adequate.

While I will be writing up responses in the near future, at the moment I will continue to think and re-think what has been said here. In particular, my OP suffers from the flaw that it equates panspermia with lithopanspermia -- when, in fact panspermia is a general idea and lithopanspermia is more specific model that I have argued is properly falsifiable in the Popperian sense.

I thought I owed this update to those who have invested time and energy in this thread, as I don't want to be one who suddenly vanishes when serious critiques are raised.

Genomicus writes: So we can see that falsifiability as a criterion for truly scientific hypotheses has become well-established within the scientific community, the objections from certain philosophical schools of thought notwithstanding.

It was considered perfectly reasonable to hypothesise the existence of planets outside our solar system before their existence was verified, but as we could never conceivably positively establish their absence from all stars in all galaxies, the hypothesis wasn't falsifiable.

Panspermia relies on the hypothesis that there is (or has been) life elsewhere in the universe. That's hypothetically verifiable, but not falsifiable. For me, that's absolutely no reason to exclude Panspermia from science. Of course it's a scientific hypothesis, although it's not actually an OOL one, of course.

The strange thing about your post is that the hypotheses you're suggesting aren't falsifiable actually are. For a start, the general hypothesis of the origin of life being on earth would have been falsified by the discovery that the planet was too young or that it was frozen for the first 4 billion years, or that it had been subject to a massive recent impact that would have sterilized it etc. etc. The fact that it's still looking O.K. for OOL on earth is a bit like the fact that we haven't observed "planets moving in squares", as Ruse puts it in the example you quote. And the general hypothesis being falsifiable in its nature means that all specific ones are.

Beyond that, some of the objections you list for "RNA" world and "Metabolism first" could conceivably be confirmed, which would be falsification. It's always hypothetical. I'd give them a better chance than observing planets moving in squares to falsify Kepler, wouldn't you?!

Genomicus writes: Indeed, this criterion [falsifiability] has been used extensively in the debate over whether intelligent design qualifies as a scientific concept.

Usually, wrongly. Although a general hypothesis of intelligent design isn't falsifiable, neither are the planets or life elsewhere hypotheses I mentioned above. It could conceivably be verified. But many specific intelligent design hypotheses could be regarded as falsifiable, as you know. The standard YEC model is an obvious example that can and has been reasonably falsified.

I've not been around for a while, and haven't read the thread, so what I'm saying may well have already been said. Firstly, Popper's falsifiability notion can easily be questioned as in the examples I've given. Secondly, the OOL hypotheses you've discussed would be regarded as falsifiable anyway. Thirdly, I'm sure there are specific Panspermia hypotheses that are falsifiable, although it's difficult to think of a falsification of the general proposition. That, however, doesn't make it unscientific, just possibly un-Popperific, and who cares?

Hey bluegenes, and welcome back. Some of the stuff you've said has indeed been overviewed, but I'll respond to your post nonetheless.

It was considered perfectly reasonable to hypothesise the existence of planets outside our solar system before their existence was verified, but as we could never conceivably positively establish their absence from all stars in all galaxies, the hypothesis wasn't falsifiable.

In this thread, I've contrasted exploratory science from properly constructed scientific hypotheses. So the notion of extrasolar planets does/did fit under the umbrella of exploratory science, but as this idea wasn't falsifiable, it could not be considered a properly constructed scientific hypothesis in the Popperian sense.

Panspermia relies on the hypothesis that there is (or has been) life elsewhere in the universe. That's hypothetically verifiable, but not falsifiable. For me, that's absolutely no reason to exclude Panspermia from science. Of course it's a scientific hypothesis, although it's not actually an OOL one, of course.

The broad idea of panspermia is not falsifiable precisely because it is a general idea and not a specific model; however, lithopanspermia is falsifiable (as I've argued here) and thus qualifies as a scientific hypothesis.

The strange thing about your post is that the hypotheses you're suggesting aren't falsifiable actually are. For a start, the general hypothesis of the origin of life being on earth would have been falsified by the discovery that the planet was too young or that it was frozen for the first 4 billion years, or that it had been subject to a massive recent impact that would have sterilized it etc. etc.

Sure, but that would falsify virtually all non-teleological models for the origin of life on Earth, including panspermia -- for the simple reason that if the Earth was, say, frozen for the first 4 billion years, then there would be only 500 million years to get from prokaryotes to fully-fledged mammalian organisms.

So this falsification scenario falsifies the general premise of a non-teleological origin of life; however, it does not allow us to falsify specific abiogenesis models in a way that would be relevant only to those models.

Beyond that, some of the objections you list for "RNA" world and "Metabolism first" could conceivably be confirmed, which would be falsification. It's always hypothetical. I'd give them a better chance than observing planets moving in squares to falsify Kepler, wouldn't you?!

Some of the objections have been confirmed, but I don't see any OoL researchers abandoning the RNA world in droves. The reason is simple: the RNA world model functions as a good framework for exploratory science; but this does not make it a properly constructed scientific hypothesis.

Usually, wrongly. Although a general hypothesis of intelligent design isn't falsifiable, neither are the planets or life elsewhere hypotheses I mentioned above. It could conceivably be verified. But many specific intelligent design hypotheses could be regarded as falsifiable, as you know. The standard YEC model is an obvious example that can and has been reasonably falsified.

Well, I'd hesitate to say that the standard YEC model is falsifiable, precisely because "Goddidit" can always be invoked when there's a seemingly insurmountable problem. That creationism has this magic card -- Goddidit -- means it's really not falsifiable and so never qualified as a properly constructed scientific hypothesis.

I've not been around for a while, and haven't read the thread, so what I'm saying may well have already been said. Firstly, Popper's falsifiability notion can easily be questioned as in the examples I've given.

Popperian falsification is IMHO a very good criterion to determine whether something is to be considered a scientific hypothesis; that exploratory science still goes on does not mean that Popperian falsificationism is a flawed concept.

Secondly, the OOL hypotheses you've discussed would be regarded as falsifiable anyway.

So how would one specifically falsify the RNA world model?

Thirdly, I'm sure there are specific Panspermia hypotheses that are falsifiable, although it's difficult to think of a falsification of the general proposition.

I've cited lithopanspermia in this thread as a panspermia hypothesis that is falsifiable; there has been discussion over that, so you may want to read the previous pages.

That, however, doesn't make it unscientific, just possibly un-Popperific, and who cares?

Well, not only would it make a model under consideration "un-Popperific," it would also mean it's not a scientific hypothesis (as accepted by most of the scientific community and many philosophy of science scholars). As to who cares, I would say it's very important to stress where in science there are properly constructed scientific hypotheses (e.g., the notion of common descent can be falsified in multiple ways, and so is a good example of a properly constructed scientific theory) and where there is only exploratory (and even conjectural science).

The abiogenesis models for the origin of life are exploratory, and not hypotheses of the Popperian kind.

But I'm not sure that this is Popper's sense. I understood him to be talking about hypotheses which are so constructed that no acquisition of data would cause one to abandon them; not merely hypotheses where we are presently unable to acquire the data.

Otherwise, as I have pointed out, we would have to say that people constructing apparatus to test a hypothesis for the first time were expending their money and effort on researching a hypothesis which was not even properly constructed. People building the large hadron collider, for example, to look for the Higgs boson, were trying to investigate something which was not even a properly constructed scientific hypothesis, and wouldn't be until they turned it on, when suddenly the nature of the hypothesis would change: it would become properly constructed at the same time that the large hadron collider was.

But, as I understand Popper, it was already properly constructed: they could say what data would confirm or disprove the existence of the Higgs boson, and so they set out to acquire the data.

Genomicus writes: Hey bluegenes, and welcome back.

Cheers.

Geno writes: In this thread, I've contrasted exploratory science from properly constructed scientific hypotheses. So the notion of extrasolar planets does/did fit under the umbrella of exploratory science, but as this idea wasn't falsifiable, it could not be considered a properly constructed scientific hypothesis in the Popperian sense.

That it wasn't Popperian was my point. But it was, demonstrably, a damned good scientific induction.

Geno writes: The broad idea of panspermia is not falsifiable precisely because it is a general idea and not a specific model; however, lithopanspermia is falsifiable (as I've argued here) and thus qualifies as a scientific hypothesis.

You mean "Popperian" hypothesis, or "properly constructed" as you put it. I might have been wrong about general panspermia being unfalsifiable. When initially proposed, it could have been falsified if it could have been demonstrated that no organism could possibly survive in space. As that doesn't appear to be the case, we could say that the general idea has passed a falsification test.

Geno writes: Sure, but that would falsify virtually all non-teleological models for the origin of life on Earth, including panspermia -- for the simple reason that if the Earth was, say, frozen for the first 4 billion years, then there would be only 500 million years to get from prokaryotes to fully-fledged mammalian organisms. So this falsification scenario falsifies the general premise of a non-teleological origin of life; however, it does not allow us to falsify specific abiogenesis models in a way that would be relevant only to those models.

Hypotheses don't become any less Popperian if possible falsifications also falsify other hypotheses. Think of your own chosen example from Ruse of "planets moving in squares". I don't know how many hypotheses that would falsify, but we could probably give the whole set an umbrella description like "cosmology"!

Geno writes: Some of the objections have been confirmed, but I don't see any OoL researchers abandoning the RNA world in droves. The reason is simple: the RNA world model functions as a good framework for exploratory science; but this does not make it a properly constructed scientific hypothesis.

It's certainly Popperian. To add to the things I've already mentioned that would falsify it, future experimentation could establish that RNA is definitely too unstable to support even the simplest life forms on its own. Future experimentation could also confirm an alternative hypothesis beyond all reasonable doubt.

Genomicus writes: Well, I'd hesitate to say that the standard YEC model is falsifiable, precisely because "Goddidit" can always be invoked when there's a seemingly insurmountable problem. That creationism has this magic card -- Goddidit -- means it's really not falsifiable and so never qualified as a properly constructed scientific hypothesis.

Not really, because their standard model is meant to be testable. The earth should appear 6,500 yrs. old and that should fit the data. That differs from other YEC models, particularly my favourite, the Omphalist version. That's the perfect example of an untestable, unfalsifiable model, because any and all data will fit.

Geno writes: Popperian falsification is IMHO a very good criterion to determine whether something is to be considered a scientific hypothesis; that exploratory science still goes on does not mean that Popperian falsificationism is a flawed concept.

The problem arises if someone implies that the hypothesis that the moon is made of cheese (Popperian) is inherently more scientific than the hypothesis that there are planets outside this solar system. The thing about the planets hypothesis is that the only reason it could be described as unfalsifiable is practical, unlike the Omphalist idea, which is untestable by its nature.

Geno writes: The abiogenesis models for the origin of life are exploratory, and not hypotheses of the Popperian kind.

They're definitely falsifiable.

That it wasn't Popperian was my point. But it was, demonstrably, a damned good scientific induction.

Yes.

Hypotheses don't become any less Popperian if possible falsifications also falsify other hypotheses. Think of your own chosen example from Ruse of "planets moving in squares". I don't know how many hypotheses that would falsify, but we could probably give the whole set an umbrella description like "cosmology"!

That would seem to eliminate the utility or purpose of Popperian falsificationism though, wouldn't it? Indeed, I suspect that if extrasolar planets were to be observed orbiting in squares throughout much of the cosmos, then the RNA World model would be falsified, as would lithopanspermia (as such an observation would have profound implications on physics and thus chemistry).

Nor does it seem to be a notion that Popper ever espoused, as all his examples of the application of falsification -- e.g., Einstein's theory of relativity -- dealt with predictions made specifically and exclusively by Einstein's theory.

It's certainly Popperian. To add to the things I've already mentioned that would falsify it, future experimentation could establish that RNA is definitely too unstable to support even the simplest life forms on its own.

As I have argued above, I do not consider your previous examples of "falsification" of the RNA World correct applications of Popper's falsificationism.

As to this next example you raise, it is far too vague in its present formulation to be of much use IMHO. It is already well known among chemists and OoL researchers that ribose is quite unstable, making this a serious challenge for the RNA World model. This problem is usually "patched up" with the addition of stabilizing chemicals, such as borate and various silicates.

In short, the RNA World doesn't exactly postulate that ribonucleic acid would ever have to support primitive cells "on its own," as the RNA World incorporates a variety of other chemicals (e.g., metal ions).

Not really, because their standard model is meant to be testable. The earth should appear 6,500 yrs. old and that should fit the data. That differs from other YEC models, particularly my favourite, the Omphalist version.

Well, I will grant that some YEC models are falsifiable. But my experience from this forum with YECers is that YEC is generally not falsifiable.

The problem arises if someone implies that the hypothesis that the moon is made of cheese (Popperian) is inherently more scientific than the hypothesis that there are planets outside this solar system. The thing about the planets hypothesis is that the only reason it could be described as unfalsifiable is practical, unlike the Omphalist idea, which is untestable by its nature.

I agree that is problematic, but that is not what I am contending here. First, I am arguing that the lithopanspermia hypothesis should be considered as a "properly constructed" -- that is, Popperian -- scientific hypothesis, by virtue of its falsifiability through phylogenomics.

Second, while the "moon is made of cheese" notion may be falsifiable, it certainly does not have the kind of gravitas that would be accorded to the idea of extrasolar planets.

This is because there simply is no reason to suspect the moon is made of cheese; and there are numerous reasons to postulate that extrasolar planets exist (and we now know they do).

Scientific hypotheses must, of course, be more than just falsifiable. It's not like falsifiability is the one thing that determines if something is science or not. But the point is this: lithopanspermia may be considered to be on basically equal footing with the RNA World model (and other abiogenesis scenarios). The RNA World model has several lines of circumstantial evidence, as well as many serious difficulties. On the other hand, lithopanpsermia also has circumstantial evidence -- as well as some other pieces of evidence, such as the molecular phylogenetics argument I presented in previous posts -- and arguably not as many difficulties as the RNA World model.

They're definitely falsifiable.

You may very well be right; however, I have yet to see a compelling, detailed falsification scenario for the RNA World model, so consider this your opportunity to present just such a scenario.

Edited by Genomicus, : No reason given.

But I'm not sure that this is Popper's sense. I understood him to be talking about hypotheses which are so constructed that no acquisition of data would cause one to abandon them; not merely hypotheses where we are presently unable to acquire the data.

You are correct, yes.

So the challenge here is to present the kind of data that would need to be acquired in order to falsify the RNA World model or the metabolism-first scenario.

Well, we'd need to know more about RNA. We could follow up on the work of Bernhardt, Kurland, and Harish & Caetano-Anollés.

Do you have any ideas as to how we could test if FUCA was capable of surviving space travel?