Although most evolutionists consider the question of the origin of life—also called “abiogenesis”—as its own discipline separate from evolutionary biology, explaining how life came to be could still be considered on aspect of neo-Darwinism. The problem, of course, is that we don’t really understand how the first living organism came to be. And what “living” means is also disputed. Our ignorance on this issue is profound, and although there have been various suggestions of how it got started (i.e., origination of life near “hot underwater vents” or “cold underwater vents”), the earliest organisms were surely soft-bodied, and that means we won’t recover them, even as fossils.
The earliest organisms we know of for sure—cyanobacteria (“blue-green algae”, but they’re really bacteria)—are about 3.4 billion years old, and are already complex, so life must have originated way before that.
Now creationists have always preyed on ignorance, with their method often being the claim “We don’t understand how X evolved via evolutionary processes, ergo Darwinism is wrong and creationism must be right.” But time after time, as we’ve seen in cases like the bacterial flagellum that made creationist biologist Michael Behe infamous, evolutionists have been able to find viable precursors to features or organisms once thought impossible to have evolved (here’s one for the flagellum).
But now we have what appear to be a pair of creationists, with decent academic credentials, publishing a paper in a respectable journal saying that the evolution of life was too improbable to have happened by evolution. (They don’t posit an alternative, but given their repeated reference to “miracles,” I suspect they think that God did it, but they don’t mention the “G word.”) Nor do they propose an alternative way life must have originated, which makes me think that they do believe in the only alternative: life was created. (Of course then life could have evolved by natural selection!)
The provocative title of their deeply misguided article is below, and if you click on it you can see a précis of the piece, but if you want to read the whole dire thing, email me for a pdf, since nothing else is publicly available.
The authors’ affiliations, in order:
Olen R. Browna,*, David A. Hullenderb
aEmeritus of Biomedical Sciences, At the University of Missouri, Columbia, MO, USA
bMechanical and Aerospace Engineering at the University of Texas at Arlington, USA
Here’s the abstract:
Abstract
The origin of life and its evolution are generally taught as occurring by abiogenesis and gene-centric neo-Darwinism. Significant biological evolutionary changes are preserved and given direction (descent with modification) by Darwin’s (Spencer’s) natural selection by survival of the fittest. Only survival of the fittest (adapted/broadened) is available to provide a ‘naturalistic’ direction to prefer one outcome/reaction over another for abiogenesis. Thus, assembly of first life must reach some threshold (the first minimal cell) before ‘survival of the fittest’ (the only naturalistic explanation available) can function as Darwin proposed for biological change. We propose the novel concept that the requirement for co-origination of vitamins with enzymes is a fundamental, but overlooked, problem that survival of the fittest (even broadly redefined beyond Darwin) cannot reasonably overcome. We support this conclusion with probability calculations. We focus on the stage of evolution involving the transition from non-life to the first, minimal living cell. We show that co-origination of required biochemical processes makes the origin of life probabilistically absurdly improbable even when all assumptions are chosen to unreasonably favor evolutionary theories.
My copy of the pdf has tiny type, but I’ll try to extract some prose. But I’ll summarize the logic of argument, which is familiar, in four steps:
1.) First, like Alfred Russel Wallace, they don’t like the term “natural selection” because it implies that an entity, nature, is doing some active “selecting”. So the two authors use “survival of the fittest” throughout the text. Well, that’s also wrong because what survives are genes, so a better phrase would be “Reproduction of the FITTER.” But so be it. Let’s move on:
2.) The simplest living organism we know of are species in the genus Mycoplasma, bacterial parasites. They lack cell walls and have “the smallest genomes of any organism that can be grown in pure culture.” The one they refer to (M. genitalium, a parasite of the urinary tract and genitals of humans) “has a minimal metabolism and little genomic redundancy.” Its simplicity, lack of genes that enable it to live independently, and small genome, have convinced Brown and Hullender that this is a model for the earliest known cell. Note, however, that it’s already highly evolved, with many genes and a mechanism for replicating, transcribing, and translating its DNA.
This is a quote about M genitalium from Wikipedia; the bolding is mine:
The genome of M. genitalium strain G37T consists in one circular DNA molecule of 580,070 base pairs. Scott N. Peterson and his team at the University of North Carolina at Chapel Hill reported the first genetic map using pulsed-field gel electrophoresis in 1991. They performed an initial study of the genome using sequencing in 1993, by which they found 100,993 nucleotides and 390 protein-coding genes. Collaborating with researchers at The Institute for Genomic Research (TIGR; now the J. Craig Venter Institute), which included Craig Venter, they made the complete genome sequence in 1995 using shotgun sequencing. Only 470 predicted coding regions were identified in 1995, including genes required for DNA replication, transcription and translation, DNA repair, cellular transport, and energy metabolism. It was the second complete bacterial genome ever sequenced, after Haemophilus influenzae. Later data from KEGG reports 476 protein-coding genes and 43 RNA genes, totaling 519. It is unclear where the “525” gene count for the G37T stems from and what gene calling procedure was used.
In 2006, the team at the J. Craig Venter Institute reported that only 382 genes are essential for biological functions. The small genome of M. genitalium made it the organism of choice in The Minimal Genome Project, a study to find the smallest set of genetic material necessary to sustain life.
There is limited divergence among clinical strains of M. genitalium. All strains retain the small genome size.
Thus this species is already an efficient replicator, and reproduces by budding off offspring with duplicated DNA. Right now it has the minimal genome of any known organism, So, since the authors think that any evolution has to begin with an organism like M. genitalium, they do this:
3.) To calculate the probability that life originated by natural selection (or “survival of the fittest”, LOL) they calculate the probability of an organism like M. genitalium originating “by chance”.
This is one big flaw in the authors’ logic, for M. genitalium is already highly evolved, and the first “living” organism must have been much simpler than this. In fact, we have no idea what it was, but it wasn’t M. genitalium or anything like it with a sophisticated replication system. And of course life did not originate “by chance”. That’s the “junkyard tornado” fallacy named by Fred Hoyle.
But rather than addressing replication, the authors just list ten biochemical pathways in living species of M. genitalium, each of which requires multiple enzymes and multiple coenzymes, which are “vitamins”. Here’s their table:
They then focus on the probabilities that the pathways above, assuming “70 unique enzymes that must co-originate with required coenzymes [k = 1o]” are necessary for the “minimal living cell. If you get the probability of that happening by chance, then, the sweating authors say, you have the probability of life originating (by chance).
Their assumption, again based on observing modern biochemistry, is that a coenzyme without an enzyme present is useless, and an enzyme without a coenzyme present is also useless. They say that both have to originate together in final form, and if you require that they do so “by random processes” (not natural selection!), getting these systems occurring by chance is infinitesimally small—so small, of course, that they imply that it could not have happened:
We propose an additional problem for the theory of evolution that, specifically, impacts the evolutionists use of ‘survival of the fittest’. We call this problem the requirement for co-origination of essential life functions. Co-origination is a fundamental and absolute requirement for functions essential for life. We conclude it is the death knell for survival of the fittest.
Specifically, we address the problem caused by the fact that many enzymes require co-enzymes for function. The likelihood of the random creation (by chance) of one enzyme is highly improbable. To arrive by chance, using evolution and natural selection, at an enzyme with an essential coenzyme is extremely improbable. For all enzymes that require co-enzymes, we propose that the concept of co-origination magnifies the absurd improbability and makes it impossible (if impossible has any meaning).
I don’t really understand how they got these probabilities, which are described in earlier papers that I haven’t read, but that’s irrelevant, because a). proteins and coenzymes do not originate by chance, but by natural selection from earlier precursor states, and b). enzymes and coenzymes must have coevolved through rudimentary precursors that we don’t know of, and must have done so together. You don’t calculate independent probabilities for each factor of a pair and multiply them together, which is what the authors do.
Then the final step:
4.) The final probabilities of course are quite small, ranging from 10 to the minus 227th power to ten to the minus 1137th power. These, of course are tiny probabilities. Ergo life could not have originated in this way. But of course they neglect both the certainty of simpler precursors and the fact that enzymes and their coenzymes evolve together. Their conclusion is this:
Calculated probabilities for the origin of life ar absurdly improbable even when highly favorable assumptions are made. This agrees with the use of ‘absurd’ for probability statements by Eigen (Eigen) and that Wald (1954) found it necessary to use ‘miracles’ to justify his use of ‘impossible becomes possible’. The origin of life and its evolution cannot be ‘explained’ by a near-infinite sequence of minute changes given direction via selection by survival of the fittest. The death knell is the necessity for co-origination in space and in time, in one genome or perhaps two contiguous genomes (or whatever assumed the function before there was a genome) of all the structures and functions that are essential for life.
The errors are multifarious here: they assume that the minimal existing organism, a complex bacterium, must have been similar to the very first organism; they assume that enzymes and coenzymes originate by chance; and they assume that enzymes and coenzymes must evolve together into their existing forms, rather than coevolving (evolving together) from simpler forms that we don’t understand. The biggest error is assuming that the present “minimal existing organism” must resemble the first form of life that originated.
All in all, they make the usual creationist mistake of assuming things originate by chance and don’t coevolve, and also that what we see today is similar to what was present in the first forms of life.
I’d love to ask the authors “what is your alternative hypothesis, then?”, which they surely should have mentioned in the paper. But they don’t, because this is supposedly in a reputable journal, “Progress in Biophysics and Molecular Biology.” Sadly, the journal was played by creationists, and should be really embarrassed. If any reader wants to do a more thorough analysis of this paper, just ask and I’ll send them the pdf.
You can see the editorial board (two editors-in-chief and six editors) here. Someone should write them and let them know what they published. and that, in science, ignorance does not equal God.
I notice that one of the authors is an engineer. And I don’t know what ‘biomedical sciences’ are, as opposed to Biology and Medicine, but my observation is that most medical men aren’t concerned with those details.
Biomedical sciences. Here you are.
https://en.wikipedia.org/wiki/Biomedical_sciences
So, two laymen in evolutionary biology want to use sleight of hand to explain to the scientific world that the origin of life was too improbable to have come about through evolution. This approach was already yawn-inducing 25 years ago (at the height of intelligent design).
And…and…the engineer’s list of community contributions over twenty years (on his about me page) seems to be totally tied with his baptist church…which may explain some anti-Darwin predisposition.
The other author appears to have written this book (‘Miracles
Everything that Is or Was or Is to Come Is a Miracle’): https://www.booktopia.com.au/miracles-olen-r-brown/book/9781419643576.html?
He’s also writing for the Discovery Institute and been pushing this nonsense since at least 2018: https://evolutionnews.org/2018/08/enzymes-are-essential-for-life-did-they-evolve/
Very embarrassing for the journal and publisher.
Elsevier appears to be the publisher and their consistent focus on financial profit from the hard work of scientists puts them beyond or least orthogonal to embarrassment IMHO.
IMO “orthogonal to embarrassment” is another very good technically apt insult, on a par with “open loop”. I await more 🙂.
It is a cliche’ that one of the authors is an engineer. The other presumably had an evolution course or two as an undergrad.
Mark, I still remember like it was yesterday, having lunch with some of my new aerospace engineer colleagues when I first went to work at Nasa in the 1970’s, and during an informal lunchroom conversation, one of them said to me: “you don’t believe all that evolution crap do you?” So that was an unexpected eye opener!
As a first-year undergraduate student in physics 40 years ago, I was surprised by how many of the engineering students in my dorm were religious creationists. To an engineer everything is engineered, I guess.
These are very interesting posts – good to check the understanding.
I’ll take this part, kindly concise-ified by PCC(E), to make a hasty comment :
“They then focus on the probabilities that the pathways above, assuming “70 unique enzymes that must co-originate with required coenzymes [k = 1o]” […]
Their assumption, again based on observing modern biochemistry, is that a coenzyme without an enzyme present is useless, and an enzyme without a coenzyme present is also useless. ”
An enzyme – say even an extant enzyme – that depends on an extant coenzyme (prosthetic group, metal ion, or other post-translational mods), …
[tries to argue without too many words.. ]
[ …]
[sigh]
The definition of enzyme is as a catalyst, that lowers the activation barrier to a chemical reaction – while leaving the overall equilibrium constant unaffected.
THAT MEANS, the actual enzyme-free reactions – if given sufficient time, as in, perhaps, on evolutionary time-scales, will still accumulate products.
I am in haste, so I’ll have to look later 😁 but I would want to find the probability for the enzyme-free reactions in their paper.
… modulo the reaction conditions, of course….
Like, vitamin C won’t pop into existence in a vacuum the way (AFAIK) sub-atomic particles pop in and out of existence.
Clusters of commonly occurring metal atoms do many of the reactions that enzymes do. They are not as efficient, and are rather promiscuous about catalyzing other reactions, but they do them. This is why many enzymes even today carry these clusters of metal atoms inside them as prosthetic groups, and then the metal atoms become much more specific about the chemical reactions that they catalyze.
“… a pair of creationists, with decent academic credentials…”
Or in common parlance, liars.
Not necessarily, just orthogonal to truth. (Like iDJT.)
This isn’t a one-off that they snuck past reviewers. They’ve published several such papers and some were in the same journal. I’ve known about them for a while because the DI always mentions their articles.
I can’t get the full pdf but I wouldn’t be surprised if they thank James Tour in the acknowledgments.
By using M. genitalium (an already complex bacterium) as their model, the authors seem to be burning down a straw man. I have no doubt that the probability of assembling a bacterium from non-life is vanishingly small (to be fair, I haven’t read their article), but that’s not at all what researchers on the origin of life claim. Their claims rely on the accumulation of innumerable small steps, each of which has a reasonable probability of occurring and each of which has some positive effect on either survival or replication. Arguing against the de novo assembly of a bacterium is like crashing through an open door. No one accepts that such an improbable event lies at the root of the origin of life.
At the close of your piece, you write: “You can see the editorial board (two editors-in-chief and six editors) here. Someone should write them and let them know what they published and that, in science, ignorance does not equal God.”
I think that you may have just done that.
It’s worse than that although to be fair I haven’t read their article either. They might be correct in asserting that M.genitalium couldn’t form de novo… but it could form from the evolutionary processes simplifying a more complex organism (which was built by un-miraculous evolutionary processes). Do they put a possibility on this or were they just cherry picking an organism which suited their arguments?
And lo, when Jesus looked down upon the lifeless Earth, and seeing that His Plan of Life was improbably and irreducibly complex, and with all the angels and cherubim and seraphim of the heavenly host, didst breathe the complex specified information into the dust of the rudimentary poly-peptides of the Earth, and said in a loud voice, “Go ye hither to multiply and fitly survive.” And it was so.
Of Pandas and People, pp. 89-90
17 years later, and I still get a laugh out of this one, probably because nothing about their arguments has changed.
https://youtu.be/eaGgpGLxLQw?si=YjxSLJfGkKMkaIsr
…and with all the angels and cherubim and seraphim of the heavenly host, didst say,
“Let there be M. genitalium”. And there was M. genitalium. And God saw that it was a pest.
“And the Lord God said, It is not good that a parasite should be alone; I will make it an host …. And made he a man, and brought it into the man.”
lol
It is very surprising that this type of argument is still made. It shows the intellectual dishonesty of the journal, its edtors, and the authors.
Phunny phrases like “probabilistically absurdly improbable.”
Hokay, this is dumb. We certainly don’t know many key details about the origin of life, but the authors could at least admit that we do know things. Alkaline vents in the ocean, for example, provide stable reducing environments that favor generation of a range of bio-molecules and even polymers, and btw coenzymes are quite do-able in these conditions. This is according to experiments. That these things are made is not a matter of natural selection. Rather, under these conditions it is simple thermodynamics that basically forces these molecules to be made as a way to draw down potential energies of precursor molecules that occur naturally. To emphasize: These products are not improbable and made by chance. They are forced to exist. It has not escaped notice that carbonaceous meteorites also contain a range of bio-molecules, including coenzymes. The laws of thermodynamics likes to make these things!
It is actually quite startling how the reducing alkaline vent environment in particular resembles core aspects of universal cell metabolism. It’s like all cells today are carrying aspects of alkaline vents inside them.
I was writing a long post here about the various steps involved in getting from there –> life, but it was taking too long. So lemme just say that there are great and very readable books on the matter. I would recommend especially The Vital Question, by Nick Lane.
Yes, there are big gaps in our understanding. But the authors were clearly not interested in including them lest it change the balance of their “math”.
People will always believe what they want to believe. In a recent Quillette article about the Scopes trial (referenced here by our Boss, I believe) the comments were polluted with “reasons” why Evolution simply cannot be true. I’m sure it disheartened Claire Lehmann to see who her subscribers actually are.
Not quite correct. I just had a look at the comments to that Quillette article and there was just one guy – someone who frequently trolls the comments there – who was arguing against evolution based on the very paper under discussion here. The other commentators were busy refuting his assertions. It was just one subscriber so Claire is unlikely to be worried.
Just looking at the number of coenzymes that incorporate adenine nucleotide into their structure – NAD, NADP, FAD, Coenzyme A ought to give a rational person reason to think, “Oh, it looks like the anchor portion of this molecule was retained [thru an evolutionary process] and [over time] different decorations were adopted to suit different enzymatic requirements.” And in fact similarities of binding sites can be detected between enzymes that utilize these cofactors, to the extent that a “nucleotide binding fold” is a motif in protein structure. (It was the crystallographer Michael Rossman who first noted this, and so it is sometimes called a Rossman Fold.)
Nice!
The only book I’ve read on abiogenesis is Addy Pross’ What is life? How Chemistry Becomes Biology, which I thought was excellent; it certainly cuts through the type of nonsense exemplified in this paper.
Can anyone recommend a possibly more recent book on the same topic? Thanks in advance.
Yes! Nick Lane – Life Ascending (2009), The Vital Question (2015, and Transformer… (2022). I haven’t read the last one, bu the first two are great.
Also, I haven’t read Jack Szostak’s new one together with an astrophysicist, but it ought to be good. Here he is with a video on it.
And Crikey – Jack’s @ U Chicago now. I thought he was still @ Harvard.
Thanks!
The use of the phrase “survival of the fittest” and the insertion of Spencer’s name is intended pejoratively, a way of poisoning the well by framing the discussion in terms with negative connotations, playing on popular misconceptions of the phrase.
Of course. I remember (before I regained my sanity) at church once, a speaker about to do a typically creationist hatchet job on Darwin quoted the full title, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, complete with theatrical shiver at the words “Favoured Races”, to imply that Darwinism/evolution = racism.
This is a fascinating topic (the origin of life) but the paper adds next to nothing to the inquiry. I agree with PCC(E) that a key flaw in the paper is choosing a present day example of small-genome-life and assuming that was the first big step. The paper is useful as an example of how not to approach the topic and it would be great if the journal published critiques
The editors should have insisted that alternate explanations be presented and given the authors a hint of where to look.
If there has been any new work in this area or a new review in Annual Reviews readers here like myself would be interested.
I can’t stand theists who challenge abiogenesis because they lack sufficient imagination, knowledge, and long for a merely 3,000 year old skydaddy who was obviously, demonstrably manmade. I always liked Hitch’s argument ‘where the hell was god 100,000 years ago when homo sapiens was struggling to survive and neanderthals went extinct? Took his time (4.5B years) to get around to us, didn’t he?’
The most profound argument from a chemical biology perspective for me is recent evidence addressing the “starting material problem.” Where did the building blocks of the DNA/RNA replicators (homochiral ribose and the A, T, G, C, U nucleobases) first come from because they are now made biochemically using enzymes? This is the ultimate chicken & egg problem. They cannot be ultrarare because of the ‘infinite dilution problem’ in terrestrial niches that would preclude their ability to be polymerized without running out of starting materials on an early Earth (i.e. no replication = death of proto-life). That is most consequential to the DNA/RNA self-replicating biopolymer world but likewise applies to the amino acid/protein biopolymer world too.
In my opinion, the 2023 Osiris-Rex space probe that returned samples from asteroid Bennu absolutely changed the game by showing Bennu contained all 5 RNA/DNA nucleobases and 14 of 20 natural amino acids. In other words in our first attempt to study this question, we found that a simple random asteroid near Earth was replete with the building blocks of our molecular replicators. How about the improbability of that, abiogenesis deniers? This means they are common due to extraterrestrial space chemistry. The only mystery now is by what mechanisms did they polymerize to create life as we know it because that is clearly what happened. This abiogenesis god-of-the-gaps argument has now been thoroughly cemented over.
Sara Walker and Lee Cronin’s development of Assembly Theory fits well with the Bennu findings. I don’t know much about Assembly Theory, but at least it’s a new way to think about life’s origins. This is a link to the Jim Rutt show where she discusses it. https://jimruttshow.blubrry.net/sara-walker/
Ok, so it’s all down to magic then……!
An overly complicated argument from personal incredulity, again.
Re “probabilistically absurdly improbable” and “the concept of co-origination magnifies the absurd improbability and makes it impossible (if impossible has any meaning)” —
First, “impossible” actually has several meanings, depending on context. There’s the precise technical meaning of the probability being exactly 0; and various non-technical meanings that are like “absurdly improbable”, the probability being very teeny tiny. Academic polemicists who beat the drum of “probability calculations” should really be more careful, lest they seem like posturing fools.
Second, only a very very … very teeny tiny non-zero prior probability is needed for applying the Weak Anthropic Principle (WAP). Simply put, it’s a sampling-bias issue. If life hadn’t happened then we wouldn’t be arguing about it. Yes, maybe we won a cosmic lottery, but if we hadn’t then exactly no one would care.
The WAP also applies to “fine tuning” arguments.
(I’ve found that WAP arguments often annoy people. I don’t know why. Maybe it’s some kind of latent existential bias. Maybe it’s me.)
I was hoping that some reader(s) would be annoyed with this use of WAP and could tell me why. Oh well.
Without even addressing the specifics of the arguments by Brown and Hullender, isn’t it intrinsically absurd to claim that something couldn’t have happened because of the odds against it? To borrow a line from Rogers and Hammerstein’s “Cinderella” — “Impossible things are happening every day.” What were the odds that Brown and Hullender would meet one another and write their paper using the exact words they used? And yet it happened. Is the remoteness of those odds proof that their paper was divinely inspired? Of course not. Indeed, what were the odds that everything that happened yesterday everywhere in the world would happen?
I’ve read that the probability of 4 bridge players receiving the particular hands they are dealt is 1 in over 53.6 octillion. Certainly, no sane person would claim that the improbability of the distribution of the cards in these four hands is proof of divine intervention.
I am an MD and it is embarrassing that of all people with college degrees the ones most likely to be taken in by pseudosciences like creationism are engineers and medical doctors.
My professional experience is military and music performance with a strong engineering background including undergrad statistics. While I’ve studied the evolution/creationism silliness for decades, I’m more than a bit of an outsider to the actual science as opposed to what I know pretty well: science translated to prose for the layman. Just for my background.
Since we have evidence life has been on Earth for at least 3.4B years and almost certainly longer than that, and we are increasing our knowledge on genetics though it’s not yet ready to explain abiogenesis, or we are waiting for the Darwin or Einstein of that subject to come along, doesn’t what we know already give us a statistical answer of 1? We have hard evidence that life is here and strong evidence it started here but we have only one example of life on a planet vs not, then we have 1/1 for a probability of 1 or 100% chance, which means we simply don’t have enough info to make a good statistical calculation. Statistical speculation on the chances of a process we don’t understand has so many unsupported assertions that the math is useless. Until we actually have an abiogenesis mechanism.
Did I miss something? Yes this is an honest question.
We know of 7 (or 8; Pluto, I’m looking at you) other planets in our solar system, none with life. So that particular statistical argument doesn’t work. It can be strengthened by positing “only those planets in the goldilocks zone, where temperatures allow liquid water to exist”. To get a larger sample size, we’re going to need much more powerful telescopes…
While I understand your point, the only real data set we have is for Earth. Everything else is so partial that you can draw few or no conclusions, especially if we are talking about abiogenesis which does NOT require the planet or moon to have life right now. As the sun expands and gets hotter, the snow line will also push further out and we will have future possibilities of abiogenesis in 2-4B years where none have existed so far. We also are not sure all planets have been or will continue to be in their current orbits – one model puts Jupiter much, much closer to the sun when formed, and the Earth’s orbit when we collided with Theia must have been altered a great deal.
Mars is showing some signs that when it still had a molten core and magnetic field, it might have had an abiogenesis moment, but we don’t know enough to be sure.
Venus’ past we don’t know – when the sun was cooler or maybe its orbit was different, did it have an abiogenesis moment? We do not know.
Additional “we do not know” applies to, at a minimum:
Europa, Ganymede, Callisto, Titan, Enceladus, and probably more. Further, panspermia, where life was delivered to Earth from an abiogenesis moment elsewhere, also remains unknown.
Biologists have also not agreed on a definition of life, so to a certain extent we cannot even intelligently form the probability question. Is a virus alive? That basic question is not settled. Is non-carbon life even possible? We do not know. Is the only requirement an energy gradient that matter/energy can exploit the only requirement, or do you need liquid water? We don’t know, but that could open up the clouds of Jupiter, Saturn, Uranus, Neptune, and Venus as possible locations. We don’t know enough to frame the question whether life is rare or common, much less a probability.
The probability equation as I see it: we have only one example, Earth, where we have enough information to give a yes/no answer though Mars is looking like a Yes but long ago. That means we have one yes out of one (or 2/2 with Mars but the same probability answer), or 100%. Given how briefly after Theia’s collision Earth had its biogenesis moment, that means that harsh, hot conditions were obviously fine. The ocean-bottom of Europa might be only slightly less active than Io, meaning a very hot, harsh environment at the bottom there, with a huge temperature gradient up to the ice.
Thank you for the article on Biological Evolution. I’d like a PDF copy as you advertised.
Thank you.
Sent!