Suppose I give you a cookbook with a recipe for muffins that goes like this:
All-purpose flour OR unmilled grain (either may or may not work, depending on conditions). Some but not too much. Be reasonable.
eggs if you have them. Not sure how many. Maybe none.
Sugars: Glucose, sucrose, and fructose are all candidates. Other carbohydrates may be possible, this is still being checked.
Salt, although ordinary dust will do if its sodium content is high enough.
Milk? Hmm, probably not. There is the problem of getting the cow first.
Vanilla? Definitely not. Vanilla beans need vanilla orchids… forget that.
Baking Soda: Okay, that’s just sodium bicarbonate and an acidic salt. Difficult, but a lot easier to get than milk or vanilla (or, frankly, wheat or eggs).
Mix well, then heat in muffin-sized containers for a while (try different intervals). Hope for the best.
Prebiotic muffins aren’t going to happen. Always.
“Prebiotic Soup Recipes”
But a cookbook is proposed for “prebiotic soup recipes” — that is, combinations of non-living chemicals that were plausibly present on early Earth and may have been key ingredients in the living state. You can read the cookbook idea here (open access): “The Prebiotic Kitchen: A Guide to Composing Prebiotic Soup Recipes to Test the Hypotheses Concerning the Origin of Life.”
The paper is clear on the Origin of Life (OOL) challenge and the need to try different recipes:
While it is well documented that many chemicals involved in biochemistry can be synthesized abiotically, the biggest open problem in understanding the origins of life is how the components of the prebiotic soup were organized into systems leading to nascent processes such as growth and self-reproduction are capable of information processing and adaptive evolution. Given that prebiotic soups may have consisted of millions of different compounds, each at low concentrations, another mystery is how processes reduced this molecular diversity to the few compounds used by biology today, a tiny subset of the many Compounds would have arisen from abiotic processes. Consequently, it is important to understand how complex mixtures of dilute organic molecules generated by environmental processes could be “tamed” to give rise to the less diverse but more organized chemistry of metabolism.1
However, if prebiotic muffins will never emerge (and no one thinks muffins will—it’s an analogy), then what justifies prebiotic soup recipes?
The paragraph quoted above provides excellent reasons – e.g. B. “Millions of different compounds, each in low concentration” – to the assumption that the bottom-up approach based on undirected chemistry first may be missing something important: namely, that “chemistry first” is actually wrong. As James Tour has often explained, undirected chemistry itself is not only indifferent to the living state, it is actively hostile.
A fork in the logic tree
But consider the rationale of the prebiotic cookbook authors (emphasis added):
We propose that the successful bottom-up research program into the origins of life is only feasible if abiogenesis is a reasonably robust phenomenon, meaning that it does not require very specific, cosmically rare conditionsthe desire to produce a perfect simulacrum of prebiotic chemistry should not prevent attempts to produce reasonable approximations that bridge some of the uncertainty.
There is a fork deep in the logic tree here that needs to be mentioned because the cookbook authors don’t say anything about it. Returning to the muffin analogy, which will now be broken down into the main premise and the conclusions drawn from it:
- REQUIREMENT: Prebiotic muffins are a fairly robust phenomenon.
- CONCLUSION: So it’s worth searching for prebiotic muffin recipes.
- CONCLUSION: Therefore we can allow ourselves a bracketing of unsolved problems. Soda, salt, and sugar may be taken for granted; use flour or unground grain for the time being; Eggs, milk and vanilla are admittedly a range. But we are working on it.
The unmentioned bifurcation, of course, occurs at (1), with “abiogenesis” taking the place of “prebiotic muffins”. What if abiogenesis – the undirected OOL from chemistry – is NOT a “fairly robust phenomenon”?
Then composing prebiotic recipes, no matter how numerous or varied, is a hopeless endeavor whose sheer unreality is apparent to anyone for whom premise (1) is an unsupported or just plain wrong guess.
The air of sheer unreality continues to the end of the prebiotic kitchen item:
Only by untargeted bottom-up methods can we determine which aspects of cellular biochemistry were inevitable for any living system, given Earth’s specific chemistry, or were instead “frozen accidents.”
But knowing that doesn’t require experimenting with “bottom-up, untargeted methods.” x (let’s say the genetic code) was a “frozen accident”, because no experiments are possible, if the origin of x WAS actually a frozen accident (probably a singularity or one off event). The whole point of invoking a frozen accident for origin x is to circumvent the total lack of repeatable experimental support or a deterministic chemical pathway. The cookbook authors recognize this early in their article when they say that bottom-up approaches are only worthwhile when “very specific, cosmically rare conditions” are present not required for abiogenesis – where “very specific, cosmically rare conditions” are equivalent with Frozen Accident.
Experiments don’t tell us which events are frozen accidents. By nature they cannot. The logical structure of every physical experiment is if precondition P then observable result Q follows. Consistent or repeatable results are what successful recipes and experiments deliver. “Frozen Accident,” on the other hand, is just an evocative term for “something happened, but we have no idea what it was, so we can’t define or reconstruct the antecedent condition.” P.” Experiments and frozen accidents thus inhabit separate universes of evidence. In one of these universes, science is possible.
The last word
Francis Crick understood this. In the much-cited 1968 paper in which he proposed the frozen accident scenario for the origin of the genetic code, he concludes with a skeptical and cautionary note on his own hypothesis. It is appropriate to give him the last word:
The theory seems plausible, but as a theory it suffers from one major flaw: it is too accommodating. In a casual way it can explain everything. A second downside is that the early steps required to get the system up and running seem to involve quite a bit of random effects. Such a theory is not necessarily useless if one can get to the bottom of the facts experimentally. Unfortunately, that is precisely what is so difficult with this problem.2
- Footnote numbers omitted.
- Francis Crick, “The Origin of the Genetic Code”, Journal of Molecular Biology 38 (1968): 367-79; P. 378.