Prebiotic Muffins and an Air of Unreality
Suppose I gave you a cookbook with a recipe for muffins that read like this:
All-purpose flour OR unmilled grain (either may work, or not, depending on conditions). Some, but not too much. Be reasonable.
Eggs if you have them. Not sure how many. Maybe none.
Sugar: glucose, sucrose, and fructose are all candidates. Other carbohydrates may be possible, still checking on that.
Salt, although ordinary dust will do if its sodium content is high enough.
Milk? Hm, probably not. There’s the problem of getting the cow first.
Vanilla? Definitely not. Vanilla beans need vanilla orchids…forget that.
Baking powder: okay, that’s just sodium bicarbonate and an acid salt. Tricky but much easier to obtain than milk or vanilla (or wheat or eggs, frankly).
Mix well, then heat for a while (try different intervals) in muffin-sized containers. Hope for the best.
Prebiotic muffins are not going to happen. Ever.
“Prebiotic Soup Recipes”
But there is a cookbook being proposed for “prebiotic soup recipes” — that is, combinations of non-living chemicals plausibly present on the early Earth, which may have been key constituents of the living state. You can read about the cookbook idea here (open access): “The Prebiotic Kitchen: A Guide to Composing Prebiotic Soup Recipes to Test Origins of Life Hypotheses.”
The paper is clear about 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 outstanding problem in understanding the origins of life is how the components of prebiotic soup came to be organized in systems capable of emergent processes such as growth, self-propagation, information processing, and adaptive evolution. Given that prebiotic soups may have been composed of millions of distinct compounds, each at a low concentration, another mystery is how processes winnowed this molecular diversity down to the few compounds it used by biology today, which are a tiny subset of the many compounds that would have arisen from abiotic processes. Consequently, it is important to understand how complex mixtures of dilute organic molecules generated by environmental processes could have been “tamed” to give rise to the less diverse but more organized chemistry of metabolism.1
If prebiotic muffins are never going to happen, however (and no one thinks muffins happen that way — it’s an analogy), what justifies prebiotic soup recipes?
The paragraph cited above provides excellent reasons — e.g., “millions of distinct compounds, each at a low concentration” — to think that the bottom-up, undirected-chemistry-first approach to the OOL may be missing something important: namely, that “chemistry first” is actually wrong. As James Tour has often explained, undirected chemistry by itself is not only indifferent to the living state, it is actively hostile.
A Fork in the Logic Tree
But consider the rationale provided by the prebiotic cookbook authors (emphasis added):
We suggest that since the successful bottom-up origins of life research program is only feasible if abiogenesis is a reasonably robust phenomenon, meaning that it does not require very specific, cosmically rare conditions, the desire to generate a perfect simulacrum of prebiotic chemistry should not prevent attempts to generate reasonable approximations that bracket some of the uncertainty.
There is a fork deep in the logic tree here which needs mentioning, because the cookbook authors don’t say anything about it. Let’s return to the muffin analogy, broken down now into the main premise and the inferences drawn from it:
- PREMISE: prebiotic muffins are a reasonably robust phenomenon.
- INFERENCE: therefore searching for prebiotic muffin recipes is worth the effort.
- INFERENCE: therefore we can allow ourselves some bracketing of unsolved problems. Baking soda, salt, and sugar may be assumed as givens; posit flour or unmilled grain for the time being; eggs, milk, and vanilla are admittedly a stretch. But we’re working on it.
The unmentioned fork, of course, occurs at (1), with “abiogenesis” taking the place of “prebiotic muffins.” What if abiogenesis — the undirected OOL from chemistry — is NOT a “reasonably robust phenomenon”?
Then composing prebiotic recipes, no matter how numerous or varied, is a hopeless endeavor, whose sheer unreality is evident to anyone for whom premise (1) is an unsupported, or simply false, conjecture.
The air of sheer unreality continues to the very end of the prebiotic kitchen article:
Only through bottom-up, untargeted methods can we determine what aspects of cellular biochemistry were inevitable for any living system given the specific chemistry of Earth, or were, instead, “frozen accidents.”
But no experimentation using “bottom-up, untargeted methods” is needed to know that x (the genetic code, let’s say) was a “frozen accident,” because no experimentation is even possible, if the origin of x actually WAS a frozen accident (probabilistically, a singularity or one-off event). The whole point of invoking a frozen accident for the origin of x is to get around the total absence of repeatable experimental support or a deterministic chemical pathway. The cookbook authors realize this early in their article, when they say that bottom-up approaches are worth pursuing only if “very specific, cosmically rare conditions” are not required for abiogenesis — where “very specific, cosmically rare conditions” are synonymous with “frozen accident.”
Experiments do not show us which events are frozen accidents. By their very nature, they can’t. The logical structure of any physical experiment is if antecedent condition p obtains, then observable outcome q follows. Regular or repeatable outcomes are what successful recipes and experiments provide. “Frozen accident,” by contrast, is only an evocative label for “something happened, but we don’t have a clue what it was, so we cannot define or reconstruct antecedent condition p.” Experiments and frozen accidents thus inhabit separate evidential universes. In one of those universes, science is possible.
The Last Word
Francis Crick understood this. In the widely cited 1968 paper where he proposed the frozen accident scenario for the origin of the genetic code, he ends with a skeptical and cautionary note about his own hypothesis. It is fitting to give him the last word:
The theory seems plausible but as a theory it suffers from a major defect: it is too accommodating. In a loose sort of way it can explain anything. A second disadvantage is that the early steps needed to get the system going seem to require rather a lot of chance effect. A theory of this sort is not necessarily useless if one can get at the facts experimentally. Unfortunately, in this problem this is just what is so difficult to do.2
- Footnote numbers omitted.
- Francis Crick, “The Origin of the Genetic Code,” Journal of Molecular Biology 38 (1968):367-79; p. 378.