origin of life
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Maverick journalist Susan Mazur, who is more willing than most reporters to ask hard questions, gave one of the most thorough views inside the minds of origin-of-life (hereafter OOL) researchers in her book The Origin of Life Circus: A How to Make Life Extravaganza. The book, organized around the metaphor of circus actors like ringmasters and lion tamers, includes lengthy statements from the leading lights of the field, drawn mostly from her own interviews with them. It's an enticing read, filled with delicious quotes for Darwin skeptics. Some researchers were extremely frank about the problems they were facing, both empirical and philosophical. A few were mostly bluffing with an overconfidence unjustified by the actual data.

Darwin defenders like to point out that Darwin did not address the origin of life. He only speculated about it in a letter to his friend Joseph Hooker in 1871, envisioning a "warm little pond all sorts of ammonia & phosphoric salts, - light, heat, electricity &c" - a statement that lit a thousand labs with sparks and flasks of organic fluids. Darwinists hasten to add that, since natural selection is not possible before replicators, his theory should be unhinged from the origin of life. Unhinged it may be, in more ways than one, but for the record, it is called "chemical evolution" and one can hardly imagine Darwinism without it. It remains a high but essential hurdle in the materialist scenario of molecules-to-man evolution.

The open-access journal Nature Communications recently published eight papers on OOL, including some by researchers interviewed in Mazur's book, like Steven Benner of the University of Florida and Nicholas Hud of Georgia Tech. Darwin doubters can find delicious quotes in some of these papers, too. But let's begin with a meta-analysis, searching all eight papers for key words (or their cognate forms) that seem particularly apropos for the subject:
  • Design (as pertains to life): zero.
  • Darwin: 6, two in references.
  • Selection (as pertains to natural processes): 24, in only 3 of the 8 papers.
  • Probability: zero.
  • Chirality: 1, but only in reference to a 1996 paper.
  • Sequence (in terms of genetic or functional information): zero, but 2 about reaction sequences.
  • Information (i.e., genetic, heritable information): 2, example: "RNA arose abiotically and is the first informational polymer of life, with its nucleotides and polymers produced entirely by geochemical reactions" in one paper, and "There is little doubt that RNA is central to the origins of genetic information and protein synthesis" in another paper.
  • Interference (in terms of human interference with natural processes): zero.
  • Intervention: 17, all in one paper about human intervention in experiments (more below).
  • Scenario: 8.
  • Prebiotic: 176.
  • Plausible: 72.
At first glance, these figures indicate that none of the researchers are tackling the origin of heritable genetic information that is the crux of the problem. Random molecules that don't "mean" anything or "function" in some way may be of interest to chemists, but not to biologists. Instead, the OOL community likes to think about "plausible prebiotic conditions" in a "scenario" where they dream of a self-sustaining replicator emerging by chance. Some are satisfied to consider scenarios in which just one necessary ingredient might emerge by chance. But what is meant by "plausible"?

Reckless Plausibility

Mazur labels Steven A. Benner the "ringmaster" in the origin-of-life circus for his entertaining style and willingness to think outside the box. Benner can discuss problems in OOL research frankly, perhaps due to his having tenure and an unassailable reputation among his peers. In his paper "Prebiotic plausibility and networks of paradox-resolving independent models," Benner puts some spicy lingo in his light-hearted critique of the word "plausible" that so many OOL researchers fling around carelessly. Recalling Leslie Orgel's free use of the word in 1974, he says, with tongue in cheek:
It was 30 years before Orgel confronted the easy transformation of "prebiotically plausible" from a phrase supported by examinable premises to instead mean: "A molecule that I desire for my model". In 2004, Orgel offered three criteria to adjudicate the prebiotic plausibility of individual molecules. The first was circular (its precursors must be prebiotically plausible). The second (reactions forming the molecule must occur in water) was rich in assumptions that excluded alternative solvents. The third was subjective (the yield of molecule must be "significant").

Orgel concluded by suggesting that "it would not be wise to define too closely" the concept of "prebiotically plausible". Aside from being another example of the endorsement of semantic and philosophical imprecision by heroes in this field, this does not offer the editors of journals guidance when evaluating manuscripts that purport to present investigator-managed chemistry, much done in Pyrex, as relevant to origins.
Today, he says, fifty years after the phrase "prebiotically plausible" became widespread in OOL studies, Nature Communications is asking for criteria in order to put "substance behind the phrase." But one of the most famous candidate molecules, HCN (hydrogen cyanide), often considered a stepping stone to life, is not prebiotically plausible, Benner argues. Why? Because "current theory holds that Earth's native atmosphere was more oxidizing than the Miller atmosphere."
Thus, the prebiotic plausibility of HCN, the other molecules, and adenine long ago vanished as Earth-made species, even though literature too voluminous to cite here continues to assume otherwise.

This creates a paradox. If one premises that life originated via an RNA-First prebiotic process that used adenine as a precursor and that adenine was formed from HCN from a Hadean terran atmosphere, then the premises that view HCN as an impossible product of our early atmosphere force the conclusion that life could not have originated on Earth. An unacceptable conclusion follows by the force of logic from seemingly acceptable premises.
You have to admire Benner's frankness and wit. He continues pulling the rug out from under models built on assumptions that are not plausible by any objective standard. But then, in the end, he doesn't give up on OOL research. To keep it going, he has to say something that itself is circular, rich in assumptions, and subjective.
Nothing is ever proven in science. However, a network of models, each subject to independent test in their own fields, makes the big picture more, shall we say, plausible.
Now he becomes the criterion of plausibility. But a network of models, each implausible, is not going to make the network plausible. And what if the "independent tests" themselves are based on assumptions of plausibility?

Lackadaisical Performances

Here are sentence summaries of the other papers, then one worth noting in more detail:
  • Krishnamurthy, "Experimentally investigating the origin of DNA/RNA on early Earth." The origin of RNA and DNA continues to be an enigma that defies explanation.
  • Stuart Harrison and Nick Lane, "Life as a guide to prebiotic nucleotide synthesis." Maybe if we keep staring at life we'll someday understand where it came from.
  • Nicholas Hud, "Searching for lost nucleotides of the pre-RNA World with a self-refining model of early Earth." Circular reasoning: "The nucleotides of RNA appear [that is, to Hud] to be products of evolution."
  • Laura Barge, "Considering planetary environments in origin of life studies." We can't understand chemical evolution here; maybe finding it on other worlds can help.
  • Becker, Schneider, Crisp and Carrell, "Non-canonical nucleosides and chemistry of the emergence of life." Maybe there used to be more nucleotides than the ones we see in life today. Maybe they got selected "in a pre-Darwinian chemical evolution process."
  • Whitaker and Powner, "Prebiotic nucleic acids need space to grow." We OOL chemists need to work together with the planetary scientists. In our labs, we "risk missing crucial aspects of the story as it unfolds."
The "Hand of God" Dilemma

The circus plays on, with old and new acts. Two performances in this particular show, however, threaten to pull the whole tent down and send the animals and clowns running. One was Benner's article noted above, where he reveals the mush in the word "plausible." The other is one by Clemens Richert, "Prebiotic chemistry and human intervention," that considers an often-overlooked flaw in OOL reasoning. He starts out gently enough:
Experimentalists in the field of prebiotic chemistry strive to re-enact what may have happened when life arose from inanimate material. How often human intervention was needed to obtain a specific result in their studies is worth reporting.
Richert reveals how the magic is done. Researchers often sneak intelligent design into the lab to make their molecules perform like they never would do on their own. His opening is a zinger:
When Diego Maradona was asked about having used his hand to score a goal in the quarter-finals of the 1986 soccer World Cup, he initially claimed that there had been divine intervention, and the term "Hand of God Goal" was coined. - There had been manual intervention, and there had been an understandable interest of the player not to admit it. - Organic chemists, if not all experimentalists in the field of prebiotic chemistry, are faced with a similar dilemma. We do our best to perform experiments that we believe re-enact possible steps of prebiotic evolution, but we know that we need to intervene manually to obtain meaningful results. Simply mixing chemicals and watching for a living system to appear from the broth seems unreasonable to me. This approach has never worked, and it is not expected to work, at least not if one is limited to the lifetime of a human, let alone the duration of a funding period or a Ph.D. thesis. So, what is a reasonable level of intervention by the experimentalist in prebiotic chemistry, and what are "plausible prebiotic conditions" in this context?
Scientists have to intervene, in other words, or they could never make any progress in realistic timescales. Richert identifies numerous sources of intervention in the lab that would never happen in the real world: using pure chemicals from a supplier, breaking up a series of reactions that need to be sequential, using high concentrations of chemicals that would be implausible in nature, eliminating contaminants that would ruin the reaction, inserting enzymes to get steps to run faster, purifying the products of one reaction, then putting the products into another process with a drastic change in conditions for the next stage, and more. Enjoy this comment:
Understandably, this has drawn the ire of those who feel that no or only minimal intervention is allowed for a process to be called prebiotically plausible. After all, it is not easy to see what replaced the flasks, pipettes and stir bars of a chemistry lab during prebiotic evolution, let alone the hands of the chemist who performed the manipulations. (And yes, most of us are not comfortable with the idea of divine intervention in this context.)
Benner was unable to rescue OOL from reckless use of plausibility arguments. Can Richert rescue OOL from reckless use of human intervention? He agrees with Benner that it is not easy to gauge the plausibility of prebiotic scenarios. He gives several more examples of how the subjective judgment of the investigator can creep in. But "plausibility is important," he says. "So, perhaps it is time to think about ways out of the 'Hand of God' dilemma."

He advises three rules: (1) report the number of interventions explicitly. He is emphatic on this point: "When it becomes unavoidable to intervene as experimentalist, just state the number of discontinuities in the experimental conditions or human interventions!" (The exclamation point is his.) (2) State what prebiotic scenario an experiment is designed to address; this will help uncover assumptions being used. (3) Reduce the number of interventions required for an experiment. Alas, even these rules will not solve the Hand of God dilemma:
A final word of caution. Life is a non-equilibrium phenomenon. It requires an energy source that drives its reactions. Assuming that simple heating/cooling cycles could have driven the formation of functional biomacromolecules that were then able to harness the energy emitted by the sun via photosynthesis, seems unrealistic to me. Achieving the level of specificity required to successfully operate a protocell with genetic apparatus, metabolism, and cell division under strongly denaturing conditions is not easy, certainly when it comes to enzyme-free replication relying on the intrinsic specificity of small molecule interactions. So, the periodic addition of a chemical condensing agent may be unavoidable to drive biochemical reactions that are endergonic, even in "minimal intervention" experiments. Without the chemical activation, equilibrium (death) sets in. So, some level of human intervention may always be required for complex, multistep processes. After all, what the dominant activation agent was before enzymes began to use ATP will remain an enigma to many of us for the foreseeable future.
Here's a suggestion they could all use to solve Benner's criticism of plausibility, and to solve Richert's concern over intervention. Sterilize a hermetically sealed, transparent tank filled with sea water, throw all the primordial chemicals at random into the tank, lock the room up, and then wait millions of years. Whatever happens, that's chemical evolution.