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Origin of Life: Cambridge Astrochemist Paul Rimmer Analyzes the Tour-Farina Debate

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Cambridge University astrochemist Paul Rimmer analyzed the debate between James Tour and Dave Farina on the podcast Capturing Christianity. Rimmer has been recognized as a rising star in the study of the origin of life (OOL). In his charitable and thoughtful demeanor, he represents the antithesis of Farina. He also displays a commitment to describing the science with precision and nuance.

In his analysis of the debate, Rimmer presents a cogent and substantive overview of the relevant research to provide a clearer understanding of the issues. I found Rimmer’s comments thoughtful and enlightening. I was particularly impressed that he recognizes that the differences between his and Tour’s assessment of the field are not primarily driven by their understanding of the scientific details but by their differing philosophical frameworks. 

I have many positive thoughts about Rimmer, and I anticipate that many people who watch his post-debate analysis will rightfully come away with a positive view of him. However, the viewer should be aware of a critical caveat: Ultimately, Paul Rimmer is far too credulous about chemical explanations for the origin of life. His stance undoubtedly reflects his membership in the field of mainstream OOL research. To those outside that community, even the research Rimmer lauds as advancing the field only further confirms that life’s originating through natural processes is impossible on scientific grounds.

Analysis of the Debate

Rimmer begins with a helpful tutorial on research into life’s origin. He includes a diagram by John Sutherland on the presumed stages leading to the first self-replicating cell and the current state of the field. Rimmer summarizes the journey toward life as a continuous series of stable systems gradually increasing in complexity until one emerges capable of Darwinian evolution.

Rimmer then expands on specific topics raised by Tour and Farina. He elucidates the research cited by Farina in response to Tour’s question about how the amino acids Asp and Lys could have linked together on the early Earth. Rimmer acknowledges that the articles Farina cited do not directly address Tour’s questions, but he claims they still provide clues as to how amino acid chains could have emerged. He describes how Leman, Orgel, and Ghadiri (2004) linked the amino acids Ala, Phe, Leu, Ser, and Try together with the assistance of carbonyl sulfide. He then describes how Singh et al. (2022) linked aminonitriles (precursors to amino acids) to amino acids by employing catalysts such as thiols.  

Rimmer continues by explaining the research referenced by Farina related to the origin of RNA. During the debate, Tour described how nucleotides often join a growing chain with 2’-5’ linkages instead of the standard 3’-5’ linkages — nucleotides connect at the wrong carbon on the ribose molecule. Farina responded to this hurdle by citing Engelhart et al. (2013) who validated that a nucleotide chain known as a hammerhead ribozyme (RNA enzyme) could still break apart an RNA molecule even if the ribozyme possessed some 2’-5’ linkages. 

Rimmer states that RNA with the wrong linkages could not have been reliably copied, posing a major hurdle to further progress toward life. A single RNA molecule would almost always break apart before it could migrate to the right local environment where it could facilitate a life-relevant reaction. It would have to be copied numerous times before it could play any role in life’s origin. 

Yet Rimmer argues that this challenge is not necessarily insurmountable since Mariani and Sutherland (2017) demonstrated a chemical pathway that replaces 2’-5’ linkages with the correct 3’-5’ linkages. Rimmer acknowledges that this study does not fully solve the problem of building RNA since the correction process is not highly efficient or reliable, but he claims such research provides a “clue” as to how RNA molecules could have emerged. There are additional problems with this research that I will describe below. 

Differing Assumptions

The differing perspectives of Tour and Rimmer result from the differences in their starting assumptions. Rimmer’s scientific education trained him to only consider the possibility that life originated from natural processes. Rimmer tacitly acknowledges this fact in his response to a question about the appearance of design in life. He essentially argues that the origin of life requires “mind” only insofar as chemistry or biology or anything else that happens in nature requires mind. This is consistent with what he has written elsewhere predicting that we will one day find a “complete biological explanation … for the question of how life first originated on Earth.” He states that he does not wish to examine the evidence for design beyond the apparent design behind the laws of physics that allow for life to exist. Consequently, he is not concerned if experiments perfectly match what could have occurred on the early Earth or even if the chemistry is prebiotically plausible. He considers progress as simply finding clues as to what might have occurred. 

In contrast, Tour considers progress in understanding life’s origin as demonstrating a chemical process that could have occurred naturally and could have produced molecules in sufficient abundance and purity to drive the next step toward life. Tour has convincingly argued that no such research exists (see for example here or here).

From Tour’s perspective, a careful analysis of the procedures used in the research Rimmer references (herehereherehere) reveals that the studies only moved chemical systems toward life by starting with carefully chosen molecules in concentrations and purities that could never have arisen naturally. The experiments also employed meticulously designed experimental protocols with only marginal similarity to what could have transpired on the ancient Earth. 

If the experiments used more realistic chemical mixtures and environmental conditions, they would not have produced anything biologically relevant. In addition, if the resulting products were deposited in any ancient environment, they would have simply degraded into biologically useless asphalts. Steven Benner describes this tendency as the Asphalt Paradox. In other words, this research, while interesting, does not mimic a realistic natural environment, nor does it produce chemical mixtures that could eventually produce life. 

Probability Paradox

The hammerhead ribozyme study cited by Farina and Rimmer poses an additional seemingly insurmountable hurdle to the RNA world hypothesis. Ribozymes with 2’-5’ bonds have primarily been shown to break apart RNA, leading to what Benner refers to as the Probability Paradox, which he describes as follows:

Experiments show that RNA molecules that catalyze the destruction of RNA are more likely to arise in a pool of random (with respect to fitness) sequences than RNA molecules that catalyze the replication of RNA, with or without imperfections.

If a system of randomly sequenced RNA had emerged on the early Earth, biologically useful ribozymes would have quickly vanished as the system degraded into simpler molecules. 

Future Presentations

As I noted, Paul Rimmer is thoughtful, civil, and his voice should be heard. He said nothing wrong in his presentation since he was asked to analyze the debate from the perspective of a scientist working in the field of OOL research. But those not working in the field can find many reasons why the research he cites is not persuasive that the chemical origin of life is possible. Perhaps in future discussions, Rimmer could explore how his philosophical framework shapes his interpretation of the results of OOL studies. Ideally, he would also explain why scientists not operating within the same framework assess the state of the field very differently. 

As someone who has also engaged in thoughtful dialogue with OOL researchers, I would be very happy to be part of such a conversation. But I do not want to put Paul Rimmer’s career in any jeopardy: Those working in the field of OOL research would be ill-advised to publicly speak with too much candor about fundamental weaknesses in that field since doing so might jeopardize their career.