Search

Friday Feature: The RNA World

Updated: Jan 19

Video Link: https://youtu.be/RLwjQt2kNFY


The question of how life arose on earth may be the greatest question science has attempted to answer. In the modern science of biological origins, researchers commonly suppose that life arose through an undirected physical process described by well-understood principles of chemistry and physics. Even though our understanding of biochemistry and genetics has flourished since the structure of DNA was discovered, we still don’t know how the chemistry of the ancient earth first gave rise to the chemistry of life. Scientists have therefore proposed schemes in which life began through undirected natural processes that formed the minimum chemistry life needed to begin. For example, one popular biology textbook describes the “RNA world” as the first step in the origin of life:

The hallmark of life—the ability to reproduce—may have been the first step toward life when chemical systems arose that were able to generate more of their starting material. RNA is such a material. RNA is able to copy itself and is widely believed to be the starting point for the evolution of the modern DNA- and RNA-based genetic system.[1]

The RNA world hypothesis[2] is the most popular theory attempting to describe how self-replicating chemistry arose from prebiotic conditions on the early earth, but it is fraught with significant difficulties. The RNA world is a bold, creative, ingenious idea, but it cannot withstand critical scrutiny.


Pause for Philosophy

Christians know that God created the world and everything in it, but this need not imply that “scientific” explanations must be excluded. Similarly, scientific theories don’t exclude God’s superintending influence or creative purposes. The important differences between “scientific” (naturalistic) explanations and the biblical explanation is driven primarily by philosophical commitments.[3] We therefore recognize that naturalistic philosophy influences the work of science, and some ideas commonly received as “scientific” are more correctly viewed as philosophies in search of support than discoveries based on evidence. We therefore consider the RNA world with these observations in mind.


What is the RNA World?

The RNA world attempts to explain the origin of self-replicating chemicals, which are thought of as primitive precursors to biological life. Ribozymes are certain RNAs that can act as enzymes that catalyze a variety of chemical reactions in biology. The enzymatic feature of ribozymes, combined with RNA’s ability to carry genetic information, has led to speculations that RNAs were present on the ancient earth and replicated themselves, each RNA transmitting genetic material to the next RNA generation.


Is It Stable?

RNA stores information in the form of a code composed of a specific arrangement of four letters of a genetic alphabet: the nucleotides adenine, cytosine, guanine, and uracil (A, C, G, U). Each nucleotide is made of three components: ribose (a sugar), a phosphate group, and a base. All of these components had to be present in the prebiotic environment to form RNA, so researchers have studied what conditions might have given rise to them. We consider ribose first.


Ribose is a sugar that together with phosphate groups, makes up the backbone of RNA. It well-known that ribose, like other sugars, is unstable at high and low pH, but chemist Stanley Miller and colleagues also studied the stability of ribose at neutral pH. The results were disappointing. Miller remarked, “ribose and other sugars have surprisingly short half-lives for decomposition at neutral pH, making it very unlikely that sugars were available as prebiotic reagents.”[4]


What’s the point? Ribose (the backbone of RNA) and similar sugars are unstable. Without protection from the external environment, the delicate ribose backbone of RNA will quickly degrade into other chemicals. Equally important, without a protected environment such as a cell wall, it’s difficult to understand how ribose could exist in sufficient concentrations to form RNA in the first place.


What about Nucleotides?

RNA’s genetic information consists of a sequence of nucleotides (A, C, G, U). Researchers Stanley Miller and Matthew Levy discovered that cytosine (‘C’) has an extremely brief lifetime, even at low temperatures. Miller and colleagues remarked that “the instability of cytosine, even at 0°C, raises a serious question of whether it would have been a suitable base for the first genetic material.”[5]

What’s the point? Cytosine is unstable, and it must be paired with guanine, so prebiotic, unprotected RNA had only half of the genetic information capacity of present day RNAs which contain sequences using all four bases (A, C, G, U). But the problems don’t end there. Instability of cytosine to make C-G pairs results in only A-U pairs in RNA sequences. These sequences, in Miller’s words, make RNA “sticky,”[6] that is, they fold in upon themselves like a pretzel.


In addition to its unstable component molecules, RNA itself is unstable. Even the biological RNAs that are now present in nature and protected by cellular membranes are unstable, a fact that highlights why RNA recycling is an essential cellular function.[7] In response to these and other difficult problems with the RNA world, Robert Shapiro concludes, “the evidence that is available at the present time does not support the idea that RNA, or an alternative replicator that uses the current set of RNA bases, was present at the start of life.”[8] It’s hard to justify giving credence to the RNA world, but scientists continue to pursue it, because so far, it’s the best naturalistic account of the origin of life-permitting chemistry.


We have examined just a few of the problems with the RNA world, but perhaps the greatest weakness of the theory is that it does not explain the origin of genetic information. Even if scientists can explain the mechanisms of genetic chemistry, life is much more than even these complex interactions. Physicist Paul Davies remarks, “the cell is also an information storing, processing and replicating system. We need to explain the origin of this information, and the way in which the information processing machinery came to exist.”[9] Life is not only based on chemical mechanisms, but upon the information handled by those mechanisms. In the decades following the discovery of the structure of DNA, scientists speculated on various naturalistic theories of the origin of the genetic code which comprises the instructions for life. But because the philosophy of their research was based in naturalism, they have persistently ignored obvious evidence of intelligent agency in the origin of the genetic code.


Conclusion: Back to Philosophy

Types of evidence routinely ignored in origin of life research are in other areas of life readily attributed to intelligent causes. For example, the SETI (Search for Extraterrestrial Intelligence) project famously promoted by the late scientist Carl Sagan continues to look for the evidence of intelligent agents. SETI employs criteria that would signal the presence of an intelligent cause at a far lower threshold than that of the origin of life research community. To illustrate this point, Stephen Meyer offers a parable of discovery in which researchers explore islands near Antarctica. They find a cave with markings reminiscent of Sumerian cuneiform script, and date the markings as more than 500,000 years old, older than any other known evidence of human writing. The markings are interpreted as an indication of intelligent agents with a sophisticated system of conveying information. If Meyer’s parable described an actual discovery, I suspect few anthropologists would disagree with the inference that an intelligent cause was responsible. Few, if any, would suspect the gradual impact of chance events working over eons of time within the framework of law-like processes could produce markings that indicated such a communication system. Instead, the natural inference would be that the activity of intelligent agents produced the markings in the cave. However, in the case of the genetic code, we have evidence of a far more sophisticated system than writing on a cave wall. We have a type of specified information intimately coupled with a processing system whose complexity is unmatched even by modern computer programs. Indeed, the sophistication of the information contained in the genetic code is such that it continues to yield new discoveries. The intelligence of a mind is the only known cause of the kind of specified information encoded in RNA, and without reference to that cause, research into the RNA world will continue to be an ultimately fruitless exercise.








[1] E. O. Wilson, Life on Earth, Unit 1: The Unity and Diversity of Life on Earth (Wilson Digital, Inc., 2014), accessed January 15, 2021, https://books.apple.com/us/book/e-o-wilsons-life-on-earth-unit-1/id888107968. [2] See for example, Bruce Alberts, Alexander Johnson, Julian Lewis, et al, Molecular Biology of the Cell (New York: Garland Science, 2002), accessed January 15, 2021, https://www.ncbi.nlm.nih.gov/books/NBK26876/. [3] Modern science’s strong commitment to methodological naturalism is particularly relevant to discussions of the RNA world. Consider this quote from Richard Lewontin that reveals a key motivation of many who work in scientific research: “Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counter-intuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door. The eminent Kant scholar Lewis Beck used to say that anyone who could believe in God could believe in anything. To appeal to an omnipotent deity is to allow that at any moment the regularities of nature may be ruptured, that miracles may happen.” (http://www.drjbloom.com/Public%20files/Lewontin_Review.htm) [4] Rosa Larralde, Michael P. Robertson, and Stanley L. Miller, “Rates of Decomposition of Ribose and Other Sugars: Implications for Chemical Evolution,” Proceedings of the National Academy of Sciences USA 92, no. 18 (1995): 8158, accessed April 18, 2020, https://doi.org/10.1073/pnas.92.18.8158. [5] Matthew Levy and Stanley L. Miller, “The Stability of the RNA Bases: Implications for the Origin of Life,” Proceedings of the National Academy of Sciences USA, 95, no. 14 (1998): 7935, accessed April 19, 2020, https://doi.org/10.1073/pnas.95.14.7933. [6] Ibid., 7936. [7] David H. Bechhofer, "Nucleotide Specificity in Bacterial mRNA Recycling," Proceedings of the National Academy of Sciences USA, 110, no. 22 (2013): 8765, accessed April 27, 2020, https://doi.org/10.1073/pnas.1307005110. [8] Robert Shapiro, “Prebiotic Cytosine Synthesis: A Critical Analysis and Implications for the Origin of Life,” Proceedings of the National Academy of Sciences USA, 96, no. 8 (1999): 4400, accessed April 19, 2020, https://doi.org/10.1073/pnas.96.8.4396. [9] Paul Davies, “The Origin of Life II: How Did It Begin?” Science Progress 84, no. 1 (2001): 27, accessed April 14, 2020, https://www.jstor.org/stable/43424187.


18 views

© 2018 by Defending Your Faith. Proudly created with Wix.com