RNA World

Currently, the leading theory on the origin of life is called the “RNA world.” During ordinary cell replication, RNA copies DNA and takes the instructions to the new cell. One of the key problems for origin of life research is the “chicken and egg” problem of DNA needing enzymes to unzip, but enzymes needing DNA to be created (for a complete explanation, see our earlier article “The Origin of Life”). The “RNA world” hypothesis seeks to solve the “chicken and egg” problem articulated elsewhere by beginning with RNA, instead of DNA. In this theory for life’s origin, RNA performed both the function of proteins as well as information storage. However, there are several reasons for doubting the plausibility of this view (These five reasons were generously taken from Stephen Meyer’s Signature in the Cell, chapter 14):

First, RNA building blocks are hard to synthesize and easy to destroy. Robert Shapiro writes that the notion that “the bases, adenine, cytosine, guanine and uracil were readily available on the early earth [is] not supported by existing knowledge of the basic chemistry of these substances.” Additionally, he writes, “The evidence that is currently available does not support the availability of ribose on the prebiotic earth, except perhaps for brief periods of time, in low concentration as part of a complex mixture, and under conditions unsuitable for nucleoside synthesis.” Meyer notes,

Either the prebiotic environment contained amino acids, which would have prevented sugars (and thus DNA and RNA) from forming, or the prebiotic soup contained no amino acids, making protein synthesis impossible… The presence of the nitrogen-rich chemicals necessary for the production of nucleotide bases prevents the production of ribose sugars. Yet both ribose and the nucleotide bases are needed to build RNA.

Second, ribosymes are poor substitutes for proteins. While RNA can produce ribosymes, these do not produce the functions of proteins. Meyer writes, “Scientists have shown that ribozymes can perform a small handful of the thousands of functions performed by modern proteins.” He compares this to a carpenter having a hammer and nails (with no other tools) in building a house. This wouldn’t bring us to a functional cell.

Third, an RNA-based translation and coding system is implausible. Because each of the ribosymes only perform specific functions, in order to create a cell—each needs to be coordinated. Even if all of the functions were present at once, it still wouldn’t result in a functioning and working cell.

Fourth, this view doesn’t explain the origin of genetic information. Meyer comments, “The information problem looms just as large in a hypothetical RNA world as it does in a DNA world… Even if a system of ribozymes for building proteins had arisen from an RNA replicator, that system of molecules would still need information-rich templates for building specific proteins. RNA-world advocates give no account of the origin of that information beyond vague appeals to chance.”

Fifth, ribosyme engineering does not simulate undirected chemical evolution. In order to get the RNA hypothesis to work, scientists have to direct the process—hence using intelligence to make the system work.