What Is The RNA World Hypothesis?

The RNA World Hypothesis proposes that chains of RNA were the first living things on Earth. Here you'll find out why.


All living creatures today reproduce and evolve using a complex gene-enzyme cycle. If we look at a cell for example, information encoded in its genes is used to produce functional proteins called enzymes. Some of those enzymes then turn around to make copies of the cell’s genes, allowing the cell to reproduce.

Because the gene-enzyme system forms a closed loop, it presents us with a classic chicken or egg conundrum: Which came first, genes or the protein enzymes they code for?

While the details are still not fully worked out, discoveries over the past few decades have lead researchers to a surprising possible solution: What really came first? Genes that act as enzymes!

The RNA World Hypothesis is the idea that before living cells, the genetic code, and the gene/protein cycle ever existed, chains of a chemical called RNA were forming naturally. Once formed, some of these chains were able to function as enzymes, and were even able to evolve by making copies of themselves with slight, accidental modifications.

In the purest form of RNA World Hypothesis, RNA came first and then gave rise to proteins and DNA. This pure form is not largely accepted. It now seems more likely that RNA, DNA, small proto-proteins, and even lipids all coexisted from the start.

While there is little doubt that RNA played a crucial role in the early development of life, the complexity of RNA and DNA nucleotides cast doubt on the idea that RNA was the first truly replicating and evolving chemical system. For this reason, alternatives to the “RNA first” view are being investigated. Most notable is a proto-RNA hypothesis being studied by the lab of Nicholas Hud, and several metabolism first hypotheses which got their start with the work of Robert Shapiro.

At this time all serious investigations into the origin of life are conducted under the overarching idea that life emerged from chemistry.

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The first RNA enzymes were discovered in 1982, now known as ribozymes. Here’s is a wonderful review of what we now know about ribozymes (well… as of 2002):

Initial RNA Nucleotide Synthesis

RNA nucleotides are not easy to make but they have been shown to form without enzymes under conditions that might have been plausible on the early Earth. That said, the reactions we’ve discovered so far do not appear robust enough to have initiated the RNA world. A search for a more efficient natural pathway continues.

RNA Replication Before Evolution Of Enzymes

In order for ribozymes to develop and evolve, they must be able to reproduce. Base pairing allows us to get RNA to easily replicate in the lab but there are several issues impeding replication in natural environments like those that would have existed on the early Earth. Below is a paper outling 8 problems with RNA replication and likely solutions to them (note: number 8 has since been solved by two different research groups independently though one is still waiting to be published:

Alternatives To The RNA First Idea

RNA certainly played an important early role in life but the difficulties of producing RNA under pre-biotic conditions raises doubts about RNA chains truely being the first replicators.