RNA Not Irreducibly Complex

A standard argument for a form of creationism known as intelligent design is that complex molecules necessary for life couldn't have formed without an intelligent designer because this would require massively improbable or impossible leaps of complexity without intermediate evolutionary steps.

One of the biggest pieces of this argument has been that the RNA, which now helps DNA produce proteins, is too complex to arise from undirected chemical reactions. New research disproves this claim.

The new findings map out a series of simple, efficient chemical reactions that could have formed molecules of RNA, a close cousin of DNA, from the basic materials available more than 3.85 billion years ago, researchers report online May 13 in Nature. . .

The new research lends support to the idea that RNA-based life-forms were the first step toward the evolution of modern life. Called the RNA world hypothesis, the idea was first proposed some 40 years ago. But until now, scientists couldn’t figure out the chemical reactions that created the earliest RNA molecules.

Today, DNA encodes the genetic blueprint for life — excluding some viruses, for those who consider viruses living — and RNA acts as an intermediary in the process, making protein from DNA. But most scientists think it’s unlikely that DNA was the basis of the origin of life, says study coauthor John Sutherland of the University of Manchester in England.

Information-bearing DNA holds the code needed to put proteins together, but at the same time, proteins catalyze the reactions that produce DNA. It’s a chicken-or-egg problem. Scientists don’t think that DNA and proteins could have come about independently — regardless of which came first — and yet still work together in this way.

It’s more plausible that the first life-forms were based on a single molecule that could replicate itself and store genetic information — a molecule such as RNA (SN: 4/7/01, p. 212). RNA world proponents speculate modern DNA and proteins evolved from this RNA-dominated early life, and RNA in cells today is left over from this early time.

RNA molecules are chains with units that include "a sugar, a base and a phosphate group." The breakthrough involves combining precursor molecules that are neither sugars nor bases, but are instead a hybrid of the two. These are more reactive than stand alone sugars or bases.