Current thinking is that early life forms used RNA alone, instead of DNA and RNA, in order to reproduce. The theory is, it would be marginally simpler for life to have got started that way.
Andy Ellington, on behalf of the RNA world origin of life hypothesis, tells us at U Berkeley’s Evolution 101: From Soup to Cells: “Origins is a huge knotty problem—but that doesn’t mean it’s an insoluble one.” It’s an interesting image because the knot problem, whether it is created by design or by chance, has this going for it: Patient untangling will usually work. That’s because the entire problem consists of one or several tangled strings. People more often lose patience than lose hope.
But an RNA origin of life is not like that. For one thing, opinions differ as to what would constitute a solution and how far we are from one. Some are convinced that much of the problem is solved already: A site for educators treats it almost as a historical problem, while calling it a hypothesis. And DNA from the beginning tells us:
RNA has great capability as a genetic molecule; it once had to carry on hereditary processes on its own. It now seems certain that RNA was the first molecule of heredity, so it evolved all the essential methods for storing and expressing genetic information before DNA came onto the scene. However, single-stranded RNA is rather unstable and is easily damaged by enzymes. By essentially doubling the existing RNA molecule, and using deoxyribose sugar instead of ribose, DNA evolved as a much more stable form to pass genetic information with accuracy.
Others say no, “ it is difficult to imagine how long RNA molecules could be formed initially by purely nonenzymatic means,” so they hypothesize precursors that have never been observed.
RNA world in general has never been observed. One supporter calls it “ the worst theory of the early evolution of life (except for all the others).” Indeed, the very same people who called RNA world “the molecular biologist’s dream” also called it “the prebiotic chemist’s nightmare.”
Science journalists, however, are undeterred by these difficulties, which is likely why the rest of us do not often hear about them. And this is the five-star hotel of origin of life theories. As I noted in the series over at Evolution News & Views,
So as mathematician David Berlinski notes, the basic problem is that RNA world proposals are “dominated by references to a number of unspecified but mysteriously potent forces and obscure conditional circumstances …” The technical term for that is magic. Nevertheless, RNA world is the best fully natural origin of life scenario today. More.
Is there a good reason to believe that life’s origin must be a fully natural event?
Does nature just “naturally” produce life?
Can all the numbers for life’s origin just happen to fall into place?
Welcome to “RNA world,” the five-star hotel of origin-of-life theories
The Science Fictions series at your fingertips (origin of life)
Earth’s crust cooled only 160 million years after solar system formed, says new Australian zircon study (Life could have started shortly afterward.)