How Did Life Begin? Scientists Propose New Theory for Where Earth's First Organisms Came From
The origins of life on our planet are so nebulous and so resistant to study that even the parts scientists agree on they still don't really understand. Our best guess about the circumstances under which life began has been that ribonucleic acid (RNA), part of our genetic material, came first and proteins came later. Though widely agreed upon by scientists, that theory has problems. Now, two scientists have a potential solution: the peptide-RNA hypothesis.
RNA is similar to DNA in that it can code genetic information and catalyze the reactions needed to produce life. But its chemical makeup is more primitive and unstable, so it's much more vulnerable to mutations.
The RNA world hypothesis says that RNA self-replicated its genetic code, leading to the evolution of proteins. But this theory fails to account for exactly how these humble nucleic acids made that kind of a leap. The RNA world hypothesis has been challenged before, and its many proponents can't explain how the nucleic acids led to small, fully functioning proteins, or peptides.
According to the peptide-RNA theory, they simply didn't. Rather, the RNA molecules would never have had the ability to catalyze life in this fashion. Instead of RNA alone predating everything else, the new theory posits that proteins were there with them from the beginning, and it was through the interaction between the two, and not a mysterious middle step, that the molecules were able to catalyze the beginnings of life.
The theory is backed up by some evidence. "Until now, it has been thought to be impossible to conduct experiments to penetrate the origins of genetics," co-author and University of North Carolina at Chapel Hill professor of biochemistry and biophysics Charles Carter said in a statement. "But we have now shown that experimental results mesh beautifully with the 'peptide-RNA' theory, and so these experiments provide quite compelling answers to what happened at the beginning of life on Earth."
Carter and his coauthor Peter Wills, a professor of physics at the University of Auckland, have published a pair of new papers in the journals Molecular Biology and Evolution and BioSystems. In the work, they explain how the body of evidence on early enzymes and amino acids supports their simpler theory. Carter's own recent research analyzed 20 enzymes known as aminoacyl-tRNA synthetases (aaRSs), which are necessary for translating genetic code into protein. These proteins are ancient enough that they exist in all living cells. Despite belonging to completely distinct families, he found that they'd been coded by the same gene.
Carter and Wills are hoping the new hypothesis will inspire fresh debate about the origins of life among the scientific community. "These interdependent peptides and the nucleic acids encoding them would have been able to assist each other's molecular self-organization despite the continual random disruptions that beset all molecular processes," Carter said in the statement. "We believe that this is what gave rise to a peptide-RNA world early in Earth's history."
