we should re-do the spiegelman’s monster experiment but with this. Keep it replicating for a long time and maybe evolution will occur, producing a totally new form of life. If it does and your starting molecules were all assembled from off the shelf chemicals in the lab then you would have man made life

“RNA is less stable than DNA, and therefore mutates faster, and the longer the strand the more mutations it will accumulate”

I have never heard this as an explanation like this… and I’m not sure it’s accurate. I will fully admit that my knowledge of mutation isn’t encyclopedic, but a) RNA has a higher thermal stability but lower chemical stability; how does instability lead to high mutation rate? Mutation rate is dependent primarily on the accuracy of the replicator, and secondarily on mechanisms of damage, repair, modification, etc, yes? Setting aside stability, I recognize that RNA viruses have high(er) mutation rates, but I understand that as an artifact of viral evolution, and then only for certain types of replication. The T7 bacteriophage RNA polymerase has a low error rate.

Ed’s article does discuss messy replicators, but I don’t think that is the question being asked or answered?

Rather: RNA is a much more flexible molecule than DNA. DNA is very rigid, forming only a few of the possible types of bonds, and sticking to certain angles. This means that a single mutation in DNA has very little effect on the overall structure. In contrast, RNA can form many, many more structures and fold into complex shapes because it can make these other bonds; this is actually *why* RNA is so cool and capable of acting like an enzyme… but it also means a single change can have a VERY big (and potentially deleterious) effect on the molecule. What this means in context is that an RNA can *tolerate* many fewer mutations than RNA before it’s structure is compromised.

If you’d like to get a very first hand demonstration of this, I strongly recommend trying out the RNA folding game eteRNA, where you will quickly see how a single base-pair change can radically alter the whole structure.

For a much, MUCH more in depth explanation of nucleotide folding, see Geometric nomenclature and classification of RNA base pairs by Leontis and Westhof: http://www.ncbi.nlm.nih.gov/pubmed/11345429

How come long strings of RNA eventually fail, but DNA doesn’t?

RNA is less stable than DNA, and therefore mutates faster, and the longer the strand the more mutations it will accumulate. If the mutation rate is too high, then harmful mutations accumulate faster than natural selection can weed them out, and your population of replicators suffers an error catastrophe and falls apart. Thus there is a maximum length which an RNA genome can be before it falls prey to error catastrophe (the largest RNA viruses approach this limit), and there is a maximum length which a DNA genome can also be, but that maximum length for DNA is billions and billions of base pairs, and as far as we currently know, no organism on earth has approached it.

Doesn’t DNA split into RNA during replication?

No. Double stranded DNA splits into single stranded DNA, each strand then becomes the template on which another strand is assembled, replicating the DNA.

DNA is transcribed into RNA which is then translated into proteins. But this is protein synthesis (gene expression) but not DNA replication.

It is refreshing to see that a few decades after the ‘RNA world’ hypothesis was advanced, we are ready to update it by suggesting that the participating RNA molecules were rather small and they interacted with each other, apparently in a cooperative mode.

For those who want to see where this hypothesis might be a few decades from now, I suggest an alternative model on the origin of life on Earth ( http://precedings.nature.com/documents/3888/version/1) in which the RNA molecules were even smaller! As a matter of fact, they were so small that initially they were represented by a single ribonucleotide!

That’s an unfortunate misunderstanding of Selfish Gene Theory. Cooperation does not contradict the theory; it is consistent with it.

Otherwise, fascinating article. I always enjoy reading your work.