Jan 13 2009
Tracey A. Lincoln and Gerald F. Joyce from the Scripps Research Institute this week published a paper in Science detailing their research into Self Sustained Replication of RNA Enzyme. What they found is that their altered RNA, which they modified so that two strands can cross-replicate without the need for any other enzymes or proteins, can replicate indefinitely, doubling their numbers every hour. This has interesting implications for our understanding of the origins of life.
RNA and DNA are the molecules that carry genetic information. It is believed that life arose from molecules that were the ancestors of modern RNA – that the ability of RNA to act as a template for its own replication was enough of a toe-hold in evolution for life to eventually develop around RNA. While it is plausible that such molecular evolution was a precursor to life and the evolution of species, molecules don’t fossilize and so we have precious little direct information about this earliest stage of the development of life. What we do know is largely inferred from laboratory experiments that try to replicate the conditions in which life probably arose.
In contrast to the creationist straw-man that evolutionists believe life arose spontaneously and directly from nothing – the current theory is that millions or even hundreds of millions of years of molecular evolution slowly build the chemistry of life and replication before coming together as a something we would call a living cell. Whether or not RNA itself can be considered “alive” is a matter of debate, but I won’t get into that as it is mostly semantics. Molecular evolution was therefore a stepping stone to biological evolution.
As an analogy, if some day humans create self-replicating artificially intelligent autonomous robots, who then promptly destroy us and all life on earth, a few million years from now their descendants might marvel at how machine “life” could have arisen spontaneously. They might not be aware that biological evolution was a stepping stone to machine evolution.
Lincoln and Joyce have provided some very provocative information that does not directly answer any questions about pre-life molecular evolution on earth, but does explore the issue of plausibility and will suggest avenues of future research. Specifically, what they found was that when they added different versions of their self-replicating RNA with limited raw material to the same test tube, the different RNA “species’ competed with each other. The more “fit” RNA species, those better able to compete for raw material and replicate, dominated the resulting brew of RNA. Further, different RNA species combined together to form new versions of RNA – the molecules evolved – with more fit molecules being selected for.
This is very significant – a single molecule can replicate, compete, and evolve. Fast forward a few hundred million years on a planetary scale, and something interesting just might turn up.
How do we get from RNA to a living cell? A lot has to happen, but each theoretical step is plausible. Those RNA molecules that replicated faster in the presence of certain proteins would have an advantage. Of those RNA molecules, any that hit upon a property that increased the concentration of those proteins would have a further advantage. We know that bilipid layers spontaneously form spheres – serving as cell membranes. An RNA molecule that could keep iself close to the proteins that make it replicate faster by gathering inside a bilipid bubble would further have an advantage. Now we have a primitive cell. Probably not yet life, but damn close (again, depending on semantics and where you draw the line).
When you think about it, all life is basically a more sophisticated version of this basic setup – RNA and DNA molecules that use proteins to make other proteins that ultimately allow them to replicate more efficiently and compete for raw material. Yes – this is hyperreductionist, and life has higher order complexity and properties, but you get the idea.
Trying to peer at molecular evolution that occurred 4 billion years ago is tricky business. Progress is understandably slow, but there is progress. This new study is incredibly interesting, but we will have to wait to see how it fairs in peer-review and what it leads to.
Meanwhile, get ready for the DiscoTute and other creationists to start their spin. They will start mowing down the straw men of their own creation in a masturbatory and ultimately futile exercise (if their past behavior is any indication). One non-sequitur they are almost certain to make is to criticize this study because it does not and cannot tell us what actually happened 4 billion years ago. But the research does not endeavor to tell us that – it is aimed as figuring out how life might have arisen by fleshing out a plausible sequence.
The scientists involved are being appropriately conservative in their statements – trying very hard not to overcall the implications of this research. That’s a good thing. Let the research speak for itself. And while this study is very interesting, I am more intrigued by what it may lead to. Let’s see how far we can take it.
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