This series of posts is intended as a basic introduction to the science of evolution for non-specialists. You can see the introduction to this series here. In this post we tackle the question of naturalism before introducing the idea of an “RNA world” that predates modern DNA-based biology.
Weizsäcker’s book The World View of Physics is still keeping me very busy. It has again brought home to me quite clearly how wrong it is to use God as a stop-gap for the incompleteness of our knowledge. If in fact the frontiers of knowledge are being pushed back (and that is bound to be the case), then God is being pushed back with them, and is therefore continually in retreat. We are to find God in what we know, not in what we don’t know; God wants us to realize his presence, not in unsolved problems but in those that are solved.
Dietrich Bonhoeffer, Letters and Papers from Prison
In the last post in this series, we left behind the comfortable confines of evolution as a theory (in the scientific sense) and headed out into one of its “frontier” areas – abiogenesis, the hypothesized transition from chemical “non-life” to life. For an American audience, “frontier” immediately calls to mind images of the Wild West – where law and order did not (yet) hold sway, outlaws and renegades were behind every barrel, and justice was dealt from the sheriff’s six-shooter (well, at least that’s how I remember the Hollywood version I saw on television as a child). In short, the frontier was a rough-and-tumble land of conflict and courage a world away from the law and order of the city – and their respective inhabitants had personalities to match.
For abiogenesis, the frontier analogy is surprisingly appropriate. When I read the scientific literature on the topic, I am instantly struck with how, well, speculative it is. This is not the scientific equivalent of quaint New England streets – this is a rough map with large swaths of uncharted territory with perhaps a few wagon tracks through it, at best. Multiple, competing hypotheses abound – was the first life a self-replicating RNA enzyme? Did life start as a metabolic pathway that only later added a heritable molecule of some sort? Did life start near deep sea vents? Did life (or some precursors to life) start somewhere else (as in not even on this planet)? All of these ideas have at least some traction in the scientific literature, and not one of them holds a majority position. It’s the scientific equivalent of the Wild West, complete with interesting personalities “dueling” each other in the scientific literature. The truth of the matter is that we just don’t know.
Let me say that again: when it comes to abiogenesis, we have almost no clue how it might have occurred.
Of course it is at this juncture, as we discussed in the last post, that a great many Christians seize on this professed ignorance to proclaim the failure of evolution as a whole. I too once did so as well, when I held antievolutionary views, so I know full well this temptation. I now realize that this makes about as much sense as claiming the map of New England to be a hopeless mess because Oregon has not yet been fully charted. Unknowns are expected at the frontier – that’s why you go there.
But Dennis, you might say, aren’t you assuming that life had a “natural” origin? Aren’t you discounting the possibility that God might have brought life about through supernatural means? Haven’t you capitulated to “naturalism” from the outset?
There is of course much to discuss here, and the topic goes well beyond the scope of this article (or even this series as a whole). Still, the question is a valid one that merits at least a brief reply. Since abiogenesis is a frontier area of science, in principle it could have either what Christians would call a “supernatural” or a “natural” explanation – we simply do not know. Of course, any explanation in science might actually have a “supernatural” explanation, but merely appear to us as the regular outworking of “natural” law. Most Christians avoid such arguments, of course, if the science is well settled – not many of us hold out for a supernatural explanation of weather patterns or human reproduction, for example – choosing rather to see these “natural” events as part of the providence of God. No, it is typically only where less is known scientifically that Christians tend to favor supernatural explanations.
Personally, I am reluctant to ascribe to miracle what is not yet well studied scientifically, since more work may reveal a “natural” explanation – “natural”, of course, meaning part of the reproducible structure of the cosmos that God has put in place and continues to uphold that allows us to investigate it using science. In this sense, “natural laws” can be seen as part of God’s covenant faithfulness to His creation, something that my colleague Arnold Sikkema has written on (PDF) and I have found helpful. So, whether the origin of life was “natural” or “supernatural” it was of God, and there is nothing to be lost by attempting to investigate it through the scientific method. Perhaps another way to put it is that, as a scientist, I am curious just how far this regular, reproducible structure of the cosmos extends – does it extend all the way to a transition between non-life and life? Did God, in His wisdom, fashion the cosmos in such a way that chemicals could become alive? Just how deep does the rabbit hole go? While I suspect that life had a “natural” origin in the sense above, I recognize that not all Christians feel the same way. The reason for this hunch – and it is a hunch – is that I see pointers in what we doknow that suggest it to be the case.
Hints & whispers
One such “pointer” to a possible chemical past for life on earth is a feature of all living things at the very heart of what it means to be alive in a molecular sense. One of the first things one learns as a biologist is that macromolecules have divided the labor between heredity and enzymatic function: DNA is for genes, and proteins are for catalyzing reactions. Then, one learns about the various forms of RNA – a class of molecules that, interestingly, in some cases have both hereditary and enzymatic function simultaneously. Then one learns that the key enzyme at the center of the cellular machinery is in fact not a protein enzyme, as one would expect, but rather an RNA molecule – the ribosome. Ribosomes are responsible for using RNA templates to direct protein synthesis, and proteins go on to complete the loop by copying the cell’s DNA, which encodes the information for making RNA. In a significant sense, it’s all about RNA: RNA enzymes using RNA templates to make proteins that copy the cell’s DNA (which contains the crucial RNA information in a more stable form). When the chemical structure of the ribosome was determined in the early 2000s it was demonstrated that the few proteins associated with it are not part of its enzymatic function – which was a significant surprise for many molecular biologists at the time. To many of them, this absolutely crucial RNA enzyme using RNA templates at the center of cellular life was suggestive – suggestive that life once passed through a stage where RNA was the major player in heredity and enzymatic function, rather than the DNA/protein world of the present.
In the next post in this series, we’ll explore this proposed “RNA world” – a hypothesis that has gained some experimental support in recent years.