Wednesday, October 30, 2013

Coincidental origin of life

Computer model of a ribosome, a protein-assembling
complex, showing proteins in blue, RNA in brown, and the
active site in red.  Image source.
Proteins are incredibly complex molecules that do all the work in and around our cells.  They are microscopic machines designed for specific jobs, and they are good at what they do.  The layout of each protein is encoded in our DNA, which is managed, duplicated, and transcribed by proteins.  Anyone attempting to explain the origin of life by naturalistic means is thus left in a bit of a pickle—proteins are made by other proteins from the plans in the DNA, and DNA is assembled and managed by the proteins.  It's a sort of microscopic chicken-and-egg problem.  One model that has gained prominence is the "RNA world hypothesis."  RNA can be thought of as single-sided DNA, as if the "ladder" shape of the DNA molecule was cut down through the middle of the ladder rungs, plus a few other small chemical differences.  RNA has several functions in our body, including carrying information from the DNA in the cellular nucleus out to the proteins (ribosomes) that assemble other proteins and taking part in the actual assemblage.  The flexibility and ubiquity of RNA in our cells led some scientists to propose that RNA was the original precursor to life and filled the roles currently held by DNA and proteins.  They imagine the primordial oceans filled with different combinations of RNA, interacting with each other and duplicating, making earth the "RNA world."  Over time, the RNA molecules became more complex and began utilizing amino acids to construct proteins within lipid bubbles, thus forming the first cells.

RNA, however, is very unstable, more so than DNA.  This fact and the lack of any experimental support has cast doubt on the RNA world hypothesis, leading some scientists to search for alternative explanations.  Enter Sankar Chatterjee, a paleontologist at Texas Tech University.  Today, possibly at the very moment I am writing this, Chatterjee is presenting an alternative model for the formation of life at the annual meeting of the Geological Society of America in Denver, Colorado.  Unfortunately, I was unable to attend the GSA meeting, so I will rely on his abstract for now.  Chatterjee proposes that comets and asteroids brought the ingredients necessary for life to earth from space, while forming deep craters in which the ingredients could safely assemble into larger molecules.  In or near the hydrothermal vents that formed in these craters, RNA and proteins self-assembled simultaneously with the help of certain mineral structures.  Over time, some of these were encapsulated in lipid bubbles, which were also brought by meteorites, and began interacting with each other.  Over millions of years and combinations, they began to divide, becoming the first life on earth.  Chatterjee claims that this explanation is much more likely than the classic RNA world hypothesis.

One might be tempted to call this the scientific explanation of the origin of life, but I maintain that it is not scientific at all.  Even if it were true, the model was not developed by the scientific method.  This is only a hypothesis, not tested by experimentation.  Even then, all that could be shown by experimentation is that such an event is possible, not that it occurred in the past.  This, I believe, is the problem with associating science with past events.  Interpretation and speculation abound, and any experiments will only demonstrate the mechanics of a phenomenon, not the history.  That is not to say that past events cannot be rigorously studied and modeled, but such means should not be confused with operational science.  I do not consider the evolutionary model or the creation model of the origin of life to be scientific, because neither was developed using the scientific method.  This, of course, does not make them any less valid or truthful per se, because science is not the only source of knowledge, as I briefly discussed in a previous post.

Creationists maintain two objections to the idea that life arose spontaneously.  First, the probability that chemicals could self-arrange into functioning complex molecules that can interact in a way that forms life as we know it is so minuscule so as to be essentially impossible, even given billions of years.  Unlike the genetic material in organisms, the primordial proto-RNA and proto-proteins would not have any sort of selective force acting upon them, discouraging errors and promoting useful sequences.  Each complex molecule would essentially have to form spontaneously with the ability to replicate and interact with others.  The second objection creationists put forth deals with the nature of information.  Generally, nobody denies that DNA and RNA contain information that codes for proteins.  However, everything we know about information indicates that it only originates from an intelligent source and cannot spontaneously arise.  The RNA world hypothesis and Chatterjee's proposal both require that information simply appears.  I may be speaking out of ignorance at this point, but neither seems to explain how RNA began coding for proteins, only how each one arose.  This, I think, is a bigger problem with Chatterjee's hypothesis, because at least in the RNA world hypothesis, RNA simply stumbles upon a sequence that can produce a functional protein.  Chatterjee, however, claims that proteins formed independently, and he somehow expects that the RNA began coding for them and eventually passed on this information later to DNA.

Evolutionists claim that creationists have no clear definition of "information," so their argument that it cannot arise spontaneously is unfounded, and it thus becomes a semantic debate.  The argument from statistics has numerous responses, none of which I find convincing.  Some of these rely on evolution acting on the primordial molecules, which, as I said earlier, cannot happen until they begin replicating, which itself requires plenty of complexity.  Other rebuttals use the lottery or a raffle as an example, saying that the odds of winning are extremely small, but somebody always, or usually, wins.  However, the odds of winning the lottery (1:175,000,000 to win the Powerball jackpot) and the odds of developing life (around 1:10^63 for a single simple cell in 1.11 billion years) are incomparable.  What exactly is necessary for "life" is still up for debate, though, so the exact statistical figures vary widely.

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