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Author Topic:   An ID hypothesis: Front-loaded Evolution
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Joined: 02-15-2012

Message 1 of 2 (653194)
02-19-2012 5:43 AM

The front-loading hypothesis is an ID hypothesis that builds on Crick and Orgel’s directed panspermia hypothesis. In 1973, in a paper published in Icarus (Directed Panspermia), Crick and Orgel proposed that the earth was intentionally seeded with unicellular life forms. Here, I will (a) describe the front-loading hypothesis, (b) provide one or two nice clues in favor of the front-loading hypothesis, and (c) list a couple of ways it can be tested.
What is front-loading?
The front-loading hypothesis proposes that (a) early in earth’s history, the earth (or the solar system) was intentionally seeded with unicellular life forms (i.e., directed panspermia) and (b) these life forms contained the necessary genomic information to shape future evolution, such that the course of evolution was biased in pre-determined trajectories. Thus, evolution would be biased by the genomic information designed into the first genomes on our planet. There is evidence for the notion of panspermia, which I will discuss briefly. A genomic clock based on increases in genome sizes throughout the history of life on earth suggests that life may be roughly 10 billion years old (Sharov, 2006), which would indicate that the first organisms from which all present taxa descended did not originate on earth.
Front-loading does not propose that all aspects of evolution were programmed and determined. There would be nothing stopping the blind watchmaker from taking its own unplanned courses alongside the front-loaded objectives. What might these objectives be? To use front-loading as a working hypothesis, it is assumed that multicellularity was an objective of the front-loading designers, as well as the origin of animals and plants. Further, the front-loading hypothesis proposes that the designers were rational agents; thus, poor, sloppy design in a biological system would count against the thesis that that system was designed into the first genomes.
The genetic code: a clue in favor of front-loading
The genetic code is highly optimized for error minimization (Freeland et al., 2000). This optimal genetic code is nearly universal across all taxa. Curiously, there is no phylogenetic tree consisting of less optimal codes present in basal lineages, with more optimal codes being in late-branching taxa. This is interesting because if the genetic code evolved gradually, starting with less optimal codes (there are far more sub-optimal codes than there are optimal codes) which were gradually fine-tuned to produce the universal optimal code, we might expect such a phylogenetic tree to exist. Arguing that the sub-optimal codes once did exist early in life’s history, but vanished once the optimal codes came on the scene (i.e., that they were outcompeted), looks awfully ad hoc. For starters, it is often argued by non-teleologists that flagellar genes would have non-flagellar homologs in the form of functional precursors. But if this truly is a prediction of the Darwinian/non-telic theory, then we must wonder why the Darwinian theory doesn’t predict that we should find a phylogenetic tree consisting of different genetic codes as described above. Significantly, the fact that less optimal genetic codes do exist in nature (see Freeland et al., 2000; note that these sub-optimal codes are secondarily derived — that is, they evolved from the canonical genetic code, not the other way around) is proof-of-concept that the universal optimal code can exist without causing less optimal codes to vanish from the scene. The below image illustrates a hypothetical phylogenetic tree consisting of less optimal genetic codes in deep-branching lineages. It exemplifies what could have been the case, with different codes evolving into more optimal codes.

Figure. Here, all branches on the tree are colored differently. Each different color represents a different genetic code; in this diagram, the deeper-branching lineages have sub-optimal codes. The higher you go on the tree, the more optimal the genetic code is. If such a tree existed in reality, it would be an extremely convincing piece of data against the front-loading hypothesis. That it does not exist is evidence in favor of the front-loading hypothesis.
Imagine that such a phylogenetic tree did, in fact, exist. It would be convincing evidence that the extant genetic code or codes was the result of the blind watchmaker’s tinkering, gradually fine-tuning some early, sub-optimal genetic code. Yet such a tree does not exist, which is exactly what we would expect if the first life forms were designed with a highly optimized code — which follows from the front-loading hypothesis. It is evidence that the first genomes were advanced and fully optimized at the dawn of life. All of this is what we would expect if the first genomes were designed by a rational agent or agents — and this is what the front-loading hypothesis proposes. It is predicted by the front-loading hypothesis, as it is good design logic to design the first life forms with a highly optimized genetic code.
Testable predictions of the front-loading hypothesis
We can test the front-loading hypothesis through several ways, two of which I will describe here:
1) The front-loading hypothesis predicts that the first genomes encoded genes that would be unnecessary (but beneficial) to early life forms, but necessary to the appearance of multicellular life forms and plants and animals. It predicts that the first organisms were not proto-cells, but highly advanced cells capable of terra-forming a hostile planet and able to shape future evolution in biased trajectories.
2) The front-loading hypothesis predicts that prokaryotic homologs of important eukaryotic/metazoan proteins will be more highly conserved in sequence identity than the average prokaryotic protein. This prediction makes sense from a rational design perspective because designing these prokaryotic homologs with functions that conserve their sequence identity will ensure that their 3D shapes will not be significantly changed by the blind watchmaker, preventing the appearance of eukaryotes (I realize that this prediction might sound a bit confusing — it’s past midnight where I am — so I’d be more than willing to elaborate on this).
There are a number of things I’m interested in discussing here. I’d be interested in hearing the criticisms and objections some of you might have to my above essay or to the front-loading hypothesis. Some of you might have questions like how would future states be front-loaded? and other questions and critiques.
P.S. Any grammatical or other errors in my essay are a reflection of the late hour, and not an indication of my education or lack thereof.
Sharov, Alexei A. Genome increase as a clock for the origin and evolution of life. Biol Direct. 2006; 1:17.
Freeland, SJ, et al. Early Fixation of an Optimal Genetic Code. Mol Biol Evol. (2000) 17 (4): 511-518.

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Message 2 of 2 (653210)
02-19-2012 8:51 AM

Thread Copied to Origin of Life Forum
Thread copied to the An ID hypothesis: Front-loaded Evolution thread in the Origin of Life forum, this copy of the thread has been closed.

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