Monday, September 04, 2006

Front Loading

In a post entitled 'Another Protozoan and Front-Loading' Mike Gene argued: "Singled-celled eukaryotic organisms known as Tetrahymena contain many features that make them a good candidate model for front-loading evolution." Gene subsequently refers to front-loading evolution as FLE. In a linked reference Gene writes the following:

In this paper, Ausio covers a lot of evidence whereby histone H1, which functions to link nucleosomes and thus more efficiently package DNA in eukaryotes, is not essential for survival and reproduction in filamentous fungi. If we eliminate H1 function in Ascolobus and Aspergillus, the cells are perfectly viable with no deleterious consequence on the sexual reproduction cycle. The same results were previously seen in the protozoan Tetrahymena. However, in the fungi mentioned, elimination of H1 does result in the cessation of growth within a week or two. In other words, elimination of H1 does not affect viability or reproduction, but only the life-span of the individual organism (however, with Aspergillus, elimination of H1 does not even effect the life span of the organism and has no apparent effect).

Three more points. First, thus far H1 is ubiquitous in eukaryotes. Secondly, H1 may not be crucial in single-celled organisms; in addition to the Tetrahymena data, Ausio observes, "These results suggest that while linker histones may be dispensable for the relatively short life span of an individual cell, they are most likely indispensable for survival of higher eukaryote organisms." Thirdly, Ausio argues that this is probably not true for multi-cellular organisms, where compaction of the genome is an important ingredient in the regulatory schemes used in generating and maintaining a multicellular body plan. Why is all this significant?

If H1 was indeed designed, given its minimal role in protozoa, it might constitute a very good example of front-loading evolution such that the initial eukaryotic state was prepared to evolve a multicellular state. In other words, the existence of H1 in protozoa may best be explained by the existence of H1 in metazoans. And that is one hypothesis that simply cannot be entertained, for the briefest of all moments, from a non-teleological perspective.

An important caveat is in order, however. Tetrahymena are fairly specialized protozoa and may not be representative of most protists. However, given that H1 is not essential in simple metazoans, such as filamentous fungi and also in specialized protozoa, we have good reason to suspect it might likewise be nonessential for less specialized protozoa. Here is yet another example where a teleological approach can generate experimental research. Instead of assuming Tetrahymena is unusual, and thus irrelevant, with regard to its lack of need for H1, we need to go into the lab and knock out H1 genes from other protozoans. And in keeping with the general argument of my speculation, we have yet another example of using a teleological approach to generate a prediction - if there is something to my hypothesis, then we will find other protists where H1 is not essential. In fact, we might even find some protists without H1.

Finally, keep in mind that "nonessential" does not mean H1 will have no role. Useless H1 is not a way to front-load (as useless things decay into nonexistence). Front-loading may entail giving a higher eukaryotic protein some role in protozoa to ensure it persists until something like higher eukaryotes evolve. But it is not until it is coopted into its primary designed role that it becomes essential.

Gene zeroes in on a histone protein known as H1 and notes that this protein plays an essential role in most eukaryotic organisms involving efficient packaging of DNA.

A commentator posted this in connection with Gene's original post: "So if the only prediction that you can make is a negative one like "natural selection is not enough," then you are at a dead end. To have a viable research program, you need to come up with positive predictions that diverge from those of natural selection."

Note the criticism. It is not unusual to see critics of ID contend that research grounded in ID based assumptions are practically indistinguishable from evolutionary counterparts. The specific complain in this instance is based on the belief that a telic based hypothesis would not diverge from those customarilly attributed to natural selection. But is that the case. Based on Gene's comments the criticism does not stand. Gene's front loaded concept is intrinsically linked to function and therefore natural selection. However, in a twist on the usual natural selection paradigms, in this case an absence of function, indicating a parallel absence of selective value, would signal the need for another explanation as to why a protein, lacking functional utility, is nevertheless found in an organism. Front loading is an attempt to offer a rational explanation for a circumstance that defies natural selection expectations. Why would functionless genes and proteins be retained by an organism? There is a metabolic cost associated with their synthesis without the yield of a benefit to the organism. That is unless the benefit is presently a potential and is to be accrued through subsequent genetic changes. Planning is the obvious inference and biological data the supporting evidence.

Critics can argue that H1 has yet undiscovered functional utility. That is a matter for further research but it does not mitigate the argument associated with the front-loading hypothesis. It merely poses a suggestion as to how the front loading concept can be falsified.

Note this quote of Mike gene:

Finally, keep in mind that "nonessential" does not mean H1 will have no role. Useless H1 is not a way to front-load (as useless things decay into nonexistence). Front-loading may entail giving a higher eukaryotic protein some role in protozoa to ensure it persists until something like higher eukaryotes evolve.

Do "useless things" really decay into nonexistence. If so how would we account for the existence of pseudogenes? If the H1 in question truly is without functional value then the front loading hypothesis would be strengthened. Front loading would then provide an explanation natural selection fails to provide.


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