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A front-loading prediction and molecular machines

January 9, 2012

Unfortunately, many proponents of ID are content with simply criticizing Darwinian evolution instead of focusing their energy on developing a robust, testable teleological hypothesis in biology. Thankfully, the front-loading hypothesis, an inherently telic hypothesis, is testable and it does make predictions about the biological world. So, let’s delve into one of the predictions it makes regarding molecular machines like cilia, etc.

First, a bit of context. Under the front-loading hypothesis, the earth was seeded with unicellular life in the distant past. These life forms had the genomic information necessary for shaping subsequent evolution. For example, such unicellular life forms would have had the genes necessary for the origin of metazoa. But what about the origin of molecular machines which are only found in non-prokaryotic life forms, such as cilia? Could such molecular systems have been front-loaded?

 

A coolish diagram of the structure of cilia. Image taken from here.

If a molecular machine has played a fairly major role in shaping evolution, then, from a front-loading perspective, it’d be a pretty safe guess to suppose that that machine was either designed into the initial cells, or it was front-loaded to exist in the future. How could something like the cilium be front-loaded? First of all, the major protein components – or homologs of these proteins – of the cilium would have to be designed into the initial cells. This would ensure that the blind watchmaker – non-teleological evolution – wouldn’t have to tinker around with genes and form a cilium from scratch, since the essential components or their homologs would be in the first cells, although they wouldn’t be functioning as a cilium: they’d probably be performing functions independent of each other.

Let’s use a simpler example. Suppose that a certain molecular machine, called X, is specific to eukaryotes. System X is composed of three basic components: A, B, and C. If a designer(s) were to front-load system X, starting with prokaryotes, homologs of components A, B, and C could be designed into the prokaryotic genome. Thus, the first life forms on earth would have had the proteins A1, B1, and C1 (the 1 at the end of each letter means that there are homologs of the components A, B, and C). However, from a rational design perspective, there is a problem. If system X is to arrive on the scene roughly a billion years after the first life forms appeared on earth, proteins A1, B1, and C1 are likely to diverge in sequence identity to such an extent that their initial sequence identity is effectively erased. This, of course, means that after this divergence, A1, B1, and C1 are extremely unlikely to be co-opted into system X, as planned, because their diverged sequence identity has totally modified their function and 3D shape, etc.

How can this problem be overcome? There’s a pretty simple solution, actually. If proteins A1, B1, and C1 are given functions such that their sequence identity is well conserved, and thus their 3D shapes, this problem is overcome.

From this simple solution that a rational designer would inevitably use, we can formulate a couple of predictions from the front-loading hypothesis:

a. Components of molecular machines/systems that are of major importance in eukaryotes will share deep homology with proteins in prokaryotes.

b. Importantly, the front-loading hypothesis predicts that these homologs of protein components in important molecular machine will be more conserved in sequence identity than the average prokaryotic protein.

c. Also, we can tentatively predict that the more essential a component is to a major molecular machine, then the greater degree of sequence conservation in its prokaryotic homolog. With this latter prediction, we can guess how important a component is to a molecular machine by the level of sequence conservation the protein shows across different taxa. Thus, the front-loading hypothesis predicts that, in general, the more highly conserved in sequence identity a protein component is in a molecular machine, then the higher the degree of sequence conservation will be in its prokaryotic homolog.

Note that non-teleological evolution does not make the last two predictions, only the first one. Thus, we can test the front-loading hypothesis on the exclusive last two predictions it makes. If these predictions are confirmed, this will be positive evidence in favor of the front-loading hypothesis.

 

 

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6 Comments leave one →
  1. Monsters From The ID permalink
    January 9, 2012 8:39 am

    It seems at least to me, that this idea of front loading telic evolution, would not really (though maybe it could) be aiming to setup ahead of time actual machines as such, but rather aiming to implement a set of pre-fabbed conserved proteins which would be able to be re-arranged and combined in many useful ways (automated telic rearrangements yet to be determined?) that could result in many different machines in the future. Or machines as required according to the environmentental conditions maybe. I’m thinking along those lines, because if the front-loaders were only intending for one machine to be “evolved” in the distant future, then I suppose one could ask, why not just set up that machine at the start? There might be some reasons why that wouldn’t be desirable I guess, but I’m just speculating. Would you agree?

    • January 10, 2012 1:58 am

      I would partially agree, and certainly from a front-loading perspective a designer(s) could set it up such that the initial cells had proteins that could easily be co-opted into various roles. However, when it comes to specific molecular machines and molecular systems, like cilia, the blood clotting cascade in mammals, sarcomeres in muscle cells, etc., all of which are systems that are very important to complex animals (and Mike Gene thinks that the cilium actually helped to shape evolution, and I agree), a designer could hardly implement these systems into the initial cells, yet it it would be ideal if these systems could arise once eukaryotic life forms arose. The cilium, for example, could hardly be used by prokaryotic life forms. Thus, it is my hunch that such systems were specifically front-loaded, and that’s where the above predictions come into play.

      Thanks for your comment!

  2. derwood permalink
    January 29, 2012 9:49 pm

    So, according to your predictions, the Intelligent Designer is constrained to only being able to reuse pre-existing modules? What mechanism does ID propose for the conservation of these modules that is not also a prediction of evolution?

    • January 29, 2012 10:01 pm

      Hello derwood,

      I’ll respond to you by quoting bits of your text and then replying.

      You said:
      “So, according to your predictions, the Intelligent Designer is constrained to only being able to reuse pre-existing modules?”

      From a front-loading perspective, yes. Since front-loading is all about designing future states through deep time through the mechanism of evolution, and since, under this hypothesis there is no intelligent intervention (except at the start, with the first genomes), then future states can only be designed from pre-existing components.

      “What mechanism does ID propose for the conservation of these modules that is not also a prediction of evolution?”

      I’m not sure I understand quite what you’re getting at here, but what the ID hypothesis of front-loading predicts is that key eukaryotic proteins will share deep homology with prokaryotic pre-cursor proteins – however, Darwinian evolution also predicts this, so we need to go a step further. Front-loading also predicts that these precursor prokaryotic proteins will be better conserved in sequence identity than the average prokaryotic protein. I explain the rationale for this prediction in this post.

      Thanks!

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  1. Molecular Clues of Teleology « The Genome's Tale
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