Irreducible Complexity

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aaqucnaona

This sentence is a lie
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flagellum.jpg


Ah, the bacterial flagellar motor. The beacon of the "irreducible complexity" in biological systems. Yes, it is irreducibly complex, in that it cannot function without all its parts, but that does not mean it has not evolved.

Here is an example of why irreducible complexity may arise by evolution.

Lets imagine a organism, an size, any taxon - it needs two components "A" and "B" from the environment ot survive. It has two pathways for the intake, transport, breakdown/simplification and use of A and B. It is subject to the natural selection pressures - predation, limited resources, genetic drift and [if its reproduces sexually] sexual selection. Over many generations and mutations, most of the variants are removed from the gene pool. However, a single or a few individuals come to have a mutuation that makes it capable to synthesize B from A, thereby lending them an advantage in habitable range. Of course, at this point, there are a few decisive factors in question, like the availability of A, the dominance of that allele, other factors in B-poor [or other new ranges] environments, cost of making the B pathway compared to A -> B pathway, speed of reproduction and related effects of that mutation. Under conditions favourable enough that selective pressures dont eradicate new mutations of A -> B, it would rapidly explode into environments where A is available but B is scarce. At this point, if the cost of A -> B is sufficiently higher than A & B, then the new population would speciate as a more extremophile relative of the ancestral population. If the cost is manageably high, same or lower, the new pathway would spread through both genepools, in the old and new ranges. At this point, the entire population of this species has a pathway that is now irreducibly complex, none of the population can now live without the A -> B pathway. This does not mean, as we saw, that the pathways for A, B and A -> B all would have to arise simultaneously - its a simple example of the power of co-option and co-dependance at the biomolecular level. Maybe the same is true for these -

flagellum.jpg


More -

Evolution of the Bacterial Flagellar motor - http://leisureguy.wordpress.com/2008/02/17/irreducible-complexity-is-reducible-after-all/

Evolution of biochemical Irreducible Complexity - http://www.pandasthumb.org/archives/2007/05/on_the_evolutio_1.html
 
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If I remember the whole argument right, the big assumption that creationists, er intelligent design proponents make is that the pieces that make up a flagella can only do what they do in the flagella, so obviously they had to be brought together as one to be functional. This of course is not true, those parts separately fulfilled functions of their own, and only when they evolved together bit by bit did they eventually merge to be what they are now. It's just a complex strawman, and probably isn't an assumption, but more of bet that laypersons won't know or research the actual details and so will be won over by the argument of incredibility.
 
I don't understand the point of this thread. We already know that the flagellum motor isn't irreducibly complex, there are existing living precursors that don't rotate.
 
spidergoat said:
I don't understand the point of this thread. We already know that the flagellum motor isn't irreducibly complex, there are existing living precursors that don't rotate.
Click to expand...

That is exactly the point of the thread. I gave a hypothetical example of how an irreducibly complex system of three biomolecular pathways can evolve and gave links to pages on the evolution of the flagellar motor and also of other similiar systems.
 
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