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Author
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Topic: Does Darwinism Predict the Absence of Irreducible Complexity?
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Josh
Member
Member # 405
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posted 30. September 2002 17:06
Here I will try to practice the quote technique (thanks for the tip)...
quote:
Again, not really true. Ever heard of cyanobacteria blooms? They happen in open water infused with nutrients, e.g. an upwelling current. Cyanobacteria IIRC don't have flagella, they keep from sinking by a passive method involving internal floats made of proteins that exclude water and thus lower density. Another exception to the "Motility is Always Good" supposition being promoted in the thread.
--You are arguing a strawman, I never said there aren't counter-examples to the claim that "motility is always good." In fact I was questioning the existence of these counter examples and my argument was constructed quite differently. I asked the reason for these examples to exist and for correlative evidence supporting such an argument, you have provided nothing along those lines. Skip microbial size issues, etc. I understand well that there are non-motile creatures.
quote:
If flagella are IC, then twitching motility is also because the twitching system has the same basic components as the archaeal flagellum.
I was referring to M. Xanthus, I thought it was crawling and using social behaviors to move, did I miss something?
quote:
But far from being something that never exists in nature, short peptides, amino acids and complex polysaccharides are found in many organic environments. Take any decent soil (under some trees is pretty good), perform an extraction and run the extract through an amino acid analyzer.
Another strawman, I never suggested that amino acids and short peptides cannot be found in nature. If you think soils are an equivalent environment to this experiment, I have nothing to say about it anymore.
quote:
Several years ago a couple grad students at Stanford U. decided to stage a Celebrity Death Match-like event between C. elegans (a worm) and M. xanthus. Both these organisms hunt bacteria for food and these students, obviously with too much time on their hands, decided to see which species would "win" if they put both in the same petri dish.
Perhaps C. elegans are picky eaters and didn't like the taste of M. xanthus? ; )
Anyways, Does any of the evidence y'all are posting convince you that evolution has the capability of producing apparent IC structures whenever they are needed, which is something I expect from the theory itself. Nothing that has been said shows me that billions of years and generations of organisms should not have produced a plethura of IC systems for any given task the cell needs to perform, as opposed to evolution deriving structures that appear IC in nature, but are highly adaptable for numerable tasks in each organism available.
Josh
[ 30. September 2002, 22:29: Message edited by: Josh ]
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Mike Gene
Member
Member # 149
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posted 01. October 2002 08:39
Andy: The whole point of labeling something as IC is to suggest that it is unlikely to have evolved, and/or to suggest that it was likely designed. If the concept of IC has any other use, I'd be interested to hear what it is.
My argument was a reaction to a specific claim proposed by Frances. Simply reread the context of my reply.
Andy: My point in raising haemoglobin and myoglobin was to show that we have two systems, both arguably IC, and compelling molecular phylogeneitc evidence that one evolved from the other. That seems to cut to the heart of whether IC is a useful concept in thinking about the origin of biochemical systems.
First we'd have to establish that hemoglobin and myoglobin are IC. But we can sidestep
this issue by simply focusing on the evolution of the former from the latter. Essentially, gene duplication, followed by adaptive tweaking, turned an oxygen-binding protein into a somewhat more complex oxygen-binding protein. Are you suggesting all IC machines are expanded (by duplication), complex versions of a simpler one-gene core, where the original stem gene carries out the same basic function as the 10-part machine? Unless that is where you are going, I'm afraid the example you provide is a very blunt cutter that gets nowhere near the heart.
The issue of the flagellum and secretory systems was meant to address your point that "That is, structural constraints that come from participating in a particular machine may prevent that component from playing any other meaningful biological role."
Yes, I said such constraints may prevent this. One counter example does not really address my point.
Besides, your counterexample is interesting. Already embedded within the flagellum is a secretory machine, such that the type III system (which likely evolved from the flagellum) can be viewed as a stream-lined flagellum. It is interesting that the example you chose to address my point actually seems to underscore it, as the meaningful role played by the type III systems is already inherent in the flagellum - there is evidence that flagella themselves secrete virulence factors.
What is the typical fate of flagellar genes when one gene is rendered functionless by a mutation?
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andyg
Member
Member # 415
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posted 01. October 2002 16:44
Quote from Mike and Andy:
quote:
Andy: My point in raising haemoglobin and myoglobin was to show that we have two systems, both arguably IC, and compelling molecular phylogeneitc evidence that one evolved from the other. That seems to cut to the heart of whether IC is a useful concept in thinking about the origin of biochemical systems.
Mike: First we'd have to establish that hemoglobin and myoglobin are IC. But we can sidestep
this issue by simply focusing on the evolution of the former from the latter. Essentially, gene duplication, followed by adaptive tweaking, turned an oxygen-binding protein into a somewhat more complex oxygen-binding protein. Are you suggesting all IC machines are expanded (by duplication), complex versions of a simpler one-gene core, where the original stem gene carries out the same basic function as the 10-part machine? Unless that is where you are going, I'm afraid the example you provide is a very blunt cutter that gets nowhere near the heart.
I hope the moderator will indulge me a post in which I quote the above and append a simple question. I am doing this to refocus the discussion:
Mike, why do you consider IC to be a useful concept in thinking about the origin of biochemical systems?
AndyG
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Argon
Member
Member # 276
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posted 01. October 2002 17:05
Josh writes (to me - Argon):
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Another strawman, I never suggested that amino acids and short peptides cannot be found in nature. If you think soils are an equivalent environment to this experiment, I have nothing to say about it anymore.
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Equivalence was not the issue. The question I addressed above was whether one finds "natural" growth conditions rich in free amino acids and short peptides.
Specifically, Josh wrote earlier:
quote:
Here, the "rich medium composed mainly of free amino acids and short peptides" satisfies condition (1) that never exists in nature (unless you can provide references). At least I don't know of an ecological niche that is infinite in resources (cells grown to stationary phase and passaged daily into fresh rich medium can be called an "infinite resource" because these cells are replenished in a great abundance of rich resources every day!) These cells have become big fat slobs.
Note: Condition (1) was: "They have unlimited resources from which to thrive"
Points of fact:
- Mixococcus xanthus is indeed found in areas rich with organic matter (and prey bacteria) -- including dung heaps. An environment rich in amino acids and short peptides is definitely something that may be found in nature. Cells in nature are indeed passaged through stationary phase and replenished with fresh media (or in this case, warm doo-doo). If this ever failed to happen, M.xanthus would go extinct.
- M.xanthus *requires* those particular medium components for growth.
- Those cells were not "big fat slobs". They were under fairly stringent selection -- competing *directly* against each other. For continuous cultures of growing cells, it is pretty easy to calculate that those cells with even slight advantages in reproduction eventually "take over" the culture.
Finally Josh writes:
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Anyways, Does any of the evidence y'all are posting convince you that evolution has the capability of producing apparent IC structures whenever they are needed, which is something I expect from the theory itself.
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Sorry for any confusion but this wasn't the point of my replies in this thread. I was discussing a rather narrow issue. Josh requested information about niches where motile systems could face negative selection. Those were provided.
[ 03. October 2002, 19:23: Message edited by: Argon ]
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