Question for evolutionists

[Chris†opher Paul]

First off, I don't have a problem with evolution.  I believe that it happens.  But just for reference, I believe that it had to be guided, but I don't want to argue that point in this thread.

My question has to do with dual biological mechanisms of certain creatures. 

There are some creatures that have a mechanism, 'A', that performs some action, but it relies on another mechanism, 'B', in order to function.  In some cases, it seems the neither A nor B would evolve via natural selection, since there is no purpose for either, by themselves.  It doesn't seem reasonable to think that either would develop by chance, since there is no reason to "keep" a genetic trait that serves no purpose.

I can't recall the list of creatures that I am talking about right now, but do you all know what I am refering to, and if so, how does evolution attempt to explain it?

Thanks

 

[Jerry Smith]

Well, simply put, mechanism A evolves to do something all by itself. Mechanism B then evolves to enhance the function of mechanism A. The presence of B allows more changes in A that require B. Eventually A & B cannot do anything without the other, though at first A could do something by itself.

I know that isn't very clear, but its the best I can do.

 

[Chris†opher Paul]

Edit...double post

 

[Chris†opher Paul]

But mechanism A has no purpose by itself. Why would it evolve via natural selection?

Your explanation is that it once had a purpose?

 

[Jerry Smith]

Well, I obviously wasn't any more clear than I thought I was being. Let me try again. A originally had a function (by itself), then after B evolved to augment that function, A lost the ability to function by itself.

A side note: The original (independent) function of A is not always very similar to the eventual function of A & B together.

 

[Morat]

http://www.talkorigins.org/faqs/behe/review.html

  This might help.  A lot of it is a rather scathing critique of Behe for poor scholarship, but you can find a great deal on how such systems evolve.

 

 

 

[Chris†opher Paul]

Originally posted by Morat
http://www.talkorigins.org/faqs/behe/review.html

  This might help.  A lot of it is a rather scathing critique of Behe for poor scholarship, but you can find a great deal on how such systems evolve. 

 

 

Hey-

I read the part of the article about the mousetrap, and honestly, I don't see how the author refuted Behe.  Behe's response seemed to answer the mousetrap problem. 

What do you think?

 

[Morat]

  Which one? John MacDonald's nifty one with graphics? It's linked at the top, under Behe's rebuttal of the main page.

  I was point you more towards the section on pseudogenes and cascades, since those are the real-world examples of the process you're talking about.

  Miller discussses another "IC" system (the blood clotting cascade) at

http://www.millerandlevine.com/km/evol/DI/clot/Clotting.html

  My personal reading of Behe is that he's stuck defending the indefensible. He made some claims about what is, and is not, an IC system. But he overlooked a critical concept, that of reduction.

  A+B = C might be an IC system. But A+B+(redundant)D =C is not.

  When the redundant D is removed, the system is now IC. By neglecting such a simple concept as duplication (and thus redundancy) and the loss of parts of the pathway, Behe set himself up for a nasty fall.

 

 

[Chris†opher Paul]

Originally posted by Jerry Smith
Well, I obviously wasn't any more clear than I thought I was being. Let me try again. A originally had a function (by itself), then after B evolved to augment that function, A lost the ability to function by itself.

A side note: The original (independent) function of A is not always very similar to the eventual function of A & B together.

Jerry-

If 'A' served some purpose, in which 'B' evolved to benefit 'A's function, wouldn't 'A' and 'B' continue to serve the original purpose?  What would cause it to change dramatically into a new function?

 

[Morat]

 It's a matter of efficiency. A does a job "well enough". A+B does it better. A change in A does it even better, but now requires B instead of B supplementing A.

  Now A+B is IC, because both parts are needed.

 

 

[Chris†opher Paul]

Originally posted by Morat
 It's a matter of efficiency. A does a job "well enough". A+B does it better. A change in A does it even better, but now requires B instead of B supplementing A.

  Now A+B is IC, because both parts are needed.

 

I understand, and that makes sense.  But why would A+B then function as something totally different than the supposed original function of 'A'?

 

[Jerry Smith]

Originally posted by s0uljah


I understand, and that makes sense.  But why would A+B then function as something totally different than the supposed original function of 'A'?

There are no hard & fast rules that it always will have a different function, but over time it can turn out that way.  I just threw that side-note in because some IC systems appear to have evolved from functionally unrelated non-IC systems, if I understood what I heard of the talk Kenneth Miller gave on it correctly. One such IC system that had some components functionally unrelated to motility was the flagellum. IIRC, the "motor" of the flagellum was co-opted from an active transport mechanism in the cell membrane.

 

[Morat]

  Who said it necessarily would? 

  A is good. Say, gets the job done 50% of the time. (Which works for the thing in question, although 100% would be best).

A duplicates. Now you have A and A1. It doesn't do anything extra, however, so you're still at 50%.

 B shows up. B effects the output of A.  A+ B + A1 = 60% now.

 A1 changes. Now B + A1 handles the process really well. 80% efficiency. A no longer adds anything.

   But, the change in A1 would have been useless had B not already been there. B was useless without A.

  But now A can disapear, leaving you with the simple IC system A1 + B. A1 and B don't perform the task without each other, but could not have evolved without A. But A won't hang around after A1 + B supplant it.

 

 

[Chris†opher Paul]

"B shows up"

Why?

"B was useless without A."

 

[LewisWildermuth]

Why not?

 

[Jerry Smith]

B shows up"

Why?

"B was useless without A."

B may have also had a use, or it may have only been useful in helping A - either way, A was there, the new mutation which produces B occurs, and B is selected for because of its helpfulness to A (or for its own function).

 

[Morat]

  Why not? It's just a mutation. If you want a more concrete (but still made up. If you want "real" examples, check the blood clotting cascade I linked to), let's play "what if" with blood clotting.

 Let's say a primitive clotting factor exists, consisting of protein X. X, when jammed up in an open wound, slows blood flow for whatever biochemical reason it does.

 X is created by gene X.

 Now, a simple mutation elsewhere causes the body to put small amounts of protein Y in the blood stream. Y, when it encounters X jamming up a cut, fills in some of the spaces, reducing blood loss even more.

  Pretty simple, and not IC. After all, X works well enough. Y needs X to be effective, but so what? X works on it's own.

 Now, let's let another mutation happen. This produces protein Z. Z, when exposed to Y in an open wound, reacts in such a way as to scab over quickly.  Z + Y, in fact, react better than X + Y did.

 X isn't needed. So if X gets turned off, the animal never notices. Y + Z continues to clog the cut, getting more efficient over time.

 End result? Y and Z, a simple IC system.

 

 

 

[Chris†opher Paul]

Ok, so 'B' is a random mutation. And it helps 'A' do its job in creature X, so it is selected by causing X to have an advantage over other creatures that it is competing against, right?

 

[Jerry Smith]

Originally posted by s0uljah
Ok, so 'B' is a random mutation. And it helps 'A' do its job in creature X, so it is selected by causing X to have an advantage over other creatures that it is competing against, right?

In a nutshell, and bearing in mind that this is an excercise in "getting the jist" of the process of building an IC system. As such, it is bound to be a gross oversimplification.

 

[Chris†opher Paul]

Hold up, we are getting off on a tangent I think.

Let me clarify.

I am asking about a physical structure 'A', that is separate, yet dependent on another physical structure 'B'

Without 'B', the creature would die because of 'A'

But 'B' has no purpose other than to add to 'A's functioning. How would A and B develop separately, if they depend on each other?