Evolution of the nervous system

[Anna55]

For vertebrates the spinal column and the skull provides great protection from damage. Thinking in evolutionary terms, why does some nerves by-pass this protective system and travel outside of the spinal cord and its protective spinal column?

When a human gets burned on the finger, the nerves in the finger transmit the signal to the spinal cord and then back to the muscles so that the finger can be removed instantly. If nerves did not travel outside the protective spinal cord, the individual would have difficulties to react to some external factors, e.g. getting burned on the finger, thus the likelihood of survival would decrease significantly. It would be difficult for nerves to receive signals from the outside environment if the nerves were protected by hard bone since the nerves cannot reach out to all vital body parts. The nerves outside the spinal cord and the skull are however slightly protected by the myelin, which is made of lipids from protein.

Is my hypothesis correct? If not, please explain the correct theory. Thank you in advance!

[canalon]

You are not technically wrong, but you are referring only to the end of the nerves that are out of the spine. However there are nerves that are completely outside of the spinal cord. Why would they.
There is an example (extreme) and some food for thought about the reason in this dailymotion video. Enjoy:
http://www.dailymotion.com/video/xdm5he ... aryng_tech

[Crucible]

From what I can see of the design of Windows OS, by Dawkins' viewpoint on this matter, I would would have to say that Windows was not designed.
If you take things for medical examination out of context (vis a vis it's development), you could say something has bad design.

It's fallacious reasoning to insist that if a single species can be found with less than optimal arrangements, that it means "no design" or "poor design".

Those are terms relating to a medical viewpoint. Since we do not know the eventual fate of the nerve in question, it's impossible to say "good" or "bad" design.

If perfection is required from the start and at all points, it must mean immortality for every living thing. That is what Dawkins insists creationists show - or else, no design.

Perfection and immortality is what a medical viewpoint would have as a theoretical goal.

[Crucible]

correction: "Dawkins insists I.D. shows - or else, no design"

That is what Dawkins insists creationists show - or else, no design.

[Gavin]

Does every thread in this forum have to devolve into the same tiresome argument? Shame on you canalon for encouraging Crucible's post. The video you linked to is not relevant to Anna55's question.

To Anna55: imagine what our bodies would be like if all nerves, up to the nerve endings of sensory nerves, were encased in bone.

[canalon]

The inanity of Crucible comments is not relevant to the point. The fact that Dawkins use it as an argument for evolution (not against creation in that vid) is just bonus.
The point is you have here a nerve that is going from the brain to the heart and back outside of the spine. Why it does that (take that convoluted path and bypass some protections at the same time) is explained in the video. And that is extremely relevant to Anna55 point, and much more so than just "all nerve can't be encased in bones" because it demonstrate why neither the vagus nerve nor the recurrent laryngeal nerve, that could both use the protection of the spine do not actually use it. And the reason is the history of the path of that nerve in our ancestors.

[Crucible]

The inanity of Crucible comments

Please do show what its inane in my comment, if you intend to start throwing crap.

is not relevant to the point.

In agreement with Gavin that you opened it up.

The fact that Dawkins use it as an argument for evolution (not against creation in that vid) is just bonus.

Untrue. Check his introductory statement, ending at 21 seconds in. Time for a retraction from you and apology for your sloppiness.

The point is you have here a nerve that is going from the brain to the heart and back outside of the spine. Why it does that (take that convoluted path and bypass some protections at the same time) is explained in the video. And that is extremely relevant to Anna55 point, and much more so than just "all nerve can't be encased in bones" because it demonstrate why neither the vagus nerve nor the recurrent laryngeal nerve, that could both use the protection of the spine do not actually use it. And the reason is the history of the path of that nerve in our ancestors.

In agreement with you here, that Gavin is wrong - that is why I recapped the angle of the organism's development and history.

Here:

If you take things for medical examination out of context (vis a vis it's development), you could say something has bad design.

Considering how it could have got that way, is the part that confers some useful info.
If, however, you show Dawkins BS ing, it's like Gavin said.

shame on you

Might I suggest you boys take your differences to PM ?

'Nuff said.-/+

[Gavin]

I understood Anna55's question to essentially be: why aren't all nerves encased in bone? Dawkin's video was demonstrating an extreme example of bad design, if design had occurred. I doubt that Anna55 got the connection, since I (a biologist) didn't.

[Cat]

I have another question(s):

Why have bone incased centralized system? Isn’t it possible to develop decentralized system with the same overall capabilities? Why have one extra long in place of 10, 20, 50, or 100 short ones?

[canalon]

Crucible,
you are spouting inanity when you say that

It's fallacious reasoning to insist that if a single species can be found with less than optimal arrangements, that it means "no design" or "poor design".

because when it comes to the recurrent laryngeal, all vertebrates have it, and its (not it's) path do not make sense in any of them, except in light of evolution. The extreme case of the Giraffe is a striking example, but the fact that in my human body that nerve travels back from my heart does not make any sense either. As for software programs, you could say that they do actually evolve, as often, only some part of the code is modified, while the part that are working are often just updated to cut programming time (i.e. costs). This is why after some iterations and updates they often end up a bit clunky and massively bigger (remember the good old times when you could have a software on a single floppy disk?).

But I will admit that I was wrong: Dawkins had some comments about ID, you are right, I was wrong.


Gavin,

I did not understand the question like you did. I read it, as " Some nerves are not using the spine at all to travel inside our body, although it would make sense, could that have a reason rooted in evolution?" to which, the answer is obviously that in our ancestors, travelling through the spine would not have made sense, and we have inherited those pathway in spite of massive changes of body plan since those times. And that is because of common descent. If you think about it, this is a much more interesting answer to a much more interesting question. And the opportunity to demonstrate a sound knowledge of evolutionary theory, as opposed to a simplistic idea of encasing nerves in bones. I might be wrong, but as an educator, that would be the kind of question that I would ask to make student think hard and give answers demonstrating a sound knowledge of the subject as well as deep thinking.

[canalon]

I have another question(s):

Why have bone encased centralized system? Isn’t it possible to develop decentralized system with the same overall capabilities? Why have one extra long in place of 10, 20, 50, or 100 short ones?

I do not know, but I know that long nerves are (relatively) slow to transmit information (compare reflexes to centrally processed actions: the latter are measurably slower than the former, even when trained), and that it makes sense to have as many of the higher functions close to one another to work at maximum speed. Similarly, encasing them in bone is a good way to protect the system from outside shocks.I remembered reading that some dinosaurs did have two brains, but it seems that this is an outdated fact that has been refuted, so I will not fantasize about that any more. Another thing might be that for the farthest of our vertebrate ancestor was one with a single nerve ganglia (sp?) and that we have been stuck with that plan since then, has adding one (or more) new brain, would have been too massive a re-engineering project to allow the intermediate forms to have any fitness in the first place. The vertebrate line was already too high on the fitness landscape to be able to go through such a fitness valley successfully. Even though the next peak might have been higher. Too late to change.

[Crucible]

Crucible,
you are spouting inanity when you say that

It's fallacious reasoning to insist that if a single species can be found with less than optimal arrangements, that it means "no design" or "poor design".

because when it comes to the recurrent laryngeal, all vertebrates have it, and its (not it's) path do not make sense in any of them, except in light of evolution.

How is that inanity ? That I said "single" ?

That is not inanity. I am well aware that there are probably uncountable numbers of such examples - though maybe not so striking. The video even mentioned the approx. length of the loop in humans

You simply are not aware of what you are saying. My statement on "single" is in reference to Dawkins' argument, where the argument could just as easily completely rest with providing only a single example, as by resting on 85 such examples or 850 of them or 850,000 of them. He thinks if he shows a medical insufficiency of some type, it shows there is no design. One such "error" from a designer, is enough to make the point. I would agree that if the argument were correct, it would take only a single example.

You do not agree ? Fine, but it's not spouting inane crap , to make the point.
My comment is that Dawkins needs only one example, to make that argument complete. Why be so insulting over that ?