Thread: Nerve/Brain Morphology, Evolutionary Advantage?

Hi all! I was just looking at a diagram of the human facial nerve. The image shows the "root" exiting the left side of the brain and extending to the right side of the face. Likewise a nerve from right to left. This is how the entire nervous system is laid out, as I understand it. Left side of brain goes to right side of body. While I can't think of any reason for this NOT to happen, neither can I think of a good reason it should be the case. Might there be some advantage here? Or is it just one of those anomalous things? Ideas?

Originally Posted by JoshuaL

Hi all! I was just looking at a diagram of the human facial nerve. The image shows the "root" exiting the left side of the brain and extending to the right side of the face. Likewise a nerve from right to left. This is how the entire nervous system is laid out, as I understand it. Left side of brain goes to right side of body. While I can't think of any reason for this NOT to happen, neither can I think of a good reason it should be the case. Might there be some advantage here? Or is it just one of those anomalous things? Ideas?

I do have some trouble lifting my right eye brow..

Originally Posted by JoshuaL

Hi all! I was just looking at a diagram of the human facial nerve. The image shows the "root" exiting the left side of the brain and extending to the right side of the face. Likewise a nerve from right to left. This is how the entire nervous system is laid out, as I understand it. Left side of brain goes to right side of body. While I can't think of any reason for this NOT to happen, neither can I think of a good reason it should be the case. Might there be some advantage here? Or is it just one of those anomalous things? Ideas?

I flat don't know the answer to your question, but I'd ask the questions: What other animals have this trait? I'd be surprised if it wasn't shared by all chordates. Then the question might be, what evolutionary advantage did it have to some ancestor hundreds of millions ago? We lots of odd things about our bodies that often don't make sense unless viewed as hold overs from our past evolution.

I know it is true in dogs (an interesting article here), and I would guess the same for most "higher" chordates at least. I simply can't dream up a reason it would happen, other than pure chance, but I have this itchy feeling that there is a very good reason indeed, be it adaptation or simple physics/chemistry of growth in these complex critters. Anyone know if this true for simple chordates as well? *runs off to learn about worms*

This is an interesting thing. i'm hoping somebody will have an answer for you.

My own ideas are that
i) maybe it reduces the likelyhood of kinking the nerves and allows for greater freedom of movement.
ii) it might have something to do with balance somehow.
iii) Maybe it somehow strengthens an organism, by entwining the body in nerve fibres?

Originally Posted by JoshuaL

Hi all! I was just looking at a diagram of the human facial nerve. The image shows the "root" exiting the left side of the brain and extending to the right side of the face. Likewise a nerve from right to left. This is how the entire nervous system is laid out, as I understand it. Left side of brain goes to right side of body. While I can't think of any reason for this NOT to happen, neither can I think of a good reason it should be the case. Might there be some advantage here? Or is it just one of those anomalous things? Ideas?

Is this because we see things upside down so everything is actually backwards.

Originally Posted by TimeLord

Is this because we see things upside down so everything is actually backwards.

Nice. For those that don't know, the images are not just inverted up and down, but also left and right. Yes, I can see that this might fit in somewhere. Great idea. Next would be to see if the critters without eyes or with only the precursor to eyes (like an earthworm) also have this nervous system crossover. I'm still reading up on that.

Update: here an article exploring this idea a bit [link].