tas8831

On 1/12/2020 at 11:36 PM, Ronald Brown said:

The wording in this documents is a little too technical/hard for me, but as I understand it claims that the recurrent laryngeal nerve is not really a bad design.

For example if I understand it right, Wolf-Ekkehard Lönnig claim that about 0.3 to 1% of the population does have a shortened laryngeal nerve (so it must have occurred already millions of times in all mammal species) but still it doesn't spread in the population, meaning that it doesn't really have a benefit and may even cause problems.

Another point that I would like to ask about this issue, when I look at the picture from Wikipedia:

https://upload.wikimedia.org/wikipedia/commons/6/64/Recurrent_laryngeal_nerve.svg

 

 

I do see a short laryngeal nerve that looks like it goes directly from the brain to the laryngeal (the green nerve in the picture), what is the different between this nerve and the recurrent laryngeal nerve? Doesn't is serve the same purpose?

 The documents that I linked to in my first post have more claims, I would be happy if someone can explain this claims in a more simple words, and say what are the arguments against it .

Thanks.

 

The green nerve is a different nerve - the Superior Laryngeal Nerve.

I don't know if the argument is that the Recurrent Laryngeal Nerve is "bad design" necessarily, rather it is an example of inefficient or weird 'design.'  It is easy to understand as an artifact of embryological development, and as a 'leftover' of evolution, a retained developmental pathway.

So basically, early in development, the region that become the larynx is 'right below' the developing brain and skull.  The Vagus Nerve travels from the brain to the thorax and abdomen, and the RLN is a branch off of this.  And during this early development, that branch goes pretty much straight to the larynx.  However, when doing so, it goes below a blood vessel, which will become the aortic arch.  The developing heart and in this case, the aorta, is much closer to the area we think of as the throat at this time, so that makes sense.

However, as embryological development continues, the heart, and its attached blood vessels (like the developing aortic arch), moves down into the thorax.  But the RLN is still 'below' the aortic arch, so it gets 'dragged down' into the thorax as well.

Now in humans, this is an oddity but not a huge deal, I suppose.

But consider the giraffe....