Wednesday, May 7, 2008

Recurrent laryngeal nerve

I got baited into another long, fruitless debate with some gentlemen, but in the process, I learned some cool stuff about biology.

The recurrent laryngeal nerve is a nerve that runs from our brain to our voicebox to provide motor function and sensation to the voicebox. Interestingly, though, instead of running a direct route from brain to larynx, it runs from the brain, all the way down the neck to the chest, and then back up the larynx. It doesn't take the straight path -- it loops. Hence, recurrent. This occurs in a whole bunch of animals, including the giraffe -- where "taking the long road" adds meters of nerve.

One gentleman in particular used this as evidence of common descent -- after all, why would the nerve take this inefficient path from the brain down to the chest and back up to the larynx in animals as diverse as men and giraffes, unless the two species were related? Having never heard of this before, and finding it interesting, I googled "laryngeal nerve," to learn what it was. On a whim, I then looked up "non-recurrent laryngeal nerve" and I found this abstract, among others, which indicated that non-recurrent laryngeal nerves occur about 1% of the time in humans.

I brought this to the attention of the gentleman, and pointed out that given the regular occurrence of non-recurrent laryngeal nerves, it would seen that if such a path were advantageous, it would have been selected by now. Thus, the fact that the other variant is set (or nearly set) in the population indicates that the recurrent version may well have some advantage. There was also another abstract which indicated that the non-recurrent variant was quite deletarious during surgery, as it increased the chance of injury. That at least provided a potential explanation.

He never responded. I wish he had. He obviously knew some stuff about biology. He obviously had a lot to teach me.

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