(un)Intelligent Design: Recurrent laryngeal nerve

I’m writing this post in the hope of informing fellow non-theists about my favorite anatomical proof of evolution emphasizing a vestigial organ. No, it’s not your appendix.

The recurrent laryngeal nerve (RLN) was first discovered in Rome during the second century AD by the legendary physician Galen, who demonstrated its function using a live pig. Though the RLN is nothing new to science, it is an excellent example of evolution’s imperfect designs and one that, I think, most people are unaware of, unless you’re a med student. Your average creationist has probably heard the appendix argument before, so here’s your chance to hit ‘em with a left.

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This nerve begins at the spinal cord and travels down into the chest cavity, loops around the arteries of the heart and finally ascends back into the throat where it connects with the voice box, enabling speech in humans and vocalization in mammals. In fact the RLN is present in every species with a larynx, including the animals with the most primitive larynx, the fish – remember that!

So, is the RLN an example of perfect design by nature? In humans the fastest route from the brain to the larynx is a distance of about a foot. This is not the route we see. By diving into the chest and ascending back into the throat the RLN takes a route that covers a distance of three feet. No one ever said Mother Nature was good at math. What makes matters worse is that this configuration makes the nerve more susceptible to injury.

The most striking example of this ridiculous configuration is seen in giraffes. The following is a clip from the mini-series Inside Nature’s Giants, originally aired on Channel 4 in the UK:

WARNING! This video contains EXPLICIT scenes from a REAL GIRAFFE DISSECTION! Animal lovers, you've been warned! See the dissection.

Impulses from the brain charge down the giraffe’s neck like riders racing down the first drop of the world’s tallest roller coaster, loop-de-loop around the heart and shoot back up to the larynx at the top of the animal’s throat, all to swallow some leafs. But why? The answer lies with our water-breathing ancestors.

“In the early fishlike embryos of all vertebrates, the nerve runs from top to bottom alongside the blood vessel of the sixth branchial arch; it is a branch of the larger vagus nerve that travels along the back from the brain. And in adult fish, the nerve remains in that position, connecting the brain to the gills and helping them pump water.

During our evolution, the blood vessel from the fifth arch disappeared, and the vessels from the fourth and sixth arches moved downward into the future torso so that they could become the aorta and a ligament connecting the aorta to the pulmonary artery. But the laryngeal nerve, still behind the sixth arch, had to remain connected to the embryonic structures that become the larynx, structures that remained near the brain. As the future aorta evolved backward toward the heart, the laryngeal nerve was forced to evolve backward along with it.” – Jerry A. Coyne, Why Evolution is True


And there you have it! A gift from our great great great great great great fish ancestors. Too bad we can't take it back to the store and trade it for something better designed.

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Tags: anatomy, proof of evolution, recurrent laryngeal nerve, science, vestigial

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Comment by OutlawGirl on August 31, 2009 at 11:26pm
You can actually SEE the recurrent laryngeal nerve in the giraffe here, but the video doesn't get to the part about the nerve until 6:45.

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