The Stupid, Unintelligent Recurrent Laryngeal Nerve: Evolution Working as Not Intended

The belief that the universe arose through the fundamental actions of a supreme entity is by itself not a problem. The systematic implications of this have prompted various individuals through the last several millennia to argue that causation is preceded at all times by a single entity, and that evolution by natural, unguided processes cannot. This has included, but is not limited to, anecdotal arguments that various biological systems are “machines” in one form or another, perpetrating the impression that if one has a machine, there must have been a designer. The metaphor backfires, and you get “no better mousetrap” arguments, the irreducible complexity nonsense, and various other issues. Dr. Matt Wedel of the Sauropod Vertebrae Picture of the Week! has taken on one particular biological system, the recurrent laryngeal nerve, to demonstrate the ludicrousness of the idea that a singular entity designed anything, simply because the system involved is so clearly bizarre that no intelligent being could have designed it.

[Note: I actually wrote this last year upon reading the draft and corrected manuscript provided to APP. This is now published, and this post (my first in so long) is finally able to be put up. Thanks go to Matt for talking to me about this — he got to read this in almost its current form and found nothing not worth my posting — fueled by the strange coincidence of a strip from Scenes from the Multiverse when the manuscript was posted to APP‘s publicly-available archive.]

Here’s Jonathan Rosenberg’s take on the subject:

Matt Wedel has approached the topic from another angle, one of that related to sauropods. Many sauropods, including the biggest, have necks far in excess of the length of any giraffe’s neck. Thus, because the laryngeal nerve is constrained in all vertebrates to approach the aorta, then reflex back up the neck near to the skull, this makes the longest-necked animals those with the longest laryngeal nerves. Wedel extends this to point out that the longest sauropods would also have the longest nerves of almost any vertebrate, as a nerve fiber would have to extend from the brain stem where it originates and progress all the way to distal end of the tail. Opponents of intelligent design, as shown above, argue that this nerve is demonstrative of the fallibility of evolution, and thus its champion, because it can only arise when the nerve used to innervate where the original larynx and the heart were adjacent; evolution produced animals with longer necks, a separated shoulder from the skull, and eventually the nerve, normally straight and without divergence, became wrapped around the aorta and eventually recurred along the esophagus to innervate the larynx. Thus was born the improbable recurrent laryngeal nerve.

Position and length of the recurrent laryngeal nerve, following Wedel (2012). On the left, Wedel’s original figure 1 with labels and arrows added, indicating the major features: aa, aortic arch of the heart, and in black the heart itself; rln, the recurrent laryngeal nerve. On the right, the same figure with the actual laryngeal nerve where it branches from the descending vagus nerve at the aortic arch of the heart, shown in yellow.

This is not a neat, perfect story though: the laryngeal nerve does, in fact, perform duties beyond that of innervating the larynx. The nerve is distinct only near the aortic arch of the heart, where it separates from the spinal cord in the upper thoracic region of the chest. There, it innervates portions of the cardiac muscles, and as it ascends the esophagus it sends branches as fine threads (each of them a separate, distinct nerve fiber) into it, before it reaches the larynx itself, where it innervates the muscles the surround it. This doesn’t supplant the larger message, that the nerves recursive tract is a major point in showing that an intelligent, perfect design is apparent in the laryngeal nerve, because it simply isn’t: no other nerve backtracks in order to innervate its original position, and the only reason it could is because over time, evolution has produced longer-necked animals that separated the origin and innervation points. The tract is, indeed, recurrent only because there are two actual points of innervation, the heart and the larynx, and these became broadly separated in terrestrial vertebrates to accommodate a mobile shoulder and thus longer neck.

It is a perfect demonstration that the “design” of the nerve’s tract was one of constant experimentation, not of elegant precision at one time and never modified, as the Creationist Intelligent Design movement believe to be true.

Wedel, M. J. 2012. A monument of inefficiency: The presumed course of the recurrent laryngeal nerve in sauropod dinosaurs. Acta Palaeontologica Polonica 57(2)251-256.