Intelligent design (ID) critics Jerry Coyne, Kelly Smith, and Richard Dawkins have all argued that the allegedly circuitous innervations of the larynx from the brain by the recurrent laryngeal nerve (RLN) is an “imperfect design” that refutes ID. What they rarely disclose, however, is that there are in fact nerves that innervate the larynx directly from the brain through the superior laryngeal nerve (SLN), without taking the longer path of the RLN–exactly as they demand. Thus, the larynx is in fact innervated from both above and below, by both the RLN and the SLN. This is clearly seen in the diagram below, from Elsevier’s Atlas of Regional Anesthesia, 3rd ed., hotlinked from here:
As noted here, damage to the SLN can in fact affect the ability of people to swallow, yell, sing, or properly control voice pitch.
Thus, the preferred design of Coyne, Dawkins and Smith actually DOES exist in our bodies, as the larynx is innervated from above, directly from the brain.
Given the different medical conditions encountered when the laryngeal nerves (such as the SLN and RLN) are damaged, it seems that the two nerves are performing distinct functions. The SLN–which innervates from above–has something to do with producing higher-pitched sounds, and the RLN–which innervates from below–has something to do with producing lower-pitched sounds.
Rather than being an “imperfect design,” perhaps the dual innervation of the larynx from both above and below is a good design principle — a form of redundancy, or complementation to help minimize the impact upon function if one of these two nerves is damaged. Thus we see hints of function and design optimization in the innervation of the larynx. Again, this is evidence of optimization for a “global function,” which ID-critic Kelley C. Smith admits is a good design principle.
In the final post we’ll explore some medical considerations for the design of the RLN.