The Recurrent Laryngeal Nerve Does Not Refute Intelligent Design
In the prior post, I discussed challenges to the claim that our supposed fish-ancestry dictates that the recurrent laryngeal nerve (RLN) must take a circuitous route from the brain to the larynx. Let's assume, for the sake of argument, that common ancestry between mammals and fish is the best explanation for the nerve's path. Would that refute intelligent design? Evolutionary biologist Jerry Coyne assumes that ID is incompatible with common ancestry, which it isn't. As one pro-ID biologist wrote me on this topic, "this is only a problem for design if one assumes design means designed from scratch for each taxon, and if one believes that the designer would necessarily use the shortest distance between two points (in other words, that the designer thinks like we do), and that there are not other design considerations at play."
But if we set aside the question of whether evolutionary history explains the RLN's path, it's also never been clear to me why "imperfect design" should refute design. I've complained before about the breakdowns and flaws I've had with computers, but obviously computers are designed. In fact, every piece of technology that has ever had a flaw shows that imperfect designs are was still designed! "Imperfect design"--a term used by Coyne--is still design.
Regardless of whether evidence for common ancestry or evidence of imperfect design actually do refute design, both Jerry Coyne and Kelly C. Smith admit that if we find some rational function or a reasonable purpose for a design, then the "imperfect" or "inferior" design objection falls apart. Coyne tells us that imperfect design doesn't refute evolution because evolution predicts that both highly functional or poorly-functional parts may exist. Therefore it seems to actually really predict nothing whatsoever on this matter.
While Coyne's argument may not be coherent, one way to refute it is to to find rational function for the RLN's pathway in normal humans.
Indeed, hints of important functions for the RLN nerve can be seen in the old authority, Gray's Anatomy, which states regarding the normal human design:
As the recurrent nerve hooks around the subclavian artery or aorta, it gives off several cardiac filaments to the deep part of the cardiac plexus. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the esophagus; branches to the mucous membrane and muscular fibers of the trachea; and some pharyngeal filaments to the Constrictor pharyngis inferior.So it seems that the RLN is innervating a lot more than just the larynx. Pro-ID biologist Wolf-Ekkehard L�nnig, in his article "The Laryngeal Nerve of the Giraffe: Does it Prove Evolution?," quotes a passage from a much more recent 1980 edition of Gray's Anatomy stating much the same thing:
As the recurrent laryngeal nerve curves around the subclavian artery or the arch of aorta, it gives several cardiac filaments to the deep part of the cardiac plexus. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the oesophagus; branches to the mucous membrane and muscular fibers of the trachea and some filaments to the inferior constrictor [Constrictor pharyngis inferior].L�nnig further states: "I have also checked several other detailed textbooks on human anatomy like Sobotta - Atlas der Anatomie des Menschen: they are all in agreement. Some also show clear figures on the topic. Pschyrembel - Germany's most widely circulated and consulted medical dictionary (262 editions) - additionally mentions 'Rr. ... bronchiales'."
(Gray's Anatomy, 1980, p. 1081, similarly also in the 40th edition of 2008, pp. 459, 588/589)
So the RLN's sole purpose, or as ID-critic Kelly Smith put it, its "intended function," is not simply to innervate the larynx, as it provides innervations for the heart and even for the esophagus. And for those organs it takes a direct, or as Coyne might put it, "rational" route from the brain.
All of this this would seem to satisfy what Kelly Smith called evidence of a "global" function, which Smith admits makes "an instance of local imperfection" (i.e. the circuitous route of the RLN) more acceptable in an argument for design (See Smith's article in the volume "Intelligent Design Creationism and Its Critcis," p. 725). So what is Smith complaining about?
Embryological Considerations for the RLN's Design
L�nnig also hints that there may be embryological reasons for the design of the RLN:
However, just to refer to one possible substantial function of the Nervus laryngeus recurrens sinister during embryogenesis: "The vagus nerve in the stage 16 embryo is very large in relation to the aortic arch system. The recurrent laryngeal nerve has a greater proportion of connective tissue than other nerves, making it more resistant to stretch. It has been suggested that tension applied by the left recurrent laryngeal nerve as it wraps around the ductus arteriosus could provide a means of support that would permit the ductus to develop as a muscular artery, rather than an elastic artery" - Gray's Anatomy, 39th edition 2005, p. 1053.Another pro-ID thinker commented to me privately about this matter as follows:
So according to this description, nerve filaments emanate along its length from the cardiac plexus to the esophagus, which if accurate might well dictate its positioning. Whether due to a requisite embryogenic sequence, for optimal nerve routing, or even an evolutionary carryover, it is a workable routing in all mammals, and therefore lacks substance as an argument against design based upon "poor design."Dr. L�nnig thus concludes:
To innervate the esophagus and trachea of the giraffe and also reach its heart, the recurrent laryngeal nerve needs to be, indeed, very long. So, today's evolutionary explanations (as is also true for many other so-called rudimentary routes and organs) are not only often in contradiction to their own premises but also tend to stop looking for (and thus hinder scientific research concerning) further important morphological and physiological functions yet to be discovered. In contrast, the theory of intelligent design regularly predicts further functions (also) in these cases and thus is scientifically much more fruitful and fertile than the neo-Darwinian exegesis (i.e. the interpretations by the synthetic theory).L�nnig goes on to make a devastating critique of Dawkins and others who use the alleged poor design of the laryngeal nerve to refute ID. See L�nnig's article, "The Laryngeal Nerve of the Giraffe: Does it Prove Evolution?," for details.
To sum up: The Nervus laryngeus recurrens innervates not only the larynx, but also the esophagus and the trachea and moreover "gives several cardiac filaments to the deep part of the cardiac plexus" etc. (the latter not shown below, but see quotations above). It need not be stressed here that all mammals - in spite of substantial synorganized genera-specific differences - basically share the same Bauplan ("this infinite diversity in unity" - Agassiz) proving the same ingenious mind behind it all.
The next post in this series will show that the exact form of direct innervations of the larynx from the brain--demanded by ID-critics--in fact exists.