The Giraffe and the Recurrent Laryngeal Nerve
Maybe it’s because it’s fresh in my mind, feeding the giraffe at Perth Zoo, but an article regarding the laryngeal nerve in the giraffe’s neck, grabbed my attention.
Apparently, Richard Dawkins made the comment that the laryngeal nerve was so poorly made, no one could believe in a designer. He quipped, “No designer would ever make a mistake like that!”
Surely this logic could be reversed? With all the perfections out there in design, it could prove there IS a creator?
As it turns out, there does exist an article that shows that it isn’t a bad design at all!
But first, what is Dawkins’ criticism?
Dawkins complains about the recurrent laryngeal nerve:
â€œIt is a branch of one of the cranial nerves, those nerves that lead directly from the brain rather than from the spinal cord. One of the cranial nerves, the vagus (the name means â€˜wanderingâ€™ and is apt), has various branches, two of which go to the heart, and two on each side to the larynx (voice box in mammals). On each side of the neck, one of the branches of the laryngeal nerve goes straight to the larynx, following a direct route such as a designer might have chosen. The other one goes to the larynx via an astonishing detour. It dives right down into the chest, loops around one of the main arteries leaving the heart (a different artery on the left and right sides, but the principle is the same), and then heads back up the neck to its destination.
â€œIf you think of it as the product of design, the recurrent laryngeal nerve is a disgrace. Helmholz would have had even more cause to send it back than the eye. But, like the eye, it makes perfect sense the moment you forget design and think history instead.â€ (p. 356)
Dawkins then argues that it makes better sense if we evolved from fish, and touching on something akin to Haeckelâ€™s discredited embryonic recapitulation theory,1 concludes:
â€œAll that we need to know, to understand the history of our recurrent laryngeal nerve, is that in the fish the vagus nerve has branches that supply the last three of the six gills, and it is natural for them, therefore, to pass behind the appropriate gill arteries. There is nothing recurrent about these branches: they seek out their end organs, the gills, by the most direct and logical route.
â€œDuring the evolution of the mammals, however, the neck stretched (fish donâ€™t have necks) and the gills disappeared, some of them turning into useful things such as the thyroid and parathyroid glands, and the various other bits and pieces that combine to form the larynx. Those other useful things, including parts of the larynx, received their blood supply and their nerve connections from the evolutionary descendants of the blood vessels and nerves that, once upon a time, served the gills in orderly sequence. As the ancestors of mammals evolved further and further away from their fish ancestors, nerves and blood vessels found themselves pulled and stretched in puzzling directions, which distorted their spatial relations one to another. The vertebrate chest and neck became a mess, unlike the tidily symmetrical, serial repetitiveness of fish gills. And the recurrent laryngeal nerves became more than ordinarily exaggerated casualties of this distortion.â€
Richard Owen and opponents of Darwin
Dawkins goes on to describe how the RLNâ€™s detour could be 15 feet long in a large giraffe. He relates witnessing the dissection of such a nerve in a young giraffe that had died in a zoo. He expressed admiration of the skill of the team of anatomists performing the dissection, which increased his respect for the creationist opponent of Darwin, Richard Owen, who had achieved this feat in 1837. Yet, says Dawkins, Owen failed to reject the idea of a designer.
This should tell us something. Itâ€™s notable that much of the opposition to Darwin came from scientists2 like Owen, as well as Professor Johann H. Blasius, director of the Ducal3 Natural History Museum of Braunschweig (Brunswick), Germany, who stated in a review of Darwinâ€™s Origin:4
â€œI have also seldom read a scientific book which makes such wide-ranging conclusions with so few facts supporting them. â€¦ Darwin wants to show that Arten [types, kinds, species] come from other Arten. I regard this as somewhat of a highhanded hypothesis, because he argues using unproven possibilities, without even naming a single example of the origin of a particular species.â€5
Design features of the recurrent laryngeal nerve
As for good reasons Owen did not draw evolutionary conclusions, there are several. The well-known textbook Grayâ€™s Anatomy states:
â€œAs 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.â€
That is, Dawkins considers only its main destination, the larynx. In reality, the nerve also has a role in supplying parts of the heart, windpipe muscles and mucous membranes, and the esophagus, which could explain its route.
Even apart from this function, there are features that are the result of embryonic developmentâ€”not because of evolution, but because the embryo develops from a single cell in a certain order. For example, the embryo needs a functioning simple heart early on; this later descends to its position in the chest, dragging the nerve bundle with it.
Also, would a circuitous route necessarily be bad design? There could be reasons for this (and in the case of the RLN we have a good idea, as per Grayâ€™s). Biologist and geologist John Woodmorappeâ€™s review of Jerry Coyneâ€™s book Why Evolution is True (which Dawkins recommends for its section on the RLN (note, p. 356) points out:
â€œHuman-designed machines and structures are full of such things as circuitous wiring and plumbing, but that hardly means that they are not the products of intelligent design.
â€œNow let us consider situations in which a circuitous route is actually harmful to its bearer. The automobile with its engine in front requires a long, tortuous exhaust system perched underneath the car. This clearly makes it more vulnerable to injury from obstructions than the short exhaust system of engine-in-back cars (I speak from personal experience). Following Coyneâ€™s logic, should we suppose that engine-in-front cars are not the products of intelligent design? No. We realize that there is an engineering trade-off between the advantages of the car with its front-situated engine and the concomitant disadvantage of its more easily-damaged long, circuitous exhaust system.â€7