The recurrent laryngeal nerve as evidence for evolution

March 2, 2019 • 12:00 pm

On pages 82-84 of Why Evolution is True I discuss the recurrent laryngeal nerve of humans (and other tetrapods) as an example of evolution. It’s evidence via “retrodiction”, which is what I call the situation when a previously unexplained and puzzling phenomenon can be understood only in light of a theory, thus supporting that theory—in this case, evolution.

Rather than describe it again, here are two videos showing it and explaining how the configuration of that nerve supports evolution.

Creationists have an explanation for it, too (there’s nothing they can’t explain via God’s will, except perhaps the peculiar species composition of oceanic islands), but the goddy story is unconvincing and less parsimonious. Whereas the evolutionary explanation tells us why only one of the twinned cranial nerves does its crazy loop, and why it’s completely comprehensible via the known evolution of tetrapods, the creationist explanation is based solely on how the nerve works: a post facto “functional” explanation of why the creator would create the nerve’s tortuous path. But it doesn’t explain why the creator made that big loop to enervate the larynx when he could have sent a branch directly to the larynx without the loop.

Here Dr. Rohin Francis, a cardiologist and researcher in London, uses his expertise to show how the nerve supports the “tinkering” aspect of evolution:

Below Richard Dawkins attends the dissection of a giraffe, which has an extraordinarily long (5 meter) recurrent laryngeal nerve. Rohin, however, notes above that some long-necked sauropod dinosaurs certainly had a recurrent laryngeal nerve about 28 meters (92 feet) long! I believe I’ve posted this video before, but it goes well with the video above:

In my only visit ever to a human anatomy lab (I get freaked out by corpses), I myself watched the dissection of this nerve by an anatomy professor. And it’s just like the one above, only shorter.

h/t: Scott

37 thoughts on “The recurrent laryngeal nerve as evidence for evolution

  1. I love the recurrent laryngeal nerve example! It is such an elegant “paper trail” left behind by evolution, and so confounding to creationists.

  2. I didn’t think I had anything to learn here, but I did! I didn’t know that the nerve cells themselves are also elongated. I just thought the the recurrent laryngeal nerve had ‘more’ cells, not longer cells. Very cool. I also liked the doctor’s corny sense of humor.

      1. And the Comments section, for once, is almost equally good. Or corny. Or both. 😎


  3. As an equine veterinarian the tortuous course of the recurrent laryngeal nerve plays a particular relevance. A common cause of exercise intolerance is laryngeal hemiplegia. It is almost 100% left sided as the left recurrent pharyngeal nerve is much more prone to damage because of the long distance it travels.

    1. Thank you,

      I wondered what damage to the nerve might do and never considered the larynx involvement during inspiration.

      Does the condition only affect a patient during exertion?

      1. At rest they are perfectly normal. With high intensity exercise they will make quite a loud noise(they are referred to as “roarers”). The left RLN has to travel further because it must pass around the L subclavian artery which originates from the 6th aortic arch while the right side regresses during development and the R subclavian artery develops from the 4th aortic arch. This extra distance can be significant in large breeds of horses such as thoroughbreds and drafts.

  4. … meaning each of the sauropod’s laryngeal axons were the length of a basketball court! Or not, since we know little of their soft anatomy, the sauropods may have made a genius hack.. perhaps rewiring from a nearby nerve controlling their feathered crest. After all, the archosaurs had all the neat stuff!

  5. The doc’s video was entertaining and informative, now all we want is for evolution to remove it…
    (wikipedia)Function. The recurrent laryngeal nerves control all intrinsic muscles of the larynx except for the cricothyroid muscle. These muscles act to open, close, and adjust the tension of the vocal cords, and include the posterior cricoarytenoid muscles, the only muscle to open the vocal cords.

    … from creationist so we don’t have to listen to their ‘delusional spread of misinformation’ in short: LIES.

  6. Very good. There are other ‘dumb’ aspects of design because embryos are constrained to tinker with the developmental programs of their ancestors rather than inventing new programs.
    The dumbest of these that I know are that we develop a series of kidneys, only to then discard them. First there is a pair that develops in our thoracic region, and as they are discarded a second and very large pair of kidneys form a bit farther down. These are then discarded to be replaced by a third pair, which is what you have now.
    Those first two pairs of kidneys correspond to those made by our earlier fish and amphibian ancestors.
    Why do we do this? There is more than one reason but one is that we need the various ancestral embryonic structures that we then discard because they provide essential cell-cell interactions for development of other structures that we need to keep.
    The list of these discarded ancestral structures is fairly long, and they include kidneys, the notochord, those additional aortic arches mentioned in the video, and a very large but empty yolk sac.

      1. Biogeography.
        As Jerry describes in his WEIT book the distribution of species is clearly describable only as a history of speciation from common ancestors in a place, where closely related species remain close together long after speciation has occurred.
        All other areas of evidence for evolution are energetically contested by creationists. Not correctly, of course, but in their minds they will think they have rebuttals for all other areas. But biogeography is tellingly left untouched by creationists. They don’t seem to know what to do with it.

        1. Biogeography is too aligned with common sense. Creationists dwell in the magical, and embryology is too small and complex for the workings of magic…it can’t be seen. Shazam! (lightning bolt insert here)

        2. I concur. Easier to grok as well. Common sense doesn’t dwell within embryology as it does Biogeography.

  7. Another anatomical feature I find counter to “intelligent design” is the fact that our respiratory tract and digestive tract cross. Why would you design a system where the air intake has to pass through the fuel intake? Especially why would a designer place the lungs ventral to the esophagus? Of course, the elaborate protections that evolved gives mammals the ability to vocalize. But if the systems didn’t cross there would be a much lessened danger of choking or aspirating.

    1. I think the crossing of the two tracts is justified because the mouth is an emergency air entrance. The nasal cavity with its amazing heat-exchange labyrinthine structure closes when inflamed and swollen, so we resort to breathing through the mouth.

      (As children, we have a joke. We tell another child not yet familiar with it: “Do you believe I can make you open your mouth?” He answers “No” and firmly shuts his mouth, thinking I will try to trick him to talk further. Instead, I quickly catch his nose with 2 fingers and press the nostrils. Surprised, he reflexively opens his mouth before pushing back my hand.)

      My favorite “unintelligent designs” are the prostate gland (which designer in his right mind would make it encircle the urethra?), the human birth canal (an unfortunate bony ring) and, at molecular level, the loss of photolyase enzyme. I regret the latter even more than the gulonolactone oxidase.

  8. And another stupidity is this: We breathe through two holes in the front of our face, which are connected to the lungs. We eat through another hole, connected to the stomach. WHY do they share the same piping down the neck? This exposes us to constant danger in that a stuck bit of food can kill us in four minutes. Insane!

    If the mouth and the nose had separate plumbing, then a stuck bit of food would just mean that we had very many hours in which to get it removed before we starved, rather than four minutes flat before we suffocate.

    For those who would argue that we talk through our mouths, there’s no reason why the larynx couldn’t be placed behind the nose. We’d sound weird but of course, since that would be ‘normal’, it wouldn’t be weird to us.

    Our necks might need to be a bit thicker, but considering their fragility and potential for damage, that would not necessarily be a disadvantage.

    Of course, ‘evolution is mindless’ explains this all perfectly.


    1. The larynx only makes the basic sounds. For speech, you need a chamber capable of being altered in many subtle ways which is what the mouth, jaw and tongue give you.

      At least, I think that is how a creationist would argue. Of course, even if you are going to reuse the chewing machinery for speech, it doesn’t mean you couldn’t put the wind pipe behind the food pipe and avoid the crossover.

    2. Is there a term for the opening created by the convergence of a surface with itself?… like a paper towel tube – the opening must have a name from topology. I know in medicine the term is “meatus”.

    3. I wrote above in response to Peter: we need the opportunity to breathe through the mouth so that not to die of suffocation when we have a runny nose.

      1. That could be achieved by a cross-connection higher up, which would be less susceptible to blockage than funnelling everything down the same hole.

        Or by simply redesigning the nostrils to be less susceptible to blockage by infected snot.

        We’d look weird but of course, to us it would appear ‘normal’.


  9. I saw Dawkin’s demonstration years ago and I’ve been waiting for an opportunity to send a link to a creationist. I haven’t yet had that opportunity, but it’s going to give them something to think about.

  10. On “god did it”: I don’t think there is any situation where “god did it” is a justified explanation. If one is committed to believing the most parsimonious explanation under identical evidence, then adding gods doesn’t help you compress information. It would be more parsimonious to accept everything as a brute fact, since all the information is compressed in the “it”.

    And so creationism fails even when compared with the least parsimonious natural “explanation”.


    1. God matched the arterial arches and the cranial nerves to the pharyngeal arches of fish. And God saw that it was good.
      Some millions years later God sent some of the fish to dry land, made them a neck and saw there the most awkward crossing between the recurrent laryngeal nerve and the 4th arterial arch. And God beat his forehead and exclaimed, “What an old fool I am!”

  11. Fun fact: I have an aberrant subclavian artery, about 1% of the population have it, in most cases, it’s completely asymptomatic. This can mean that the recurrent laryngeal nerve doesn’t do its detour and is non-recurrent. So when I got my thyroid removed the surgeons had to be extra careful. They almost sounded disappointed when they found the nerve completely normal.

    1. I am glad that your recurrent laryngeal nerve was not damaged by the surgery! This nerve is the nemesis not only of creationists but also of incompetent surgeons. A lady I know was damaged by one, could barely breathe and not talk at all after the surgery, and even today breathes with difficulty and her speech is almost all whispering.

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