Revisiting “Design Flaws” in the Human Breathing System

A reader named Andrew has offered a couple of interesting comments on the post “Design Flaws” in the Human Breathing System. I think some worthwhile points have been made in our exchange, so I am copying his comments and my responses to this new entry. This will also allow me to include some of the images and animations cited; plus my second response hit the 4096 character limit for Blogger comments, so it wouldn’t fit in the comment box.

His initial comment:

This article completely misses the point. The problem is not that both tubes have two openings (mouth and nose), but that the esophagus lies above the trachea in the throat, allowing food & liquid to fall into the trachea where they cross. An intelligent design would have the esophagus below the trachea (i.e. at the front of the neck) so gravity would help keep us from choking. You can trace our "wrong" arrangement all the way back to the amphibians and fish from which we evolved. Evolution cannot fix this as it is topologically constrained. But a putative intelligent designer could.

My response:

Thank you for your comment.

Since this article is a response to the claim that the shared opening to the esophagus and trachea is a flawed design and that a "better" design would have independent tubes for breathing and eating, it seems that if anyone has missed the point it is Professor Burdo and the authors of the "If Humans were Built to Last" article.

Second, it is very easy to say that putting the esophagus below the trachea would solve the choking problem, but can you actually demonstrate that this is more than just fanciful speculation? It seems that many of these "design flaw" arguments depend on such hand-waving and speculation as "proof" that a particular design is flawed and that a real intelligent designer would do it this way. See this post on the design of the eye for another common example of this flawed argument.

Third, if you look at diagrams (see below) of the trachea and esophagus, one is not really "above" or "below" the other. When a person is vertical, both tubes are pretty much parallel, and when a person swallows, the more direct route is down the esophagus, while the trachea is the more diverted passageway. It certainly does not seem obvious that gravity would be any help if the two tubes were switched, as you suggested.

imageimage

Also, there are some good reasons why the esophagus is deeper inside the throat than the trachea. For one, the act of swallowing requires the coordinated workings of a number of muscles; thus switching the location of the esophagus would require a significant reworking of the musculature of our necks, with unpredictable consequences. The point being that again, what seems like such a simple "fix" can have drastic and undesirable consequences, which was the whole point of this article.

 

Andrew’s 2nd comment:

Hi Ken, thanks for your quick reply.

OK, I admit I didn't read the article you critique, which seems a little silly if it proposes completely separate breathing & eating tubes. As you point out, there are advantages to having multiple openings and also the ability to widen the intake as needed but keep it small most of the time.

Thanks for the diagrams. In both diagrams it seems quite obvious to me that it is risky to have the trachea wide open at the back of the mouth almost all the time. The only thing stopping us from choking to death (or at least coughing like crazy) every time we swallow is the epiglottis flipping down to cover the tracheal opening. That's a neat mechanism, but it has to be extremely reliable. I estimate that we swallow several million times in a lifetime (mostly saliva every minute or so), so a failure rate of just one in a million could lead to premature death by choking. It is an active safety system which needs to work very well because there is no plan B. It would be far more fail-safe to have passive safety designed in, perhaps with an active system on top for extra safety (so that a failure of the active system would not be life-threatening). The only time we are not at risk of something falling down our trachea is when it is covered, but this also stops us from breathing so it must be left open, and at risk, most of the time. It would be much safer to have no connection between the mouth and trachea most of the time, and only connect them on the rare occasions it is needed.

Now, I'm not omniscient so perhaps I'm missing something here, but if I were given this design brief:

1. Get food and liquid into the stomach
2. Get air into the lungs through small openings which can be enlarged if needed on relatively rare occasions
3. Do not under any circumstances let solids or liquids into the lungs

I would:

a. have the esophagus at the front of the neck, directly connected to the back of the mouth without having to leap over the trachea
b. have the trachea behind the esophagus and connected to the back of the sinuses
c. for safety, have no connection between the trachea and mouth under normal circumstances, but have a flap (perhaps like the soft palate) which could open to connect the two as needed for occasional heavy breathing, vocalisation, clearing mucus from the sinuses, etc. - and obviously not when eating or drinking. And have this connection high up at the back of the mouth so that gravity would assist in preventing choking.

True, there may be unforseen problems with this related to musculature etc, but I don't think these would be beyond the problem-solving capacity of a God claimed to be powerful & intelligent enough to create the entire universe from nothing.

-Andrew

My response:

Hi Andrew,

Thank you for your additional commentary on this article. Sorry to keep you waiting. Let me see if I can address some of the things you said:

"The only thing stopping us from choking to death (or at least coughing like crazy) every time we swallow is the epiglottis flipping down to cover the tracheal opening. That's a neat mechanism, but it has to be extremely reliable."

I completely agree with you that the epiglottis is a neat mechanism. I found this wonderful animation (above) showing the process of swallowing. Observe how many steps and parts work together to get food down to the stomach and to protect the respiratory system.  I also agree that the epiglottis must be—and I would add that it indeed is—extremely reliable. Considering how many billions of people are talking and eating at the same time and how there are only a few hundred deaths from choking every year, I would say that the mechanism for protecting people from choking is very reliable from a statistical standpoint.

"It is an active safety system which needs to work very well because there is no plan B. It would be far more fail-safe to have passive safety designed in, perhaps with an active system on top for extra safety (so that a failure of the active system would not be life-threatening)."

Here I would offer some points of disagreement. First, the epiglottis does indeed have passive safety designed in. Note in the animation how in the process of swallowing the epiglottis is levered close by the food being swallowed, such that even if something was preventing the epiglottis from automatically covering the trachea, the epiglottis would still be pushed into position.

Second, there is indeed a "plan B" for the rare instances when the epiglottis does not do its job perfectly. You even mentioned it yourself in your comment. The instant that something other than air begins to pass into the trachea, sensitive nerves trigger the cough reflex to expel the foreign object. This is exactly the kind of redundant active safety system that you seemed to find wanting in the actual design.

"It would be much safer to have no connection between the mouth and trachea most of the time, and only connect them on the rare occasions it is needed."

Safer perhaps in reducing the risk of choking to death (which I must reiterate is already an extremely rare occurrence), but would it necessarily be better? The issue that I have with those who raise the "flawed design" argument is that they tend to focus on just one narrow aspect of the function of a system, and their proposals for "better" designs often ignore many of the other features and functions of the existent design. This is addressed in another article on the supposed design flaws of the vertebrate eye (another common target of the "flawed design" argument). I hope that you can read it and offer your thoughts on it.

"c. for safety, have no connection between the trachea and mouth under normal circumstances, but have a flap (perhaps like the soft palate) which could open to connect the two as needed for occasional heavy breathing, vocalisation, clearing mucus from the sinuses, etc. - and obviously not when eating or drinking. And have this connection high up at the back of the mouth so that gravity would assist in preventing choking."

In this case, I think you greatly underestimate the frequency in which having a connection between the mouth and the trachea is important. As quoted in the article, Richard Deem describes how the mouth and tongue are essential for speech, something that you acknowledge as one of your "as needed" circumstances. But in general humans spend much more time talking and communicating than they do eating and drinking. Thus, under "normal circumstances" it seems logical that the system should be geared for vocalization—with an open connection between mouth and trachea—with a flap (namely, the epiglottis) that is able to close off the connection as needed for eating and drinking.

"True, there may be unforseen problems with this related to musculature etc, but I don't think these would be beyond the problem-solving capacity of a God claimed to be powerful & intelligent enough to create the entire universe from nothing."

This assumes that it is obvious that the current system is not already the most economical and functional design for its purposes, and that your proposed system would indeed be better, but I have to say that you have not convinced me that this is the case.

 

Diagrams obtained from http://pennstatehershey.org/healthinfo/graphics/images/en/1118.jpg and http://www.tracheostomy.com/resources/surgery/yoursurgery/trachanat2.jpg

“Swallowing” animation from: http://www.linkstudio.info/images/portfolio/medani/Swallow.swf

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