The Supposed Bad Design of the Human Pharynx
Howard Glicksman and Steve Laufmann
Editor’s note: We are delighted to present this excerpt adapted from Your Designed Body, the new book by engineer Steve Laufmann and physician Howard Glicksman.
In our book, Your Designed Body, we apply a five-part test for evaluating ostensible instances of bad design. This test can help determine whether we’re looking at a bad design, or simply a bad argument. Let’s consider the example of the human pharynx. Is it poorly engineered?
The figure below shows that the pharynx is the common entry for both the respiratory and gastrointestinal tracts. Whatever is ingested can potentially go down the airway and cause obstruction, which can result in death by choking.
Some insist that the pharynx is therefore miserably designed, something no wise designer would engineer, but that evolution, with its trial-and-error messiness, very well might. “The biggest danger in the human throat’s design is choking,” writes Nathan Lents. “If we had separate openings for air and food, this would never happen. Swallowing is a good example of the limits of Darwinian evolution. The human throat is simply too complex for a random mutation — the basic mechanism of evolution — to undo its fundamental defects. We have to resign ourselves to the absurdity of taking in air and food through the same pipe.”1
Abby Hafer, in her pointedly titled book, The Not-So-Intelligent Designer: Why Evolution Explains the Human Body and Intelligent Design Does Not, sounds a similar note. “A better designed system would keep the tubes for air and food separate to avoid unnecessary fatalities,” she writes. “If we were designed why did the Designer do this job so badly? Or is it that the Creator likes other animals better? There are creatures in which the air passages and food passages are entirely separate. The whale’s respiratory system is separate from its digestive system. This means that a whale, unlike a human, can’t choke on its food by inhaling it. If the Creator could do that for the whales, I don’t know why he couldn’t do it for us?”2
These arguments are riddled with problems. To see why, we need to take a closer look at the human pharynx.
How It Works
In addition to the structures identified in the figure above, fifty different pairs of muscles, connected by six different nerves, are needed to swallow. After food in the mouth has been formed into a small ball (bolus), the tongue voluntarily moves it to the pharynx, which automatically triggers the involuntary swallow reflex.
As the bolus enters, the pharynx sends sensory information to the swallow center in the brainstem, which immediately turns off respiration so that air is not breathed in during swallowing. This prevents the lungs from drawing food into the airway. The brainstem also sends precisely ordered signals telling the various muscles to contract and move the bolus downward into the esophagus, bypassing the airway. This takes about a second.
As swallowing begins, several muscles contract to move the bolus into the pharynx, while moving the back of the palate and the upper pharynx close together to close off the path to the nose.
Next comes the tricky part. The bolus has been blocked from going up into the nose, and muscular contraction is hurtling it down towards the airway and the esophagus. Three separate actions take place to protect the airway. First, muscles contract to close the larynx, which is the gateway to the lungs. Second, other muscles move the larynx up and forward (which you can feel in the front of your neck while swallowing) to hide it under the floor of the mouth and the base of the tongue while being protected by the epiglottis. Third, this action, combined with other muscular activity, opens the upper esophagus to allow the bolus to enter.3The timing and coordination are remarkable. The swallow center must send the right signals via the right nerves to the right muscles, with the exact right split-second timing. Since all this is triggered by the bolus entering the pharynx, the signals from throat to brainstem and back to the many muscles involved (with their reaction times) must be fast enough to prevent choking.
While critics seem to miss the amazing design of this system, it should give the reader pause. Somehow, swallowing happens, usually without incident, a thousand times a day.
Where did the information come from that specifies the size, shape, position, and range of movement of the pharynx, each of its nearby structures, and the fifty pairs of muscles involved in swallowing? How could such a system come about gradually, by accident?
Where did the information come from to make the swallow center in the brainstem and the logic it uses to control safe swallowing? Where is the repository for the information needed to orchestrate the precisely ordered, well-coordinated contraction sequence of fifty pairs of muscles?
Scoring the Pharynx-Is-Poorly-Designed Argument
With that primer on the pharynx and the swallowing system of which it’s a part, let’s now score the argument that the pharynx is badly designed and therefore not intentionally designed.
1. Not Understanding the Design of the Pharynx
The pharynx affords us the dual abilities to breathe and swallow food and water, but it does much more. It affords the ability for speech, language, and tonal activities like lyrical speech and singing. The percussion and acoustic shaping of the tongue, teeth, throat, oral and nasal cavities, and most of the other parts of the pharynx, are absolutely required for the nuanced communication that’s essential to the human experience. So the pharynx has at least three major functional design objectives. If you were asked to design a system with these capabilities, how would you approach it? How would your design make the trade-offs needed to do all this with a single system? If you used separate systems, as advocated by the critics above, how would you achieve the right kinds of functions, and how would this affect how these functions are packaged into the body as a whole? The critics ignore these questions, apparently because they haven’t bothered to understand the design of the system, as a system — either its core objectives or the orchestration of its many parts.
2. Not Considering Trade-Offs when Criticizing the Pharynx
Clearly, the pharynx’s main three functions cause design conflicts that must be solved. We could use two or maybe even three separate systems to achieve these vastly different goals. However, since all three functions need similar components, two or possibly three copies of many of these structures would be necessary. If, as the critics recommend, we were structured to use the mouth only for swallowing food and water, and not for breathing, thereby precluding speech and language as we know it, the nasal passageways would need to be much larger to bring in enough oxygen during high levels of activity.
To keep all three functions, duplication of parts may be an option. We’d need two mouths, one for eating and another for breathing and speaking, and we’d need two large pipes, one for air and the other for food. We’d need two tongues, one for manipulating food in the eating mouth, and another for speaking in the breathing/speaking mouth. For making the hard-consonant sounds in speech, we’d need something like teeth in the breathing/speaking mouth, but we’d also need teeth for chopping up food in the eating mouth. For making complex tonal sounds, the nasal cavities would need to be attached to the breathing/speaking mouth. But we’d also need the nose’s smell sensors in the eating mouth in order to fully experience the taste of our food. We could go on, but you get the idea.In the end, the anatomical changes for either scenario, precluding or preserving speech and language as we know it, would require a complete reconfiguration of the head and neck and possibly also some parts of the lungs and stomach in the body’s core. At a minimum, an increase in the size of the nasal passageways would require the head and face to be much wider. But to house duplicate systems, the volume of the head and neck would need to roughly double, and depending on the positioning of the two mouths, the passageways to the lungs and stomach would likely need to be rearranged too.
Maybe if our bodies were shaped more like a whale, this would work better, but of course this might make it harder to climb mountains. Or even to turn our heads quickly.
Building these different functions into a single set of components, with the programming and orchestration to make them work properly, is another example of elegant invention. The obvious trade-off is that it’s possible to choke, never mind how well-designed the system that’s in place to avoid this problem. Of course, the critics also neglect to consider whether it would be easier or harder to choke in a system with two mouths, as the risk of this happening would be their relative positions to each other.
The marvel is that the system combines these three separate functions in such a compact space, and the whole works so well at all three of its core functions.
3. Not Acknowledging Pharynx Degradation over Time
How and why do humans die from choking? One common cause of swallowing problems is neuromuscular injury or degeneration related to aging or disease. Since swallowing requires precisely orchestrated contractions of many different muscles, any condition that compromises nerve or muscle function can lead to difficulties in swallowing. Common conditions include stroke, Parkinson’s disease, and multiple sclerosis (MS), each of which puts the person at risk for aspirating food into their lungs and choking to death. These represent about half of the annual deaths by choking. One could argue that the body’s inability to fight off Parkinson’s or MS is also a design flaw, but these are also instances of degradation. Complex systems always degrade over time and generations, so it’s unrealistic to think this should never happen to the human body if it were well designed.
Another common cause of choking is user abuse. When a healthy adult takes in too large a piece of food, or doesn’t chew sufficiently, or a child takes in a foreign object like a small toy, these objects can get stuck in the airway and choking results. One could insist that the design should have been foolproof against such abuses, but this merely takes us back to the question of trade-offs.
To even hope to make the system abuse-proof, the three functions of the pharynx would have to be divided out into two or three separate systems, and we’ve already seen all the problems that attend that strategy. Moreover, no matter how carefully an engineer designs a product, it’s always at risk of being misused and, due to wear and tear, its functional capacity lessening over time.
4. Jumping from Poor Design of the Pharynx to No Intentional Design
Even if we were to grant for the sake of argument that the pharynx is a case of shoddy engineering, it wouldn’t follow from this alone that it wasn’t intentionally designed (as the Yugo car and Tacoma Narrows bridge aptly illustrate). The evolutionists who reach this unsound conclusion perhaps get there by embracing the false premise that poorly designed things must be unintentionally designed things, and combining it with the equally mistaken view that the pharynx is a botched design. But perhaps the error is a bit subtler.
In logic, one of the formal fallacies is known as affirming the consequent. That logical fallacy runs like this:
Major Premise: If A is true, then B is true.
Minor Premise: B is true.
Conclusion: Therefore, A is true.
That’s an invalid syllogism. For it to be valid, the major premise would need to be “If B is true, then A is true.” As it is, the conclusion simply doesn’t follow. This is affirming the consequent, or put more generally, it’s a non sequitur. This may be how the evolutionists above have reached their invalid conclusion, thus:
Major Premise: If A (something came about without intention), then B (it is poorly constructed).
Minor Premise: B is the case: the human pharynx is poorly constructed.
Conclusion: A is true: the pharynx came about without intention.
Even if we granted both premises, the conclusion wouldn’t follow, since it’s an invalid syllogism guilty of affirming the consequent.
It’s not clear that this is exactly how evolutionists are reasoning, but it well may be close to the mark based on their statements.
But wait, there’s more. Professor Lents asserts that “if we had separate openings for air and food, [choking] would never happen.” But in any system that requires breathing air into the body, the opening for the air can become blocked — no matter where you put it on the body or how it’s configured. How will these critics’ “improved” system prevent choking from ever happening?
Even a design that is truly suboptimal in one respect cannot demonstrate that it’s a poor design, since the “suboptimal” feature may simply be the natural outcome of a perfectly reasonable design trade-off. (And as noted, even if a suboptimal feature were a true design blunder, this would not be sufficient warrant to claim that it wasn’t intentionally designed.)
Another error in reasoning: “The human throat is simply too complex for a random mutation — the basic mechanism of evolution — to undo its fundamental defects,”4 Lents insists. But if the human throat is too complex for a random mutation to undo a “design defect,” how could random mutations have built such a complex feature in the first place? And if it works and the species thrives, can it be called a defect?
Or recall this argument from Hafer: “If the Creator could [separate the respiratory from the digestive systems] for the whales, I don’t know why he couldn’t do it for us?”5 Being capable of doing something doesn’t make it a good idea. We could design an iPhone with tires, but this may not be helpful to that device’s purpose. Whales are also able to live their whole lives in the ocean. Why couldn’t the Creator give humans that ability, too? It would certainly cut down on skateboard injuries and fatal traffic accidents. Maybe it just wasn’t the plan.
While the above are likely intended as arguments to poor design, in the end they come across as logical “rubbish,” to borrow a phrase from our British colleagues.
5. Aesthetic Considerations in Evaluating the Pharynx
The two critics above, at least in the quotations above, do not level aesthetic objections against the design of the pharynx. The irony is that if the designer of the human body had taken their advice and used the vastly clunkier and less elegant approach of creating two or three separate systems for breathing, eating/drinking, and communicating in order to minimize choking, the anti-design critics might have lodged an aesthetic argument against such a choice, namely that no properly ingenious “tidy-minded engineer” would have failed to elegantly combine the three primary functions into a single clever system.
Engineers know this game — damned if you do and damned if you don’t, with critics ignoring the question of trade-offs. Engineers develop thicker skins as a natural coping mechanism. (Which, come to think of it, is another clever adaptive design feature of the human body!)
Ingenious Design
Most people swallow a thousand times a day without incident, all the while breathing in enough air, swallowing enough food and water, verbally communicating with nuance, and sometimes even singing. Thus, the rare possibility of choking to death provides little actual evidence of incompetent design. Rather, the human pharynx is more accurately viewed as a clever, elegant solution to a complicated set of competing design objectives, with justifiable choices regarding design trade-offs, within rigid constraints. Further, the solution is profoundly well packaged and even provides a way to equalize the air pressure in the middle ear. This is ingenious design.
No comments:
Post a Comment