[00:00:04] Speaker A: ID the Future, a podcast about evolution and intelligent design.
[00:00:12] Speaker B: Welcome to id the future. I'm your host, Andrew McDermott. Today I'm sitting down again with Dr. Jonathan McClatchey, fellow and resident biologist at the Discovery Institute's center for Science and Culture. Jonathan was previously an assistant professor at Sadler College in Boston, where he lectured biology for four years. He holds a bachelor's degree in forensic biology, a master's degree in evolutionary biology, a second master's degree in medical and molecular bioscience, and a PhD in evolutionary biology. His research interests include the scientific evidence for design and nature, arguments for the existence of God, and New Testament scholarship. Jonathan is also founder and director of Talkaboutdoubts.com. Jonathan, good to have you back.
[00:00:58] Speaker C: Great to be here. How are you doing, Andrew?
[00:01:00] Speaker B: I'm doing wonderfully. It's a gray day in Seattle, but our hearts are bright as we're sharing the great evidence that we have for intelligent design. What do you think of that?
[00:01:09] Speaker C: Yeah, absolutely.
[00:01:10] Speaker B: Well, you know, the more we're learning about the human body, the more we understand it to be a masterpiece of engineering. The human body contains a vast network of integrated systems all working together to keep us alive. The laws of nature by themselves don't tend toward life. They actually tend toward degradation and death. Without our body's ability to innovate and circumvent these natural inclinations, we'd be toast. So today I'd like to talk with you about one of those amazing systems, our sense of hearing. You've written recently at Evolution News on the topic, and I'd like to amplify the discussion here.
First, let's get the lay of the land by reviewing the basic anatomy of the inner and outer ear. Now, this background information can be found in any good anatomy and physiology textbook, and a good discussion of it's also available in chapter eleven of the book your design body by Steve Loughman and Howard Glixman. But let's break it down here for listeners. How about the key parts of the outer ear first?
[00:02:11] Speaker C: Absolutely. So the outer ear is composed of the oracle, more commonly known as the ear lobe, as well as the ear canal. And the oracle, or the eArlobe, is composed of skin covered cartilage.
Now, in humans, it doesn't particularly matter as far as the sense of hearing is concerned, if we didn't have an oracle or an earlobe. But in dogs that have movable ears, the oracle actually is able to serve as a funnel for sound waves. And so it's more important in canines.
[00:02:48] Speaker B: Okay, so that's the inner ear. And you say it's called the oracle, this outer part that we can touch.
[00:02:54] Speaker C: Yeah. The earlobe is known as the oracle.
[00:02:56] Speaker B: Nice.
[00:02:58] Speaker C: So the ear canal, which is also known as the external auditory metus, is lined with skin that contains ceraminous glands, which, of course, secrete ceramin, which is more popularly known as earwax. And the ear canal is essentially a tube like structure that extends from the outer ear to the middle ear. And its job is to direct sound waves into the ear, which then travel through the ear canal, and they end up arriving at the eardrum, which is also known as the tympanic membrane, which is in the middle ear. And then that causes the eardrum to vibrate as a result of these sound waves, and the vibrations are, in turn, transmitted to the bones in the middle ear.
[00:03:51] Speaker B: Okay, so that brings us to the middle ear, this part between the oracle, or outer ear and that inner ear sanctum. What's going on in the middle ear, then?
[00:04:01] Speaker C: All right, so, so far we've come to the eardrum, or the tympanic membrane, which is essentially this membrane that separates the middle ear from the outer ear, and it's stretched across the end of the ear canal. And then if we move behind the eardrum, we come to three. In humans, there are three small bones, and these are known as oscills, or the middle ear bones. And they're known as the malleus, incas, and stapes. Another alternative name for them is the hammer, anvil, and stirrup. And these oscills essentially form a chain. They're connected to each other. And when the eardrum vibrates as a result of the sound waves, it results in the malleus moving, which in turn causes the incus and stapies to move as well. And so this mechanical linkage helps to amplify the vibrations, and it transmits them from the eardrum to the inner ear. The middle ear is also connected to the neosopharynx, which is at the back of the throat through a tube that's known as the eustachian tube. And that tube basically helps to equalize the air pressure on both sides of the eardrum. And this is really important for maintaining equilibrium of air pressure between the middle ear and the external atmospheric pressure, which allows the eardrum to properly vibrate.
[00:05:31] Speaker B: And, you know, in the articles that you have written, you do include some helpful illustrations and diagrams that show these parts. So, listeners, if you want to see this, go to his articles. The nice thing is, though, that we're not being quizzed on this stuff. And even though it's important to know these terms, I think that's the first step in understanding the complexity that we're dealing with. We don't have to memorize it all. We can trust folks like Jonathan to do that for us. So tell us about the inner sanctum then. We're getting to the inner ear now.
[00:06:04] Speaker C: Sure. So the inner ear is also a cavity within the temporal bone. It's called the bony labyrinth, and it's lined with a membrane called the membranous labyrinth. And between the bone and the membrane is a fluid called the perilimph.
And within the membraneous structure of the inner earlier is a fluid called endolymph. And three of these structures, namely the utricle, the sacule, and the semicircular canals, are important for equilibrium and balance. And the other, namely the cochlea, is important for Hearing. So if you look at an anatomy textbook and you look at the structure of the cochlear, you'll see that it has the appearance of a snail, has a snail like appearance.
And if we were to move inside the cochlear, we would find that it is partitioned into three different canals, and these are all filled with fluid. So you have the uppermost canal called the scalar vestibuli, and it's filled with paralymph, which is similar to the cerebrospinal fluid.
So sand vibrations travel through the cochlea, and they arrive at the scala tympani. And the middle canal is known as the scala media.
Another name for it is the cochlear duct, and it's separated from the scalar vestibuli by the Reisner's membrane and from the scala tympany by the baszler membrane. So the scala media contains endolymph, and it's where the sensory cells of the cochlea, which are also known as hair cells, are located. And now, these aren't actually hair, but they are rather specialized macroville. And these are crucial for converting vibrations of sound into electrical signals that our brains can interpret.
And then above the hair cells is another membrane called the tictorial membrane, which is absolutely fundamental for hearing as well.
[00:08:03] Speaker B: Okay. And what's cool is all these parts are in both of our ears operating all the time. So we can relate, even though this might be new to us, some of this. Well, tell us as simply as you can, what the process is of how our ears actually hear. What's the process of hearing?
[00:08:22] Speaker C: Sure. So the first stage is sound waves being produced from the source of sound. And sound wave is essentially pressure fluctuations, which are transmitted through medium, normally air, although sometimes water. And these waves are funneled into the ear canal by the external part of the ear, that's known as the pena. And the ear canal carries the sound waves to the tympanic membrane, or the eardrum, and that results in the eardrum vibrating. And then these vibrations get transmitted to the malleus, incus and stapes, and that causes the vibrations to be amplified.
And the stapies is connected to the oval window, which is a membrane covered opening to the inner ear. So the vibration of the stapies bone against the oval window creates pressure waves in the fluid filled cochlea. And as the pressure waves pass through the fluid in the cochlear, they cause vibration of the basalar membrane. And this results in the hair cells bending against the tutorial membrane, which triggers the release of neurotransmitters that convert the mechanical vibrations into electrical signals. And then these get transmitted to the brain by the auditory nerve and get interpreted as sound by the auditory areas in the temporal lobes of the cerebral cortex.
And what's really fascinating is that the auditory nerve fibers that carry information from one ear partially cross the opposite side at a structure in the brain stem that's known as the trapezoid body. And this means that signals from both ears get sent to both sides of the brain. And this is crucial in localization of the sound and spatial processing. It allows the brain to compare the intensity and the timing of signals from both ears. And that helps us to identify which direction a particular sound is coming from.
And so, as the impulses arrive from each of the inner ears, the auditory areas essentially count and compare these impulses in order to work out the direction of the sound. And so, for example, if we have more impulses coming from the right cochlear than from the left one, then the brain will project that sound to the right. So you know where the sound is coming from. It's a remarkable engineering.
[00:10:54] Speaker B: Okay, well, our ears are not only responsible for how we hear, they also aid in maintaining equilibrium for the body. Can you explain that?
[00:11:02] Speaker C: A little, yeah. So I mentioned that the cochlear is concerned with sound, and the utricle and sacula are concerned with equilibrium. So the utricle and sacule are, these are two structures within the vestibuli, which is the central part of the inner ear. And they contain sensory cells that are known as autolith organs, which are responsible for detecting linear acceleration. And head position relative to gravity. So within each autolith organ, there are small calcium carbonate crystals that are known as autoliths. And when you move your head, these autoliths shift, and that causes movement of the hair cells and triggers nerve impulses. And so the utricle primarily senses horizontal acceleration, whereas the sacule is more sensitive to vertical acceleration. There's also the semicircular canals, which are three fluid filled tubes that are arranged in perpendicular planes. They each correspond to a different dimension of head movement.
And these canals are responsible for detecting rotational movements of the head, such as turning or nodding. And at the base of each canal is a region called the ampula, which contains sensory hair cells. And the hair cells are embedded in a gel like structure called the cupula. And rotational head movements cause the fluid within the canals to move, and that leads to deflection of the cupilla and stimulation of the hair cells. And this stimulation generates nerve signals that inform the brain about the direction and speed of the head movement. And so the input from the uterus, the sacule, and the semicircular canals provides the brain with important information about the head position, linear acceleration, rotational movements, et cetera. And so this is crucial for maintaining balance and equilibrium, which allows us to adjust our posture, to coordinate our movements in response to changes in the environment and so forth. So, it's, again, remarkable instance of design.
[00:13:20] Speaker B: Yeah, fascinating. Interesting how those two functions are worked within the same system, the equilibrium of our body and also hearing itself. Well, how does the human hearing system stack up to other mammals and animals?
[00:13:38] Speaker C: So, the anatomy of hearing that we just discussed is, of course, the system that's found in humans, other terrestrial mammals, but there are other organisms that have less advanced systems for hearing. So, for instance, fish, they don't have external ears, and they have autoliths that detect vibrations and changes in the water pressure. Reptiles, birds and amphibians also, they don't have an external ear, but they have a single middle ear bone instead of the three found in mammals. And so there's a simpler system. The majority of invertebrates, like mollusks and crustaceans, they don't have ears, don't have a sense of hearing altogether.
It's often thought that the sense of hearing evolved by natural selection. And in discussions of the evolution of the sense of hearing, there's a tendency to focus on these as intermediate stages because you have simpler systems. And so it's thought that you have some organisms that only have one middle ear bone, for example, which is a simpler system than humans, where there are three. And so this could be seen as intermediate stages in the evolution of hearing.
And in fact, the incus mellies and stabies, which are the three middle ear bones found in humans, are thought to have arisen from three reptilian bones associated with the jaw. So, specifically the quadrate bone, the articular bone, and the columnela, respectively.
[00:15:15] Speaker B: Okay, so in your article, you write about the irreducible complexity of vertebrate hearing systems. Now, in case we have anyone tuning in who is not familiar with the concept of irreducible complexity, can you remind us what that is?
[00:15:28] Speaker C: So, the concept of irreducible complexity, that term was coined by Michael Beehy in 1996, and it's the idea that there are many systems in biology which are comprised of multiple, interdependent, and well crafted components, each of which contributes to the system's function, whereby removal of any one of the sub functions causes the overall system to cease to function. And so removing any one of the components results in a system that works not half as well as it used to or quarters well as it used to, but it's completely broken. And so, by an unguided, mindless search driven by chance and physical necessity. How would you build up such an irredimably complex system without knowing where the target is? It seems to require a cause. With foresight, and only intelligence can visualize a complex end goal and bring everything together needed to realize that end goal.
[00:16:23] Speaker B: Okay, so it's not enough to point to simpler systems, which may be simpler by design, and say, oh, well, ours just came from that look, that's simpler. That doesn't equate, does it? Because a common designer could have created simpler systems that are not necessarily connected to or have a pedigree with more complex systems just coming from the same designer. Is that fair?
[00:16:51] Speaker C: Well, I mean, as I said before, there are simpler systems where there will be some organisms that lack one or two of the middle ear bones found in humans. But I would say that one middle ear bone, I would say, is essential for the sense of hearing. So I would say that at least one middle ear bone would be part of the irredisplic complex core of the sense of hearing. And there are other components of the sense of hearing which are absolutely fundamental. So, for example, the cochlea, which contains the hair cells, is absolutely crucial for transducing sound vibrations into electrical signals that can be interpreted by the brain. And one of the leading causes of hearing loss is actually damage to the hair cells. So these are absolutely crucial. You don't have a sense of hearing without those hair cells. In order for sound waves to be interpreted by the brain, you need the auditory nerve, which carries the electrical signals from those hair cells to the brain. And so this is absolutely fundamental and crucial for transmitting the auditory information to the central nervous system.
And in cases when the auditory nerve is damaged, like certain infections, like meningitis, for example, or injuries that can result in a complete and permanent loss of hearing in that ear. So the auditory nerve is absolutely fundamental.
Moreover, the tympanic membrane, or the eardrum, which vibrates in response to sound waves and transmits these vibrations to the middle ear oscills, it's also absolutely crucial to the sense of hearing. If you have a perforated or damaged eardrum, the result of that can be deafeness. You also need the oval window, which is the membrane covered opening between the middle and inner ear, which is located at the base of the sapie's bone. So vibrations are transmitted by the oscars, are transferred to the fluid within the cockway through the oval window. And if you don't have the oval window, there's no hearing.
And as I said before, you need a minimum of one middle ear oscill for the sense of hearing, even if you don't need all three.
So there are irritably complex features associated with the sense of hearing. And so I would argue that this does, in fact, pose a significant challenge to an evolutionary account of the origins of hearing.
[00:19:18] Speaker B: Right. Well, in your article, you say it strains credulity to suppose that an unguided process of random variation, sifted by natural selection could assemble such a delicately arranged system. Are you saying the vertebrate hearing system is beyond the reach of a darwinian process? How do proponents of darwinian evolution typically suggest that this comes about? Yeah.
[00:19:39] Speaker C: So it's widely thought that the middle ear bones and mammals have evolved from bones that were originally part of the jaw joint in early vertebrates. So in ancient jawed fish, the skeletal elements that supported the gill arches were repurposed over evolutionary time to serve different functions. This is the received wisdom. And one of these skeletal elements, known as the hyomandibula, played a crucial role in the jaw joint. And as vertebrates evolved, the story goes that some of these hyomandibula bones became detached from the jaw joint and migrated toward the middle ear region in the ancestors of mammals. And over time, these bones underwent further modifications, leading to the formation of the melleus and incus and the stapes that sought to have originated from a different bone, possibly the hyomendibula or a similar structure. So this is the received wisdom of the evolutionary origins of the middle ear bones. As I mentioned earlier, there's a lot more to the sense of hearing than merely the middle earbones. And this is often what is brought up when one talks about the design of the sense of hearing and the anatomy of the ear and so forth. But as we've already discussed, the ear exhibits iridescent complexity and therefore is, I think, difficult to account for in terms of an evolutionary sort of explanation.
[00:21:09] Speaker B: Right. Just waiting for things to come along slowly and surely. Well, what are some methods we can use to determine irreducible complexity? I think that's pretty interesting, too.
[00:21:20] Speaker C: Yeah. So sometimes this is done naturally by human diseases where part of the anatomy or part of a structure is not functioning as it should. And so you can see what the consequences are, or you can also conduct experiments to knock out various aspects of a system to see what the consequences are of knocking out one particular structure versus another. As I mentioned earlier, in the case of hearing, we know that one of the leading causes of hearing loss is damage to the hair cells, for example. And so that serves as a natural test of the indispensability of hair cells for the sense of hearing.
[00:22:02] Speaker B: Okay, well, where can listeners learn more about the intelligent design and irreducible complexity of our sense of hearing?
[00:22:08] Speaker C: Sure. So they can check out my article, evolutionnews.org. They can also check out the book, your designed body, and in particular chapter eleven, which is on the sense of hearing and the anatomy of the ear.
[00:22:23] Speaker B: Right. And your pieces we can link to in the show description. They're on evolutionnews.org, as you said. And we'll include some other resources as well. But definitely chapter eleven in your design body is a good place to start for more on this amazing system. Well, Jonathan, as always, thanks for taking time to unpack this for us.
[00:22:43] Speaker C: Thank you. Great to be here, as always.
[00:22:45] Speaker B: If you enjoy what you hear on this podcast, consider leaving us a written review at Apple Podcasts helps new listeners find the show, and we do want to share this amazing evidence with as many people as possible. Thanks in advance for your help with that. Well, until next time, I'm andrew Mcdermott. This is Jonathan McClatchey for idthefuture. Thanks for listening.
[00:23:09] Speaker A: Visit
[email protected] and intelligentdesign.org. This program is Copyright Discovery Institute and recorded by its center for Science and Culture.
