[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 concluding a three part conversation with Dr. Jonathan McClatchy, fellow and resident biologist at the Discovery Institute's center for Science and Culture. It 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 of design in nature, arguments for the existence of God, and New Testament scholarship. Jonathan is also founder and director of talkaboutdoubts.com. Jonathan, welcome back.
[00:00:58] Speaker C: Great to be here. Thanks for having me back.
[00:01:00] Speaker B: You're welcome. Well, I've enjoyed this series and we're wrapping it up today. I want to start with this. This is an interesting quote. Charles Darwin's grandfather, Erasimus Darwin, once said that sexual reproduction is the chef duo, the masterpiece of nature. In the first episode of this series, we discussed why the process of sexual reproduction is the queen of problems for evolutionary theory. You explained some of the reasons for that. It's a waste of resources that doesn't provide short term advantages, the very type that a blind, gradual process like natural selection would select for. You also explained that it requires a completely different type of cell division, as well as layers of male and female complementarity, both unlikely products of an evolutionary process. Then we switched gears and unpacked how sex instead bears the hallmarks of a system governed by forethought and engineering. We talked about the design and complexity of key parts of the process of sexual reproduction, including sperm cells, seminal fluid, and sperm capacitation. We also dug a little deeper into the concept of irreducible complexity, how it was coined by biochemist Michael Behy in his 1996 book Darwin's Black Box, what the term means, and a summary of some of the ways that Behe and other ID scientists have refuted arguments against irreducible complexity that have been proposed in the last 25 years. In this concluding episode, we're going to discuss a few more parts of that irreducibly complex core of components involved in sexual reproduction, and we'll remind listeners where you can get additional resources on this topic. First, the design of sperm cells for successful reproduction is only part of the story, as you detail in a recent article. Also essential is the capability of the male genitalia to deliver sperm effectively, and there are multiple biochemical and physiological processes that are all working together in an incredibly coordinated manner. Indeed, if any one piece is missing, as you say, the objective fails and reproduction is a no go. Jonathan, can you walk us through male erectile function? It all starts in the brain, right?
[00:03:12] Speaker C: Yes, that's absolutely right, Andrew. Sexual arousal originates in the brain as a result of sensory stimuli and it leads to the activation of the parasympathetic nervous system. There's a neurotransmitter known as acetylcholine that gets released in response to nerve signals. And the acetylcholine goes on to stimulate the release of nitric acid from nerve endings. And the endothelium, which is the inner lining of the penile arteries, which diffuses into the smooth muscle cells of the penile arteries and the spongy erectile tissue that's known as the corpus cavernosum, where it binds to an enzyme called guanylate cyclase. And if the bioactivity of the nitric oxide signaling pathway is impaired, then that has actually been documented in the literature to be a contributor to erectile dysfunction. And so we know that that is critical for the erectile function. In the male, the binding of nitric oxide to guanylate cyclase facilitates the conversion of guanosine triphosphatep into cyclic guanosine monophosphate, or cgmp, which then binds to and activates an enzyme that's known as protein kinase g. Now this is a kinase enzyme and what's a kinase? So a kinase is essentially a class of enzymes that phosphorylate substrates to result in a conformational change. And in the case of protein kinase G, its role is to phosphorylate the myosin light chain in Smith muscle cells, a component of the contractal machinery in these cells, which results in a decrease in myosine's sensitivity to calcium ions, which are essential for the contraction of muscle. And there have been experiments conducted in mice that have shown that mice lacking the cgmp dependent kinase one have a very low ability to reproduce and that their corpora cavernosa fail to relax on activation of the nitric oxide cgmp signaling cascade. So in smooth muscle cells, calcium ions bind to a protein known as chlomodulan, and this forms a complex that activates myosin light chain kinase. And when activated, this kinase goes on to phosphorylate the myosin light chain and that promotes muscle contraction.
But elevated levels of the cyclic guanosine monophosphate and subsequent activation of the protein kinase g results in inhibition of the mousein light chain kinase. And that makes it less effective at phosphorylating the mausin light chain. So as a result of the decreased levels of phosphorylated myosin light chain, the contractile interactions between the mousin and the actin get impaired. And this leads to the relaxation of the smooth muscle cells as they are unable to contract effectively. So in the flaccid state, the penis exists in a constant, moderate state of contraction.
And as a result, the muscle cells don't exert force, allowing the blood vessels to widen or dilate. And the smooth muscles within the erectile tissue to relax and become enlarged become engorged with blood. And so the increased blood flow fills the erectile tissue, causing the penis to enlarge and become erect. And the erectile tissue also exerts pressure on the veins that normally drain blood from the penis. And this pressure compresses the veins and reduces the outflow of blood from the penis. And this helps to maintain the erection. And in order for the erection to be sustained, the balance between the release of nitric oxide and the breakdown of cgmp has to be maintained. And so phosphodiesterase five is an enzyme that is responsible for breaking down the cyclic guanazine monophosphate by cleaving its cyclic phosphate bond, converting it to inactive guanosine monophosphate. And then this leads to the reversal of smooth muscle relaxation and allows the blood vessels and tissues to return to their normal state. And so when sexual arousal subsides or the sexual activity is finished, the stimulus for nitric oxide release diminishes. And then this leads to decrease in the production of cgmp and the role of phosphate esterase five in breaking down. CaGMP thus serves as a natural regulatory mechanism to ensure that erections don't persist indefinitely. So it's extraordinary engineering and design.
[00:07:51] Speaker B: Yeah, sounds like it. And it's not something we think about too often. And I remember you talking in another episode about one way to look at irreducibly complex systems is to reverse engineer them. And also another place that comes up is when you're looking at disease and when things are not functioning as they are designed or as they should. And so we do see that if we look at these systems, whether it's erectile dysfunction or infertility, we don't often get close to this complexity until there's a problem. But there is also cause to get into it a little bit and appreciate it more. Well, equally important in the process is the ejaculatory reflex. How does this system work?
[00:08:37] Speaker C: Right. So it's essential to be able to deposit the sperm cells and the seminal fluid into the vaginal cavity. And so not only is the erectile function important, but so is the ejaculatory reflex, which deposits the sperm and the seminal fluid. So sexual stimuli activate sensory receptors in the genital region, particularly in the head of the penis, which is known as the glands and surrounding areas, which in turn send nerve signals through sensory nerves to the spinal cord.
So these nerves are part of the pudental nerve pathway, which transmits sensory information from the genitalia to the sacral region of the spinal cord, where they're processed by a network of interneurons which relay the signals to motor neurons that control the muscles that are involved in ejaculation. So within the sacral spinal cord, there is a specific region that's known as the spinal ejaculation generator. And this center integrates sensory information and coordinates the activation of motor neurons that control the muscles that are involved in ejaculation, which include smooth muscles of the vast deference, seminal vesicles and prostate gland, as well as the skeletal muscles in the pelvic floor region. So the initial phase of the jacular de reflex is known as emission. And during this phase, the smooth muscles of the vas, deference and the associated structures contract rhythmically, propelling the sperm and the seminal fluid from the testes epidibidmus and the accessory glands, which include the seminal vesicles and the prostrate into the ejaculatory ducts. And the ejaculation reflex also includes the closure of the bladder neck, preventing the backflow of semen into the bladder.
There are rhythmic contractions of the skeletal muscles in the pelvic floor that propel the semen through the urethra and out of the penis. And this is accomplished by intense pleasurable sensations known as orgasm, which are mediated by the release of neurochemicals such as dopamine and endorphins in the brain. And then after ejaculation is finished, males typically experience a refractory period during which further sexual arousal and ejaculation are not possible. And so we see incredible design in the ejaculatory reflex as well as the male erectile function.
[00:11:00] Speaker B: Fascinating. Well, you've also done some research on the irreducible complexity of female egg cells. You were telling me the other day about a sort of homing device for sperm to help them move closer to an egg during the process of fertilization. Can you explain the process of sperm chemotaxis?
[00:11:17] Speaker C: Yeah, absolutely. So egg cells release chemicals are known as chemo attractants, and these serve as signaling molecules that generate a concentration gradient. And the sperm cell is capable of process known as chemotaxis that results in the sperm cell moving up the concentration gradient towards higher chemo attractant concentrations. And so changes in concentration of the chemo attractants are detected by specialized receptors on the surface of sperm cells. And when they detect an increase in concentration, that triggers a signaling cascade within the cell, which influences the beating pattern of the sperm flagellum. And thus the sperm moves progressively in the direction of the egg, which is a source of chemo attractance. And as the sperm swims towards the egg, the concentrations of chemo attractants is continuously being measured, which allows it to make adjustments to its course in order to fine tune its movements. And once the sperm gets within close proximity of the egg, it encounters other signaling molecules that further guide the sperm cells and direct it towards the egg's plasma membrane, which is a site of fertilization.
[00:12:26] Speaker B: Wow. See, that's a process I did not know about and didn't get in school. Well, what happens upon contact between the sperm and the egg cell?
[00:12:34] Speaker C: Yeah. So upon reaching the egg, the sperm cell encounters the zonapalucida, which is this glycoprotein rich matrix that surrounds the egg and sperm. Egg recognition begins with the interaction between glycoproteins on both the sperm surface and the zona polucida, thereby guiding the sperm cell towards the egg cell surface. So in a previous episode, we talked about the acrosome, which is a specialized structure that's possessed by sperm cells, that contains enzymes that aid in penetrating the egg's protective barriers. And so contact between the sperm and the zonapalucida results in the acrosome undergoing exocytosis, releasing these enzymes. And these enzymes then help to create a pathway for the sperm to arrive at the plasma membrane of the egg, and once through fusion, occurs between the egg and the sperm's plasma membrane, thereby allowing the sperm's genetic material to come into proximity with the egg's cytoplasm. So upon fusion of the plasma membranes of the sperm and egg, various changes are triggered in the egg. These are collectively referred to as egg activation. So first, the egg's membrane becomes less permeable to other sperm in order to prevent a single egg from being fertilized by more than one sperm. So the fastblock to polyspermy involves changing the electrical properties of the egg's plasma membrane. So when the sperm's outer layers are successfully penetrated by the sperm cell, it triggers the release of calcium ions from intracellular stores in the egg. And the influx of calcium ions serves as a signal to initiate changes in the egg's membrane potential. Iron channels on the egg's membrane are opened and facilitate the entry of sodium ions. And the consequence is that the egg's plasma membrane depolarizes. Normally, the egg's membrane is maintained at a negative resting potential, but the influx of positive sodium ions neutralizes that negative potential, making the membrane potential less negative. And the altered membrane potential makes it more difficult for other sperm to initiate the fusion process and thereby creates a temporary electrical barrier that inhibits additional sperm from fusing with the egg.
And the depolarization is a temporary phenomenon. So after a brief period, the egg membrane potential is restored to its normal resting state, which is often referred to as resetting the egg. Now, there's also a secondary defense against polyspermy that's known as the slow block or the cortical reaction. So as calcium ions are released upon fertilization, this triggers the exocytosis of cortical granules located just beneath the x plasma membrane containing enzymes. And the glycoproteins in the zonapalucida are cross linked by these enzymes, and this results in the hardening of the zonapalucida, reducing its permeability. And the modified zonapalucida forms a structure known as the fertilization envelope, which surrounds the egg and that forms a barrier that physically blocks additional sperm from gaining access to the egg's surface. Changes also take place in the egg cell that promote the completion of meiosis and initiate early embryonic development. So the genetic material of the sperm and egg, which consists of a single set of chromosomes, each 23 chromosomes in humans combine together to form a diploid cell, which is known as a zygote, which contains the full set of chromosomes needed to develop a new individual. And this instantly determines characteristics like gender and eye color and many other traits. So, after fertilization has occurred, the zygote then begins to undergo a series of rapid cell divisions through a process known as cleavage. And this results in the development of a multicellular embryome, which travels through the fallopian tube towards the uterus and eventually arrives at the uterus and attaches to the uterine lining. And this is, of course, called implantation, and the development of the infant can commence.
[00:16:28] Speaker B: Well, what about the process by which egg cells are formed, known as eugenesis. What can you tell us about this?
[00:16:35] Speaker C: Yeah. So, eugenesis begins during embryonic development, when the primordial germ cells are specified, and these cells migrate to the genital ridges, which later develop into the female ovaries. Before the female is born, the primordial germ cells undergo mitotic divisions to form ugonia, which are the precursor cells for eggs. And these ugonia transform into primary oocytes, which are diploid. Cells are arrested in prophase, one of meiosis, and this arrest typically occurs before or shortly following birth. So they're essentially locked in prophase, one of meiosis.
The primary oocytes are surrounded by somatic cells to form primordial follicles, which go through a process known as folliculogenesis, where they develop into primary, secondary, and ultimately tertiary follicles. So as the female reaches sexual maturity, some primary usytes are activated each menstrual cycle. And the activated primary usyte completes meiotic division one, resulting in the formation of a secondary usyte in a polar body. But the secondary usyte is arrested in metaphase two, and the mature follicle ruptures during ovulation, releasing the secondary oocyte into the fallopian tube. So if it's fertilized by a sperm cell, the secondary oocyte completes meiotic division two, and this results in a mature egg or an ovum and another polar body. And if fertilization does not occur, then it doesn't complete meiosis two. So, following ovulation, the remaining follicle transforms into the corpus luteum, which secretes hormones like progesterone to prepare the uterus for a potential pregnancy. And if fertilization doesn't take place, the corpus luteum degenerates, resulting in a drop in the levels of hormone, and this triggers menstruation, and the cycle resets and begins again.
[00:18:32] Speaker B: Very interesting. Well, in one of your articles, you say this. It is implausible that such a complex system arose in a stepwise fashion, as envisioned by neodarwinian evolution. Why do you call these processes involved in sexual reproduction irreducibly complex?
[00:18:49] Speaker C: So, we've seen through this series of podcasts several different aspects of sexual reproduction that are indispensable or essential for the process to work. You have to have the various components of the sperm cell. You have to have the head, with its acrosome and the middle piece and the flu gellum or some alternative arrangement for the sperm cell to actually make it to the egg to fertilize it. So that is essential. You also have properties of the seminal fluid which are crucial for fertilization, such as its alkaline properties, for example, which neutralizes the acidic ph of the vaginal cavity of the female. You have to have the means of transporting the seminal fluid and the sperm to the female. So you have to have the erectile equipment and the ejaculatory reflex has to work. The egg cell has to be very carefully designed in order to respond appropriately upon fertilization and so forth. And so if any of these aspects of sexual reproduction were different or nonexistent, then sexual reproduction couldn't take place. And so you require multiple codependent sub functions to work together to achieve the higher level purpose of sexual reproduction.
[00:20:05] Speaker B: Yeah, and we've tried to tease out a little bit of detail on irreducible complexity in this series because it is the key component here. And listeners, if you're wanting to dive deeper, there's plenty of places for that. And we'll mention that next here. So, Jonathan, where can listeners turn for more information and resources on this particular.
[00:20:27] Speaker C: Topic so they can go to my
[email protected]? On the topic of sexual reproduction. There's also discussion of it in your design body by Howard Glixman and Steve Laughman. These would be some good resources. I would recommend going to, to learn more about this topic.
[00:20:48] Speaker B: Okay. Yeah, they have three or four chapters in your design body on these particular topics that we're mentioning. So that is definitely a good book to turn to for that, as well as Jonathan's different articles, which we will certainly link to in the show notes for this series. Well, by the way, listeners, in case you're not a regular visitor to it, evolutionnews.org, where a lot of Jonathan's articles are stored and appear at, is about the best place you can go, at least online, for timely and dependable coverage of intelligent design science and the debate over darwinian evolution. As I said, it's where you'll find Dr. McClatchy's articles, as well as a host of other scientists and scholars. It's great for the latest news, as in what just happened yesterday or this week in these things, but it's also got a robust archive going back 1015 years. So all you need to do is search a keyword that you've heard somewhere and off you are with multiple articles at your disposal. So be sure to bookmark evolutionnews.org as a great resource. Well, Jonathan, I appreciate you taking the time to unpack some of your writing on this topic of sexual reproduction. Like a lot of remarkable biological systems, we tend to take this one for granted. But as Michael B. He says in Darwin's black box, in order to understand the barriers to evolution, we have to, quote, bite the bullet of complexity.
He also says, to appreciate complexity, you have to experience it. So, listeners, it might be a little difficult to follow what Jonathan says at times, but just stick in with it, because we do. We have to bite the bullet and experience that complexity in order to truly understand it and see what's capable of it. You're helping us experience Jonathan, this complexity by carefully explaining it and also helping us to understand it. So thank you very much.
[00:22:46] Speaker C: Thanks for having me.
[00:22:47] Speaker B: If you missed parts one and two of this series on sexual reproduction, be sure to go back and enjoy them. You'll find them in your favorite podcast player. And you can also access every episode on YouTube now as well. Learn more about Dr. McClatchy's work at his website, jonathanmcclachey.com, and for hundreds more episodes of id the future, including show notes. For every episode, you can go to idthefuture.com. Well, for idthefuture, I'm Andrew McDermott. Thank you for listening.
[00:23:19] Speaker A: Visit us
[email protected] and intelligentdesign.org. This program is copyright Discovery Institute and recorded by its center for Science and Culture.
