[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. Well, today I'm kicking off a discussion 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 Sattler 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 Talkabouts.com. Jonathan, welcome to id the future.
[00:00:58] Speaker A: Great to be here. Thanks for having me back.
[00:01:00] Speaker B: You're welcome. Well, in an article for Evolution news some years ago, you declared that sex, sexual reproduction is the queen of problems for evolutionary theory. Today, I'd like to dive into some of the reasons for that. You note that the origin of sexual reproduction from asexual reproduction has stumped evolutionary biologists for ages. The origin and maintenance of sex and recombination is not easily explainable by evolutionary processes. We're going to look at why that is. And in this and a few upcoming episodes, we're also going to discuss the design and irreducible complexity of some of the systems involved in sexual reproduction. Today we'll cover the irreducible complexity of sperm cells. First, the process of sexual reproduction itself. Why is it such a headache for darwinian processes? Well, Jonathan, let's start with the first reason you give that it's a waste of resources in producing males. Popular science writer Carl Zimmer has written that sex is not only unnecessary, but it ought to be a recipe for evolutionary disaster. Can you explain what he's talking about there?
[00:02:09] Speaker A: Absolutely. So there are a number of reasons why the origin of sex is a conundrum for evolutionary theory. For one thing, there is, as you mentioned, the waste of resources in producing males. So remember that only the female can get pregnant and give birth to offspring, and that's, of course, roughly 50% of the population. So if we assume that a sexually reproducing female gives birth to an equal number of male and female offspring, then only half of the progeny are going to be able to go on to have more offspring, in contrast to the asexually reproducing species where all the offspring are able to go on to reproduce. And so it's to be expected that the asexual individual is going to be able to proliferate, on average, at twice or double the rate of the sexually reproducing species. And so one would expect, given this disadvantage, that the sexually reproducing species would be very quickly outcompeted by the asexually reproducing species. And also we have to keep in mind that in contrast to the asexual species, the females of the sexually reproducing species perpetuate only half of their successful genotype. Right. Because they're only passing on one of each of the pairs of homologous chromosomes to their offspring. And so to transition from a state of asexuality to sexual reproduction is, in effect, to gamble with half of one's successful genotype. But given that the whole point of natural selection is the preservation of those organisms which pass on their successful genes, this seems to strike at the heart of the evolutionary rationale. So this is, I think, a formidable challenge to account for the origins of sexual reproduction. And yes, there are some benefits that could be acquired through transitioning from asexual to sexual reproduction. We'll talk about some of these later, but these are only realized in the long term, whereas natural selection is blind to long term advantages and can only preserve what is advantageous in the here and now. And it seems that in view of those very profound short term disadvantages, the sexually reproducing species would, in the short run, be outcompeted by the asexually reproducing species. And so it seems that it is difficult to envision sexual reproduction getting off the ground in terms of an evolutionary account.
[00:04:37] Speaker B: Right? Yeah, it certainly reduces the selective advantage there. Well, another problem lies in the type of cell division that's involved in sexual reproduction. Tell us about the differences between meiosis and mitosis.
[00:04:50] Speaker A: So mitosis is the mechanism by which somatic cells in our body divide. Now, somatic cells, of course, it's derived from the greek word soma, which means body. And these refer to cells are not sex cells. Right. So most cells in our body divide by mitosis, which eukaryotic cell division is made up of interphase, which makes up the majority of the eukaryotic cell cycle. And then the culmination of the eukaryotic cell cycle is what we call mphase, or mitosis, which is made up of a number of different stages, prophase, prometophase, metaphase, anaphase and telophase. And at metaphase, the chromosomes are aligned along the equatorial plane of the cell, along the equator, the midpoint of the cell, and the sister chromatids are tethered together by a protein called cohesion. And upon onset of anaphase, the cohesion ring gets cut and the sister chromatids separate and are pulled apart towards the poles of the cell. And so that is how the genetic information is segregated from one generation to the next of cells. Now, when it comes to meiosis, there are a number of important differences. So meiosis pertains to the germ cells. So the germ cells undergo meiosis to give rise to the sperm and the eggs. And essentially, it's a form of cell division that results in daughter cells that have one half the chromosome numbers as the original cell. Mitosis results in two diploid cells that have two copies of each chromosome, whereas meiosis results in four haploid cells, so they have one complete set of chromosomes instead of two. So in humans, this means that the chromosome number is reduced from 46 chromosomes to 23, and then the joining together of a sperm egg during fertilization returns the number of the chromosomes to 46. And meiosis involves two rounds of cell division, as opposed to just one. So, like in mitosis, you have s phase, where the genetic material, the dna, divides, but you only have one round of s phase. So you have one round of dna duplication, and then you have two rounds of cell division. So in meiosis one, you have the homologous pairs of chromosomes that get separated into different nuclei. So chromosome number is divided in half, and then in meiosis two, which is very similar to mitosis, the cystic chromatids are separated into separate nuclei. And so there are some significant differences between mitosis and meiosis. And it's not at all obvious that you can simply transition from one to the other by an easy evolutionary pathway.
[00:07:39] Speaker B: Okay, so two very distinct types of cell division with no clear evolutionary pathway between them, you're saying? Well, what about the problem of male and female complementarity? Is that just a remarkable coincidence of coevolution as well?
[00:07:54] Speaker A: Yeah. So, as we'll discuss further in due course, the sperm cell needs to be particularly designed to encounter and penetrate the egg cell. And moreover, the male anatomical parts need to be designed in a manner compatible with the female anatomical parts so that the sperm may be delivered. So the need for male and female complementarity depends upon codependent evolution, coordinated evolutionary changes. And so this, again, is an enigma, I think, for the standard evolutionary account.
[00:08:24] Speaker B: Sure. Well, when you originally wrote the article on this, you reported on two studies with very different claims about the origin of sexual reproduction. One claimed it was to prevent death by parasite, while the other claimed it evolved to limit evolvability. Let's start with the first claim. Why would sex evolve to prevent parasite infections?
[00:08:45] Speaker A: Sure. So this is based on a study that was published in 2011 in the journal Science. The title is running with the red queen. Host parasite coevolution selects for bi parental sex. So the red queen hypothesis is named after the red queen from Lewis Carroll's through the looking glass, where the red queen famously tells Alice, it takes all the running you can do to stay in the same place. And so the idea is that sex provides the benefit of producing variation so that the species can have an advantage that allows it to survive. And so in this particular paper, the researchers used the roundworm canohabditis elegance and the pathogenic bacteria seratia markhenzins to create a host parasite coevolutionary system. So they genetically manipulated the sea elegance mating system, resulting in populations mating either sexually or by self fertilization or a mixture of the two. And populations were then exposed to the bacterial parasite, and it was discovered that the population itself fertilized were driven to extinction, whereas the sexually reproducing organisms were not. And so there is a benefit that is conferred by sexual reproduction there in terms of allowing the sexually reproducing species to survive because it has more variability than the asexually reproducing species.
[00:10:13] Speaker B: Okay, but what's the biggest problem with this proposal then?
[00:10:17] Speaker A: Yeah, absolutely. So the fact of this obvious advantage obviously doesn't explain how sexual reproduction arose in the first place, right? Indeed, such immense genetic flexibility is of benefit only to future generations and not to the present population. But natural selection, of course, doesn't have foresight. Right. It's not able to retain biological features or phenomena for their potential future utility. And so the problems that we discussed already, I think, are potent short term disadvantages which would have mitigated against sexual reproduction evolving in the first place. And moreover, sexual reproduction is a phenomenon of such complexity that sufficient to render extremely unlikely to evolve by mutation on a frequent enough basis that we might expect it to become fixed by virtue of a few organisms somehow surviving. These obvious disadvantages and the efficacy of the red queen hypothesis has been increasingly challenged of late. And moreover, in order for theory to work and provide enough of a selection pressure, presumably there would have to be an awful lot of parasites that have quite significant effects. So I don't buy this red queen hypothesis as being an adequate account of the origins of sexual reproduction.
[00:11:35] Speaker B: Okay, well, what about the second proposal you previously reported on, that sex evolve to constrain macroevolution, which is large scale species level evolution. What's wrong with that?
[00:11:48] Speaker A: Yeah, so this is from paper by Heng and Gorillik.
And Heng. And it was published in the journal Evolution in 2011. And they reviewed evidence that sex actually acts as a constraint on genetic variation in order to promote the survival of a species identity, so preventing species a from morphing into species b. And so they argue that sex, in fact, acts as a course filter, weeding out major genetic changes, such as chromosome mole rearrangements, but permitting minor variations, such as changes at the nucleotide or gene level, that are often neutral. But thesis that sex evolved in order to prevent macroevolution, I think renders it even more implausible that the grander claims of evolution, that all extant species are the product of descent with modification as a result of random variation acted upon by selection.
[00:12:44] Speaker B: Yeah, well, these are certainly creative proposals, but they don't seem to be addressing the difficulties that arise from an evolutionary framework. Well, you use a quote in your writing about this that seems fitting here. David Tyler, a professor emeritus at Manchester Metropolitan University, says this, time and time again, Darwinists fill the gaps in knowledge with their theoretical models. But sooner or later, the next generation of scholars will realize that Darwinists have constructed a virtual world that does not match the real world revealed by research. So is that what's going on here with regard to explanations of sexual reproduction?
[00:13:23] Speaker A: Yes, I think many attempts at offering an evolutionary explanation of sexual reproduction and indeed other biological phenomena fail to seriously grapple with the incredible organized complexity and delicate regulation and control of these systems that we observe in biology in the real world.
[00:13:43] Speaker B: Yeah, and I think that virtual world that they set up with some of these proposals, Beh makes a distinction between conceptual precursors and physical precursors. So I think you can have a lot of conceptual precursors, things that make sense in your mind, theoretical models in this virtual world, but it doesn't match up to the real world that research reveals. Well, let's switch gears here and talk about some of your recent writing on this topic. In a recent series of articles for evolution News, you've been discussing some of the key systems involved in sexual reproduction, starting with a look at the irreducible complexity of sperm cells. Here's a bit of what you wrote. Human reproduction is perhaps the quintessential example of teleology in biology. The process by which a fertilized egg develops into an infant over the space of nine months reveals exquisite engineering and ingenious design. Before this intricate process can even begin, there is a need for a sperm cell to fuse with an ovum, each carrying, in the case of humans, 23 chromosomes. This incredible feat bears the unmistakable hallmarks of conscious intent and foresight. Now, for those listeners who are new to intelligent design science, Jonathan, can you elaborate on what is meant by irreducible complexity and why it challenges conventional evolutionary explanations? What are the different parts of the sperm cell that exhibit this irreducible complexity?
[00:15:13] Speaker A: Sure. So the sperm cell is made up of essentially three main parts. You have the sperm head, you have the middle piece, and you have the flagellum. So the head carries densely coiled chromatin fibers containing the haploid genome, totaling half of the genetic material that will be inherited by the next generation. And the other half, of course, is going to come from the mother's egg cell. And the type packaging of the dna serves to minimize its volume for transport. And then on the tip of the sperm head is a membraneous organelle that's known as the acrosome, and it contains various hydrolytic enzymes. And when these are secreted, they actually digest the egg cell membrane, and that facilitates penetration of the ovum or the egg cell. And so if we didn't have the acrosome, the sperm cell wouldn't be able to penetrate the egg cell membrane in order to fertilize the ovum. And so the head, for a number of reasons, is absolutely crucial for the sperm cell's function, which is, of course, to fertilize the egg cell. And then you have the middle piece, which is not the most technical term that you might find, but it is the term that is used in the literature. And the middle piece consists of a central filamentous core around which are many strategically placed mitochondria that synthesize the energy molecule adenosine triphosphate. And the complexity and design of energy generation within the mitochondria, including the processes of glycolysis and the citric acid cycle, which is also known as the krebs cycle or the tricarboxylic acid cycle, as well as the electron transport chain and oxidative phosphorylation, are absolutely mind blowing and a real testimony to the reality of design that could be, of course, a whole set of podcasts in itself. And then, of course, you finally come to the flagellum, which is the organelle that propels the sperm cell towards the egg. And so the flagellum basically beats with a whip like motion to propel the sperm in the direction of the egg. And the sperm cell is essential in humans for reproduction in order for it to arrive at the egg cell in order to fertilize it in the fallopian tube. Flagellated sperm cells are found in almost all sexually reproducing animals. Of course, there are exceptions. So, for example, some crustaceans, like barnacles, produce nonflagellated sperm. And so during reproduction, a barnacle extends its penis out of its protective shell and it reaches towards a neighboring barnacle. And interestingly, since barnacles are permanently attached to a surface, there is a strong selection pressure for penis size in order to reach the neighboring barnacles. And they have, in fact, the largest penis size relative to body length among all animals, which is pretty incredible. So the penis contains a sperm and is inserted directly into the nearby barnacle's reproductive opening. And this transfer takes place through direct contact such that the sperm cells don't need to swim through water. And the proximity of the eggs to the sperm within the reproductive tract ensures fertilization. In the case of barnacles, you can also find nonflagellated sperm in some red algae, such as polysephonia, which, upon release, are dispersed by water currents. Also, the roundworm, sea elegance, produces nonflagellated sperm, although these sperm cells are amoboid. So that means that they move by extending retracting protrusions, similar to how amoeba move by pseudopod formation. That type of movement is known as amobid crawling. And so even though these cells don't have a flagellum, they are able to use their amoboid movement to travel through the hermaphrodite reproductive tract and locate and fertilize the egg cells. But in the case of cligons, of course, in spite of being nonflagellated, they nonetheless possess an alternative system that serves the same role as flagella in conferring motility. So just to summarize then, although the flagellum is absolutely critical for human reproduction, and it's critical, in fact, in most sexually reproducing organisms, there are some exceptions there. But in regards to the head and the middle piece that energizes the sperm motility, these are, of course, crucial for fertilization to take place.
[00:19:49] Speaker B: Yeah, some very interesting and fascinating components there. Well, what about the design and complexity of sperm cells, do you think, challenges evolution and provides evidence of intelligent design?
[00:20:01] Speaker A: Yeah. As we've seen, there are three main parts to the sperm cell. You have the head, the middle piece, and the flagellum, we saw that the head has the acrosome, which releases enzymes that are needed to digest the egg cell membrane in order for the sperm cell to penetrate the egg cell in order for fertilization to occur. And in fact, there was a review paper published in frontiers in Cell and Developmental Biology which says, and I quote, any structural or functional acrosomal abnormality could impair sperm fusion and ultimately result in infertility. Moreover, studies have shown that intracytoplasmic insemination with sperm containing acrozomal abnormalities did not lead to successful fertilization, even in the absence of fertilization barriers, because the usyte was unable to be efficiently activated. Thus, the acrosome is indispensable for fertilization. And the manner in which the acrosome is formed is itself an incredible evidence of design. So, it's divided into four stages. So the first stage, which is known as the Golgi phase, is dependent upon the Golgi apparatus, which produces in packages the proteins and enzymes needed for acrosome formation. And then these proteins then get transported into the developing acrosome vesicle. So, in regards to the middle piece of the sperm cell. So the atp that's generated by the mitochondria obviously is needed to energize the power strokes of flagellum during its journey through the female cervix and uterus and uterine tubes. And as such, the middle piece of the sperm cell is absolutely critical to its function of swimming through the female uterus and fallopian tube in order to fertilize her egg. And so, without the middle piece and its mitochondria, the sperm cells are completely immobile. And now, what about the flagellum? Well, the flagellum is incredibly exquisitely designed. So, unlike a bacterial flagellum, which rotates like a motor, a sperm flagellum beats with a whiplike motion to produce motility. So how does a flagellum work? So, in 2018, Jennifeng Lin and Daniela Nicastro elucidated the mechanism of flagellar motility. Their data indicated that bending was generated by the asymmetric distribution of danine activity on opposite sides of the flagellum. So Danines are ATP powered molecular motors that walk along macrotubules towards their minus end. And their results also revealed that alternating flagellar bending occurs due to a switch inhibition mechanism, in which force imbalance is generated by inhibiting dines on alternating sides of the flagellum. So in other words, regulatory signals lead to the inhibition of dine motors on one side of the flagellum, and meanwhile, on the other side, the dines walk along the macrotubules, and the flagellum bends in one direction due to molecular linkers that resist this sliding. And then the flagellum bending alternates by repeatedly switching the side of dianine inhibition. So could the eukaryotic flagellum be arrived at by a blind evolutionary process? Well, it seems unlikely. To add one dine protein at a time would not lead to a series of intermediate stages, all of which can fare a selective advantage. Moreover, the sperm flagellum is of little utility until the emergence of the alternating regulatory signals that inhibit the dine motors on one side of the flagellum and then the other in a coordinated fashion. And sperm that have flagella are also significantly costlier to produce in terms of energy and time. And this fitness cost has to be offset by a strong advantage, which is only realized after the flagellum is fully operational. And so a proposed intermediate stage is likely to be eliminated by purifying selection rather than preserved. So these are a number of, I think, significant challenges to evolution, and I think that they might make much better sense on a design framework.
[00:23:56] Speaker B: Yeah, so we have strong evidence here that these components are irreducibly complex. We're going to unpack irreducible complexity a bit more in our next episode together, but I think you've teased that out a little bit for our listeners today. Well, as I said, I think this is a good place to pause the discussion, but in another couple of episodes, we'll continue discussing the design and irreducible complexity of key components of sexual reproduction. Jonathan, thank you for your time today.
[00:24:25] Speaker A: Thank you so much. It's been a pleasure.
[00:24:27] Speaker B: We'll include links to jonathan's articles on this topic in the show notes for this episode. You can find show notes for every episode we do and search through our extensive archive of
[email protected]. That's idthefuture.com. Until next time, I'm andrew mcdermott for idthuture. Thanks for listening.
[00:24:49] Speaker A: Visit
[email protected] and intelligentdesign.org. This program is copyright Discovery Institute and recorded by its center for Science and Culture.
