Welcome to Stuff to Blow Your Mind production of My Heart Radio. Hey you welcome to Stuff to Blow your Mind. My name is Robert Lamb and I'm Joe McCormick. And for the next few episodes we're going to be doing a series on a symmetry. And to introduce this series, I wanted to talk a little bit about a favorite animal of ours, the nar wall. Yes, the what is it, the corpse whale um of of the ocean, the unicorn of the sea. Right, yeah, so corpse whale. That's literally what its name means, whale of course wall, but nar meaning corpse. So yeah, it's like a dead body whale, having to do with its gray and modeled appearance as it sort of floats around near the top of the water. But the more famous feature of this whale, apart from looking like a corpse, is its horn or tusk or we can dispute what's the best word to use for it here, but yeah, as you say, it is the unicorn of the polar seas. So the nor wall is a medium sized Arctic marine mammal in the suborder of toothed whales or Odonto ceti. And it is immediately recognizable because most males of the nar walls, and occasionally some females as well, possess a giant spike or tusk growing straight out of their faces. And this tusk can grow absurdly long, up to about three meters or ten feet, and the orientation of this tusk looks very unusual compared to most other mammals. So you think about other mammals with horns or tusks. Uh, you might think about bo vines in which the horns rise up off the top of the head, or you might think about the rhinoceros where it points up from the end of the snouts kind of you know, up from the ground. Or you might think about the tusks of a bore an elephant kind of coming out of the mouth at an angle. But but no, in the In the narwhall, you have a whales body, which again is a sort of modeled gray tube that can grow about four to five meters long in adulthood, and then the tusk just juts straight out of the face, adding another three ms or so or up to another three ms or so in length. So when the tusk is present, the animal is sort of shaped like a dart. Or like a spear. Now, when we've talked about in Our Walls before, I think, especially in our episodes on the unicorn legend, uh, we we talked a lot about the theories behind the origin and the purpose of the tusk. We're not going to completely rehash that discussion here, though, I did want to note a development which was in a more recent paper I came across addressing the biological function of the tusk. So a long running question for marine biologists who study the nar wall is why this giant tusk it's it looks very unwieldy. What is it for? What is the evolutionary justification? And this can be difficult to study because it is not a trivial task to go out and just observed in our walls. In the wild, not only do they live underwater, but they live under the Arctic ice. So they remain veiled in a great deal of mystery. But we're not without some clues. And I guess the place to start is that the tusk looks so threatening to the naive human brain that we immediately want to say it is a weapon, right, you know, it is a spear, It is a dark that That's what I without even thinking about it compared the animal too, right, right, you think of it being some sort of a javelin or spear um harpoon on the front of this, uh, this whale that it's using to to skewer things, or that it's using this to sort of fence with other whales. Yeah, so you think it must be for you know, stabbing sharks or skewering fish prey or something. Though it's funny that people think, oh, yeah, it's for for skewering fish that they're going to eat. But if that were true, wouldn't that be a little awkward? Like how would it get the fish to its mouth after that? Like you would normally you don't need a stab and then eat. If you're a whale, you just eat, You just bite and then swallow. Anyway, there have been some accounts of what appeared to be various offensive uses of the tusk, but these might be coincidental or secondary behaviors. And then there are all other odd proposals, including things like stabbing through surface ice to create holes for breathing. Of course, remember the nar walls and air breathing mammal, but the fact that the tusk is hollow and filled with sensitive nerve endings, has led some researchers to believe it is a sensory organ and there there is some evidence that it can be used for gathering and even potentially for sharing information about the characteristics of seawater, maybe things like temperature, salinity, and so forth. However, one of the most important clues about the primary evolutionary justification of the tusk is the fact of sexual dimorphism. So the tusks are almost always found in males, and one obvious conclud lusion from this is that the tusk can't be necessary for survival, or else females would have them as well. Right, so it can't provide a major individual survival advantage, or else you'd expect all individuals to have them, or we would at least observe, uh, you know, the the whales that have them out competing the other one the ones that don't have them in survival, which is not the case. So one of the leading theories then is that it's a sexually selected trade. It's a body feature without a major role in survival, which grows very prominent in males because it increases reproductive success, maybe by being more appealing to female in our walls, or maybe by causing rival males to stay away and so forth and anyway. As so, the recent paper I found was one by Graham at All published in Biology Letters called the longer the Better evidence that narwhal tusks are sexually selected. This was from and of course this paper acknowledges that it's really difficult to study nar walls in the wild to figure out what the tusk is for, so instead it asks if we can infer anything about tusk function from examining the natural variation in narwhal tusk measurements that have been taken over the course of the last thirty five years. And so their sample comprised two D forty five individual adult males, and based on these measurements, the authors conclude that the evidence does suggest the primary driver of tusk evolution is sexual selection. Quote. By combining our results on tusk scaling with known material properties of the tusk, we suggest that the narwhal tusk is a sexually selected signal that is used during male male contests. So how would you conclude this? Well, the tusk demonstrates a growth pattern known as hyper alimentary, which means a body feature that grows faster than the body as a whole. So, for example, most body features are roughly alometric. They're linearly allometrics. They grow in size proportional to the rest of the body. If your body is bigger overall, you probably also have longer shin bones and larger hands and so forth. Some features might be hypo allometric or you know, sublimetric, they grow less than the body as a whole. But narwhal tusks are hyper alometric. In the largest individuals, the tusks grow longer than simple linear scaling would predict. So they're not just big in proportion to the rest of the body, they're way bigger than that. There they just they get ridiculously huge. And so this is not proof, but it is characteristic of traits that are sexually selected. And the authors write in their conclusion quote, sexually selected signals used in mail mail competition are more likely to exhibit hyper elimetry when compared to other sexually selected traits. Because the information being signaled is simple, I am bigger than you. To convey this message, males exaggerate the size of their signals, which facilitate the detection of size discrepancies. Between individuals, reducing the likelihood of engaging in potentially dangerous fights, and they note that this could explain the so called tusking behavior that's been observed, where male narwhales sometimes appear to be crossing tusks are almost like dueling with their tusks um, which could actually be not a form of fighting, but a way for the animals to compare the size of their tusks in order to avoid a fight. So, in an interesting twist, it could be the case that our naive intuition that this tusk is a weapon is true in a sense, but it's a weapon designed specifically to look scary because it will discourage actual fighting between males and sexual competition most of the time. So it's you know, two rival males are are competing for a chance to mate, and one of them goes, wow, that that other one's tusk is absurdly long. No need to fight this out, my mistakes, see you later. Now. They say that the existing evidence sort of points us in this direction, but it's not conclusive. Their alternate explanations. Maybe the large tusk plays a role in mate choice itself. Maybe females prefer males with larger tusks, but they're in general, there's still just a lot we don't know about these animals, so so the book is not completely closed on this question. And it's also possible that the tusk has multiple secondary functions, for example, as a sensory organ like we talked about earlier. Though again, as I mentioned earlier, that those secondary functions can't be all that crucial for survival or we would see that, you know, we would see that playing out in nar whale populations, the ones with the tusks would be more likely to survive, and that's not what we find now. To bring it back to the reason I wanted to talk about narwhals in today's episode, you may remember one strange fact about the narwhal's tusk from our previous episodes where these animals came up, and it's that the normals tusk is not an external caratinous horn like that of the rhinoceros. Instead, it is a tooth. And I don't just mean it is made out of the same stuff as a tooth. It is literally a tooth. It is a tooth from the upper jaw that has been repurposed by evolution to grow into a tusk. By changing the orientation of growth so that it grows straight out forward forward, out of the jaw and then erupts from the flesh of the face. It literally grows through the flesh of the upper lip and then continues growing rapidly, and as we've seen, even hyper elemetrically. But here's what I've been getting hung up on. The nor Wals tusk is not only a tooth. In almost all cases, it is the left canine, the left maxillary canine tooth having erupted from the upper lip. And this is this is certainly something when you learn for the first time it does it does feel a little bit wrong. I mean, a number of these these factoids about the norwell perhaps feel a little wrong, you know, because ultimately it's just a far weirder and perhaps sillier animal than than most of us assumed. It is not silly, is deadly serious, but it does have one tooth just poking out of its lip for I don't know, ten feet. But you're not allowed to laugh, um so, But yeah, anyway, So, to quote from a paper from in the Anatomical Record by Nuilla at all quote, males usually exhibit an erupted tusk on the left side and an unerupted embedded tusk on the right. So it's got two of these teeth. It's got, you know, that's symmetrical. There's one on each side, except usually one just kind of grows a little bit and then stays inside the upper jaw and doesn't do anything, while the other one breaks through the skin and grows up to ten feet long. So that's what you usually see. But then the quote continues, whereas females usually have two embedded tusks, neither erupting. Other less common expressions of narwhal dentition include males with two tusks, males with two embedded tusks so neither one comes out, females with one erupted and one embedded tusk, and females with two erupted tusks. And I checked. I think there's only been one documented case of the ladder of the females with two tusks coming out. But the authors of this paper do extensive analysis to confirm that these are not horns, they are teeth, and they figure out exactly what teeth they are. They are the upper canines, and in almost all cases, the left upper canine. Now I don't know if I'm alone in this, but I am just as struck by the fact that the tusk is actually the left canine as I am about the fact that it's a tooth to begin with. Why the left canine, As the paper mentions, narwhal's occasionally have two erupted tusks, two tusks of about the same length coming out to other It's rare, but you find some like that, And if you see pictures of the narwhals with two tusks, they look much more appropriate to the preferences of nature. You can look up images of this online. In fact, even though they're much more rare in the wild. Uh. A lot of the images of narwhal skulls have two tusks. I guess because the rare ones get photographed more often. Well, I mean, I guess. On one hand, the left handed side is the sinister side the sinstral side. So if you're going to have a crazy, super long tooth emerged from your face and maybe the sinister side makes sense, well, that's just your twisted mind working. It's it's fancy. I mean, no, come on, like the two tusks, they look more like something that you would just buy intuition expect to find in the ocean, much more so than the common one tusk skull, which when I see it, I mean, it is beautiful, but it also it looks unbalanced and wrong. Though. I will say that the two tusks or wall, if you look up images of specimens of this creature like this one is perplexing as well because it kind of it doesn't form um. They're not perfectly parallel to each other. It creates kind of a V shape that is a little confusing and certainly makes you lean more into possibilities. Yeah, that this is not about stabbing or using these uh these tusks for some sort of a a physical practical use, but something else like that they look more like communications array when you see two of them as opposed to just one. Well, yeah, I think having two of them even further highlights that these are obviously not practically useful for something like like catching prey or eating you know, you just you look at that and it's like, how how's that going to work? And it's obviously they're not using it for that, at least not most of the time. I know. There are these little anecdotes of somebody saying that you know, they saw a nar wall like tap a fish with a tusk or something, so maybe, but that that clearly does not appear to be a prime very use of them. But I wanted to come back to the idea that it looks it looks wrong at least even though of course you know this is what evolution selected. It is, uh, it is right for something, it has a use, but it looks wrong to our brains, and so it causes you to ask the question, well, first of all, why is it that evolution drove the narwhall to be unbalanced in this way? And and second, why is it that my intuition tells me incorrectly that a long, single tusk should not emerge from the socket of the left maxillary canine, like if an animal has one tusk, it should come out of a hole right in the middle. And so this is going to be the beginning of a series of episodes. We're gonna do at least two maybe more. What we'll see, uh, but there will be on a symmetry in the animal world when an animal's left and right do not match. So in future episodes we will we will explore some theoretical questions about about embryonic developed meant and how animal asymmetry comes about. Uh, probably look at some crabs and other crustaceans. But today I think we're gonna we're gonna look especially at like whales and uh and other swimming creatures of the sea, UH, and just generally highlights some interesting examples of asymmetry in the natural world. Now, I think it's important to acknowledge at the beginning that the kind of symmetry or asymmetry we're talking about, the kind of symmetry we expect to see in animals is only one specific type of symmetry, called bilateral symmetry, and not all animals actually possess it, even in an approximate sense. So bilateral symmetry is actually a fairly restricted type of symmetry. There are three dimensions of space, and if you plot a human body on those three dimensions, you'll notice we are actually only symmetrical along one of those three axes. So on height, our head in our feet, of course, are not mirror images of each other. On depth, we're also not symmetrical. Our backs do not mirror our fronts. We don't have faces or butts on both sides. It's only across our width that you find approximate symmetry our left side. Roughly mirrors are right side. And in three dimensional space, the most perfectly symmetrical form is actually a sphere, since if you divide a sphere in half along any plane you want, no matter it's orientation, the two sides will match. Uh. And I hesitate because I'm about to make a generalization about geometry. I'm always afraid I'm gonna say something wrong there. But I tried to look this up and confirm it. I believe this is unique to the sphere, that all other three D shapes can be bisected in ways where the two halves may have equal volume but will not match an outline. But if you cut a sphere in half, it's always two perfect hemispheres, no matter what direction you cut from. And this actually connects to a passage in a book I came across by the mathematician Herman Vile called Symmetry from Princeton University Press in nineteen fifty two, and Vile is writing about about the history of association between symmetry in the geometric sense and the concept of beauty. Uh. You know, moral virtue, and perfection, and he writes quote because of their complete rotational symmetry, the circle in the plane and the sphere in space were considered by the Pythagoreans the most perfect geometric figures, and Aristotle ascribed spherical shape to the celestial bodies because any other would detract from their heavenly perfection. Now it's interesting, knowing what we know now about the cause of spherical objects in space, namely gravity, right that as as the mass of an object increases, it tends to become more and more perfectly spherical, with the I guess the end point of that being that a black hole theoretically is pretty much perfectly spherical, whereas smaller objects in space, because gravity is not as strong a force on the on the smoothing of their outer edges, they can have more irregular shapes. This is why you get irregular potato shaped comets and asteroids. But you know, you start getting up into planet size and you move closer and closer to spherical perfection. But anyway, Vile goes on to quote a poet named Anna Wickham, which was actually the pseudonym of a modernist poet named Edith Alice Mary Harper uh in connecting the idea of symmetry to God or the divine being, so Wickham rights quote, God, thou great symmetry, who put a biting lust in me? From whence my sorrow spring for all my frittered days that I have spent in shapeless ways, Give me one perfect thing, and then vile rights. Symmetry, as wide or as narrow as you may define its meaning, is one idea by which man, through the ages has tried to comprehend and create order. Beauty and perfection. And equating symmetry with beauty, goodness and perfection and even divinity can be found all throughout literature. I think of Blake's The Tiger. You know what immortal hander eye could frame thy fearful symmetry. I guess it makes you want to say symmetry there, But this clearly is has not just a geometric meaning, where you will the two halves of the tiger do match one another roughly because it is an animal with bilateral symmetry, but that it means something more than that. Symmetry here is in some sense synonymous with greatness or divinity. Yeah, it's so that the tiger is is a perfect organism and Blake's I here, um yeah, And you know, I can be said about our obsession with with symmetry to the point where it's like a flawed obsession with it. Like we think that we want, say, perfectly symmetrical faces, when most faces are certainly not a symmetrical And if you take even famous and you know, often held up his beautiful faces and you do the trick of creating a symmetrical symmetrical face out of it, it's going to look wrong to your eyes. It may it may look very well look unnatural. Well. The the whole quest for symmetry in in aesthetic beauty um is one of those where it's like there's almost a kind of inverse uncanny valley. It seems like people's natural preferences or something that tends very close to symmetry. But then if you get right up to it and go to actual symmetry, it's like, oh no, no, no, that that looks all wrong. So you want to be like right in the zone where you're approaching symmetry, but not there. Yeah, though there, Certainly when you get into design it gets it gets weird because take airplanes, for example, airplanes tend to look best to our I when they are perfectly symmetrical, and then there are various reasons for that. And if you see an asymmetrical airplane, and there there have been certainly done some some very asymmetrical looking airplane designs uh uh here and there throughout aviation history, they do look incredibly wrong to the eye. Um, and that shouldn't fly. Yeah, Like how how how is that a good idea? But I mean it can work, it's just you you generally don't see it. Well, there's a different logic at work here. But that just sort of reminds me, incidentally of how I'm always surprised at the idea that a plane can continue to fly with one engine, you know, as like two jet engines, Like one engine fails, but it can keep flying with the other one, which makes that that doesn't seem right. It seems like, well, if only one engine is going, then shouldn't it just sort of like spin out of control? But no, I mean, as long as it's generating forward thrust, it can keep going usually Yeah. But anyway, so there's always a strong argument, you know, that much of what we find beautiful and good is biologically contingent, that it has at least in part to do with the kind of animals we are and how we relate to our environment. And of course we are part of that clade of animal all is known as biolateria. These these are the animals featuring bilateral symmetry during embryonic development. Now, of course this is always approximate, right, because while you're left and you're right in one sense do match. There are mirror images of each other, as you were just talking about, they're not perfect mirror images of each other, and especially on the inside, because we have say, asymmetric distribution of our internal organs, like the hearts more to one side, the livers more to the other, and so forth. But for it, for approximate terms, at least externally are left in our right sides match. But not all animals exhibit bilateral symmetry. Some have radial symmetry, meaning they grow in like repeated structures in a more spiral pattern. And there are some like sponges for example, those are animals, but they have no symmetry at all. But most animals, like humans, are bilaterally symmetrical. As as our bodies grow during embryonic development, they grow into basically mirrored halves on the left and right. But as we've already seen with the narwhale, some animals with bodies that mostly adhere to bilateral symmetry present with isolated but radical deviations, such as the nar walls left maxillary canine turning into a tusk almost as long as the animal itself. And this is not even the only example of fascinating a symmetry in the bodies of whales. Yeah, yeah, I want to get into something that we may have touched on this a little bit in the past, But despite the number of times the whales come up, I don't think we've really gotten into everything here. And it concerns the nature of the blowhole of of whales. Um Again, it just drives home just how mysterious and weird whales really are. Um So I want to start sort of back up before we get to where we're going with this discussion of blowholes, and start with the baileeen whale. You know, these are filter feeders, which, as Ryan Tucker Jones points out in red Leviathan uh the book about Soviet whaling, and interviewed uh Ryan last week on the show. It's really fun episode. If anyone wants to go back and listen to that. But there's he touches on just sort of how intertwined folk tale and legend and mythology is with our understanding of whales and misunderstanding of whales. I want to read this one passage quote. Ancient Greeks knew far less about whales than did the whaling Scandinavians. And as these word origins suggests, whales remain mysterious for Russians. For one thing, baleen whales methods of feeding perplexed them. Lacking teeth, the giants seemed to have no way of capturing prey. One tenth century Russian poem wondered whether wales quote the mother of all fish unquote fed themselves on quote heavenly fragrances. Direct experience was not necessarily more helpful. A medieval Western whaler who cut into a stranded whale stomach and found a gray mass of food included that it had fed on quote internal fog. That's great. So yes, whales are mysterious, and yeah, you can you can imagine if you really didn't know what was going on with the baleen whale, you might have trouble figuring out what's going on with their with with their mouths. What do they truly feed on? What? What is there enough of on the ocean for them to consume if they're not eating our ships and so forth. So anyway, if you look at a baleen whale and you look away from its mouth, you'll notice, yes, it has it has the blowholes. The blowhole falls well in line with bilateral anatomy. There are two of them, in kind of a V shape. And uh, and guess what if you weren't aware of this, here's your your fun Uh. Initial fact, they are repositioned nostrils. Imagining the evolutionary journey of those nose holes. Yes, because that's it is a journey, the nose holes traveling from the front of the snout all the way to the top of the head. I mean, we can imagine it. It's hard to imagine with our own face, but imagine it with a much bigger and more prolonged heading. So, as Raston and Roth point out in a paper published in the Journal of Anatomy, uh, the nasal passage in in these whales has rotated dorsally over the course of evolution and early in development cessation embryos have head morphologies that resemble other mammals, so you can actually look up embryo images and observe the nasal openings shift from the tip of the snout to the back of the head. If you want to see some some some easily accessed examples of this panda's thumb. A science blog has some great images of this in their post whale evolution The Blowhole, and I included these for you to look at here, Joe Um. If you if you look up this blog post, you'll see a trio of images with the embryo and there's a little white ero pointing out where the nostrils are and then where they travel to. It's just as you say, yeah, so earlier in development there there towards the front like they would be on the snout, and more like they would have been on the whales, on the whales land walking ancestors. But yeah, then as development moves on, they move up the head up to where I don't know, I don't know if this is the right terminology, but you might call like the forehead and then further and further. Yeah. Yeah, now it's it's obviously natural selection went this way. Um and it's easy to just sort of assume, okay, natural um evolution and natural selection and knows what it's doing. Who are we to question it? So it's easy to sort of overlook the basic question and all of this, why why does the nostril why did the nose open on? The nasal openings on these creatures wander over the course of their evolutionary development until they're on the top of the head. The basic answer is that while these creatures, yes, technically could still ether through their nostrils when they were positioned at the end of their snouts, they would have to lift their snouts out of the water to do so, and that requires more energy. If it's if you have the nose and the nasal openings positioned higher up on the snout, well, that's less lift required to do so, less energy, And so this is why we have that gradual movement of the nasal openings. And we have fossil evidence to back this up, and there are examples of this in that panda's thumb post as well. We for instance, we have fossil evidence of of Rhodo satus. This is a whale from roughly forty six million years ago, and this one offers a midpoint where we see the nasal opening, not at the end of the snout like we see in uh in really ancient UH whale ancestors, and also not at the top of the head like we see with modern whales, but that midpoint in between. No, I'm not speaking from an expert perspective here, but it seems very sgnificant that the that the blowhole eventually moves back to above where the eyes are right because you can imagine if a whale has to lift its eyes above the surface of the water every time it wants to breathe, or at least to point its eyes up away from where it's scanning. That's really it's not just taking energy. I mean, of course, the energetic investment is significant. Imagine if you had to like lift your head up every time you wanted to breathe, that would that would get tiring after a while. But also if you basically like couldn't see what was going on around you every time you had to take a breath, because you know, you need if you're living under the water, you want to keep your eyes fixed below the water, that's where the relevant stuff is going on. If you have to lift your eyes above the surface of the water. Uh you are you are losing sight of your surroundings exactly. Yeah, this is the world that the whale has adapted to the marine environment, and so over time it just gets to the point where as little of the animal as possible has to breach the surface of the water. Thank So that's basically the symmetrical whale blow hole. But here's the here's where it gets fun. This is where it gets asymmetrical because not all whales have two blow holes. Not all have those two nasal openings repurpose nasal openings on the top of their head. Toothed whales like the sperm whale, have just one. In fact, on the sperm whale, this single blowhole is at an angle on the left side of the head, and this causes it to blow forward and slightly to the left. So this can actually make sperm whale spouts harder to spot for humans, but also makes them easier to identify if you do spot them, because it's not just blasting straight up again, it's blasting forward and slightly to the left. But this, oh, this is this is putting me back in our wall tusk territory. So it has one nostril. So this is not just the nostrils have moved back along the center line of the skull of cross evolutionary time. The nostrils have actually split and one of them has moved back here and the other one, I don't know what it's doing something else, Yeah, the other one. The crazy thing is essentially the one is still open and active. The other one has sealed over the other. So the other nasal passage is there. It just does not connect to the surface anymore. Uh. That doesn't mean it's not doing anything. It has another purpose. So instead of connecting to the exterior of the animal, this other nasal passage supplies air to the phonic lips. The phonic lips produce clicks that travel the length of the nose and through the spermssete oregon of the head UH to aid in echolocation, or at least this is the most well accepted theory of what's going on here with the structure of the sperm whale's head. So echolocation is using sound waves in order to be able to UH image underwater to see where things are not with vision, but by producing clicks that like hit things in the water and then come back to the sensory organs on the whale so they can navigate their environment. And as specifically, I think nowhere prey is in the dark waters. Yeah, so if you dive in down to eat yourself some some squids, some giant squid maybe, uh, this is what you would you would use. Now. The evolutionary divergence likely occurred during the oligo scene. This would have been thirty three to twenty three million years ago, as toothed whales diverged from the ancestors of filter feeding whales, and this would totally make sense of predatory Toothed whales develop asymmetry related to their ability to echo locate because they need to use echolocation to hunt. Filter feeding whales do not have the same hunting needs, so their skulls remain balanced on the left and right. Um and uh rob I I thought this was a really interesting end and so I was looking at to support this. I found a paper on the cranial asymmetry of whales and this was by Ellen J. Coombs at all published in BMC Biology in and for this paper, making use of museum collections, the researchers compared whale skulls across time, reaching back to whale ancestors that lived fifty million years ago, and the author's write quote early ancestors of living whales had little cranial asymmetry and likely we're not able to echo locate our cho seats display high levels of asymmetry in the rostrum, potentially related to directional hearing, which is lost in early neo seats. The tax on, including the most recent common ancestor of living cetaceans naso facial asymmetry. So again, asymmetrical placement of the nostrils in the face becomes a significant feature of odonto cetti or toothed whales in the early oligo scene, just like you said, um reaching its highest levels in extant taxa. Separate evolutionary regimes are reconstructed for odonta seats living in acoustically complex environments, suggesting that these niches impose strong selective pressure on echolocation ability and thus increased cranial asymmetry. So, to summarize the skulls of toothed whales, specifically, the toothed ones just keep getting weirder and more asymmetrical over evolutionary time. Uh So, as the millions of years march on, the heads are getting less and less symmetrical, and this is especially true apparently in places where echolocation is more difficult due to environmental conditions. And what could be an example of this, Well, I was looking in the paper and this could be a coincidence, but they note that the nar wall has an unusually asymmetrical skull apart from the tusk that juts out on one side. So to read a quote from this paper with a bit of paraphrasing, uh, and remember the genus of the narwhall is Monodon one tooth, meaning Monodon monodon remains the most asymmetric skull in the sample, even when the rostrum is removed, which rules out the possibility that an asymmetric tusk and residual teeth may be skewing the overall result. Their unique sound repertoire narrow band structured in BS is ideal for projecting and receiving signals in icy shallow waters where the animals can detect targets in high levels of ambient noise and back scatter. So that's interesting. This could be a total coincidence. I would not want to suggest a causal connection, but I don't know. It's stuck out to me that nar walls have both strongly asymmetrical skulls, probably to aid in echolocation in a difficult environment, and also extreme asymmetrical teeth, producing these tusks, probably as a sexually selected trade. Yeah. I mean again, it just goes to show you just how weird whales are. Like, they're just so delightfully strange. Um and and again it's easy to it's easy to take it for granted if you don't, you don't lean in closely enough, you know. But as wonderful as as whale bodies are, they are not the only creatures in the sea with striking and fascinating imbalances between their left and right sides. Yeah, they're There are a number of fascinating examples we could turn to, and I don't know, we may we may come back to some more in future episodes. But one that really caught my attention is histeo tooth, the cock eyed squid. So this is another example of essentially divided attention and divided bodies in the deep ocean. Uh So, histeotoothis resides and the mesopelagic zone or the twilight zone of the ocean. And you can certainly think of this as a realm situated between different kingdoms of illumination because above the zone above the creatures of this realm, well, there there's the that there's the distant kingdom of light. Okay. Uh, there's a dim illumination coming down from the sun from the more sunlit portions of the ocean, and so silhouettes can be viewed of creatures above you against that that faint light below you. Well, there's the great darkness of the of the depths. But in that great dark darkness you'll glimpse or if you're a squid to mule, glimpse uh, sparkles and pulsations of bioluminescence here and there. Uh. And of course both of these sightings are important because they both have to do with organisms that may be a threat that maybe food, et cetera. Oh, well, this is so interesting because we know of lots of examples on the surface world, say like lots of herbivores on the this world that have one eye on each side of their head to try to provide a sort of you know, as wide field of you as possible, so you can see things approaching you. But this is a scenario where you might have a head structured like that, but you have totally different seeing needs on either side exactly. And so that's that's what we see with his teo toothis as as described by Thomas, Robinson and Johnson in their paper in the Philosophical Transactions of the Royal Society B it is a creature with quote two eyes for two purposes. So the squids two eyes here are dimorphic in size, shape and sometimes lens pigmentation. I included an image for you to look at here, Joe, and you can folks listening, and you can look up images this as well. Um, not all images of the squid are going to really capture this, but you'll find some that do. And it's it's very weird when you can see both eyes at once because one, uh, the image I was looking at. One eye is this great, big, kind of swollen looking eye that has kind of a yellowish or greenish tint to it. Um it may appear to be glowing the way that the light is catching it, and the other eye appears a smaller, flatter um. You know, almost looks like if you didn't know what you're looking at, you might think, oh, this poor squid, one of its eyes is inflamed and swollen, or one of its eyes has been severely wounded and doesn't look like it's it's operating anymore. But no, both eyes are operating. They're just pointed in different directions, and they have evolved to see differently depending on uh the environments that they're gazing into. It's beautiful, one looks like a setting gangrenous sun, and the other looks like a blueberry that's a little bit rotten. Right, So it's thought that the larger of the two eyes is honed to spot objects silhouetted against that dim light above, while the smaller eye specializes in spot the sources of bioluminescence in the darkness below, and the squid will actually position itself in a tail up position in order to maximize the split vision. Furthermore, the authors share that that the there that we do seem to have yellow pigments in the larger eye that may serve to break the counter illumination camouflage of their prey above. Counter illumination is an active camouflage method by by which lights are produced on the body to match background lights. So this would be used by a creature to blend in with the light above it, so the creatures below them don't so cleanly make out their dark bodies against the dim lights above. Oh, that's a good survival strategy. Yeah, you have lights on your underside to mimic the sunlight. Yeah. And so that the yellow pigments in this larger eye apparently helps to sort of break through some of that. So the theory is that we see dimorphic specializations in each eye as an adaptation to the split visual world. And this actually reminded me of of a bit from a Doctor Seuss book. I had trouble in getting to Solo Salu, where you have this character who's dealing with a bunch of threats and it goes So I said to myself, now, I'll just have to start to be twice as careful and be twice as smart. I'll watch out for trouble in front and back sections by aiming my eyeballs in different directions. And you have this character that's kind of like a little bear creature in his eyes are gazing off in different directions. But essentially like that's that's kind of what is going on with the with the cock eyed squid here. That's great. It is, so I was trying to imagine what scenario could give rise to something like this on a on a land dwelling herbivore. You know, so you have like a bo vine that's grazing what it needs have totally different types of eyes or vision on one side of the head. And I imagine what about some kind of bovine that lives on a tidally locked world, and it it lives at the terminator line. So it's I one eye needs to be like shielded because it's always facing towards the hot side of the planet, and the other eye needs to be very sensitive because it's always facing towards the dark side. I don't know, Oh that's interesting. Uh yeah, I mean I guess that would be the region that you a life form might be likely to to live in because you would have less of an extreme of heat or cold. But of course it would also be a like a chaotic region as well. You would have probably have a lot of climactic weather going on there. It's highly locked planet. It's probably not great for goats. But I was just trying to imagine, you know, that that's conceivably that's the kind of environment that might require some sort of drastic change in the positioning of the eyes and the specialization of the eyes. Um, I mean it I feel like we I mean, we're so hardwired for our surface world environment. It is difficult for us. It's it's a little challenging to put ourselves in the mindset and ultimately the the ocular world of something like a goat or something like a you know, a purely predatory cat or something much less, to put ourselves in the mind said, in the ocular world of the squid or or you know, to get into the sense worlds of whales and so forth. It's, uh, you know, it's it's it's a different environment altogether. And these environments, as we see from these examples, we've looked like they almost literally can pull us in in half. You know, they can they can change it. They can break whatever uh seeming symmetry was there in the body originally as it adapts, as it evolves to fit this environment over time. This raises a question that comes to my mind actually quite often, uh, when you think about, like if there were other clades of animals that that became very intelligent and had something like art what would what would they find beautiful and how would it be different from what we find beautiful based on on our brains and our biology. Yeah, but I maybe we're gonna have to call the first episode there. We will certainly be back with with more marvels of asymmetry, and in subsequent episodes we're gonna talk about uh, crabs and crustaceans, and I think we'll talk about snakes some probably come back to some fish and maybe some larger developmental theoretical concerns about where asymmetry comes from. In in the Kingdoms of Life. That's right. Uh. In the meantime, you can check out other episodes of Stuff to Blow Your Mind and the Stuff to Blow Your Mind podcast feed, which you can find wherever you get your podcast. Tuesdays and Thursdays are our core episodes. Uh. We have a short form artifact or monster fact on Wednesday, Little listener mail on Monday, and and then on Friday we do Weird How Cinema. That's our time to set aside most serious concerns and just talk about a strange film. Huge thanks as always to our excellent audio producer Seth Nicholas Johnson. If you would like to get in touch with us with feedback on this episode or any other, to suggest a topic for the future, or just to say hello, you can email us at contact. That's Stuff to Blow Your Mind dot com. Stuff to Blow Your Mind is production of I Heart Radio. For more podcasts for my heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you're listening to your favorite shows.