The Lesser of Two Crab Claws, Part 3

that first, then you'll be all caught up. But in the last episode of this series, we were talking about asymmetrical development in the clause of the American lobster or Homarus americanus, and how during larval development, the lobsters previously symmetrical clause differentiate into one real thick boy. It's a crusher claw, it's gigantic, it's got like moler like teeth

on it, and it's got slow muscle fiber. And then the other one turns into a sharper cutter, pincher claw that can close very fast because of its fast muscle fiber. And we talked about attempts to pin down exactly why and how this happens at this these early stages in lobster development. But there are other crustaceans where the mismatch between left and right is much more extreme than it is even in the American lobster. And I think we should begin this episode by considering the male of the

many species of fiddler crabs. So fiddler crabs comprise it's not just one species of animal, its many species within a family of crustaceans known as O. C. Pot to day And uh. Once again, I think we keep saying it during the series, but this is one you should go and look up pictures of because you need to have it in your head. In some species, male fiddler crabs have one claw that grows not just bigger than the other one, not not even just significantly bigger than

the other one, but hilariously bigger than the other one. Yeah. Like, like going back to lobsters for a second, you'd be forgiven if you were just not aware of the fact that lobster has had this different this this difference between one claw and the next. Uh. You know, certainly many illustrations I'm thinking, like restaurant logos and whatnot, may not even bother to make one claw look different from the other. But with the fiddler crab, it is very pronounced. It

is it is absurdly different one side from the other. Yeah.

And for a bit of experts summary on what life is like for your average fiddler crab, I wanted to quote from a New York Times interview I was reading with a researcher named Sophie L. Moles, who is a scientist at Anglia Ruskin University in Cambridge and has done some research on fiddler crabs, including the use of a robotic fiddler crab claw that I want to come back to later in this episode, but just in summarizing fiddler crab life, she says, they live in burrows and you

only see them at low tide. At high tide, they go back into the burrow and they seal it up. They feed on mud flats by sifting the sediment through their mouth parts and eating micro organisms. That's the buffet of life. You just sift the mud in your mouth and get the microbes out. But Moles goes on. The female has two little claws to normal size claws for her which she uses to help that feeding, to help

pass the sediment up to her mouth. The male has one that it uses for feeding, and the other is huge. It's greatly enlarged to the point that it can be approximately half of his body weight. It's often really brightly colored as well. Now, what the males do is they wave this claw in a species specific pattern. So each species of fiddler crab has its own kind of wave, and they do this to maintain a territory but also

to attract a female. Uh So, for for a rough analogy on the size and appearance of a fiddler crab claw, uh just imagine an adult human that had one normal sized right hand, but then a left hand with a digit span of about four ft in that hand washs eighty pounds. Yeah. One uh. One example of this is that is Brobabing, a book I'm going to reference in

a bit Um Animal Weapons by Douglas j Emlyn. Uh. He says, if you're if you're basically if you're at the store, go pick up the largest bag of dry dog food that you can find and start carrying it around, and that will give you approximately what we might think of is the male fiddler crab experience. So yeah, so imagine the largest sized bag of dog food. Not just you're carrying it around, but that is one of your hands, and again the other one is regular sized. So what

what is going on with having a crab claw that big. Well, it turns out that the main theory explaining this asymmetric size difference in fiddler crab claws is much like the main theory for explaining the narwhal tusk, that this hugely asymmetrically exaggerated feature found in males is probably primarily a sexually selected trait, meaning it's more important for maximizing reproductive success than it is for direct survival value, though it

may be in part reproductively attractive attractive to mates because of some value it has in helping maximize like burrowing. So, for example, things that have been cited are that a male that has a very big claw can also probably dig a very big burrow, which is better for a

female to go into to incubate her eggs. And also, like crustaceans, tend to just keep getting bigger as they as they grow as they grow older, So a bigger crab with a bigger asymmetric claw is also probably an older male, which is good in crab mating terms because that probably means he has served I have more seasons of life, and is just generally fitter, better able to survive and has good genes. Yeah, yeah, And I mean part of the obvious display here too is like, look

at this thing I have grown. It is so big, and yet I am still alive. I am able to sustain myself. Plus this massive claw, it's like the sports car of the crab anatomy. Yeah. That that's another thing that has often been put up. There's sort of a theory in some sexually selected traits in biology that says, well, they may operate on the basis of essentially advertising a handicap.

They offer a good faith display that even by working at a disadvantage, you're still fit enough to to do well within your environment by having this ridiculous thing attached to you. So a male fiddler crab is running around also basically advertising. I mean, this would be true of all the males with the big the big claw, and that they have basically have to their capacity to eat,

you know. So these crabs eat by shoving mud and to bring into their mouths, and that's true for males and females, but of course you can't do that with that gigantic claw. So essentially the male fiddler crabs they got them one good eating hand. Whereas females have to. Yes, absolutely, And you know this is something that that that Emelyn gets into an animal weapons um, basically getting into just

the energy costs of having this gigantic claw. Uh So some of this is gonna be repeated what we just said, but it all kind of builds together. So, first of all, male fiddlers, he says, burn a lot of energy just to have these, just to you know, develop them and carry them around resting. Metabolic rates of males with big claws are almost twenty percent higher than females due to the cost of the claw. And then, of course, on top of this, you're gonna have to scamper around. We

see everyone out there. I think it's probably seen crabs about doing their business on the beach. You've got to scamper around, You've got to run with that giant claw, and so this is going to be energetically demanding as well. Yeah I can how fast can you run holding that dog food bag? Exactly? Yeah, this is this is where he originally brought up the dog food bag. But um, he also cites a study This one was really fun.

This is two thousand seven study that was published in Functional Ecology by Alan and Levinton, and they were testing this out by putting male fiddler crabs on treadmills, little treadmills inside of air tight boxes. Now, sadly I could not find photos of this that I brought up the original paper and there were no photos or illustrations, so

I only have my imagination to go on. Here. This is the shrimp shrimp on a treadmill paper that you promised in previous parts, right right, Yeah, shrimp on a treadmill for anyone not familiar, That frequently brought up as there was an actual shrimp on a treadmill study, and it was used as an outrageous example of like, look at what the scientists are doing. They won't cure cancer,

but they'll put a shrimp on a treadmill. And as we've discussed in the show before, that's that's kind of ridiculous. I mean, these are not the scientists that would be developing the cure for cancer. These are the ones that would be studying, say, the metabolic rates of shrimp or in this case crabs, right there, not mutually exclusive pursuits to begin with. But then also sometimes you don't even know what benefits that new knowledge about animal life could

lead to down the road. Yeah. Absolutely, And so the study put the crabs on the treadmills inside of the air tight boxes. And you might be one of will, why the air tight box It sounds like something from a Saw movie. Uh No, it's because as the crabs exert themselves, uh, they burn through oxygen and they produce c O two. And so the researchers are then able to measure the gas concentrations inside of the little boxes, and they use these readings to calculate the exact metabolic

costs of running. As one might expect, the males with big claws burned more energy to run compared to smaller males, males with the smaller claw or females and of course just have two regularly sized claws, and these big males with the big claws also tired out more quickly. And then there's the impact on feeding, which we've already alluded to. You know, we we've all seen a crab eat. I know, we've talked about it on the show. Crabs disassemble their food.

Their claws and mouth bits work very hard to break everything down, or in the case of Fiddler, crabs are often just sifting through and finding those little tiny pieces to eat. Anyway, it's what Inland describes as quote delicate and tedious, and with the females it means it often means the feeding claws are just working incessantly. Yeah, you can see video of this. So there's just like a conveyor belt. They're just machines kind of shoveling the sediment

into the mouth. But the male, on the other hand, like we said, only has the one claw that's suitable to eat with anymore. He's got that big claw just setting there, and then the other claud the normal size claws, is the one that he's using to eat. So, uh, this cuts their energy intake in half, just as lugging the giant claw around increases their energy output. So they generally have to feed faster and or more often in

order to make up the difference. Right again, because you've got to they've they've divided their body into eating hand and and handsome hand. Right, And this is this complicates things for the crabs even more because remember, uh, this is not an apex predator we're talking about here. The crab and the fiddler crab especially, they have to concern

themselves with predators especially of the avian variety. Send So of the of this crab with this big claw that's having to do extra feeding, that means extra exposure to potential predation. In fact, studies have proven out that these males are picked off by birds at an enhanced rate. Right, So you're saying because it eats slower, because it can only eat with one of its claws, it has to spend more time outside the burrow, and that's got a

target on its back. Exact. Yeah, it's more time out in the open, more time exposed to predators, and the predators in many cases they they have advanced tactics for dealing with these. Um, these these either tired or distracted or essentially one claude crab at this point when it

comes to the feeding process. Uh Inland points to a study from Christy Blackwell and Cooga regarding fiddler crabs in Panama getting basically taken out by grackles fed on by grackles who as the type of bird that have devised a diagonal faint attack um where they kind of they come in, they kind of fake the crab out and apparently this is even more effective on the male crabs.

Now you might think, well, but wait a minute, Um, having a bigger claw surely also means that that crab can pinch with greater force, which you would think could make it able to defend itself better. Right, Yeah, I mean you you might you might think that, but but then you know, as we'll into like these claws, uh, this big claw anyway, it doesn't seem to be that useful when you're dealing with something like a hungry grackle

that's sweeping in at you. Uh So, like the end result is that the big claude males, they're easier to find, they're easier to pick off, they're potentially more tired, and also they're a better uh they're they're a better kill for the predator because that big old claw has big old meat in it. So there's every reason in the world to kill them and eat them if you were

a grackle or some other hungry bird. Now, from what I've read about fiddler crab claws, it seems like what they are most of the time used for is is is probably visual signaling, but they are on occasion actually used for fighting or actually used as a weapon. Yeah. Yeah. Emlin gets into this in the book as well. Highlighting particularly the work of John Christie. I believe he was in the second study that that was cited there that we decided. Uh So basically, yeah, they wave them around

to communicate their reproductive fitness. They do fight other male fiddler crabs with them, so they do serve as actual weapons in contests for those burrows that we were talking about. But inland rights that quote, for every few minutes of outright fighting, mail spend dozens of hours waving, in other words, communicating, showing off that claw, saying look, you know, look at this mighty claw. I imagine what I can do with it.

That happened. That's that's what's going on. Most of the time, a very small amount of the time they're actually using it. So it's ultimately more of a deterrence than anything. And this is evolutionarily sound because fighting is dangerous. The battle itself is dangerous and can certainly be fatal to an organism, but fights can also just wound you, making you more susceptible pupredation. It may distract you and allow the grackle or some other creature to come in and take you out.

So even though there are hard disadvantages to developing such a deterrence, and he compares this to other animals as well, like anytime you see something that you might label an elaborate weapon. Uh in some sort of an animals anatomy, there's a huge payoff there. Nothing is free, nothing is cheap. When it comes to the development of these things, there's

an energy cost involved. Uh So even though they're there are all these disadvantages to growing, say a giant crab claw, there are also strong benefits in not having to actually fight all of the time. Yeah. I mean I think this this goes against our intuition because we think of fighting in terms of winning and losing. So like fight it fight as a winner who wins and thus they come out good the effect for them is positive, and a loser who loses, and of course the effect for

them is negative. But in fact, in nature, I would argue that most fighting is probably actually lose lose because even the winner is probably blee, somewhat injured or tired out by the fight, putting them at a later disadvantage for survival, even if they come out on top in that particular struggle. Yeah. Yeah, And all of this makes even more sense when you we start looking at the closer to the scenario of these of of fighting and

protecting these burrows and trying to to move females. Again, the male set up shop in front of key burrows that are offered as brooding burrows to prospective females, and this is where they make their show and this is where they fight if it comes to that. And the numbers here are apparently great. They're just tons of crabs out there and they're they're just face off after face off. Uh. And again, most of these face offs are not going to result in a big, drag out fight. A lot

of them are just going to be uh displays. But still uh. Lifting that that crab claw in the air and to signal with it, that's going to have an energy cost and so this is ultimately exhausting too many crabs. Crabs will eventually they have to bow out and work their way back up to good burrows. So there's like

this whole system of communication. Uh. Most of the these faceoffs don't rise to the level of full intensity battle, and the display of the claw allows the male crabs to easily determine who they have a chance against, so they're able to size each other up like Okay, this is a battle, um that I definitely can win, and he knows I can win it, so we're done. This is a display only situation. Okay, he's a crab that can definitely beat me, so I'm not gonna mess with him. Uh,

We're just gonna carry on our ways. This one, however, we're gonna have to communicate a little bit and we might have to fight because we seem to be evenly matched. Yeah. That's actually the most dangerous situation is when it's not clear which one is stronger than. All right, Well, I

wanted to come back to something which was earlier. I mentioned that New York Times interview with the researchers Sophie Moles, who was one of the authors of a paper published in ten in Biology Letters UH called Robotic Crabs, revealed that female fiddler crabs are sensitive to changes in male display rate. The other authors here were Michael D. Jenions and Patricia are Why Backwell, yes, I might have referred to her earlier as Blackwell, my apologies. Oh I didn't

catch that. You should apologize. Well, I just want to make sure I get the names right. I think I had a type in my notes there, so but from the crabs perspective, I think it is important to realize that this really is a study that involved creating crab sex robots like this is creating that it was an attempt to create the hunkiest male robot crab clause that have ever been put together with the explicit purpose of attracting female fiddler crabs. So I'm just gonna read directly

from their abstract. Uh they write quote. Males often produced dynamic, repetitive courtship displays that can be demanding to perform and might advertise male quality to females. A key feature of demanding displays is that they can change in intensity, escalating as a male increases his signaling effort, but de escalating as a signal or becomes fatigued. Here we investigated whether female fiddler crabs of the species Uka mio Bergi are sensitive to changes in male courtship wave rate how fast

the arm is waving. We performed playback experiments using robotic male crabs that had the same mean wave rate but either escalated, de escalated, or remained constant. Females demonstrated a strong preference for escalating robots, but showed mixed responses to robots that de escalated fast too slow compared to those

that waved at a constant medium rate. These findings demonstrate that females can discern changes in male display rate and prefer males that escalate, but that females are also sensitive to pass display rates indicative prior vigor. So if you are a male fiddler crab, it's not just important to have a big claw, but it apparently, at least with this species, is more attractive to females if you start waving it faster and faster as the female comes close

to you. And from this New York Times interview with the lead author of their moles, uh it was there was the question where the female is terribly disappointed when

they realized they'd been tricked. You know what happened once they finally got up to the waving robot arm that they were so interested in, Well, Mole says quote, once they got to the robot, they would touch the baseplate of it and realize there's something wrong here, it's not real, and they would usually at that point stop moving or runaway. Some of them actually responded as if he were a

real male crab, which is by tickling him. What the females do is go up to the mail and use their legs on one side of their body to tickle him. This communicates to him that she's interested in him as a mate and not just trying to steal his home. So this this study did indeed implicate female fiddler crabs tickling metal base plates because they thought it just that claw is so huge, it's swinging so fast, I've got

to believe it's it might be a real crab. This sounds like something that could be factored into, I don't know, Battlestar Galactica sort of situation like that. The replicants, the robots, they look just like us, they behave just like us, except um tickling them will reveal their true nature. Anyway, in the spirit of of our enthusiasm for the shrimp on the treadmill, the crab on the treadmill, I want

more studies with robot crab hunks. We have to build the most attractive male crab that has ever been that has ever existed on Earth. And uh, but I guess we have to be careful with it because we don't want to drive crabs to to extinction by like now

now the real crabs only desire the robot. It's weird how this does line up with the sort of trope of them the muscle man on the beach attracting the women and in the in the nerd that's that's also inevitably on the beach as well and make get sand kicked in his face or whatnotum, But it also does bring to mind, like even with with humans, there's sort of there's there's fitness, and there's like visible fitness, but then there's also like fitness to the level where it's

no no longer purely functional anymore. Like there's like, for instance, there's the muscle that might aid in the delivery of a punch, and then there's like the the the muscle build up that say, makes it harder to move around or or makes it, you know, more difficult to say, touch portions of your back, the sort of thing. I

totally know what you're saying. Though, Also that reminds me I always want to caution people, you know, just don't don't try to extrapolate too much from from animal sex and attractiveness studies to humans, because you know, crabs and humans are pretty different, right right, And certainly the reasons that humans do things um and uh, and the way they react to things are generally there's a lot a lot more going on. There's there's this whole level of

human complication. It's taking place on the surface of whatever else is going on all Right, after we've talked about all of these examples of animals that broadly have bilateral symmetry but then some major deviation from it, I've been thinking about how symmetry and asymmetry come about at the cellular level, because you know, you can imagine why it would be genetically efficient to have bilateral symmetry, like you you just basically need half of a body plan and

then you just copy it over on the other side. But within that broadly symmetrical framework, you know, we get these deviations major and minor. And it's not all narwhal tusks and fiddler crab claws things that are like huge and noticeable. There are plenty of forms of a symmetry that are common but harder to spot, such as the

orientation of internal organs. You know, you're digestive tract and it's associated organs and your heart and circulatory system, or all asymmetrical they have different organs and pathways situated on the left and right of the body cavity, and there are also minor more invisible variations at the cellular level in within mostly symmetrical creatures like us. So how do these deviations from perfect symmetry come about at the level of cell division, which is actually you know, actively building

your body's tissues. How do the cells know which side is which and how to do something different on the left than what they're doing on the right. Well, one jumping off point here is I came across an interesting article about this in Quantum Magazine from January by Tim Vernemon called how Life Turns a symmetric which is worth a read in its entirety, but I just wanted to summarize and jump off from a few things I learned

from it. And one of the big takeaways is that I think we have some good answers about at least some strong factors for like mammalian or vertebrate symmetry and symmetry breaking something. We know some things about the genetic and cellular basis for a symmetry in the body, but we still don't know everything yet, And so one of the ideas thin gets brought up in this article is the nodal lefty genetic connection, and it goes like this.

Since the nine nineties, scientists have been studying a gene called nodal in O d A L which appears specifically on the left side of the developing embryo of At the time this article is written, they said every vertebrate animal yet studied and associated with this gene is a somewhat confusingly named gene called lefty, which appears to work specifically to suppress the nodal genes activity on the right

side of the vertebrate embryo. So the purpose of lefty, if I understand core, actually appears to be something like telling the right side of the body not to do left side of the body stuff. According to the Harvard biologist Cliff Tabin, the nodal lefty gene combination seems to be the main genetic factor guiding asymmetry in animals, or at least invertebrates. So how does this difference get expressed? Well, another biologist named Nobo taka Hirokawa has offered an explanation

that has to do with cilia. Cilia are little hair like or thread like projections Technically, they're a type of organelle which stick up from cell membranes within the cells or of eukaryotes, and they serve various functions like gathering sensory information for cells or facilitating the movement of cells through fluid. So you might read about us silia motility. These these things often moved back and forth, though actually

they're divided into motile and nonmotile cilia. So how would tiny hairs sticking up off of cell membranes have anything to do with the body of a vertebrate splitting from perfect symmetry into a differentiated left and right half. Well, one fascinating clue came in the form of a rare

genetic disorder found in humans known as cartagen or syndrome. Actually, I'm not sure if I'm saying that right, but it's spelled k A R T A G E N E R cartagen Or syndrome, which presents most often in patients as patients with continued respiratory problems such as recurrent lung infections and sinus problems, and also sometimes infertility. It turns out this condition is caused by a congenital defect that

prevents the bodies sillia from functioning as needed. So these little hair like projections on cells don't function as they normally would. Now why that affect respiration? Well? Of course, the inside of our breathing passages are aligned with cilia, and the cilia need to move in synchronization for I think multiple purposes, but one of them is to help clear breathing passages of mucus. And this disorder causes the cilia to have trouble again with motility, with movement, and

so they can't really synchronize. They can't really work together to get the mucus out of the lungs uh and out to the throat to prevent infections. Now, strangely, this disorder affecting cilia also frequently coincides with a seemingly totally unrelated issue. About half of people diagnosed with cartagon or syndrome also have their internal organs flipped. Their body is a mirror image of what a thoracic surgeon would expect

to see if they open you up. So you know, the heart on the right and the liver on the left and so forth. That's right. Yeah, the the if we're looking to spy literature, of course, if we look at Ian Flemings, the doctor No. We might remember Doctor No has this where his heart is on the other side of his body, survives. I think he survives an assassination attempt at some point because of this anatomical quirk. Oh,

somebody shoots him on the wrong side. That's a good twist than than than well anyway, So you have that association people who have this, who have this congenital condition affecting proteins that in turn effect cilia. Uh. They also half of the time their organs are are flipped opposite

of what you normally see. On top of that, there was a paper in Nature by Lee at All which Vernamon in the article points to called global Genetic Analysis in Mice unveil central role for cilia in congenital heart disease.

And this paper apparently found multiple instances of genes where if the gene was defective, the mouse presented with some kind of unusual issue related to symmetry and asymmetry in the body, some issue with that the haves left and right, and in those instances the gene was somehow also related to cilia. So these clues UH indicate that somehow silia may play a role in symmetry breaking during mammalian development.

So how could this be Well, A leading explanation has to do with something called dorsal flow and a little patch on the surface of mammalian embryos called the ventral node. So, if you're looking at like a mammalian embryo, the ventral node is a little pit or depression on the underside or the bottom surface, and the pit is ciliated, meaning it's covered in cilia, these little hair like or thread

like projections. And the explanation goes that the waving of cilia in this little pit create a consisder stant direction of flow in the fluid around the ventral node. So the cilia rotate to get the fluid moving, and then they keep it moving in a consistent direction. The fluid is always moving to the left along with the with the way the silly are waving, and the direction of this flow seems to cause a chain reaction that results in changes in gene expression, specifically in the a symmetry

genes coming back to again no dole and lefty. So apparently, if the cilia are having trouble with motility, the unidirectional left word current of fluid is not established, and the symmetry breaking genes aren't expressed as they would normally be, which can lead to deviations from the type of mammalian a symmetry we would we would see in most most members of that species, such as creating a condition where the body fifty of the time can have its internal

organs flipped. However, this be the only factor leading to standard symmetry breaking in animal bodies. Vernemon's article also cites a Toughs University biologist named Michael Levin who points out that some animals, even some mammals, don't have that ciliated dorsal node we were just talking about, and Levin believes there's some involvement of a factor called the cellular skeleton or the cytoskeleton. Did you know that your cells have

a skeleton of their own? I I don't know. I guess I'd heard the word cytoskeleton, but I hadn't quite put it together. It's not exactly like your your bigger skeleton. I mean, it's not like bones. The cytoskeleton is a system of protein filaments that are, at least in a metaphorical sense, sort of like the bones of a cell. Uh to describe them, I want to quote from a

review in Nature by Fletcher and Mullins. Quote. The ability of a eukaryotic cell to resist deformation, to transport intrust cellular cargo, and to change shape during movement depends on the cytoskeleton, an interconnected network of filamentous polymers and regulatory proteins. Recent work is demonstrated that both internal and external physical forces can act through the cytoskeleton to affect local mechanical

properties and cellular behavior. Attention is now focused on how cytoskeletal networks generate, transmit, and respond to mechanical signals over both short and long time scales. An important insight emerging from this work is that long lived cytoskeletal structures may act as epigenetic determinants of cell shape, function, and fate.

And it's exactly this last comment that I think is most relevant here, because in the case of symmetry breaking, it may be that features of this cellular skeleton, this system of sort of strands of of polymers and proteins that helped give a cell its shape and help it resist deformation when it's under pressure and things like that, that this system may ultimately epigenetically determine the development of cells and ultimately the handedness or asymmetry of the whole body.

This was so this next part was also a surprise to me. I don't think I knew this. Apparently sells themselves have a kind of handedness or asymmetry. Some cells are sort of left oriented and some are right oriented, and you can see this in their behavior when they're moving through fluid and they come up against an obstacle. So that you can have experiments where you show that cells are flowing around along in a controlled environment and then they bump up against something, a bump a surface.

When that happens, the cell will tend to turn in one direction or the other, and that preference for a particular way of turning tends to remain consistent for each cell. You have sort of left turning cells and right turning cells, and experiments in fruit flies demonstrate that these small differences at the cellular level can snowball into major morphological differences

at the body level. Vernamon's article mentions researchers named Leo Juan and Kinji Matsuno, who each identified proteins within the cellular skeleton specifically the actin and myosin's as having an influence on whether a cell becomes left handed or right handed. And there there may also be some interplay between proteins in the cytoskeleton and the asymmetrical expression of the nodal gene,

each playing a role. But then there's one more thing that gets mentioned towards the end of this article, uh that the Quanta article that I thought was interesting, which is that other factors leading to asymmetry. Of course, there might be some that haven't been discovered yet, but one candidate has to do with communication between cells, for instance, based on the relative prevalence of proteins on a cell surface, which would in turn determine how cells trade electrical charges

back and forth between each other. And the Quanta article cites Michael Levin again saying quote, if we block the communication channels, asymmetrical development always goes awry. And by manipulating this system, we've been able to guide development in surprising but predictable directions, creating six legged frogs, four headed worms, or froglet's with an eye for a gut without changing their genomes at all. And in a final twist, bringing

this back to medicine. UH, it's interesting that all of this knowledge might one day be useful in finding treatments for pathological growth and development patterns and somatic cells by sort of harnessing these systems, by harnessing the bodies existing mechanisms for detecting and UH and directing its own shape, you know, the way the cells come together to to form larger structures that might be harnessed for for treating

cases where cell cell development is going wrong. Yeah, that's that's fascinating, you know, coming back to what you said earlier, I don't know if prior to this, if someone had just stopped me on the street, like a man on the street reporters situation asked me if sells off a skeleton, if I would have been able to correctly answer regarding the site of skeleton. Here this is this is pretty fascinating.

And then to get into its um sort of the ramifications of that and how that ends up being reflected in the left handedness of the of the overall system or the right handeds, whichever the case may be. You know, I have to think back once more to the cock eyed squid histeo tooth that we discussed in this was the first episode. One of the reasons to marvel of this amazing creature is that its eyes have evolved to look in different directions to different realms of the ocean,

light and dark. And this seems understandably strange and alien to us, but perhaps less so when we remember things like left handed in right end and this whenly thing about neural asymmetry that defines us on the inside. Uh. And of course it's not just us. A Symmetries between left and right side of the nervous system are present

throughout the animal kingdom, from invertebrates to mammals. And as one source I was looking at this is by Concha, Bianco and Wilson in Encoding Asymmetry within Neural Circuits, published in in Nature Reviews Neuroscience. UH. The theoretical advantages of brain asymmetry include the capacity for parallel processing, the specialization of left and right side for distinct computations, and the restriction of information processing within local circuits with short, fast connections.

But while there are obvious advantages to brain asymmetry, are there advantages to brain symmetry. As I was looking into this little bit and I read some thoughts from Marco Data of the University of Padua who experimented with the often lateralized fish species the gold belly top minnow in

two thousand and nine. Basically, what this experiment consisted of was dividing these UH top minnows, these gold belly top minnows, into groups of left lateralized, right lateralized, and non lateralized specimens. So the seeming advantage to the non lateralized came when judging stimuli to either side of the creature through either eye. The experiments involved judging advantageous shoals of fish to join

on either side. Remember you're a small fish in the ocean. Uh, there's a lot of survival advantage of being able to determine which shoal of fish you should take refuge in. Uh, you know their strength in numbers, and so it seems that in these fish having a lateral tendency, most uh, most often, they just joined the shoal that they saw with their dominant eye. So I guess, I guess the take home here is that in some cases, yeah, it's and it may come down to your dominant side is

just going to be the tendency that you go in. Uh. And it's maybe going to potentially get in the way of properly evaluating in this case, two different shows of fish. I don't have evidence of this in front of me, but it makes me think that surely things like this must also be true even with uh, you know, brains we would think of as more complex. I mean, I'm sure even with humans, handedness probably plays a role in like directional reactions to fast stint. You know, something pops

up and scares you, which direction do you bolton? I will. I would be surprised if there is not some kind of tendency there that's not purely dictated by where the stimulus is, but also has to do with like body side dominance. Yeah, and body side dominance and left handedness and right handedness and human beings. This is something I

think we'll have to come back to in a future episode. Uh, there's a lot of great research out there, particularly when again it comes back to what we're saying earlier about how you have whatever is going on on the animal level and then you have the human complications involved there, because yeah, when you start getting into the whole situations of okay, you have a right handed dominant society and then you have left handed individuals within that society. Uh,

you know, what what is the impact? And uh and of course there's a there's a lot of There have been a number of interesting studies over the years that have looked at this, how it plays into sports, how it plays into conflict and combat, how it just plays into thinking about the world around you. So that would be a fun one to come back and uh and do. And I know that the lefties especially it will love it. But right e's you're most of our audience, so don't worry.

You'll like it too, You're just less special. Sorry, Okay, should we wrap it up there? I suppose we should. Uh. So we hope, we hope that you've enjoyed this uh partial journey through a symmetry. Like we said there, there are plenty of other examples of a symmetry in the animal world. We we tried to focus on some of the uh, the examples that you know illustrated uh the

topic the best. But perhaps you're thinking of something we didn't mention that bears mentioning, right in, let us know, uh, let us know if you're interested in an episode in the future about left handedness and right handedness in in in Humans anyway you look at it just right in We'd love to hear from you past episodes, future episodes,

present episodes. It's all fair game. We read those on Mondays on listener mail and the Stuff to Blow Your Mind podcast feed We have our core episodes on Tuesdays and Thursday's short form artifact or monster fact episode on Wednesdays, and on Fridays, we put aside most serious concerns and we just watch a weird film on Weird House Cinema. 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 at 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 listening to your favorite shows.