Evolution of the Anus

role they might play. Uh, you know, I think back to the the the ancient Egyptians and their idea that the heart was far more important than the brain, and the brain was just to be removed and discarded, whereas the heart had a privileged place in the funeral preparations of dead pharaohs. But of course it's impossible for us to underestimate the value of the heart and the brain

now since we know them to be so important. But there are all kinds of body parts you have that you probably just don't stop to be very thankful for or think about very much, but they do you a lot of good. I think about the underrated facility of the toes. Yeah, yeah, to toes are granted toes maybe fetishized, as as can any part of the human anatomy. Oh no, I didn't mean that way. No, I mean they're like

usefulness and balance and movement. Oh yeah, yeah, certainly, but but it's not something that we tend to attach our identity to. Whereas the brain. Yeah, I mean our podcast has had a brain on its logo in the past. You know, the heart has all these symbolic meanings where we want to attach our identity to them in addition

to the functions that they play. But then there are parts of the body that we generally don't want to think about, and we don't think about unless they are giving us grief, unless there's something wrong with them, and then they become the center of our existence. Right. It's the same way that you never think about your internet

connection unless it's not working. Right. There are parts of the body that you probably just never think about unless something's going wrong, right, or we go to great pains not to think about them. You know, we kind of have all these blinders up. Really, the part of many and animals anatomy that we're going to discuss here today the anus. The anus today it's anus science on stuff to blow your mind, right, and I I wanted to do this episode really since I guess that's when I

really first found out about anus. Is. Yeah, I had no idea. I had no idea what it would happened. And then I read this, uh, this cool science paper and I was like, whoa, this is this is this is where it all comes from. This is this is the center of all the activity. I really appreciate you suggesting this topic because the anus turned out to be far more interesting than I had ever imagined it is. And that's what we're going to try and outline in

this this episode. Now, we we do have to drive home since we are talking about the anus and there is there's just so much not not really. I don't think taboo is going to be a stumbling block for us here, but the anus is so tied into our our systems of humor, Like it is so giggle inducing. When you when you saw this title pop up on your your your your device or whatever program you used to listen to your podcast, you may have giggled at the prospect of listening to say in an hour's podcast

about the anus. Yeah, you'll probably notice that we talk about biology a lot on the podcast. I've gotten to where it's extremely easy to talk about, say, the biology of sex, without making any jokes. That's something a high school or might not be able to do. But you know, when you talk about it enough, it's just an interesting subject on its own. Well, sexist is its humor appeal? Well,

sex is one of these things. Sexual reproduction is a case where I feel like most people, at least, you know, most adults are capable of having both a humorous conversation about and a serious conversation about. You reach that point where you realize there is this entirely serious side to the discussion, and you can switch back from one and

the other. But with the anus, there's it's almost gotten there. Yeah, it's almost all humorous, unless you yourself are are a proctologist or or or just a medical professional, or you have had to deal with health issues related to the anus. Otherwise it's just all the realm of body humor. Or maybe you're somebody who studies the evolution of the anus, which is something that we will definitely be touching on today. These questions about whence this hole in the backs of

our bodies? Where does it come from? And what is it doing. That's not so much what is it doing that's pretty obvious, yes, but but the way that it does it, the way that it's come to do it, and just how how it functions. Uh, hopefully you will leave this this episode with a whole new respect for the anus of any animal. Okay, Now we wanted to start with an interesting fact, Robert, that you came across, actually a curious little book that you found on the internet, right,

that's right. So I was casting about for some mythology related to the anus and we'll we'll get to some of that later on gods and so forth. Yeah, yeah, I figured, you know, it's always good to throw in a little mythology a few monsters when we can. And

I was just plugging in different ancient cultures. I plugged in the ancient Egyptians to see what what was up, and I ran across this book, The herbal Lore of Wise Women and Warp Cunners The Healing Power of Medicinal Plants by wolf D. Storrel, and he points out that the doctors of ancient cultures were part of the priesthood, and for the ancient Egyptians, each physician was responsible for

curing only one illness. So the pharaoh was attended by such specialist as the Royal Keeper of Pharaoh's left eye, the Royal Keeper of the Pharaoh's right eye, and then most importantly of all, perhaps the shepherd of the royal anus or the nerofoot. If I am reading that correctly, the Shepherd of the Royal anus. Now laugh, you may laugh, you may, but this is actually a kind of interesting because it's an early example of medical special realizations, something

that we've seen again in the modern world. There are a lot of reasons that a pharaoh might have need needed to have a special attendant to problems dealing with their anus, because a lot of the problems you can have with your ans can be related to, say, certain types of over indulgent diet. Yeah, I mean just in general, there's just so many digestive ailments they can occur in one's life. You see this pop up in a number

of different traditional practices, for instance, moodras. Are you're familiar with moodra's, I'm not sure. So this is a whenever you see someone in a yoga pose and they're making or they're a meditative state and they're making a particular little hand uh motions. They're holding their fingers together in a particular pattern. That is a moodra And I've read up on them in the past, and when you start looking at the different moods that they have them for

different things, it's you know, it's about channeling energy and whatnot. Uh. But it seems like most of them are related to digestion, which which makes sense when you when you think about all the digestive ailments that can afflict an individual over the course of their lifetime. Totally, now the sky's storial that I want to say, this book does appear to be kind of in a liminal or less than totally authoritative space. I think this guy deals in some some

kind of natural apathy areas and stuff. But it was curious and had some fun ideas in it. Yeah, he's he's not an Egyptologist or anything. But but I I have to point out that I did find this bit about the Shepherd of the Royal Anist backed up in some other works, including Medicine in the Days of the Pharaohs by dermatologist Bruno Hella and cardiologist Bernard Ziskins from two thousand five. Yes, I think that fact is well attested, but also I just wanted to follow up on this

other idea. In his book, Storial argues that every culture has a primary external metaphor that it uses to understand medical insights, which is like a model through which to visualize health and human function. So for the ancient Mesopotamians, he says, this moll was the movements of the planets through the zodiac. For the ancient Indians, he says one of the models they used most often was the cycle of the seasons from spring to pre monsoon to monsoon.

And for the ancient Egyptians, this model, he says, was the Nile River quote regularly cleansing and fertilizing the thousand mile long oasis. Just as the Nile flows from Nubia to the Mediterranean, so the elementary tract, also known as the digestive tract, flows from the mouth to the organs of elimination in the human body, bringing health and cleaning

out impurities. Now, upon reading this, I couldn't help but notice that if this is true, what what he says about the you know, this metaphor of human health being the Nile River, the Nile River delta, which is this lush, fertile, agriculturally productive region that sustains the civilization around it. In the metaphor, the delta would be the rectum in the anus. Yeah, this reminds me of something that that I was thinking

about researching this topic as well. Like we think about the the the track of digestion in the human experience, the linear experience of digestion, uh, And I wondered what extent uh that plays a role and just our understanding of time. When we were talking about time in our episode that this present moment we talked about comparing time to the river we see flowing past us and so forth. But here we have this river flowing inside us that is an even closer uh metaphor, that's that makes itself

readily available. So you're thinking, maybe if we had evolved to have large brains, but to not have a one way digestive tract instead to have I don't know, one of these open sack mouths We're going to talk about more as the episode goes on, where you just sort of like eat and digest and poop all through the same one orifice and sack. Would that lead us to have a different conception of sort of the the order of things in history, and the meaning of structure and

our lives. Yes, I, as we proceed here, I challenge anyone out there too imagine an alien life woman, intelligent alien life form with one of these sort of rival digestive systems, and imagine how that rival digestive system might impact their perception of time or the universe. Take up the challenge. Alright, Well, on that note, we should probably begin, uh, well at the beginning or at the end if you'd rather, by discussing just what the anus is and what it does? Yeah,

what is your anus and what does it do? Uh? The anus? Of course I shouldn't giggle, should I know? I think a little a little giggling is uh just cannot be avoided thanks human culture. The anus, of course, as we all know, is the point of termination for the digestive system. It's the exit point for solid waste in the body. And I think one of the things we should regularly stop and be thankful for is the fact that we have an anus. It does one job.

It is dedicated to the elimination of solid waste. There are lots of complex animals that are not like this. Um. We are going to talk more about some simpler animals that have like a single opening through which everything takes place, but even complex animals like birds, reptiles, amphibians, monitory ms do not have an anus, but a cloaca, which serves as a general purpose opening for solid waste, liquid waste, and reproduction, kind of a fusing of the different categories

together exactly. So, if you imagine we had evolved from birds instead of mammals, we would probably still defecate, urinate, and give birth all through the same hole. Now, maybe if that was how we were, we wouldn't mind, But I don't know. I think most humans are probably glad that things don't have to be that way. Well, I think we should also be thankful that humans don't yet have the power to decide like where their waste elimination or if this will be and how it functions, because

we would we put it down there. We'd probably put it down there on our heel, so we could discreetly defecate as far from the rest of our our body as possible. I have often wondered that same exact thing. Why doesn't defecation happen at like the end of a tale or something? Something farther away from you. But then again, why would it need to And once you've got a tale that you need to defecate through, what happens if it gets chopped off something? And that will come up

in this episode. Hey, it has come up in the previous episode. Uh, there's it's the anus is important and therefore it really needs to be core and center to the the primary trunk of the body. Now, if you're thinking, come on, guys, or if you're not on board yet, right, you know you're thinking, like, how can we really do an episode on the anus? It's just a hole that stuff comes out of. What could there be to say

about it? I would say that the anus is a surprisingly complex organ, uh, and so I think maybe we should look at its complexity and what it has to do. Indeed, so as we dive in here, I want to turn to the words of Mary Roach, who wrote a wonderful book several years back, Gulp Adventures on the Alimentary Canal. I've referenced this in other episodes. It's just a wonderful

exploration of human digestion and some additional topics. For instance, there's a whole section in the book where she talks about the practice of smuggling things in one's rectum and sort of the science of that practice. But here's a here's a wonderful quote where she talks about the anus quote. Anal tissue is among the most densely innervated on the human body. It has to be. It requires a lot

of information to do its job. The anus has to be able to tell what's knocking at its door, is it solid, liquid, or gas, and then selectively release either all of it or one part of it. The consequences of a misread are dire. They certainly are. Now. Yeah, though I wonder I've had this thought before. Okay, So, in modern polite society, you don't want to just whoop anytime, right, you know, you want to be able to control that for like cultural and privacy reasons, and maybe for some

hygiene reasons. But if you imagine us living in the wild, what's the reason that you would need to be able to control when you poop? Why does that matter? Well, I mean, controlling when you defecate is really important because outside of the particular human concerns, this is an issue of hygiene but also survival. Being able to choose where

and how you defecate. It's tremendously important and it entails everything from not pooping where you eat, to say, pooping in a place where you can easily hide the stuff. That we see this every day, or at least cat owners do with a litter box, that the cat wants to poop where it can hide its poop because it has this uh evolved necessity to disguise the scent of its of its activity. And then also sometimes you want to produce the right sort of round poop that will

roll away from your body. This is apparently the case with with goats. If you've ever been to a petting zoo with a child, for instance, you probably noticed that the round poop is basically falling out of the goats at all times. And uh and and that he's round so that it can roll away. Is this kind of like when it comes out sort of like a spray of coffee beans. Yeah, just kind of like tumbling coffee beans and the pebbles. Yeah. And apparently the purpose is

these things would roll away. It's self hiding poop. They don't have to bury anything at all. Now I'm curious about what you said about the idea that controlling when you defecate plays a role in survival? What what would the role in survival be? Well, I ran across a paper a few years back because from two thousand thirteen, The Control of Defecation in Humans and Evolutionary Advantage by Italian bowl experts UH G. Besati and V. Villainacci, And

it breaks down the particular human side of this. Uh and this is something I've explored before when I was looking at the Monster or Science of the Googlies. You remember Googlies right before film. The cover was a little monster popping out of the toilet. Yeah, tagline taste, They'll get you in the end. But it made me think it's like, all right, well, humans are are vulnerable when they're on the toilet. All animals are vulnerable to some

extent when they are defecating. So how does evolution plan to all of this? Well, in this case, the authors point out that human fecal matter would have certainly put early humans at risk from the apex predators of your So if you run a human fecal sample, modern or ancient, through complex gas uh chromatographic or mass us spectrometric analysis, you'll discover that quote, human feces are rich in volatile compounds likely to be identified by potential predators. So volatile compounds,

what does that mean? Smell? Yeah, And as we've driven home before on the podcast, I think our human sense of smell is rather limited, like we're seeing in grungy black and white, whereas something like an apex predator or something like even our our pet dogs and cats, especially the dogs, they have an entirely different, like full color HD experience of things. Well, Robert, have you ever owned a dog. It's been a very long time. I've mostly

been a cat owner my entire adult life. I think most people who have dogs will know what I'm talking about. Dogs love poop. They want to smell all of the poop. When I take my dog out on a walk, it's disgusting. Other people's dogs leave their poop on the sidewalk wherever, and he wants to go to all of it. And if you try to pull him away, like no, Charlie, you don't want to get into that, He's like no, no,

I need to. Well, there's information there. There's there's information on a level that that that humans can barely grass. We just know it doesn't smell pleasant, or it certainly Lena doesn't look pleasant, but this is important environmental information to the dog, right right. So to take us back to the paper, then the idea is that while we are pooping, we're producing smells that advertise our vulnerability to potential predators exactly. And the full conclusion from the from

the paper I think is rather great. They say, quote, we hypothesize that the voluntary control of defecation by our ancestors, together with greater brain volume, erect stature, opposable thumbs, and other changes, may have contributed to the successful march of

hominids along the road of evolution. In fact, by deciding when, how and where to defecate may have several advantages in the complex prey predator relationship because spores are left in places undetectable by predators, or there are no fecal tracks who sent maybe easily individualated by prey genius. So we've we figured out evolutionarily speaking, that you need to know when to poop, because if you just poop anytime, you may be squandering opportunities or putting yourself in danger exactly.

So let's break down how that actually functions biologically, though, Like, what is the actual biology of pooping. Okay, So the first step is six to eight times a day a peristaltic muscle contraction, called a mass movement, squeezes the contents of the colon along the path. Yeah, and peristalsis is the word for a wave of muscle contraction and relaxation

that travels down the length of a tube inside the body. So, if you've ever run your fingers down the length of a sausage casing to squeeze the sausage out, or if you've ever tried to push the last bits of icing out of a piping bag, you have roughly simulated peristalsis on that on that tube. I want to say, this is also akin to how an earthworm moves, right, It's

kind of this. Uh. This wave a wave of muscle contraction running down the length of of a cylindrical object, And in the sense of a hollow tube, that cylindrical object has its contents continually pushed down the length of it. So what happens next. The material pushes against the rectum wall with enough pressure to trigger the stretch receptors, and this triggers the defication reflects now. This entails a simultaneous contraction of the rectal wall muscles and a relaxation of

the anal sphincter. Little known fact people actually have. I had no idea until last night. Two anal sphincters. Did you know you have to? No? No, I just thought there was the one. No, You've got to The internal anal sphincter is involuntary, so it holds up everything until a certain threshold of rectal wall stretching is reached, at which point it automatically says, okay, time to open the gate.

But then you've still got the external anal sphincter. And this is what's under conscious executive control, perhaps for the reasons hypothesized by the researchers we were just talking about. It's like in a submarine movie when they're gonna launch a nuclear missile. Yeah, you have to have like both the key individuals push the button at the same time because otherwise there will be disastrous consequence. Right, I've got the missile key. Al right. So yeah, this is where

human choice enters the picture. Uh A, poop your own adventure book, if you will, So you might choose to bear down, and this will raise the pressure on the rectum walls to prematurely trigger deification. So this is again part of the choice. It's not only the idea of the well I'm not getting ready to go yet inner sphincter. I'm going to go seek a spot behind a bush. You can also say, actually, I'm ready now, let's go ahead and expedite this process. But again, likewise you can

hold it back. But the larger and more liquid the load, the harder this is. Roacha quotes so one gut expert in gulp as saying, quote, not even the sphincter of Hercules can hold back water. I just I like that by the sphincter of Hercules. I like the idea that since Hercules is very strong, like he's got big muscles on his arms and legs and back, he must also have an especially strong sphincter muscle. Of course he would.

I mean, just if you have the blood of God's running through your body, if you're a hybrid of of humanity and deity, like, why would the why would the anus be off limits? Why would that be untouched by by the I corps. I want to hear from the health and wellness experts out there in the audience, if you know this fact does muscle training actually make your

sphincter stronger? I want to know. Uh. Interbook Roach also quotes physician Robert Rosenbluth who says, think of it, no engineer could design something as multi functional and fine tuned as an anus. And then he points out that to to call someone an anus or another crude word for anus, that you're ultimately quote really bragging them up. Yeah, it's saying like you are a fine tuned specimen. Nature made you perfect. Yeah. And this comes back to the idea

of the shepherd of the anus. I think because when we were talking about this in an email chain yesterday before we recorded the episode, it was brought up, well, there's only one anus, why would you need a shepherd. A shepherd tends to a flock of sheep, and I would wondering, Well, maybe the scenario here is more than the anus is the shepherd, because the anus controls what comes in and out. It has such a vital role. It's kind of like the shepherd. It's the well, the

shepherd is the gatekeeper. Yeah, it is the shepherd of poops, the gatekeeper of fecal matter. Yeah. Alright, Well, on that note, we should probably take our first break, and when we come back, we're gonna talk a little bit about mythology and monsters before we descend into the world of anal evolution.

Than all right, we're back now. If you have been listening to the show for a while, you've probably listened to our episode on the Cuteness Monster Spectrum we discussed back in October, where we talked about monsters, especially monsters from Japanese folklore that combine elements of cuteness and horror and monstrosity. And one of those monsters we talked about

was a little water dwelling demon called the Kappa. Oh yes, Now, the cap will hang out in the river and if you get too close, so pull you in and drown you. But it gets more interesting than that, Michael Dillon Foster writes in a paper called the Metamorphosis of the Kappa from Asian Folklore Studies in uh he writes the following quote.

Not only does the Kappa have a penchant for pulling both children and adults into the water, but it often does this in order to steal the liver, a feet it achieves by reaching its arm up through the victims anus to snatch the desired organ. So in order to steal the liver, uh, they believed that the kappa had to uncork the butt, had to uncork the human anus, removing this organ known as the shii kodama, which is quote a ball once thought to be at the mouth

of the anus. This is this is fascinating because you have not only you have an imaginary creature here in the Kappa, but it is interacting with imaginary parts of the human body. Yeah, imagine ary organs. Now, of course, one read on this myth is that is that this all has to do with the observation of the corpses of drowning victims, right, that when people were pulled from the water, they would be found to have a gaping anus, and so it looked like something had been removed that

had been corking it up before. But in fact this is just caused by you know, relaxation of the muscles upon death. Right. But it also I think comes back to this idea that maybe we don't really we don't really think about the anus much, so you could smuggle in an imaginary body part and maybe people would be sort of a blind to it, are okay with They're like, okay, yeah,

I guess there's a cork down there. Yeah, I guess if you were going to invent an imaginary organ for any you know, semi external part of the body, that'd be the place to do it, right, But that would be the place where people might buy it. Now, there's another Japanese of folkloreic creature. This is a a member of the Okai, you know, the sort of fabulous pantheon of spirits that encounter in Japanese folklore, and it's known

as the shira May. Now. I can't find a lot about the chira May from academic writings, but it's at least enough of a thing that it pops up a lot in Japanese art and in Japanese pop culture. In fact, it apparently even shows up in the studio ghibli film pom Poco, which is a wonderful film. It's a it's an animated adventure that involves these shape shifting tonukis with magical testicles, which is a whole subject unto itself. But uh,

this this Japanese your CoA shows up. It is a humanoid creature with an eyeball in its anus, and that's how it kind of looks around at the world. You'd think, given the nature of the human posterior and glutes and all that, that that might not be a great place to put an eyeball, because it would be kind of hard to see out of a lot of the time. Well, but you have the fantastic body of a of a

spirit creature. I guess if everything is possible. Now. I've looked around for some their myths related to the anus, and I couldn't find a lot. So certainly, listeners out there, if you have run across some wonderful folk tales or myths are certainly mythological or folkloric monsters, uh with some sort of cool anal curio about them, be sure to let us know. But I did find one cool example in a text by John beer Horse titled Mythology of

the Lenape Guide and Texts. He points out that there's an ice giant cannibal in the traditions of the Lenape people known as the Mooe, and it's similar to other cannibal ogre traditions that you encounter in Native North American people's such as most famously the Windigo. But the movie is this this cannibalistic monster. It's basically impervious to harm, but it's also rather stupid, and you can kill it

by driving a steak into its anus. Wow, that that is a great variation on vampire lore, because the vampire doesn't really need a heart, does it? I mean, come on, it's dead. Why does it really does it really need to oxygenate all its tissues? But then again, it's we know it's drinking blood. So if it's drinking blood, it's got to be pooping, right. It's a creature defined by its hunger, so why is it not equally defined by its defecation? At least we see that with this creature.

This creature is defined by its ravenous hunger. And then it's it's a Kelly's heel is essentially it's a Kelly's anus. I have an interesting question, or you can judge whether it's interesting. Why are giants in so many folklore traditions believed to be dim witted? M hmm, well, you know, giant monsters, they're usually not the smartest. I don't know,

but you don't you see that a lot? I guess maybe part of it has to do with with something we've touched on already, ancient humans having to compete with apex predators creatures that are that have far superior physical strengths. But then how are humans able to overcome them and even eradicate them? In many cases they use their intellect, they use their cunning, and so so many of these cases are a giant monster is threatening the smaller human

and how do they defeat them? They outsmart them. So maybe the giants are modeled on sabretooth cats and bears and stuff. Maybe. So that's just my you know, off the hip. Read on that. I'm sure there are papers out there to dive a lot deeper into it. We'll have to look into it. The stupidity of giants coming soon to stuff to plow your mind. Well, now that also makes me wonder if anybody ever hunted bear or

sabretooth tigers by attacking the anus? Mm hmmm, we we can we can move on, Okay, so we should talk about the evolution of the anus. Where does this organ

come from? So for this portion the podcast, we turned to a couple of key sources, including Getting to the Bottom of Anal Evolution by Andreas Heynal and jose M Martin Duran, both from the University of Burke and Our Way, and Hey, nol seems to be the key figure in some of these studies because he's also the primary author on another piece, The Mouth The Anus in the Blast,

a poor colon open questions about questionable openings. And that's when he wrote with Mark Q. Martindale, I love how both titles here remind us that you probably have to have a sense of humor if you're an anus researcher. I wonder if anus puns in in the titles makes it harder or easier to get published in serious academic journals. I don't know. I feel like that the anus is

a special case. It kind of comes back to the sexual reproduction thing was mentioning earlier, Like we most most of us have an ability to switch back and forth between the serious and the comedic, but not so with the anus. And it seems to even spill over into into the academic world. Yeah, okay, Well, these start with an observation, which is a pretty simple one, right, the anus is not actually universal in animals. Obviously, lots of organisms don't have an anus. A plant doesn't need an anus,

it doesn't eat mushrooms don't need anuses. But even not all animals have anus, is right, That's right. Some lineages of animals such as uh Poropera, the sponges, Placazoa, the which are simple multicellular animals, UM Cestoda. Those are flat worms, including the tape worm and a can'to Cephala. This is another group of parasitic worms. They don't have a digestive track seas no digestive track, no, no digestive track. Now UH sea sponges and tape worms are good examples specifically

for these. Others have a gut with a single opening that both the takes in food and excretes waste, such as UH the to no offera, comb jellies, UH the Nigeria, which is a large invertebrate phylum that includes the hydra, jellyfish, sea an enemy, and coral. And then you also have acyl A morpha and these simple soft bodied plankton animals that live in the water uh. And then you also

have various flatworms and jaw worms as well. And the the Acyla morpha are going to come up several times because they are a really interesting reference organism when we're trying to understand our evolutionary history and go back to the beginning of what it was like when bilateral animals first appeared. But a great many animals do have what

is called a through gut, a linear track. Food goes in one specialized in for food uptake, and travels through specialized regions for nutrient absorption, and then it all leaves through a specialized excretion valve. And this of course is the anus. Now, the anus actually becomes very evolutionarily relevant here because you can't have a one way digestive tract without an anus. Right has to go some Well, we have some special cases lat on, but for the most part,

what goes in has to come out. That's right. I guess there are a few exceptions, but generally, yeah, this is how it works. If you don't have anus, then you've just got another one of these digestion buckets. Basically, you have a bucket in your body where food comes in and digestion happens and waste comes out. Yet again, this is one of those things that I maybe you would like it if you were like that, but given that you're not like that, you're probably glad you're not

like that. Well, hey, no has brought this up, he says, Can you imagine if we had a digestive system like this, what do you eat? And then you have to wait eight hours or more until you can eat again, Like there's no snacking. If you're hungry, it doesn't matter. Maybe you wouldn't be hungry in this case, but you have to wait until you can defecate out your mouth and then eat again. How would that change your perception of of everything in life? Yeah, and it's not just what's

appealing to you. I mean, Heynal points out in multiple places that there are several reasons that having a through gut, a one way digestive tract with an anus, is very evolutionarily appealing. There's a lot of advantage to it. So one of the things that's a real advantage here is what you just mentioned, the simultaneity of digestive stages. Yeah, you can eat more food while you're while you're you're

still digesting your last meal. Yeah, you can eat one big mac and while it's digesting, you can eat another big mac. Maybe in bed it doesn't matter. You can do whatever you want instead of just sitting around waiting to poop, So you can eat the second one. It's getting cold, but the second one, the second one is

really interesting. I think a one way through gut allows more efficient metabolism of food because different parts of the digestive system can specialize in different things, and you can perform those special functions in the best possible order so that one gets done definitely before the other one. If you're doing all of your gut stuff in just one bucket, it's going to be pretty much impossible to sequence these

specializations like this. But what would these specializations be. How about you've got a tongue and a sensitive mouth and that it's useful because it can detect the nutritional value of foods or reject potentially dangerous substances. Then you've got teeth at the top of the track to begin the processing chop stuff up. You've got a stomach full of hydrochloric acid and other chemicals to break down foods and trigger digestive enzymes. Uh, You've got a liver to secrete

bile and help with fatty foods. And then you've got a long curled up in testine to absorb nutrients, and then a colon to shuffle waist out the door. And it's important that all this stuff happens in the order that it happens. Yeah, I can't help but think of an assembly line. You know. It's the difference between a clockmaker's shop where material raw materials go in and a single shop maker goes through every stage of production, testing and then the clock comes right back out the front

door when it's ready. And if you compare like the time involved there with a an assembly line where you have multiple individuals, specialized individuals working on different parts of the clock's production and testing and and raw materials coming in one section, and at the end of the line you have finished clocks just rolling off the conveyor belt. Yeah.

I think that's a great analogy, or one analogy to the sack like gut might be that maybe you've got all these maybe you've even got all these specialized workers, but they're not in a line. They're just all standing in a huge room and waiting for their turn or kind of you know, reaching over each other's shoulders to work on the clock. Yeah. Um. Yeah. And you can imagine if you try to imagine your body working this way, where you don't have well ordered organs to specialize in

all of the stages of your metabolism as it goes on. Uh, not too good, is it? Chief right? Yeah. One more thing I'd say is that you can also have different species within the through gut organisms which specialize their body parts to adapt to their diet. So, for example, once you've got a one way digestive tract, you can say, well, I want to have this certain type of teeth to take advantage of this hard, chewy stuff that most people around me can't eat, and that will be my biological niche.

So it gives you more ways to evolve. It also means that you can grow to greater size because ultimately you have improved digestion. You can you can you can harvest more nutrients, and you're also not limited by I believe. Hey. No, it makes this point as well. If you have a particularly long organism, if it had to swallow its food and then digest it and then send it right back up to the head, that would be ridiculous. Imagine a

giraffe having to do that. A giraffe does not have to do that because everything can come right out the giraffe. As He also points out that there are two sets of genes in particular that are tied up here, known as the barrack. Your a gene and the para hawks gene UH, which is also referred to as just c d X for caudal c d x UH. And these are present and nearly all animals, and they play a

key role in the formation of the anal orifice. Yes, so he's saying that if you see these genes being expressed and tissue is the brachi re gene or the Caudal c d x often just c d X, you know that that tissue is forming an anal orifice almost every time. And if the animal loses its anus, and yes, we will mention to some animals that have lost their anus entirely, it often loses these genes as well. It

can't be true. How could you lose an anus? Well, you know it's it's not just a matter of misplacing it. It's just uh, it no longer becomes necessary to the functions of the organism. Alright, So hen Al and his colleagues they they set out to explore the evolution of the anus, right because they said it while it had been studied some, it hadn't gotten as much attention, especially through genetic research, as some other types of evolutionary innovations had.

That's right, we see that's the same for the same reasons that various ancient cultures have have either focused more on the heart or more Today we just focus on the brain. It seems like the anus has just received less attention. No fewer people have asked the question, where did the anus come from? What is the evolutionary heritage of the anus? But studying the anus is actually pretty interesting for learning about where at what points in evolutionary

history organisms divided off from one another. Yeah. They point out that studying the anus and animals is difficult in part because it appears and disappears again within many animal groups convergent evolution. Yeah. For instance, that most flat worms are anus lists, but others have independently independently evolved one. And then there's the polyclad flatworm actually has multiple anuses all over their backs. How many anuses multiple? It's like,

I think it's less than fifty. I'd say it's more like six to a dozen. Based on the image that I saw in the paper. What if you had fifty anuses on your back and they all just pooped a little? I don't know if that would be helpful. I mean, it does not seem adaptive for our ecological niche up. Thankfully that is not a design that really was picked up by natural selection. But most of this is interesting.

Most members of the super phylum due to Rostomes, which includes everything from c cucumbers to all vertebrates, they have anuses. But see stars have dropped the anus from its anatomical lineup completely. Okay, so they were in this group, but then they lost the anus, right, These are the losers of the anus. And then some animals develop anuses as they grow. This is I feel like I've touched on this in the past, but lacewings, you know, a small insect,

they don't poop during their larval stages. They have what's called a blind gut, in which everything just pushes to the back of the gut as they eat. And then after they go through metamorphosis they gain an anus, and then immediately upon emerging they poop out everything they ever ate prior to their metamorphosis. That's beautiful. And then the adults probably say, oh to be young and anus list again. And then there of course animals that lose their anus

during the course of their lifetime. A big example here, and this is one we've touched on before in our our our two part are on tails, is that of a certain scorpions that shed their tails an act of autotommy. This is like when lizards are attacked and they drop a tail, that sort of thing. Well take that, I'll run away. Yeah, I'd rather you just eat my tail

than eat my entire body. But the thing is with the scorpions, they have their anus on one of their tail segments, and if they lose it, uh, they lose their anus and then they simply never poop again. They simply fill up with poop for the rest of their lives, swelling with their their own excrement, unable to release it. That's no good. And this is a super fun too. Anuses can be multi purpose. Oh yeah, so this is

where we're going to talk about c cucumbers right. Oh yes, So the c cucumber does have an anus that it defecates through it's anial opening, but it also breathes through its anus. That is an interesting trick. Yeah. I have not figured out how to do that yet, I would say, I dare say most of you out there haven't either,

but yeah, amazing. So the c cucumber lives under the water and it can contract and expand its anal cavity to draw in breaths of water in much the same way that we expand and contract our lungs to draw in air. Right, So we've got like a diaphragm. We can open up the lungs, suck in the air, and

get the oxygen we need out of it. They expand the anal cavity, suck in the water, and then they extract dissolved oxygen from the water where the water it's fed into this large branching set of tissues known as a respiratory tree, kind of like the you know the pathways you see in the lungs when they expand, and then when you've extracted the oxygen, the water is pushed back out of the anus. Another fact about the c cucumber's anus that I found interesting it is often inhabited

by a crafty little stowaway. One of the best parasite riders out there, Ed Young has a great blog post from sixteen where he tells a story about this, and I have to relate it. So in this story he tells in ninety a biologist named Victor ben o'myer Rachao was diving in the water off an island in Indonesia when he collected a leopard sea cucumber. So it was about forty centimeters long and fourteen centimeters wide. And he gets the sea cucumber home and he stores it in

a bucket of water under refrigeration. Quote. Sometime later, a slender eel like fish swam out of the sea cucumber's anus. It was a star pearl fish, and it wasn't alone. Another wriggled out, and another. After ten hours, fourteen pearl fish had evacuated from the animal's bomb, each between eight and sixteen centimeters long. Another one stayed inside, so fifteen pearl fish in its anus. Now there is more than one species of pearl fish, and they occupied the bodies

of lots of different marine animals, even oysters. It writes that the pearl fish get their name from a case when a dead specimen was found not only inside an oyster, but buried inside a pearl uh and some species of pearl fish merely hide inside the sea cucumber, leaving the anus to forage for prey and then returning, but others have been thought to parasitize the host, like eating its

gonads in the walls of the respiratory tree. So does the does the cea cucumber get anything out of this or is it not that I found Uh, if they do get anything back, I've not discovered it yet. So that is a good question. If the sea cucumber doesn't get anything out of it, why doesn't it just close off its anus and restrict access to the pearl fish. Well, wait a minute, it has to breathe, remember, breathes through

its anus. So for the full body horror equivalent, try to imagine a parasite that wanted to get in your lungs and you could try to plug up your nose in your mouth to deny it access, but you'd have to breathe sometime. Interesting, so we we we've probably are seeing the trade off to an adaptation here. Like it's on one level, yes, you can breathe through your anus, but then the tradeoff is this opens your anus to even more parasitic activity. Yes, exactly. Now, to go back

to autotomy. When we talked about the scorpion that drops its own tail as a defense mechanism, see, cucumbers have an even more amazing version of anal defensive autotomy. It's known as quote evisceration. This is a defensive ejection of one's own internal organs, Like, is it nearly turning itself inside out? Is it uh an inversion of its body cavity, or is it just straight spraying sprays its own guts

out and lets them go. So if you go handle a c cucumber, which we are not recommending, do not be surprised if it poops all of its guts out at you. When the c cucumber opts for defensive advisceration, it contracts its muscles to push much of its respiratory tree out through its anus at the perceived attacker, and once ejected, the respiratory tree kind of turns into this sticky net which can confuse and entrap a predator. And it also contains toxins called saponins. So after doing this,

the sea cucumber can regenerate it's lost tissues. Not sure why it doesn't do this to protect to protect against the pearl fish. I think we don't know the answer there yet. I wonder it just basically breaks down to like the cost of spraying out its gusts and then regenerating them versus the cost of having the parasites there, and maybe it's just not quite worth the effort, Like it's it's ultimately cheaper to allow the parasites to do their thing. It could be the case. But one more thing.

When it comes to anal breathing, it is not just the sea cucumber. I don't know if you've read about this, Robert, but some turtles breathe through their butts. Oh no, this is all new to me. Yeah. So some water dwelling turtles, such as, for example, the Fitzroy River turtle, use a anal respiration or I guess I should be saying more accurately cloacal respiration. Yeah, honoring the distinction there, but uh, anal chloacle, whichever way you call it. They breathe out

of the backside opening of their their digestive tract. Uh. It's sort of like having gills in your rectum. They suck water into the cloaca, absorb oxygen, and then expel the water that they've taken the oxygen out of. Huh. I wonder if the if the kappa would be capable of a similar feat. I don't know, I'm not considered it. All right, we're gonna take one more break and when we come back, we will touch on the topic of

transient anuses. All right, we're back, Okay, Roberts. So we've discussed the evolutionary benefits of anuses, what creatures can do with their multi purpose annuses. But what's this idea that transient anuses some organisms can gain and lose their anus. Yeah. According to hay Now quote, there are several cases in which additional openings, connections between openings of different organ systems, and reductions of a through gut to a sack like gut can be identified. So there's a jaw worm called

Haplognatia and it has an anal poor. And then there's a microscopic uh platozoan animal known as Limnognathia, And this is actually a fairly recently discovered organism, and it has a temporary opening that likely serves as an anus. But it's never been caught or at least as a as of the publication of this paper, it has never been caught in the act of defecating. Wow, So it can get an opening that appears and people suspect it's ananus,

but they've never seen it poop. Right, And in both cases, these are on the creature's dorsal side, and H. Haynal. Points out that the secondary evolution of the anal openings this seems to be connected with the evolution of the of the extension of body length or overall size of the body. Okay, Well, this would go with the general idea that as organisms become larger and longer, they have more of an incentive to develop a through gut instead of just a sack gut. Yes, and thus the invention

of the anus or the evolution of the anus. Okay, But I want to ask a kind of different question. Now, how did the anus come to be? We've established that the anus has evolved multiple times in different animal lineages, so it's sort of a convergent evolution. Different clades figured out over time that they want to that they want to have a back opening of the digestive system. And also that the anus evolved in animals as they grew larger. As your body grows larger, it makes less and less

sense to have a sack shaped or bucket shaped digestive system. Um. So, so you've got all these advantages. That's how evolution pays for the through gut and the anus. But how did it happen? How did animals go from one gut opening to two? Well? To answer that question, I think we first want to go back to a paper that Hainal was one of the authors of in two thousand eight. So this was by Hanal and another researcher named Mark Q.

Martin Day. I think we already mentioned him also, But yeah, the two of these published paper in Nature in two eight called a seal development indicates the independent evolution of the Bilaterian mouth and anus. All right, now that that paper title is lacking in a humor department, I would admit, yeah, they didn't. They had didn't have their pun game going yet. So what did they find? How do you get from

one opening to two? Well, in previous thinking, and this was expressed in a Nature News article on the paper by a researcher named debt Leva Rent who's at the European Molecular Biology Laboratory in Heidelberg, it doesn't make sense for a new hole on the opposite end of the body from the mouth to just appear, so instead a Rent and others believed that over time what happened is the mouth elongated and eventually separated into two mouths more

side by side connecting to the same digestive sack, So you wouldn't have a one way through gut, yet you'd have sort of a U shaped digestive sack with two mouths. Okay, so the ideas imagine an alien species eats through its mouth, digest and then poops at its mouth, and then it evolves to where it just has two mouths, the pooping mouth and the eating mouth. Yeah, exactly. So you've got to all purpose mouths that go both ways, and this evolves over time to a through gut that goes one way.

And you know, once you have these two mouth openings, one of them could sort of migrate back over time and go down to the bottom of the organism, developed different specialization and eventually become an anus. Of course, we do have some organisms where they still have that essential you shape, uh say, say snails and slugs. Slugs even though they have no shell, evolved from shelled snails and

therefore they still have the front loaded defecation model. Oh but deem know if in their case, is it just two mouths and it goes either way or is it a one way system? I believe it is a one way system. Yes, okay, I'm thinking back to pass slug and snail research. All right. Uh, so here's where Hanal and Martindale disagreed. So they so that that was the old view, right, that you'd have two mouths and eventually the two mouths became a mouth and an anus differently specialized,

but Hanal and Martindale disagreed. They studied an organism called convolo taloba longefic euro, which is a flat worm with this kind of U shaped two gut or two mouth gut, and they compared it to worms with a one way gut containing a mouth and an anus. Now, earlier we mentioned that there are genes associated with the presence of an anus, right, Uh, there were the two genes we mentioned earlier. Now, when those get expressed, the body is

usually building anal tissue. Well, in this earlier case from two thousand eight, Hanal and Martindale discovered that longer Ficura expressed mouth building genes, not anal or hind gut building genes when building its two mouths. So both of those genes were genetically reading as mouths or both of those mouths. Sorry, we're genetically reading his mouths. But but the longer ficure did express hindgut or anal building genes found in other

species at the rear end of its body. And this suggests that a mouth did not turn into an anus, but the anus developed from some other structure being expressed at the rear end of the animal. So if it wasn't a mouth that turned into an anus, what is this structure or tissue at the rear end of the animal that could give rise to the development of an anus.

And they thought, what about sexual tissue exactly? So this brings us back to the two fifteen paper by Hano and Martin Duran, and all of this relates to something known as the gonopour. This is an opening that releases sperm. In the Aceila class of simple or at least evolutionarily simple invertebrates, they have no through gut, no circulatory system, no respiratory system, and no anus. And the researchers think that the origin of the gnipur may be linked to

the origin of the anus. Yeah, going back to that point about the genes, they say the gene expression of the seal orthologues of Brachii and the caudal c d X gene c d X in the posterior male gonopore, meaning the male sex organ at the back of these little organisms. It suggests that instead there is quote an evolutionary relationship between the bilaterryan hindgut and the acal gonopre.

So they're looking at the way genes are expressed and saying like, there there appears to be a genetic to tissue link between this sex organ in this very simple multicellular organism and what eventually turns into the anus in more complex creatures that have an anus. But they admit in their paper that this is not a lock. It's not like we know exactly where the anus came from or that it's linked to the secial gonopre. They say it's still vague, quote how the acal gonop or should

be related to the bilaterryan hindgut. A possible scenario, they write, could be the connection of the male reproductive organ system to the bilatery in digestive tract forming back to the cloaca. So so you'd get a cloaca because remember, as we said earlier, the cloaca combines a hole that deals with reproduction, It deals with excretion of liquid waste, and excretion of

solid waste. It puts it all in one hole. So they're saying, what if what happened is you got this, uh, you know, this ancient double duty hole that became a cloaca, And then they say, quote, this would thus provide an alternative hypothesis which would connect first the male reproductive system with the gut and later with the female reproductive system. Alright, So if I'm understanding this argument correctly, something like the

ganabar is an arcade serves as an archaic body opening. Yes, this primitive sex organ that we think something like it was present in our way way distant, and sters with that had bilateral symmetry, and as such it's something of not only a primitive sex organ, it's sort of a protoanus. Yes, it becomes the proto anus, which eventually joins together the reproductive and the digestive tract, and then over time, in

much later organisms, those things can separate again. In two thousand fifteen, when this paper came out of the BBC talked to Hainal and he had this wonderful quote that he shared. Our own hypothesis is that the anal opening has some evolutionary connection to the male ghanipour. This of course makes the whole subject even more delicate, But this is how nature is. Nature does not care about taboos

in human society. Look at him flout in those taboos. Yeah. Yeah, and it's you know, it's just another example of how if we ignore the anus, we do ourselves a disservice, in this case, in the realm of evolutionary biology. Yeah, don't don't let social morays keep you from studying ancient anus. Is exactly so. I I hope at the end of this episode everyone does have a new respect for the anus, and new respect for the development of the anus and how we we got to the point that we have them.

Because unless you had some sort of magical idea in your head that you know, a fallen Titan brought the Promethean anus to the people of Earth and and and thus relieve them of their uh, their dire constipation, you know it had to come from somewhere. And I think part of that whole like taboo aspect of the anis don't think about the anus. It makes us often not

question where it came from and how it developed over time. Well. Also, one thing you will hear from doctors and proctologists is uh, you know, you you might want to pay attention to your anus. You might want to think about it. Like some anal cancers can be caught early if you pay attention to it. Also, one thing I randomly came across while we were preparing for this episode. Apparently you shouldn't sit on the toilet for a really long time. Doctors said, don't.

Don't just sit there on your phone for an hour. I know people do that now sometimes phone the sun games are better than ever before, so it's understand bole. But apparently that's not good for your anus. Okay, So if you are listening to this podcast right now on the toilet, and you have listened to the entire episode on the toilet, it's probably time to move. Can I

add one more thing about the research process here? While we were reading, uh, you know, I was looking for good scientific articles about the anus, uh, And one thing I came across was this article full of obvious lies about how brown recluse spiders make nests in the human anus. It's not true, but I laughed a very hard. I'm not sure what prompted the writing of such a thing. I ran across a few things that made me giggle. One in particular, though, I saw one of these questions sites.

I forget which one it was, but it's the one where you click on the answer and like it slides, you click on the question and it slides over and gives you an answer. It's also users submitted. Oh boy, Yeah, some good answers of it. Yeah. The question was do butterflies have anuses? And the answer was yes, they have the second largest on Earth. I do not the leave that is is accurate, but it it made me laugh.

Oh man, they have the second largest on Earth and it's often colonized by brown recluse nests, probably according to you know, user generated scientific knowledge. So yeah, hopefully you're leaving this episode more knowledgeable of the anus uh than you were when you came in. Yeah, the anus. It's scientifically interesting, it's useful. You should appreciate it. All right, As we uh reach the posterior end of the podcast,

we should drive home that. Hey, if you want to check out more episodes of Stuff to Blow Your Mind, if you want to explore some blog posts and find links to our very social media accounts, head on over to stuff to Blow your Mind dot com. Big thanks as always to our audio producers Alex Williams and Tarry Harrison.

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