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Comb Jelly Digestion
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0:00
[Music] in 2016 a room of scientists gasped while watching a video of a comb jelly known to science as Tina for comb jellies are translucent gelatinous creatures of the sea and they're so ancient that they're probably the oldest animal lineage out there they were likely drifting around the world's oceans by at least 600 million years ago and researchers have studied the ins and outs of Comb jellies for centuries literally like other animals with ancient roots from sponges to anemones
0:34
they were long thought to use just one hole to eat and poop their gut was thought to be like a culdesac where food goes in gets digested and then is shot back out but the video showed fish that had been genan edited to glow in the dark moving through the Jelly's digestive system and once the jelly was done breaking down its luminous food two holes in its bottom suddenly appeared and it pooped out of a pair of mysterious holes now while watching a see-through jelly poop might not strike
1:06
you as that exciting it upended much of what scientists thought they knew about how and when animals evolved anuses in the first place and it turns out that while the evolution of the butthole was a major breakthrough in animal development its story might actually end with redefining what it means to have a butthole at all
1:30
we wanted to let you know about our new ammonite and troby fridge magnets just in time for magnet giving season the ammonite was 3D scanned from a ctitious fossil about 145 to 66 million years old found in Madagascar and the trilobyte was modeled after a 390 milliony old or divition fossil found in Morocco who is the cutest look at this you can find these magnets and our other merch at the link in the description or head over to complexly do store now there are a couple different
1:58
ways that animals can eat food and then excrete it and a butthole an opening at the end of the digestive tract where waste is pushed out of the body is only one of those ways some creatures completely lack digestive tracts like adult giant tube worms at the bottom of the ocean who get their nutrients from bacteria living inside their bodies but most ancient and simple organisms those that originated over 500 million years ago like jellyfish sea anemones and some
2:27
flat worms have sacklike digestion Ive systems with literal potty mouths stuff comes out the same way it came in from the same hole now this simple plan can have some disadvantages like every meal needs to be completely digested before new food can come in so it's pretty limiting if you need a lot of energy to grow develop and do stuff and since these sacks have dead ends they can't really have different segments and compartments doing slightly different jobs which means they miss out on the
2:58
benefits of having different microbes and enzymes breaking down different components of the meal at the same time later in the evolutionary history of animals it's thought some creatures solved this problem by evolving through guts which are more tube likee digestive systems where nutrients come in one way and go out another way TAA the birth of the butthole this it's long been thought was a necessary step towards animals becoming more complex because they could
3:28
eat more without without waiting to have digested everything else now exactly when and how this happened is a mystery scientists are still trying to solve the first attempt to explain the thr gut came in the late 1800s when a German zoologist applied his theory of recapitulation to the problem recapitulation was the idea that you could tell how animals had evolved by watching how they developed through their embryonic stages but no one could replicate his drawings of embryos later
3:58
in another attempt to explain how anuses evolved scientists started using the Velvet worm as a template this led them to claim that anuses originated from the same opening as the mouth see in velvet worms the embryo is a spherical blob that develops a first hole in the middle called a blastopore although not everybody agrees it's a true blastopore over time the circular like organism becomes more elongated and the blastopore becomes more Furrow like the furrow slowly starts to divide its labor
4:31
sucking water and microscopic nutrients in from one side and then spitting them out the other eventually This Groove pinches in the middle to create two separate holes and as the holes drift farther and farther apart the sack like gut folds inside where the pinch is and slowly turns into a tube this tube then is the through gut maybe this journey that velvet worms go on as they develop shows us how The evolutionary process of the anus unfolded and this became the
5:02
longest standing hypothesis about anuses according to this school of thought the first anuses appeared in this manner sometimes between 600 and 540 million years ago before animals became more sophisticated bilaterians with a right side left side bottom and top and in 1908 an Austrian zoologist studying the embryonic development of other animals noticed that they didn't go through the same Journey as the Velvet worm instead instead of becoming a Groove that formed
5:31
two holes the blastopore Hol stayed a single hole through embryonic development and in some animals that hole develops into a mouth in others the same hole develops into an anus then the hole grows into a tube that becomes elongated through the body until it meets the other side forming an anus or a mouth respectively according to this Theory the butthole is basically the bottom of the gut that slowly poked its way out of the body and scientists actually started using this process to
6:01
categorize animals into two different groups when the blastopore first forms the mouth the animal is a protoo meaning first mouth starfish are protostomes for example and when the blastopore becomes the anus first the animal is a deutero a second mouth earthworms are deuterosomes and so are we this school of thought suggested that the but hole was basically just turned on during Evolution when organisms evolved in directions where a butthole would be helpful to their success and that it
6:32
could sometimes be lost again when it's not helpful anymore if buttholes can break out of the body during the evolution of an animal to fit its lifestyle and not through the complicated tubing of a single hole this helps explain anomalies that the theory of recapitulation couldn't explain like for example the marine worm ramicus multi codada evolved a branched gut with hundreds of different buttholes along its entire body likely because that's what worked for its life strategy or the
7:03
AAL flatworm which doesn't have an anus at all even though some of its ancestors did building off of this a slew of scientists came up with new ideas for how exactly the Breakthrough happened in the 1940s for instance one German scientist theorized that the digestive system poked its way out of the body by connecting to the genital opening which was already there as another hole before the anus while another Austrian zoologist suggested animals first had a sacklike gut they stored their ovaries
7:35
in too and the through got developed together with the genital tract when the ovary started getting more complex hypotheses that bring the genital cavity into the picture help us understand why birds and reptiles today have cloas not exactly butth holes but instead one hole for reproducing and excreting waste so this growing body of research has built on top of itself throughout the decades sometimes dismantling or upsetting older ideas and there are still some big unanswered questions that keep
8:07
researchers on the fence like is it one hole splitting into two or one hole that poked out after the other but most hypotheses tend to agree on a similar Trend in all of these ideas the scientists have painted a linear Progressive picture of increasing complexity animals were simple with sacklike guts and then they evolved through guts when they became more complex and sophisticated and that's why that 2016 video of the comb jelly pooping was so shocking it completely
8:40
upends this picture because these seemingly simple animals apparently didn't have the seemingly simple gut that scientists had assumed simple animals had this initial bias is probably why it was so hard to find those anuses on comb jellies even though they've been studied for so long back in 18 1950 a biologist had even speculated the jellies probably had a through gut but because he never really observed any excrement coming from anus likee pores his idea quickly fell flat so when
9:12
scientists saw that their comb jellies were expelling waste from the same hole the food had entered their body they assumed it was the way their digestive system worked but it turns out the jellies were probably just puking this whole time maybe because because they were fed too much during the experiments or fed something they didn't like they hadn't been pooping at all if one of the most ancient organisms on the planet already had a through gut this invalidates the core belief that the
9:43
butthole evolved when organisms started getting bigger and more sophisticated or even that buttholes allowed for animals to start to grow and develop and diversify so much see back when scientists began asking questions about the anus they were assuming that EV ution was about progress and that complex was just better but maybe through guts were instead the most simple solution for the digestive system to start off as and maybe we need to rethink what we assume is simple and
10:14
what is complex in the evolution of Life once we rethink these categories new possibilities emerge like maybe ancient sea anemones and Jellyfish initially already had through guts with bum holes but close them up over time because they weren't all that useful to their success or maybe buttholes evolved independently in unique ways at different times throughout history and maybe there are some radically different ways to be a butthole after all if some animals
10:44
evolved their mouth and butthole at the same time some evolved mouths first and others evolved buttholes first some animals have two butth holes and others have hundreds what exactly is a butthole we just don't know yet Which hypothesis is correct with some scientists maintaining aspects of the Original Soul hole concept probably ring true While others favor other ideas it's hard to track this down through prehistory because there aren't many fossils to work from
11:15
jellies don't exactly fossilize well and up to the modern day we didn't really have the technology to fill some of these holes in our knowledge it's only now that scientists can study the cells molecules that make up these different holes in different animals that we can start to figure out what butth holes are molecularly and what cells they came from for instance scientists don't yet know whether comb jellies activate the same genes other animals do when growing
11:46
an anus maybe they're triggering something completely different with no Affinity to what we now call a butthole maybe it's something completely different and new butthole 2.0 but what we do know is that evolution is about finding solutions that work for all different animals with all their different Lifestyles not about following a linear path from sack to tube and from simple to complex and with modern advancements in technology and maybe a few more blind ends the next decade of
12:18
research will hopefully get to the bottom of
12:25
this okay listen up because we want to hear your feedback every year PBS digital Studio sends out an audience survey which we use to help understand what you enjoy on YouTube and what you want to see us make more of you also get to vote on new show ideas so it' be great if eon's fans were well represented in the polls there's a link in the description thanks in advance at a site in South America at least 22 giant ground sloths met their end one of the hypotheses that
12:52
researchers proposed for what killed the sloth has to do with their butts find out more in our episode did these giant ground sloths poop themselves to death and we can't leave behind this month's e onls Addie Annie and Eric Higgins Carl wolle Juan M Melanie lamb carnavale Nico Robin and Raphael hassa by becoming an eonite at patreon.com you can get fun perks like access to a monthly digital puzzle of eon's commissioned paleo art and as always thank you for joining me in the kin
13:28
Barnes Studio subscribe at youtube.com/ eons for more fantastic
13:36
[Music] fossils and maybe there are some radically different ways to be a but
13:51
hole oh my God man that's really hard to keep the straing great job oh maybe I won't be on screen for
14:03
that I said butthole or butth holes 21 times oh no Now 23 times in this episode that has to be some kind of record right
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