Why We Only Have Ten Toes (It's a Long Story)
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- Опубликовано: 27 апр 2024
- Check out our podcast Eons: Mysteries of Deep Time: ow.ly/2J4450Iu69U
Today, all mammals from humans to bats have five fingers or fewer. Yes, even whales, whose finger bones are hidden in their fins. Birds have four or fewer and amphibians get the best of both worlds, often having four digits on their “hands” and five on their “feet.” But no species of vertebrates have more than five digits, let alone eight!
Thanks to these paleoartists for allowing us to use their incredible work in this episode!
Julio Lacerda: / juliotheartist
Fabrizio de Rossi: / artoffabricious
Franz Anthony: franzanth.com/
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References: docs.google.com/document/d/1a...
Many of you have correctly pointed out that reptiles usually have five toes. Unless you're counting snakes, with no toes. So maybe it averages out? Regardless, sorry about that mix-up and thanks to those of you who sent us that correction!
Also, the extra digits on ichthyosaurs always fascinated me. Yes tetrapods settled on five as the ancestral condition for all living land vertebrates.
@@sahb8091 EA I
Please cut the jokes part we all know it's awkwardly corny.
I'd rather have facts trivia at the end of each episode...
Like: Do you know that water is wet? Or.. Every 60 seconds in Africa, a minute passes... Lol just kidding corny as heck too 🥲🤣
I really wonder: how is it possible that footprints fossilized eras ago, that have been exposed to the elements for who knows how long, are still preserved? I'd love an episode dedicated to trace fossils!
Because they were mostly not exposed to the elements.
As an amateur's guess: raw statistical occurrence, luck, and paleontologists having learned very carefully how to look for them. Of all the footprints an animal makes in its life, taken over the thousands to millions of years that species/lineage could be around, ploriferating to incredible numbers, at least some of them will be covered up in such a way that the mud will dry up into s clear fossilized shape. Most of those fossils are effectively buried forever for us, lost as a grain of sand in a beach of searchable locations, but the few places we've learned hold these fossils (due to soil composition or access to ancient eons of earth) and experts in their fields have learned how to find them and how not to break them while excavating.
That said, yes, I would absolutely love an episode dedicated to how Trace fossils form and how they're found by paleontologists. I Dinosaurs and Funky Little Walking Fish as much as anyone else, but I wish paleontology as a form of study got more of a spotlight, because the little I've seen makes it look really really cool
I thought this was about to turn into a "dinosaurs aren't real" comment.
I legit met a man who believed that.
Fossilized footprints are generally Footprints in mud that quickly get covered up by something like ocean floor sediments. Or they get covered up by something like a landslide or ash from a volcano eruption. They remain covered up for thousands or millions of years and then through natural plate tectonics, weather changes, and other factors, the fossilized footprints are exposed again for us to find. If they remain exposed to the elements, then they don't fossilize.
Pederpes looks exactly like Pederpes should look with a name like that. I love it.
I legit lolled much when that came up
“This thing looks kinda derpy… what are we gonna call it?”
“Can you imagine if we called them ‘derpies’?!”
“OMG! Well, the scientific community won’t accept that (even though there’s a bird called a booby, another bird called a tit, and a fish called ‘Boops Boops’), but maybe we can try to hide it ever so slightly. Only we will know ;) “
Final name: Pederpes
Yeah, I smiled a lot at the name. I think it means something like "foot of Peter" though. Anyway, definitely naming my next Quagsire that.
@@rasmusn.e.m1064 Peter means stone as well, so the well goes deeper
pederpy
Pandas basically have six fingers and I guess got around the whole, "the DNA that codes for how many fingers you have would mess a bunch of other stuff up if it mutated," by not really adding another finger. Its just a finger sized outcrop of bone, no joint involved. So they basically have 5 fingers and a hand stick.
Interestingly they also evolved from the omnivorous diet of their ancestors to a diet of bamboo only. Perhaps the "hand stick" has something to do with the diet modification. I'm certainly no expert though.
@@gaufrid1956 from what I've been told its basically to help them hold bamboo. You can watch them eat and they use all six "fingers" to hold the stalk properly.
Perhaps all of this 'hand stick' accounts for why pandas don't breed as much as they maybe should. 😐
@@tsopmocful1958 I dont see how that would affect pandas breeding
and hedgehogs which have a modified wrist bone to create a sixth digit to improve burrowing.
Imagine if we had 8 fingers each hand then we would calculate everything in hexadecimal 😄
Good point.
I doubt it, for the reason that we were also used to count to 60 with our two hands (the Sumerians started with it, things like a circle being 360 degrees is a relic of that time), yet we lost it over time to only using a decimal system
@@bartelvandervelden9894 I think the point is that we only used a decimal system in the first place because we have 10 fingers. We don’t use base-60 or base-16 because they’re a lot less intuitive to count on your hands
@@Srothics there’s also the binary system of counting things, besides the decimal, hexadecimal, base-60 systems. But, you’re right, base-10 is our preferred methods because of its more intuitive to us.
@@bartelvandervelden9894 sumerians counted using their finger folds
Wow I haven't been this early since the devonian period.
I was never even early
Same
@Leo the Anglo-Filipino ur parents may be related.
Lol
Left yourself open there my friend :P
Never have I ever thought to myself "what I really need here is an extra three fingers"
A third arm and hand? Absolutely! But I struggle to see a scenario where fingers beyond five give an evolutionary advantage, but they are extra complexity which is a disadvantage.
I completely agree! A few extra fingers wouldn't benefit me much, but I could go for a third or fourth arm!
More groceries you can carry at ones from car to door.
You clearly have never played piano :D
Another index finger would be awesome
There's also playing guitar, doing crafts where you have to hold things down with your fingers, having more fingers to hold An Piece Of Tape when you're gearing up to tape the heck out of something... I still kinda agree - I do wish for an extra arm more frequently, but I do still regularly wish for more digits lol
having another thumb by your pinky would make it rather easy to open stuff like bottles with just one hand, so theres that lol
3:23, is it just me, or do the three fingers together here look like a proto-thumb with four other fingers???? Did those three fuse into one??? If so, that is AWESOME! If not, it could still show that an angled set of fingers plus four straight ish fingers was somehow ideal for these tetrapods , and that is FASCINATING!!!
It’s very difficult for existing structures to fuse as opposed to duplicating or expanding upon a single structure. Losing extra fingers and reinforcing existing ones is a more feasible evolutionary path, which you will see if you look more into how genes tent to express morphologically. You also won’t see thumbs appear for hundreds of millions of years. I suppose anything is possible but it’s difficult to see this being a plausible bath of evolution
it's not just you; I had the same reaction the the 3+4 config.
That thought occurred to me as well.
@@W333L Don't we have tons of examples of structures fusing, both evolutionarily and developmentally? Aren't bird wings three fused dino fingers?
@@seleuf think about the central claim. In all tetrapod derived groups we see each digit vary in shape, size, location etc. Your example is a great illustration of wrist and hand bones for example, where fusion and reorientation happens constantly among related species, though these bones rarely fuse into a single undivided structure. Bird wing skeletons have clear division clefts between each digit to form a structure that looks nothing like a paw or flipper, though each digit is a self contained bone that attaches to the other arm bones (we even see some digit deletions). What you don’t see, however, is two finger digits fusing into a thumb. We would have a clear division cleft at some point in the fossil record to explain this, and it’s simply astronomically easier for an organism to lose an unwanted digit through a deletion mutation or gene silencing rather than spend hundreds of thousands of years melding the bones into one.
Genes affecting digit development absolutely control other parts of development. I have congenital thumb hypoplasia, and also scoliosis. My daughter likely has the same gene mutation, she also has thumb hypoplasia, scoliosis, as well as radial dysplasia. She also had to be screened for heart and kidney deformities since they are common seen alongside these conditions
Very interesting. About regaining more digits. There is sixfingered dwarfism. That leads to diminutitive growth and other health issues. So the hypothesis of the gene being used for more than one purpose rings true.
I was wondering, are those 6 fingers fully functional? Are the just as strong and gripping as 5 fingers? I imagine that it's not only the existance of the digit, the true power of the hand is in the arm, the muscles pulling on the tendons to make me type this.
@@rickglorie I know there is a family where every single person has 6 fully functional fingers on each hand
@@rickglorie “the true power of the hand” *avengers theme intensifies*
The genes involved in having a sixth finger also control the likelihood the person will kill Inigo Montoya's father and need to prepare to die, thus explaining why it remains a rare trait.
It's no hypothesis: the gene regulatory network that produce digits in tetrapods is pretty well known and some of the genes involved, like Sonic hedgehog and the hox genes, play key roles in the developments of other organs, such as the central nervous system for Sonic hedgehog and the spine for hox.
Someone mentioned pandas, and I would love an episode on how one of the most fearsome carnivores on the planet eventually sprung a lineage that is strictly herbivorous.
The thing is, bears aren't carnivores.
@@aaaaa359 that I know but they’re in the order Carnivora. That’s what I was meaning.
They are just faking it! They eat parts of the bamboo that are super high protein and still have the digestive tract of carnivores.
The first bear (dawn bear) was believed to be omnivorous, I think. And then evolved and diverged into mostly omnivores, with carnivorous polar bears on one end of the spectrum and herbivorous panda bears on the other. So basically the fearsome carnivore aspect came later.
Totally irrelevant answer. "Religion".😂😂
Wouldn’t the larger number of digits be vestiges of being evolved from fins that would slowly disappear due to a lack of selective pressure for more digits than necessary? I think that’s one of those things I always assumed without really thinking about it.
No. Fins aren’t hands. Look up the fish skeleton, it has bones driving four limbs built out as fins, but more fins are controlled by just muscles. Fins are cartilage with skin stretched over them, think of them like your foot slipped into a scuba fin.
The wiring and subroutines to use digits need to be accounted for - five, set up as two, two, one (opposing digit) comes from ancient claws and works well. Add a sixth and it gets ferociously complicated!
@@elizabethclaiborne6461, Hmmm. Well, I know they aren’t the same, but every depiction I have ever seen of the land vertebrate ancestor(s) has been a lungfish like creature with little, arm-like, stubs between its body and fins. Every text book I’ve looked at (granted that was decades ago) has described the transition from fully aquatic vertebrates to fully terrestrial vertebrates as involving air bladders evolving into lungs and fins evolving into limbs.
If I’m wrong, and hands, feet, arms and legs did not evolve from fins, I must say I am positively mystified as to how we evolved such appendages and what from.
Selective pressure is provided by the environment and actively selects the surviving traits. Selective pressure allowed five - digit-handed creatures to live on and pass their genes on while those with more digits could not use them efficiently to live to pass on their genes. The polydactal animals were selected against. That is how selective pressure works.
Another example: amphibians come out on land, but they are still tied to water in order to lay and fertilize their jelly - like eggs. They cannot stay out of water their entire lives.
Reptiles had developed the shell - enclosed egg, and when they ventured into land, they could stay there permanently because the eggs could fend off the drying effects of weather and still allow embryos to develop into offspring.
Frogs cannot spawn on land. Selective pressure prevents them from living on land and spawning there. There was no selective pressure to keep reptiles like alligators spawning in water, though there is an advantage gained from returning to the water for some activities. But reptiles can lay eggs, eat and live in even the most arid of environments.
Outside a civilization where it's necessary to wear five-fingered, industrially produced gloves that stands for, at the very least, hundreds of thousands of years but doesn't invent the technology necessary to cut off supernumerary digits, what's the selection pressure that makes 5 the ideal number?
Whale hind limbs became weak and useless due to a change in lifestyle; they disappeared because even vestigial hind limbs create extra drag relevant for survival.
On the other hand, if a lineage that just so happened to have five fingers per hand/foot, rather than seven, four, or three, also had something else that gave them an advantage, the number 5 would be mostly preserved without any real pressure -unless a specific descendant lineage (horses...) developed into a very specific direction.
@@adlockhungry304 limbs absolutely evolved from fins, they even use the same genes that fish use for fins. Since we are lobed finned fish our genes for our limbs should be more related to the genes in a coelacanth than in marlin or any other ray finned fish.
Ironically, while it is supposed that whales won't gain legs again, we can point to them as an example of tetrapods gaining fins again.
Only sort of. These are in no way similar to the old fins. It's just a covergently evolved structure that functions as fins.
It's still impossible to truly regain what was lost.
But note how they haven't regained their gills yet & still use lungs, despite being aquatic.
Well, ichthyosaurs went kinda crazy with hand/finger bones. Granted those were embedded in a flipper, not fingers
I don’t know if any will actually read this, but THANK YOU for respecting the audience’s intelligence in this video. Still concise and informative without being boring. Perfect middle ground.
0:58 "…but no species of vertebrates have _more_ than five digits."
Hemingway cats: "Please allow me to introduce myself…"
I've heard somewhere that the reason certain species of fish from the Devonian such as Tiktaalik evolved limbs that allowed them to go on land was so they could escape from perusing predators. But overtime these fish and their descendants evolved to become more terrestrial. This was because insects were already abundant all over the land, so evolving to become land-bound opened up a new ecological niche for these prehistoric fish, as now they can hunt for insects that were already on land.
the alternate earth of an arthropod, fungi and plant land life, where vertebrates just didn't bother, seems like a dope concept lol
do we know if tiktaalik generated an environmental change which suited early insects (eg perhaps by depositing concentrated food supplies on beaches?...)
Most of the stuff about early tetrapods is almost entirely speculation will very little evidence. In fact I remember reading an article which did a fairly comprehensive study of several of these early tetrapods which were sufficiently well preserved that their muscle scar attachments of skeletal digits sufficiently preserved to allow the muscles to be reconstructed and worse many of them lacked the spinal musculature to even crawl on land any better than a beached whale generally indicate the early tetrapods couldn't support their weight out of the water at all. Couple that with work showing they likely lacked the sensory apparatus to see effectively on land based on the shape of their eye sockets (though one of them ironically one of the earlier ones did have eyes that were probably adapted for land as they were positioned like a crocodile to see out of the water while submerged and its jaws left no doubt about what it was using those eyes to do. Still that was one of the fossils that would fare about as well as a beached whale on land so it was probably a pretty risky strategy dependent on its ability to drag prey back into the water in a sudden strike)
It has been several years but I remember reading a fascinating article which looked at some changes in musculature which identifies several changes which seem to line up temporally with molecular clock estimates for a polypoidal hybridization event where the lobe finned fish genome in the tetrapod ancestor was effectively duplicated. Unfortunately I was only able to access that paper on campus via my University journal subscription so it would be hard to find again. Point is from what I have read the predator escape hypothesis doesn't seem very likely if they lack the skeletal and muscular strength to actually move or support their weight at all on land. Those papers seem to argue for a aquatic walking scenario with the terrestrial switch happening around the time of the full genome duplication event which seems to align with the Devonian extinction events. I'm not sure we can say what or why but it does seem plausible that tetrapods might not have been able to go on land without an evolutionary fluke.
That makes sense considering most of the ones that couldnt make it back to the water died haha.
@@Dragrath1 The more recent information about Parmastega backs up the idea of water-walking tetrapods long before anything vertabrate actually got out of the water. It was a mostly cartilaginous tetrapod from earlier than tiktaalik; it was shore-dwelling instead of the later freshwater tetrapods, and it appears to have been an evolutionary dead end, but one which lived quite well for a while. It couldn't get out of the water, but it walked around in the shallows gathering washed up food just fine.
Seems to me that more digits would make for a wider surface area to use while paddling, but get in the way when trying to move on land.
Exactly what I was thinking, you only need those in the middle. Kind of like how horses and many other hoofed animals lost their digits.
@@taxidermiedhuman1523 fewer digits means more tensile strength per digit. Highly evolved diggers also lose digits in their hands
I guess when it comes to land bound locomotion, fewer is better.
Agreed. I would think being on land requires thicker stronger bones, so it may have been a fair tradeoff to make fewer but stronger bones.
Nah, they just kept getting messed up when they tried to count things. Eventually, they were simply unable to fall asleep while tending their sheep herds, and thus died out.
My nephew is polydactyl. He has 6 fingers on each hand and 6 toes on each foot. The toes are well formed and fully functional. The extra pinky finger on each hand is more just floating there and should probably be removed surgically.
Does he climb walls??
I heard that polydactyl has dominant genes, so even if he get a surgery, his children might still be affected.
@@mrvn000 Probably not but no doubt as a child he had no problem learning his 6 times table 😉
Your nephew is Stanford Pines from Gravity Falls
In India they think that your nephew is extremely lucky.
Others have probably mentioned it, but I'm curious how Polydactylism plays into this.
I think tetrapod anatomy and evolution is so fascinating, like I’ve spent hours just navigating through the phylogenetic tree of tetrapods on Wikipedia and then just obsessively researching some obscure lineage of ancient animals because I feel like it.
cool. nice way to nerd.
I’ve gone down some pretty random rabbit holes doing that too.
@@patsysadowski1546 this is the internet not field of cuddly bunnies
@@kyptos2252same thing if you squint
Wow! This video came at a perfect time- we’ve been discussing this topic in my evolution course just this week
What come first Male or female
@@ezpeasy3967 the egg the chicken no wait I know what they're going to say they're going to try to tell you both like a hermaphrodite. Then they're going to say stop assuming genders. Then after that they are going to tell you stop using those terms male and female because it has the word male in it, then after that they're going to say don't use man or woman because woman has the word man in it.
Ichthyosaurs are probably the few exceptions where a whole large clade had extreme polydactyly. Looking at their fins genuinely feels like you're looking at a corn cob, lots of finger segments and lots of fingers.
@6:07 "Pederpes" describes that species very effectively. Derpy indeed!
I always found Ichthyosaurs to be interesting because they evolved six, or sometimes more, digits. Probably through the typical extra digit mutation. They are, of course, the exception.
Ah, and also brilliant swimmers - perhaps there's some heft to the "' motion "on land" vs "in water" theory '"? Maybe given enough time, Aligators might gain a sixth digit? :')
@@OddcessiveNooBurrito Now, I wonder if the terrestrial part of crocodilian life still plays too much of an important role for that to happen though....
Perhaps the cetaceans will gain extra digits spontaneously over time?
@@OddcessiveNooBurrito It might just be that they had not evolved enough dexterity for more fingers to be redundent.
Moles also have an extra finger.
0:53 “birds and reptiles have 4 or fewer”
My bearded dragon chilling in his tank would like to disagree with you by offering you a crisp high-5
Australians, always gotta be different.
I don't remember lizards with 4 fingers...
6:51 I’ve been randomly attacked by cuteness!
How do Hemingway cats figure into this, though? I've been told that they don't really seem to suffer the usual problems asociated with the polydactyl condition, but the most I've ever had in the way of explanation was that, and I quote, "they're a red herring," without any greater context.
All this talk about digits makes me want a video about how we evolved opposable thumbs. Talking about how we used to have more digits specifically makes me think about what the world would look like if we had more than one opposable thumb, either on the same or opposite side as the one we do have.
Koalas basically have two thumbs on each hand.
I think it is because our ancestors started using and or making tools more and more
It's interesting to think how easily there could be an alternate timeline in which everything evolved much the same, but humans and other vertebrates all had 7 fingers on each hand. The worst thing about finding yourself there would be that you'd have to relearn simple math because people would most likely use a base-14 numbering system.
Or in Hexadecimal
There's actually a school house rock that's kinda about that
Base 14 is not inherently worse than base 10, given 14 has the exact same amount of factors (1,2,7,14). Base 12, on the other had, has many more (1,2,3,4,6,12)
@@sohopedeco yup! but we're just used to a base 10 numbering system so we can kost easily go in forms of 10
(10,20,30,40 etc) where their numbering system would likely be different to compensate if that makes any sense?
(sorry if this is slightly off context)
@@l.zevicreations 12 would just be the next ten and would be easy just for whoever uses it just as 10 is for us
Man, I love this channel, answering questions I've barely thought about :)
love this channel! pretty much every Video and for sure everyone of you hosts are awesome! keep up the great work
I was amazingly lucky to study with Jenny Clack who was so instrumental in making some of these key discoveries. It is a period which never ceases to amaze me.
Can you please do a video explaining the fossilisation process? For instance, how long do bones stay bones until the material turns to stone? Are recent discoveries fossils or are they just well preserved organic matter? How do paleontologists tell what rock to remove to reveal the fossil inside? That sort of thing. Thanks.
I've read that it has to do with weight distribution. Our bodies add a bone to each distal segment below each joint. An example : our legs: one femur, knee joint, two lower leg (tibia, fibula), ankle joint, 3 tarsals, chopart joint, 4 metatarsals, lisfranc joint, 5 phalanges. We all have 5 digits because we all follow this pattern. We don't have more digits because there is no advantage to locomotion by adding additional joint segments.
I have a question : Do all tetrapods belong to the same lineage and then some branches lost fingers?
Or are there multiple lineages of four-legged vertebrates which evolved indepently, each one with a unique number of fingers?
Maybe having more than 5 fingers was pretty common in the past, but by just luck, the common ancestor of all living tetrapods had only 5 fingers and that triassic 7-6 digits reptile was the last decendant of a sister clade of 5+ finger tetrapods
I guess if our common ancestor had four fingers, we would be like people from The Simpsons.
mmmm no.
I mean some people do have more then five fingers, people who have Polydactyly.
I don't know about that but I believe the polydactyl mutation is dominant in human heredity.
@@justforplaylists Yeah it would have had to have evolved all the reptile like traits independently I would instead based on the abundance of oddities in the Triassic be more willing to bet it might have been a polypoidal hybrid organism since all 4 of the polypoidal hybridization events recorded in the amniotic genome happen to line up with a major mass extinction event and stressed conditions in modern times have been linked to increased likelihood of polypoidal offspring being born.
Its possible with two copies of the developmental genes that the expression of them could then be split to allow one copy to take over the brain and spinal functionalities and the other to take over limb development avoiding the deformities that tend to occur alongside digit duplication events.
Or maybe some other gene or mutation countered those detrimental factors to make it ecologically viable to increase the number of digits?
The Devonian is an amazing time period! Could you do a video on the ceratopsians? Don’t remember seeing an episode on those guys!
I believe there is an important omission in this video that is only suggested at the end - that the genes that control 5 fingeredness are shared by other features, and one feature of particular importance: the reproductive system. People with polydactyly such as Bardet-Biedl syndrome tend to have reduced fertility with mutations to the internal reproductive organs in females. This is additional to other issues like congenital heart defects, but the problems with fertility might be the important factor that sustains 5 fingeredness in animals, because organisms with a mutation of different number of digits don't tend to produce offspring.
My dog was born with 6 fingers on it's paws. I don't remember if it was the case both with front and back legs.. it was a double thumb, but the extra one looked like it was not well attached with the joint, although it looked perfectly fine. However due to possible complications or injuries we had them removed surgically. The thumb is of little use to dogs, so I don't think this mutation would have any benefits, but it's cool to know these things happen
Another amazing Eons video. It’s incredible how you guys keep finding new interesting topics and then make both a well researched and engaging piece of content
There's one form (out of dozens) of Six-Fingered Polydactyly in humans (a fully functional duplication of the middle finger) which appears to be a genetically dominant trait. Perhaps having greater dexterity from more digits is advantagious trait in the modern human environment..?
If I could quadruple flip someone off, I would be so happy
Typing like a boss, I bet.
The Digital Era?
Better keyboard and gaming input
@@ASLUHLUHCE Play the F Chord on a guitar like a boss.
They didn't "trade" gills for lungs.
Lungs are the swim bladder.
Fish in Amazonas use this today.
There are a tube from the mouth.
These type of fish are eating other fishes that gets stuck when the water level get lower, and the oxygen in the water drop to a level that all other fish can't move, or die.
This seems like the perfect place to share this little nugget. My pupper was a genetic abomination! My Golden Pyrenees had polydactyly, he had six completely formed dewclaws: four up front and two in the rear!
I miss my little sin against nature, but he's chasing butterflies in heaven 🥲❤
Ps. Golden Pyrenees are guardian dogs, they laze around the house until there's something weird afoot. It could be anything... frankly it can be downright disconcerting sometimes. Once when I brought my pupper Zeus to my grandparents house. He was lazing about in the grass when out of nowhere he was off like a bat out of hell. He had spotted a hair a good 200 feet away and the chase was on. My grandma laughed and called out "good luck ya oaf!" She was absolutely speechless when he brought us back dinner 😆 (this was also six months before we put him down from old age)
My other Pyrenees Xena often barks at "nothing"... as in every few hours... except it's never nothing. Sometimes its the neighbors working outside. They live a mile away. Sometimes it's an animal, the most legendary of which was an ermine (a small weasel). It was atleast a half mile away and I needed binoculars to see it 😂
God I love my pups, always keepin their pack safe!
I don't want to go to biology class tomorrow. I just want to keep learning from this channel!!!!!
this is the problem with schooling.. if this interest you then you have an interest in biology but the class and test scoring system prevents student from simply enjoying new information for the sake of learning
Love your videos. I love to learn and the videos usually lead me to researching more about the subject on my own.
Ye
People who have the condition polydactyly have an extra finger on one or both hands or feet. It would be interesting to know if these people find it better with six fingers or worse, and why. This could give some insight into why the normal number does not go above 5, so if paleontologists who are studying this subject haven't consulted with polydactyls yet they probably should.
Saw something on that. They generally have it better, if the extra digit is controllable.
Is the extra finger usable though?
Pederpes seems to be a close contender of being the last common ancestor to all living tetrapods from frogs to humans which is calculated to have live around 350 million years ago which is about the same time that pederpes lived!
Some cats are polydactyl which gives them 6 digits. From what I have heard they can be fully functional healthy digits at that.
Do you have a twitter?
There's also a dog breed that at its height was very polydactyl. Can't remember the name of it, but they used it to hunt puffins.
@@SupersuMC Norsk Lundehund
Once traits are lost, supposedly they don't come back.
And yet, crabs reappear through the millions of years of life.
Somewhere, Blake just let out a scream while thinking of coconut crabs.
That's what make crabs so unusual
There's a clause in that hypothesis: "except crabs, of course. Dang crabs."
Very interesting topic, and a great video! Thanks for the content.
I knows it's a weird topic but I'd like to see an episode on how mammals transitioned away from cloacas.
Okay, but... polydactyly is a thing. If it messed up other systems, youd think it was way less common than it is...
Yeah, what about Hemingway's cats?
I only hear about it in cats and when they said 5 or less I was like what about cats
It's quite common in cats. They seem to do just fine and have no obvious problems.
Our polydactyl cat was the clumsiest cat I've ever known. He did have a couple health problems including something with the nerves in his back/back legs as he aged, no idea if it was related at all to the mitten feet
It happens in humans too, actually. ^^'
I would imagine there's a certain amount of selective pressure towards more sturdy individual digits, since if you have a bunch of small digits with thin bones and are trying to walk on land, each digit would be at greater risk of serious damage like a bone fracture or getting severed, which by itself could seriously hinder movement (or require strategies for mitigating damage like we see in reptiles). Fewer, stronger digits would provide greater durability while still distributing pressure and providing sufficient dexterity. Two digits would be the minimum to provide balance on a single axis, three digits for two axes, and five is probably just the maximum typically needed for whatever use the animal has. Added complexity is also costly by itself, just to provide extra bones, joints, muscles, nerves, etc. and with the fact that it's hard to spontaneously gain lost traits as you explained, I'm not surprised we don't see extra digits today.
In short, basically more digits = decreased durability/increased risk of damage, and gives diminishing returns on maneuverability/dexterity would be my theory on the downward selective pressure at play.
Many years ago, I went on a tour of the prehistoric caves in France, and I very surprised to see the number of hand paintings that had six fingers -- the only people I know who have polydactyly are me and members of my family. Interestingly enough, polydactyly is a dominant trait on humans. Even with early intervention (removal of the sixth digit to ensure better hand development as the sixth finger relies heavily upon the fifth finger), polydactyly is becoming an oddity of genetics, much like left-handedness (which hovers at 10-12% globally -- BECAUSE SCISSORS ARE A DEATH TRAP FOR THE SOUTHPAW!!!).
4:07 This should be qualified as "*most* quadrupeds" since camels and giraffes have that same gait when walking.
I do not want extra fingers. However, an extra pair or two of arms (plus wrists, hands, and fingers like normal) would be lovely.
As someone who does spec evo, these kinds of videos are so helpful!
How does one "do" spec evo?
@@MM-jf1me Making diagrams, art, and flowcharts for fictional evolutionary lineages.
isnt having 6 digits on a hand a recessive gene in humans?
I thought polydactyly was actually a dominant trait
@@alinaowen2635 I believe there are multiple variants. The Amish one, for example, is recessive iirc
I read its dominant.
I’ll never stop smokin as long as y’all making theses videos
Finally learning why we count to ten
(And not eight, or sixteen which both would've made our counting system so much smarter and easier to put into 2 bit computer language)
Do a video on evolution of the eye
Eyes have evolved many times. Be more specific. Cephalopod eyes, arthropod eyes, vertebrate eyes, which?
How did hooves turn to flipers for whales? And balleen teeth?
This would be so interesting!
I also want these topics in upcoming videos.
Whales seem to have totally lost their teeth before they evolved baleen (and baleen doesn't derive from the same tissue as teeth), probably they were suction feeding for a while
Early land living cetaceans like Pakicetus didn't have hooves like a deer etc, even though it was an artiodactyl. But we see that with some other living ungulates, e.g. rhinos don't have hooves in the way deer do.
Pretty sure they have an episode called “when whales walked”
One interesting idea I read few years ago was, taking into account that we have evidence of footprints of a fully terrestrial teprapod that lived before the earliest semiacuatic tetrapods we know, it might be possible that Acanthostega and Ichtyostega were a lineage that went back to the water (retaining secondarily terrestrial traits instead of showing novelties to colonize land) therefore, terrestrial animals might appeared way back. Unfortunately that section of the carboniferous is quite poor to give any certainty.
This is my new favorite series and I love it.
If we had evolved with a different number of digits, would our understanding of mathematics have developed "differently"?
Hard to say. The Babylonians and the Phoenicians used a base 12 system despite only having 10 fingers.
@@erraticonteuse i thought it was base 360.
We would simply be using a different base system
@@tompatterson1548 OK Google says that it was actually base 60, which is also divisible by both 12 and 10. However the Egyptians did use base 12.
So, short answer, no. We’ve settled on base 10 for arithmetic, but mathematics is much larger than your base system and arithmetic.
I'm loving her lethargic cadence.
Early tetrapods are very interesting topic. Hopefully there will be more early carboniferous (and maybe even middle devonian) fossils of tetrapods.
Polydactyly can be also seen among hupehsuchids and ichtyosaurs.
I got to learn a few things, and also watch a kitten chewing on a hand :) Bonus! Cats are known for throwing up individuals with polydactyly, and I have a paper somewhere about a cat with a fifth (not very functional) leg, from a family that had polydactyly in its lineage, but that's more genetic mutation rather than a species getting missing digits back.
• our ancestors used to have six or more digits per hand; then [cut to scene of kitten chewing on a hand]
• "Cats are known for throwing up." oh, there's more to that sentence.
I love this show especially the host. Please do a video on the split in our evolution once the dinosaurs became extinct
Could you do an video on Spinosaurs and it’s family members in Evolution?
maybe even include Iberospinus!
They’ve done spinosaurs already.
Just thinking this through a bit, it makes sense that mechanically 5 fingers allow for a sort of balance with slight redundancy and flexibility. I.e. if you start to tip left, you can begin to catch yourself with one or two, but if one fails you you have the other so as not to lose that ability altogether.
Considering nutrients and the sort of laziness when it comes to genes, think blind translucent cave animals, while 7 might make just as much sense as 5, 5 is the minimum necessary for most semi complex movements. More require greater competence to manage and more nutrients to maintain.
Three makes similar sense, and 4 is workable but lacks that center digit to balance things out, but anything more is overkill with the same potential downsides to each (odd versus even numbers of digits).
I think that's a fairly decent reason. But like the video said, good luck testing it. Seeing this on one of those ai learning videos would be super interesting.
Hey that was pretty neat can you do one on the shrimp that live in the cedar trees on the California coast line.
It's funny that you add bird songs to images of Devonian animals, considering they wouldn't exist for another 250 million years, give or take! But it did make me think about how quiet the earth must have been back then. Other than sounds of locomotion, I imagine insects and early amphibians weren't producing any sounds. Do we see evidence that they could have produced sounds like some modern amphibians can?
Given cicadas, I wouldn't assume the insects were quiet in the Devonian. Modern insects make noise with assorted body parts that we didn't always recognize as noisemakers until fairly recently (e.g., how crickets chirp).
@@Eloraurora Oh true, I had honestly forgotten about cicadas and crickets...neither of those appear until the Triassic, but I suppose it's possible their predecessors could have made sounds.
Amazing. Can u explain why the different eye, hair, and skin colors? And did we have more in the past?
Because of the sun exposure. Some places it is more than others so thousands of years the melatonin changes to suit the environment.
Michelle has come into their role as host seamlessly. Actually, I don't think Eons has ever had a bad host, and that includes guest hosts and former hosts.
thank you for this beautiful and instructive piece of paleonthology 🤗❤
And then we all evolve into crabs
It's kind of fun to hear "anytime soon" in a video about evolution. I assume she meant in the next few hundred million years.
Some fish can hunt on land and live for a very long time there without needing to lift their underside off the ground. Without tetrapods filling in land niches, they could probably live mostly on land pretty well.
Woooooooo ! New episode !!! I absolutely love these ! So much ! Especially when they are about funky looking guys like these !
I want to see a video about how chordates beat cephalopods.
"There are no tetrapods with more than 5 digits." Um, what about the cats with polydactyly? Or does that not count for some reason?
That’s rare, so it’s not being included.
It's a mutation, not a trait of the species
@@KellyClowers a mutation that keeps appearing in cats that are not directly related. Not to mention mutation is part of evolution.
It’s a developmental anomaly.
@@phantomreaver85 still not a trait of the species. If six toed cats end up displacing 5 toed as the vast majority of the population, then we could talk
1:57 getting a strong “staying in the primordial soup to avoid days like this” vibe from this picture
I wonder if the polydactyl trait was in place of webbing, pulling itself through water and soupy mud would be made easier by the additional traction offered by the additional digits. I also wonder if the three separated from four formation of the hind limbs was a design for digging into the mud either for locomotive purposes, or maybe even displacing dirt and root for something akin to a den.
I love your attitude and style. Very soothing while being informative
Agreeeee
Interesting video. Could 'energy' be part of the reason for 'losing' digits? I.e. It cost the creature more in energy to grow 'unnecessary' digits and resulted in retaining 5 or fewer digits to do all the work required.
They probably wouldn’t be a high enough cost for it to be a selective pressure. It’s an interesting hypothesis tho!
I recall some mathematical models I stumbled across a few years ago coming to the conclusion that between five and six was the lowest energy solution, and in that case, you're probably best rounding down.
Take that with a grain of salt though: it was a few years ago, and I can't pull up any references.
I remember seeing a documentary on how fingers developed(I don't remember the name), but the genes responsible were named "Hedgehog" and "Sonic Hedgehog". I thought it was amusing that they decided to go with the video gave reference.
Genes can have lots of funny names.
I would like to see how you feel about the possibility of regressive genetic resurgence being responsible for polydactylism. While being extremely rare in humans it is comparatively common in cats and a few other species.
So given enough time... all vertebrates would eventually have only one finger like a horse? Since it is easier to loose them than to gain them back.
Like imagine if most animals went extinct except for horses and they now have to fill all of the niches, would it be likely for additional fingers to develop or not?
Very interesting.
Not necessarily, at least for non-cursorial (running vertebrates). The multiple fingers of climbing vertebrates like primates serve that locomotory purpose very well. Now for the scenario you imagined, while it _could_ be possible to re-evolve multiple metacarpal/metatarsal and phalanges bones, it's also possible that other bones like the carpals and tarsals (wrist and ankles respectively) would then be used to take over this function. Something like the "extra" thumb of giant pandas which is actually a modified wrist bone.
Species that relied on them would keep them. A squirrel would have a hard time climbing without them. But the evolutionary pressure for fewer digits keeps them from proliferating pointlessly
I really like Kallie's presentation. Somehow all the presenters in this show are great
I had heard somewhere long ago that among that “other stuff” affected by the same genes are the sex organs, thus ensuring any mutations not be passed on. However, I have not heard that this is the case with the rare six-fingered human, so I don’t know what to think. I always thought it had more to do with all other lineages dying out by pure chance and there being no strong pressure for new additional digits (except in notable cases like pandas and some primate I forget which one).
It would be great to hear about what does the gene for digits development affect
Base 8 or 16 would have been easier to convert to binary than decimal
You improved a lot since your first episode 😄
Having a second thumb on each hand would be really useful. Assuming we would never evolve a 6th digit converting the pinky finger into a thumb would work in a pinch.
As a guitarist an extra functional finger could occasionally come in handy. 😉
You guys seem to forget people, cats, and dogs with polydactyly exist.
that's a mutation not a trait of the species
It’s a developmental anomaly.
@Catarina Barbosa It's all mutations really, everything. There are entire families of people with 6 fingers on each hand. There is a breed of dog that have an extra digit on the back feet, there are cats who naturally have bigger paws with extra digits who live in snowy areas. All of these examples are lineages that are being carried through generations.
When I think of fish developing limbs and breathing air as the first animals to live in land I can't wrap my head around the development of insects. Imagine being this sick proto-amphibian animal just to end up evolving into an ant.
An episode on the rise of bugs some day?
.....they didn't turn into bugs. Arthropods are the original dominant lifeforms on the planet they were also the first on land. It is from their lineage that we get insects, arachnids, and crustaceans. Our evolutionary history is completely seperate, we share no lineage in any way with insects. Look up Anomalocaris (considered to be the first apex predator) or Brontoscorpio.
The arthropods moved onto the land long before the tetrapods. Insects are arthropods, not tetrapods.
What ? I had NO idea we had old old trackways from tetrapods ! I thought there was nothing from this era but some insect and arthropod tracks
Imagine if we actually still had eight fingers per hand, we'd probably be counting in hexadecimal.
Octal. Base 8 is octal.
@@AndrewTBP but we would have 16 fingers total, so hexadecimal.