Speaker 1: Hey, welcome to Sign Stuff, a production of iHeartRadio. I'm
Speaker 1: horhitch Ham, and today we're asking why do we have
Speaker 1: five fingers and toes each hand or foot? Why not
Speaker 1: three or four or six or seventeen? Who decided we
Speaker 1: would have five digits in each hand? Now it turns
Speaker 1: out there is a culprit which we'll get to at
Speaker 1: the end. And to get there, we'll be talking to
Speaker 1: two finger evolution experts who say there are three things
Speaker 1: that explain the number of fingers in your hands, so
Speaker 1: to recap count starting with your thumb will answer one question.
Speaker 1: Talking to two experts learning three key facts, all under
Speaker 1: fourty minutes, and the question is why do we have
Speaker 1: five fingers? Enjoy? Hey everyone, Okay, here are some interesting facts.
Speaker 1: Dogs and cats have five toes on the front legs,
Speaker 1: but only four toes in each of their back legs.
Speaker 1: Birds have three fingers on their wings and four toes
Speaker 1: on their feet, Horses have one finger on each leg,
Speaker 1: and cows and camels have two toes per leg. The
Speaker 1: number of toes can even vary in the same type
Speaker 1: of animal. Some salamanders have four front toes and five
Speaker 1: back toes, and some have four toes all around. Clearly
Speaker 1: there's a big variation in the number of fingers and
Speaker 1: toes in the animal kingdom. But here's the weird thing.
Speaker 1: There are no species of animals with six or more
Speaker 1: fingers or toes on their limbs. Why is that it's five?
Speaker 1: Somehow the maximum? What determines how many fingers each animal has?
Speaker 1: And why do we have five fingers and toes? To
Speaker 1: figure this out, I talk to two evolutionary biologists who
Speaker 1: specialize in finger evolution. The first one is Jacob Scott,
Speaker 1: a researcher at the University of Florida. Well, thank you
Speaker 1: so much, Jacob for joining us.
Speaker 2: You are welcome, glad to be here.
Speaker 1: So my first question for you is how many fingers
Speaker 1: am I holding up?
Speaker 2: Five?
Speaker 1: Good? Although you can't see my other hands, it was
Speaker 1: kind of a trick question.
Speaker 2: That's true.
Speaker 1: Well, to get us started, I was wondering if you
Speaker 1: could tell us where did fingers and toes come from?
Speaker 2: Yeah, so all vertebrates with limbs that live on land,
Speaker 2: they ultimately evolved from something much more fish like or
Speaker 2: a fish itself.
Speaker 1: Okay, so a quick refresher here about evolution. All vertebrates
Speaker 1: with limbs meaning all animals with bones and arms and legs,
Speaker 1: which include all mammals like us, dogs and horses, and
Speaker 1: awesome birds, reptiles, and amphibians all came from a common
Speaker 1: ancestor which evolved from fish and which had fingers on
Speaker 1: its feet. But here's the shocker. That animal probably had
Speaker 1: more than five fingers on each limb.
Speaker 2: They didn't have five fingers, they had somewhere between six
Speaker 2: and eight. We've got fossil showing some of these like
Speaker 2: sort of fish like tetrapods with six digits on their limbs,
Speaker 2: with seven digits on their limbs, and with eight, so
Speaker 2: we think it was more than five.
Speaker 1: Originally what we used to have more than five fingers. Yes,
Speaker 1: that's right, our long ago ancestor and the ancestor of
Speaker 1: all mammals, reptiles, birds, amphibians, et cetera, had potentially up
Speaker 1: to eight fingers on each limb. Okay, let's back up
Speaker 1: a little bit. I asked Jacob to lay out the
Speaker 1: history of all land animals starting with this common ancestor.
Speaker 2: It was a very just an ancestor that looks, you know,
Speaker 2: a lot more like a fish salamander type creature, and
Speaker 2: they evolved in these tide pools or swamps just otherwise
Speaker 2: shallow water where they kind of have the opportunity to
Speaker 2: be embracing that fish side of it, but then occasionally
Speaker 2: maybe would push up out of the water or move
Speaker 2: between different tide pools. So the first land animals were
Speaker 2: fishes that started adapting to living on dry land. They
Speaker 2: started to develop lungs, their chests and hip bones started
Speaker 2: to shift so they could push themselves out of the
Speaker 2: water and kind of waddle around, and that's when fingers
Speaker 2: or digits came into the picture. The conventional thinking right
Speaker 2: now is that digits helped kind of in that transition
Speaker 2: moving from water to land or transitioning between different shallow
Speaker 2: water areas.
Speaker 1: So fingers kind of came from fins.
Speaker 2: Yeah, Ultimately, ultimately it came from fins.
Speaker 1: That's a short answer, right, Okay, here, it's worth taking
Speaker 1: a little dive into fins. Almost all fish that are
Speaker 1: alive today have what are called ray fins, like a
Speaker 1: bunch of spikes coming out of the fish's body with
Speaker 1: webbing between them, sort of like those traditional folding fans
Speaker 1: that come from Asia. But those are not the fins.
Speaker 1: Our arms and legs and Brut's wings come from about
Speaker 1: four hundred million years ago. There were other species of
Speaker 1: fish with what are called lobe fins, and these look
Speaker 1: more like paddles or stubby little tails on the side
Speaker 1: of the fish's body. They extended out with little armlike
Speaker 1: bony segments, and they ended on a group of bones
Speaker 1: which fanned out to form fins. And they just happened
Speaker 1: to have four of those fins, and those are where
Speaker 1: our arms and legs come from. Eventually, those low fin
Speaker 1: fish started to wattle out of the water and they
Speaker 1: used those paddle like fins to push themselves around. Then
Speaker 1: there's a little bit of a gap in the fossil record,
Speaker 1: but about three hundred and sixty million years ago you
Speaker 1: start to see animals like a Cantostega gunari, which looked
Speaker 1: like a cross between a salamander and the fish, or Idiostega,
Speaker 1: which looked like a cross between a crocodile and the fish.
Speaker 1: But here's the thing. Fossils of Acantostega and Ikiostega show
Speaker 1: they had more than five fingers on their limbs. Idiostega
Speaker 1: had seven toes in its back leg, and a Cantostega
Speaker 1: had eight fingers in its front legs, So it's very
Speaker 1: likely that our ancestors had a lot more than five fingers.
Speaker 1: I mean, imagine if we still had eight fingers on
Speaker 1: each of our hands. It might look weird, but think
Speaker 1: about how much faster we could type, or what kind
Speaker 1: of masterpieces we could play on the piano. Our numbering
Speaker 1: system would be different. Instead of base ten, which is
Speaker 1: based on how many fingers we have right now, we
Speaker 1: would all be using Hexa decimal numbers, which begs the
Speaker 1: question what happened. Well, according to our expert, what happened
Speaker 1: was digit loss. That is, during evolution, you can lose fingers,
Speaker 1: and actually it happens a lot.
Speaker 2: It's actually really common to evolve digit loss, especially in mammals. Well,
Speaker 2: I think the king of reducing your digits is the horse.
Speaker 2: Horses have functionally just one digit on each foot. They
Speaker 2: do have little bones from the palm, but they're fuse
Speaker 2: to that one major digit. So if you look at
Speaker 2: a horse leg, it sort of ends in just one digit,
Speaker 2: which ends in a hoof. So they're basically standing on
Speaker 2: just their middle finger.
Speaker 1: So whenever a horse rears up, it's giving you the
Speaker 1: middle finger basically.
Speaker 2: Exactly, it's flipping you off. So, actually, horses are a
Speaker 2: really cool example of this because we have an awesome
Speaker 2: fossil record all through their digit loss. First they lost
Speaker 2: their equivalent to their big toe. They lost it on
Speaker 2: the hind limb first, and then you can see if
Speaker 2: they would lose the pinky next, and then the pointer
Speaker 2: finger and the ring finger were slowly just reduced in
Speaker 2: length until they're basically nothing.
Speaker 1: Now, oh, we can see it in the fossil record. Yeah, yeah,
Speaker 1: I had no idea. A horse's hoof is basically its
Speaker 1: last remaining finger. Okay, as tacob to give me more
Speaker 1: examples of animals losing fingers.
Speaker 2: I'll give you all the examples I can think of.
Speaker 2: Most salamanders have lost at least one digit. Plenty of reptiles.
Speaker 2: So modern birds they have three digits on their forelim
Speaker 2: on their wing. The wing is the whole arm, and
Speaker 2: then it ends in these three digits, and then four
Speaker 2: digits on their hind limb. There's a big debate about
Speaker 2: whether the identities of those digits on the wing are
Speaker 2: some pointer middle or if they're pointer middle index.
Speaker 1: Wow, fascinating. So they're mixing it up three and four yeah.
Speaker 2: Yeah, So actually the digit loss tends to evolve more
Speaker 2: or less independently between the forelam and the hind limb,
Speaker 2: So there's plenty of species that only have digit loss
Speaker 2: in one of the limbs and not the other. You'll
Speaker 2: see different numbers in a lot of species, Like what
Speaker 2: so dogs and cats they've both lost their big toe
Speaker 2: on the hind limb. So if you go home and
Speaker 2: look at your dog or your cat, you'll see that
Speaker 2: they have, you know, full five digits on their front paws,
Speaker 2: but only four on the back.
Speaker 1: Really, yeah, well, I've never thought to count dogs or
Speaker 1: cats as fingers.
Speaker 2: It's something that I only like really noticed after I
Speaker 2: started doing this research. I was like, oh, does my
Speaker 2: dog also have you know, only four digits? And it
Speaker 2: turns out yeah, he's a dog, so he will whoa.
Speaker 2: And there's plenty of other examples, like guinea pigs have
Speaker 2: four on their front legs and only three on the back.
Speaker 1: Are there any animals with two fingers or toes?
Speaker 2: Yes, So that's the group that includes things like cow
Speaker 2: and bison and giraffes. So all three of those have
Speaker 2: at least functionally two digits, And that's in comparison to
Speaker 2: the horses, rhinos, and tape ears, which are odd toe animals,
Speaker 2: so they'll always have one or three digits.
Speaker 1: It's like two big branches in evolution. Yep, exactly, all right,
Speaker 1: So it seems like the common ancestor to all animals
Speaker 1: with fingers started off with six to eight fingers in
Speaker 1: their limbs. But now there are plenty of animals that
Speaker 1: have much less than that we have five. Others have
Speaker 1: evolved to have four, three, two, and even one finger
Speaker 1: or toe per hand or foot. So my next question
Speaker 1: was what causes this species to lose a finger or
Speaker 1: a toe? All right, when we come back, we're gonna
Speaker 1: put our finger on this mystery, which honestly sticks out
Speaker 1: like a sore thumb. So stay with us. We'll be
Speaker 1: right back. And we're back all right. We are counting
Speaker 1: the number of fingers in our hand and asking why
Speaker 1: do we have five fingers? Why not four or six?
Speaker 1: In the last segment, we learned that the ancestor of
Speaker 1: all four limb vertebrates, that is, the ancestor of mammals us, birds, reptiles,
Speaker 1: and amphibians, lived about three hundred and sixty million years ago,
Speaker 1: and fossils show it probably had six to eight fingers
Speaker 1: or toes on each limb, but we have five fingers
Speaker 1: and toes on each extremity. So what happened Well, according
Speaker 1: to our expert scientists think one of the main reasons
Speaker 1: is locomotion.
Speaker 2: For most animals, that's the primary use of their limbs
Speaker 2: and their digits is getting around. Usually, the cause of
Speaker 2: loss tends to be associated with the method of locomotion.
Speaker 2: So a lot of animals that are really specialized for
Speaker 2: running will lose digits. So think again, cats, horses, bison,
Speaker 2: All of these animals that basically hunted, chase for food,
Speaker 2: or try to get away from predators tend to have
Speaker 2: reduced digits.
Speaker 1: Generally, why does losing your finger help you run?
Speaker 2: I can't give you a super confident answer on that,
Speaker 2: but I can give you some associated evidence. One of
Speaker 2: the thoughts on why horses were able to lose so
Speaker 2: many digits was because they evolved that trait during an
Speaker 2: ice age when the ground was more compact. If you're
Speaker 2: trying to walk around on like marshy, swampy, muddy ground,
Speaker 2: you kind of want more digits because you can disperse
Speaker 2: your weight a little bit more evenly and not sink right, right,
Speaker 2: But when the ground is harder, you can kind of
Speaker 2: just slam your whole weight down on one point really
Speaker 2: efficiently without the ground breaking around you.
Speaker 1: It's sort of like, I guess if you're walking on snow,
Speaker 1: it's better to have a snowshoe.
Speaker 2: Yes, exactly, that's exactly right.
Speaker 1: But if you're running on a track like at the Olympics,
Speaker 1: you don't want to be wearing snowshoes.
Speaker 2: That's a good way to think about it.
Speaker 1: You almost want sort of like a pogo stick on
Speaker 1: your feet, right, Yeah, it's kind of what it is.
Speaker 1: So one reason so many species of lost fingers or
Speaker 1: toes is low commotion. Animals need to move and run fast,
Speaker 1: and sometimes having a lot of toes can be a
Speaker 1: bad thing. If you're trying to go as fast as
Speaker 1: you can, think having a bunch of toes flapping around
Speaker 1: when you hit the ground could actually slow you down.
Speaker 1: I mean, think about why us humans wear shoes to
Speaker 1: walk and run. It essentially reduces our number of toes
Speaker 1: to one. And this idea doesn't just apply to feet
Speaker 1: and toes, It can apply to fingers and hands.
Speaker 2: There's some animals like spider monkeys that they swing from
Speaker 2: vine to vine. They've lost their thumb because it's more
Speaker 2: efficient to swing just kind of using your other forge
Speaker 2: just as a hook, when the thumb would just get
Speaker 2: in the way there. So that's the current thinking at least.
Speaker 1: Yeah, there are monkeys out there without opposable thumbs. If
Speaker 1: you look up spider monkeys, their hands don't have thumbs.
Speaker 1: So there are lots of examples in nature of animal
Speaker 1: species that have loss fingers or toes. Our ancestors started
Speaker 1: with six to eight. At some point that became five,
Speaker 1: and since then some have gone down to four, three, two,
Speaker 1: and even one finger or toe. This means the history
Speaker 1: of fingers and toes in animals. It's not that some
Speaker 1: animals evolved two digits and others four or five from scratch.
Speaker 1: We all started with eight and progressively lost fingers and
Speaker 1: toes over millions of years. But there is something odd
Speaker 1: about this pattern, which is that you rarely see a
Speaker 1: species evolved to gain a finger or a toe. Now,
Speaker 1: sometimes an individual animal of a species might be born
Speaker 1: with an extra finger or toe, but that's not quite
Speaker 1: the same.
Speaker 2: Like in labs, we can knock out genes and it
Speaker 2: will cause mice to develop extra digits. We know that
Speaker 2: there are human congenital diseases where people will be born
Speaker 2: with extra digits, or there's certain dog breeds that tend
Speaker 2: to have extra digits, there's certain populations of cats, But
Speaker 2: in terms of like a whole species, nothing has evolved
Speaker 2: more digits stably, like a brand new digit with its
Speaker 2: own identity being formed. It's very, very very uncommon, like
Speaker 2: to the point where I can't think of a single
Speaker 2: example offhand.
Speaker 1: Okay, what Jacob is saying is that while you might
Speaker 1: get a person or an individual animal here and there
Speaker 1: to grow an extra finger or toe, it usually doesn't stick. Overall.
Speaker 1: It's extremely rare for a species to gain a finger
Speaker 1: or toe, and yet, as you heard before, losing a
Speaker 1: toe or losing multiple toes is extremely common in evolution.
Speaker 1: What this means is that in nature there are no
Speaker 1: species of anim animals with more than five fingers or toes.
Speaker 1: We started with six or eight when fishes first of
Speaker 1: all to walk on land, and then there spent a
Speaker 1: gradual decline overall species, our branch of the evolutionary tree
Speaker 1: of life got down to five fingers or toes, and
Speaker 1: at least for us stop there. But other species kept
Speaker 1: losing more digits, and no species alive today hasn't gained any.
Speaker 1: So this answer is part of the question of why
Speaker 1: we have five fingers. We don't have six fingers because
Speaker 1: our ancestors lost that six finger a long time ago,
Speaker 1: and it's super rare for any animal to gain a digit,
Speaker 1: so we're left with five. But this brings up two
Speaker 1: very important questions. Number one, why is finger evolution so biased?
Speaker 1: Meaning why is it easier to lose a finger during
Speaker 1: evolution but so hard to gain one? And number two,
Speaker 1: we need to answer the second half of today's question,
Speaker 1: which is why do we have five fingers and toes
Speaker 1: not four or three? I mean, when's the last time
Speaker 1: you use your pinky toe for anything? We'll answer both
Speaker 1: those questions when we come back, so don't twiddle your thumbs.
Speaker 1: Stay with us, we'll be right back. Welcome back.
Speaker 2: All right.
Speaker 1: We're asking why we have five fingers, and so far
Speaker 1: we've learned that the ancestor of all animals with fingers
Speaker 1: and toes had somewhere between six and eight fingers on
Speaker 1: each limb, and we learned that basically it's all been
Speaker 1: downhill from there. The history of the evolution of digits
Speaker 1: is dominated by animal species losing fingers and toes and
Speaker 1: almost never gaining them.
Speaker 2: It seems to be a.
Speaker 1: Pretty prevalent rule of thumb unintended. So another question is
Speaker 1: why is that? Why is it easier to lose a
Speaker 1: finger than to gain one? And also why haven't we
Speaker 1: lost more fingers or toes? I mean, it's not like
Speaker 1: our pinkies or our pinky toes or any toe for
Speaker 1: that matter, are that essential for survival. Why do we
Speaker 1: still have them? The point of finger At the answer,
Speaker 1: I reached out to another finger evolution expert, doctor Friedson Gallis. Well,
Speaker 1: thank you Tolis for joining us. Can please tell us
Speaker 1: who you are and what you do.
Speaker 3: I'm an evolutionary biologist and I work at the Naturalist
Speaker 3: Biodiversity Center in Liden, Than, Netherlands, and I am interested
Speaker 3: in how body plans can change, what kind of mechanisms
Speaker 3: make it difficult for evolutionary changes to occur, like why
Speaker 3: we have two eyes two years and.
Speaker 1: Things like that. Great, I think that makes you the
Speaker 1: perfect expert for our question here today we're trying to
Speaker 1: find out why finger evolution is so one directional.
Speaker 3: Yeah, Well, what you see is the losses of digits
Speaker 3: happen very often, but there are never gains of digits.
Speaker 3: And I can explain why that is if you want
Speaker 3: to know that.
Speaker 1: Okay, Doctor Gallas says. The secret to understanding why it's
Speaker 1: easier in evolution to lose a finger than to gain
Speaker 1: one is to understand how fingers grow in the body,
Speaker 1: especially when we're just tiny embryos in the womb during
Speaker 1: what's called development.
Speaker 3: So the number of digits is determined very early during development.
Speaker 3: You have a very small embryo, and in this embryo,
Speaker 3: to get development, you need to have interactions between different parts.
Speaker 3: And because the embryo is so small at the stage,
Speaker 3: these interactions there are in the very interactive stage, and
Speaker 3: all parts are in communication with all other parts.
Speaker 1: Okay, what doctor Gals is saying is that during development,
Speaker 1: when we're just a tiny clump of generic cells multiplying,
Speaker 1: the way the cells know what to turn into is
Speaker 1: by talking to each other. There's a complex network of
Speaker 1: signals between all the cells that basically tell each other
Speaker 1: you should be where the arm is, and you should
Speaker 1: be where the brain is going to be, and you
Speaker 1: should be where the lungs are. And this keeps going
Speaker 1: until all of the body parts form and the shapeless
Speaker 1: blob of cells that you were starts to look more
Speaker 1: like an embryo and eventually like a baby animal. It's
Speaker 1: all a very complex, coordinated process, and that's when fingers
Speaker 1: start to get formed.
Speaker 3: So this number of digits is determined, then the number
Speaker 3: of eyes and the number of little structures are determined. Then,
Speaker 3: because there are all these many interactions with all the
Speaker 3: other parts, if you make a change, you get more changes.
Speaker 3: So maybe what is easy to imagine is the eye
Speaker 3: development is very early and there are many interactions with
Speaker 3: their brain. Now, if you get an extra eye or
Speaker 3: you have one less eye, that has incredible effect on
Speaker 3: the brain development.
Speaker 1: What doctor Gallas means is that it's such a complex
Speaker 1: coordination process when all your cells are trying to figure
Speaker 1: out how to grow into you, that if you mess
Speaker 1: with one thing, like say an eye, it's going to
Speaker 1: mess up the process and all the other parts are
Speaker 1: not going to grow the way they're supposed to grow.
Speaker 3: You get all kinds of monstrosities you have that that
Speaker 3: are not viable. And then the same happens with digit
Speaker 3: because the development of digits is connected with also all
Speaker 3: kinds of other parts of the body. So if you
Speaker 3: change the number of digits, you get other changes as well.
Speaker 1: Okay, so this explains why any mutation can be potentially
Speaker 1: disastrous for any growing embryo. Suddenly growing, say an extra finger,
Speaker 1: could mess up the complex signaling between the different parts
Speaker 1: that are growing, and it could cause your lungs, or
Speaker 1: your spinal column or your head to grow the wrong way.
Speaker 1: But this limitation applies to both gaining a finger and
Speaker 1: losing a finger. We still haven't explained why in the
Speaker 1: evolution of fingers it's way more common to lose fingers
Speaker 1: than to gain them. Well, according to doctor Gallis, the
Speaker 1: reason for that is that there's a way to fool
Speaker 1: your developing embryo.
Speaker 3: There's a way evolutionary way around it. What you get
Speaker 3: is that you have the earliest development, and this needs
Speaker 3: to happen because these interactions you need them. So what
Speaker 3: you have is that you get your digits, then development
Speaker 3: stoops after this stage, and then it gets destroyed.
Speaker 1: Okay, So the trick is that let's say you're a
Speaker 1: horse that could run faster if you had fewer toes,
Speaker 1: or a monkey that could swing easier with fewer fingers.
Speaker 1: You don't want to not grow your fingers because that
Speaker 1: would mess up the signaling in your embryo. Instead, you
Speaker 1: grow all five fingers when you're a young embryo, and
Speaker 1: once the signaling for that extra finger stops or becomes
Speaker 1: less important, you stop growing that finger and let it
Speaker 1: shrivel off. In other words, you sort of fake out
Speaker 1: your embryo. You fool it into thinking it's going to
Speaker 1: have all five fingers and toes, but then you drop
Speaker 1: the ones you don't want, which makes for some interesting
Speaker 1: surprises when the embryo is growing.
Speaker 3: Yeah, and for example, horses during development, they still have five.
Speaker 1: Digits really like a horse embryo has five toes exactly.
Speaker 3: And then what happens and then the development stops and
Speaker 3: it's broken down.
Speaker 1: Huh and only one finger remains. Yes, And this is
Speaker 1: why it's easier during evolution to lose a finger than
Speaker 1: to gain one. It's easier to fool the embryo into
Speaker 1: thinking it's getting a finger and then later stop growing it.
Speaker 1: Then it is to fool it into thinking it's not
Speaker 1: getting an extra finger, and then at the last minute
Speaker 1: grow a whole finger out of the blue. Okay, so
Speaker 1: this explains why we don't have six fingers. It's hard
Speaker 1: to gain a finger as a species once you lose it.
Speaker 1: Now the question is why don't we have four fingers?
Speaker 1: If we're under the thumb of this bi towards loosing fingers,
Speaker 1: how come we haven't lost anymore. I mean, it's not
Speaker 1: like the pinky toe is that useful, or any of
Speaker 1: our toes for that matter. And here, as I promise,
Speaker 1: we have a very specific culprit, one that I've been
Speaker 1: hinting at throughout the whole episode, and it has to
Speaker 1: do with the order in which fingers grow when we're embryos.
Speaker 1: They don't all grow at the same time. They start
Speaker 1: one after the other, and it turns out that the
Speaker 1: order in which they start to grow determines which one
Speaker 1: is most likely to get lost. Here's Jacob Scott again.
Speaker 2: So it tends to be the first digit that gets
Speaker 2: lost in evolution usually is the last digit to form
Speaker 2: during development. So in mammals, digit one, so equivalent to
Speaker 2: the thumb or the big toe, that's the last one
Speaker 2: to form, and it's usually the first one to be lost.
Speaker 1: This makes sense. Remember I said that to lose a finger,
Speaker 1: you kind of have to fool the embryo so you
Speaker 1: don't mess up the coordination between all the different parts. Well,
Speaker 1: it's easier to do this if you're the last finger
Speaker 1: to form, because being the last one you sort of
Speaker 1: fly under the radar. But the time you come around,
Speaker 1: things are more settled. And in our case, the last
Speaker 1: digit to form is the thumb.
Speaker 2: I would say in humans, the digit were most likely
Speaker 2: to evolve the loss of would be our thumb, and
Speaker 2: we really need our songs.
Speaker 1: I see, I see. It's like, evolutionarily, the thumb would
Speaker 1: be the first to go, but because it's so useful,
Speaker 1: it's like, uh, you know, it's not going anywhere, right, Oh,
Speaker 1: that's fascinating. Even though the pinky is maybe the least
Speaker 1: useful finger. It's like, way in the back of the line,
Speaker 1: it's like the thumb is running cover for the pinky.
Speaker 2: Yeah, so we're we're stuck with the pinkies.
Speaker 1: And there you have it. The reason we have five
Speaker 1: fingers and not four is the thumb. Evolutionarily, the thumb
Speaker 1: would be the next to go, but it's so useful
Speaker 1: we can't get rid of it. And because we can't
Speaker 1: get rid of it, it ends up protecting all the
Speaker 1: other fingers. In other words, we can't lose the pinky
Speaker 1: without first losing the thumb, which for us is too
Speaker 1: useful to lose. And if you go back through the episode,
Speaker 1: you'll notice I was hinting at this from the start.
Speaker 1: You can cut the number of times I used the
Speaker 1: word thumb with your fingers. Okay, I think we answered
Speaker 1: today's question. Why do we have five fingers? Well, we
Speaker 1: don't have six or more because once you lose a
Speaker 1: finger during evolution, it's really hard to get one back.
Speaker 1: And we don't have four or fewer because our thumbs
Speaker 1: are too good to lose. So that's our show. I
Speaker 1: hope you give it a thumbs up. See you next
Speaker 1: time you've been listening to Science Stuff. Production of iHeartRadio
Speaker 1: written and produced by me or hitch Hamp credited by
Speaker 1: Rose Seguda, executive producer Jerry Rowland, and audio engineer and
Speaker 1: mixer Jasey Peckram, and you can follow me on social media.
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Speaker 1: and please tell your friends. We'll be back next Wednesday
Speaker 1: with another episode.