Speaker 1: Bodies contain blood, bones, muscles, and everything in between. How
Speaker 1: is this all controlled at the level of the gene?
Speaker 1: How many unique cell types are inside of me? I
Speaker 1: count eighty three? Do you agree?
Speaker 2: Do clever tools require thumbs that neatly oppose? Or could
Speaker 2: alien minds build ships with tentacles? Or who knows?
Speaker 1: Whatever questions keep you up at night, Daniel and Kelly's
Speaker 1: answers will hopefully make it right.
Speaker 2: Welcome to Daniel and Kelly's Extraordinary Universe of Alien Biology.
Speaker 1: Listener Questions, episode number thirty seven.
Speaker 2: Hi Daniel, I studied particle physics and aliens.
Speaker 1: Hello, I'm Kelly Waidersmith. I studied parasites and space, and
Speaker 1: twenty five years ago I studied developmental biology. Do I
Speaker 1: remember any of it? Today? We find out.
Speaker 2: It's Kelly on the hot seat today, answering questions from
Speaker 2: listeners about how everything works inside these crazy meat sacks
Speaker 2: we call bodies.
Speaker 1: Right, And just to be clear, I'm not actually relying
Speaker 1: on what I learned twenty five years ago. I spent
Speaker 1: a lot of time reading about developmental biology again, but
Speaker 1: these are great questions and it was fun to revisit
Speaker 1: the field.
Speaker 2: And we thank you, thank you, thank you so much
Speaker 2: for sharing your curiosity with us, sending in the things
Speaker 2: that puzzle you, the things you would like to hear about.
Speaker 2: We thrive on your curiosity. It literally drives all of science,
Speaker 2: and so we're very glad to hear that you're curious
Speaker 2: about how the universe works, and we want to answer
Speaker 2: your questions about the universe. This podcast is not just
Speaker 2: a it's a conversation between you and us.
Speaker 1: Yes, and we are chatty people, so send us your
Speaker 1: questions at questions at Danielankelly dot org or join us
Speaker 1: on our discord channel. We have the world's best moderators,
Speaker 1: so our conversations are fascinating, funny and civil, which I
Speaker 1: love the civil parts.
Speaker 2: An actually friendly place on the internet.
Speaker 1: It's amazing. This is the only corner where you can
Speaker 1: find that friends join us, And if you go to
Speaker 1: Daniel and Kelly dot org you can find a link
Speaker 1: to our discord page and you can join us over there.
Speaker 2: And if you've written to us and haven't heard back, sorry,
Speaker 2: please try again. You may have been caught in our
Speaker 2: spam filter. We really try to get back to everybody
Speaker 2: within a couple of days, so please, please, please, reach
Speaker 2: out to us. We love to hear the things that
Speaker 2: make you wonder, and on today's episode, we're answering three
Speaker 2: fascinating questions from listeners, focusing on how the human body
Speaker 2: develops and how alien bodies might develop as well.
Speaker 1: That's right, and we're going to start with two questions
Speaker 1: I got that were related, and so usually each segment
Speaker 1: we air a question at the beginning of each segment.
Speaker 1: This time around, I'm gonna air two questions together because
Speaker 1: Ali and Brian had very similar questions, and then I'm
Speaker 1: going to spend two segments doing my best to answer them,
Speaker 1: and then I will air their responses at the end
Speaker 1: of segment two. So let's go ahead and listen to
Speaker 1: these fantastic questions.
Speaker 3: Hello, O, Kelly, could you explain how DNA results into
Speaker 3: different cell behaviors, like when a fetus develop how does
Speaker 3: one cell end up as a muscle cell another as
Speaker 3: a bone sell?
Speaker 4: Thank you, hey, Kelly, it's Brian. As Daniel likes to say,
Speaker 4: this Rube Goldberg machine of a body is insanely complicated.
Speaker 4: I understand the basics of how cells differentiate and specialize
Speaker 4: based on which genes are turned on or off, but
Speaker 4: I've always wondered how many different types of cells there
Speaker 4: are in the human body. More specifically, I was hoping
Speaker 4: you could explain what actually makes them different. I remember
Speaker 4: building a cell diagram with Arts and Crafts in middle school,
Speaker 4: and it got me thinking, what about a cell's internal structure?
Speaker 4: Separates a cell in a tendon from a cell and
Speaker 4: a bone, muscle, artery, white blood cell, brain cell, and
Speaker 4: so on. As a related and follow up question, I'd
Speaker 4: also love to hear how new cells like know what
Speaker 4: to become in the first place, both as we grow
Speaker 4: in the womb and as we age out in the world.
Speaker 1: Thanks, oh boy.
Speaker 2: All right, So when you got these questions, Kelly, did
Speaker 2: you go yeah, I wonder that too, Or did you
Speaker 2: go ooh, here's a chance to learn developmental biology? Or
Speaker 2: did your stomach drop and you went uh oh, I
Speaker 2: should have paid attention in dev cell thirty years ago.
Speaker 1: I paid a lot of attention in dev bio. And
Speaker 1: if Professor Eileen Underwood were he, I think she'd tell
Speaker 1: you that I got an A in developmental biology.
Speaker 2: Nice.
Speaker 1: Yeah, but it was twenty five years ago, and.
Speaker 2: How much could have changed in twenty five years?
Speaker 1: Maybe everything you know I think even if nothing changed,
Speaker 1: the probability that I could answer this question without doing
Speaker 1: more research is pretty much zero. So I did a
Speaker 1: lot of different research. One thing that was particularly helpful
Speaker 1: in case anyone's interested in learning more was I found
Speaker 1: a book called Life Unfolding How the Human Body Creates
Speaker 1: Itself by James A. Davies. He's a professor of experimental anatomy.
Speaker 1: It's from twenty fifteen, so it's not, you know, from
Speaker 1: this year, but you know, it's got some general principles
Speaker 1: that have decades of research behind them. So that's what
Speaker 1: we're going with.
Speaker 2: And so we have a lot of related questions here.
Speaker 2: How are we going to tackle this whole big question
Speaker 2: and all the sub questions?
Speaker 1: Yeah? Okay, so I split it into four questions. I'm
Speaker 1: going to tell you what those four questions are, and
Speaker 1: then we'll tackle them one at a time. Great, So,
Speaker 1: question one is how do sells in a fetus know
Speaker 1: what they need to become? How do you sells in
Speaker 1: adults know what to become? How many cell types do
Speaker 1: we have? And what makes these cell types different?
Speaker 2: Okay?
Speaker 1: And right, there is just no way the answer can
Speaker 1: be comprehensive because there is a lot of variability depending
Speaker 1: on what cell type you're talking about. And so my
Speaker 1: strategy here is to kind of give like an overview
Speaker 1: of strategies that can be used by cells to figure out,
Speaker 1: you know, for example, what they need to become. Maybe
Speaker 1: dig into an example that I thought was particularly interesting.
Speaker 1: And if folks are just like, holy cow, we need
Speaker 1: like twenty more episodes on developmental biology, then I will
Speaker 1: find a developmental biologist to come on the show for
Speaker 1: twenty episodes, or I'll buy a textbook and this will
Speaker 1: be a series. But for this point, it's got to
Speaker 1: be a bit of an overview.
Speaker 2: Awesome. Well, our friend Matt Georgiani, who's been on the
Speaker 2: show a few times, he's a developmental biologist.
Speaker 1: Oh oh, why didn't you tell me that sooner? I
Speaker 1: guess I shouldn't let you know that I was spending
Speaker 1: the weekend with my nose in a developmental biology book.
Speaker 2: But my bad, which is good for you anyway. All right, Well,
Speaker 2: why don't we start in question one? And maybe a
Speaker 2: good way to start is for me to explain to
Speaker 2: you my understanding, which is probably wrong, so you can
Speaker 2: get a sense for where we're starting. Yeah, great, So
Speaker 2: question one is how does the cell and the feet
Speaker 2: is know what to become? To me, this is a
Speaker 2: fascinating question because the fetus begins with one cell. Right,
Speaker 2: you start with the egg and it's fertilized, but you
Speaker 2: have a single cell and everything that comes after that
Speaker 2: comes from that same cell. So literally, every cell in
Speaker 2: your body, even though they're different kinds, nerve, muscle, brain, whatever,
Speaker 2: have the same origin, right, the same grandpappy or grandma
Speaker 2: sell and so that means that they must have differentiated
Speaker 2: but they have the same origin. So like, that's confusing
Speaker 2: to me, Like this one became nerve, that one became muscle.
Speaker 2: If they have the same ancestry, how does that happen
Speaker 2: to me? That's the essence of the question.
Speaker 1: Yeah, it's fascinating. What's the answer? Keep going, that's a
Speaker 1: good start.
Speaker 2: The answer is, I have no idea why this part
Speaker 2: turns into head and that part turns into tail. It
Speaker 2: could be environmental, Like there's more hormones over here as
Speaker 2: this thing developing, and so maybe different genes are turned on.
Speaker 2: I mean, I know that every cell has a lot
Speaker 2: of genes, and not all of them are used. Some
Speaker 2: of them are turned on and some of them are not.
Speaker 2: But I have no idea what's controlling which get turned
Speaker 2: on and which aren't.
Speaker 1: Okay, all right, great, so that's where I come in.
Speaker 2: Great.
Speaker 1: So, first, I'd like to start by noting that most
Speaker 1: of what we know here comes from things like studies
Speaker 1: in fruit flies and mice, and for ethical reasons, we
Speaker 1: can't do the kind of manipulative experiments we'd like to
Speaker 1: do on human fetuses that you'd like to, sorry, that
Speaker 1: you would need to do to answer these questions definitively,
Speaker 1: but that for ethical reasons you will not do, don't
Speaker 1: want to do, but that you don't want to do
Speaker 1: because we are good people. Yes, I'm sorry, bad choice
Speaker 1: of words there, I was reading my notes well speaking,
Speaker 1: I do not want to experiment on fetuses. Okay, okay,
Speaker 1: So you've got this group of cells. How do you
Speaker 1: start telling quote unquote telling these cells what they need
Speaker 1: to become? Yeah, well, so very early on, one way
Speaker 1: the cells can start to figure out, like, you know,
Speaker 1: how do we know that we're different is that you
Speaker 1: can say, okay, well, some cells are on the inside
Speaker 1: of the ball and some cells are on the outside.
Speaker 1: So you start doing replication and when you've got enough
Speaker 1: cells that there are some cells that are touching other
Speaker 1: cells on all of their sides, but some cells are
Speaker 1: not touching other cells on the exterior because they're on
Speaker 1: the outside of the ball. Then they can say, Okay,
Speaker 1: we're going to do something different, and so they start
Speaker 1: turning on different genes when they realize that they've got
Speaker 1: part of their body that's not touching other cells.
Speaker 2: So already we have a way for the environment to
Speaker 2: influence what the cell turns into, not just the recipe. Now,
Speaker 2: it's input from the outside.
Speaker 1: Yes, right, And in things like insects, moms can get
Speaker 1: the ball rolling by doing things like putting stuff in
Speaker 1: the early embryo. And that stuff, in particular is what
Speaker 1: we call transcription factors. And I'm gonna not use a
Speaker 1: lot of jargon because I know Daniel's eyes are gonna
Speaker 1: roll back at his head and they might end up
Speaker 1: hurting his eyeball.
Speaker 2: I was just gonna ask, is there a Latin phrase
Speaker 2: for transcription factors?
Speaker 1: We could use, right, probably, but I'm gonna try to
Speaker 1: avoid it anyway. But so, essentially, what a transcription factor
Speaker 1: does is it turns on certain genes, and so what
Speaker 1: they do is they dump a bunch of transcription factors
Speaker 1: into the early egg, and as the cells start dividing,
Speaker 1: the cells that are, for example, at the bottom of
Speaker 1: the egg are going to end up with more transcription
Speaker 1: factors in them than the cells at the top, because
Speaker 1: there's more transcription factors at the bottom than at the top.
Speaker 1: And that's how you start getting differences in the top
Speaker 1: of the egg from the bottom of the egg. Does
Speaker 1: that makes sense?
Speaker 4: Hey?
Speaker 2: That was my basically totally uninformed guests.
Speaker 1: Oh, fantastic, All right, I know.
Speaker 2: Okay, so transcription factor, because transcription is how DNA turns
Speaker 2: into proteins, right, You transcribe DNA into proteins, so that
Speaker 2: must be related, like, yeah, which ones get transcribed and
Speaker 2: which ones don't?
Speaker 1: Yes, I always forget translation and transcription. They're both teas,
Speaker 1: but I think, yes, that's if the first you translate,
Speaker 1: then you transcribe. Okay, Yeah, they're not just tea's their
Speaker 1: t are a. You see where I'm going. This is
Speaker 1: very complicated, but that's.
Speaker 2: The level we need to understand. It's just that helps
Speaker 2: determine what gets turned on and what doesn't.
Speaker 1: Yes, okay, all right, so those are early stage what
Speaker 1: gets turned on, what doesn't. Our embryos also have structures
Speaker 1: that like literally just show up in embryos so that
Speaker 1: they can be there to release cues to tell parts
Speaker 1: of our body to start becoming things. And then as
Speaker 1: our embryos get more advanced, these structures are told to
Speaker 1: die and then they disappear, so they're only there to
Speaker 1: be like you know, I'm just making up an example
Speaker 1: like this is where the head goes, this is where
Speaker 1: the anus goes, and then they disappear. They're just sort
Speaker 1: of like helping with layout stuff and then they go away.
Speaker 1: A lot of how things determine where they're going to go, though,
Speaker 1: are from cells releasing signals to impact what's happening with
Speaker 1: nearby cells. And so one cell will release a protein,
Speaker 1: and since a least question was about genes, I want
Speaker 1: to hammer home the point that when a cell is
Speaker 1: releasing a protein, proteins are coded for by genes. So
Speaker 1: there there is a cell that has a gene turned on,
Speaker 1: it's making a protein, it's releasing it out of the cell,
Speaker 1: and that protein is then going and like diffusing over
Speaker 1: to a nearby cell and it's essentially telling that nearby cell,
Speaker 1: Hey turn on some genes. We got to do something
Speaker 1: coordinated together, and that's turning on yeah, genes in the
Speaker 1: nearby cell. And so by communicating with each other nearby,
Speaker 1: they're able to tell each other like, all right, we
Speaker 1: need to coordinate to make a muscle cell together, or
Speaker 1: we are going to be the heart.
Speaker 5: Yeah.
Speaker 1: And so there's a bunch of signaling molecules that get
Speaker 1: used so that cells can communicate to one another.
Speaker 2: Does that make sense, Yeah, And so cells turn on
Speaker 2: these genes to make proteins to signal to other cells
Speaker 2: that they need to work together. Yes, But something must
Speaker 2: have told that cell to start that signal, right, So
Speaker 2: there's something upstream from that that's some environmental factor like
Speaker 2: we're in this part of the body, or we're close
Speaker 2: to the anus, or there's this guy thing on our outsides.
Speaker 1: Yeah, or it could be that the structure that showed
Speaker 1: up just to tell us where we're supposed to become
Speaker 1: has started to release that signal. And you know, so,
Speaker 1: like very early on in development, there are cells with cilia,
Speaker 1: which are like hairs that are on the outside of
Speaker 1: the cell, and they are told to beat in a
Speaker 1: certain direction. And when they beat in that particular direction.
Speaker 1: They start sending a bunch of compounds in a certain direction,
Speaker 1: so that cells that are in that direction get a
Speaker 1: lot more of this stuff than cells on the other
Speaker 1: side of the body or sells on the other side
Speaker 1: of the fetus. And this starts setting up the fact
Speaker 1: that not everything in our body is symmetrical. And so
Speaker 1: this sets up that, like, your heart goes on this
Speaker 1: side of the body, and the stuff that's getting sent
Speaker 1: to one side of the body are things like transcription factor,
Speaker 1: so it's like your body has more of chemicals on
Speaker 1: one side that will tell your body like this is
Speaker 1: the side that the heart goes on, and stuff like that.
Speaker 1: So there's different like so there's environmental cues that we
Speaker 1: talked about earlier, Like I'm on the outside. There's cues
Speaker 1: like we are beating in a certain direction, so that
Speaker 1: fluids in the embryo are getting sent in a particular direction,
Speaker 1: so this side has a higher concentration than the other side.
Speaker 1: And then there's cells talking to one another. These are
Speaker 1: all sort of various ways that your body can communicate
Speaker 1: where things need to go and what needs to be happening.
Speaker 2: So there really is a very rich environmental content for
Speaker 2: all of these cells. The idea that how your body
Speaker 2: is built comes just from your DNA is missing a
Speaker 2: big part of the picture, right, Like these structures and
Speaker 2: the relative context and all these cues are a huge
Speaker 2: part of the recipe for building your body. Right, It's
Speaker 2: not just encoded in your DNA.
Speaker 1: Well, I mean, so DNA, most of this stuff is
Speaker 1: like proteins moving around and telling cells what to do,
Speaker 1: and those proteins are made by the genes, and so
Speaker 1: you know, none of this happens without the genes for
Speaker 1: the most part.
Speaker 2: I see. So for example, those structures you talked about
Speaker 2: that say, like put the mouth here, that's from proteins
Speaker 2: that are encoded by the genes.
Speaker 1: Yeah, So that structure needs to be made by genes,
Speaker 1: and then they're releasing chemicals that say, see the structure
Speaker 1: goes here, and those chemicals, yeah, are encoded by genes.
Speaker 2: But there's a reason that structure is created over here
Speaker 2: in the mouth the area, right, and not over there
Speaker 2: in the finger area. And that comes down to environmental
Speaker 2: cues that happen upstream. Right.
Speaker 1: So when I talked about the environmental cues early on,
Speaker 1: as I understand it, those environmental cues like I am
Speaker 1: on the outside of the ball are helpful for like
Speaker 1: maybe the first week or something very very early on.
Speaker 1: But once you start getting to things like you know,
Speaker 1: the head is here, the high knees here, stuff like that,
Speaker 1: A lot of that has to do with chemical cues.
Speaker 1: And those chemical cues are emanating from things like what's
Speaker 1: called the notochord, which is one of those structures I
Speaker 1: was talking about that gets made and then mostly disappears
Speaker 1: in humans. I think it still shows up as like
Speaker 1: the discs in between our vertebra, but it is hugely
Speaker 1: important in developmental biology for giving us cues for what
Speaker 1: goes where, but then becomes, you know, something that we
Speaker 1: mostly forget about unless our back hurts when we're older.
Speaker 1: So yeah, I think environmental cues become less important after
Speaker 1: the very very early phases, and then it's a lot
Speaker 1: more about what cues are being found where, and that
Speaker 1: is coded for by genes I see.
Speaker 2: But those later signals which come from genes are just
Speaker 2: like cascades from the original environmental cues, right Otherwise, every
Speaker 2: cell is the same originally, so even though they're coming
Speaker 2: from proteins which are encoded in the DNA you can
Speaker 2: like trace them upstream to environmental cues earlier.
Speaker 1: Right, Yeah, I think you could probably make that argument.
Speaker 2: The picture I have in my mind is like every
Speaker 2: cell is like go into the hardware store, Like, yes,
Speaker 2: you can make a cabinet, or you could make a
Speaker 2: sculpture or whatever. All the things you need are there,
Speaker 2: but somebody has to decide, like what we're building today.
Speaker 1: Yeah, yeah, OK. I was looking for an example that
Speaker 1: I could give that would be like really satisfying, Like
Speaker 1: here's how a liver is made. But the problem with
Speaker 1: trying to explain this sort of stuff is that a
Speaker 1: fetus has layers that are not easily analogous to you know,
Speaker 1: like our human body, right, And so in order to
Speaker 1: explain it, it's hard to do without pictures, and it's
Speaker 1: hard to do in a podcast and without like introducing
Speaker 1: a bunch of jargon. And so to try to give
Speaker 1: a better sense for how this kind of thing works,
Speaker 1: I'm going to go ahead and use an example from
Speaker 1: an adult and so this isn't a fetus, but this
Speaker 1: is going to give you a sense for how genes
Speaker 1: help cells decide how to behave and how to make
Speaker 1: decisions about what to become every cell in your body
Speaker 1: needs to be able to get oxygen and like relieve waste.
Speaker 1: But you like grow over time, right, and so or
Speaker 1: I grow over time. And when you grow and you
Speaker 1: end up with like more cells in an area, your
Speaker 1: body needs a way to say, Okay, you know what,
Speaker 1: Actually I need more blood vessels over here because there's
Speaker 1: like more cells and no, they're no longer getting as
Speaker 1: much oxygen as they need. So how does your body
Speaker 1: know when an area needs more blood vessels? So what
Speaker 1: happens is that your cells make a protein all of
Speaker 1: the time. And this protein whose name I'm not going
Speaker 1: to burden you with for Daniel's sake, this protein is
Speaker 1: actually constantly made, and when your cell is getting enough oxygen,
Speaker 1: your body just regularly destroys it. It's like I got
Speaker 1: enough oxygen, I'm getting rid of this protein. I don't
Speaker 1: need it. But when you don't get enough oxygen, this
Speaker 1: protein stops getting broken down and it goes into the
Speaker 1: nucleus of the cell and it starts activating more genes.
Speaker 1: And one of the things that it does is it
Speaker 1: tells your cell, hey, we are in a low oxygen situation.
Speaker 1: You should stop multiplying you should stop doing anything that
Speaker 1: isn't critical because we only have so much oxygen. And
Speaker 1: then the other thing that it does is it gets
Speaker 1: the cell to start producing something else. And this is
Speaker 1: a signal that gets released from the cell, and this
Speaker 1: signal calls the blood vessels over to it, and it's like,
Speaker 1: you need to start heading over to me because I
Speaker 1: am not getting enough oxygen. And so now it starts
Speaker 1: growing towards the cell that needs or oxygen. And once
Speaker 1: that cell starts getting all of the oxygen that it needs,
Speaker 1: it goes back to destroying the protein that it was making,
Speaker 1: just like it usually does. So as I mentioned earlier,
Speaker 1: when it has enough oxygen, it just regularly destroys this protein.
Speaker 1: And so now that it's got as much of the
Speaker 1: protein as it needs, it just destroys it. It's got
Speaker 1: the blood vessel giving it as much oxygen as it needs,
Speaker 1: and so now it's fine. So does that kind of
Speaker 1: make sense?
Speaker 2: The body is building cell types of different kinds based
Speaker 2: on signals that come from the body.
Speaker 1: Itself, right, that are coated for by genes, and proteins
Speaker 1: are acting on genes to try to like tell the
Speaker 1: blood vessels that hey, you need to make more cells
Speaker 1: to come over here to feed us, and then that
Speaker 1: is acting on the genes again to tell the cell Okay,
Speaker 1: I've got enough oxygen. I can go back to destroying
Speaker 1: this protein, and then the cycle stops.
Speaker 2: It's amazing to me how complicated this is. It's amazing
Speaker 2: to me that this ever works, and it's also amazing
Speaker 2: to me that it mostly always works. I know, every
Speaker 2: time I learn more about biology, I'm terrified.
Speaker 1: Yes, right, okay, and you will be even more terrified
Speaker 1: when after the break we start talking about stem cells
Speaker 1: and adults.
Speaker 2: Okay, we're back, and we're exploring Kelly's understanding of developmental
Speaker 2: biology as explained to a physicist in response to questions
Speaker 2: from listeners than today, Mostly we're talking about how our
Speaker 2: bits know to turn into various bits. Kelly, where are
Speaker 2: we in the grander explanation?
Speaker 1: All right? So now we are asking how do our
Speaker 1: cells know what to do after we're born? Like, how
Speaker 1: does your body know I need to make another red
Speaker 1: blood cell? For example? One thing your body could do
Speaker 1: is it could always just say like, hey, you know,
Speaker 1: when your skin cell is dying, your neighbor could be like, oh,
Speaker 1: we need to make another one, so I'm just gonna replicate.
Speaker 1: But one problem with that is that, like if the
Speaker 1: skin cell next to you is dying, maybe that's because
Speaker 1: you just got hammered by some UV radiation. You know,
Speaker 1: you just got a sunburn, and so maybe the neighbor
Speaker 1: is not in great shape either, So you probably don't
Speaker 1: want to be replicating using like the neighboring cell all
Speaker 1: the time. And so what we do instead of like
Speaker 1: constantly replicating with neighbors is we have what are called
Speaker 1: stem cells. And these are cells that we keep in
Speaker 1: very protected areas so they're not likely to get damaged.
Speaker 1: We make sure that these cells have very active repair
Speaker 1: mechanisms so that they are keeping these cells in like
Speaker 1: the best shape possible. And these stem cells are able
Speaker 1: to make new cells that are in like the best
Speaker 1: shape that we're able to make given our age. But
Speaker 1: these stem cells in adults, we're not gonna deal with
Speaker 1: fetal stem cells. We're talking about stem cells and adults,
Speaker 1: and at this point they tend to be able to
Speaker 1: make a smaller subset of cells. So, for example, if
Speaker 1: you're talking about stem cells that you find in your
Speaker 1: bone marrow, they're able to make things like red blood cells,
Speaker 1: white blood cells.
Speaker 2: Do they make them or do they turn into them?
Speaker 2: Do they like split and then half of them becomes
Speaker 2: a red blood cell or they like factories that pump
Speaker 2: out other cells.
Speaker 1: Yeah, so they create daughter cells, so they like split,
Speaker 1: and then the daughter cell could either become like a
Speaker 1: stem cell and continue to like stay in this safe
Speaker 1: area and do the splitting, or they can then go
Speaker 1: on to become like a red blood cell or something
Speaker 1: else like that.
Speaker 2: So every cell in your body was a stem cell before.
Speaker 1: Some cells. So the other day we were talking about
Speaker 1: Langer hand cells, which are like immune cells that are
Speaker 1: in your skin. Some of them are able to self renew,
Speaker 1: which means they can replicate. So some of your cells
Speaker 1: can split and renew on their own. It's just that
Speaker 1: a lot of them don't. And so some of your
Speaker 1: Langer hand cells in your skin, you know, replicated from
Speaker 1: a previous lang orhand cell, which probably did come from
Speaker 1: a stem cell in your bone marrow. Does that answer
Speaker 1: your question?
Speaker 2: Yeah? I think that's fascinating. Also, how cells can replicate
Speaker 2: a certain number of times and then they basically kill
Speaker 2: themselves off.
Speaker 1: Right, So let's go through an example. So, like you've
Speaker 1: got the lining of your intestine, and the lining of
Speaker 1: your intestine is constantly exposed to like you know, acid
Speaker 1: and enzymes and bile salts. It's a really harsh environment.
Speaker 1: You got stuff scraping the lining of your intestine. And
Speaker 1: so the surface cells in mice last for about five days,
Speaker 1: and it's you know, reasonable to assume that it's something
Speaker 1: like that for humans. And these cells are probably not
Speaker 1: replaced by replicating but they're replaced by stem cells. So
Speaker 1: what happens is inside the lining of your intestinal wall
Speaker 1: you have compartments known as crips, and these are sort
Speaker 1: of like deep inside the lining of your wall. And
Speaker 1: cryps is such a great word, cryps.
Speaker 2: Like crypt like the crypt keeper or cryps like the
Speaker 2: gang members.
Speaker 1: Isn't that spelled the same way?
Speaker 2: No, that's crip crip like sure for cripple.
Speaker 1: Oh is it?
Speaker 2: Yeah?
Speaker 1: That's not nice.
Speaker 2: Do you prefer the bloods or the bloods?
Speaker 1: I'm not making any Okay, you know what we're moving on.
Speaker 1: It's crips spelled like at a mausoleum.
Speaker 2: Okay, crypt okay?
Speaker 1: And so did I. I just went on the record
Speaker 1: saying gangs aren't nice anyway?
Speaker 2: So, uh, this is why Kelly doesn't publish her address.
Speaker 1: That's exactly right, that's exactly right. So anyway, these crips
Speaker 1: are deep inside your intestine. They're protected by cells that
Speaker 1: are called panet cells, and these secrete proteins that kill bacteria.
Speaker 1: There's also cells that secrete mucus around them, and so
Speaker 1: they're like very protected. And inside these cryps you get
Speaker 1: the intestinal stem cells. The intestinal stem cells are able
Speaker 1: to make more panet cells. They're able to make the
Speaker 1: cells that like lie your cell wall. They're able to make,
Speaker 1: you know, a variety of cells related to your intestine,
Speaker 1: and they split to produce daughter cells. The daughter cell
Speaker 1: will either decide to stay behind to create another stem
Speaker 1: cell if needed, or it will start crawling up the
Speaker 1: wall of the crypt and it keeps replicating as it goes.
Speaker 1: So this one replication can result in sixty four additional
Speaker 1: cells that can become a variety of different cells, and
Speaker 1: then it crawls out into the intestinal wall, and by
Speaker 1: the time it makes it out into the intestine, it's
Speaker 1: mature enough to like replace the cells that are out there.
Speaker 1: And so that's how intestinal cell walls work.
Speaker 2: Fascinating.
Speaker 1: Yeah, and so one of the things that's interesting to
Speaker 1: me is how does the cell know what kind of
Speaker 1: cell it's supposed to become. Yeah, and in this book
Speaker 1: for the intestine, they didn't really know the answer, but
Speaker 1: we kind of know the answer for bone marrow. So
Speaker 1: can we switch to that system?
Speaker 2: Tell me?
Speaker 1: Okay, So in your bone marrow, you have a different
Speaker 1: kind of stem cell, and for example, it's trying to
Speaker 1: decide how many red blood cells it needs to make.
Speaker 1: Red blood cells are the cells that carry oxygen to
Speaker 1: different parts of your body. So what you really want
Speaker 1: to know is do I have enough oxygen going to
Speaker 1: all the different cells in my body or don't I.
Speaker 1: And so there's a part of your kidney that already
Speaker 1: is a sort of low oxygen part of your kidney,
Speaker 1: and it monitors how much oxygen that part of the
Speaker 1: kidney is getting. And if oxygen starts getting low in
Speaker 1: that part of the kidney, a hormone is released. And
Speaker 1: when that hormone is released, it goes to the stem
Speaker 1: cells in your bone marrow, and that hormone talks to
Speaker 1: your bone marrow stem cells and says more red blood cells, please, wow.
Speaker 1: And once you have a lot more red blood cells
Speaker 1: in circulation, you're going to have a lot more oxygen
Speaker 1: in your blood. And once you have a lot more
Speaker 1: oxygen in your blood, your kidneys stop releasing that hormone,
Speaker 1: and so your stem cells in your bone marrow stop
Speaker 1: getting the message that hey, we need more red blood cells.
Speaker 1: So they make fewer red blood cells because they're not
Speaker 1: getting the message anymore.
Speaker 2: So it's like a feedback system.
Speaker 1: Yeah, So it's like a feedback system. And again, hormones
Speaker 1: are essentially sending like a message that then gets translated,
Speaker 1: you know, like at the level of DNA into you
Speaker 1: need to start making a particular kind of cell.
Speaker 2: All right, Kelly, we're almost there.
Speaker 1: Okay, okay, all right.
Speaker 2: You've taken this through fetal cell development, now adult stem cells.
Speaker 2: But now we want to understand like how many different
Speaker 2: kinds of cells are there and what really makes them different,
Speaker 2: like in the inner workings.
Speaker 1: Yeah, so, first of all, I want to be clear
Speaker 1: that in the poem I said I count eighty three.
Speaker 1: Do you agree? Brian never said eighty three. I was
Speaker 1: just trying to make the poem interesting.
Speaker 2: But what the d you would just search it for
Speaker 2: a rhyme.
Speaker 1: I was searching for a rhyme because frankly, I'm not
Speaker 1: good at this, but I was having fun. So the
Speaker 1: estimate I found is that we have over two hundred
Speaker 1: different types of cells, which is a lot. Yeah, but
Speaker 1: you know, when you think about it, like we've got
Speaker 1: different kinds of bone cells. We've got osteocytes, osteoclasts, osteoblasts.
Speaker 1: This is the part of the show where I revel
Speaker 1: in saying lots of different you know jargon. Well, Daniel,
Speaker 1: world's eyes. We've got blood cells, platelets, red blood cells,
Speaker 1: white blood cells, which are like neutral fills and basil fills.
Speaker 1: We've got sex cells. We've got lots of different kinds
Speaker 1: of cells.
Speaker 2: Right, I think you're being unfair. Go on, I'm not
Speaker 2: an eye roller. I don't roll my eye.
Speaker 1: It's true. You don't roll your eyes, It's true.
Speaker 2: You really it's a metaphorical eye roll, that's right.
Speaker 1: That's right. You tell me verbally that you would prefer
Speaker 1: if I stop doing it, and I guess I'm not
Speaker 1: a very good friend.
Speaker 2: But my question is are these really clean categories? Because
Speaker 2: you know, humanity likes to draw dotted lines across things
Speaker 2: that are really just a smooth spectrum. Are there really
Speaker 2: clean categories here? Are there two hundred and seventy one
Speaker 2: or is it just a bunch of distinctions of humans
Speaker 2: made up?
Speaker 1: I mean, I think for a lot of these you
Speaker 1: could make a very clean case. So for example, for
Speaker 1: muscle cells, you know, they argue that there's three different
Speaker 1: kinds skeletal, smooth, and cardiac. Right, And so if you
Speaker 1: were to remove the cardiac muscle cells and replace them
Speaker 1: with skeletal muscle cells, your heart would stop and you'd die.
Speaker 1: So you'd be like, that type counts. And then if
Speaker 1: you removed platelets and then somebody cut you and you
Speaker 1: bled out, you'd be like, platelets probably counted as a
Speaker 1: real blood cell type. And so we do have a
Speaker 1: lot of types that are distinct, and I think you
Speaker 1: could argue for probably most of the two hundred different
Speaker 1: cell types that they do distinct jobs.
Speaker 2: But could somebody else out there, alternative biologist be like
Speaker 2: I would draw different categories? Oh is there fuzziness there?
Speaker 3: Yeah?
Speaker 1: Yeah, there could be. You know, I can imagine someone saying, oh,
Speaker 1: each kind of T cell is a different kind of cell. Yeah,
Speaker 1: And so T cells are part of your immune response
Speaker 1: that goes after very particular kinds of bacteria and viruses,
Speaker 1: and I could imagine someone arguing that, like, the T
Speaker 1: cell that goes after a particular version of the flu
Speaker 1: is different than the T cell that goes after a
Speaker 1: different version of the flu. I don't have a list
Speaker 1: of all the two hundred different cells that they named.
Speaker 2: Really, because I wanted to hear all the names.
Speaker 1: One day, we should get together and I'll read all
Speaker 1: the different names, and then you can read me the
Speaker 1: names of all the particles and the subparticles, and we
Speaker 1: can both have the most fun we've ever.
Speaker 2: Had and nobody will learn anything.
Speaker 1: That's right. Yes, we'll both zone out five words in
Speaker 1: and it'll be amazing, all right.
Speaker 2: But I think the lesson here is that there are
Speaker 2: lots of different types. Whether it's two hundred or four
Speaker 2: hundred or whatever, there's many many different types of cells,
Speaker 2: but not ten million and.
Speaker 1: Not two Yes, that's right. Yes, that's a nice way
Speaker 1: to put it, okay, And so what makes these different?
Speaker 2: First?
Speaker 1: I want to highlight what I think is the most
Speaker 1: interesting thing here, which is that they look very, very
Speaker 1: very different.
Speaker 5: You know.
Speaker 1: So, for example, if you think about the cells in
Speaker 1: your brain, you've got like a neuron that has you know,
Speaker 1: like the spidery looking head parts and then the very long,
Speaker 1: thin connecting parts. And that looks so different than your
Speaker 1: red blood cell. That looks like, you know, almost kind
Speaker 1: of like a frisbee that bulges on both ends or
Speaker 1: something like that.
Speaker 2: This is a fascinating insight into Kelly's mind. Wow, you
Speaker 2: think neurons look like spiders. So when you look at
Speaker 2: somebody and you imagine their brain, are you imagining like
Speaker 2: a skull full of spiders?
Speaker 5: Yeah?
Speaker 1: What No, I'm trying to overcompensate for the fact that
Speaker 1: I've used a lot of jargons, so I didn't want
Speaker 1: to say, you know, they've got dendritic you know, ends,
Speaker 1: and I'm just not doing a good job.
Speaker 2: I guess to me, a neuron looks like an egg
Speaker 2: that fell on the sidewalk. It's like kind of like
Speaker 2: a big explode.
Speaker 1: Yeah, okay, egg that fell on a sidewalk. What does
Speaker 1: the red blood cell look like like a pillow with
Speaker 1: like where someone punched their fist in the middle.
Speaker 2: No, I think your frisbee was pretty good. Yeah, I
Speaker 2: agree with frisbee.
Speaker 1: Yeah yeah, oh good. All right, so they look very different.
Speaker 2: But are you going to say that they're actually very
Speaker 2: very similar.
Speaker 1: Oh, okay, they're very very different. But what's amazing is
Speaker 1: that they all are made from the same genetic code,
Speaker 1: you know, like you've got the same genome, but by
Speaker 1: turning on or off different genes, you end up with
Speaker 1: these cells that look incredibly different. Amazingly, Like you know,
Speaker 1: our red blood cells, they have hemoglobin, which is a
Speaker 1: molecule that like binds to oxygen and helps us carry
Speaker 1: oxygen throughout our body. This is also one of the
Speaker 1: few cell types in our body where the nucleus gets
Speaker 1: like taken out at some point, so it doesn't have
Speaker 1: a nucleus amazingly, though in birds it does still have
Speaker 1: a nucleus. Did you know that bird red blood cells
Speaker 1: have nucleuses nuclei?
Speaker 2: Oh, I didn't know that our red blood cells didn't
Speaker 2: have nuclei.
Speaker 1: Did you know that in the fetus we have three
Speaker 1: pairs of kidneys?
Speaker 2: What what I know? Crazy?
Speaker 1: That is crazy? And then two of them kind of disappear,
Speaker 1: although one of them sort of gets integrated into the
Speaker 1: male reproductive system. Yeah, thank your kidneys. Next, never mind,
Speaker 1: moving on.
Speaker 2: So I saw my kidneys.
Speaker 1: Are you okay?
Speaker 2: I'm fine, But I had an ultrasound done, and they
Speaker 2: usually tilt the ultrasound screen away from you, and I
Speaker 2: was like, hey, can I watch and they were like,
Speaker 2: we don't usually do that. I'm like, but I want
Speaker 2: to see inside of me, and so they tilted the
Speaker 2: screen over and I'm like, oh, that's what my kidney
Speaker 2: looks like. Look it looks like a kidney.
Speaker 1: Yeah, and they were like, oh, the physicist is surprised
Speaker 1: that the kidney looks like a kidney.
Speaker 2: And then I said, what's the weirdest thing you've ever
Speaker 2: seen inside a person while doing an ultrasound? And they said,
Speaker 2: we're not at liberty to discuss other patients. So then
Speaker 2: I said, well, if you saw something weird inside of me,
Speaker 2: like a huge nest of worms, because I was channeling Kelly,
Speaker 2: you would you say something? And they were like no.
Speaker 2: So then I was worried, like, oh my gosh, what
Speaker 2: are they saying? That's why I wanted to see the screen.
Speaker 1: I get that.
Speaker 2: I get that anyway. So you're telling me that the
Speaker 2: cells are really quite different, that when you go to
Speaker 2: the human hardware store, the codes that let you build
Speaker 2: red blood cell can let you build something really really different,
Speaker 2: like a nerve cell. That's really incredible, And I think
Speaker 2: Brian wants to know, like what is really different about
Speaker 2: these cells? Like how different are they on the inside,
Speaker 2: you know, their internal structures and inner workings.
Speaker 1: Yeah. So I struggled a lot to figure out the
Speaker 1: answer because the two hundred different cell types differ a lot. Yeah,
Speaker 1: I mean a lot of them have you know, a nucleus? Okay,
Speaker 1: but you know that's not even true for your red
Speaker 1: blood cells. I don't think that's true for your caratinocytes.
Speaker 1: And so we were talking about these when we were
Speaker 1: talking about the langerhand cells in the previous Listener Questions episode.
Speaker 1: These are the cells that are like making up your
Speaker 1: outer layer of skin. I don't think they have nuclei either.
Speaker 5: Wow.
Speaker 1: You know, it's hard to like summarize what differs between
Speaker 1: them because we have so many different cell types that
Speaker 1: are so different.
Speaker 2: It's like saying, how does the bicycle differ from a ferrari.
Speaker 2: It's totally different.
Speaker 1: Yeah, And you're like, well where do I start. I mean,
Speaker 1: they need they probably probably most of them have mitochondriac
Speaker 1: because they need a power source, like vehicles need power sources.
Speaker 1: And so I, yeah, I came up a little bit
Speaker 1: short trying to figure out an answer. So I give
Speaker 1: Brian one hundred points for kind of stumping me.
Speaker 2: No, I think that's an answer, right. The answer is
Speaker 2: there can be totally different kinds of cells, right. I
Speaker 2: think the question sort of assumes that there some similarity,
Speaker 2: that you can bring parallels between these various kinds of cells.
Speaker 2: But your answers that the spectrum of cells are so
Speaker 2: different that there isn't really anything to say about what
Speaker 2: they might.
Speaker 1: Have in common, or at least Kelly couldn't come up
Speaker 1: with anything clever to say. And so if other listeners
Speaker 1: would like to chime in, I'd love to hear. But
Speaker 1: but yeah, that's that's kind of what I came up with.
Speaker 1: They're just they're so different, and and to me, that's
Speaker 1: what's amazing. Yeah, Like, the same set of instructions can
Speaker 1: come up with these cells that are so different.
Speaker 2: Yeah.
Speaker 1: Wow, Wow, that's what I've got. That's what I've got.
Speaker 1: The answer Brian is wow.
Speaker 2: The thing again that amazes me is that it works
Speaker 2: so well so often. Like before I was a parent,
Speaker 2: I was just like, yeah, of course people are born,
Speaker 2: then they developed, big whoop. But then when I became
Speaker 2: a parent, I was like, suddenly very invested in the
Speaker 2: specific development of this one critter. And then I was like,
Speaker 2: oh my gosh, all these complicated things have to go
Speaker 2: right for my boy to grow into an actual human being,
Speaker 2: and all of a sudden, I've had very little faith
Speaker 2: in any of that happened.
Speaker 1: Please please work? Yes, yes, you feel very powerless?
Speaker 2: Right? Yeah? All right, Well let's ship these questions off
Speaker 2: to our listeners to hear if we scratched their developmental itch.
Speaker 1: That's right, or if I have just made them crazy
Speaker 1: and now they feel like their brains are full of spiders.
Speaker 3: Hi again, thanks for your explanation. I really enjoyed and
Speaker 3: it helped a lot. Super interesting. I have been thinking
Speaker 3: about it and I have a few follow up questions. Well,
Speaker 3: I have many, but I will ask on you too often.
Speaker 3: You mentioned transcription factors being more concentrated towards the bottom
Speaker 3: of the egg. Do you mean that literally because of
Speaker 3: gravity or is bottom more about orientation like the site
Speaker 3: facing the uterinevolved And if gravity matters, would development of
Speaker 3: fetus be affected in zero gravity? And how do cells
Speaker 3: figure out left versus right during the development of fetus?
Speaker 3: Like what actually makes heart end up on the left side.
Speaker 2: Thank you very much.
Speaker 3: I love the show.
Speaker 1: Ooh, great questions. Okay, keeping me on my toes. So
Speaker 1: for the transcription factors and stuff that are at the
Speaker 1: bottom of the cell, it's not that they are just
Speaker 1: free floating at the bottom of the cell. So they're not,
Speaker 1: as I understand, it's subject to things like gravity, because
Speaker 1: that would be too susceptible to issues. So for example,
Speaker 1: you know, if you had a fetus developing, you'd have
Speaker 1: to be careful to not jump around the time that
Speaker 1: your cells were dividing or something. And so I believe
Speaker 1: that everything is sort of held in place by things
Speaker 1: like you know, spindles or just basically structures that hold
Speaker 1: the transcription factors and stuff in particular parts of the cell,
Speaker 1: so that when the cell divides, you end up with
Speaker 1: different quantities of the transcription factors and stuff ending up
Speaker 1: in different cells. When the cells divide, one cell will
Speaker 1: end up with more of it than another cell because
Speaker 1: of the way that the quantities of the transcription factors
Speaker 1: were sort of divided up and held into place. And
Speaker 1: so hopefully that wouldn't get messed up if you were
Speaker 1: in space and in a low or no gravity environment.
Speaker 1: But that might depend on whether or not the creation
Speaker 1: of those spindles that hold everything in place is impacted
Speaker 1: by having no gravity, because that's just not an environment
Speaker 1: we evolved in or are adapted to. Okay, So then
Speaker 1: how does your body know how to handle the asymmetrical stuff?
Speaker 1: So you don't have hearts on both sides of your body.
Speaker 1: Your heart is on one specific side of your body,
Speaker 1: and so how does your body know what side that
Speaker 1: heart should be on? So early in development, your fluids
Speaker 1: are moving in a particular way. So you have cells
Speaker 1: that have cilia, which are like little hairs that are
Speaker 1: moving things in a very particular direction. So the cilia
Speaker 1: are beating in a very particular direction and at a
Speaker 1: particular angle, and the way that they are beating it
Speaker 1: ends up resulting in the fluids moving in one direction.
Speaker 1: And when the fluids are moving in that direction, they
Speaker 1: have a bunch of like good stuff in them, And
Speaker 1: because of the way the fluids are moving, that good
Speaker 1: stuff is getting used up. And so one side of
Speaker 1: your body is getting to use up that stuff, and
Speaker 1: the other side of your body by the time it
Speaker 1: gets there, the good stuff has already been used up,
Speaker 1: and so one side of your body gets a lot
Speaker 1: of the signal and the other side of your body
Speaker 1: gets less of the signal. And this is essentially how
Speaker 1: your body learns that one side is going to be
Speaker 1: different than the other side. And we have done this
Speaker 1: because we've watched the cilia spinning and we've sort of
Speaker 1: modeled the way that they flow, and we also have
Speaker 1: created mutants that essentially move the cilia in the opposite direction,
Speaker 1: and the organs in the body of those mutant animals
Speaker 1: show up on the opposite side that you would expect
Speaker 1: them to show up on, which is pretty cool. Thank
Speaker 1: you for the follow up questions.
Speaker 4: Hey, Kelly, you did an amazing job. After listening to this,
Speaker 4: I have to say I'm with Daniel. I am astonished
Speaker 4: that we function at all. Two any follow up questions
Speaker 4: to even know where to start. Keep an eye on
Speaker 4: your inbox for future episodes.
Speaker 1: All right, Next up, we have Sarah from Louisville asking
Speaker 1: about opposable thumbs.
Speaker 5: We've done on and Kelly, this is Sarah from Lousville, Kentucky.
Speaker 5: My question is are opposable thumbs necessary for the development
Speaker 5: of tools and technology? Would aliens need to have fingers
Speaker 5: and thumbs to make spaceships to visit us, Thank you
Speaker 5: and keep up the good work.
Speaker 1: Well, I'm personally glad we have opposable thumbs for thumbs up,
Speaker 1: but we probably need them for other things too. What
Speaker 1: are what are our posable thumbs good for? Daniel?
Speaker 2: Or you can stick them into things? You know? I
Speaker 2: guess you can pick stuff up. You can throw them
Speaker 2: at each other. You can write there you get down.
Speaker 1: Throw thumbs at each other. Tell me about your thumbs, Daniel.
Speaker 1: How do your thumbs work?
Speaker 2: They're detachable, aren't yours? Oh my gosh, Kelly, your dificion. No,
Speaker 2: you can pick things up to throw at each other,
Speaker 2: you know, happy things like sandwiches, And I don't know.
Speaker 1: That's not the right way to deliver a sandwich to
Speaker 1: a loved one, Daniel. Oops, I tend to disassemble when
Speaker 1: you do that.
Speaker 2: Well, already you get the sense that maybe I'm not
Speaker 2: fully qualified to answer this question. And you know, when
Speaker 2: questions come into the inbox, we have a little triage.
Speaker 2: I look at a question, I'm like, is this a
Speaker 2: Daniel question? Or is this a Kelly question? And this
Speaker 2: one I was like, Okay, well it's kind of about biology,
Speaker 2: but it's also kind of about aliens and spaceships, so
Speaker 2: it's really on the edge for me. But because it
Speaker 2: had the word aliens in it, I was like, I'm
Speaker 2: going for it. I'm gonna take this one.
Speaker 1: Oh. I took a tiger beetle question that I actually
Speaker 1: think was a Daniel question. Yeah, and I's been sitting
Speaker 1: on my desk for a long time. I might find
Speaker 1: some secret way to kick it to you.
Speaker 2: Do it, bring it on, put it in a sandwich,
Speaker 2: and throw it over to me.
Speaker 1: All right, I'm going to toss it your way.
Speaker 2: My head full of spiders will take it on.
Speaker 1: Okay, good.
Speaker 2: But I love thinking about this kind of question because
Speaker 2: while it's kind of about earth based biology, it's really
Speaker 2: about the larger context, like why do we have thumbs?
Speaker 2: Could it have been different? Is it likely that we
Speaker 2: find thumbs on alien planets? Or are there like a
Speaker 2: vast number of ways that critters can grasp their tools
Speaker 2: on alien planets? Really fun and kind of philosophical, and
Speaker 2: so we're not going to be totally constrained by biology today,
Speaker 2: which is why I took on this question.
Speaker 1: Now, all right, all right, so how do other animals
Speaker 1: manipulate objects. Yeah, so thumbs are bring biology, thank you.
Speaker 2: I know, usually it's my job to bring us back
Speaker 2: on track. But so what are thumbs good for?
Speaker 4: Right?
Speaker 2: What do we do with them? You're right, we manipulate stuff,
Speaker 2: you know, but it's not just that. We also use
Speaker 2: them to really apply a lot of power. Like we
Speaker 2: can squeeze really pretty hard with our hands and with
Speaker 2: our thumbs. And humans have been doing this for a
Speaker 2: long long time, right, our ancestors have had opposable thumbs
Speaker 2: for millions of years. And you can find things like
Speaker 2: stone tools that are millions of years old, and the
Speaker 2: context of that boggles my mind. You know, imagine holding
Speaker 2: something in your hand that was shaped by a human
Speaker 2: like creature a million years ago, you know, purposefully to
Speaker 2: do a job, you know, hand access and things like this.
Speaker 2: You can find them just lying on the ground. So cool.
Speaker 2: The other amazing thing about this to me is that
Speaker 2: a lot of those things were lying on the ground
Speaker 2: for a long time before anybody recognized what they were.
Speaker 2: You know, people were just like, oh, they're just stones,
Speaker 2: and only upon further examination you're like, this is not
Speaker 2: just a stone. This is an obvious pattern of work
Speaker 2: on it. This is a tool. It goes to show
Speaker 2: you how many things can be discovered just by changing
Speaker 2: your paradigm.
Speaker 1: And in some cases they were taken from really far away,
Speaker 1: Like I was listening to a special episode of The
Speaker 1: Rest is History, and it was like a flint I
Speaker 1: think it was like a piece of flint for making
Speaker 1: a fire that they realized wasn't found in that area
Speaker 1: and must have been carried a very long distance. And
Speaker 1: it's like, oh my goodness, like this was a precious
Speaker 1: stone that had been anyway. Yes, very exciting.
Speaker 2: One of my favorite stories about special stones is the
Speaker 2: one that looks like a human face. They found this
Speaker 2: pebble which looks sort of like a human face. I
Speaker 2: mean it's got like two eyes and doesn't look like
Speaker 2: anybody made it, but it's out of place geologically, which
Speaker 2: suggests that like somebody picks it up and like, hey,
Speaker 2: look this looks like org you know, and carried it
Speaker 2: with them because it's like a rock that randomly looks
Speaker 2: like a person, and they're like, hey, that's cool.
Speaker 5: Yeah.
Speaker 2: So it's not like creating art, but it's like found art,
Speaker 2: you know, from millions of years ago. To me, that's
Speaker 2: an amazing connection with like a person from a long
Speaker 2: time ago. Yeah, anyway, we're far off track, but we're
Speaker 2: talking about like the use of opposable thumbs. And I
Speaker 2: think this is the inspiration for Sarah's question. And is
Speaker 2: it possible to have the same kind of experience and
Speaker 2: build technology in spaceships and launch yourself into the universe
Speaker 2: if you didn't have apposable thumbs. Well, already here on
Speaker 2: Earth we see lots of options for grasping biology. Right,
Speaker 2: Like Octopi they don't have opposable thumbs, but they can
Speaker 2: definitely manipulate stuff. You can see videos of Octopy like
Speaker 2: opening jars right even from the inside, Like, these are
Speaker 2: clever beings and they very obviously have a precise sense
Speaker 2: of the world and how to manipulate it in great
Speaker 2: detail and with great intelligence.
Speaker 1: M I love watching them open jars. It always blows
Speaker 1: my mind, especially when they're stuck inside the jar.
Speaker 2: I know, I often can't open jars from the outside,
Speaker 2: imagine how to open it from the inside, Like, it's crazy.
Speaker 2: They might be smarter than we are. And then you
Speaker 2: have like crows. Crows only have a beak, right, there's
Speaker 2: no arms there at all. They don't have like clever
Speaker 2: thumbs on their feet, but with their beak, they can
Speaker 2: do a lot of really incredible stuff, right. They can
Speaker 2: solve puzzles, they can manipulate the world. Birds build really
Speaker 2: complicated nests for themselves. In fact, this weekend I discovered
Speaker 2: an LBJ in my garage, clearly building a nest for itself.
Speaker 1: Aw this, we're almost at the swallow time of year
Speaker 1: for my barns, so we're going to get the barn
Speaker 1: swallow nests.
Speaker 2: Nice.
Speaker 1: Yeah, they're really cute. They make a lot of poop,
Speaker 1: but they're really cute, so I let them poop on
Speaker 1: my stuff and then just clean it up afterwards.
Speaker 2: But it's definitely a kind of engineering, right, they are
Speaker 2: building stuff, they're manipulating the world. I don't know if
Speaker 2: it's the kind of technology that can sort of boost
Speaker 2: yourself into space travel, right, there's sort of a threshold
Speaker 2: there where you build technology that can do things you
Speaker 2: can't do biologically, and then you can escape the limitations
Speaker 2: of your biology. I'm not sure if birds could ever
Speaker 2: do that, though I'm pretty sure octopi could eventually. And
Speaker 2: then of course there's elephants right their trunk lets them
Speaker 2: pick stuff up and poke it and manipulate it. And
Speaker 2: so it's definitely examples of critters out there who do
Speaker 2: not have thumbs but have a similar ability to manipulate
Speaker 2: the world and apply their intelligence to make it the
Speaker 2: way that they need it. So then you might ask
Speaker 2: is that enough for technology? Right? Like could elephants, if
Speaker 2: left alone, develop factories to fabricate silicon chips at two nanometers? Right?
Speaker 2: The way the humans have? Is that what we're really
Speaker 2: talking about, So make me think about, like what do
Speaker 2: you need for technology? Well, you need to be able
Speaker 2: to like manipulate stuff, but you also need to be
Speaker 2: able to like stick stuff together, to like handle small
Speaker 2: bits of it, to have like really fine control in
Speaker 2: like lots of different directions. I mean we're talking about
Speaker 2: like artisanal work, you know, at an early stage in
Speaker 2: technological development, but you need like fine control, not just
Speaker 2: like roughly grasping things. But it also seems to me
Speaker 2: like you could do that in lots of ways. Like
Speaker 2: if you look at the spiders inside Kelly's brain for example, right,
Speaker 2: they have lots of mandibles, like they are building a web,
Speaker 2: Like that's definitely a way to have fine control over
Speaker 2: the materials in front of you.
Speaker 1: So just to clarify, we're just we're assuming that these
Speaker 1: organisms end up having the intelligence to do it, and
Speaker 1: we're just asking if they're able to manipulate it. But like,
Speaker 1: so we're able to do things that are much more
Speaker 1: fine scale, Okay, So, like I've got friends who manipulate
Speaker 1: fruit fly brains. Yeah, and I think that some of
Speaker 1: them do that through computers, where like you know, they
Speaker 1: do a much bigger motion and then the computer makes
Speaker 1: that motion fine scale, because we can't work at that
Speaker 1: fine scale, right, So I guess the you know, the
Speaker 1: crow or the elephant would just have to make a
Speaker 1: device that could work on a finer scale.
Speaker 2: I think that's the crucial thing, right, if you can
Speaker 2: build some tech and then bootstrap beyond your biology so
Speaker 2: that the tech that you build can help you build
Speaker 2: other tech that can do things that you and your
Speaker 2: immediately build tech can't do, okay, right, And so I
Speaker 2: think to make that leap, you need to be able
Speaker 2: to build things using fine control. You need to be
Speaker 2: able to sh materials, you need to be able to
Speaker 2: handle small bits to build enough complexity into your text
Speaker 2: so that it can then do things that you can't do.
Speaker 2: But you know, also a worry there that we're thinking
Speaker 2: too narrowly. You know, that we're thinking about the way
Speaker 2: that we have progressed to technology, which is mostly like,
Speaker 2: you know, by constructing things, and so trying to think
Speaker 2: about how an alien civilization might find a completely different
Speaker 2: path to developing technology, Like, rather than assembling a spaceship,
Speaker 2: could you imagine growing one? You know, like, okay, you
Speaker 2: don't need hammers and arms if you can like manipulate
Speaker 2: biology or some other kind of species and their development,
Speaker 2: tinker with nature's technologies to manipulate it into like developing
Speaker 2: the objects that you need somehow, so you don't need
Speaker 2: the same sort of technological route that we have. Just
Speaker 2: you know, one crazy idea, But the larger point is that,
Speaker 2: you know, we shouldn't be too constrained by imagining elephants
Speaker 2: or birds or octopy trying to recreate our path to technology,
Speaker 2: because there could be lots of different ways to get there.
Speaker 1: Yeah, yeah, agreed, And frankly, I think this is a
Speaker 1: really great opportunity for you to tell everybody about the
Speaker 1: great book that you wrote about imagining what aliens might
Speaker 1: be doing out there.
Speaker 2: Well, I hope that This is what inspired Sarah to
Speaker 2: write in the question I didn't write a book recently
Speaker 2: called Do Aliens Speak Physics? Which is all about whether
Speaker 2: aliens have followed a similar trajectory to understanding the universe
Speaker 2: that we have. Have they built similar explanations? Is our
Speaker 2: explanation unique and singular and inevitable, or is it is
Speaker 2: one of many possible ways to explain the universe? Is
Speaker 2: our history of science different or is it common around
Speaker 2: the universe. These are the kind of things we explore
Speaker 2: in the book, which I had a lot of fun
Speaker 2: doing research for and writing. Thank you Kelly for giving
Speaker 2: me the opportunity to shout it out, though I'm pretty
Speaker 2: sure everybody on the podcast has heard me talk about
Speaker 2: it many times by.
Speaker 1: Now, Well, Daniel does not have a brain full of spiders,
Speaker 1: and so it is a truly amazing book. Highly recommend.
Speaker 2: Thank you. So, you know, trying to think most broadly
Speaker 2: about what's needed, trying to like move away from the
Speaker 2: specifics of thumbs or even appendages and mandibles. You know,
Speaker 2: I think that any species to develop technology is going
Speaker 2: to need some kind of memory, and then you want
Speaker 2: some sort of way to pass your learning on to
Speaker 2: the next generation, so you can build on itself.
Speaker 4: You know.
Speaker 2: The reason that like your grandpa can't program the VCR,
Speaker 2: or that I'm even making VCR references because I'm basically
Speaker 2: a grandpa, is because technology advances, right, and the next
Speaker 2: generation becomes fluent in the technology and then builds upon it.
Speaker 2: Because we have this social learning, and the key to
Speaker 2: that is some kind of symbolic communication. The ideas I
Speaker 2: have in my head don't die with me. I can
Speaker 2: write them down, I can communicate them somehow broadly, so
Speaker 2: that I don't like show individual people how I make fire.
Speaker 2: We can store that information. It can last for a
Speaker 2: thousand years. This allows the sort of cumulative culture. I
Speaker 2: don't know if you need the specifics of like electronics,
Speaker 2: you know, which require like mining and manipulation of fire.
Speaker 2: That would be hard for OCTOPI to do. But I
Speaker 2: think most broadly that's what you need is any kind
Speaker 2: of memory and ability to communicate your learning to the
Speaker 2: next generation, so you can get sort of cumulative understanding
Speaker 2: of how to manipulate the universe. I think that's really
Speaker 2: the essentials everything else. I think probably an intelligent enough
Speaker 2: critter could learn.
Speaker 1: To overcome excellent well, that was a fantastic answer. And
Speaker 1: let's see if Sarah thinks that the octopodes will be
Speaker 1: going to space when the humans are gone.
Speaker 5: Thank you for answering my question, Daniel and Kelly. It's
Speaker 5: fun to think that one day we might get to
Speaker 5: shape the tent cause of an alien that arrives in
Speaker 5: a biologically grown ship.
Speaker 2: All right, thank you very much everybody for sending us
Speaker 2: your questions. We want to hear from the spiders in
Speaker 2: your skull. What makes them curious? Do they want to know?
Speaker 2: Can they write emails?
Speaker 1: So right to us spiders at Questions at Danielankelly dot
Speaker 1: org or join us over on discord. You can find
Speaker 1: an invite over at danielan Kelly dot org. We hope
Speaker 1: to hear from you.
Speaker 2: Thanks everybody for listening. Please go and do us a
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Speaker 2: It really helps people find us.
Speaker 1: Daniel and Kelly's Extraordinary Universe is edited by the amazing
Speaker 1: Matt Kesselman.
Speaker 2: He really is a wizard. You can also find us
Speaker 2: online on Blue Sky, Instagram, and x D and Kuniverse.
Speaker 2: Come in cage with us.
Speaker 1: You can email us at questions at Daniel and Kelly
Speaker 1: dot org. We really do want to hear from you,
Speaker 1: and you.
Speaker 2: Can find our website www dot danieland Kelly dot org,
Speaker 2: where you'll also find an invitation to join our discord
Speaker 2: where everybody comes an talks about the amazing universe.
Speaker 1: And we also have the most amazing moderators. This is
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