Speaker 1: Hey, welcome to Stuff to Blow your Mind. It is Saturday,
Speaker 1: so once more we have a vault episode for you.
Speaker 1: This is going to be Life in the Hapogean World,
Speaker 1: Part one. This one was originally published three five, twenty
Speaker 1: twenty four. This is going to be part one out
Speaker 1: of four, so we'll be publishing the other three episodes
Speaker 1: in this series on the Saturdays to come.
Speaker 2: Welcome to Stuff to Blow Your Mind, a production of iHeartRadio.
Speaker 1: Hey, welcome to Stuff to Blow your Mind. My name
Speaker 1: is Robert.
Speaker 3: Lamb and I am Joe McCormick. And hey here we
Speaker 3: are together again, Rob. After you were out for a
Speaker 3: little bit.
Speaker 1: Oh yeah, yeah, we've recorded a few thanks here there.
Speaker 1: So I keep forgetting that, you know, when the actual
Speaker 1: new core episodes are that I'm around for. So yeah,
Speaker 1: I am back. I was just in a little vacation
Speaker 1: with my family.
Speaker 3: Wait a minute, now, you refreshed my brain because I
Speaker 3: forgot that we did a listener mail episode before this.
Speaker 3: So listeners, are you are reacclimated to Rob? Now?
Speaker 1: Yeah? I mean listeners I think always have a skewed
Speaker 1: understanding of when we're out when we're present, because there's
Speaker 1: you know, even if one of us is out. You
Speaker 1: may hear us on a vault episode on the weekend.
Speaker 1: We might have recorded through on something recorded ahead of
Speaker 1: time on one piece of content, but not on other
Speaker 1: pieces of content. So you know, you'll just have to
Speaker 1: take our word for it. Sometimes we are away, sometimes
Speaker 1: we were present.
Speaker 3: We're like a duo of mysterious time traveling cats that
Speaker 3: appear in your ears.
Speaker 1: Yeah all right, Well, you know I have to say,
Speaker 1: on this most recent journey with my family, I did
Speaker 1: not venture into a cave. I don't think I ventured
Speaker 1: into a cave. Let me refresh. No, no cave venturing,
Speaker 1: no school.
Speaker 3: I would think you'd remember. Come on, I.
Speaker 1: Mean, sometimes you know, these trips, you see a lot
Speaker 1: of things, and you know, and you know, cave environments
Speaker 1: are are always fascinating, but they're not necessarily always going
Speaker 1: to be like the top of a particular trip. It
Speaker 1: just varies. But you know, we frequently discussed biological wonders
Speaker 1: on the show that leads us to consider extreme environments,
Speaker 1: and the cave environment is one such environment. I tend
Speaker 1: to find caves endlessly fascinating, even if it's a lower
Speaker 1: tier cave. You know, and I've been to some of
Speaker 1: those where it's like, okay, this is this one was
Speaker 1: opened by humans a while back. It doesn't have much
Speaker 1: in the way of a robust ecosystem and so forth,
Speaker 1: but it's still fascinating. There's still something about the subterranean world.
Speaker 3: Have you ever done the cave exploring experience where you
Speaker 3: go down into a cave and all artificial light sources
Speaker 3: are turned off and you get to see like the
Speaker 3: blackest black night you've ever seen. It's a kind of
Speaker 3: darkness that you cannot imagine otherwise.
Speaker 1: Yeah. Absolutely done this in a couple of Tennessee caves,
Speaker 1: I think growing up. One that was like one of
Speaker 1: these big official caves. I'm blanking on which one it
Speaker 1: would have been, but went there was like a scout group.
Speaker 1: And then there was another like local cave that was
Speaker 1: just on somebody's land and got to go in there
Speaker 1: and see the main cavern and then have the lights
Speaker 1: go out. Sometimes they'll do the lights out with a
Speaker 1: little ghost story or something right, just sort of drive
Speaker 1: home the creepiness of it. But yeah, you find yourself
Speaker 1: in just the absolute darkness.
Speaker 3: We did this with our tour guide years ago at
Speaker 3: Oregon Caves National monument in southwestern Oregon, which is a
Speaker 3: very cool cave system. And it's hard to explain because
Speaker 3: again I had not seen anything like this anywhere before,
Speaker 3: where you just eyes are totally wide and you see
Speaker 3: not even a pinprick of light, just nothing.
Speaker 1: Yeah, it's it's haunting and it's and it is key
Speaker 1: to understanding cave environments, as we'll be discussing in this episode. Now.
Speaker 1: Not only are caves home to rather unique organisms in
Speaker 1: certain caves, as we'll discuss more as we progress, but
Speaker 1: they've of course always fascinated humans, and our global myths
Speaker 1: and traditions are full of caverns that house monsters, passages
Speaker 1: to the underworld, magical treasures, and much more. Also, as
Speaker 1: we've discussed, these were some of the first enclosed spaces
Speaker 1: that humans entered and were occupied to some degree in
Speaker 1: a way, laying the groundwork for the humble and elaborate
Speaker 1: shelters that we would construct thereafter. You know, because what
Speaker 1: is what are some of the rooms in our houses
Speaker 1: but caves that we have built for ourselves.
Speaker 3: Some houses are more cave like than others.
Speaker 1: Yeah. Yeah, so we may not think of ourselves as
Speaker 1: cave people, but we are in many respects still people
Speaker 1: of the cave at home, with enclosed spaces, sometimes with windows,
Speaker 1: sometimes without places in general like this, be it constructed,
Speaker 1: be it like a large enclosed concert hall, or an
Speaker 1: underground facility, or a naturally occurring cave or some sort
Speaker 1: of a tunnel. I mean, you can't help but dream
Speaker 1: about those spaces, to find dread and fascination in those spaces.
Speaker 1: And you know now that I mention it. On my
Speaker 1: family vacation, I don't think we went We did not
Speaker 1: go into a cave system, but we did go through
Speaker 1: tunnels at times, and we were stuck in traffic in
Speaker 1: a tunnel at one point. And so that alone gives
Speaker 1: one enough room for pause.
Speaker 4: It's just as good almost well, I wouldn't say it's
Speaker 4: not as good, but it does. It summons possibilities, maybe
Speaker 4: even the possibility of talking about the strange world of
Speaker 4: cave biology. And that's what we're going to be looking
Speaker 4: at in this series.
Speaker 1: Right, that's right, talking about the cave environment, talking about
Speaker 1: some of the organisms and life forms that live there.
Speaker 1: And to get into this, I want to talk a
Speaker 1: little bit about just sort of the idea of there
Speaker 1: being a dual world something that again is quite reflected
Speaker 1: in some of our more supernatural understandings of the surface
Speaker 1: world and the world beneath it, the earth, you know,
Speaker 1: the world of the living, the world of the dead,
Speaker 1: and so forth. I was reading a twenty eleven article
Speaker 1: in The American Scientist by Autamaro Romero, and he pointed
Speaker 1: out that cave biologist or biospileiologists divide the world into two.
Speaker 1: There's the epigean world, or the world upon the earth,
Speaker 1: the world of light that we predominantly think of as
Speaker 1: our home. And then there's this other world, this underworld,
Speaker 1: the hypogean world beneath the soil.
Speaker 3: I've never thought of the surface as epigean before, but
Speaker 3: I love that because I guess with the Greek there yet,
Speaker 3: like you say, it means upon the earth, on the earth,
Speaker 3: so not just like exposed, but it's like like an
Speaker 3: epiphyte plant that grows on another plant. The epigean world
Speaker 3: of the surface world isn't like the thing that grows
Speaker 3: on the surface of this ball of iron.
Speaker 1: Yeah, and then everything else, the underworld, the hypogean world
Speaker 1: beneath the soil, and the world beneath the soil. To
Speaker 1: make no mistake here is vast. So just as the
Speaker 1: epigean world consists of any part of the biosphere that
Speaker 1: is even partially or periodically exposed to light, the hypogean
Speaker 1: world consists of any underground part of the biosphere. So
Speaker 1: this includes the living soil in your backyard, networks of
Speaker 1: mycilium that rooting through it, as well as life between
Speaker 1: grains of sand buried under the beach, underground waters, and indeed,
Speaker 1: cave environments, which, to be clear, can also be part
Speaker 1: of the epigaean world because they of course are gateways
Speaker 1: and there are going to be transition spaces the mouth
Speaker 1: of a cave, for example. Yeah, Now, caves, as Ramera
Speaker 1: points out in this article, are also This is also
Speaker 1: a very broad categorization, entailing everything from ice caves to
Speaker 1: lava tubes, and indeed caves are merely the subterranean spaces
Speaker 1: into which humans can venture. There are plenty of subterranean
Speaker 1: environments and even cavernous spaces in the earth that are
Speaker 1: just inaccessible to us because there are no openings to
Speaker 1: the surface.
Speaker 3: That's a really good point, and there's so much that
Speaker 3: goes on in those those small or tiny spaces that
Speaker 3: you can't like walk into and observe. You know, you
Speaker 3: mentioned like the idea of the myceelium that underlies that.
Speaker 3: You know, you find a mushroom in the forest. It's
Speaker 3: hard to remember this sometimes, but like the mushroom you
Speaker 3: find is just like one organ of the fungus organism
Speaker 3: as a whole. It's the fruiting body that comes up
Speaker 3: above the surface. But underneath there's gonna be this whole network.
Speaker 3: That's sort of where the organism really is, is under
Speaker 3: the soil, and you don't even see it. You don't
Speaker 3: even think to look down there.
Speaker 1: Yeah, there's there's an there's a vital and rich world
Speaker 1: in there, and it's not a space that human beings
Speaker 1: can venture into in the way that we can venture
Speaker 1: into a cave environment, you know. I mean we can
Speaker 1: study it, we can explore it, we can dig it up,
Speaker 1: but it's a different sort of world. Now. Romero also
Speaker 1: mentions the freatic environments of underground lakes and rivers, but
Speaker 1: the word cave is generally reserved for again, those spaces
Speaker 1: we can access ourselves where human explorers and scientists or
Speaker 1: at least their technological minions can physically investigate the world below.
Speaker 1: At least you can get you can get a robot
Speaker 1: in there, you can stick a probe in, somehow invoke
Speaker 1: your presence there.
Speaker 3: A cave is like a space that can be spilunked,
Speaker 3: and maybe our standards for how small a space can
Speaker 3: be spilunked are changing.
Speaker 1: Right when we had Lee Burger on the show, the
Speaker 1: author of Cave of Bones, who was talking about exploring
Speaker 1: various cave environments, a specific cave environment in fact, looking
Speaker 1: at pre human skeletal remains. And one of the really
Speaker 1: telling things about his experience is there was this part
Speaker 1: of the cave that for the longest he could not access.
Speaker 1: It was like a grueling experience, and you had to
Speaker 1: send a like very young specialized scientists down there to
Speaker 1: physically occupy the space. And he was able to, you know,
Speaker 1: send them down, have them look around. He was able
Speaker 1: to look at video footage from that space. But eventually
Speaker 1: he could not resist. And he talks about this at length,
Speaker 1: like he had to go down there, he lost weight
Speaker 1: in order to fit through, narrowly fit through the passageways
Speaker 1: that were acquired a grueling experience to actually make it there.
Speaker 1: So there is something about like the human exploratory experience
Speaker 1: and all of this, Like, even when you have the
Speaker 1: technology and the organization, there's something about it. You have
Speaker 1: to be there. You want to be there in the space.
Speaker 3: Man. I know I'm not unique in this, but that
Speaker 3: is one of the things that truly gives me the
Speaker 3: creeps to like barely trying to wedge your way through
Speaker 3: passageways inside a cave under the earth. That is just ugh.
Speaker 1: Yeah, it gave maybe all of is here in some
Speaker 1: of the details in his book, and I think there
Speaker 1: was also covered in a Netflix special If Memory Is Serving,
Speaker 1: And yeah, just the idea of like having to squeeze
Speaker 1: through a space, getting momentarily stuck like the wrench and
Speaker 1: a chimney, and then having to press on potentially like
Speaker 1: you know, risk dislocating bones and so forth to do it.
Speaker 1: It's yeah, not for me, but I respect anyone who
Speaker 1: is capable of it totally. Now, the most common caves
Speaker 1: are carstick or limestone. I believe we've discussed this before
Speaker 1: talking about various geological formations. Limestone, which covers roughly fifteen
Speaker 1: percent of the world above water, is highly soluble at
Speaker 1: least fifty percent calcium carbonate. According to romero, so acidic
Speaker 1: rain water easily modifies it over time. And so the
Speaker 1: world is littered with such cave systems, some only partially
Speaker 1: exposed to the surface world but in important ways, Others
Speaker 1: with key openings that permit light to influence the environments
Speaker 1: of their interior. So you know, some kind of cave systems.
Speaker 1: Some rather famous ones even do have sunlight spilling into them,
Speaker 1: at least in part, so you end up with this
Speaker 1: kind of like mixed environment. But the lack of natural
Speaker 1: light as a whole is extremely important to understanding the
Speaker 1: individual organisms that make their homes and caves, as well
Speaker 1: as the overall ecosystems in which they thrive.
Speaker 3: Right because when you think about it, basically everywhere else
Speaker 3: on Earth, I mean, there are some extreme exceptions, but
Speaker 3: for most of the world, the food chain is built
Speaker 3: on access to sunlight. The sunlight powers the powers the
Speaker 3: photosynthesis of the autotrophs that are the base of the
Speaker 3: food chain. Then things start eating them, then other things
Speaker 3: eat those organisms, and on and on up. If you
Speaker 3: don't have sunlight to power the autotrophs at the base,
Speaker 3: what do you do?
Speaker 1: I know, yeah, yeah, we'll get back to this in
Speaker 1: just a minute here. But the humans, of course, we're
Speaker 1: not the first adventure into the subterranean worlds. Countless other
Speaker 1: creatures ventured in, resulting in rich, a rich, specialized world
Speaker 1: of troglofauna, And not every creature becomes a permanent denizen
Speaker 1: of the dark, which if you watch enough sci fi
Speaker 1: and horror movies, you would think, oh, yeah, they're just
Speaker 1: people and creatures fallen in all the time and evolving
Speaker 1: in the chuds. But no, that doesn't happen all the time.
Speaker 1: But plenty of creatures have specialized evolutionarily, often evolving defining
Speaker 1: troglomorphic features that we often associate with these environments, namely
Speaker 1: blindness and loss of pigmentation, with.
Speaker 3: The chutification if you will.
Speaker 1: Chutification, I guess yeah. You know, you see movies like
Speaker 1: The Descent and so forth. I love all these movies,
Speaker 1: you know, more Locks and so forth. But maybe we'll
Speaker 1: continue to discuss the possibilities there. But briefly, I want
Speaker 1: to just do a refresher on the various types of
Speaker 1: troglofauna before we continue. You we have troglo bites. These
Speaker 1: are obligate cave dwellers strictly bound to the under their
Speaker 1: underground environments, so they are not going to live, they're
Speaker 1: not going to thrive outside of the darkness of the caves.
Speaker 1: Then we have troglasines. These are cave guests, creatures that
Speaker 1: can be found underground sporadically but cannot establish permanent underground populations.
Speaker 1: Then we have troglophiles. These are creatures that live predominantly
Speaker 1: above ground, but can also reside in underground habitats. There
Speaker 1: are two subsets. There's u trogleophiles, surface species that are
Speaker 1: also able to maintain in a permanent subterranean population, and
Speaker 1: then there are subtroglophiles, creatures that can and do live
Speaker 1: underground at least temporarily, but are more associated with life
Speaker 1: above ground. So again you can think about the idea
Speaker 1: that there's not just surface creatures and underground creatures. You know,
Speaker 1: there's a lot of back and forth, and there are
Speaker 1: various phases between what we might think of as a
Speaker 1: purely surface creature and a purely subterranean creature.
Speaker 3: I see none of.
Speaker 1: This to be confused with a troglodyte. They're a handful
Speaker 1: of different uses is for this term. It can refer
Speaker 1: either to a human cave dweller or and I believe
Speaker 1: in one case of an outdated classification of early hominid.
Speaker 1: But there are also a small genus of small birds
Speaker 1: related to wrens that are called troglodytes. These birds are
Speaker 1: rarely found in caves apparently, but they're so named because
Speaker 1: they'll venture into various crevices and spaces, including caves, in
Speaker 1: search of food.
Speaker 3: So we have these various kinds of spilunking organisms, those
Speaker 3: that do still live life on the surface, but have
Speaker 3: the ability and sometimes the desire to venture into caves
Speaker 3: or subterranean regions for very various reasons. Maybe they want
Speaker 3: to shelter there for a certain period, maybe they want
Speaker 3: to go in there to retrieve some kind of resource,
Speaker 3: who knows. But then there's the other kind, the ones
Speaker 3: that are fully adapted to life in the caves and
Speaker 3: it has shaped their evolution, has shaped their morphology. Now
Speaker 3: their bodies are made for the caves. One of the
Speaker 3: examples that people listening are probably thinking of are sightless fish.
Speaker 3: Fish that live in cave based in underground waterways and
Speaker 3: have evolved to completely lose their vision or their eyes.
Speaker 3: And this has long been a really captivating image within
Speaker 3: evolution that the idea. You know, people usually think of
Speaker 3: evolution as a constructive process that sort of powers up
Speaker 3: an organism. It gives it a new ability or a
Speaker 3: new adaptation that better suits it to an environment or
Speaker 3: an environmental niche that it's currently occupying, and so it
Speaker 3: gets upgraded in some way. These are these are ways
Speaker 3: that we sometimes discourage people from thinking about evolution, by
Speaker 3: the way, but it is still in the popular consciousness
Speaker 3: that that's how it works. This is evolution by what
Speaker 3: might be thought of as regression, like losing a trait
Speaker 3: that you previously had. So that raises a lot of
Speaker 3: questions about how evolution works and and why something like
Speaker 3: that would happen.
Speaker 1: You know, it's it's fascinating to think about this about
Speaker 1: our our, our our often human focused bias, and considering
Speaker 1: evolution along these lines. Like we think of that classic
Speaker 1: illustration of the ascent of man, you know, the various
Speaker 1: uh Hamonid species evolving towards man, and we we it's
Speaker 1: easy to look at him and like think, wow, look,
Speaker 1: with each step he just gets hotter. With each step,
Speaker 1: he just looks more like us. He becomes more perfect,
Speaker 1: like clearly modern Homo sapiens are, but even in that
Speaker 1: we're seeing the loss of various features. We're seeing like
Speaker 1: the loss of body hair and so forth.
Speaker 3: Yeah, totally, and as big asterisk, if you see an
Speaker 3: old illustration like that, there's probably a lot of that's
Speaker 3: inaccurate about it. But some things that broadly would be
Speaker 3: true is that our ancestors do appear to have lost
Speaker 3: adaptations that made them really good tree climbers, and those adaptations,
Speaker 3: those are adaptations that were very useful for our ancestors,
Speaker 3: and we sort of lost them in favor of other things.
Speaker 1: Yeah. And it is also interesting again to think about
Speaker 1: the world of the dark, the world of the caves, because,
Speaker 1: like we said, we can have this experience of turning
Speaker 1: out the lights in the cavern and experiencing the true darkness.
Speaker 1: But for the most part, ever since human beings were
Speaker 1: able to capture fire, we have been able to bring
Speaker 1: light into these spaces, and today when we explore caves,
Speaker 1: at least on our own terms, we have that light
Speaker 1: that we bring with us, and we therefore we don't
Speaker 1: have to we change the environment by bringing light into it,
Speaker 1: the cavern changing us over evolutionary time of course, is
Speaker 1: not on the table.
Speaker 3: That's all right, But without the ability to modify the
Speaker 3: features of the environment like that other animals have had
Speaker 3: to adapt evolutionarily.
Speaker 1: Yeah, and in all this we have to again recognize
Speaker 1: just how vital light is for organisms for the evolution
Speaker 1: of life on our planet. Both sunlight and moonlight are
Speaker 1: in play here. As pointed out by Lauren Summer Rooney
Speaker 1: in The Kingdom of the Blind, published in a twenty
Speaker 1: eighteen edition of Integrated and Comparative Biology, light is a
Speaker 1: fundamental biological cue for almost every animal on Earth. So
Speaker 1: it's not just about oh can I see the inside
Speaker 1: of the cave or not? You know, it plays in
Speaker 1: a navigation foraging, predator avoidance, mate selection, and just like
Speaker 1: general daily rhythms. So to abandon the world of light
Speaker 1: is no small thing, right, and yet we do see
Speaker 1: plenty of organisms that have done just that over time,
Speaker 1: not only cave organisms but certain creatures of the deep ocean.
Speaker 1: Though we have to remember that site is still important
Speaker 1: at varying levels of the water column and in the
Speaker 1: presence of phosphorescent glows, so there is a fair amount
Speaker 1: of complexity there. The soil and even interiors of host
Speaker 1: organisms for various parasites are also dark environments that species
Speaker 1: have adapted to now. As Romero points out, Charles Darwin
Speaker 1: himself was somewhat stumped by the loss of sight and cavefishes,
Speaker 1: and apparently ultimately landed on more of a Lamarchian idea
Speaker 1: that they lost their eyes by simply not using them.
Speaker 3: Oh, that's kind of interesting. So Lamarckism or Lamarchianism named
Speaker 3: after a figure named I believe you, Jean Baptiste Lamarck.
Speaker 3: It was the sort of alternative theory of inheritance to
Speaker 3: what would eventually become Mendalian genetics, which in some ways
Speaker 3: has been partially superseded now. But instead of the kind
Speaker 3: of Mendalian genetic inheritance, Lamarck would say that, like the
Speaker 3: way that an animal uses its body shapes the way
Speaker 3: its offspring the way their bodies are formed. So like
Speaker 3: if you are reaching up a lot or something, you
Speaker 3: might grow your children might have longer arms, or like
Speaker 3: that a giraffe maybe is reaching its neck up to
Speaker 3: reach higher leaves, and that means its children will be
Speaker 3: born with longer necks and so forth. For the most part,
Speaker 3: evolution doesn't actually work that way, there are some kind
Speaker 3: of things of gene expression and regulatory functions epigenetics that
Speaker 3: some people have argued in minor ways can kind of
Speaker 3: vindicate Lamarckian thinking, but for the most part that's not
Speaker 3: really how inheritance works.
Speaker 1: Right right, Yeah, I've been to evolutionary talks, I believe
Speaker 1: the World Science Festival for some biologists have been like, yeah, yeah,
Speaker 1: we're kind of we to start talking about epigenetics. Sometimes
Speaker 1: we do get a little Lamarckian way we're talking, so
Speaker 1: it is it is kind of fascinating.
Speaker 3: But the Lamarckian idea would be okay, so fish go
Speaker 3: down in a cave and then they don't use their
Speaker 3: eyes because they're living in the dark. Therefore their children
Speaker 3: or their offspring are born without them or born with
Speaker 3: eyes that regress. We can talk about that difference in
Speaker 3: a minute, and in a way you could say that
Speaker 3: that's loosely kind of right, but but it's somewhat different.
Speaker 3: I think I would say that the important thing is
Speaker 3: not that the fish don't use their eyes, it's that
Speaker 3: they don't need them, so that the eye no longer
Speaker 3: confers a survival or reproductive advantage.
Speaker 1: I think the one of the infectious things about it,
Speaker 1: at least at least for non scientists, is that it
Speaker 1: can feel right in certain ways. Right. It can sort
Speaker 1: of match up with at least the individual human experience.
Speaker 1: So we might not think, like, man, I bet I
Speaker 1: better go to the gym, and you need a pump
Speaker 1: iron so that my offspring will will have strong arms.
Speaker 1: But we might think, uh, oh, well, I've got to
Speaker 1: keep pumping iron otherwise my arms will get smaller. You know,
Speaker 1: I've got to do X so that why doesn't happen?
Speaker 1: And uh, you know, I think we do see this
Speaker 1: infectious idea in some of our fictions of subterranean monsters,
Speaker 1: including The Descent of the Hobbit Snekeel and the Lord
Speaker 1: of the Rings, who becomes a trogloditic gollum in the
Speaker 1: course of a single, though of course magically sustained lifetime.
Speaker 1: He doesn't really become blind or anything, but generally he's
Speaker 1: depicted as you know, he's changed a lot. He's lost
Speaker 1: his hair, his pimitation has changed, his eyes have gotten larger,
Speaker 1: I believe.
Speaker 3: Yeah, though, I think the morphotypical changes of Gollum could
Speaker 3: be largely due to the corruption of the one ring.
Speaker 1: That's the thing. The one ring changes everything you've got.
Speaker 1: You've got a huge magical factor to consider in that scenario.
Speaker 1: But sort of just the idea of it is like, Yeah,
Speaker 1: people go into caves, they get weird, they turn into monsters,
Speaker 1: or if they're not a monster, you know weight three generations,
Speaker 1: then just pure monsters.
Speaker 3: Caves will do that.
Speaker 1: Now, Summer Rooney points out that we're still working out
Speaker 1: all the details, but we know much more than Darwin
Speaker 1: did in his time. Of course, the science has come
Speaker 1: quite a way since then in our understanding of how
Speaker 1: creatures evolved and what sort of changes are taking place
Speaker 1: over revolutionary time. The author rights quote. Eye loss appears
Speaker 1: to be driven at least in part by direct selective pressure,
Speaker 1: but both pliotrophy and genetic drift are also key influencers.
Speaker 1: Despite substantial recent progress thanks to a combination of developmental
Speaker 1: and molecular techniques, it is not yet clear how these
Speaker 1: drivers interact, or crucially, whether their relationships are similar across
Speaker 1: taxa and habitat types.
Speaker 3: Yeah, so this was really interesting and I ended up
Speaker 3: going kind of deep on what we do know about
Speaker 3: eye loss and a related issue of pigmentation loss. In cavefish.
Speaker 3: But I wanted to break down some of the terms
Speaker 3: that this author uses in that paragraph you just read.
Speaker 3: So selective pressure, of course, would mean an advantage in
Speaker 3: terms of survival or reproduction, a direct advantage. That's the
Speaker 3: kind of evolution we think about most often. But there
Speaker 3: are two other factors that could be influencing the loss
Speaker 3: of eyes or the loss of pigmentation in fish that
Speaker 3: the author mentions, and those are plyotrophy and genetic drift. Plyotropy,
Speaker 3: to sort of oversimplify, means when one gene determines multiple
Speaker 3: outcomes in the phenotype, and the phenotype is like the
Speaker 3: body or the behavior of the organism. It's what the
Speaker 3: genes produce in the animal. So, for example, imagine there
Speaker 3: is a mutation at one locust, and that one mutation
Speaker 3: happens to both give you smaller eyes but also longer arms.
Speaker 3: Or maybe there's a mutation that happened to give you
Speaker 3: both higher rates of cancer and higher average fertility. And
Speaker 3: pliotropies like these can they're very interesting because they can
Speaker 3: sometimes explain the evolution of traits that would seem to
Speaker 3: be disadvantageous because the seemingly bad trait is actually part
Speaker 3: of a hidden package deal, a genetic package deal with
Speaker 3: an even more advantageous trait balancing it out, and you
Speaker 3: can get either both or neither, but not one by itself.
Speaker 3: So in the case of cavefish, it's possible there is
Speaker 3: a single mutation that both causes the loss of eyes
Speaker 3: but also does something else that helps the fish survive
Speaker 3: and reproduce. And since there's little to no penalty attending
Speaker 3: the loss of vision in the pitch black cave environment,
Speaker 3: the helpful half of that pliotropy wins out and the
Speaker 3: two for one version of the gene is selected for.
Speaker 3: And then the final factor mentioned here is genetic drift.
Speaker 3: Genetic drift is change in the frequency of gene variants
Speaker 3: within a population due to random chance. So genes becoming
Speaker 3: more or less prevalent within a group of organisms, not
Speaker 3: for selective reasons, not because they help or hurt the organism,
Speaker 3: but just randomly, you know. And this happens all the time.
Speaker 3: Gene variants just become more common less common within a population,
Speaker 3: and it happens due to random factors, though sometimes if
Speaker 3: a population is small enough. And interesting thing is that
Speaker 3: traits resulting from random genetic drift can become what's called fixed,
Speaker 3: meaning that you kind of hit a genetic tipping point
Speaker 3: and a trait that was randomly fluctuating up and down
Speaker 3: in the population, it becomes prevalent enough that suddenly it's fixed,
Speaker 3: and then all the individuals within the population have the
Speaker 3: gene for that trait. Going forward, Yeah.
Speaker 1: Now, now going back to what you mentioned about about
Speaker 1: the idea of there possibly being like an advantage and
Speaker 1: a disadvantage tied up in one change. But the thing is,
Speaker 1: you find yourself, if you're this fish undergoing this change
Speaker 1: or some other organism, you find yourself in a lightless environment,
Speaker 1: and so in this you dip over into the neutral
Speaker 1: mutation hypothesis, This idea that while naturally occurring mutations for
Speaker 1: in this case blindness would otherwise spell doom for a
Speaker 1: fish in a typical environment in a lighted environment, it
Speaker 1: doesn't matter in the darkness, and therefore these mutations can
Speaker 1: flourish along with whatever other changes they might be bringing.
Speaker 3: That's right. Then they can flourish for multiple reasons. They
Speaker 3: could flourish because they're part of a plotropy that has
Speaker 3: an advantage on the other half, or they can just
Speaker 3: flourish randomly through genetic drift because there's no penalty to
Speaker 3: the loss of sight in the darkness.
Speaker 1: Yeah, this I can't help be reminded of various gaming
Speaker 1: rules and gaming systems and all of this. Like, it's like,
Speaker 1: imagine that you're playing Dungeons and Dragons and let's say
Speaker 1: you're venturing into the under dark. You're venturing in a
Speaker 1: lightless environment, and you have a weapon that gives you,
Speaker 1: say a plus two on attack. But if you're in
Speaker 1: the sunlight, it has your hit points or something like
Speaker 1: something that would make this all right. It has advantages
Speaker 1: to it, but the disadvantage is far outweigh it in
Speaker 1: a different environment, but you're not in that environment. Now,
Speaker 1: you're in an environment where the disadvantage does not matter.
Speaker 3: Right. Yes, that's a good analogy, and it's also a
Speaker 3: good reason to remember to check your build when your
Speaker 3: environment changes. But yeah, so there is, as we're saying,
Speaker 3: some possibility for all of these options and explaining the
Speaker 3: evolution of kvefish blindness. There could be direct selective pressure,
Speaker 3: there could be indirect selective pressure through pliotropy or the
Speaker 3: package deal, and there could be random genetic drift. However,
Speaker 3: it seems that there is some pretty good evidence for
Speaker 3: the presence of a direct selective pressure for fish to
Speaker 3: lose their eyes when they live in a lightless environment,
Speaker 3: and there might be some evidence for pliotropy as well.
Speaker 3: So to get a more concrete idea of what we're
Speaker 3: talking about, I wanted to focus on a particular species
Speaker 3: of fish that has been studied a lot, and that
Speaker 3: species is called Astianax mexicanus, also known as the blind
Speaker 3: Mexican cave fish, also known as the blind cave tetra.
Speaker 3: These are small minnow like fish with silver scales. I
Speaker 3: saw different size estimates for them. Some said they grow
Speaker 3: to a maximum length of about nine centimeters. Other sources
Speaker 3: said about twelve centimeters, but they're relatively small in any case.
Speaker 3: One thing that makes these Astianax fish very interesting is
Speaker 3: that there exist both surface or epigean and cave or
Speaker 3: hypogean variants of the same fish species, and they have
Speaker 3: different body features. And scientists can learn a lot by
Speaker 3: comparing these extremely closely related populations of animals to one another,
Speaker 3: cross checking genomic information back and forth, and seeing what
Speaker 3: that correlates to in terms of their phenotypic traits. So
Speaker 3: the cave variant of Astianax lives in this big network
Speaker 3: of underground waterways in the mountainous areas of northeastern Mexico.
Speaker 3: And they've been in these caves since. One source I
Speaker 3: was reading said they colonized them probably around the end
Speaker 3: of the Pleistocene epic, so you know, roughly twelve thousand
Speaker 3: years ago or so. There are photos you can find
Speaker 3: online which I'd recommend looking up, which not only show
Speaker 3: the cave variant of ASTIANAX, but they depict the cave
Speaker 3: variant and the surface variant side by side to highlight
Speaker 3: the differences in their bodies. So the cave version is
Speaker 3: much more pale and translucent. And indeed, in the places
Speaker 3: where the surface variant has a big old bulging fish
Speaker 3: eye on either side of its skull, the cave variant
Speaker 3: has only a strange, fatty looking lump underneath its scales,
Speaker 3: just in front of the red flap of the gill.
Speaker 1: Yeah, these are haunting images to look at. Again, we
Speaker 1: can't help but think of like various sneakels and so
Speaker 1: forth when looking at it.
Speaker 3: Yeah, exactly, And I bet these fish are good at
Speaker 3: riddle games. Now, one thing that I was reading this
Speaker 3: kind of interesting about these The eyeless variant of the
Speaker 3: Astianax fish is that they undergo what's called eye regression.
Speaker 3: So I don't know if this is true of all populations,
Speaker 3: because they are like different cave populations of this fish
Speaker 3: that have been studied, and they have some differences between them.
Speaker 3: But I was reading, at least in some populations, what
Speaker 3: happens is not that these fish never have eyes, but
Speaker 3: they begin to grow eyes during embryonic development, and then
Speaker 3: as they developed the they acquire eyes and then lose
Speaker 3: the eyes in development, and the eye sockets are paved
Speaker 3: over by skin and scales, and there remain these little
Speaker 3: fatty lumps where the sockets used to be, and the
Speaker 3: bone kind of collapses around it. So I thought this
Speaker 3: was kind of interesting. It's not just that they never
Speaker 3: have eyes. They get eyes and then they lose them,
Speaker 3: all in the process of a single animal growing up.
Speaker 1: Fascinating, you know. I also have to throw in, okay,
Speaker 1: Astianax part of the scientific name for the creature. This
Speaker 1: is the son of Hector in the Iliad, and I'm
Speaker 1: guessing here I couldn't find anything just definitive offhand, but
Speaker 1: I'm assuming the naming here is because Astianax, the child
Speaker 1: of Hector, is hidden in the tombs. That is the
Speaker 1: way that they try to ensure his survival. And so
Speaker 1: you know, we see some version of that here, a
Speaker 1: survival in the underworld of the caves as opposed to
Speaker 1: the tomb.
Speaker 3: I did not make that connection. That is interesting. So
Speaker 3: I mentioned that there was some evidence that actual selection
Speaker 3: pressure a direct selection pressure, drove the evolution of eyelessness
Speaker 3: in these fish, as well as some possible evidence for pliotropy.
Speaker 3: Let's look at a paper to learn more. So the
Speaker 3: paper I was reading is called Cavefish and the Basis
Speaker 3: for Eye Loss by Jaya Krishnan and Nicholas Rohner, published
Speaker 3: in Philosophical Transactions of the Royal Society b Biological Sciences
Speaker 3: twenty seventeen, and in the section of their paper discussing
Speaker 3: the reasons for eye loss, the authors note that it
Speaker 3: is not unique to the example of these blind Mexican
Speaker 3: cavefish for an animal to evolve by losing a trait
Speaker 3: or characteristic that was once positively selected for in that
Speaker 3: animal's ancestors. Examples include the law of tails in some primates,
Speaker 3: including us, the loss of teeth in birds and the
Speaker 3: loss of legs in whales. All of these are examples
Speaker 3: where an animal lineage acquired an adaptation that was useful
Speaker 3: long ago, and then some branch of that lineage entered
Speaker 3: a new ecological niche in which that trait was no
Speaker 3: longer useful or was actively harmful, and evolved once again
Speaker 3: to lose the trait that its ancestors' bodies had constructed
Speaker 3: so long ago. And the example of cavefish that lost
Speaker 3: their eyes was long simply assumed to be a result
Speaker 3: of genetic drift. Eyelessness appears in the gene pool, and
Speaker 3: then with no selection pressure favoring eyes to keep the
Speaker 3: eyelessness suppressed, it would just randomly fluctuate in frequency in
Speaker 3: the gene pool until at some point it became fixed. However,
Speaker 3: the authors say that in roughly the last decade before
Speaker 3: this paper, and this was again twenty seventeen, there had
Speaker 3: been more attention to the possibility of a positive selection
Speaker 3: pressure favoring the loss of eyes. There's a reason to
Speaker 3: lose the eyes, either directly or through pliotropy, so let's
Speaker 3: talk direct selection first. The main explanation offered for direct
Speaker 3: selection against eyes is energy conservation also sometimes expressed as
Speaker 3: metabolic cost. It costs energy the energy that animals get
Speaker 3: from food to have functioning organs, and some types of
Speaker 3: organs are more energy hungry than others. In fact, the
Speaker 3: authors demonstrate that neural tissue, which includes brain cells and
Speaker 3: also eyes and nerves, that type of tissue is one
Speaker 3: of the most expensive types that an animal can grow
Speaker 3: and maintain, So any animal's evolution is guided by a
Speaker 3: balancing of interests, the benefits provided by sensory awareness and
Speaker 3: the high metabolic cost of having this neural tissue of
Speaker 3: having these systems. This is true in any animal in
Speaker 3: any environment, but the balance is especially crucial in harsh
Speaker 3: environments like caves, where food energy is more scarce than
Speaker 3: on the surface. It's harder to come by food energy
Speaker 3: in a cave than it is in the surface waters
Speaker 3: where the surface variant of the Mexican cavefish lives. And
Speaker 3: in favor of this explanation the energy cost explanation, the
Speaker 3: author's cite of paper from twenty fifteen by Moran, Softly
Speaker 3: and Warrant published in Science Advances called the Energetic Cost
Speaker 3: of Vision and Evolution of Eyeless Mexican cavefish. Summarizing the
Speaker 3: findings of Moran at all Krishna and Rohner Wright quote.
Speaker 3: This study calculated significant metabolic costs for the optic tectum,
Speaker 3: and the tectum is the part of the fish's brain
Speaker 3: that is used to process visual information going on with
Speaker 3: the quote and the eyes adding up to fifteen percent
Speaker 3: of the resting metabolism needs in juvenile fish. Such a
Speaker 3: high cost of vision, almost reaching the cost of the
Speaker 3: human brain at twenty to twenty five percent, makes an
Speaker 3: adaptive loss of eyes owing to energy constraints highly probable.
Speaker 3: So usually there's a high energy cost. You need to
Speaker 3: eat a lot of food to grow and sustain the
Speaker 3: sensory organs and visual processing in the brain tissue. But
Speaker 3: on the surface, evolution is usually willing to pay that
Speaker 3: cost because it's really beneficial to get visual information about
Speaker 3: your surroundings that really helps you survive and reproduce. If
Speaker 3: getting visual information about your surroundings becomes impossible because you
Speaker 3: live in total darkness, it's time to make budget cuts.
Speaker 3: Another possible direct selection factor. I haven't come across direct
Speaker 3: evidence for this, but it's just mentioned as a possibility
Speaker 3: by several sources and that is that eyes are also
Speaker 3: a liability in that they are prone to injury and
Speaker 3: an entry way for infection. So it's kind of like
Speaker 3: why you put a windshield on your armored vehicle if
Speaker 3: you're driving in pitch black with no headlights, it would
Speaker 3: just be a functionless weak point in the armor of
Speaker 3: the vehicle that provides no benefit. And it's possible that
Speaker 3: eyes are like this also, once there's nothing to see,
Speaker 3: all they would be is a soft spot to let
Speaker 3: germs and sharp objects in.
Speaker 1: Yeah. Kind of like with sci fi visions of spaceships, right,
Speaker 1: like why have an actual observation lounge or observation bubble
Speaker 1: or so forth, Why have actual glass there or any
Speaker 1: kind of like transparent wall when you can if you
Speaker 1: have like ubiquitous abilities to have video footage and screens
Speaker 1: around you. Basically the Star Trek principle exactly.
Speaker 3: If it's not actually providing you a benefit, then it's
Speaker 3: just a liability.
Speaker 1: Yeah.
Speaker 3: Also, the authors of this paper mention some evidence for
Speaker 3: indirect selection or pliotropy. Specifically, they bring up a signaling
Speaker 3: pathway identified in the scientific literature as SHH. And do
Speaker 3: you want to guess what SHH stands for? Now tell
Speaker 3: me what stands for sonic hedgehog. That's really what they say,
Speaker 3: and that's what it is really, Yes, scientific papers, this
Speaker 3: is the sonic hedgehog signaling pathway. There's also just an
Speaker 3: HH or hedgehog pathway, so I don't know attacking on
Speaker 3: maybe that was discovered first and then they tacked on
Speaker 3: sonic to be funny for this other pathway. I don't
Speaker 3: know for sure, but it is called the sonic hedgehog
Speaker 3: signaling pathway. And the signaling pathway, by the way, is
Speaker 3: it's like a series of chemical reactions in the body
Speaker 3: that controls and coordinates the activity of cells in order
Speaker 3: to do things like grow new tissue during development, or
Speaker 3: cause an immune system response or something like that. The
Speaker 3: sonic hedgehog pathway, in particular, it seems important during embryonic development.
Speaker 3: It sort of guides growth and plays a role in
Speaker 3: the patterning of tissues that emerge from the growth process.
Speaker 3: So Krishnan and Rohner point to a study by Yamamoto
Speaker 3: at all from twenty nine from not twenty nineteen, from
Speaker 3: two thousand and nine sorry in Developmental Biology, which found
Speaker 3: that by altering expression of the sonic hedgehog signaling pathway
Speaker 3: in embryos of the surface dwelling relative of the blind
Speaker 3: Mexican cavefish. You would actually get multiple changes together. This
Speaker 3: is our package deal. You would get regression of the
Speaker 3: eyes like we talked about, so the eyes would sort
Speaker 3: of like be absorbed and you would no longer have
Speaker 3: functioning eyes as an adult fish. But you would also
Speaker 3: get enhancement of taste buds and jaws. So that's your
Speaker 3: package deal. And in the dark you can imagine why
Speaker 3: that would be a good package deal. The author's write
Speaker 3: quote SAHH has wide range effects on the development of
Speaker 3: various organs, and it has been identified as a strong
Speaker 3: candidate for eye regression. It's elevated expression in the oral
Speaker 3: pharyngeal region in cavefish taste buds, and the fact that
Speaker 3: eye size and number of taste buds are correlated in
Speaker 3: hybrids makes SAHH a promising candidate for functional studies. So
Speaker 3: that's another factor possibly at work here. So to review,
Speaker 3: you got eyes in visual tissue in the brain require
Speaker 3: a lot of food to sustain, and food is especially
Speaker 3: scarce in the cave. Also, the eyes are not really
Speaker 3: useful in the cave, so you know the trade off
Speaker 3: there seems pretty obvious. There's less evidence for this, but
Speaker 3: it has been suggested that eyes are also a liability
Speaker 3: in terms of infection and injury, and it seems there
Speaker 3: are certain genetic and developmental changes that offer a package
Speaker 3: deal where you get eye regression, your eyes are absorbed,
Speaker 3: you have no eyes as an adult fish, but more
Speaker 3: taste buds and in the dark, that's a good deal
Speaker 3: to take because remember taste buds. We think of them
Speaker 3: mainly in terms of like providing pleasure, but taste buds
Speaker 3: give you important survival information. They are your your body's
Speaker 3: chemistry set along with your ural factory. Can you know,
Speaker 3: smell and taste together help you sort of test incoming
Speaker 3: materials for safety and nutritional value. And that is actually
Speaker 3: a very valuable thing in the wild, especially if you
Speaker 3: can't look at stuff you're gonna eat.
Speaker 1: Yeah. Yeah, we have to be reminded of that because
Speaker 1: we are such site dependent organisms that we easily think
Speaker 1: of like the world we can see and then the
Speaker 1: other senses that provide sort of backup information, right, or
Speaker 1: at least it's easy to think about that in terms
Speaker 1: of a lot of stimuli. Obviously it's different once you
Speaker 1: get into, say, you know, the actual experiences of consuming food.
Speaker 1: But even that, the visual factor is a huge part
Speaker 1: of it totally. When you pay for a nice meal,
Speaker 1: when you pay for a nice cocktail or zero proof cocktail,
Speaker 1: whatever floats your boat, you know, I mean presentation. Visual
Speaker 1: presentation is a huge part of what you're signing up for.
Speaker 3: It absolutely is. Even I would say this, even if
Speaker 3: you think you quote no better. Do you know what
Speaker 3: I mean about that?
Speaker 1: Row like that?
Speaker 3: Some people can think like, oh, you know, I'm just
Speaker 3: in it for the tasty food. I don't really care
Speaker 3: if it looks good, But actually you do care in
Speaker 3: subconscious ways that you're not admitting to yourself.
Speaker 1: Yeah, on some level, you were still anticipating the flavor,
Speaker 1: anticipating the taste experience based on and to a large
Speaker 1: degree on visual data totally.
Speaker 3: So one more thing I want to say about these
Speaker 3: the blind Mexican cavefish, because I was looking into this
Speaker 3: cavefish species and it seems that eye loss or I
Speaker 3: regression is strongly associated with a parallel morphotype, which is
Speaker 3: pigmentation loss. So a source I was using on pigmentation
Speaker 3: loss in cavefish is a chapter in a book. The
Speaker 3: chapter is called Evolutionary Genetics of Pigmentation Loss in Blind
Speaker 3: Mexican Cavefish by Joshua B. Gross and Clifford Jay Tabin.
Speaker 3: It is from the book In Search of the Causes
Speaker 3: of Evolution, From Field Observations to Mechanisms, Princeton University Press,
Speaker 3: twenty eleven, edited by Peter and Rosemary Grant. So most
Speaker 3: of this chapter is focused on the specific genetic mutations
Speaker 3: and regulatory changes that result in the reduction in or
Speaker 3: total loss of pigment in blind Mexican cavefish, the reduction
Speaker 3: in the milanophores and color molecules in the fish's body,
Speaker 3: and they find that in different populations they're actually you
Speaker 3: get these similar, similar adaptations of the loss of pigment
Speaker 3: in the body, but they have different underlying genetic or
Speaker 3: regulatory mechanisms. So it's evolved in different ways to get
Speaker 3: sort of the same results in these different cavefish populations.
Speaker 3: But also this chapter gets a little bit into what
Speaker 3: the environmental selection pressure is related to or the lack
Speaker 3: of selection pressures related to pigmentation might be. So, for example,
Speaker 3: on the surface, biological pigments like melanin help protect the
Speaker 3: cells of animals from ultraviolet radiation in the sunlight. In
Speaker 3: the cave, there's no light, so this radiation shielding effect
Speaker 3: is useless. On the surface, pigments are also arranged in
Speaker 3: patterns on the body as ornamentation, which plays a role
Speaker 3: in sexual selection. So a fish with certain types of
Speaker 3: pigmentation patterns might be seen as a more desirable mate,
Speaker 3: but in the cave, your mate can't see you, so
Speaker 3: it doesn't matter. On the surface, pigmentation can also play
Speaker 3: a role in camouflage, conceealing your body within the environment,
Speaker 3: but in the cave, once again, this doesn't make any difference.
Speaker 3: So much like with eyes, pigmentation would be a phenotypic
Speaker 3: trait that confers huge advantages on the surface where there's light,
Speaker 3: and it suddenly confers little to no advantage underground. Even
Speaker 3: if it's just subject to genetic drift, Pigmentation, like eyes,
Speaker 3: could fluctuate out of the population. But are there any
Speaker 3: reasons to think it is actively selected against. It seems
Speaker 3: like there is less evidence for this than there is
Speaker 3: in the case of eyes. There's probably good reason to
Speaker 3: think that eyes are being selected against in the cave,
Speaker 3: less so for pigmentation. The authors here cite research by
Speaker 3: protests at All from two thousand and seven indicating it's
Speaker 3: more likely a result of drift, though some amount of
Speaker 3: indirect selection through pleiotropy is possible.
Speaker 1: Okay, all right, we have more complex understanding, perhaps than
Speaker 1: of what might be going on here with these changes.
Speaker 1: All Right, we're going to go ahead and close out
Speaker 1: this episode of stuff to blow your mind. But we'll
Speaker 1: be back with part two in this series on Thursday.
Speaker 1: And don't worry, we will get into the guano. We
Speaker 1: will get into that back guano because it is vitally
Speaker 1: important to this discussion. And also, I think we're going
Speaker 1: to discuss I guano in a way that may turn
Speaker 1: the concept on its head for you. I know when
Speaker 1: I was reading about it in the way that we're
Speaker 1: going to discuss it, it made me think about it
Speaker 1: in a new light.
Speaker 3: I can't wait.
Speaker 1: In the meantime, we'd love to hear from you if
Speaker 1: you have thoughts about particular caves that you've been to,
Speaker 1: cave environments that you're familiar with, if you have thoughts
Speaker 1: on scientists naming things after everything from the Iliad to
Speaker 1: Sonic the hedgehog. We'd also love to hear from you
Speaker 1: on that point as well. But yeah, yeah, particular cave
Speaker 1: environments that you've really enjoyed. Like I say, I always
Speaker 1: enjoy checking out caves. I believe Colossal Cave in Tucson,
Speaker 1: Arizona is one that I visited many years back, and
Speaker 1: I really want to go back there in the future
Speaker 1: because this is one of memory serves was discovered late
Speaker 1: enough that they were able to preserve the cave environment
Speaker 1: to a large degree by use of essentially like an
Speaker 1: air lock system, so that they're not just opening up
Speaker 1: this environment in a way that destabilizes what has evolved
Speaker 1: beneath the surface. But anyway, more on this sort of
Speaker 1: thing in the next episode. In the meantime, we'll remind
Speaker 1: you once more that Stuff to Blow Your Mind is
Speaker 1: primarily a science podcast Science and culture podcasts with core
Speaker 1: episodes on Tuesdays and Thursdays. Mondays we do listener mail,
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