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Speaker 1: Hey, welcome to Stuff to Blow your Mind. It is Saturday,

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Speaker 1: so once more we have a vault episode for you.

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Speaker 1: This is going to be Life in the Hapogean World,

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Speaker 1: Part one. This one was originally published three five, twenty

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Speaker 1: twenty four. This is going to be part one out

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Speaker 1: of four, so we'll be publishing the other three episodes

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Speaker 1: in this series on the Saturdays to come.

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Speaker 2: Welcome to Stuff to Blow Your Mind, a production of iHeartRadio.

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Speaker 1: Hey, welcome to Stuff to Blow your Mind. My name

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Speaker 1: is Robert.

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Speaker 3: Lamb and I am Joe McCormick. And hey here we

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Speaker 3: are together again, Rob. After you were out for a

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Speaker 3: little bit.

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Speaker 1: Oh yeah, yeah, we've recorded a few thanks here there.

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Speaker 1: So I keep forgetting that, you know, when the actual

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Speaker 1: new core episodes are that I'm around for. So yeah,

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Speaker 1: I am back. I was just in a little vacation

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Speaker 1: with my family.

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Speaker 3: Wait a minute, now, you refreshed my brain because I

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Speaker 3: forgot that we did a listener mail episode before this.

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Speaker 3: So listeners, are you are reacclimated to Rob? Now?

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Speaker 1: Yeah? I mean listeners I think always have a skewed

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Speaker 1: understanding of when we're out when we're present, because there's

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Speaker 1: you know, even if one of us is out. You

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Speaker 1: may hear us on a vault episode on the weekend.

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Speaker 1: We might have recorded through on something recorded ahead of

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Speaker 1: time on one piece of content, but not on other

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Speaker 1: pieces of content. So you know, you'll just have to

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Speaker 1: take our word for it. Sometimes we are away, sometimes

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Speaker 1: we were present.

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Speaker 3: We're like a duo of mysterious time traveling cats that

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Speaker 3: appear in your ears.

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Speaker 1: Yeah all right, Well, you know I have to say,

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Speaker 1: on this most recent journey with my family, I did

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Speaker 1: not venture into a cave. I don't think I ventured

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Speaker 1: into a cave. Let me refresh. No, no cave venturing,

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Speaker 1: no school.

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Speaker 3: I would think you'd remember. Come on, I.

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Speaker 1: Mean, sometimes you know, these trips, you see a lot

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Speaker 1: of things, and you know, and you know, cave environments

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Speaker 1: are are always fascinating, but they're not necessarily always going

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Speaker 1: to be like the top of a particular trip. It

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Speaker 1: just varies. But you know, we frequently discussed biological wonders

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Speaker 1: on the show that leads us to consider extreme environments,

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Speaker 1: and the cave environment is one such environment. I tend

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Speaker 1: to find caves endlessly fascinating, even if it's a lower

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Speaker 1: tier cave. You know, and I've been to some of

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Speaker 1: those where it's like, okay, this is this one was

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Speaker 1: opened by humans a while back. It doesn't have much

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Speaker 1: in the way of a robust ecosystem and so forth,

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Speaker 1: but it's still fascinating. There's still something about the subterranean world.

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Speaker 3: Have you ever done the cave exploring experience where you

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Speaker 3: go down into a cave and all artificial light sources

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Speaker 3: are turned off and you get to see like the

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Speaker 3: blackest black night you've ever seen. It's a kind of

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Speaker 3: darkness that you cannot imagine otherwise.

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Speaker 1: Yeah. Absolutely done this in a couple of Tennessee caves,

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Speaker 1: I think growing up. One that was like one of

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Speaker 1: these big official caves. I'm blanking on which one it

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Speaker 1: would have been, but went there was like a scout group.

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Speaker 1: And then there was another like local cave that was

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Speaker 1: just on somebody's land and got to go in there

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Speaker 1: and see the main cavern and then have the lights

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Speaker 1: go out. Sometimes they'll do the lights out with a

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Speaker 1: little ghost story or something right, just sort of drive

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Speaker 1: home the creepiness of it. But yeah, you find yourself

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Speaker 1: in just the absolute darkness.

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Speaker 3: We did this with our tour guide years ago at

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Speaker 3: Oregon Caves National monument in southwestern Oregon, which is a

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Speaker 3: very cool cave system. And it's hard to explain because

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Speaker 3: again I had not seen anything like this anywhere before,

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Speaker 3: where you just eyes are totally wide and you see

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Speaker 3: not even a pinprick of light, just nothing.

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Speaker 1: Yeah, it's it's haunting and it's and it is key

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Speaker 1: to understanding cave environments, as we'll be discussing in this episode. Now.

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Speaker 1: Not only are caves home to rather unique organisms in

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Speaker 1: certain caves, as we'll discuss more as we progress, but

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Speaker 1: they've of course always fascinated humans, and our global myths

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Speaker 1: and traditions are full of caverns that house monsters, passages

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Speaker 1: to the underworld, magical treasures, and much more. Also, as

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Speaker 1: we've discussed, these were some of the first enclosed spaces

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Speaker 1: that humans entered and were occupied to some degree in

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Speaker 1: a way, laying the groundwork for the humble and elaborate

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Speaker 1: shelters that we would construct thereafter. You know, because what

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Speaker 1: is what are some of the rooms in our houses

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Speaker 1: but caves that we have built for ourselves.

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Speaker 3: Some houses are more cave like than others.

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Speaker 1: Yeah. Yeah, so we may not think of ourselves as

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Speaker 1: cave people, but we are in many respects still people

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Speaker 1: of the cave at home, with enclosed spaces, sometimes with windows,

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Speaker 1: sometimes without places in general like this, be it constructed,

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Speaker 1: be it like a large enclosed concert hall, or an

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Speaker 1: underground facility, or a naturally occurring cave or some sort

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Speaker 1: of a tunnel. I mean, you can't help but dream

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Speaker 1: about those spaces, to find dread and fascination in those spaces.

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Speaker 1: And you know now that I mention it. On my

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Speaker 1: family vacation, I don't think we went We did not

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Speaker 1: go into a cave system, but we did go through

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Speaker 1: tunnels at times, and we were stuck in traffic in

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Speaker 1: a tunnel at one point. And so that alone gives

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Speaker 1: one enough room for pause.

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Speaker 4: It's just as good almost well, I wouldn't say it's

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Speaker 4: not as good, but it does. It summons possibilities, maybe

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Speaker 4: even the possibility of talking about the strange world of

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Speaker 4: cave biology. And that's what we're going to be looking

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Speaker 4: at in this series.

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Speaker 1: Right, that's right, talking about the cave environment, talking about

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Speaker 1: some of the organisms and life forms that live there.

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Speaker 1: And to get into this, I want to talk a

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Speaker 1: little bit about just sort of the idea of there

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Speaker 1: being a dual world something that again is quite reflected

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Speaker 1: in some of our more supernatural understandings of the surface

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Speaker 1: world and the world beneath it, the earth, you know,

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Speaker 1: the world of the living, the world of the dead,

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Speaker 1: and so forth. I was reading a twenty eleven article

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Speaker 1: in The American Scientist by Autamaro Romero, and he pointed

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Speaker 1: out that cave biologist or biospileiologists divide the world into two.

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Speaker 1: There's the epigean world, or the world upon the earth,

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Speaker 1: the world of light that we predominantly think of as

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Speaker 1: our home. And then there's this other world, this underworld,

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Speaker 1: the hypogean world beneath the soil.

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Speaker 3: I've never thought of the surface as epigean before, but

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Speaker 3: I love that because I guess with the Greek there yet,

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Speaker 3: like you say, it means upon the earth, on the earth,

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Speaker 3: so not just like exposed, but it's like like an

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Speaker 3: epiphyte plant that grows on another plant. The epigean world

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Speaker 3: of the surface world isn't like the thing that grows

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Speaker 3: on the surface of this ball of iron.

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Speaker 1: Yeah, and then everything else, the underworld, the hypogean world

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Speaker 1: beneath the soil, and the world beneath the soil. To

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Speaker 1: make no mistake here is vast. So just as the

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Speaker 1: epigean world consists of any part of the biosphere that

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Speaker 1: is even partially or periodically exposed to light, the hypogean

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Speaker 1: world consists of any underground part of the biosphere. So

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Speaker 1: this includes the living soil in your backyard, networks of

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Speaker 1: mycilium that rooting through it, as well as life between

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Speaker 1: grains of sand buried under the beach, underground waters, and indeed,

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Speaker 1: cave environments, which, to be clear, can also be part

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Speaker 1: of the epigaean world because they of course are gateways

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Speaker 1: and there are going to be transition spaces the mouth

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Speaker 1: of a cave, for example. Yeah, Now, caves, as Ramera

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Speaker 1: points out in this article, are also This is also

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Speaker 1: a very broad categorization, entailing everything from ice caves to

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Speaker 1: lava tubes, and indeed caves are merely the subterranean spaces

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Speaker 1: into which humans can venture. There are plenty of subterranean

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Speaker 1: environments and even cavernous spaces in the earth that are

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Speaker 1: just inaccessible to us because there are no openings to

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Speaker 1: the surface.

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Speaker 3: That's a really good point, and there's so much that

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Speaker 3: goes on in those those small or tiny spaces that

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Speaker 3: you can't like walk into and observe. You know, you

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Speaker 3: mentioned like the idea of the myceelium that underlies that.

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Speaker 3: You know, you find a mushroom in the forest. It's

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Speaker 3: hard to remember this sometimes, but like the mushroom you

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Speaker 3: find is just like one organ of the fungus organism

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Speaker 3: as a whole. It's the fruiting body that comes up

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Speaker 3: above the surface. But underneath there's gonna be this whole network.

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Speaker 3: That's sort of where the organism really is, is under

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Speaker 3: the soil, and you don't even see it. You don't

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Speaker 3: even think to look down there.

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Speaker 1: Yeah, there's there's an there's a vital and rich world

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Speaker 1: in there, and it's not a space that human beings

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Speaker 1: can venture into in the way that we can venture

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Speaker 1: into a cave environment, you know. I mean we can

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Speaker 1: study it, we can explore it, we can dig it up,

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Speaker 1: but it's a different sort of world. Now. Romero also

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Speaker 1: mentions the freatic environments of underground lakes and rivers, but

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Speaker 1: the word cave is generally reserved for again, those spaces

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Speaker 1: we can access ourselves where human explorers and scientists or

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Speaker 1: at least their technological minions can physically investigate the world below.

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Speaker 1: At least you can get you can get a robot

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Speaker 1: in there, you can stick a probe in, somehow invoke

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Speaker 1: your presence there.

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Speaker 3: A cave is like a space that can be spilunked,

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Speaker 3: and maybe our standards for how small a space can

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Speaker 3: be spilunked are changing.

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Speaker 1: Right when we had Lee Burger on the show, the

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Speaker 1: author of Cave of Bones, who was talking about exploring

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Speaker 1: various cave environments, a specific cave environment in fact, looking

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Speaker 1: at pre human skeletal remains. And one of the really

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Speaker 1: telling things about his experience is there was this part

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Speaker 1: of the cave that for the longest he could not access.

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Speaker 1: It was like a grueling experience, and you had to

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Speaker 1: send a like very young specialized scientists down there to

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Speaker 1: physically occupy the space. And he was able to, you know,

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Speaker 1: send them down, have them look around. He was able

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Speaker 1: to look at video footage from that space. But eventually

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Speaker 1: he could not resist. And he talks about this at length,

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Speaker 1: like he had to go down there, he lost weight

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Speaker 1: in order to fit through, narrowly fit through the passageways

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Speaker 1: that were acquired a grueling experience to actually make it there.

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Speaker 1: So there is something about like the human exploratory experience

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Speaker 1: and all of this, Like, even when you have the

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Speaker 1: technology and the organization, there's something about it. You have

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Speaker 1: to be there. You want to be there in the space.

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Speaker 3: Man. I know I'm not unique in this, but that

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Speaker 3: is one of the things that truly gives me the

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Speaker 3: creeps to like barely trying to wedge your way through

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Speaker 3: passageways inside a cave under the earth. That is just ugh.

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Speaker 1: Yeah, it gave maybe all of is here in some

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Speaker 1: of the details in his book, and I think there

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Speaker 1: was also covered in a Netflix special If Memory Is Serving,

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Speaker 1: And yeah, just the idea of like having to squeeze

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Speaker 1: through a space, getting momentarily stuck like the wrench and

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Speaker 1: a chimney, and then having to press on potentially like

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Speaker 1: you know, risk dislocating bones and so forth to do it.

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Speaker 1: It's yeah, not for me, but I respect anyone who

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Speaker 1: is capable of it totally. Now, the most common caves

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Speaker 1: are carstick or limestone. I believe we've discussed this before

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Speaker 1: talking about various geological formations. Limestone, which covers roughly fifteen

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Speaker 1: percent of the world above water, is highly soluble at

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Speaker 1: least fifty percent calcium carbonate. According to romero, so acidic

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Speaker 1: rain water easily modifies it over time. And so the

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Speaker 1: world is littered with such cave systems, some only partially

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Speaker 1: exposed to the surface world but in important ways, Others

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Speaker 1: with key openings that permit light to influence the environments

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Speaker 1: of their interior. So you know, some kind of cave systems.

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Speaker 1: Some rather famous ones even do have sunlight spilling into them,

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Speaker 1: at least in part, so you end up with this

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Speaker 1: kind of like mixed environment. But the lack of natural

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Speaker 1: light as a whole is extremely important to understanding the

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Speaker 1: individual organisms that make their homes and caves, as well

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Speaker 1: as the overall ecosystems in which they thrive.

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Speaker 3: Right because when you think about it, basically everywhere else

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Speaker 3: on Earth, I mean, there are some extreme exceptions, but

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Speaker 3: for most of the world, the food chain is built

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Speaker 3: on access to sunlight. The sunlight powers the powers the

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Speaker 3: photosynthesis of the autotrophs that are the base of the

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Speaker 3: food chain. Then things start eating them, then other things

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Speaker 3: eat those organisms, and on and on up. If you

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Speaker 3: don't have sunlight to power the autotrophs at the base,

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Speaker 3: what do you do?

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Speaker 1: I know, yeah, yeah, we'll get back to this in

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Speaker 1: just a minute here. But the humans, of course, we're

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Speaker 1: not the first adventure into the subterranean worlds. Countless other

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Speaker 1: creatures ventured in, resulting in rich, a rich, specialized world

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Speaker 1: of troglofauna, And not every creature becomes a permanent denizen

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Speaker 1: of the dark, which if you watch enough sci fi

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Speaker 1: and horror movies, you would think, oh, yeah, they're just

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Speaker 1: people and creatures fallen in all the time and evolving

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Speaker 1: in the chuds. But no, that doesn't happen all the time.

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Speaker 1: But plenty of creatures have specialized evolutionarily, often evolving defining

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Speaker 1: troglomorphic features that we often associate with these environments, namely

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Speaker 1: blindness and loss of pigmentation, with.

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Speaker 3: The chutification if you will.

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Speaker 1: Chutification, I guess yeah. You know, you see movies like

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Speaker 1: The Descent and so forth. I love all these movies,

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Speaker 1: you know, more Locks and so forth. But maybe we'll

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Speaker 1: continue to discuss the possibilities there. But briefly, I want

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Speaker 1: to just do a refresher on the various types of

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Speaker 1: troglofauna before we continue. You we have troglo bites. These

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Speaker 1: are obligate cave dwellers strictly bound to the under their

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Speaker 1: underground environments, so they are not going to live, they're

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Speaker 1: not going to thrive outside of the darkness of the caves.

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Speaker 1: Then we have troglasines. These are cave guests, creatures that

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Speaker 1: can be found underground sporadically but cannot establish permanent underground populations.

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Speaker 1: Then we have troglophiles. These are creatures that live predominantly

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Speaker 1: above ground, but can also reside in underground habitats. There

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Speaker 1: are two subsets. There's u trogleophiles, surface species that are

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Speaker 1: also able to maintain in a permanent subterranean population, and

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Speaker 1: then there are subtroglophiles, creatures that can and do live

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Speaker 1: underground at least temporarily, but are more associated with life

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Speaker 1: above ground. So again you can think about the idea

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Speaker 1: that there's not just surface creatures and underground creatures. You know,

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Speaker 1: there's a lot of back and forth, and there are

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Speaker 1: various phases between what we might think of as a

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Speaker 1: purely surface creature and a purely subterranean creature.

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Speaker 3: I see none of.

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Speaker 1: This to be confused with a troglodyte. They're a handful

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Speaker 1: of different uses is for this term. It can refer

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Speaker 1: either to a human cave dweller or and I believe

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Speaker 1: in one case of an outdated classification of early hominid.

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Speaker 1: But there are also a small genus of small birds

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Speaker 1: related to wrens that are called troglodytes. These birds are

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Speaker 1: rarely found in caves apparently, but they're so named because

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Speaker 1: they'll venture into various crevices and spaces, including caves, in

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Speaker 1: search of food.

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Speaker 3: So we have these various kinds of spilunking organisms, those

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Speaker 3: that do still live life on the surface, but have

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Speaker 3: the ability and sometimes the desire to venture into caves

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Speaker 3: or subterranean regions for very various reasons. Maybe they want

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Speaker 3: to shelter there for a certain period, maybe they want

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Speaker 3: to go in there to retrieve some kind of resource,

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Speaker 3: who knows. But then there's the other kind, the ones

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Speaker 3: that are fully adapted to life in the caves and

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Speaker 3: it has shaped their evolution, has shaped their morphology. Now

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Speaker 3: their bodies are made for the caves. One of the

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Speaker 3: examples that people listening are probably thinking of are sightless fish.

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Speaker 3: Fish that live in cave based in underground waterways and

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Speaker 3: have evolved to completely lose their vision or their eyes.

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Speaker 3: And this has long been a really captivating image within

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Speaker 3: evolution that the idea. You know, people usually think of

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Speaker 3: evolution as a constructive process that sort of powers up

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Speaker 3: an organism. It gives it a new ability or a

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Speaker 3: new adaptation that better suits it to an environment or

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Speaker 3: an environmental niche that it's currently occupying, and so it

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Speaker 3: gets upgraded in some way. These are these are ways

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Speaker 3: that we sometimes discourage people from thinking about evolution, by

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Speaker 3: the way, but it is still in the popular consciousness

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Speaker 3: that that's how it works. This is evolution by what

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Speaker 3: might be thought of as regression, like losing a trait

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Speaker 3: that you previously had. So that raises a lot of

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Speaker 3: questions about how evolution works and and why something like

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Speaker 3: that would happen.

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Speaker 1: You know, it's it's fascinating to think about this about

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Speaker 1: our our, our our often human focused bias, and considering

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Speaker 1: evolution along these lines. Like we think of that classic

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Speaker 1: illustration of the ascent of man, you know, the various

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Speaker 1: uh Hamonid species evolving towards man, and we we it's

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Speaker 1: easy to look at him and like think, wow, look,

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Speaker 1: with each step he just gets hotter. With each step,

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Speaker 1: he just looks more like us. He becomes more perfect,

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Speaker 1: like clearly modern Homo sapiens are, but even in that

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Speaker 1: we're seeing the loss of various features. We're seeing like

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Speaker 1: the loss of body hair and so forth.

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Speaker 3: Yeah, totally, and as big asterisk, if you see an

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Speaker 3: old illustration like that, there's probably a lot of that's

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Speaker 3: inaccurate about it. But some things that broadly would be

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Speaker 3: true is that our ancestors do appear to have lost

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Speaker 3: adaptations that made them really good tree climbers, and those adaptations,

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Speaker 3: those are adaptations that were very useful for our ancestors,

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Speaker 3: and we sort of lost them in favor of other things.

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Speaker 1: Yeah. And it is also interesting again to think about

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Speaker 1: the world of the dark, the world of the caves, because,

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Speaker 1: like we said, we can have this experience of turning

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Speaker 1: out the lights in the cavern and experiencing the true darkness.

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Speaker 1: But for the most part, ever since human beings were

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Speaker 1: able to capture fire, we have been able to bring

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Speaker 1: light into these spaces, and today when we explore caves,

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Speaker 1: at least on our own terms, we have that light

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Speaker 1: that we bring with us, and we therefore we don't

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Speaker 1: have to we change the environment by bringing light into it,

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Speaker 1: the cavern changing us over evolutionary time of course, is

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Speaker 1: not on the table.

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Speaker 3: That's all right, But without the ability to modify the

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Speaker 3: features of the environment like that other animals have had

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Speaker 3: to adapt evolutionarily.

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Speaker 1: Yeah, and in all this we have to again recognize

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Speaker 1: just how vital light is for organisms for the evolution

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Speaker 1: of life on our planet. Both sunlight and moonlight are

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Speaker 1: in play here. As pointed out by Lauren Summer Rooney

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Speaker 1: in The Kingdom of the Blind, published in a twenty

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Speaker 1: eighteen edition of Integrated and Comparative Biology, light is a

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Speaker 1: fundamental biological cue for almost every animal on Earth. So

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Speaker 1: it's not just about oh can I see the inside

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Speaker 1: of the cave or not? You know, it plays in

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Speaker 1: a navigation foraging, predator avoidance, mate selection, and just like

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Speaker 1: general daily rhythms. So to abandon the world of light

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Speaker 1: is no small thing, right, and yet we do see

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Speaker 1: plenty of organisms that have done just that over time,

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Speaker 1: not only cave organisms but certain creatures of the deep ocean.

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Speaker 1: Though we have to remember that site is still important

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Speaker 1: at varying levels of the water column and in the

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Speaker 1: presence of phosphorescent glows, so there is a fair amount

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Speaker 1: of complexity there. The soil and even interiors of host

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Speaker 1: organisms for various parasites are also dark environments that species

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Speaker 1: have adapted to now. As Romero points out, Charles Darwin

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Speaker 1: himself was somewhat stumped by the loss of sight and cavefishes,

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Speaker 1: and apparently ultimately landed on more of a Lamarchian idea

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Speaker 1: that they lost their eyes by simply not using them.

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Speaker 3: Oh, that's kind of interesting. So Lamarckism or Lamarchianism named

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Speaker 3: after a figure named I believe you, Jean Baptiste Lamarck.

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Speaker 3: It was the sort of alternative theory of inheritance to

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Speaker 3: what would eventually become Mendalian genetics, which in some ways

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Speaker 3: has been partially superseded now. But instead of the kind

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Speaker 3: of Mendalian genetic inheritance, Lamarck would say that, like the

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Speaker 3: way that an animal uses its body shapes the way

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Speaker 3: its offspring the way their bodies are formed. So like

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Speaker 3: if you are reaching up a lot or something, you

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Speaker 3: might grow your children might have longer arms, or like

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Speaker 3: that a giraffe maybe is reaching its neck up to

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Speaker 3: reach higher leaves, and that means its children will be

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Speaker 3: born with longer necks and so forth. For the most part,

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Speaker 3: evolution doesn't actually work that way, there are some kind

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Speaker 3: of things of gene expression and regulatory functions epigenetics that

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Speaker 3: some people have argued in minor ways can kind of

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Speaker 3: vindicate Lamarckian thinking, but for the most part that's not

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Speaker 3: really how inheritance works.

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Speaker 1: Right right, Yeah, I've been to evolutionary talks, I believe

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Speaker 1: the World Science Festival for some biologists have been like, yeah, yeah,

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Speaker 1: we're kind of we to start talking about epigenetics. Sometimes

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Speaker 1: we do get a little Lamarckian way we're talking, so

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Speaker 1: it is it is kind of fascinating.

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Speaker 3: But the Lamarckian idea would be okay, so fish go

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Speaker 3: down in a cave and then they don't use their

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Speaker 3: eyes because they're living in the dark. Therefore their children

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Speaker 3: or their offspring are born without them or born with

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Speaker 3: eyes that regress. We can talk about that difference in

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Speaker 3: a minute, and in a way you could say that

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Speaker 3: that's loosely kind of right, but but it's somewhat different.

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Speaker 3: I think I would say that the important thing is

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Speaker 3: not that the fish don't use their eyes, it's that

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Speaker 3: they don't need them, so that the eye no longer

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Speaker 3: confers a survival or reproductive advantage.

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Speaker 1: I think the one of the infectious things about it,

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Speaker 1: at least at least for non scientists, is that it

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Speaker 1: can feel right in certain ways. Right. It can sort

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Speaker 1: of match up with at least the individual human experience.

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Speaker 1: So we might not think, like, man, I bet I

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Speaker 1: better go to the gym, and you need a pump

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Speaker 1: iron so that my offspring will will have strong arms.

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Speaker 1: But we might think, uh, oh, well, I've got to

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Speaker 1: keep pumping iron otherwise my arms will get smaller. You know,

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Speaker 1: I've got to do X so that why doesn't happen?

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Speaker 1: And uh, you know, I think we do see this

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Speaker 1: infectious idea in some of our fictions of subterranean monsters,

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Speaker 1: including The Descent of the Hobbit Snekeel and the Lord

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Speaker 1: of the Rings, who becomes a trogloditic gollum in the

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Speaker 1: course of a single, though of course magically sustained lifetime.

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Speaker 1: He doesn't really become blind or anything, but generally he's

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Speaker 1: depicted as you know, he's changed a lot. He's lost

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Speaker 1: his hair, his pimitation has changed, his eyes have gotten larger,

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Speaker 1: I believe.

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Speaker 3: Yeah, though, I think the morphotypical changes of Gollum could

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Speaker 3: be largely due to the corruption of the one ring.

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Speaker 1: That's the thing. The one ring changes everything you've got.

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Speaker 1: You've got a huge magical factor to consider in that scenario.

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Speaker 1: But sort of just the idea of it is like, Yeah,

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Speaker 1: people go into caves, they get weird, they turn into monsters,

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Speaker 1: or if they're not a monster, you know weight three generations,

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Speaker 1: then just pure monsters.

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Speaker 3: Caves will do that.

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Speaker 1: Now, Summer Rooney points out that we're still working out

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Speaker 1: all the details, but we know much more than Darwin

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Speaker 1: did in his time. Of course, the science has come

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Speaker 1: quite a way since then in our understanding of how

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Speaker 1: creatures evolved and what sort of changes are taking place

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Speaker 1: over revolutionary time. The author rights quote. Eye loss appears

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Speaker 1: to be driven at least in part by direct selective pressure,

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Speaker 1: but both pliotrophy and genetic drift are also key influencers.

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Speaker 1: Despite substantial recent progress thanks to a combination of developmental

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Speaker 1: and molecular techniques, it is not yet clear how these

433
00:24:36,720 --> 00:24:41,200
Speaker 1: drivers interact, or crucially, whether their relationships are similar across

434
00:24:41,280 --> 00:24:42,919
Speaker 1: taxa and habitat types.

435
00:24:44,040 --> 00:24:46,719
Speaker 3: Yeah, so this was really interesting and I ended up

436
00:24:47,119 --> 00:24:50,240
Speaker 3: going kind of deep on what we do know about

437
00:24:50,520 --> 00:24:56,200
Speaker 3: eye loss and a related issue of pigmentation loss. In cavefish.

438
00:24:56,240 --> 00:24:58,879
Speaker 3: But I wanted to break down some of the terms

439
00:24:58,920 --> 00:25:01,960
Speaker 3: that this author uses in that paragraph you just read.

440
00:25:03,119 --> 00:25:07,000
Speaker 3: So selective pressure, of course, would mean an advantage in

441
00:25:07,080 --> 00:25:11,200
Speaker 3: terms of survival or reproduction, a direct advantage. That's the

442
00:25:11,280 --> 00:25:13,560
Speaker 3: kind of evolution we think about most often. But there

443
00:25:13,560 --> 00:25:17,800
Speaker 3: are two other factors that could be influencing the loss

444
00:25:17,840 --> 00:25:21,159
Speaker 3: of eyes or the loss of pigmentation in fish that

445
00:25:21,200 --> 00:25:26,320
Speaker 3: the author mentions, and those are plyotrophy and genetic drift. Plyotropy,

446
00:25:26,520 --> 00:25:32,719
Speaker 3: to sort of oversimplify, means when one gene determines multiple

447
00:25:32,880 --> 00:25:36,120
Speaker 3: outcomes in the phenotype, and the phenotype is like the

448
00:25:36,160 --> 00:25:39,000
Speaker 3: body or the behavior of the organism. It's what the

449
00:25:39,160 --> 00:25:43,360
Speaker 3: genes produce in the animal. So, for example, imagine there

450
00:25:43,440 --> 00:25:46,520
Speaker 3: is a mutation at one locust, and that one mutation

451
00:25:46,720 --> 00:25:52,440
Speaker 3: happens to both give you smaller eyes but also longer arms.

452
00:25:53,320 --> 00:25:56,119
Speaker 3: Or maybe there's a mutation that happened to give you

453
00:25:56,320 --> 00:26:01,600
Speaker 3: both higher rates of cancer and higher average fertility. And

454
00:26:01,760 --> 00:26:05,040
Speaker 3: pliotropies like these can they're very interesting because they can

455
00:26:05,080 --> 00:26:08,960
Speaker 3: sometimes explain the evolution of traits that would seem to

456
00:26:09,000 --> 00:26:14,359
Speaker 3: be disadvantageous because the seemingly bad trait is actually part

457
00:26:14,359 --> 00:26:18,080
Speaker 3: of a hidden package deal, a genetic package deal with

458
00:26:18,200 --> 00:26:22,639
Speaker 3: an even more advantageous trait balancing it out, and you

459
00:26:22,640 --> 00:26:26,399
Speaker 3: can get either both or neither, but not one by itself.

460
00:26:26,960 --> 00:26:30,320
Speaker 3: So in the case of cavefish, it's possible there is

461
00:26:30,359 --> 00:26:34,240
Speaker 3: a single mutation that both causes the loss of eyes

462
00:26:34,640 --> 00:26:38,280
Speaker 3: but also does something else that helps the fish survive

463
00:26:38,359 --> 00:26:41,960
Speaker 3: and reproduce. And since there's little to no penalty attending

464
00:26:42,080 --> 00:26:44,560
Speaker 3: the loss of vision in the pitch black cave environment,

465
00:26:44,920 --> 00:26:48,359
Speaker 3: the helpful half of that pliotropy wins out and the

466
00:26:48,400 --> 00:26:50,680
Speaker 3: two for one version of the gene is selected for.

467
00:26:51,600 --> 00:26:54,800
Speaker 3: And then the final factor mentioned here is genetic drift.

468
00:26:54,880 --> 00:26:58,200
Speaker 3: Genetic drift is change in the frequency of gene variants

469
00:26:58,200 --> 00:27:02,200
Speaker 3: within a population due to random chance. So genes becoming

470
00:27:02,240 --> 00:27:06,080
Speaker 3: more or less prevalent within a group of organisms, not

471
00:27:06,400 --> 00:27:10,840
Speaker 3: for selective reasons, not because they help or hurt the organism,

472
00:27:11,040 --> 00:27:13,720
Speaker 3: but just randomly, you know. And this happens all the time.

473
00:27:14,200 --> 00:27:18,000
Speaker 3: Gene variants just become more common less common within a population,

474
00:27:18,640 --> 00:27:22,479
Speaker 3: and it happens due to random factors, though sometimes if

475
00:27:22,480 --> 00:27:25,560
Speaker 3: a population is small enough. And interesting thing is that

476
00:27:25,960 --> 00:27:30,720
Speaker 3: traits resulting from random genetic drift can become what's called fixed,

477
00:27:31,200 --> 00:27:34,800
Speaker 3: meaning that you kind of hit a genetic tipping point

478
00:27:35,280 --> 00:27:38,080
Speaker 3: and a trait that was randomly fluctuating up and down

479
00:27:38,080 --> 00:27:43,080
Speaker 3: in the population, it becomes prevalent enough that suddenly it's fixed,

480
00:27:43,119 --> 00:27:46,080
Speaker 3: and then all the individuals within the population have the

481
00:27:46,119 --> 00:27:48,760
Speaker 3: gene for that trait. Going forward, Yeah.

482
00:27:48,640 --> 00:27:51,760
Speaker 1: Now, now going back to what you mentioned about about

483
00:27:51,760 --> 00:27:55,000
Speaker 1: the idea of there possibly being like an advantage and

484
00:27:55,119 --> 00:27:59,600
Speaker 1: a disadvantage tied up in one change. But the thing is,

485
00:27:59,640 --> 00:28:03,200
Speaker 1: you find yourself, if you're this fish undergoing this change

486
00:28:03,280 --> 00:28:07,040
Speaker 1: or some other organism, you find yourself in a lightless environment,

487
00:28:07,520 --> 00:28:11,359
Speaker 1: and so in this you dip over into the neutral

488
00:28:11,440 --> 00:28:16,720
Speaker 1: mutation hypothesis, This idea that while naturally occurring mutations for

489
00:28:16,840 --> 00:28:19,760
Speaker 1: in this case blindness would otherwise spell doom for a

490
00:28:19,800 --> 00:28:23,119
Speaker 1: fish in a typical environment in a lighted environment, it

491
00:28:23,160 --> 00:28:26,520
Speaker 1: doesn't matter in the darkness, and therefore these mutations can

492
00:28:26,640 --> 00:28:30,600
Speaker 1: flourish along with whatever other changes they might be bringing.

493
00:28:31,680 --> 00:28:34,000
Speaker 3: That's right. Then they can flourish for multiple reasons. They

494
00:28:34,040 --> 00:28:37,320
Speaker 3: could flourish because they're part of a plotropy that has

495
00:28:37,320 --> 00:28:39,480
Speaker 3: an advantage on the other half, or they can just

496
00:28:39,520 --> 00:28:43,720
Speaker 3: flourish randomly through genetic drift because there's no penalty to

497
00:28:43,800 --> 00:28:45,880
Speaker 3: the loss of sight in the darkness.

498
00:28:46,800 --> 00:28:51,880
Speaker 1: Yeah, this I can't help be reminded of various gaming

499
00:28:52,000 --> 00:28:55,200
Speaker 1: rules and gaming systems and all of this. Like, it's like,

500
00:28:55,280 --> 00:28:57,840
Speaker 1: imagine that you're playing Dungeons and Dragons and let's say

501
00:28:57,880 --> 00:29:00,200
Speaker 1: you're venturing into the under dark. You're venturing in a

502
00:29:00,240 --> 00:29:04,200
Speaker 1: lightless environment, and you have a weapon that gives you,

503
00:29:05,000 --> 00:29:08,840
Speaker 1: say a plus two on attack. But if you're in

504
00:29:08,840 --> 00:29:12,800
Speaker 1: the sunlight, it has your hit points or something like

505
00:29:12,840 --> 00:29:15,360
Speaker 1: something that would make this all right. It has advantages

506
00:29:15,360 --> 00:29:19,120
Speaker 1: to it, but the disadvantage is far outweigh it in

507
00:29:19,160 --> 00:29:21,720
Speaker 1: a different environment, but you're not in that environment. Now,

508
00:29:21,760 --> 00:29:24,720
Speaker 1: you're in an environment where the disadvantage does not matter.

509
00:29:25,160 --> 00:29:28,000
Speaker 3: Right. Yes, that's a good analogy, and it's also a

510
00:29:28,040 --> 00:29:30,560
Speaker 3: good reason to remember to check your build when your

511
00:29:30,640 --> 00:29:37,200
Speaker 3: environment changes. But yeah, so there is, as we're saying,

512
00:29:37,240 --> 00:29:40,520
Speaker 3: some possibility for all of these options and explaining the

513
00:29:40,560 --> 00:29:45,320
Speaker 3: evolution of kvefish blindness. There could be direct selective pressure,

514
00:29:45,520 --> 00:29:49,400
Speaker 3: there could be indirect selective pressure through pliotropy or the

515
00:29:49,440 --> 00:29:52,800
Speaker 3: package deal, and there could be random genetic drift. However,

516
00:29:53,960 --> 00:29:57,160
Speaker 3: it seems that there is some pretty good evidence for

517
00:29:57,200 --> 00:30:00,800
Speaker 3: the presence of a direct selective pressure for fish to

518
00:30:00,880 --> 00:30:03,440
Speaker 3: lose their eyes when they live in a lightless environment,

519
00:30:03,840 --> 00:30:06,560
Speaker 3: and there might be some evidence for pliotropy as well.

520
00:30:06,720 --> 00:30:08,640
Speaker 3: So to get a more concrete idea of what we're

521
00:30:08,640 --> 00:30:11,440
Speaker 3: talking about, I wanted to focus on a particular species

522
00:30:11,480 --> 00:30:14,800
Speaker 3: of fish that has been studied a lot, and that

523
00:30:14,920 --> 00:30:19,680
Speaker 3: species is called Astianax mexicanus, also known as the blind

524
00:30:19,960 --> 00:30:23,920
Speaker 3: Mexican cave fish, also known as the blind cave tetra.

525
00:30:25,040 --> 00:30:30,000
Speaker 3: These are small minnow like fish with silver scales. I

526
00:30:30,040 --> 00:30:32,840
Speaker 3: saw different size estimates for them. Some said they grow

527
00:30:32,840 --> 00:30:36,520
Speaker 3: to a maximum length of about nine centimeters. Other sources

528
00:30:36,600 --> 00:30:40,280
Speaker 3: said about twelve centimeters, but they're relatively small in any case.

529
00:30:41,640 --> 00:30:45,960
Speaker 3: One thing that makes these Astianax fish very interesting is

530
00:30:46,000 --> 00:30:50,720
Speaker 3: that there exist both surface or epigean and cave or

531
00:30:50,800 --> 00:30:54,800
Speaker 3: hypogean variants of the same fish species, and they have

532
00:30:54,880 --> 00:30:58,720
Speaker 3: different body features. And scientists can learn a lot by

533
00:30:58,760 --> 00:31:03,959
Speaker 3: comparing these extremely closely related populations of animals to one another,

534
00:31:04,320 --> 00:31:07,960
Speaker 3: cross checking genomic information back and forth, and seeing what

535
00:31:08,000 --> 00:31:12,200
Speaker 3: that correlates to in terms of their phenotypic traits. So

536
00:31:12,400 --> 00:31:16,360
Speaker 3: the cave variant of Astianax lives in this big network

537
00:31:16,480 --> 00:31:21,680
Speaker 3: of underground waterways in the mountainous areas of northeastern Mexico.

538
00:31:22,360 --> 00:31:25,000
Speaker 3: And they've been in these caves since. One source I

539
00:31:25,040 --> 00:31:27,920
Speaker 3: was reading said they colonized them probably around the end

540
00:31:28,080 --> 00:31:31,160
Speaker 3: of the Pleistocene epic, so you know, roughly twelve thousand

541
00:31:31,200 --> 00:31:33,520
Speaker 3: years ago or so. There are photos you can find

542
00:31:33,560 --> 00:31:36,520
Speaker 3: online which I'd recommend looking up, which not only show

543
00:31:36,600 --> 00:31:41,120
Speaker 3: the cave variant of ASTIANAX, but they depict the cave

544
00:31:41,240 --> 00:31:45,240
Speaker 3: variant and the surface variant side by side to highlight

545
00:31:45,280 --> 00:31:48,480
Speaker 3: the differences in their bodies. So the cave version is

546
00:31:48,600 --> 00:31:53,080
Speaker 3: much more pale and translucent. And indeed, in the places

547
00:31:53,120 --> 00:31:56,600
Speaker 3: where the surface variant has a big old bulging fish

548
00:31:56,640 --> 00:31:59,640
Speaker 3: eye on either side of its skull, the cave variant

549
00:32:00,120 --> 00:32:05,120
Speaker 3: has only a strange, fatty looking lump underneath its scales,

550
00:32:05,480 --> 00:32:07,400
Speaker 3: just in front of the red flap of the gill.

551
00:32:07,920 --> 00:32:11,480
Speaker 1: Yeah, these are haunting images to look at. Again, we

552
00:32:11,520 --> 00:32:14,440
Speaker 1: can't help but think of like various sneakels and so

553
00:32:14,520 --> 00:32:16,200
Speaker 1: forth when looking at it.

554
00:32:16,440 --> 00:32:18,520
Speaker 3: Yeah, exactly, And I bet these fish are good at

555
00:32:18,600 --> 00:32:21,480
Speaker 3: riddle games. Now, one thing that I was reading this

556
00:32:21,560 --> 00:32:26,080
Speaker 3: kind of interesting about these The eyeless variant of the

557
00:32:26,520 --> 00:32:33,920
Speaker 3: Astianax fish is that they undergo what's called eye regression.

558
00:32:34,200 --> 00:32:36,680
Speaker 3: So I don't know if this is true of all populations,

559
00:32:36,720 --> 00:32:39,720
Speaker 3: because they are like different cave populations of this fish

560
00:32:39,760 --> 00:32:42,760
Speaker 3: that have been studied, and they have some differences between them.

561
00:32:43,360 --> 00:32:46,120
Speaker 3: But I was reading, at least in some populations, what

562
00:32:46,200 --> 00:32:50,520
Speaker 3: happens is not that these fish never have eyes, but

563
00:32:50,560 --> 00:32:54,080
Speaker 3: they begin to grow eyes during embryonic development, and then

564
00:32:54,120 --> 00:32:58,280
Speaker 3: as they developed the they acquire eyes and then lose

565
00:32:58,360 --> 00:33:02,680
Speaker 3: the eyes in development, and the eye sockets are paved

566
00:33:02,720 --> 00:33:06,080
Speaker 3: over by skin and scales, and there remain these little

567
00:33:06,120 --> 00:33:08,600
Speaker 3: fatty lumps where the sockets used to be, and the

568
00:33:08,600 --> 00:33:11,680
Speaker 3: bone kind of collapses around it. So I thought this

569
00:33:11,760 --> 00:33:13,560
Speaker 3: was kind of interesting. It's not just that they never

570
00:33:13,680 --> 00:33:16,600
Speaker 3: have eyes. They get eyes and then they lose them,

571
00:33:16,680 --> 00:33:19,600
Speaker 3: all in the process of a single animal growing up.

572
00:33:20,040 --> 00:33:23,040
Speaker 1: Fascinating, you know. I also have to throw in, okay,

573
00:33:23,120 --> 00:33:28,520
Speaker 1: Astianax part of the scientific name for the creature. This

574
00:33:28,680 --> 00:33:33,160
Speaker 1: is the son of Hector in the Iliad, and I'm

575
00:33:33,240 --> 00:33:37,320
Speaker 1: guessing here I couldn't find anything just definitive offhand, but

576
00:33:37,400 --> 00:33:41,320
Speaker 1: I'm assuming the naming here is because Astianax, the child

577
00:33:41,320 --> 00:33:44,640
Speaker 1: of Hector, is hidden in the tombs. That is the

578
00:33:44,640 --> 00:33:47,400
Speaker 1: way that they try to ensure his survival. And so

579
00:33:48,160 --> 00:33:50,600
Speaker 1: you know, we see some version of that here, a

580
00:33:50,600 --> 00:33:55,320
Speaker 1: survival in the underworld of the caves as opposed to

581
00:33:55,320 --> 00:33:55,720
Speaker 1: the tomb.

582
00:33:56,520 --> 00:34:08,920
Speaker 3: I did not make that connection. That is interesting. So

583
00:34:09,600 --> 00:34:12,480
Speaker 3: I mentioned that there was some evidence that actual selection

584
00:34:12,600 --> 00:34:16,600
Speaker 3: pressure a direct selection pressure, drove the evolution of eyelessness

585
00:34:16,600 --> 00:34:20,959
Speaker 3: in these fish, as well as some possible evidence for pliotropy.

586
00:34:21,640 --> 00:34:24,080
Speaker 3: Let's look at a paper to learn more. So the

587
00:34:24,120 --> 00:34:27,640
Speaker 3: paper I was reading is called Cavefish and the Basis

588
00:34:27,680 --> 00:34:32,880
Speaker 3: for Eye Loss by Jaya Krishnan and Nicholas Rohner, published

589
00:34:32,920 --> 00:34:37,160
Speaker 3: in Philosophical Transactions of the Royal Society b Biological Sciences

590
00:34:37,200 --> 00:34:42,359
Speaker 3: twenty seventeen, and in the section of their paper discussing

591
00:34:42,400 --> 00:34:45,960
Speaker 3: the reasons for eye loss, the authors note that it

592
00:34:46,040 --> 00:34:49,520
Speaker 3: is not unique to the example of these blind Mexican

593
00:34:49,560 --> 00:34:52,960
Speaker 3: cavefish for an animal to evolve by losing a trait

594
00:34:53,080 --> 00:34:56,680
Speaker 3: or characteristic that was once positively selected for in that

595
00:34:56,760 --> 00:35:02,160
Speaker 3: animal's ancestors. Examples include the law of tails in some primates,

596
00:35:02,200 --> 00:35:05,560
Speaker 3: including us, the loss of teeth in birds and the

597
00:35:05,600 --> 00:35:09,040
Speaker 3: loss of legs in whales. All of these are examples

598
00:35:09,400 --> 00:35:13,560
Speaker 3: where an animal lineage acquired an adaptation that was useful

599
00:35:13,680 --> 00:35:17,400
Speaker 3: long ago, and then some branch of that lineage entered

600
00:35:17,920 --> 00:35:20,960
Speaker 3: a new ecological niche in which that trait was no

601
00:35:21,040 --> 00:35:24,680
Speaker 3: longer useful or was actively harmful, and evolved once again

602
00:35:24,800 --> 00:35:28,200
Speaker 3: to lose the trait that its ancestors' bodies had constructed

603
00:35:28,239 --> 00:35:32,560
Speaker 3: so long ago. And the example of cavefish that lost

604
00:35:32,600 --> 00:35:36,480
Speaker 3: their eyes was long simply assumed to be a result

605
00:35:36,520 --> 00:35:40,520
Speaker 3: of genetic drift. Eyelessness appears in the gene pool, and

606
00:35:40,560 --> 00:35:44,120
Speaker 3: then with no selection pressure favoring eyes to keep the

607
00:35:44,160 --> 00:35:48,480
Speaker 3: eyelessness suppressed, it would just randomly fluctuate in frequency in

608
00:35:48,520 --> 00:35:52,400
Speaker 3: the gene pool until at some point it became fixed. However,

609
00:35:52,880 --> 00:35:55,640
Speaker 3: the authors say that in roughly the last decade before

610
00:35:55,640 --> 00:35:58,279
Speaker 3: this paper, and this was again twenty seventeen, there had

611
00:35:58,280 --> 00:36:01,960
Speaker 3: been more attention to the possibility of a positive selection

612
00:36:02,120 --> 00:36:05,400
Speaker 3: pressure favoring the loss of eyes. There's a reason to

613
00:36:05,480 --> 00:36:10,640
Speaker 3: lose the eyes, either directly or through pliotropy, so let's

614
00:36:10,719 --> 00:36:15,600
Speaker 3: talk direct selection first. The main explanation offered for direct

615
00:36:15,640 --> 00:36:20,560
Speaker 3: selection against eyes is energy conservation also sometimes expressed as

616
00:36:20,680 --> 00:36:26,200
Speaker 3: metabolic cost. It costs energy the energy that animals get

617
00:36:26,280 --> 00:36:31,000
Speaker 3: from food to have functioning organs, and some types of

618
00:36:31,120 --> 00:36:34,799
Speaker 3: organs are more energy hungry than others. In fact, the

619
00:36:34,800 --> 00:36:38,879
Speaker 3: authors demonstrate that neural tissue, which includes brain cells and

620
00:36:38,960 --> 00:36:41,879
Speaker 3: also eyes and nerves, that type of tissue is one

621
00:36:41,880 --> 00:36:45,040
Speaker 3: of the most expensive types that an animal can grow

622
00:36:45,080 --> 00:36:48,759
Speaker 3: and maintain, So any animal's evolution is guided by a

623
00:36:48,840 --> 00:36:53,759
Speaker 3: balancing of interests, the benefits provided by sensory awareness and

624
00:36:54,040 --> 00:36:57,719
Speaker 3: the high metabolic cost of having this neural tissue of

625
00:36:57,760 --> 00:37:01,560
Speaker 3: having these systems. This is true in any animal in

626
00:37:01,600 --> 00:37:05,280
Speaker 3: any environment, but the balance is especially crucial in harsh

627
00:37:05,520 --> 00:37:10,480
Speaker 3: environments like caves, where food energy is more scarce than

628
00:37:10,520 --> 00:37:13,160
Speaker 3: on the surface. It's harder to come by food energy

629
00:37:13,200 --> 00:37:15,200
Speaker 3: in a cave than it is in the surface waters

630
00:37:15,239 --> 00:37:19,640
Speaker 3: where the surface variant of the Mexican cavefish lives. And

631
00:37:19,719 --> 00:37:24,000
Speaker 3: in favor of this explanation the energy cost explanation, the

632
00:37:24,040 --> 00:37:27,480
Speaker 3: author's cite of paper from twenty fifteen by Moran, Softly

633
00:37:27,520 --> 00:37:31,120
Speaker 3: and Warrant published in Science Advances called the Energetic Cost

634
00:37:31,160 --> 00:37:36,520
Speaker 3: of Vision and Evolution of Eyeless Mexican cavefish. Summarizing the

635
00:37:36,560 --> 00:37:40,040
Speaker 3: findings of Moran at all Krishna and Rohner Wright quote.

636
00:37:40,360 --> 00:37:45,280
Speaker 3: This study calculated significant metabolic costs for the optic tectum,

637
00:37:45,520 --> 00:37:48,280
Speaker 3: and the tectum is the part of the fish's brain

638
00:37:48,840 --> 00:37:52,000
Speaker 3: that is used to process visual information going on with

639
00:37:52,040 --> 00:37:55,640
Speaker 3: the quote and the eyes adding up to fifteen percent

640
00:37:55,840 --> 00:37:59,799
Speaker 3: of the resting metabolism needs in juvenile fish. Such a

641
00:38:00,120 --> 00:38:02,920
Speaker 3: high cost of vision, almost reaching the cost of the

642
00:38:03,000 --> 00:38:06,759
Speaker 3: human brain at twenty to twenty five percent, makes an

643
00:38:06,800 --> 00:38:10,880
Speaker 3: adaptive loss of eyes owing to energy constraints highly probable.

644
00:38:12,120 --> 00:38:15,319
Speaker 3: So usually there's a high energy cost. You need to

645
00:38:15,320 --> 00:38:19,040
Speaker 3: eat a lot of food to grow and sustain the

646
00:38:19,160 --> 00:38:23,880
Speaker 3: sensory organs and visual processing in the brain tissue. But

647
00:38:24,080 --> 00:38:27,600
Speaker 3: on the surface, evolution is usually willing to pay that

648
00:38:27,719 --> 00:38:31,600
Speaker 3: cost because it's really beneficial to get visual information about

649
00:38:31,640 --> 00:38:34,920
Speaker 3: your surroundings that really helps you survive and reproduce. If

650
00:38:34,960 --> 00:38:39,120
Speaker 3: getting visual information about your surroundings becomes impossible because you

651
00:38:39,160 --> 00:38:42,120
Speaker 3: live in total darkness, it's time to make budget cuts.

652
00:38:42,880 --> 00:38:46,480
Speaker 3: Another possible direct selection factor. I haven't come across direct

653
00:38:46,600 --> 00:38:49,160
Speaker 3: evidence for this, but it's just mentioned as a possibility

654
00:38:49,200 --> 00:38:52,800
Speaker 3: by several sources and that is that eyes are also

655
00:38:52,960 --> 00:38:56,319
Speaker 3: a liability in that they are prone to injury and

656
00:38:56,400 --> 00:38:59,560
Speaker 3: an entry way for infection. So it's kind of like

657
00:38:59,680 --> 00:39:03,359
Speaker 3: why you put a windshield on your armored vehicle if

658
00:39:03,360 --> 00:39:06,560
Speaker 3: you're driving in pitch black with no headlights, it would

659
00:39:06,600 --> 00:39:11,279
Speaker 3: just be a functionless weak point in the armor of

660
00:39:11,320 --> 00:39:14,840
Speaker 3: the vehicle that provides no benefit. And it's possible that

661
00:39:14,920 --> 00:39:17,720
Speaker 3: eyes are like this also, once there's nothing to see,

662
00:39:18,360 --> 00:39:20,839
Speaker 3: all they would be is a soft spot to let

663
00:39:21,000 --> 00:39:22,920
Speaker 3: germs and sharp objects in.

664
00:39:23,760 --> 00:39:27,120
Speaker 1: Yeah. Kind of like with sci fi visions of spaceships, right,

665
00:39:27,200 --> 00:39:34,600
Speaker 1: like why have an actual observation lounge or observation bubble

666
00:39:35,640 --> 00:39:39,359
Speaker 1: or so forth, Why have actual glass there or any

667
00:39:39,440 --> 00:39:42,719
Speaker 1: kind of like transparent wall when you can if you

668
00:39:42,800 --> 00:39:48,160
Speaker 1: have like ubiquitous abilities to have video footage and screens

669
00:39:48,239 --> 00:39:52,080
Speaker 1: around you. Basically the Star Trek principle exactly.

670
00:39:52,120 --> 00:39:55,279
Speaker 3: If it's not actually providing you a benefit, then it's

671
00:39:55,400 --> 00:39:56,319
Speaker 3: just a liability.

672
00:39:56,600 --> 00:39:56,920
Speaker 1: Yeah.

673
00:39:57,120 --> 00:40:00,160
Speaker 3: Also, the authors of this paper mention some evidence for

674
00:40:00,400 --> 00:40:05,000
Speaker 3: indirect selection or pliotropy. Specifically, they bring up a signaling

675
00:40:05,080 --> 00:40:10,200
Speaker 3: pathway identified in the scientific literature as SHH. And do

676
00:40:10,239 --> 00:40:14,960
Speaker 3: you want to guess what SHH stands for? Now tell

677
00:40:15,000 --> 00:40:19,239
Speaker 3: me what stands for sonic hedgehog. That's really what they say,

678
00:40:19,280 --> 00:40:22,640
Speaker 3: and that's what it is really, Yes, scientific papers, this

679
00:40:22,680 --> 00:40:25,719
Speaker 3: is the sonic hedgehog signaling pathway. There's also just an

680
00:40:25,920 --> 00:40:28,840
Speaker 3: HH or hedgehog pathway, so I don't know attacking on

681
00:40:29,160 --> 00:40:31,480
Speaker 3: maybe that was discovered first and then they tacked on

682
00:40:31,560 --> 00:40:34,120
Speaker 3: sonic to be funny for this other pathway. I don't

683
00:40:34,160 --> 00:40:36,680
Speaker 3: know for sure, but it is called the sonic hedgehog

684
00:40:36,960 --> 00:40:39,400
Speaker 3: signaling pathway. And the signaling pathway, by the way, is

685
00:40:40,000 --> 00:40:43,440
Speaker 3: it's like a series of chemical reactions in the body

686
00:40:43,520 --> 00:40:47,680
Speaker 3: that controls and coordinates the activity of cells in order

687
00:40:47,760 --> 00:40:51,359
Speaker 3: to do things like grow new tissue during development, or

688
00:40:51,800 --> 00:40:55,319
Speaker 3: cause an immune system response or something like that. The

689
00:40:55,560 --> 00:41:00,560
Speaker 3: sonic hedgehog pathway, in particular, it seems important during embryonic development.

690
00:41:00,640 --> 00:41:03,960
Speaker 3: It sort of guides growth and plays a role in

691
00:41:04,040 --> 00:41:07,440
Speaker 3: the patterning of tissues that emerge from the growth process.

692
00:41:08,000 --> 00:41:11,600
Speaker 3: So Krishnan and Rohner point to a study by Yamamoto

693
00:41:11,680 --> 00:41:14,440
Speaker 3: at all from twenty nine from not twenty nineteen, from

694
00:41:14,440 --> 00:41:18,520
Speaker 3: two thousand and nine sorry in Developmental Biology, which found

695
00:41:18,600 --> 00:41:23,480
Speaker 3: that by altering expression of the sonic hedgehog signaling pathway

696
00:41:23,600 --> 00:41:27,200
Speaker 3: in embryos of the surface dwelling relative of the blind

697
00:41:27,239 --> 00:41:31,759
Speaker 3: Mexican cavefish. You would actually get multiple changes together. This

698
00:41:31,840 --> 00:41:34,640
Speaker 3: is our package deal. You would get regression of the

699
00:41:34,680 --> 00:41:36,640
Speaker 3: eyes like we talked about, so the eyes would sort

700
00:41:36,680 --> 00:41:38,799
Speaker 3: of like be absorbed and you would no longer have

701
00:41:38,880 --> 00:41:41,840
Speaker 3: functioning eyes as an adult fish. But you would also

702
00:41:41,960 --> 00:41:47,239
Speaker 3: get enhancement of taste buds and jaws. So that's your

703
00:41:47,239 --> 00:41:50,520
Speaker 3: package deal. And in the dark you can imagine why

704
00:41:50,600 --> 00:41:53,759
Speaker 3: that would be a good package deal. The author's write

705
00:41:53,800 --> 00:41:57,400
Speaker 3: quote SAHH has wide range effects on the development of

706
00:41:57,480 --> 00:42:00,480
Speaker 3: various organs, and it has been identified as a strong

707
00:42:00,560 --> 00:42:04,359
Speaker 3: candidate for eye regression. It's elevated expression in the oral

708
00:42:04,360 --> 00:42:08,680
Speaker 3: pharyngeal region in cavefish taste buds, and the fact that

709
00:42:08,800 --> 00:42:11,600
Speaker 3: eye size and number of taste buds are correlated in

710
00:42:11,719 --> 00:42:16,640
Speaker 3: hybrids makes SAHH a promising candidate for functional studies. So

711
00:42:16,960 --> 00:42:21,160
Speaker 3: that's another factor possibly at work here. So to review,

712
00:42:21,440 --> 00:42:24,080
Speaker 3: you got eyes in visual tissue in the brain require

713
00:42:24,120 --> 00:42:27,080
Speaker 3: a lot of food to sustain, and food is especially

714
00:42:27,120 --> 00:42:29,520
Speaker 3: scarce in the cave. Also, the eyes are not really

715
00:42:29,640 --> 00:42:32,480
Speaker 3: useful in the cave, so you know the trade off

716
00:42:32,480 --> 00:42:35,600
Speaker 3: there seems pretty obvious. There's less evidence for this, but

717
00:42:35,680 --> 00:42:38,520
Speaker 3: it has been suggested that eyes are also a liability

718
00:42:38,560 --> 00:42:41,960
Speaker 3: in terms of infection and injury, and it seems there

719
00:42:41,960 --> 00:42:45,880
Speaker 3: are certain genetic and developmental changes that offer a package

720
00:42:45,920 --> 00:42:49,280
Speaker 3: deal where you get eye regression, your eyes are absorbed,

721
00:42:49,320 --> 00:42:52,160
Speaker 3: you have no eyes as an adult fish, but more

722
00:42:52,360 --> 00:42:54,919
Speaker 3: taste buds and in the dark, that's a good deal

723
00:42:54,960 --> 00:42:57,920
Speaker 3: to take because remember taste buds. We think of them

724
00:42:57,920 --> 00:43:00,800
Speaker 3: mainly in terms of like providing pleasure, but taste buds

725
00:43:00,840 --> 00:43:05,560
Speaker 3: give you important survival information. They are your your body's

726
00:43:05,680 --> 00:43:09,799
Speaker 3: chemistry set along with your ural factory. Can you know,

727
00:43:09,920 --> 00:43:12,920
Speaker 3: smell and taste together help you sort of test incoming

728
00:43:13,000 --> 00:43:17,840
Speaker 3: materials for safety and nutritional value. And that is actually

729
00:43:17,880 --> 00:43:20,719
Speaker 3: a very valuable thing in the wild, especially if you

730
00:43:20,719 --> 00:43:22,200
Speaker 3: can't look at stuff you're gonna eat.

731
00:43:22,560 --> 00:43:24,720
Speaker 1: Yeah. Yeah, we have to be reminded of that because

732
00:43:24,719 --> 00:43:28,759
Speaker 1: we are such site dependent organisms that we easily think

733
00:43:28,800 --> 00:43:31,600
Speaker 1: of like the world we can see and then the

734
00:43:31,640 --> 00:43:35,360
Speaker 1: other senses that provide sort of backup information, right, or

735
00:43:35,360 --> 00:43:37,279
Speaker 1: at least it's easy to think about that in terms

736
00:43:37,320 --> 00:43:39,920
Speaker 1: of a lot of stimuli. Obviously it's different once you

737
00:43:39,960 --> 00:43:43,720
Speaker 1: get into, say, you know, the actual experiences of consuming food.

738
00:43:43,719 --> 00:43:46,560
Speaker 1: But even that, the visual factor is a huge part

739
00:43:46,600 --> 00:43:48,879
Speaker 1: of it totally. When you pay for a nice meal,

740
00:43:48,880 --> 00:43:51,520
Speaker 1: when you pay for a nice cocktail or zero proof cocktail,

741
00:43:51,560 --> 00:43:55,240
Speaker 1: whatever floats your boat, you know, I mean presentation. Visual

742
00:43:55,280 --> 00:43:58,080
Speaker 1: presentation is a huge part of what you're signing up for.

743
00:43:58,480 --> 00:44:01,200
Speaker 3: It absolutely is. Even I would say this, even if

744
00:44:01,239 --> 00:44:04,400
Speaker 3: you think you quote no better. Do you know what

745
00:44:04,400 --> 00:44:05,000
Speaker 3: I mean about that?

746
00:44:05,120 --> 00:44:05,920
Speaker 1: Row like that?

747
00:44:06,280 --> 00:44:09,239
Speaker 3: Some people can think like, oh, you know, I'm just

748
00:44:09,280 --> 00:44:11,719
Speaker 3: in it for the tasty food. I don't really care

749
00:44:11,880 --> 00:44:14,920
Speaker 3: if it looks good, But actually you do care in

750
00:44:15,000 --> 00:44:18,080
Speaker 3: subconscious ways that you're not admitting to yourself.

751
00:44:18,400 --> 00:44:21,520
Speaker 1: Yeah, on some level, you were still anticipating the flavor,

752
00:44:21,600 --> 00:44:26,040
Speaker 1: anticipating the taste experience based on and to a large

753
00:44:26,040 --> 00:44:28,560
Speaker 1: degree on visual data totally.

754
00:44:28,719 --> 00:44:31,239
Speaker 3: So one more thing I want to say about these

755
00:44:31,480 --> 00:44:35,239
Speaker 3: the blind Mexican cavefish, because I was looking into this

756
00:44:35,320 --> 00:44:38,759
Speaker 3: cavefish species and it seems that eye loss or I

757
00:44:38,920 --> 00:44:44,640
Speaker 3: regression is strongly associated with a parallel morphotype, which is

758
00:44:44,880 --> 00:44:49,640
Speaker 3: pigmentation loss. So a source I was using on pigmentation

759
00:44:49,800 --> 00:44:52,680
Speaker 3: loss in cavefish is a chapter in a book. The

760
00:44:52,800 --> 00:44:56,440
Speaker 3: chapter is called Evolutionary Genetics of Pigmentation Loss in Blind

761
00:44:56,480 --> 00:44:59,720
Speaker 3: Mexican Cavefish by Joshua B. Gross and Clifford Jay Tabin.

762
00:45:00,280 --> 00:45:02,640
Speaker 3: It is from the book In Search of the Causes

763
00:45:02,680 --> 00:45:07,439
Speaker 3: of Evolution, From Field Observations to Mechanisms, Princeton University Press,

764
00:45:07,440 --> 00:45:12,320
Speaker 3: twenty eleven, edited by Peter and Rosemary Grant. So most

765
00:45:12,360 --> 00:45:16,440
Speaker 3: of this chapter is focused on the specific genetic mutations

766
00:45:16,480 --> 00:45:20,640
Speaker 3: and regulatory changes that result in the reduction in or

767
00:45:20,719 --> 00:45:25,920
Speaker 3: total loss of pigment in blind Mexican cavefish, the reduction

768
00:45:26,120 --> 00:45:32,400
Speaker 3: in the milanophores and color molecules in the fish's body,

769
00:45:32,880 --> 00:45:35,600
Speaker 3: and they find that in different populations they're actually you

770
00:45:35,640 --> 00:45:41,000
Speaker 3: get these similar, similar adaptations of the loss of pigment

771
00:45:41,080 --> 00:45:45,680
Speaker 3: in the body, but they have different underlying genetic or

772
00:45:45,719 --> 00:45:50,120
Speaker 3: regulatory mechanisms. So it's evolved in different ways to get

773
00:45:50,120 --> 00:45:53,200
Speaker 3: sort of the same results in these different cavefish populations.

774
00:45:54,200 --> 00:45:57,160
Speaker 3: But also this chapter gets a little bit into what

775
00:45:57,280 --> 00:46:00,839
Speaker 3: the environmental selection pressure is related to or the lack

776
00:46:00,880 --> 00:46:05,200
Speaker 3: of selection pressures related to pigmentation might be. So, for example,

777
00:46:05,640 --> 00:46:09,960
Speaker 3: on the surface, biological pigments like melanin help protect the

778
00:46:10,000 --> 00:46:14,400
Speaker 3: cells of animals from ultraviolet radiation in the sunlight. In

779
00:46:14,440 --> 00:46:17,760
Speaker 3: the cave, there's no light, so this radiation shielding effect

780
00:46:17,880 --> 00:46:22,080
Speaker 3: is useless. On the surface, pigments are also arranged in

781
00:46:22,160 --> 00:46:25,719
Speaker 3: patterns on the body as ornamentation, which plays a role

782
00:46:25,719 --> 00:46:29,000
Speaker 3: in sexual selection. So a fish with certain types of

783
00:46:29,040 --> 00:46:33,640
Speaker 3: pigmentation patterns might be seen as a more desirable mate,

784
00:46:33,880 --> 00:46:36,560
Speaker 3: but in the cave, your mate can't see you, so

785
00:46:36,640 --> 00:46:40,399
Speaker 3: it doesn't matter. On the surface, pigmentation can also play

786
00:46:40,400 --> 00:46:43,960
Speaker 3: a role in camouflage, conceealing your body within the environment,

787
00:46:44,440 --> 00:46:47,560
Speaker 3: but in the cave, once again, this doesn't make any difference.

788
00:46:47,880 --> 00:46:51,400
Speaker 3: So much like with eyes, pigmentation would be a phenotypic

789
00:46:51,400 --> 00:46:55,120
Speaker 3: trait that confers huge advantages on the surface where there's light,

790
00:46:55,480 --> 00:47:00,520
Speaker 3: and it suddenly confers little to no advantage underground. Even

791
00:47:00,560 --> 00:47:04,760
Speaker 3: if it's just subject to genetic drift, Pigmentation, like eyes,

792
00:47:04,800 --> 00:47:08,959
Speaker 3: could fluctuate out of the population. But are there any

793
00:47:09,000 --> 00:47:13,080
Speaker 3: reasons to think it is actively selected against. It seems

794
00:47:13,080 --> 00:47:15,440
Speaker 3: like there is less evidence for this than there is

795
00:47:15,440 --> 00:47:17,759
Speaker 3: in the case of eyes. There's probably good reason to

796
00:47:17,800 --> 00:47:20,319
Speaker 3: think that eyes are being selected against in the cave,

797
00:47:20,520 --> 00:47:24,719
Speaker 3: less so for pigmentation. The authors here cite research by

798
00:47:24,760 --> 00:47:28,319
Speaker 3: protests at All from two thousand and seven indicating it's

799
00:47:28,400 --> 00:47:31,960
Speaker 3: more likely a result of drift, though some amount of

800
00:47:32,000 --> 00:47:34,480
Speaker 3: indirect selection through pleiotropy is possible.

801
00:47:35,480 --> 00:47:39,919
Speaker 1: Okay, all right, we have more complex understanding, perhaps than

802
00:47:40,160 --> 00:47:42,640
Speaker 1: of what might be going on here with these changes.

803
00:47:43,080 --> 00:47:44,480
Speaker 1: All Right, we're going to go ahead and close out

804
00:47:44,520 --> 00:47:46,319
Speaker 1: this episode of stuff to blow your mind. But we'll

805
00:47:46,320 --> 00:47:48,759
Speaker 1: be back with part two in this series on Thursday.

806
00:47:49,280 --> 00:47:52,480
Speaker 1: And don't worry, we will get into the guano. We

807
00:47:52,520 --> 00:47:55,040
Speaker 1: will get into that back guano because it is vitally

808
00:47:55,080 --> 00:47:59,480
Speaker 1: important to this discussion. And also, I think we're going

809
00:47:59,520 --> 00:48:02,480
Speaker 1: to discuss I guano in a way that may turn

810
00:48:02,520 --> 00:48:04,520
Speaker 1: the concept on its head for you. I know when

811
00:48:04,520 --> 00:48:06,319
Speaker 1: I was reading about it in the way that we're

812
00:48:06,360 --> 00:48:08,640
Speaker 1: going to discuss it, it made me think about it

813
00:48:09,320 --> 00:48:10,000
Speaker 1: in a new light.

814
00:48:10,280 --> 00:48:10,839
Speaker 3: I can't wait.

815
00:48:12,000 --> 00:48:13,719
Speaker 1: In the meantime, we'd love to hear from you if

816
00:48:13,760 --> 00:48:16,640
Speaker 1: you have thoughts about particular caves that you've been to,

817
00:48:17,160 --> 00:48:20,760
Speaker 1: cave environments that you're familiar with, if you have thoughts

818
00:48:20,800 --> 00:48:25,960
Speaker 1: on scientists naming things after everything from the Iliad to

819
00:48:26,200 --> 00:48:29,040
Speaker 1: Sonic the hedgehog. We'd also love to hear from you

820
00:48:29,200 --> 00:48:33,200
Speaker 1: on that point as well. But yeah, yeah, particular cave

821
00:48:33,280 --> 00:48:35,640
Speaker 1: environments that you've really enjoyed. Like I say, I always

822
00:48:35,719 --> 00:48:40,400
Speaker 1: enjoy checking out caves. I believe Colossal Cave in Tucson,

823
00:48:40,480 --> 00:48:42,759
Speaker 1: Arizona is one that I visited many years back, and

824
00:48:43,120 --> 00:48:44,880
Speaker 1: I really want to go back there in the future

825
00:48:44,960 --> 00:48:49,640
Speaker 1: because this is one of memory serves was discovered late

826
00:48:49,800 --> 00:48:54,160
Speaker 1: enough that they were able to preserve the cave environment

827
00:48:54,360 --> 00:48:56,920
Speaker 1: to a large degree by use of essentially like an

828
00:48:56,920 --> 00:48:59,960
Speaker 1: air lock system, so that they're not just opening up

829
00:49:00,120 --> 00:49:04,880
Speaker 1: this environment in a way that destabilizes what has evolved

830
00:49:04,920 --> 00:49:08,200
Speaker 1: beneath the surface. But anyway, more on this sort of

831
00:49:08,200 --> 00:49:11,240
Speaker 1: thing in the next episode. In the meantime, we'll remind

832
00:49:11,239 --> 00:49:12,600
Speaker 1: you once more that Stuff to Blow Your Mind is

833
00:49:12,640 --> 00:49:16,399
Speaker 1: primarily a science podcast Science and culture podcasts with core

834
00:49:16,440 --> 00:49:21,120
Speaker 1: episodes on Tuesdays and Thursdays. Mondays we do listener mail,

835
00:49:21,160 --> 00:49:23,400
Speaker 1: Wednesdays we do a short form episode, and on Fridays

836
00:49:23,400 --> 00:49:25,680
Speaker 1: we set aside most serious concerns to just talk about

837
00:49:25,719 --> 00:49:29,279
Speaker 1: a weird film on Weird House Cinema. Check us out

838
00:49:29,320 --> 00:49:32,239
Speaker 1: on social media. If you haven't, We're on What're We're

839
00:49:32,280 --> 00:49:34,480
Speaker 1: on the Instagram. You can find us on the other

840
00:49:34,480 --> 00:49:38,560
Speaker 1: major social platforms. I think we're on TikTok. I had

841
00:49:38,560 --> 00:49:41,480
Speaker 1: to be reminded of this. We have some wonderful folks

842
00:49:41,480 --> 00:49:43,359
Speaker 1: that are helping us handle our social these days, and

843
00:49:43,400 --> 00:49:47,040
Speaker 1: I think we're on TikTok. We look for us there.

844
00:49:47,080 --> 00:49:51,120
Speaker 1: I guess I think we're there. But yeah, if you

845
00:49:51,200 --> 00:49:53,719
Speaker 1: use social media and you have the power to follow

846
00:49:53,800 --> 00:49:56,239
Speaker 1: us in any of these places, yeah, give us a follow.

847
00:49:56,400 --> 00:49:58,640
Speaker 1: We appreciate it. If you can give the show some

848
00:49:58,680 --> 00:50:00,960
Speaker 1: stars where if you listen to the podcas cast downloaded

849
00:50:01,040 --> 00:50:02,719
Speaker 1: and subscribe, that also.

850
00:50:02,520 --> 00:50:05,320
Speaker 3: Helps us out huge thanks as always to our excellent

851
00:50:05,360 --> 00:50:08,440
Speaker 3: audio producer JJ Posway. If you would like to get

852
00:50:08,480 --> 00:50:10,560
Speaker 3: in touch with us with feedback on this episode or

853
00:50:10,560 --> 00:50:12,719
Speaker 3: any other, to suggest a topic for the future, or

854
00:50:12,840 --> 00:50:15,320
Speaker 3: just to say hello, you can email us at contact

855
00:50:15,360 --> 00:50:24,600
Speaker 3: at stuff to Blow your Mind dot com.

856
00:50:25,000 --> 00:50:27,920
Speaker 2: Stuff to Blow Your Mind is production of iHeartRadio. For

857
00:50:28,040 --> 00:50:30,799
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858
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