1 00:00:03,040 --> 00:00:06,840 Speaker 1: Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. 2 00:00:12,600 --> 00:00:14,520 Speaker 2: Hey, welcome to Stuff to Blow your Mind. 3 00:00:14,640 --> 00:00:18,000 Speaker 3: My name is Robert Lamb and I am Joe McCormick. 4 00:00:18,040 --> 00:00:20,520 Speaker 3: And hey, here we are together again, Rob. After you 5 00:00:20,680 --> 00:00:21,680 Speaker 3: you were out for a little bit. 6 00:00:21,880 --> 00:00:24,560 Speaker 2: Oh yeah, yeah, we've recorded a few things here or there, 7 00:00:24,560 --> 00:00:27,320 Speaker 2: so I keep forgetting that, you know, when the actual 8 00:00:27,400 --> 00:00:30,319 Speaker 2: new Core episodes are that I'm around for. So yeah, 9 00:00:30,400 --> 00:00:32,879 Speaker 2: I am back. I was just in a little vacation 10 00:00:33,040 --> 00:00:33,839 Speaker 2: with my family. 11 00:00:34,360 --> 00:00:36,640 Speaker 3: Wait a minute, now, you refreshed my brain because I 12 00:00:36,680 --> 00:00:39,080 Speaker 3: forgot that we did a listener mail episode before this, 13 00:00:39,360 --> 00:00:42,760 Speaker 3: So listeners, you are reacclimated to Rob. 14 00:00:42,800 --> 00:00:46,320 Speaker 2: Now, yeah, I mean listeners I think always have a 15 00:00:46,360 --> 00:00:49,400 Speaker 2: skewed understanding of when we're out when we're present, because 16 00:00:49,400 --> 00:00:51,320 Speaker 2: there's you know, even if one of us is out, 17 00:00:51,360 --> 00:00:54,880 Speaker 2: you may hear us on a vault episode on the weekend. 18 00:00:55,560 --> 00:00:58,560 Speaker 2: We might have recorded through on something recorded ahead of 19 00:00:58,600 --> 00:01:02,280 Speaker 2: time on one piece of content, but not on other 20 00:01:02,320 --> 00:01:05,240 Speaker 2: pieces of content, So you know, you'll just have to 21 00:01:05,280 --> 00:01:08,280 Speaker 2: take our word for it. Sometimes we are away, sometimes 22 00:01:08,360 --> 00:01:08,959 Speaker 2: we were present. 23 00:01:09,160 --> 00:01:12,200 Speaker 3: We're like a duo of mysterious time traveling cats that 24 00:01:12,240 --> 00:01:13,200 Speaker 3: appear in your ears. 25 00:01:13,680 --> 00:01:17,119 Speaker 2: Yeah all right, Well, you know, I have to say, 26 00:01:17,120 --> 00:01:19,640 Speaker 2: on this most recent journey with my family, I did 27 00:01:19,680 --> 00:01:22,679 Speaker 2: not venture into a cave. I don't think I ventured 28 00:01:22,720 --> 00:01:26,160 Speaker 2: into a cave. Let me refresh. No, no cave venturing. 29 00:01:26,920 --> 00:01:29,000 Speaker 3: No, I would think you'd remember. 30 00:01:29,080 --> 00:01:31,600 Speaker 2: Come on, I mean, sometimes, you know, these trips, you 31 00:01:31,600 --> 00:01:34,119 Speaker 2: see a lot of things, and yeah, you know, and 32 00:01:34,319 --> 00:01:38,399 Speaker 2: you know, cave environments are are always fascinating, but they're 33 00:01:38,440 --> 00:01:40,959 Speaker 2: not necessarily always going to be like the top of 34 00:01:41,000 --> 00:01:45,240 Speaker 2: a particular trip. It just varies. But you know, we 35 00:01:45,240 --> 00:01:48,600 Speaker 2: we frequently discussed biological wonders on the show that leads 36 00:01:48,680 --> 00:01:52,600 Speaker 2: us to consider extreme environments, and the cave environment is 37 00:01:52,680 --> 00:01:58,400 Speaker 2: one such environment. I tend to find caves endlessly fascinating, 38 00:01:58,440 --> 00:02:00,400 Speaker 2: even if it's a lower tier cave, you know, And 39 00:02:00,400 --> 00:02:02,279 Speaker 2: I've been to some of those where it's like, okay, 40 00:02:02,320 --> 00:02:06,640 Speaker 2: this is this one was opened by humans a while back. 41 00:02:06,720 --> 00:02:09,240 Speaker 2: It doesn't have much in the way of a robust 42 00:02:09,280 --> 00:02:13,079 Speaker 2: ecosystem and so forth, but it's still fascinating. There's still 43 00:02:13,120 --> 00:02:14,760 Speaker 2: something about the subterranean world. 44 00:02:15,280 --> 00:02:19,680 Speaker 3: Have you ever done the cave exploring experience where you 45 00:02:19,760 --> 00:02:22,640 Speaker 3: go down into a cave and all artificial light sources 46 00:02:22,680 --> 00:02:24,880 Speaker 3: are turned off and you get to see like the 47 00:02:25,000 --> 00:02:28,600 Speaker 3: blackest black night you've ever seen. It's a kind of 48 00:02:28,680 --> 00:02:31,160 Speaker 3: darkness that you cannot imagine otherwise. 49 00:02:31,480 --> 00:02:36,200 Speaker 2: Yeah, absolutely done this in a couple of Tennessee caves, 50 00:02:36,240 --> 00:02:39,040 Speaker 2: I think growing up. One that was like one of 51 00:02:39,040 --> 00:02:41,239 Speaker 2: these big official caves. I'm blinking on which one it 52 00:02:41,280 --> 00:02:43,200 Speaker 2: would have been, but went there was like a scout group, 53 00:02:43,520 --> 00:02:45,960 Speaker 2: and then there was another like local cave that was 54 00:02:46,000 --> 00:02:48,560 Speaker 2: just on somebody's land and got to go in there 55 00:02:48,639 --> 00:02:51,320 Speaker 2: and see the main cavern and then have the lights 56 00:02:51,320 --> 00:02:53,280 Speaker 2: go out. Sometimes they'll do the lights out with a 57 00:02:53,320 --> 00:02:56,320 Speaker 2: little ghost story or something right, just sort of drive 58 00:02:56,400 --> 00:02:58,920 Speaker 2: home the creepiness of it. But yeah, you find yourself 59 00:02:58,919 --> 00:03:00,720 Speaker 2: in just the appsol darkness. 60 00:03:01,160 --> 00:03:03,959 Speaker 3: We did this with our tour guide years ago at 61 00:03:04,120 --> 00:03:08,480 Speaker 3: Oregon Caves National Monument in southwestern Oregon, which is a 62 00:03:08,600 --> 00:03:11,480 Speaker 3: very cool cave system. And it's hard to explain because 63 00:03:11,600 --> 00:03:14,480 Speaker 3: again I had not seen anything like this anywhere before, 64 00:03:14,520 --> 00:03:17,920 Speaker 3: where your eyes are totally wide and you see not 65 00:03:18,160 --> 00:03:20,520 Speaker 3: even a pinprick of light, just nothing. 66 00:03:21,440 --> 00:03:25,639 Speaker 2: Yeah, it's haunting and and it is key to understanding 67 00:03:25,720 --> 00:03:30,480 Speaker 2: cave environments, as we'll be discussing in this episode. Now, 68 00:03:31,080 --> 00:03:35,040 Speaker 2: not only are caves home to rather unique organisms in 69 00:03:35,080 --> 00:03:39,000 Speaker 2: certain caves, as we'll discuss more as we progress, but 70 00:03:39,080 --> 00:03:42,560 Speaker 2: they've of course always fascinated humans, and our global myths 71 00:03:42,600 --> 00:03:46,320 Speaker 2: and traditions are full of caverns that house monsters, passages 72 00:03:46,360 --> 00:03:50,720 Speaker 2: to the underworld, magical treasures, and much more. Also, as 73 00:03:50,720 --> 00:03:54,280 Speaker 2: we've discussed, these were some of the first enclosed spaces 74 00:03:54,320 --> 00:03:58,280 Speaker 2: that humans entered and were occupied to some degree in 75 00:03:58,720 --> 00:04:01,640 Speaker 2: a way, laying the ground for the humble and elaborate 76 00:04:01,640 --> 00:04:05,000 Speaker 2: shelters that we would construct thereafter. You know, because what 77 00:04:05,200 --> 00:04:07,440 Speaker 2: is what are some of the rooms in our houses 78 00:04:07,480 --> 00:04:09,920 Speaker 2: but caves that we have built for ourselves. 79 00:04:10,080 --> 00:04:11,960 Speaker 3: Some houses are more cave like than others. 80 00:04:12,520 --> 00:04:14,640 Speaker 2: Yeah. Yeah, So we may not think of ourselves as 81 00:04:14,680 --> 00:04:17,559 Speaker 2: cave people, but we are, in many respects still people 82 00:04:17,600 --> 00:04:21,159 Speaker 2: of the cave at home, with enclosed spaces, sometimes with windows, 83 00:04:21,200 --> 00:04:26,600 Speaker 2: sometimes without places in general like this, be it constructed, 84 00:04:26,680 --> 00:04:31,200 Speaker 2: be it like a large, you know, enclosed concert hall, 85 00:04:31,720 --> 00:04:36,240 Speaker 2: or an underground facility, or a naturally occurring cave or 86 00:04:36,240 --> 00:04:38,360 Speaker 2: some sort of a tunnel. I mean, you can't help 87 00:04:38,440 --> 00:04:42,520 Speaker 2: but dream about those spaces, to find dread and fascination 88 00:04:42,600 --> 00:04:44,880 Speaker 2: in those spaces. And you know now that I mention it. 89 00:04:45,880 --> 00:04:48,120 Speaker 2: On my family vacation, I don't think we went We 90 00:04:48,160 --> 00:04:50,479 Speaker 2: did not go into a cave system, but we did 91 00:04:50,480 --> 00:04:52,880 Speaker 2: go through tunnels at times, and we were stuck in 92 00:04:52,920 --> 00:04:55,719 Speaker 2: traffic at a tunnel at one point. And so that 93 00:04:55,839 --> 00:04:59,040 Speaker 2: alone gives one enough room for pause. It's just as 94 00:04:59,080 --> 00:05:02,200 Speaker 2: good almost well, I wouldn't say it's not as good, 95 00:05:02,240 --> 00:05:07,440 Speaker 2: but it does. It summons possibilities, maybe even the possibility 96 00:05:07,480 --> 00:05:10,520 Speaker 2: of talking about the strange world of cave biology. And 97 00:05:10,560 --> 00:05:12,719 Speaker 2: that's what we're going to be looking at in this series, right, 98 00:05:13,240 --> 00:05:17,000 Speaker 2: that's right, talking about the cave environment, talking about some 99 00:05:17,040 --> 00:05:20,360 Speaker 2: of the organisms and life forms that live there. And 100 00:05:20,520 --> 00:05:21,960 Speaker 2: to get into this, I want to talk a little 101 00:05:21,960 --> 00:05:24,200 Speaker 2: bit about just sort of the idea of there being 102 00:05:24,240 --> 00:05:28,479 Speaker 2: a dual world, something that again is quite reflected in 103 00:05:28,600 --> 00:05:32,120 Speaker 2: some of our more supernatural understandings of the surface world 104 00:05:32,160 --> 00:05:35,520 Speaker 2: and the world beneath the earth, you know, the world 105 00:05:35,600 --> 00:05:37,839 Speaker 2: of the living, the world of the dead, and so forth. 106 00:05:38,680 --> 00:05:42,080 Speaker 2: I was reading a twenty eleven article in The American 107 00:05:42,160 --> 00:05:46,080 Speaker 2: Scientist by Abamaro Romero, and he pointed out that cave 108 00:05:46,120 --> 00:05:51,880 Speaker 2: biologist or biospileiologists divide the world into two. There's the 109 00:05:51,920 --> 00:05:55,080 Speaker 2: epigean world, or the world upon the earth, the world 110 00:05:55,160 --> 00:05:57,600 Speaker 2: of light that we predominantly think of as our home, 111 00:05:58,080 --> 00:06:01,920 Speaker 2: and then there's this other world, this underworld, the Hypogean 112 00:06:01,960 --> 00:06:03,360 Speaker 2: world beneath the soil. 113 00:06:03,960 --> 00:06:07,080 Speaker 3: I've never thought of the surface as epigean before, but 114 00:06:07,120 --> 00:06:09,719 Speaker 3: I love that because I guess with the Greek there Yet, 115 00:06:09,760 --> 00:06:12,760 Speaker 3: like you say, it means upon the earth, on the earth, 116 00:06:13,080 --> 00:06:17,240 Speaker 3: so not just like exposed, but it's like like an 117 00:06:17,320 --> 00:06:21,239 Speaker 3: epiphyte plant that grows on another plant. The epigean world 118 00:06:21,279 --> 00:06:24,039 Speaker 3: of the surface world isn't like the thing that grows 119 00:06:24,080 --> 00:06:26,680 Speaker 3: on the surface of this ball of iron. 120 00:06:27,400 --> 00:06:31,000 Speaker 2: Yeah, And then everything else, the underworld, the Hypogean world 121 00:06:31,440 --> 00:06:35,839 Speaker 2: beneath the soil, and the world beneath the soil. No 122 00:06:35,920 --> 00:06:39,640 Speaker 2: mistake here is vast. So just as the epigean world 123 00:06:39,960 --> 00:06:42,200 Speaker 2: consists of any part of the biosphere that is even 124 00:06:42,279 --> 00:06:46,760 Speaker 2: partially or periodically exposed to light, the Hypogean world consists 125 00:06:46,760 --> 00:06:50,440 Speaker 2: of any underground part of the biosphere. So this includes 126 00:06:50,520 --> 00:06:53,400 Speaker 2: the living soil in your backyard, you know, networks of 127 00:06:53,440 --> 00:06:57,800 Speaker 2: mycilium that rooting through it, as well as life between 128 00:06:57,880 --> 00:07:02,360 Speaker 2: grains of sand buried under the beat underground waters, and 129 00:07:02,680 --> 00:07:06,600 Speaker 2: indeed cave environments, which to be clear, can also be 130 00:07:07,080 --> 00:07:10,240 Speaker 2: part of the Epigean world because they of course are 131 00:07:10,320 --> 00:07:13,680 Speaker 2: gateways and they are going to be transition spaces the 132 00:07:13,720 --> 00:07:15,280 Speaker 2: mouth of a cave, for example. 133 00:07:15,640 --> 00:07:16,840 Speaker 3: Mmmmm yeah. 134 00:07:17,280 --> 00:07:20,200 Speaker 2: Now, caves, as Ramera points out in this article, are 135 00:07:20,240 --> 00:07:24,320 Speaker 2: also This is also a very broad categorization, entailing everything 136 00:07:24,360 --> 00:07:29,040 Speaker 2: from ice caves to lava tubes. And indeed, caves are 137 00:07:29,080 --> 00:07:33,680 Speaker 2: merely the subterranean spaces into which humans can venture. There 138 00:07:33,680 --> 00:07:37,440 Speaker 2: are plenty of subterranean environments and even cavernous spaces in 139 00:07:37,480 --> 00:07:40,040 Speaker 2: the Earth that are just inaccessible to us because there 140 00:07:40,040 --> 00:07:42,080 Speaker 2: are no openings to the surface. 141 00:07:42,600 --> 00:07:44,520 Speaker 3: That's a really good point. And there's so much that 142 00:07:44,560 --> 00:07:47,480 Speaker 3: goes on in those those small or tiny spaces that 143 00:07:47,520 --> 00:07:50,960 Speaker 3: you can't like walk into and observe. You know, you 144 00:07:51,040 --> 00:07:54,600 Speaker 3: mentioned like the idea of the myceelium that underlies that. 145 00:07:54,720 --> 00:07:58,480 Speaker 3: You know, you find a mushroom in the forest. It's 146 00:07:58,520 --> 00:08:01,200 Speaker 3: hard to remember this sometimes, but like the mushroom you 147 00:08:01,280 --> 00:08:05,520 Speaker 3: find is just like one organ of the fungus organism 148 00:08:05,560 --> 00:08:07,880 Speaker 3: as a whole. It's the fruiting body that comes up 149 00:08:07,920 --> 00:08:10,840 Speaker 3: above the surface but underneath there's going to be this 150 00:08:10,960 --> 00:08:15,040 Speaker 3: whole network that's sort of where the organism really is 151 00:08:15,040 --> 00:08:17,640 Speaker 3: is under the soil, and you don't even see it. 152 00:08:17,680 --> 00:08:19,360 Speaker 3: You don't even think to look down there. 153 00:08:19,920 --> 00:08:24,440 Speaker 2: Yeah, there's a vital and rich world in there, and 154 00:08:24,480 --> 00:08:27,760 Speaker 2: it's not a space that human beings can venture into 155 00:08:28,360 --> 00:08:31,240 Speaker 2: in the way that we can venture into a cave environment, 156 00:08:31,280 --> 00:08:32,640 Speaker 2: you know. I mean we can study it, we can 157 00:08:32,679 --> 00:08:35,440 Speaker 2: explore it, we can dig it up, but it's a 158 00:08:35,440 --> 00:08:39,400 Speaker 2: different sort of world. Now. Romero also mentions the freatic 159 00:08:39,679 --> 00:08:44,040 Speaker 2: environments of underground lakes and rivers, but the word cave 160 00:08:44,320 --> 00:08:48,000 Speaker 2: is generally reserved for again, those spaces we can access ourselves, 161 00:08:48,120 --> 00:08:52,080 Speaker 2: where human explorers and scientists or at least their technological minions, 162 00:08:52,520 --> 00:08:55,280 Speaker 2: can physically investigate the world below. At least you can 163 00:08:55,280 --> 00:08:57,640 Speaker 2: get you can get a robot in there, you can 164 00:08:57,640 --> 00:09:02,160 Speaker 2: stick a probe in somehow invoke your presence there. 165 00:09:02,600 --> 00:09:05,360 Speaker 3: A cave is like a space that can be spilunked, 166 00:09:05,400 --> 00:09:08,440 Speaker 3: and maybe our standards for how small a space can 167 00:09:08,520 --> 00:09:09,800 Speaker 3: be spilunked are changing. 168 00:09:10,720 --> 00:09:14,280 Speaker 2: Right When we had Lee Burger on the show, the 169 00:09:14,320 --> 00:09:17,640 Speaker 2: author of Cave of Bones, he was talking about exploring 170 00:09:18,280 --> 00:09:23,160 Speaker 2: various cave environments, a specific cave environment in fact, looking 171 00:09:23,280 --> 00:09:28,960 Speaker 2: at pre human skeletal remains. And one of the really 172 00:09:28,960 --> 00:09:31,240 Speaker 2: telling things about his experience is there was this part 173 00:09:31,280 --> 00:09:34,280 Speaker 2: of the cave that for the longest he could not access. 174 00:09:34,360 --> 00:09:36,920 Speaker 2: It was like a grueling experience, and you had to 175 00:09:37,720 --> 00:09:44,040 Speaker 2: send like very young specialized scientists down there to physically 176 00:09:44,120 --> 00:09:46,760 Speaker 2: occupy the space. And he was able to send them 177 00:09:46,800 --> 00:09:49,320 Speaker 2: down have them look around, he was able to look 178 00:09:49,360 --> 00:09:53,520 Speaker 2: at video footage from that space, but eventually he could 179 00:09:53,559 --> 00:09:55,840 Speaker 2: not resist. You know, he talks about this at length, 180 00:09:55,880 --> 00:09:58,000 Speaker 2: like he had to go down there. He had to, 181 00:09:58,240 --> 00:10:02,000 Speaker 2: like he lost weight in order to fit through, narrowly 182 00:10:02,080 --> 00:10:06,160 Speaker 2: fit through the passageways that were acquired, a grueling experience 183 00:10:06,520 --> 00:10:08,959 Speaker 2: to actually make it there. So there is something about 184 00:10:09,000 --> 00:10:12,320 Speaker 2: like the human exploratory experience in all of this, Like 185 00:10:12,320 --> 00:10:15,760 Speaker 2: even when you have the technology and the organization, there's 186 00:10:15,800 --> 00:10:17,960 Speaker 2: something about it. You have to be there, you want 187 00:10:18,000 --> 00:10:19,800 Speaker 2: to be there in the space. Man. 188 00:10:19,880 --> 00:10:22,400 Speaker 3: I know I'm not unique in this, but that is 189 00:10:22,400 --> 00:10:24,400 Speaker 3: one of the things that truly gives me the creeps 190 00:10:24,480 --> 00:10:28,160 Speaker 3: to like barely trying to wedge your way through passageways 191 00:10:28,200 --> 00:10:31,120 Speaker 3: inside a cave under the earth that is just ugh. 192 00:10:31,800 --> 00:10:33,680 Speaker 2: Yeah, it gave me the all overs here in some 193 00:10:33,760 --> 00:10:37,400 Speaker 2: of the details in his book, and I think there 194 00:10:37,480 --> 00:10:40,320 Speaker 2: was also covered in a Netflix special if Memory Is Serving, 195 00:10:40,440 --> 00:10:42,640 Speaker 2: And yeah, just the idea of like having to squeeze 196 00:10:42,640 --> 00:10:46,520 Speaker 2: through a space, getting momentarily stuck like the wrench and 197 00:10:46,520 --> 00:10:49,880 Speaker 2: a chimney, and then having to press on potentially like 198 00:10:49,920 --> 00:10:55,120 Speaker 2: you know risk you know, dislocating bones and so forth 199 00:10:55,160 --> 00:10:57,440 Speaker 2: to do it. It's yeah, not for me, but I 200 00:10:57,480 --> 00:11:00,520 Speaker 2: respect anyone who is capable of it totally. Now, the 201 00:11:00,520 --> 00:11:03,400 Speaker 2: most common caves are karstick or limestone. I believe we've 202 00:11:03,400 --> 00:11:08,880 Speaker 2: discussed this before, talking about various geological formations. Limestone, which 203 00:11:08,880 --> 00:11:11,559 Speaker 2: covers roughly fifteen percent of the world above water, is 204 00:11:11,880 --> 00:11:15,880 Speaker 2: highly soluble at least fifty percent calcium carbonate according to Romero, 205 00:11:16,400 --> 00:11:20,440 Speaker 2: so acidic rain water easily modifies it over time, and 206 00:11:20,520 --> 00:11:23,160 Speaker 2: so the world is littered with such cave systems, some 207 00:11:23,240 --> 00:11:27,199 Speaker 2: only partially exposed to the surface world but in important ways. 208 00:11:27,760 --> 00:11:30,920 Speaker 2: Others with key openings that permit light to influence the 209 00:11:31,040 --> 00:11:34,520 Speaker 2: environments of their interior. So you know, some cave systems, 210 00:11:34,880 --> 00:11:38,720 Speaker 2: some rather famous ones even do have sunlight spilling into 211 00:11:38,760 --> 00:11:41,960 Speaker 2: them at least in part, so you end up with 212 00:11:41,960 --> 00:11:45,200 Speaker 2: this kind of like mixed environment. But the lack of 213 00:11:45,320 --> 00:11:49,800 Speaker 2: natural light as a whole is extremely important to understanding 214 00:11:50,600 --> 00:11:53,839 Speaker 2: the individual organisms that make their homes and caves, as 215 00:11:53,880 --> 00:11:56,920 Speaker 2: well as the overall ecosystems in which they thrive. 216 00:11:57,440 --> 00:12:01,160 Speaker 3: Right because when you think about it, basically everywhere else 217 00:12:01,200 --> 00:12:04,000 Speaker 3: on Earth. I mean, there are some extreme exceptions, but 218 00:12:04,040 --> 00:12:08,040 Speaker 3: for most of the world, the food chain is built 219 00:12:08,120 --> 00:12:12,040 Speaker 3: on access to sunlight. To the sunlight powers the powers 220 00:12:12,080 --> 00:12:14,840 Speaker 3: the photosynthesis of the autotrophs that are the base of 221 00:12:14,880 --> 00:12:17,840 Speaker 3: the food chain. Then things start eating them, then other 222 00:12:17,920 --> 00:12:20,600 Speaker 3: things eat those organisms, and on and on up. If 223 00:12:20,600 --> 00:12:24,320 Speaker 3: you don't have sunlight to power the autotrophs at the base, 224 00:12:24,480 --> 00:12:25,160 Speaker 3: what do you do? 225 00:12:25,720 --> 00:12:28,520 Speaker 2: I know, yeah, yeah, we'll get back to this in 226 00:12:28,600 --> 00:12:32,040 Speaker 2: just a minute here, But yeah, humans, of course, we're 227 00:12:32,040 --> 00:12:35,400 Speaker 2: not the first to venture into the subterranean worlds. Countless 228 00:12:35,400 --> 00:12:38,960 Speaker 2: other creatures ventured in, resulting in rich a rich, specialized 229 00:12:38,960 --> 00:12:43,480 Speaker 2: world of troglofauna, and not every creature becomes a permanent 230 00:12:43,480 --> 00:12:47,760 Speaker 2: denizen of the dark, which, if you watch enough sci 231 00:12:47,760 --> 00:12:49,480 Speaker 2: fi and horror movies, you would think, oh, yeah, they're 232 00:12:49,520 --> 00:12:51,920 Speaker 2: just people and creatures fallen in all the time and 233 00:12:52,240 --> 00:12:56,160 Speaker 2: evolving into chuds. But no, that doesn't happen all the time. 234 00:12:56,160 --> 00:13:02,800 Speaker 2: But plenty of creatures have specialized evolution narily often evolving 235 00:13:03,000 --> 00:13:07,760 Speaker 2: defining troglomorphic features that we often associate with these environments, 236 00:13:08,200 --> 00:13:12,760 Speaker 2: namely blindness and loss of pigmentation with the chutification. 237 00:13:12,880 --> 00:13:13,640 Speaker 3: If you will. 238 00:13:13,720 --> 00:13:18,360 Speaker 2: Chutification, I guess yeah. You know, you see movies like 239 00:13:18,400 --> 00:13:21,480 Speaker 2: The Descent and so forth. I love all these movies, 240 00:13:21,520 --> 00:13:25,160 Speaker 2: you know, more Locks and so forth. But maybe we'll 241 00:13:25,160 --> 00:13:29,040 Speaker 2: continue to discuss the possibilities there. But briefly, I want 242 00:13:29,080 --> 00:13:31,440 Speaker 2: to just do a refresher on the various types of 243 00:13:31,480 --> 00:13:36,240 Speaker 2: troglofauna before we continue. We have troglobites. These are obligate 244 00:13:36,280 --> 00:13:39,600 Speaker 2: cave dwellers, strictly bound to the under their underground environments, 245 00:13:39,640 --> 00:13:41,760 Speaker 2: so they are not going to live, they're not going 246 00:13:41,800 --> 00:13:46,280 Speaker 2: to thrive outside of the darkness of the caves. Then 247 00:13:46,320 --> 00:13:50,199 Speaker 2: we have troglasines. These are cave guests, creatures that can 248 00:13:50,200 --> 00:13:55,280 Speaker 2: be found underground sporadically but cannot establish permanent underground populations. 249 00:13:57,120 --> 00:14:00,640 Speaker 2: Then we have troglophiles. These are creatures that live dominantly 250 00:14:00,679 --> 00:14:03,880 Speaker 2: above ground, but can also reside in underground habitats. There 251 00:14:03,960 --> 00:14:08,880 Speaker 2: are two subsets. There's u trogleophiles, surface species that are 252 00:14:08,920 --> 00:14:12,440 Speaker 2: also able to maintain in a permanent subterranean population, and 253 00:14:12,480 --> 00:14:15,640 Speaker 2: then there are subtroglophiles creatures that can and do live 254 00:14:15,720 --> 00:14:19,280 Speaker 2: underground at least temporarily, but are more associated with life 255 00:14:19,320 --> 00:14:22,680 Speaker 2: above ground. So again you can think about the idea 256 00:14:22,680 --> 00:14:26,360 Speaker 2: that there's not just surface creatures and underground creatures. You know, 257 00:14:27,120 --> 00:14:30,000 Speaker 2: there's a lot of back and forth, and there are 258 00:14:30,080 --> 00:14:32,840 Speaker 2: various phases between what we might think of as a 259 00:14:33,120 --> 00:14:36,720 Speaker 2: purely surface creature and a purely subterranean creature. 260 00:14:37,040 --> 00:14:38,360 Speaker 3: I see none of. 261 00:14:38,360 --> 00:14:42,000 Speaker 2: This to be confused with a troglodyte. There are a 262 00:14:42,000 --> 00:14:44,760 Speaker 2: handful of different uses is for this term. It can 263 00:14:44,840 --> 00:14:48,760 Speaker 2: refer either to a human cave dweller or and I believe, 264 00:14:48,800 --> 00:14:53,880 Speaker 2: in one case of an outdated classification of early hominid. 265 00:14:54,280 --> 00:14:57,760 Speaker 2: But there are also a small genus of small birds 266 00:14:57,920 --> 00:15:01,240 Speaker 2: related to rims that are called rolodides. These birds are 267 00:15:01,320 --> 00:15:04,280 Speaker 2: rarely found in caves apparently, but they're so named because 268 00:15:04,320 --> 00:15:08,440 Speaker 2: they'll venture into various crevices and spaces, including caves, in 269 00:15:08,480 --> 00:15:09,120 Speaker 2: search of food. 270 00:15:19,960 --> 00:15:23,480 Speaker 3: So we have these various kinds of spilunking organisms, those 271 00:15:23,560 --> 00:15:26,080 Speaker 3: that do still live life on the surface, but have 272 00:15:27,120 --> 00:15:31,280 Speaker 3: the ability and sometimes the desire to venture into caves 273 00:15:31,320 --> 00:15:35,120 Speaker 3: or subterranean regions for various reasons. Maybe they want to 274 00:15:35,120 --> 00:15:37,160 Speaker 3: shelter there for a certain period, maybe they want to 275 00:15:37,160 --> 00:15:39,960 Speaker 3: go in there to retrieve some kind of resource, who knows. 276 00:15:40,440 --> 00:15:43,000 Speaker 3: But then there's the other kind, the ones that are 277 00:15:43,040 --> 00:15:46,880 Speaker 3: fully adapted to life in the caves and it has 278 00:15:46,960 --> 00:15:50,480 Speaker 3: shaped their evolution, has shaped their morphology. Now their bodies 279 00:15:50,520 --> 00:15:54,400 Speaker 3: are made for the caves. One of the examples that 280 00:15:54,440 --> 00:15:59,440 Speaker 3: people listening are probably thinking of are sightless fish, fish 281 00:15:59,480 --> 00:16:03,600 Speaker 3: that live in cave based in underground waterways and have 282 00:16:03,680 --> 00:16:08,680 Speaker 3: evolved to completely lose their vision or their eyes. And 283 00:16:08,800 --> 00:16:12,920 Speaker 3: this has long been a really captivating image within evolution 284 00:16:13,200 --> 00:16:16,680 Speaker 3: that the idea, you know, people usually think of evolution 285 00:16:16,920 --> 00:16:21,160 Speaker 3: as a constructive process that sort of powers up an organism. 286 00:16:21,200 --> 00:16:24,320 Speaker 3: It gives it a new ability or a new adaptation 287 00:16:24,480 --> 00:16:28,400 Speaker 3: that better suits it to an environment or an environmental 288 00:16:28,520 --> 00:16:32,800 Speaker 3: niche that it's currently occupying, and so it gets upgraded 289 00:16:32,840 --> 00:16:34,600 Speaker 3: in some way. These are these are ways that we 290 00:16:34,680 --> 00:16:37,400 Speaker 3: sometimes discourage people from thinking about evolution. By the way, 291 00:16:37,440 --> 00:16:39,680 Speaker 3: but it is still in the popular consciousness that that's 292 00:16:39,680 --> 00:16:43,440 Speaker 3: how it works. This is evolution by what might be 293 00:16:43,480 --> 00:16:47,320 Speaker 3: thought of as regression, like losing a trait that you 294 00:16:47,440 --> 00:16:51,400 Speaker 3: previously had. So that raises a lot of questions about 295 00:16:51,400 --> 00:16:54,840 Speaker 3: how evolution works and why something like that would happen. 296 00:16:55,600 --> 00:16:58,040 Speaker 2: You know, it's it's fascinating to think about this about 297 00:16:58,040 --> 00:17:02,640 Speaker 2: our our are often human focused bias and considering evolution 298 00:17:02,720 --> 00:17:06,000 Speaker 2: along these lines. Like we think of that classic illustration 299 00:17:06,080 --> 00:17:09,399 Speaker 2: of the ascent of man, you know, the various Homonid 300 00:17:09,440 --> 00:17:14,280 Speaker 2: species evolving towards man, and it's easy to look at 301 00:17:14,359 --> 00:17:16,879 Speaker 2: him and like think, wow, look, with each step he 302 00:17:17,080 --> 00:17:19,480 Speaker 2: just gets hotter. With each step, he just looks more 303 00:17:19,600 --> 00:17:23,440 Speaker 2: like us, he becomes more perfect, like clearly modern Homo 304 00:17:23,480 --> 00:17:28,040 Speaker 2: sapiens are. But even in that, we're seeing the loss 305 00:17:28,080 --> 00:17:30,840 Speaker 2: of various features. We're seeing like the loss of body 306 00:17:30,880 --> 00:17:31,800 Speaker 2: hair and so forth. 307 00:17:32,240 --> 00:17:35,280 Speaker 3: Yeah, totally, And as you know, big asterisk, if you 308 00:17:35,320 --> 00:17:37,439 Speaker 3: see an old illustration like that, there's probably a lot 309 00:17:37,480 --> 00:17:41,200 Speaker 3: of that's inaccurate about it. But some things that broadly 310 00:17:41,240 --> 00:17:43,600 Speaker 3: would be true is that our ancestors do appear to 311 00:17:43,720 --> 00:17:46,960 Speaker 3: have lost adaptations that made them really good tree climbers 312 00:17:47,480 --> 00:17:51,119 Speaker 3: and those adaptations. Those are adaptations that were very useful 313 00:17:51,119 --> 00:17:53,639 Speaker 3: for our ancestors, and we sort of lost them in 314 00:17:53,680 --> 00:17:54,679 Speaker 3: favor of other things. 315 00:17:55,320 --> 00:17:58,480 Speaker 2: Yeah. And it is also interesting again to think about 316 00:17:58,800 --> 00:18:01,560 Speaker 2: the world of the dark, the world of the caves, because, 317 00:18:01,960 --> 00:18:05,320 Speaker 2: like we said, we can have this experience of turning 318 00:18:05,320 --> 00:18:08,520 Speaker 2: out the lights in the cavern and experiencing the true darkness. 319 00:18:09,920 --> 00:18:13,480 Speaker 2: But for the most part, ever since human beings were 320 00:18:13,480 --> 00:18:16,560 Speaker 2: able to capture fire, we have been able to bring 321 00:18:16,680 --> 00:18:21,000 Speaker 2: light into these spaces. And today when we explore caves, 322 00:18:21,000 --> 00:18:23,960 Speaker 2: at least on our own terms, we have that light 323 00:18:24,000 --> 00:18:28,200 Speaker 2: that we bring with us, and we therefore we don't 324 00:18:28,240 --> 00:18:31,280 Speaker 2: have to we change the environment by bringing light into 325 00:18:31,359 --> 00:18:36,280 Speaker 2: it the cavern. Changing us over evolutionary time, of course, 326 00:18:37,160 --> 00:18:39,640 Speaker 2: is not on the table, that's all right. 327 00:18:39,680 --> 00:18:42,919 Speaker 3: But without the ability to modify the features of the 328 00:18:43,040 --> 00:18:46,399 Speaker 3: environment like that other animals have had to adapt evolutionarily. 329 00:18:46,920 --> 00:18:49,960 Speaker 2: Yeah. And in all this we have to again recognize 330 00:18:50,000 --> 00:18:54,320 Speaker 2: just how vital light is for organisms for the evolution 331 00:18:54,440 --> 00:18:58,680 Speaker 2: of life on our planet. Both sunlight and moonlight are 332 00:18:58,760 --> 00:19:02,400 Speaker 2: in play here, as pointed out by Lauren Summer Rooney 333 00:19:02,440 --> 00:19:04,800 Speaker 2: in the Kingdom of the Blind, published in a twenty 334 00:19:04,840 --> 00:19:09,520 Speaker 2: eighteen edition of Integrated and Comparative Biology. Light is a 335 00:19:09,640 --> 00:19:13,280 Speaker 2: fundamental biological cue for almost every animal on Earth, So 336 00:19:13,520 --> 00:19:15,639 Speaker 2: it's not just about oh can I see the inside 337 00:19:15,680 --> 00:19:17,480 Speaker 2: of the cave or not? You know, it plays in 338 00:19:17,480 --> 00:19:22,000 Speaker 2: a navigation foraging, predator avoidance, mate selection, and just like 339 00:19:22,160 --> 00:19:26,320 Speaker 2: general daily rhythms. So to abandon the world of light 340 00:19:26,960 --> 00:19:29,520 Speaker 2: is no small thing, right, and yet we do see 341 00:19:29,520 --> 00:19:32,960 Speaker 2: plenty of organisms that have done just that over time, 342 00:19:33,560 --> 00:19:36,760 Speaker 2: not only cave organisms but certain creatures of the deep ocean. 343 00:19:37,400 --> 00:19:39,960 Speaker 2: Though we have to remember that site is still important 344 00:19:40,000 --> 00:19:42,840 Speaker 2: at varying levels of the water column and in the 345 00:19:42,880 --> 00:19:48,960 Speaker 2: presence of phosphorescent glows, so there's a fair amount of 346 00:19:48,960 --> 00:19:54,400 Speaker 2: complexity there. The soil and even interiors of host organisms 347 00:19:54,440 --> 00:19:59,080 Speaker 2: for various parasites are also dark environments that species have 348 00:19:59,160 --> 00:19:59,760 Speaker 2: adapted to. 349 00:20:00,200 --> 00:20:00,560 Speaker 3: Mm hmm. 350 00:20:01,160 --> 00:20:03,879 Speaker 2: Now, as Romero points out, Charles Darwin himself was somewhat 351 00:20:03,920 --> 00:20:07,600 Speaker 2: stumped by the loss of sight and cavefishes, and apparently 352 00:20:07,680 --> 00:20:11,240 Speaker 2: ultimately landed on more of a Lamarchian idea that they 353 00:20:11,760 --> 00:20:14,520 Speaker 2: lost their eyes by simply not using them. 354 00:20:14,880 --> 00:20:19,720 Speaker 3: Oh that's kind of interesting. So Lamarckism or Lamarchianism named 355 00:20:19,720 --> 00:20:22,760 Speaker 3: after a figure named I believe you, Jean Baptist Lamark. 356 00:20:23,880 --> 00:20:26,840 Speaker 3: It was a sort of alternative theory of inheritance to 357 00:20:27,000 --> 00:20:30,920 Speaker 3: what would eventually become Mendalian genetics, which in some ways 358 00:20:30,920 --> 00:20:34,280 Speaker 3: has been partially superseded now. But also but instead of 359 00:20:34,320 --> 00:20:38,640 Speaker 3: the kind of Mendalian genetic inheritance, Lamark would say that, 360 00:20:39,080 --> 00:20:42,960 Speaker 3: like the way that an animal uses its body shapes 361 00:20:43,080 --> 00:20:48,240 Speaker 3: the way its offspring the way their bodies are formed. 362 00:20:48,320 --> 00:20:51,159 Speaker 3: So like if you are reaching up a lot or something, 363 00:20:51,240 --> 00:20:54,720 Speaker 3: you might grow your children might have longer arms, or 364 00:20:54,760 --> 00:20:57,960 Speaker 3: like that a giraffe maybe is reaching its neck up 365 00:20:58,000 --> 00:21:01,240 Speaker 3: to reach higher leaves, and that means it's children will 366 00:21:01,240 --> 00:21:03,879 Speaker 3: be born with longer necks and so forth. For the 367 00:21:03,920 --> 00:21:07,160 Speaker 3: most part, evolution doesn't actually work that way. There are 368 00:21:07,240 --> 00:21:12,360 Speaker 3: some kind of things of gene expression and regulatory functions 369 00:21:12,400 --> 00:21:16,399 Speaker 3: epigenetics that some people have argued in minor ways can 370 00:21:16,520 --> 00:21:19,400 Speaker 3: kind of vindicate Lamarckian thinking, but for the most part, 371 00:21:19,440 --> 00:21:21,480 Speaker 3: that's not really how inheritance works. 372 00:21:21,640 --> 00:21:25,280 Speaker 2: Right right, Yeah, I've been to evolutionary talks, I believe 373 00:21:25,280 --> 00:21:28,000 Speaker 2: the World Science Festival for some biologists have been like, yeah, yeah, 374 00:21:28,000 --> 00:21:31,000 Speaker 2: we're kind of we to start talking about epigenetics, sometimes 375 00:21:31,000 --> 00:21:33,960 Speaker 2: we do get a little Lamarckian in the way we're talking, 376 00:21:34,040 --> 00:21:36,200 Speaker 2: so it is kind of fascinating. 377 00:21:36,400 --> 00:21:38,879 Speaker 3: But the Lamarckian idea would be okay, so fish go 378 00:21:38,960 --> 00:21:41,080 Speaker 3: down in a cave and then they don't use their 379 00:21:41,720 --> 00:21:45,200 Speaker 3: eyes because they're living in the dark. Therefore their children 380 00:21:45,680 --> 00:21:49,280 Speaker 3: or their offspring are born without them or born with 381 00:21:49,320 --> 00:21:51,720 Speaker 3: eyes that regress. We can talk about that difference in 382 00:21:51,720 --> 00:21:55,880 Speaker 3: a minute, and in a way you could say that 383 00:21:55,880 --> 00:21:59,800 Speaker 3: that's loosely kind of right, but it's somewhat different. I 384 00:21:59,800 --> 00:22:02,679 Speaker 3: think think I would say that the important thing is 385 00:22:02,800 --> 00:22:05,560 Speaker 3: not that the fish don't use their eyes, it's that 386 00:22:05,600 --> 00:22:08,560 Speaker 3: they don't need them, so that the eye no longer 387 00:22:08,640 --> 00:22:11,360 Speaker 3: confers a survival or reproductive advantage. 388 00:22:11,880 --> 00:22:14,120 Speaker 2: I think the one of the infectious things about it, 389 00:22:14,200 --> 00:22:18,359 Speaker 2: at least for non scientists, is that it can feel 390 00:22:18,520 --> 00:22:21,120 Speaker 2: right in certain ways. Right. It can sort of match 391 00:22:21,280 --> 00:22:24,879 Speaker 2: up with at least the individual human experience. So we 392 00:22:24,960 --> 00:22:27,639 Speaker 2: might not think, like, man, I better go to the 393 00:22:27,680 --> 00:22:30,200 Speaker 2: gym and need to pump iron so that my offspring 394 00:22:30,240 --> 00:22:34,199 Speaker 2: will will have strong arms. But we might think, oh, well, 395 00:22:34,200 --> 00:22:36,400 Speaker 2: I've got to keep pumping iron otherwise my arms will 396 00:22:36,400 --> 00:22:38,600 Speaker 2: get smaller. You know, I've got to do X so 397 00:22:38,640 --> 00:22:41,960 Speaker 2: that why doesn't happen? And you know, I think we 398 00:22:42,280 --> 00:22:45,560 Speaker 2: do see this infectious idea in some of our fictions 399 00:22:45,600 --> 00:22:49,600 Speaker 2: of subterranean monsters, including the Descent of the Hobbit Smeekeel 400 00:22:49,640 --> 00:22:51,840 Speaker 2: and the Lord of the Rings, who becomes a trogloditic 401 00:22:51,880 --> 00:22:54,640 Speaker 2: Gollum in the course of a single though of course 402 00:22:54,720 --> 00:22:58,480 Speaker 2: magically sustained lifetime. He doesn't really become blind or anything, 403 00:22:58,520 --> 00:23:01,120 Speaker 2: but generally he's depicted as you know, he's changed a lot. 404 00:23:01,160 --> 00:23:04,400 Speaker 2: He's lost his hair, his pigmentation has changed, his eyes 405 00:23:04,440 --> 00:23:05,800 Speaker 2: have gotten larger, I believe. 406 00:23:06,480 --> 00:23:09,560 Speaker 3: Yeah, though I think the morphotypical changes of Gollum could 407 00:23:09,560 --> 00:23:12,480 Speaker 3: be largely due to the corruption of the one Ring. 408 00:23:13,040 --> 00:23:15,680 Speaker 2: That's the thing. The one ring changes everything. You've got 409 00:23:16,160 --> 00:23:22,679 Speaker 2: a huge magical factor to consider in that scenario. But 410 00:23:22,800 --> 00:23:24,760 Speaker 2: sort of just the idea of it is like, yeah, 411 00:23:24,760 --> 00:23:27,600 Speaker 2: people go into caves, they get weird, they turn into monsters, 412 00:23:28,119 --> 00:23:30,600 Speaker 2: or if they're not a monster, you know, weight three generations, 413 00:23:30,640 --> 00:23:31,840 Speaker 2: then just pure monsters. 414 00:23:32,520 --> 00:23:33,359 Speaker 3: Caves will do that. 415 00:23:34,760 --> 00:23:36,960 Speaker 2: Now, Summer Rooney points out that we're still working out 416 00:23:36,960 --> 00:23:39,280 Speaker 2: all the details, but we know much more than Darwin 417 00:23:39,359 --> 00:23:41,199 Speaker 2: did in his time. Of course, the science has come 418 00:23:42,320 --> 00:23:44,800 Speaker 2: quite a way since then in our understanding of how 419 00:23:44,960 --> 00:23:48,359 Speaker 2: creatures evolve and what sort of changes are taking place 420 00:23:48,359 --> 00:23:53,360 Speaker 2: over revolutionary time. The author rights quote eye loss appears 421 00:23:53,359 --> 00:23:56,640 Speaker 2: to be driven at least in part by direct selective pressure, 422 00:23:57,280 --> 00:24:03,040 Speaker 2: but both pliotrophy and genetic are also key influencers. Despite 423 00:24:03,080 --> 00:24:06,720 Speaker 2: substantial recent progress thanks to a combination of developmental and 424 00:24:06,760 --> 00:24:10,720 Speaker 2: molecular techniques, it is not yet clear how these drivers interact, 425 00:24:10,800 --> 00:24:15,040 Speaker 2: or crucially, whether their relationships are similar across taxa and 426 00:24:15,080 --> 00:24:16,080 Speaker 2: habitat types. 427 00:24:17,200 --> 00:24:19,879 Speaker 3: Yeah, so this was really interesting, and I ended up 428 00:24:20,280 --> 00:24:23,360 Speaker 3: going kind of deep on what we do know about 429 00:24:23,680 --> 00:24:28,200 Speaker 3: eye loss and a related issue of pigmentation loss in 430 00:24:28,600 --> 00:24:31,320 Speaker 3: cave fish. But I wanted to break down some of 431 00:24:31,359 --> 00:24:34,520 Speaker 3: the terms that this author uses in that paragraph you 432 00:24:34,680 --> 00:24:39,359 Speaker 3: just read. So selective pressure, of course would mean an 433 00:24:39,440 --> 00:24:43,640 Speaker 3: advantage in terms of survival or reproduction, a direct advantage. 434 00:24:44,119 --> 00:24:46,280 Speaker 3: That's the kind of evolution we think about most often. 435 00:24:46,480 --> 00:24:50,440 Speaker 3: But there are two other factors that could be influencing 436 00:24:50,520 --> 00:24:53,359 Speaker 3: the loss of eyes or the loss of pigmentation in 437 00:24:53,440 --> 00:24:56,920 Speaker 3: fish that the author mentions, and those are plyotrophy and 438 00:24:57,280 --> 00:25:03,200 Speaker 3: genetic drift. Plyotropy, to sort of oversimplify, means when one 439 00:25:03,560 --> 00:25:08,720 Speaker 3: gene determines multiple outcomes in the phenotype, and the phenotype 440 00:25:08,760 --> 00:25:11,560 Speaker 3: is like the body or the behavior of the organism. 441 00:25:11,600 --> 00:25:15,680 Speaker 3: It's what the genes produce in the animal. So, for example, 442 00:25:15,840 --> 00:25:18,919 Speaker 3: imagine there is a mutation at one locust, and that 443 00:25:19,000 --> 00:25:23,560 Speaker 3: one mutation happens to both give you smaller eyes but 444 00:25:23,800 --> 00:25:28,800 Speaker 3: also longer arms. Or maybe there's a mutation that happened 445 00:25:28,840 --> 00:25:33,040 Speaker 3: to give you both higher rates of cancer and higher 446 00:25:33,080 --> 00:25:37,600 Speaker 3: average fertility. And pliotropies like these can They're very interesting 447 00:25:37,640 --> 00:25:40,840 Speaker 3: because they can sometimes explain the evolution of traits that 448 00:25:41,280 --> 00:25:46,600 Speaker 3: would seem to be disadvantageous because the seemingly bad trait 449 00:25:46,760 --> 00:25:49,840 Speaker 3: is actually part of a hidden package deal, a genetic 450 00:25:49,920 --> 00:25:54,600 Speaker 3: package deal with an even more advantageous trait balancing it out. 451 00:25:55,680 --> 00:25:58,640 Speaker 3: You can get either both or neither, but not one 452 00:25:58,720 --> 00:26:02,880 Speaker 3: by itself. So in the case of cavefish, it's possible 453 00:26:03,040 --> 00:26:06,800 Speaker 3: there is a single mutation that both causes the loss 454 00:26:06,840 --> 00:26:10,720 Speaker 3: of eyes but also does something else that helps the 455 00:26:10,760 --> 00:26:13,919 Speaker 3: fish survive and reproduce. And since there's little to no 456 00:26:14,119 --> 00:26:16,920 Speaker 3: penalty attending the loss of vision in the pitch black 457 00:26:16,920 --> 00:26:20,760 Speaker 3: cave environment, the helpful half of that pliotropy wins out 458 00:26:21,160 --> 00:26:23,159 Speaker 3: and the two for one version of the gene is 459 00:26:23,200 --> 00:26:26,879 Speaker 3: selected for. And then the final factor mentioned here is 460 00:26:27,160 --> 00:26:30,520 Speaker 3: genetic drift. Genetic drift is change in the frequency of 461 00:26:30,560 --> 00:26:34,240 Speaker 3: gene variants within a population due to random chance. So 462 00:26:34,440 --> 00:26:38,160 Speaker 3: genes becoming more or less prevalent within a group of organisms, 463 00:26:39,160 --> 00:26:43,320 Speaker 3: not for selective reasons, not because they help or hurt 464 00:26:43,320 --> 00:26:46,359 Speaker 3: the organism, but just randomly, you know. And this happens 465 00:26:46,359 --> 00:26:49,840 Speaker 3: all the time. Gene variants just become more common less 466 00:26:49,880 --> 00:26:54,000 Speaker 3: common within a population, and it happens due to random factors. 467 00:26:54,560 --> 00:26:58,080 Speaker 3: Though sometimes if a population is small enough. An interesting 468 00:26:58,160 --> 00:27:02,040 Speaker 3: thing is that traits result from random genetic drift can 469 00:27:02,160 --> 00:27:06,360 Speaker 3: become what's called fixed, meaning that you kind of hit 470 00:27:06,400 --> 00:27:10,040 Speaker 3: a genetic tipping point and a trait that was randomly 471 00:27:10,080 --> 00:27:14,200 Speaker 3: fluctuating up and down in the population it becomes prevalent 472 00:27:14,320 --> 00:27:17,600 Speaker 3: enough that suddenly it's fixed, and then all the individuals 473 00:27:17,640 --> 00:27:21,040 Speaker 3: within the population have the gene for that trait. Going forward. 474 00:27:21,600 --> 00:27:24,879 Speaker 2: Yeah, now, now, going back to what you mentioned about 475 00:27:24,920 --> 00:27:28,160 Speaker 2: the idea of there possibly being like an advantage and 476 00:27:28,240 --> 00:27:32,800 Speaker 2: a disadvantage tied up in one change, but The thing is, 477 00:27:32,840 --> 00:27:36,359 Speaker 2: you find yourself, if you're this fish undergoing this change 478 00:27:36,440 --> 00:27:40,200 Speaker 2: or some other organism, you find yourself in a lightless environment. 479 00:27:40,680 --> 00:27:44,520 Speaker 2: And so in this you dip over into the neutral 480 00:27:44,600 --> 00:27:49,879 Speaker 2: mutation hypothesis, This idea that while naturally occurring mutations for 481 00:27:50,000 --> 00:27:52,919 Speaker 2: in this case blindness would otherwise spell doom for a 482 00:27:52,960 --> 00:27:56,280 Speaker 2: fish in a typical environment, in a lighted environment, it 483 00:27:56,320 --> 00:27:59,640 Speaker 2: doesn't matter in the darkness, and therefore these mutations can 484 00:27:59,720 --> 00:28:03,760 Speaker 2: flirt along with whatever other changes they might be bringing. 485 00:28:04,840 --> 00:28:05,280 Speaker 2: That's right. 486 00:28:05,320 --> 00:28:07,720 Speaker 3: Then they can flourish for multiple reasons. They could flourish 487 00:28:07,800 --> 00:28:11,160 Speaker 3: because they're part of a plotropy that has an advantage 488 00:28:11,200 --> 00:28:13,800 Speaker 3: on the other half, or they can just flourish randomly 489 00:28:13,880 --> 00:28:17,359 Speaker 3: through genetic drift because there's no penalty to the loss 490 00:28:17,359 --> 00:28:19,040 Speaker 3: of sight in the in the darkness. 491 00:28:19,960 --> 00:28:24,280 Speaker 2: Yeah, this I can't help be reminded of various like 492 00:28:24,640 --> 00:28:27,320 Speaker 2: gaming rules and gaming systems and all of this. Like 493 00:28:27,400 --> 00:28:30,440 Speaker 2: it's it's like, imagine that you're playing Dungeons and Dragons 494 00:28:30,480 --> 00:28:32,800 Speaker 2: and let's say you're venturing into the under dark. You're 495 00:28:32,880 --> 00:28:35,760 Speaker 2: venturing into a lightless environment, and you have a weapon 496 00:28:36,200 --> 00:28:40,920 Speaker 2: that gives you, say a plus two on attack. But 497 00:28:41,520 --> 00:28:45,320 Speaker 2: if you're in the sunlight, it has your hit points 498 00:28:45,360 --> 00:28:47,600 Speaker 2: or something like something that would make this all right. 499 00:28:47,640 --> 00:28:51,080 Speaker 2: It has advantages to it, but the disadvantage is far 500 00:28:51,160 --> 00:28:53,960 Speaker 2: outweigh it in a different environment, but you're not in 501 00:28:54,000 --> 00:28:57,000 Speaker 2: that environment. Now you're in an environment where the disadvantage 502 00:28:57,040 --> 00:28:57,880 Speaker 2: does not matter. 503 00:28:58,320 --> 00:29:01,720 Speaker 3: Right. Yes, that's analogy, and it's also a good reason 504 00:29:01,720 --> 00:29:04,680 Speaker 3: to remember to check your build when your environment changes. 505 00:29:08,160 --> 00:29:11,440 Speaker 3: But yeah, so there is, as we're saying, some possibility 506 00:29:11,520 --> 00:29:14,520 Speaker 3: for all of these options in explaining the evolution of 507 00:29:15,240 --> 00:29:19,120 Speaker 3: cavefish blindness. There could be direct selective pressure, there could 508 00:29:19,120 --> 00:29:23,320 Speaker 3: be indirect selective pressure through pliotropy or the package deal, 509 00:29:23,640 --> 00:29:27,720 Speaker 3: and there could be random genetic drift. However, it seems 510 00:29:28,080 --> 00:29:30,960 Speaker 3: that there is some pretty good evidence for the presence 511 00:29:31,000 --> 00:29:34,520 Speaker 3: of a direct selective pressure for fish to lose their 512 00:29:34,560 --> 00:29:37,239 Speaker 3: eyes when they live in a lightless environment, and there 513 00:29:37,320 --> 00:29:40,280 Speaker 3: might be some evidence for plotropy as well. So to 514 00:29:40,280 --> 00:29:42,280 Speaker 3: get a more concrete idea of what we're talking about, 515 00:29:42,360 --> 00:29:45,080 Speaker 3: I wanted to focus on a particular species of fish 516 00:29:45,600 --> 00:29:48,760 Speaker 3: that has been studied a lot, and that species is 517 00:29:48,800 --> 00:29:54,560 Speaker 3: called Astianax mexicanus, also known as the blind Mexican cave fish, 518 00:29:55,000 --> 00:29:59,240 Speaker 3: also known as the blind cave tetra. These are small 519 00:30:00,360 --> 00:30:04,920 Speaker 3: like fish with silver scales. I saw different size estimates 520 00:30:04,960 --> 00:30:06,920 Speaker 3: for them. Some said they grow to a maximum length 521 00:30:06,960 --> 00:30:11,120 Speaker 3: of about nine centimeters. Other sources said about twelve centimeters, 522 00:30:11,120 --> 00:30:15,400 Speaker 3: but they're relatively small in any case. One thing that 523 00:30:15,520 --> 00:30:19,880 Speaker 3: makes these Astianax fish very interesting is that there exist 524 00:30:20,080 --> 00:30:25,800 Speaker 3: both surface or epigean and cave or hypogean variants of 525 00:30:25,840 --> 00:30:29,400 Speaker 3: the same fish species, and they have different body features. 526 00:30:29,800 --> 00:30:33,880 Speaker 3: And scientists can learn a lot by comparing these extremely 527 00:30:34,000 --> 00:30:38,280 Speaker 3: closely related populations of animals to one another, cross checking 528 00:30:38,760 --> 00:30:41,920 Speaker 3: genomic information back and forth, and seeing what that correlates 529 00:30:41,960 --> 00:30:46,080 Speaker 3: to in terms of their phenotypic traits. So the cave 530 00:30:46,320 --> 00:30:50,360 Speaker 3: variant of Astianax lives in this big network of underground 531 00:30:50,360 --> 00:30:55,960 Speaker 3: waterways in the mountainous areas of northeastern Mexico, and they've 532 00:30:55,960 --> 00:30:58,600 Speaker 3: been in these caves since. One source I was reading 533 00:30:59,000 --> 00:31:01,440 Speaker 3: said they colonize them probably around the end of the 534 00:31:01,480 --> 00:31:04,760 Speaker 3: Pleistocene epic, so you know, roughly twelve thousand years ago 535 00:31:04,880 --> 00:31:07,280 Speaker 3: or so. There are photos you can find online which 536 00:31:07,280 --> 00:31:10,320 Speaker 3: I'd recommend looking up, which not only show the cave 537 00:31:10,600 --> 00:31:15,120 Speaker 3: variant of Astianax, but They depict the cave variant and 538 00:31:15,200 --> 00:31:19,040 Speaker 3: the surface variant side by side to highlight the differences 539 00:31:19,080 --> 00:31:22,320 Speaker 3: in their bodies. So the cave version is much more 540 00:31:22,520 --> 00:31:26,600 Speaker 3: pale and translucent. And indeed, in the places where the 541 00:31:26,640 --> 00:31:30,160 Speaker 3: surface variant has a big, old, bulging fish eye on 542 00:31:30,200 --> 00:31:33,840 Speaker 3: either side of its skull, the cave variant has only 543 00:31:33,880 --> 00:31:38,920 Speaker 3: a strange, fatty looking lump underneath its scales, just in 544 00:31:38,920 --> 00:31:40,560 Speaker 3: front of the red flap of the gill. 545 00:31:41,080 --> 00:31:44,640 Speaker 2: Yeah, these are haunting images to look at. Again, we 546 00:31:44,680 --> 00:31:47,600 Speaker 2: can't help but think of like various sneakels and so 547 00:31:47,680 --> 00:31:49,360 Speaker 2: forth when looking at it. 548 00:31:49,600 --> 00:31:51,680 Speaker 3: Yeah, exactly, And I bet these fish are good at 549 00:31:51,760 --> 00:31:54,640 Speaker 3: riddle games. Now. One thing that I was reading this 550 00:31:54,720 --> 00:31:59,240 Speaker 3: kind of interesting about these the eyeless variant of the 551 00:31:59,640 --> 00:32:07,080 Speaker 3: Asti annex fish, is that they undergo what's called eye regression. 552 00:32:07,360 --> 00:32:09,840 Speaker 3: So I don't know if this is true of all populations, 553 00:32:09,880 --> 00:32:13,000 Speaker 3: because they're like different cave populations of this fish that 554 00:32:13,040 --> 00:32:15,880 Speaker 3: have been studied, and they have some differences between them. 555 00:32:16,520 --> 00:32:19,280 Speaker 3: But I was reading at least in some populations what 556 00:32:19,360 --> 00:32:23,640 Speaker 3: happens is not that these fish never have eyes, but 557 00:32:23,720 --> 00:32:27,239 Speaker 3: they begin to grow eyes during embryonic development and then 558 00:32:27,280 --> 00:32:31,440 Speaker 3: as they develop. They they acquire eyes and then lose 559 00:32:31,520 --> 00:32:35,840 Speaker 3: the eyes in development, and the eye sockets are paved 560 00:32:35,880 --> 00:32:39,000 Speaker 3: over by skin and scales, and they there remain these 561 00:32:39,000 --> 00:32:41,640 Speaker 3: little fatty lumps where the sockets used to be, and 562 00:32:41,680 --> 00:32:44,800 Speaker 3: the bone kind of collapses around it. So I thought 563 00:32:44,800 --> 00:32:46,400 Speaker 3: this was kind of interesting. It's not just that they 564 00:32:46,440 --> 00:32:49,760 Speaker 3: never have eyes. They get eyes and then they lose them, 565 00:32:49,840 --> 00:32:52,760 Speaker 3: all in the process of a single animal growing up. 566 00:32:53,200 --> 00:32:56,160 Speaker 2: Fascinating, you know. I also have to throw in, okay, 567 00:32:56,280 --> 00:33:01,080 Speaker 2: ASTI annex part of the scientice name for the creature. 568 00:33:01,600 --> 00:33:05,160 Speaker 2: This is the son of Hector in the Iliad, and 569 00:33:05,640 --> 00:33:09,760 Speaker 2: I'm guessing here. I couldn't find anything just definitive offhand, 570 00:33:10,400 --> 00:33:14,040 Speaker 2: but I'm assuming the naming here is because Astianax, the 571 00:33:14,160 --> 00:33:17,680 Speaker 2: child of Hector, is hidden in the tombs. That is 572 00:33:17,720 --> 00:33:20,440 Speaker 2: the way that they try to ensure his survival. And 573 00:33:20,480 --> 00:33:23,360 Speaker 2: so you know, we see some version of that here, 574 00:33:23,400 --> 00:33:28,400 Speaker 2: a survival in the underworld of the caves as opposed 575 00:33:28,400 --> 00:33:28,880 Speaker 2: to the tomb. 576 00:33:29,680 --> 00:33:42,040 Speaker 3: I did not make that connection. That is interesting. So 577 00:33:42,280 --> 00:33:46,200 Speaker 3: I mentioned that there was some evidence that actual selection pressure, 578 00:33:46,320 --> 00:33:49,840 Speaker 3: a direct selection pressure, drove the evolution of eyelessness in 579 00:33:49,920 --> 00:33:54,120 Speaker 3: these fish, as well as some possible evidence for pliotropy. 580 00:33:54,800 --> 00:33:56,520 Speaker 3: Let's look at a paper to learn more. 581 00:33:57,040 --> 00:33:57,160 Speaker 1: So. 582 00:33:57,200 --> 00:34:00,240 Speaker 3: The paper I was reading is called Cavefish and the 583 00:34:00,280 --> 00:34:05,120 Speaker 3: Basis for Eye Loss by Jaya Krishnan and Nicholas Rohner, 584 00:34:05,560 --> 00:34:09,879 Speaker 3: published in Philosophical Transactions of the Royal Society b Biological 585 00:34:09,880 --> 00:34:14,200 Speaker 3: Sciences twenty seventeen, and in the section of their paper 586 00:34:14,840 --> 00:34:18,239 Speaker 3: discussing the reasons for eye loss, the authors note that 587 00:34:19,040 --> 00:34:22,280 Speaker 3: it is not unique to the example of these blind 588 00:34:22,280 --> 00:34:25,840 Speaker 3: Mexican cavefish for an animal to evolve by losing a 589 00:34:25,920 --> 00:34:29,680 Speaker 3: trait or characteristic that was once positively selected for in 590 00:34:29,760 --> 00:34:34,160 Speaker 3: that animal's ancestors. Examples include the loss of tails in 591 00:34:34,239 --> 00:34:38,400 Speaker 3: some primates, including us, the loss of teeth in birds, 592 00:34:38,480 --> 00:34:41,480 Speaker 3: and the loss of legs in Wales. All of these 593 00:34:41,480 --> 00:34:45,960 Speaker 3: are examples where an animal lineage acquired an adaptation that 594 00:34:46,120 --> 00:34:49,319 Speaker 3: was useful long ago, and then some branch of that 595 00:34:49,360 --> 00:34:53,800 Speaker 3: lineage entered a new ecological niche in which that trait 596 00:34:53,880 --> 00:34:57,320 Speaker 3: was no longer useful or was actively harmful, and evolved 597 00:34:57,360 --> 00:35:00,600 Speaker 3: once again to lose the trait that its ancestor bodies 598 00:35:00,640 --> 00:35:05,239 Speaker 3: had constructed so long ago. And the example of cavefish 599 00:35:05,280 --> 00:35:08,880 Speaker 3: that lost their eyes was long simply assumed to be 600 00:35:09,040 --> 00:35:13,240 Speaker 3: a result of genetic drift. Eyelessness appears in the gene pool, 601 00:35:13,560 --> 00:35:17,160 Speaker 3: and then with no selection pressure favoring eyes to keep 602 00:35:17,200 --> 00:35:21,480 Speaker 3: the eyelessness suppressed, it would just randomly fluctuate and frequency 603 00:35:21,560 --> 00:35:25,520 Speaker 3: in the gene pool until at some point it became fixed. However, 604 00:35:26,040 --> 00:35:28,800 Speaker 3: the authors say that in roughly the last decade before 605 00:35:28,800 --> 00:35:31,440 Speaker 3: this paper, and this was again twenty seventeen, there had 606 00:35:31,440 --> 00:35:35,120 Speaker 3: been more attention to the possibility of a positive selection 607 00:35:35,280 --> 00:35:38,520 Speaker 3: pressure favoring the loss of eyes. There's a reason to 608 00:35:38,640 --> 00:35:43,799 Speaker 3: lose the eyes, either directly or through pliotropy, So let's 609 00:35:43,880 --> 00:35:48,760 Speaker 3: talk direct selection first. The main explanation offered for direct 610 00:35:48,800 --> 00:35:53,719 Speaker 3: selection against eyes is energy conservation, also sometimes expressed as 611 00:35:53,840 --> 00:35:59,359 Speaker 3: metabolic cost. It costs energy the energy that animals get 612 00:35:59,440 --> 00:36:04,040 Speaker 3: from food food to have functioning organs, and some types 613 00:36:04,040 --> 00:36:07,799 Speaker 3: of organs are more energy hungry than others. In fact, 614 00:36:07,880 --> 00:36:11,800 Speaker 3: the authors demonstrate that neural tissue, which includes brain cells 615 00:36:11,840 --> 00:36:14,840 Speaker 3: and also eyes and nerves, that type of tissue is 616 00:36:14,840 --> 00:36:17,920 Speaker 3: one of the most expensive types that an animal can 617 00:36:17,960 --> 00:36:21,799 Speaker 3: grow and maintain. So any animal's evolution is guided by 618 00:36:21,840 --> 00:36:26,279 Speaker 3: a balancing of interests. The benefits provided by sensory awareness 619 00:36:26,719 --> 00:36:30,800 Speaker 3: and the high metabolic cost of having this neural tissue 620 00:36:30,800 --> 00:36:34,160 Speaker 3: of having these systems. This is true in any animal 621 00:36:34,600 --> 00:36:38,040 Speaker 3: in any environment, but the balance is especially crucial in 622 00:36:38,160 --> 00:36:43,360 Speaker 3: harsh environments like caves, where food energy is more scarce 623 00:36:43,480 --> 00:36:45,920 Speaker 3: than on the surface. It's harder to come by food 624 00:36:46,040 --> 00:36:47,960 Speaker 3: energy in a cave than it is in the surface 625 00:36:48,000 --> 00:36:51,960 Speaker 3: waters where the surface variant of the Mexican cavefish lives. 626 00:36:52,640 --> 00:36:56,400 Speaker 3: And in favor of this explanation the energy cost explanation 627 00:36:57,000 --> 00:36:59,879 Speaker 3: the author's side of paper from twenty fifteen by Moran 628 00:37:00,080 --> 00:37:03,319 Speaker 3: and Softly and Warrant published in Science Advances called the 629 00:37:03,480 --> 00:37:08,800 Speaker 3: Energetic Cost of Vision and Evolution of Eyeless Mexican Cavefish, 630 00:37:08,840 --> 00:37:13,200 Speaker 3: summarizing the findings of Meranatol, Krishnan and Rohner write quote, 631 00:37:13,520 --> 00:37:18,480 Speaker 3: this study calculated significant metabolic costs for the optic tectum, 632 00:37:18,680 --> 00:37:21,440 Speaker 3: and the tectum is the part of the fish's brain 633 00:37:22,000 --> 00:37:25,160 Speaker 3: that is used to process visual information going on with 634 00:37:25,200 --> 00:37:28,800 Speaker 3: the quote and the eyes adding up to fifteen percent 635 00:37:29,000 --> 00:37:33,040 Speaker 3: of the resting metabolism needs in juvenile fish. Such a 636 00:37:33,200 --> 00:37:36,040 Speaker 3: high cost of vision almost reaching the cost of the 637 00:37:36,160 --> 00:37:39,920 Speaker 3: human brain at twenty to twenty five percent makes an 638 00:37:39,960 --> 00:37:44,040 Speaker 3: adaptive loss of eyes owing to energy constraints highly probable. 639 00:37:45,280 --> 00:37:48,480 Speaker 3: So usually there's a high energy cost you need to 640 00:37:48,480 --> 00:37:52,200 Speaker 3: eat a lot of food to grow and sustain the 641 00:37:52,320 --> 00:37:57,040 Speaker 3: sensory organs and visual processing in the brain tissue. But 642 00:37:57,239 --> 00:38:00,759 Speaker 3: on the surface, evolution is usually willing to pay that 643 00:38:00,880 --> 00:38:04,759 Speaker 3: cost because it's really beneficial to get visual information about 644 00:38:04,800 --> 00:38:08,080 Speaker 3: your surroundings that really helps you survive and reproduce. If 645 00:38:08,120 --> 00:38:12,279 Speaker 3: getting visual information about your surroundings becomes impossible because you 646 00:38:12,320 --> 00:38:15,280 Speaker 3: live in total darkness, it's time to make budget cuts. 647 00:38:16,040 --> 00:38:19,680 Speaker 3: Another possible direct selection factor I haven't come across direct 648 00:38:19,719 --> 00:38:22,319 Speaker 3: evidence for this, but it's just mentioned as a possibility 649 00:38:22,360 --> 00:38:25,960 Speaker 3: by several sources, and that is that eyes are also 650 00:38:26,120 --> 00:38:29,480 Speaker 3: a liability in that they are prone to injury and 651 00:38:29,520 --> 00:38:32,719 Speaker 3: an entry way for infection. So it's kind of like 652 00:38:32,840 --> 00:38:36,160 Speaker 3: why would you put a windshield on your armored vehicle 653 00:38:36,360 --> 00:38:39,400 Speaker 3: if you're driving in pitch black with no headlights. It 654 00:38:39,400 --> 00:38:44,320 Speaker 3: would just be a functionless weak point in the armor 655 00:38:44,360 --> 00:38:47,880 Speaker 3: of the vehicle that provides no benefit. And it's possible 656 00:38:47,920 --> 00:38:50,880 Speaker 3: that eyes are like this also. Once there's nothing to see, 657 00:38:51,480 --> 00:38:54,000 Speaker 3: all they would be is a soft spot to let 658 00:38:54,160 --> 00:38:56,120 Speaker 3: germs and sharp objects in. 659 00:38:56,920 --> 00:39:00,279 Speaker 2: Yeah, kind of like with sci fi visions of spaceships, right, 660 00:39:00,360 --> 00:39:07,760 Speaker 2: like why have an actual observation lounge or observation bubble 661 00:39:07,960 --> 00:39:12,520 Speaker 2: or so forth, Why have actual glass there or any 662 00:39:12,600 --> 00:39:15,880 Speaker 2: kind of like transparent wall when you can if you 663 00:39:15,960 --> 00:39:21,320 Speaker 2: have like ubiquitous abilities to have video footage and screens 664 00:39:21,400 --> 00:39:23,320 Speaker 2: around you. Basically the star. 665 00:39:23,160 --> 00:39:27,480 Speaker 3: Trek principle exactly, if it's not actually providing you a benefit, 666 00:39:27,920 --> 00:39:29,480 Speaker 3: then it's just a liability. 667 00:39:29,760 --> 00:39:30,120 Speaker 2: Yeah. 668 00:39:30,280 --> 00:39:33,279 Speaker 3: Also, the authors of this paper mention some evidence for 669 00:39:33,520 --> 00:39:38,160 Speaker 3: indirect selection or pliotropy. Specifically, they bring up a signaling 670 00:39:38,239 --> 00:39:43,359 Speaker 3: pathway identified in the scientific literature as SHH. And do 671 00:39:43,400 --> 00:39:46,040 Speaker 3: you want to guess what SHH stands for? 672 00:39:47,760 --> 00:39:47,920 Speaker 2: Now? 673 00:39:47,960 --> 00:39:51,920 Speaker 3: Tell me what stands for sonic hedgehog. That's really what 674 00:39:51,960 --> 00:39:55,560 Speaker 3: they say, and that's what it is, really, Yes, scientific papers, 675 00:39:55,640 --> 00:39:58,680 Speaker 3: this is the sonic hedgehog signaling pathway. There's also just 676 00:39:58,719 --> 00:40:01,880 Speaker 3: an HH or hedgehog pathway, so I don't know attacking 677 00:40:01,920 --> 00:40:04,520 Speaker 3: on maybe that was discovered first, and then they tacked 678 00:40:04,560 --> 00:40:07,080 Speaker 3: on sonic to be funny for this other pathway. I 679 00:40:07,080 --> 00:40:09,280 Speaker 3: don't know for sure, but it is called the sonic 680 00:40:09,360 --> 00:40:12,359 Speaker 3: hedgehog signaling pathway and the signaling pathway, by the way, 681 00:40:12,480 --> 00:40:16,200 Speaker 3: is it's like a series of chemical reactions in the 682 00:40:16,200 --> 00:40:20,520 Speaker 3: body that controls and coordinates the activity of cells in 683 00:40:20,640 --> 00:40:24,200 Speaker 3: order to do things like grow new tissue during development, 684 00:40:24,400 --> 00:40:27,560 Speaker 3: or cause an immune system response or something like that. 685 00:40:28,320 --> 00:40:33,719 Speaker 3: The sonic hedgehog pathway in particular seems important during embryonic development. 686 00:40:33,800 --> 00:40:37,120 Speaker 3: It sort of guides growth and plays a role in 687 00:40:37,200 --> 00:40:40,880 Speaker 3: the patterning of tissues that emerge from the growth process. 688 00:40:41,160 --> 00:40:44,759 Speaker 3: So Krishnan and Rohner point to a study by Yamamoto 689 00:40:44,840 --> 00:40:47,719 Speaker 3: at all from twenty nine, not twenty nineteen, from two 690 00:40:47,760 --> 00:40:51,840 Speaker 3: thousand and nine, sorry, in Developmental biology, which found that 691 00:40:52,040 --> 00:40:56,840 Speaker 3: by altering expression of the sonic hedgehog signaling pathway in 692 00:40:56,960 --> 00:41:01,400 Speaker 3: embryos of the surface dwelling relative of the blind Mexican cavefish, 693 00:41:01,760 --> 00:41:05,239 Speaker 3: you would actually get multiple changes together. This is our 694 00:41:05,280 --> 00:41:08,279 Speaker 3: package deal. You would get regression of the eyes like 695 00:41:08,320 --> 00:41:10,040 Speaker 3: we talked about, so the eyes would sort of like 696 00:41:10,120 --> 00:41:12,799 Speaker 3: be absorbed and you would no longer have functioning eyes 697 00:41:12,840 --> 00:41:16,440 Speaker 3: as an adult fish. But you would also get enhancement 698 00:41:16,640 --> 00:41:21,160 Speaker 3: of taste, buds and jaws. So that's your package deal. 699 00:41:21,600 --> 00:41:24,120 Speaker 3: And in the dark you can imagine why that would 700 00:41:24,160 --> 00:41:28,000 Speaker 3: be a good package deal. The author's write quote SAHH 701 00:41:28,160 --> 00:41:31,520 Speaker 3: has wide range effects on the development of various organs, 702 00:41:31,840 --> 00:41:34,319 Speaker 3: and it has been identified as a strong candidate for 703 00:41:34,400 --> 00:41:38,640 Speaker 3: eye regression. Its elevated expression in the oral pharyngial region 704 00:41:38,880 --> 00:41:42,600 Speaker 3: in cavefish taste buds, and the fact that eye size 705 00:41:42,600 --> 00:41:46,120 Speaker 3: and number of taste buds are correlated in hybrids makes 706 00:41:46,280 --> 00:41:50,680 Speaker 3: SAHH a promising candidate for functional studies. So that's another 707 00:41:50,880 --> 00:41:54,959 Speaker 3: factor possibly at work here. So to review, you got 708 00:41:55,040 --> 00:41:57,560 Speaker 3: eyes and visual tissue in the brain require a lot 709 00:41:57,560 --> 00:42:00,759 Speaker 3: of food to sustain, and food is especially scarce in 710 00:42:00,800 --> 00:42:03,360 Speaker 3: the cave. Also, the eyes are not really useful in 711 00:42:03,400 --> 00:42:06,160 Speaker 3: the cave, so you know, the trade off there seems 712 00:42:06,160 --> 00:42:09,120 Speaker 3: pretty obvious. There's less evidence for this, but it has 713 00:42:09,160 --> 00:42:12,160 Speaker 3: been suggested that eyes are also a liability in terms 714 00:42:12,200 --> 00:42:15,680 Speaker 3: of infection and injury, and it seems there are certain 715 00:42:15,760 --> 00:42:19,839 Speaker 3: genetic and developmental changes that offer a package deal where 716 00:42:19,880 --> 00:42:22,719 Speaker 3: you get eye regression, your eyes are absorbed, you have 717 00:42:22,800 --> 00:42:26,320 Speaker 3: no eyes as an adult fish, but more taste buds 718 00:42:26,400 --> 00:42:28,479 Speaker 3: and in the dark. That's a good deal to take 719 00:42:28,920 --> 00:42:31,520 Speaker 3: because remember taste buds. We think of them mainly in 720 00:42:31,600 --> 00:42:34,279 Speaker 3: terms of like providing pleasure, but taste buds give you 721 00:42:34,320 --> 00:42:39,800 Speaker 3: important survival information. They are your your body's chemistry set, 722 00:42:40,160 --> 00:42:43,840 Speaker 3: along with your ural factory, you know, smell and taste 723 00:42:43,840 --> 00:42:48,319 Speaker 3: together help you sort of test incoming materials for safety 724 00:42:48,400 --> 00:42:52,080 Speaker 3: and nutritional value. And that is actually a very valuable 725 00:42:52,080 --> 00:42:54,400 Speaker 3: thing in the wild, especially if you can't look at 726 00:42:54,400 --> 00:42:55,359 Speaker 3: stuff you're going to eat. 727 00:42:55,719 --> 00:42:57,880 Speaker 2: Yeah. Yeah, we have to be reminded of that because 728 00:42:57,880 --> 00:43:01,919 Speaker 2: we are such site dependent organists that we easily think 729 00:43:01,960 --> 00:43:04,520 Speaker 2: of like the world we can see and then the 730 00:43:04,800 --> 00:43:08,520 Speaker 2: other senses that provides sort of backup information, right, or 731 00:43:08,520 --> 00:43:10,439 Speaker 2: at least it's easy to think about that in terms 732 00:43:10,480 --> 00:43:13,080 Speaker 2: of a lot of stimuli. Obviously it's different once you 733 00:43:13,120 --> 00:43:16,879 Speaker 2: get into, say, you know, the actual experiences of consuming food. 734 00:43:16,880 --> 00:43:19,719 Speaker 2: But even that, the visual factor is a huge part 735 00:43:19,760 --> 00:43:22,040 Speaker 2: of it totally. When you pay for a nice meal, 736 00:43:22,040 --> 00:43:24,680 Speaker 2: when you pay for a nice cocktail or zero proof cocktail, 737 00:43:24,719 --> 00:43:28,400 Speaker 2: whatever floats your boat, you know, I mean presentation, visual 738 00:43:28,440 --> 00:43:31,239 Speaker 2: presentation is a huge part of what you're signing up for. 739 00:43:31,640 --> 00:43:34,359 Speaker 3: It absolutely is. Even I would say this, even if 740 00:43:34,400 --> 00:43:37,560 Speaker 3: you think you quote know better, do you know what 741 00:43:37,560 --> 00:43:40,040 Speaker 3: I mean about that rot like that? Some people can 742 00:43:40,040 --> 00:43:42,800 Speaker 3: think like, oh, you know, I'm just in it for 743 00:43:43,239 --> 00:43:46,040 Speaker 3: the tasty food. I don't really care if it looks good. 744 00:43:46,080 --> 00:43:49,880 Speaker 3: But actually you do care in subconscious ways that you're 745 00:43:49,960 --> 00:43:51,240 Speaker 3: not admitting to yourself. 746 00:43:51,560 --> 00:43:54,680 Speaker 2: Yeah, on some level, you were still anticipating the flavor, 747 00:43:54,760 --> 00:43:59,520 Speaker 2: anticipating the taste experience based on to a large degree, 748 00:43:59,560 --> 00:44:01,200 Speaker 2: on visual data. 749 00:44:01,280 --> 00:44:04,160 Speaker 3: Totally. So one more thing I want to say about 750 00:44:04,200 --> 00:44:07,800 Speaker 3: these the blind Mexican cavefish, because I was looking into 751 00:44:08,280 --> 00:44:11,840 Speaker 3: this cavefish species and it seems that eye loss or 752 00:44:11,880 --> 00:44:17,600 Speaker 3: I regression is strongly associated with a parallel morphotype, which 753 00:44:17,719 --> 00:44:21,960 Speaker 3: is pigmentation loss. So a source I was using on 754 00:44:22,120 --> 00:44:25,120 Speaker 3: pigmentation loss in cavefish is a chapter in a book. 755 00:44:25,600 --> 00:44:29,279 Speaker 3: The chapter is called Evolutionary Genetics of Pigmentation Loss in 756 00:44:29,320 --> 00:44:32,880 Speaker 3: Blind Mexican Cavefish by Joshua B. Gross and Clifford J. Tabin. 757 00:44:33,400 --> 00:44:35,800 Speaker 3: It is from the book In Search of the Causes 758 00:44:35,840 --> 00:44:40,600 Speaker 3: of Evolution, From Field Observations to Mechanisms, Princeton University Press, 759 00:44:40,600 --> 00:44:45,480 Speaker 3: twenty eleven, edited by Peter and Rosemary Grant. So most 760 00:44:45,520 --> 00:44:49,600 Speaker 3: of this chapter is focused on the specific genetic mutations 761 00:44:49,640 --> 00:44:53,799 Speaker 3: and regulatory changes that result in the reduction in or 762 00:44:53,880 --> 00:44:59,080 Speaker 3: total loss of pigment in blind Mexican cavefish, the reduction 763 00:44:59,280 --> 00:45:05,560 Speaker 3: in the melanophores and color color molecules in the fish's body, 764 00:45:06,040 --> 00:45:08,759 Speaker 3: and they find that in different populations they're actually you 765 00:45:08,800 --> 00:45:14,160 Speaker 3: get these similar, similar adaptations of the loss of pigment 766 00:45:14,239 --> 00:45:18,840 Speaker 3: in the body, but they have different underlying genetic or 767 00:45:18,880 --> 00:45:23,279 Speaker 3: regulatory mechanisms, so it's evolved in different ways to get 768 00:45:23,280 --> 00:45:26,360 Speaker 3: sort of the same result in these different cave fish populations. 769 00:45:27,360 --> 00:45:30,359 Speaker 3: But also this chapter gets a little bit into what 770 00:45:30,440 --> 00:45:34,000 Speaker 3: the environmental selection pressure is related to, or the lack 771 00:45:34,040 --> 00:45:38,320 Speaker 3: of selection pressures related to pigmentation might be. So, for example, 772 00:45:38,800 --> 00:45:43,120 Speaker 3: on the surface, biological pigments like melanin help protect the 773 00:45:43,160 --> 00:45:47,560 Speaker 3: cells of animals from ultraviolet radiation in the sunlight. In 774 00:45:47,600 --> 00:45:50,920 Speaker 3: the cave, there's no light, so this radiation shielding effect 775 00:45:51,040 --> 00:45:55,239 Speaker 3: is useless on the surface. Pigments are also arranged in 776 00:45:55,320 --> 00:45:58,879 Speaker 3: patterns on the body as ornamentation, which plays a role 777 00:45:58,880 --> 00:46:02,160 Speaker 3: in sexual selection. So a fish with certain types of 778 00:46:02,200 --> 00:46:06,760 Speaker 3: pigmentation patterns might be seen as a more desirable mate, 779 00:46:07,040 --> 00:46:09,719 Speaker 3: but in the cave, your mate can't see you, so 780 00:46:09,800 --> 00:46:13,560 Speaker 3: it doesn't matter. On the surface, pigmentation can also play 781 00:46:13,560 --> 00:46:17,120 Speaker 3: a role in camouflage concealing your body within the environment, 782 00:46:17,600 --> 00:46:20,719 Speaker 3: but in the cave. Once again, this doesn't make any difference. 783 00:46:21,040 --> 00:46:24,560 Speaker 3: So much like with eyes, pigmentation would be a phenotypic 784 00:46:24,560 --> 00:46:28,279 Speaker 3: trait that confers huge advantages on the surface where there's light, 785 00:46:28,640 --> 00:46:33,040 Speaker 3: and it suddenly confers little to no advantage underground. So 786 00:46:33,400 --> 00:46:37,880 Speaker 3: even if it's just subject to genetic drift, pigmentation, like eyes, 787 00:46:37,960 --> 00:46:42,120 Speaker 3: could fluctuate out of the population. But are there any 788 00:46:42,200 --> 00:46:46,240 Speaker 3: reasons to think it is actively selected against? It seems 789 00:46:46,239 --> 00:46:48,600 Speaker 3: like there is less evidence for this than there is 790 00:46:48,640 --> 00:46:50,920 Speaker 3: in the case of eyes. There's probably good reason to 791 00:46:50,960 --> 00:46:53,520 Speaker 3: think that eyes are being selected against in the cave, 792 00:46:53,680 --> 00:46:57,879 Speaker 3: less so for pigmentation. The authors here cite research by 793 00:46:57,920 --> 00:47:01,200 Speaker 3: protests at all from two thousand and seven than indicating 794 00:47:01,280 --> 00:47:05,000 Speaker 3: it's more likely a result of drift, though some amount 795 00:47:05,040 --> 00:47:07,640 Speaker 3: of indirect selection through pleiotropy is possible. 796 00:47:08,640 --> 00:47:13,080 Speaker 2: Okay, all right, we have more complex understanding, perhaps than 797 00:47:13,320 --> 00:47:15,800 Speaker 2: of what might be going on here with these changes. 798 00:47:16,239 --> 00:47:17,600 Speaker 2: All Right, We're going to go ahead and close out 799 00:47:17,680 --> 00:47:19,480 Speaker 2: this episode of Stuff to Blow your mind, but we'll 800 00:47:19,480 --> 00:47:21,920 Speaker 2: be back with part two in this series on Thursday, 801 00:47:22,440 --> 00:47:25,640 Speaker 2: and don't worry, we will get into the guano. We 802 00:47:25,680 --> 00:47:28,200 Speaker 2: will get into that back guano because it is vitally 803 00:47:28,239 --> 00:47:32,640 Speaker 2: important to this discussion. And also I think we're going 804 00:47:32,719 --> 00:47:35,759 Speaker 2: to discuss guano in a way that may turn the 805 00:47:35,800 --> 00:47:37,799 Speaker 2: concept on its head for you. I know when I 806 00:47:37,840 --> 00:47:39,640 Speaker 2: was reading about it in the way that we're going 807 00:47:39,680 --> 00:47:42,560 Speaker 2: to discuss it, it made me think about it in 808 00:47:42,600 --> 00:47:43,160 Speaker 2: a new light. 809 00:47:43,440 --> 00:47:44,000 Speaker 3: I can't wait. 810 00:47:45,160 --> 00:47:46,880 Speaker 2: In the meantime, we'd love to hear from you if 811 00:47:46,920 --> 00:47:49,799 Speaker 2: you have thoughts about particular caves that you've been to, 812 00:47:50,320 --> 00:47:53,920 Speaker 2: cave environments that you're familiar with, If you have thoughts 813 00:47:53,960 --> 00:47:59,120 Speaker 2: on scientists naming things after everything from the Iliad to 814 00:47:59,320 --> 00:48:02,200 Speaker 2: Sonic the Hedge. We'd also love to hear from you 815 00:48:02,360 --> 00:48:06,399 Speaker 2: on that point as well. But yeah, yeah, particular cave 816 00:48:06,480 --> 00:48:08,800 Speaker 2: environments that you've really enjoyed. Like I say, I always 817 00:48:08,880 --> 00:48:13,560 Speaker 2: enjoy checking out caves. I believe Colossal Cave in Tucson, 818 00:48:13,640 --> 00:48:15,920 Speaker 2: Arizona is one that I visited many years back, and 819 00:48:16,280 --> 00:48:18,040 Speaker 2: I really want to go back there in the future 820 00:48:18,120 --> 00:48:22,799 Speaker 2: because this is one if memory serves was discovered late 821 00:48:22,960 --> 00:48:27,320 Speaker 2: enough that they were able to preserve the cave environment 822 00:48:27,520 --> 00:48:30,080 Speaker 2: to a large degree by use of essentially like an 823 00:48:30,080 --> 00:48:33,200 Speaker 2: air lock system. So that they're not just opening up 824 00:48:33,280 --> 00:48:38,080 Speaker 2: this environment in a way that destabilizes what has evolved 825 00:48:38,080 --> 00:48:41,360 Speaker 2: beneath the surface. But anyway, more on this sort of 826 00:48:41,360 --> 00:48:44,400 Speaker 2: thing in the next episode. In the meantime, we'll remind 827 00:48:44,400 --> 00:48:45,759 Speaker 2: you once more that Stuff to Blow your Mind is 828 00:48:45,800 --> 00:48:49,560 Speaker 2: primarily a science podcast Science and culture podcasts, with core 829 00:48:49,600 --> 00:48:54,279 Speaker 2: episodes on Tuesdays and Thursdays. Mondays we do listener mail. 830 00:48:54,320 --> 00:48:56,560 Speaker 2: Wednesdays we do a short form episode, and on Fridays 831 00:48:56,560 --> 00:48:58,840 Speaker 2: we set aside most serious concerns to just talk about 832 00:48:58,880 --> 00:49:02,440 Speaker 2: a weird film on Weird House Cinema. Check us out 833 00:49:02,480 --> 00:49:05,399 Speaker 2: on social media. If you haven't, We're on What're We're 834 00:49:05,440 --> 00:49:07,640 Speaker 2: on the Instagram. You can find us on the other 835 00:49:07,640 --> 00:49:11,719 Speaker 2: major social platforms. I think we're on TikTok. I had 836 00:49:11,719 --> 00:49:14,360 Speaker 2: to be reminded of this. We have some some wonderful 837 00:49:14,360 --> 00:49:16,399 Speaker 2: folks that are helping us handle our social these days, 838 00:49:16,400 --> 00:49:20,200 Speaker 2: and I think we're on TikTok. We look for us there. 839 00:49:20,239 --> 00:49:24,279 Speaker 2: I guess I think we're there. But yeah, if you 840 00:49:24,360 --> 00:49:26,879 Speaker 2: use social media and you have the power to follow 841 00:49:26,960 --> 00:49:29,399 Speaker 2: us in any of these places, yeah, give us a follow. 842 00:49:29,560 --> 00:49:31,799 Speaker 2: We appreciate it. If you can give the show some 843 00:49:31,840 --> 00:49:35,080 Speaker 2: stars where if you listen to the podcast downloaded and subscribe, 844 00:49:35,200 --> 00:49:35,880 Speaker 2: that also. 845 00:49:35,680 --> 00:49:38,480 Speaker 3: Helps us out huge things. As always to our excellent 846 00:49:38,520 --> 00:49:41,600 Speaker 3: audio producer JJ Posway. If you would like to get 847 00:49:41,640 --> 00:49:43,719 Speaker 3: in touch with us with feedback on this episode or 848 00:49:43,719 --> 00:49:45,880 Speaker 3: any other, to suggest a topic for the future, or 849 00:49:46,000 --> 00:49:48,480 Speaker 3: just to say hello, you can email us at contact 850 00:49:48,520 --> 00:49:58,040 Speaker 3: at stuff to Blow your Mind dot com. 851 00:49:58,160 --> 00:50:00,680 Speaker 1: Stuff to Blow Your Mind is production of iHeart Radio. 852 00:50:01,000 --> 00:50:03,959 Speaker 1: For more podcasts from my heart Radio, visit the iHeartRadio app, 853 00:50:04,120 --> 00:50:20,440 Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.