1 00:00:00,960 --> 00:00:04,360 Speaker 1: Hey, welcome to sign Stuff, a production of iHeartRadio. I'm 2 00:00:04,400 --> 00:00:09,160 Speaker 1: hoore Chim and today we're asking why can't we regrow limbs? 3 00:00:09,800 --> 00:00:11,600 Speaker 1: If you lose an arm or a leg, we know 4 00:00:11,720 --> 00:00:15,160 Speaker 1: that that arm or leg is not going to grow back, 5 00:00:15,600 --> 00:00:17,919 Speaker 1: but we know there are animals in nature that can 6 00:00:18,040 --> 00:00:20,599 Speaker 1: do that. If you cut off a starfish arm or 7 00:00:20,640 --> 00:00:24,520 Speaker 1: a salamander's leg, it'll regrow a new one. There's even 8 00:00:24,560 --> 00:00:27,600 Speaker 1: a fish that can regrow its heart if you cut 9 00:00:27,600 --> 00:00:30,760 Speaker 1: off a piece of it. So how do they do 10 00:00:30,800 --> 00:00:34,120 Speaker 1: it and why can't we do it? We're going to 11 00:00:34,200 --> 00:00:37,800 Speaker 1: talk to several regeneration and animal experts and we're gonna 12 00:00:37,840 --> 00:00:41,800 Speaker 1: find out if it's possible to activate that ability in people. 13 00:00:42,400 --> 00:00:44,479 Speaker 1: So get ready to go out on a limb with 14 00:00:44,560 --> 00:00:48,839 Speaker 1: us as we explore the regeneration of body parts. I 15 00:00:48,960 --> 00:00:52,080 Speaker 1: promise it won't cost you an arm and a leg. 16 00:00:52,920 --> 00:01:00,640 Speaker 1: Enjoy Hey everyone. To answer this question, I started by 17 00:01:00,640 --> 00:01:03,920 Speaker 1: looking up a list of animals that can regrow their 18 00:01:03,920 --> 00:01:07,280 Speaker 1: body parts. Not all animals can do it, but a 19 00:01:07,360 --> 00:01:09,680 Speaker 1: few if you cut off a part of their body 20 00:01:09,920 --> 00:01:15,400 Speaker 1: doultes regrow it back. On this list are starfish, flatworms, 21 00:01:15,800 --> 00:01:19,679 Speaker 1: salamanders like the axe lotto and some fishes like the 22 00:01:19,800 --> 00:01:23,760 Speaker 1: zebrafish and the Mexican tetrafish. We're going to talk to 23 00:01:23,840 --> 00:01:26,560 Speaker 1: experts in each of these animals, and while we talk 24 00:01:26,640 --> 00:01:30,600 Speaker 1: to them, we're going to learn three things. Number one, 25 00:01:30,800 --> 00:01:34,880 Speaker 1: how these animals regrow their limbs, like what's their secret? 26 00:01:35,440 --> 00:01:40,560 Speaker 1: Number two why humans can't regrow our limbs or can we? 27 00:01:41,240 --> 00:01:44,959 Speaker 1: And three why do some animals evolve this ability and 28 00:01:45,080 --> 00:01:49,360 Speaker 1: others don't? It seems like a pretty handy skill to have, 29 00:01:50,440 --> 00:01:53,080 Speaker 1: all right. The first expert I talked to was doctor 30 00:01:53,240 --> 00:01:56,840 Speaker 1: Andrew Wolff. Doctor Wolf is a researcher at the University 31 00:01:56,880 --> 00:02:03,000 Speaker 1: of Maryland, Baltimore County who studies regenerate in starfish and flatworms. 32 00:02:03,600 --> 00:02:05,960 Speaker 1: The first thing I wanted to know is can these 33 00:02:06,000 --> 00:02:11,120 Speaker 1: animals really regrow anything? Well, let's start with the starfish 34 00:02:11,120 --> 00:02:12,559 Speaker 1: and then we'll do the flatworms. 35 00:02:12,960 --> 00:02:16,359 Speaker 2: So starfish are what are called a kinoderm, so that's 36 00:02:16,360 --> 00:02:20,000 Speaker 2: a phylum of animals. So it's things like sea urchins, 37 00:02:20,040 --> 00:02:23,800 Speaker 2: sea cucumbers, things called sea lilies or crinoids, where they 38 00:02:23,840 --> 00:02:26,680 Speaker 2: also have sort of called feather stars that can move, 39 00:02:26,720 --> 00:02:32,440 Speaker 2: and also brittle stars, so they're somewhat closely related. To vertebrates. 40 00:02:32,680 --> 00:02:35,960 Speaker 1: What do we know about tissue regeneration in sea stars 41 00:02:36,000 --> 00:02:37,120 Speaker 1: and sea urchins? 42 00:02:37,440 --> 00:02:42,360 Speaker 2: So my work was understanding regeneration in their larvae. So 43 00:02:42,400 --> 00:02:46,080 Speaker 2: they're very small, probably like a millimeter or so, very clear. 44 00:02:46,200 --> 00:02:48,880 Speaker 2: They started to swim around the ocean for about two 45 00:02:48,880 --> 00:02:51,799 Speaker 2: months or so until they metamorphous into the adult. So 46 00:02:51,840 --> 00:02:55,280 Speaker 2: you can cut them in half, but those halves will regenerate. 47 00:02:55,520 --> 00:02:57,720 Speaker 1: Okay, so you're saying, if you cut at the bottom, 48 00:02:57,720 --> 00:02:59,720 Speaker 1: half will grow a top and the top will grow 49 00:02:59,800 --> 00:03:04,760 Speaker 1: by and you'll get too identical animals. Yes, huh. And 50 00:03:05,160 --> 00:03:06,280 Speaker 1: what about the flatworm? 51 00:03:06,440 --> 00:03:08,600 Speaker 2: That's what I'm interested now. And so it not only 52 00:03:08,639 --> 00:03:11,680 Speaker 2: does it regrow what's lost, it sort of reshapes everything 53 00:03:11,680 --> 00:03:14,639 Speaker 2: else such that it's not out of proportion. So let's 54 00:03:14,639 --> 00:03:16,760 Speaker 2: say you cut a worm in the three pieces like 55 00:03:16,840 --> 00:03:18,880 Speaker 2: a top, of a middle, on a bottom. They'll all 56 00:03:19,080 --> 00:03:22,680 Speaker 2: regrow what was lost, but the actual ending size of 57 00:03:22,680 --> 00:03:24,840 Speaker 2: that worm is going to be smaller than the original 58 00:03:25,000 --> 00:03:29,240 Speaker 2: wholeworm because if the tail regrows to be really small, 59 00:03:29,240 --> 00:03:31,000 Speaker 2: the brain is going to be too big for the 60 00:03:31,160 --> 00:03:34,520 Speaker 2: new body size. So now it needs to reshape everything 61 00:03:34,680 --> 00:03:37,840 Speaker 2: to be in proportion to the new size that it is. 62 00:03:39,360 --> 00:03:43,120 Speaker 1: So these animals will pretty much regenerate anything. If you 63 00:03:43,160 --> 00:03:46,560 Speaker 1: cut them in half or in three pieces, each piece 64 00:03:46,760 --> 00:03:49,520 Speaker 1: will regrow what's missing, and then you'll end up with 65 00:03:49,640 --> 00:03:54,440 Speaker 1: almost identical copies of the original. Next, I talked to 66 00:03:54,520 --> 00:03:58,640 Speaker 1: doctor Nadia f. Frobish, who is an expert in salamanders. 67 00:04:00,080 --> 00:04:02,880 Speaker 3: My name is Nadia Flebish. I work at the Natural 68 00:04:02,960 --> 00:04:07,040 Speaker 3: History Museum in Berlin and at Humboldt University. I'm a 69 00:04:07,080 --> 00:04:12,400 Speaker 3: professor for evolutionary biology. Actually, everything that's alive can regenerate 70 00:04:12,480 --> 00:04:16,480 Speaker 3: tissue to a certain degree, which is very convenient because 71 00:04:16,560 --> 00:04:19,359 Speaker 3: otherwise I think we would all grow up with a 72 00:04:19,360 --> 00:04:22,919 Speaker 3: lot of open scrapes and scratches as we go through childhood. 73 00:04:23,560 --> 00:04:24,880 Speaker 1: That makes sense, Yeah. 74 00:04:24,920 --> 00:04:27,680 Speaker 3: So of course we can all do wound healing to 75 00:04:27,800 --> 00:04:31,400 Speaker 3: a certain degree, but some animals are even better at 76 00:04:31,440 --> 00:04:35,359 Speaker 3: it than we are among vertebrates. So the animals that 77 00:04:35,440 --> 00:04:39,560 Speaker 3: have a background, it's only salamanders that are the masters 78 00:04:39,600 --> 00:04:42,640 Speaker 3: of regeneration. I think a lot of people are familiar 79 00:04:42,720 --> 00:04:46,560 Speaker 3: with lizards regenerating tales and sort of throwing them off 80 00:04:46,600 --> 00:04:51,080 Speaker 3: as a decoy for predators. But lizards, in contrast to salamanders, 81 00:04:51,120 --> 00:04:54,479 Speaker 3: only get sort of like a fake tale back. It's 82 00:04:54,520 --> 00:04:59,400 Speaker 3: more like a rotch of cartilage that's in there. And salamanders, 83 00:04:59,440 --> 00:05:01,720 Speaker 3: if they lose their tail, they get a brand new 84 00:05:01,760 --> 00:05:06,520 Speaker 3: tail with retever column and you know, spinal cord and musculature, 85 00:05:06,680 --> 00:05:09,679 Speaker 3: so just like it was before. And they cannot only 86 00:05:09,720 --> 00:05:13,080 Speaker 3: do that with their tails. They can also regenerate their limbs. 87 00:05:13,200 --> 00:05:16,440 Speaker 3: They can regenerate the lenses of their eyes, a huge 88 00:05:16,480 --> 00:05:22,920 Speaker 3: portion of their hearts, liver, so they're really really excellent regeneration. 89 00:05:23,360 --> 00:05:26,799 Speaker 1: Pretty much any part of the body has been tested. 90 00:05:27,520 --> 00:05:30,680 Speaker 3: Oh yes, this has been tested. Not any part, but 91 00:05:30,839 --> 00:05:32,880 Speaker 3: a lot of the parts of the body. So they 92 00:05:32,920 --> 00:05:36,360 Speaker 3: cannot lose their entire heart, for instance, and then regenerated. 93 00:05:36,400 --> 00:05:38,880 Speaker 3: There still has to be like a critical amount left 94 00:05:39,080 --> 00:05:41,560 Speaker 3: in order for regeneration to proceed. 95 00:05:41,400 --> 00:05:45,080 Speaker 1: So the muscles, toenails, everything indeed. 96 00:05:44,880 --> 00:05:49,040 Speaker 3: And sometimes it's really amazing because when the salamanders bite 97 00:05:49,040 --> 00:05:53,080 Speaker 3: each other they can have quite gruesome injuries, so where like, 98 00:05:53,160 --> 00:05:55,719 Speaker 3: for instance, the upper arm bone is sticking out and 99 00:05:55,800 --> 00:05:58,839 Speaker 3: all the soft tissue is gone. Looking at it, you 100 00:05:58,839 --> 00:06:01,160 Speaker 3: would think, oh my god, this is never going to 101 00:06:01,240 --> 00:06:04,919 Speaker 3: grow back, but it does, and it's really quite amazing. 102 00:06:06,400 --> 00:06:09,839 Speaker 1: And the last expert I talked to was Ezra Sengul, 103 00:06:10,279 --> 00:06:15,960 Speaker 1: a graduate researcher at Oxford University who studies Mexican cavefish. 104 00:06:17,600 --> 00:06:23,200 Speaker 4: I am Estra, and I use animal models, particularly Mexican 105 00:06:23,279 --> 00:06:25,239 Speaker 4: cavefish and zebra fish. 106 00:06:25,760 --> 00:06:29,920 Speaker 1: Okay, what do we know about tissue regeneration from zebrafish 107 00:06:29,960 --> 00:06:30,680 Speaker 1: and cayfish? 108 00:06:30,839 --> 00:06:34,560 Speaker 4: To start with zebra fish. Together with zebrafish, there are 109 00:06:34,600 --> 00:06:39,359 Speaker 4: certain kinds of cavefish have regeneration catasity, and they have 110 00:06:39,400 --> 00:06:44,400 Speaker 4: a remarkable precision. While doing that, they repair their sins, 111 00:06:44,800 --> 00:06:48,479 Speaker 4: they replace it with an new functional one. They also 112 00:06:48,560 --> 00:06:53,800 Speaker 4: regenerate their heart, spinal cord, retinas, and kidneys. They use 113 00:06:53,880 --> 00:06:58,160 Speaker 4: them to study heart repay it in particular because unlike humans, 114 00:06:58,240 --> 00:07:02,279 Speaker 4: the heart damage leads to starting in unspins, and zebra 115 00:07:02,360 --> 00:07:06,360 Speaker 4: fish the heart cells replace that lost tissue. 116 00:07:08,400 --> 00:07:12,800 Speaker 1: So all these animals basically have a superpower. If you're 117 00:07:12,840 --> 00:07:16,440 Speaker 1: thinking of Deadpool or Wolverine from the Marvel movies, these 118 00:07:16,480 --> 00:07:19,680 Speaker 1: animals can do what they do and they're real. Chop 119 00:07:19,720 --> 00:07:22,680 Speaker 1: off leg and a new one grows back. Cut some 120 00:07:22,760 --> 00:07:26,600 Speaker 1: of them in half, and both halves regrow into whole 121 00:07:26,840 --> 00:07:31,960 Speaker 1: new organisms. I had a lot of questions. First of all, 122 00:07:32,200 --> 00:07:35,760 Speaker 1: how do you even regrow a limb? And second of all, 123 00:07:35,960 --> 00:07:39,800 Speaker 1: why can't we and other animals like cats and dogs 124 00:07:39,840 --> 00:07:44,120 Speaker 1: and birds do this? To start, I asked our experts 125 00:07:44,240 --> 00:07:47,160 Speaker 1: to give me a play by play of what actually 126 00:07:47,240 --> 00:07:51,200 Speaker 1: happens when these animals are missing a body part. According 127 00:07:51,240 --> 00:07:54,480 Speaker 1: to them, it's a step by step process, and it's 128 00:07:54,520 --> 00:07:58,760 Speaker 1: pretty similar whether you're a starfish or a flatworm or 129 00:07:58,800 --> 00:08:03,600 Speaker 1: a salamander. Step one is basically stop the bleeding. 130 00:08:06,480 --> 00:08:09,640 Speaker 3: So the very first thing that's happening and that has 131 00:08:09,720 --> 00:08:13,120 Speaker 3: to happen in order for regeneration to proceed is the 132 00:08:13,160 --> 00:08:16,200 Speaker 3: wound healing. So the wound has to close over just 133 00:08:16,280 --> 00:08:18,920 Speaker 3: like you know, we would have a wound if you. 134 00:08:18,880 --> 00:08:20,800 Speaker 2: Think you're in the water. You don't want a bunch 135 00:08:20,800 --> 00:08:23,280 Speaker 2: of stuff coming in and bacteria and all that stuff. 136 00:08:23,320 --> 00:08:26,160 Speaker 2: So you have to heal the wound. There's different mechanisms 137 00:08:26,160 --> 00:08:28,800 Speaker 2: that they do. Think like a purse string it sort 138 00:08:28,840 --> 00:08:31,600 Speaker 2: of steals it, or you just have cells that spread 139 00:08:32,040 --> 00:08:35,079 Speaker 2: that just close it up. Obviously, if you don't heal, 140 00:08:35,160 --> 00:08:38,760 Speaker 2: then you're gonna fall apart. So there's a structural component. 141 00:08:38,800 --> 00:08:43,160 Speaker 1: But that's the first thing, okay that makes sense. You 142 00:08:43,200 --> 00:08:45,960 Speaker 1: first have to close off the gaping wound. That happens 143 00:08:46,000 --> 00:08:48,320 Speaker 1: when you get an arm or a leg cut off, 144 00:08:48,840 --> 00:08:52,400 Speaker 1: but that also happens when we get cut Our bodies 145 00:08:52,559 --> 00:08:55,800 Speaker 1: also close the wounds. So why do we stop there 146 00:08:56,240 --> 00:08:58,400 Speaker 1: and those animals don't. 147 00:08:59,400 --> 00:09:02,680 Speaker 2: And it's really interesting is that the wound itself can 148 00:09:03,080 --> 00:09:06,199 Speaker 2: signal to the rest of the body that regeneration needs 149 00:09:06,240 --> 00:09:09,000 Speaker 2: to happen, big major thing that needs to happen for 150 00:09:09,200 --> 00:09:13,080 Speaker 2: regeneration to proceed. So it's like a general response to 151 00:09:13,120 --> 00:09:15,439 Speaker 2: a wound. But then from there it either says now 152 00:09:15,480 --> 00:09:17,040 Speaker 2: I need to regrow or not. 153 00:09:18,360 --> 00:09:19,679 Speaker 1: It says different signals. 154 00:09:19,880 --> 00:09:22,880 Speaker 2: There's some sort of mechanism that they can detect that 155 00:09:23,160 --> 00:09:26,080 Speaker 2: tissue was lost versus I just sort of made a cut. 156 00:09:26,400 --> 00:09:29,960 Speaker 2: Something from the wound itself is able to recognize now 157 00:09:30,040 --> 00:09:31,679 Speaker 2: I need to regrow ahead. 158 00:09:33,160 --> 00:09:36,679 Speaker 1: So this is a key part of the process. Somehow 159 00:09:36,880 --> 00:09:40,679 Speaker 1: these animals as bodies are able to tell it's missing 160 00:09:40,840 --> 00:09:43,960 Speaker 1: a limb or a body part. There's some kind of 161 00:09:44,120 --> 00:09:48,000 Speaker 1: signaling that happens that says, hey, this isn't just a 162 00:09:48,160 --> 00:09:51,360 Speaker 1: flesh wound. We're missing an arm or a leg, and 163 00:09:51,400 --> 00:09:58,640 Speaker 1: that calls in the cavalry. So once this signal goes out. 164 00:09:58,679 --> 00:10:00,920 Speaker 1: You said it mobilizes things. What does that mean? 165 00:10:01,320 --> 00:10:06,240 Speaker 2: So for regeneration, you need cells to make stuff right. 166 00:10:06,720 --> 00:10:09,439 Speaker 2: Anything that you need that was lost needs to regrow, 167 00:10:09,640 --> 00:10:13,000 Speaker 2: so you need to have cells for that. They have 168 00:10:13,280 --> 00:10:17,439 Speaker 2: some sort of stem cells that mobilizes, stay, divide, then 169 00:10:17,720 --> 00:10:20,320 Speaker 2: move to whatever they need to be, and they become 170 00:10:20,600 --> 00:10:22,200 Speaker 2: the tissues that need to become. 171 00:10:22,559 --> 00:10:25,839 Speaker 3: In salamanders, you have a few stem cells that are 172 00:10:25,880 --> 00:10:28,560 Speaker 3: still in the system, but you also have cells that 173 00:10:28,720 --> 00:10:32,560 Speaker 3: are sort of losing their identity that are sort of 174 00:10:32,960 --> 00:10:37,320 Speaker 3: re entering the cell cycle to become something you're everywhere 175 00:10:37,320 --> 00:10:39,880 Speaker 3: in the body, and then are recruited to that side. 176 00:10:40,240 --> 00:10:41,000 Speaker 1: They actually move. 177 00:10:41,280 --> 00:10:45,000 Speaker 3: Yeah, cells move a lot all the time. Actually, really. 178 00:10:47,440 --> 00:10:50,239 Speaker 1: Okay. The next step is for the body to recruit 179 00:10:50,480 --> 00:10:53,800 Speaker 1: a bunch of cells where you want the missing body 180 00:10:53,840 --> 00:10:57,360 Speaker 1: part to grow. But these aren't just any cells. They 181 00:10:57,400 --> 00:11:00,040 Speaker 1: have to be stem cells. If you haven't heard what 182 00:11:00,120 --> 00:11:03,760 Speaker 1: these are. Stem cells are cells that can become any 183 00:11:03,840 --> 00:11:06,640 Speaker 1: other kind of cell. If you think about it, the 184 00:11:06,679 --> 00:11:10,040 Speaker 1: cells in your skin are very different than your eye cells, 185 00:11:10,480 --> 00:11:14,000 Speaker 1: or your muscle cells, or your brain cells. That's because 186 00:11:14,040 --> 00:11:18,040 Speaker 1: these are all cells that have become specialized parts of 187 00:11:18,080 --> 00:11:21,320 Speaker 1: their DNA have been switched on or off so that 188 00:11:21,360 --> 00:11:25,240 Speaker 1: they grow a stertin way. That's good because you wouldn't 189 00:11:25,240 --> 00:11:28,640 Speaker 1: want your skin cells to suddenly turn into an eyeball cell, 190 00:11:29,080 --> 00:11:31,760 Speaker 1: or you wouldn't want your brain cells to suddenly become 191 00:11:32,160 --> 00:11:35,560 Speaker 1: muscle cells. Stem cells are cells that still have all 192 00:11:35,600 --> 00:11:38,440 Speaker 1: their options open, and these are the cells that get 193 00:11:38,480 --> 00:11:42,679 Speaker 1: called up to regrow a missing body part. Now, what's 194 00:11:42,760 --> 00:11:46,600 Speaker 1: interesting is that some animals just have stem cells floating 195 00:11:46,600 --> 00:11:50,200 Speaker 1: around their bodies, and some animals are also able to 196 00:11:50,840 --> 00:11:55,840 Speaker 1: roll back their specialized cells to become stem cells. This 197 00:11:55,960 --> 00:11:58,160 Speaker 1: part is going to be important later, but for now, 198 00:11:58,559 --> 00:12:02,120 Speaker 1: just imagine a whole bunch of stem cells congregating at 199 00:12:02,120 --> 00:12:05,640 Speaker 1: the wound site where the animal lost a body part. 200 00:12:08,960 --> 00:12:12,040 Speaker 2: And they form this sort of massive cells at the 201 00:12:12,080 --> 00:12:16,840 Speaker 2: wound site. Oh okay, last, it's a term for sort 202 00:12:16,840 --> 00:12:19,720 Speaker 2: of they haven't fully met their fate. Yeah, they sort 203 00:12:19,720 --> 00:12:22,120 Speaker 2: of accumulate at the wound site, which. 204 00:12:21,920 --> 00:12:24,520 Speaker 3: Is sort of like a nose if you want to, 205 00:12:24,679 --> 00:12:27,319 Speaker 3: like a cone on the end of the limb, which 206 00:12:27,360 --> 00:12:30,600 Speaker 3: is the gross thoughe where all the cells are proliferating. 207 00:12:32,920 --> 00:12:35,360 Speaker 1: Okay, so where you cut off a limb or a 208 00:12:35,440 --> 00:12:38,280 Speaker 1: piece of heart or a fin A blob of stem 209 00:12:38,320 --> 00:12:42,120 Speaker 1: cells forms, and from that blob grows the new part. 210 00:12:42,640 --> 00:12:45,400 Speaker 1: We're gonna talk about how that blob knows what shape 211 00:12:45,400 --> 00:12:49,240 Speaker 1: to grow into, which is super fascinating, and we'll talk 212 00:12:49,240 --> 00:12:52,640 Speaker 1: about why us humans can't do any of this. But 213 00:12:52,720 --> 00:13:09,040 Speaker 1: first let's take a quick break. You're listening to sign stuff. Okay, 214 00:13:09,120 --> 00:13:11,720 Speaker 1: all right, So now we've got this massive of cells 215 00:13:11,760 --> 00:13:15,319 Speaker 1: who are there to regrow whatever's missing. How do they 216 00:13:15,360 --> 00:13:16,160 Speaker 1: know what to regrow? 217 00:13:16,840 --> 00:13:20,280 Speaker 2: It's a great question, a very complicated question that we 218 00:13:20,400 --> 00:13:23,640 Speaker 2: don't quite one hundred percent know the answer to. It 219 00:13:23,679 --> 00:13:27,000 Speaker 2: depends on sort of what the tissue is. There's some 220 00:13:27,080 --> 00:13:29,160 Speaker 2: sort of way that the animal is able to detect 221 00:13:29,480 --> 00:13:31,400 Speaker 2: this is what's missing, and I think it's related to 222 00:13:31,480 --> 00:13:33,280 Speaker 2: the idea of physitional information. 223 00:13:35,120 --> 00:13:37,000 Speaker 1: Okay, we talked about how when you cut off a 224 00:13:37,080 --> 00:13:40,679 Speaker 1: limb or a body part, these animals with this superpower 225 00:13:41,000 --> 00:13:44,600 Speaker 1: start by closing the wound and then amassing a lump 226 00:13:44,600 --> 00:13:47,760 Speaker 1: of stem cells where the body part used to be. 227 00:13:48,640 --> 00:13:51,719 Speaker 1: The next question is how do these cells know what 228 00:13:51,800 --> 00:13:54,880 Speaker 1: to grow into? I mean, you wouldn't want a tail 229 00:13:55,120 --> 00:13:58,360 Speaker 1: or a brain to grow where your arm used to 230 00:13:58,360 --> 00:14:01,160 Speaker 1: be and The answer is that every cell in your 231 00:14:01,200 --> 00:14:07,199 Speaker 1: body gets signals about its positional information. That is, somehow 232 00:14:07,360 --> 00:14:10,960 Speaker 1: cells seem to know where they are or where they 233 00:14:11,000 --> 00:14:13,600 Speaker 1: should be in the body. And this is something that 234 00:14:13,640 --> 00:14:17,680 Speaker 1: scientists don't fully understand yet, but it involves basically every 235 00:14:17,760 --> 00:14:23,120 Speaker 1: cell talking to every other cell through special chemicals and molecules. 236 00:14:23,520 --> 00:14:26,960 Speaker 1: And in this case, scientists have noticed an interesting pattern 237 00:14:27,320 --> 00:14:29,080 Speaker 1: about how this works. 238 00:14:30,840 --> 00:14:33,520 Speaker 3: The way it works is that the tip of what 239 00:14:33,720 --> 00:14:38,240 Speaker 3: has been lost is sort of specified first genetically, and 240 00:14:38,280 --> 00:14:41,800 Speaker 3: then you have sort of a dissonance between that very 241 00:14:41,880 --> 00:14:45,920 Speaker 3: tip and whatever the stump area is, and that dissonance 242 00:14:46,040 --> 00:14:50,440 Speaker 3: or that disconnect between those two genetic identities leads to 243 00:14:50,520 --> 00:14:54,120 Speaker 3: that growth and to the exact replacement of everything that's. 244 00:14:53,920 --> 00:14:57,560 Speaker 1: In the middle betweening. Wow, how does the tip not 245 00:14:57,760 --> 00:14:58,680 Speaker 1: to turn into the tip? 246 00:14:59,360 --> 00:15:02,760 Speaker 3: It's a genetic marker sort of their genes expressed there 247 00:15:02,840 --> 00:15:05,360 Speaker 3: that are saying you are the tip now and like 248 00:15:05,480 --> 00:15:06,760 Speaker 3: giving it that identity. 249 00:15:07,000 --> 00:15:09,560 Speaker 1: Oh I see. It's like the distensios that are at 250 00:15:09,560 --> 00:15:11,520 Speaker 1: the tip, they're like, okay, I don't see anyone else 251 00:15:11,560 --> 00:15:14,760 Speaker 1: around us. We must be the tip exactly. That's fascinating. 252 00:15:15,040 --> 00:15:16,600 Speaker 1: But then how do the cells in the middle know 253 00:15:16,880 --> 00:15:18,160 Speaker 1: how to fill in the middle. 254 00:15:18,280 --> 00:15:21,920 Speaker 3: Well, we haven't actually sort of researched all the details 255 00:15:22,000 --> 00:15:25,360 Speaker 3: of that entire process. It's really it's sort of an 256 00:15:25,520 --> 00:15:30,440 Speaker 3: interplay between cells dividing and genetic markers giving those cells 257 00:15:30,440 --> 00:15:34,560 Speaker 3: positional identity, like saying this is where you are now 258 00:15:34,640 --> 00:15:37,320 Speaker 3: you are a wrist bone, or you will be part 259 00:15:37,360 --> 00:15:40,200 Speaker 3: of the wrist area, or you will be part of 260 00:15:40,240 --> 00:15:43,120 Speaker 3: the musculature that is in the lower arm, kind of 261 00:15:43,200 --> 00:15:46,440 Speaker 3: like that. It's an incredibly complex process actually, so it's 262 00:15:46,480 --> 00:15:48,160 Speaker 3: quite amazing that it works so well. 263 00:15:49,840 --> 00:15:53,320 Speaker 1: In other words, scientists don't quite know how the cells 264 00:15:53,320 --> 00:15:58,200 Speaker 1: in animals that regrow body parts know what's missing or 265 00:15:58,320 --> 00:16:01,400 Speaker 1: where they are or what shape they're supposed to. Mank, 266 00:16:01,920 --> 00:16:06,440 Speaker 1: they just do, Like all of that is in our 267 00:16:06,520 --> 00:16:11,640 Speaker 1: DNA to recognize, Oh, I'm between the tip, I'm about 268 00:16:11,640 --> 00:16:14,520 Speaker 1: three quarts of the way between the tip and the shoulder. 269 00:16:14,720 --> 00:16:17,920 Speaker 1: I must be you know, for our bicyle cell. 270 00:16:18,680 --> 00:16:21,480 Speaker 3: Wow, Yes, it's all in the genetic markers. 271 00:16:23,720 --> 00:16:27,000 Speaker 1: Like I said, it's a superpower. But as our experts 272 00:16:27,000 --> 00:16:30,040 Speaker 1: point out, it's basically what happens when you grow in 273 00:16:30,080 --> 00:16:33,000 Speaker 1: the first place, when you go from a fertilized egg 274 00:16:33,240 --> 00:16:37,160 Speaker 1: to a fetus and eventually to a grown person. Somehow 275 00:16:37,400 --> 00:16:40,440 Speaker 1: your cells know how to grow every part of you. 276 00:16:41,040 --> 00:16:45,240 Speaker 1: Animals that regrow their body parts basically just reactivate that 277 00:16:45,400 --> 00:16:49,320 Speaker 1: growing ability we all have in our DNA. Okay, the 278 00:16:49,360 --> 00:16:53,600 Speaker 1: next big question is why don't all animals have this ability? 279 00:16:54,000 --> 00:16:58,520 Speaker 1: How's a starfish, a flatworm, or a salamander different than 280 00:16:58,760 --> 00:17:03,720 Speaker 1: us or dogs or cats or monkeys. Why can't every 281 00:17:03,760 --> 00:17:09,560 Speaker 1: animal regrow limbs? What do you think it is that 282 00:17:09,640 --> 00:17:12,439 Speaker 1: flatworms and starfish have the humans don't have? 283 00:17:12,840 --> 00:17:16,679 Speaker 2: Yeah, the million dollar questions people always like, if you 284 00:17:16,720 --> 00:17:19,359 Speaker 2: find something in the lab, can I just grind up 285 00:17:19,400 --> 00:17:21,240 Speaker 2: the worms and inject it into my arm? 286 00:17:22,600 --> 00:17:23,960 Speaker 1: You could be a starfish man. 287 00:17:24,320 --> 00:17:27,080 Speaker 2: Yeah, I mean, hey, that wouldn't be too bad, I guess. 288 00:17:27,240 --> 00:17:27,359 Speaker 1: So. 289 00:17:27,440 --> 00:17:30,840 Speaker 2: One other thing that I haven't mentioned so far is scarring. 290 00:17:32,080 --> 00:17:35,280 Speaker 2: It stops regeneration and a lot of context. So if 291 00:17:35,320 --> 00:17:38,280 Speaker 2: you cut off your hand, God forbid, you have obviously 292 00:17:38,280 --> 00:17:40,160 Speaker 2: a wound response, and it's going to heal and it's 293 00:17:40,160 --> 00:17:43,560 Speaker 2: going to scar. When a lot of these other things regenerate. 294 00:17:43,600 --> 00:17:46,919 Speaker 2: The starfish, the worms, even things like a salamander, an 295 00:17:46,920 --> 00:17:50,320 Speaker 2: axle auto, they don't scar. It's a major sort of 296 00:17:50,400 --> 00:17:54,480 Speaker 2: block of regeneration, and also that inflammation prevents a lot 297 00:17:54,520 --> 00:17:57,439 Speaker 2: of these other steps that could be happening. There's little 298 00:17:57,480 --> 00:18:00,359 Speaker 2: to no inflammation and a lot of these animals that 299 00:18:00,400 --> 00:18:03,399 Speaker 2: can regenerate. So it's a relationship between scar and inflammation 300 00:18:03,520 --> 00:18:05,440 Speaker 2: and ability to regrow. 301 00:18:07,040 --> 00:18:10,359 Speaker 1: Ah, here's the first piece of the puzzle. Animals with 302 00:18:10,400 --> 00:18:14,359 Speaker 1: the ability to regrow body parts don't scar and they 303 00:18:14,400 --> 00:18:18,240 Speaker 1: don't get inflammation when they get cut. Making a scar 304 00:18:18,520 --> 00:18:21,000 Speaker 1: is basically like patching a hole in your wall with 305 00:18:21,080 --> 00:18:25,240 Speaker 1: a giant pile of bricks. Scar tissue is thick and 306 00:18:25,400 --> 00:18:28,240 Speaker 1: tough and dense, and it basically gets in the way 307 00:18:28,600 --> 00:18:30,840 Speaker 1: of regrowing a new body part. 308 00:18:32,480 --> 00:18:36,320 Speaker 2: But these simpler animals, they just seal it up and 309 00:18:36,359 --> 00:18:37,440 Speaker 2: that seems to be enough. 310 00:18:37,720 --> 00:18:40,879 Speaker 1: They don't make a scar, basically, they do not, So 311 00:18:40,920 --> 00:18:43,879 Speaker 1: that's one factor. The other fact that you said was inflammation. 312 00:18:44,000 --> 00:18:46,879 Speaker 1: So when we get cut, it becomes inflamed, and how 313 00:18:46,920 --> 00:18:48,600 Speaker 1: does that make things hard to regenerate? 314 00:18:48,840 --> 00:18:52,880 Speaker 2: So it prevents any of the later steps from happening. 315 00:18:53,160 --> 00:18:56,920 Speaker 2: It just prevents the ability of the tissue to regrow. 316 00:18:57,280 --> 00:19:01,159 Speaker 1: It's not a happy state for cells to regenerate. No, 317 00:19:01,480 --> 00:19:05,960 Speaker 1: that is not. What doctor Wolf is saying is that 318 00:19:06,000 --> 00:19:08,480 Speaker 1: when we get an arm or a leg cut off, 319 00:19:08,680 --> 00:19:13,320 Speaker 1: our body basically overreacts. It rushes to patch up the wound, 320 00:19:13,600 --> 00:19:18,200 Speaker 1: building thick SCRs that block any regrowth, and it deploys 321 00:19:18,200 --> 00:19:22,320 Speaker 1: the immune system, which makes everything so inflame that it 322 00:19:22,400 --> 00:19:25,960 Speaker 1: prevents all the steps needed to regrow the body part. 323 00:19:26,400 --> 00:19:30,200 Speaker 1: Cells don't revert back to stem cells, they don't divide well, 324 00:19:30,440 --> 00:19:33,159 Speaker 1: so they don't form that block of generic cells that 325 00:19:33,240 --> 00:19:36,560 Speaker 1: can then become the missing part. So now the question 326 00:19:36,680 --> 00:19:39,520 Speaker 1: is why do we do that? Why do our bodies 327 00:19:39,640 --> 00:19:43,199 Speaker 1: react that way, especially because at some point in our 328 00:19:43,240 --> 00:19:50,480 Speaker 1: evolutionary history it seems we did something different. Okay, now 329 00:19:50,520 --> 00:19:53,720 Speaker 1: the question is why can't humans regrow our lips or 330 00:19:53,760 --> 00:19:55,200 Speaker 1: can we? Is that possible? 331 00:19:55,720 --> 00:19:58,560 Speaker 3: Well, that's a question that always comes to all people 332 00:19:58,600 --> 00:20:02,480 Speaker 3: who who work the regeneration. We always get that question, 333 00:20:03,080 --> 00:20:06,760 Speaker 3: and that's not an easy question to answer because it's 334 00:20:06,840 --> 00:20:11,320 Speaker 3: probably a combination of very complex factors that play the 335 00:20:11,400 --> 00:20:11,919 Speaker 3: role in this. 336 00:20:12,480 --> 00:20:13,440 Speaker 1: But we know from the. 337 00:20:13,320 --> 00:20:16,320 Speaker 3: Fossil record that a lot of the ancient amphibians could 338 00:20:16,359 --> 00:20:20,760 Speaker 3: regenerate too, and lungfish are the closest living relatives of 339 00:20:21,080 --> 00:20:26,560 Speaker 3: os fourlimd vertebrates can also regenerate very similar to salamanders. 340 00:20:26,560 --> 00:20:29,840 Speaker 3: So it is likely that regeneration as we see it 341 00:20:29,880 --> 00:20:32,920 Speaker 3: in salamanders now is actually not something that is special 342 00:20:32,960 --> 00:20:37,160 Speaker 3: to modern salamanders that evolved. But salamanders probably are the 343 00:20:37,200 --> 00:20:41,919 Speaker 3: only living vertebrates today that can still regenerate. Back in 344 00:20:41,960 --> 00:20:46,400 Speaker 3: evolutionary history, that was probably a widespread feature that then 345 00:20:46,440 --> 00:20:48,680 Speaker 3: got lost in the course of evolution. 346 00:20:49,040 --> 00:20:52,320 Speaker 1: Oh so interesting. It's not like they developed the special ability, 347 00:20:52,359 --> 00:20:56,560 Speaker 1: they're the only ones who kept it exactly. Oh my goodness. 348 00:20:56,720 --> 00:20:59,399 Speaker 1: What doctor Frobish is saying is that at some point 349 00:20:59,600 --> 00:21:06,920 Speaker 1: basic all animals were able to regrow their body parts. Salamanders, starfish, flatworms. 350 00:21:07,040 --> 00:21:09,840 Speaker 1: They don't have a superpower. It used to be a 351 00:21:09,960 --> 00:21:15,800 Speaker 1: standard feature of all animals. But evolution at some point said, eh, 352 00:21:15,880 --> 00:21:18,600 Speaker 1: you know what, let's not do that. It's not a 353 00:21:18,640 --> 00:21:24,040 Speaker 1: skill some species evolved, it's a skill some of us lost. Okay. 354 00:21:24,280 --> 00:21:27,840 Speaker 1: The obvious next two questions are why did evolution choose 355 00:21:28,080 --> 00:21:31,719 Speaker 1: not to regrow limbs in species like ours? And if 356 00:21:31,760 --> 00:21:35,879 Speaker 1: it's something we had but lost, could we bring it back. 357 00:21:36,440 --> 00:21:40,040 Speaker 1: We'll answer both those questions after the break. We'll be 358 00:21:40,200 --> 00:21:51,800 Speaker 1: right back, and we're back all right. We just learned 359 00:21:51,840 --> 00:21:56,000 Speaker 1: a shocking piece of information, which is that scientists believe 360 00:21:56,400 --> 00:22:01,520 Speaker 1: it's likely that basically all animals, these ambiotes, which are 361 00:22:01,560 --> 00:22:05,280 Speaker 1: all for legged animals, used to be able to regrow 362 00:22:05,560 --> 00:22:08,639 Speaker 1: missing body parts, but at some point in our evolution 363 00:22:09,080 --> 00:22:12,720 Speaker 1: this ability was selected as not being the best for 364 00:22:12,880 --> 00:22:16,880 Speaker 1: our survival, which is strange because you think that being 365 00:22:16,880 --> 00:22:20,840 Speaker 1: able to regrow limbs would be a good thing. I mean, 366 00:22:20,920 --> 00:22:23,080 Speaker 1: if you use a leg you can't really run away 367 00:22:23,119 --> 00:22:26,119 Speaker 1: from a predator that's trying to eat you. So I 368 00:22:26,119 --> 00:22:29,600 Speaker 1: asked our experts, why would we lose this ability? 369 00:22:31,280 --> 00:22:34,520 Speaker 3: It seems like something so useful to have, right, that 370 00:22:34,680 --> 00:22:38,080 Speaker 3: capacity to regenerate, but it also comes at the cost. 371 00:22:38,800 --> 00:22:42,959 Speaker 3: So during the course of evolution, it probably was a 372 00:22:43,000 --> 00:22:46,040 Speaker 3: matter of a trade off, and it's probably for that 373 00:22:46,280 --> 00:22:51,040 Speaker 3: reason that regeneration was selected against during evolution at some 374 00:22:51,200 --> 00:22:54,800 Speaker 3: point in amniote evolution. And it could have happened once, 375 00:22:54,880 --> 00:22:57,680 Speaker 3: it probably had happened multiple times. 376 00:22:58,080 --> 00:22:59,760 Speaker 1: Oh well, what's the trade of. 377 00:23:00,280 --> 00:23:04,600 Speaker 3: Salamander's a giant cells, So they have like huge cells 378 00:23:04,640 --> 00:23:07,880 Speaker 3: because they do have a lot of DNA that they accumulate. 379 00:23:08,000 --> 00:23:10,879 Speaker 3: They just can afford to have all that DNA, But 380 00:23:11,000 --> 00:23:14,159 Speaker 3: all that DNA has to be the transcribed, right, it 381 00:23:14,200 --> 00:23:17,240 Speaker 3: has to be done for a second copy, and that 382 00:23:17,440 --> 00:23:20,080 Speaker 3: caused a lot of energy and resources. 383 00:23:22,040 --> 00:23:24,720 Speaker 1: Okay, the first reason we might have lost our ability 384 00:23:24,760 --> 00:23:28,119 Speaker 1: to regrow body parts is that there's a cost to 385 00:23:28,280 --> 00:23:32,600 Speaker 1: having that ability. First of all, it requires extra DNA. 386 00:23:33,160 --> 00:23:36,800 Speaker 1: The program to regrow LIMB takes extra instructions and extra 387 00:23:36,880 --> 00:23:40,520 Speaker 1: genes that can come at a cost, especially if you 388 00:23:40,560 --> 00:23:45,679 Speaker 1: want to move faster and have a faster metabolism. I 389 00:23:45,720 --> 00:23:48,760 Speaker 1: wonder if what you're saying is that at some point 390 00:23:48,840 --> 00:23:52,119 Speaker 1: in our lineage, the evolution pressure was to like, hey, 391 00:23:52,240 --> 00:23:54,760 Speaker 1: let's make things more efficient. We don't need all this DNA, 392 00:23:54,880 --> 00:23:58,159 Speaker 1: and maybe one of the cuts was our ability to regenerate. 393 00:23:58,520 --> 00:24:01,479 Speaker 3: Yes, that's it. So it's not just that we lost DNA. 394 00:24:01,600 --> 00:24:05,000 Speaker 3: It's also that we have to go through cell cycles 395 00:24:05,080 --> 00:24:07,760 Speaker 3: at a certain speed in order to keep our very 396 00:24:07,840 --> 00:24:12,120 Speaker 3: high metabolism that allows us to run really fast, to 397 00:24:12,240 --> 00:24:16,520 Speaker 3: sustain a constant body temperature, and do really powerful energy 398 00:24:16,920 --> 00:24:20,800 Speaker 3: consuming things like run and fly and do these kind 399 00:24:20,880 --> 00:24:24,199 Speaker 3: of things. If you have a very high metabolism, you 400 00:24:24,320 --> 00:24:27,679 Speaker 3: have to go through these processes of making new cells 401 00:24:27,760 --> 00:24:31,600 Speaker 3: quicker than when you're an organism with a very slow metabolism. 402 00:24:31,680 --> 00:24:36,720 Speaker 3: We're constantly building new cells all the time, regenerate your skin, 403 00:24:37,000 --> 00:24:40,840 Speaker 3: your hair is growing, You're making new blood cells all 404 00:24:40,880 --> 00:24:45,120 Speaker 3: the time. Salamander's day can regenerate because they don't have 405 00:24:45,200 --> 00:24:49,639 Speaker 3: to sustain such a high metabolism. We cannot regenerate, but 406 00:24:49,760 --> 00:24:53,159 Speaker 3: we can run fast and keep our body temperature or 407 00:24:53,240 --> 00:24:54,919 Speaker 3: fly in these kind of things. 408 00:24:57,840 --> 00:25:01,280 Speaker 1: What doctor Frobish is saying is that any extra ability 409 00:25:01,680 --> 00:25:05,000 Speaker 1: meets extra DNA, and that can come at a cost 410 00:25:05,280 --> 00:25:08,160 Speaker 1: if you want to be more active, because being more 411 00:25:08,200 --> 00:25:11,600 Speaker 1: active means you're cycling through cells more. And each time 412 00:25:11,640 --> 00:25:14,960 Speaker 1: you make new cells, you have to copy all that DNA, 413 00:25:15,400 --> 00:25:18,840 Speaker 1: which takes a lot of energy. And the other cost 414 00:25:19,080 --> 00:25:21,560 Speaker 1: is that it's just a lot to grow a new 415 00:25:21,720 --> 00:25:24,119 Speaker 1: arm and a leg. I mean, you have to make 416 00:25:24,119 --> 00:25:26,280 Speaker 1: a whole new limb from nothing. 417 00:25:27,840 --> 00:25:30,399 Speaker 2: Can you imagine having a stump for how long to 418 00:25:30,440 --> 00:25:33,760 Speaker 2: regrow all of this complex tissue. It would take a 419 00:25:33,760 --> 00:25:35,560 Speaker 2: lot of energy and it'd take a lot of time. 420 00:25:36,200 --> 00:25:38,480 Speaker 2: If the best thing to do is just to close 421 00:25:38,520 --> 00:25:41,080 Speaker 2: it and seal it and make sure the structure there. 422 00:25:41,119 --> 00:25:45,280 Speaker 2: With that scar is sound. Then maybe that's for the best, 423 00:25:46,560 --> 00:25:50,359 Speaker 2: maybe more advantageous energetically and also just structurally to do that. 424 00:25:50,760 --> 00:25:54,680 Speaker 1: Oh interesting, Maybe we don't need that extra arm. Maybe huh, 425 00:25:54,680 --> 00:25:56,840 Speaker 1: I guess you don't. Technically, you don't need an extra 426 00:25:56,920 --> 00:25:58,240 Speaker 1: arm to have more babies. 427 00:25:59,080 --> 00:26:00,720 Speaker 2: Yes, that is all true. 428 00:26:02,040 --> 00:26:06,240 Speaker 1: So that's the reason we can't regrow limbs. We, meaning 429 00:26:06,359 --> 00:26:10,040 Speaker 1: four legged animals, used to be able to, but evolution 430 00:26:10,160 --> 00:26:13,879 Speaker 1: at some point decided it's not worth it. Losing an 431 00:26:14,040 --> 00:26:16,159 Speaker 1: arm or a leg is a huge deal if it 432 00:26:16,200 --> 00:26:19,639 Speaker 1: happens to one of us, but as a species, maybe 433 00:26:20,240 --> 00:26:24,000 Speaker 1: it's okay. Maybe it's better to just cut our losses, 434 00:26:24,200 --> 00:26:27,080 Speaker 1: patch things up quickly with scar tissue, clean it up, 435 00:26:27,200 --> 00:26:31,280 Speaker 1: and move on if it means everyone collectively being more 436 00:26:31,320 --> 00:26:36,439 Speaker 1: efficient and having a faster metabolism. Now you're probably thinking, 437 00:26:36,640 --> 00:26:39,399 Speaker 1: if the ability to regrow body parts was in the 438 00:26:39,520 --> 00:26:43,359 Speaker 1: DNA of our animal ancestors, could we revive it somehow 439 00:26:43,440 --> 00:26:47,040 Speaker 1: so that we can all regrow limbs again. I'll get 440 00:26:47,080 --> 00:26:48,800 Speaker 1: to that in a minute, but first I wanted to 441 00:26:48,800 --> 00:26:51,760 Speaker 1: tell you about something kind of cool about the Mexican 442 00:26:52,040 --> 00:26:56,240 Speaker 1: tetrafish that sort of proves the whole hypothesis about why 443 00:26:56,320 --> 00:27:04,200 Speaker 1: we can't regrow limbs. Here's how Ezra describe these fish. 444 00:27:04,240 --> 00:27:07,680 Speaker 4: It is such a unique and perfectly slitted model organism 445 00:27:07,800 --> 00:27:10,520 Speaker 4: to study it because it has two different sometimes. So 446 00:27:10,760 --> 00:27:16,400 Speaker 4: the surface dewelling version has this silver colored functional eyes 447 00:27:16,480 --> 00:27:19,919 Speaker 4: and dailian streams. They look very much like what we 448 00:27:20,080 --> 00:27:24,760 Speaker 4: know f fish. But the cave dwelling version is tail pink. 449 00:27:25,200 --> 00:27:28,800 Speaker 4: It is almost translucent. They don't have functional eyes. 450 00:27:30,240 --> 00:27:33,919 Speaker 1: Okay, the Mexican tetarfish is fascinating because it's at a 451 00:27:33,960 --> 00:27:39,200 Speaker 1: point where it's about to possibly evolve into two different species. 452 00:27:39,640 --> 00:27:42,840 Speaker 1: There are currently two kinds of Mexican tetarfish. The ones 453 00:27:42,840 --> 00:27:45,800 Speaker 1: that live normally in the rivers above ground. Those are 454 00:27:45,840 --> 00:27:49,160 Speaker 1: called the surface dwelling kind, and there are the ones 455 00:27:49,200 --> 00:27:52,840 Speaker 1: that live inside of caves. And the ones that live 456 00:27:52,920 --> 00:27:56,240 Speaker 1: in the rivers on the surface can regenerate their hearts, 457 00:27:56,400 --> 00:27:59,800 Speaker 1: but the ones that live in caves can't, even though 458 00:27:59,840 --> 00:28:05,080 Speaker 1: the still technically the same species, So some of them 459 00:28:05,160 --> 00:28:07,439 Speaker 1: can and some of them cannot. You said, it's related 460 00:28:07,440 --> 00:28:09,919 Speaker 1: to where they live. What do you mean it's related 461 00:28:09,920 --> 00:28:10,600 Speaker 1: to where they live. 462 00:28:10,880 --> 00:28:15,119 Speaker 4: During evolution, the cave dwelling version lost its ability to 463 00:28:15,200 --> 00:28:19,400 Speaker 4: regenerate their hearts, and it is because they entered the caves, 464 00:28:19,400 --> 00:28:23,000 Speaker 4: they got thropped there and they had to continue living 465 00:28:23,240 --> 00:28:27,679 Speaker 4: in a complete darkness with no enough food and no 466 00:28:28,119 --> 00:28:33,400 Speaker 4: external food sources. They had to minimize their metabolism, and 467 00:28:33,600 --> 00:28:36,720 Speaker 4: they had to find a way to compromise from the 468 00:28:36,800 --> 00:28:40,120 Speaker 4: things that they don't really need to survive, and heart 469 00:28:40,160 --> 00:28:42,800 Speaker 4: regeneration happened to be one of them. 470 00:28:44,440 --> 00:28:47,600 Speaker 1: So basically we're seeing the whole theory of why we 471 00:28:47,680 --> 00:28:51,040 Speaker 1: can't regrow limbs play out right in front of us. 472 00:28:51,360 --> 00:28:54,680 Speaker 1: Some of the tetrafish have migrated to live deep inside 473 00:28:54,720 --> 00:28:58,920 Speaker 1: caves and because there is little food, low oxygen, and 474 00:28:59,000 --> 00:29:02,320 Speaker 1: not as many predators, we can see evolution in real 475 00:29:02,440 --> 00:29:07,120 Speaker 1: time basically say, eh, we don't really need to regenerate hearts. 476 00:29:07,520 --> 00:29:13,800 Speaker 1: It's better to throw out that skill and save energy. Wow, 477 00:29:14,000 --> 00:29:17,320 Speaker 1: that's so interesting that they would lose that ability. Do 478 00:29:17,400 --> 00:29:19,360 Speaker 1: they know how they lost it? 479 00:29:19,600 --> 00:29:23,040 Speaker 4: There are some genes that are responsible, but there are 480 00:29:23,160 --> 00:29:25,880 Speaker 4: so many we only started exploring these. 481 00:29:27,000 --> 00:29:29,160 Speaker 1: And this is where we get to the edge of 482 00:29:29,320 --> 00:29:33,360 Speaker 1: current signs, because if we can figure out how exactly 483 00:29:33,480 --> 00:29:36,480 Speaker 1: we lost our ability to regrow limbs, like if we 484 00:29:36,480 --> 00:29:40,040 Speaker 1: figure out which genes got turned off or lost, then 485 00:29:40,080 --> 00:29:43,640 Speaker 1: maybe we can get that ability back. I asked our 486 00:29:43,720 --> 00:29:48,800 Speaker 1: experts if they thought this was possible. All right, last question, 487 00:29:48,880 --> 00:29:52,200 Speaker 1: doctor Wolf. If you could enable humans to regenerate limbs, 488 00:29:52,360 --> 00:29:54,479 Speaker 1: parts of our organs, how would you do it? 489 00:29:54,760 --> 00:29:59,320 Speaker 2: Ooh, okay, Well, technically, I will say we do have 490 00:29:59,400 --> 00:30:03,320 Speaker 2: some regeneritive capacity, so parts of your liver can regenerate. 491 00:30:04,000 --> 00:30:07,440 Speaker 2: There's also a lot of research and information about the 492 00:30:07,520 --> 00:30:11,200 Speaker 2: tips of your fingers, so kids could regrow the tips 493 00:30:11,400 --> 00:30:12,080 Speaker 2: through your fingers. 494 00:30:12,960 --> 00:30:14,000 Speaker 1: I've had that happen to me. 495 00:30:14,120 --> 00:30:14,440 Speaker 4: Yeah. 496 00:30:14,560 --> 00:30:16,280 Speaker 1: Yeah, So we do have. 497 00:30:16,200 --> 00:30:20,040 Speaker 2: Some ability, but over time you just begin to lose 498 00:30:20,040 --> 00:30:25,000 Speaker 2: that ability, so we're not quite the worst. I believe 499 00:30:25,040 --> 00:30:28,400 Speaker 2: birds are famously not that regenerative. But if I had 500 00:30:28,440 --> 00:30:31,560 Speaker 2: to make a human regenerate, I think there's several things 501 00:30:31,640 --> 00:30:36,160 Speaker 2: that need to happen. One is, scarring needs to be minimized, 502 00:30:36,480 --> 00:30:40,560 Speaker 2: Inflammation needs to be minimized. We need to mobilize those 503 00:30:40,600 --> 00:30:41,640 Speaker 2: cells enough. 504 00:30:42,280 --> 00:30:44,800 Speaker 1: What you said that it's probably the same kind of 505 00:30:44,800 --> 00:30:48,240 Speaker 1: signaling that happens when we're first growing to art. Originally, yes, 506 00:30:48,520 --> 00:30:49,520 Speaker 1: that would be the idea. 507 00:30:49,640 --> 00:30:52,760 Speaker 2: So how is it that digits were made in an embryo, 508 00:30:53,440 --> 00:30:56,400 Speaker 2: take some of that information and see if those sorts 509 00:30:56,400 --> 00:30:58,880 Speaker 2: of things can be turned on again because we have 510 00:30:59,000 --> 00:30:59,480 Speaker 2: them now. 511 00:31:00,400 --> 00:31:04,520 Speaker 3: There might be a sheer genetic program in all forlimp 512 00:31:04,600 --> 00:31:08,680 Speaker 3: vertebrates that is still present to a certain degree. 513 00:31:08,520 --> 00:31:11,200 Speaker 1: Meaning it might still be hidden somewhere in our DNA, 514 00:31:11,360 --> 00:31:14,719 Speaker 1: but somehow it's not activated. How would that work, like 515 00:31:14,760 --> 00:31:17,800 Speaker 1: through gene editing, go into human DNA and like, oh wait, 516 00:31:17,960 --> 00:31:20,600 Speaker 1: here's something that needs to be tweaked, and this here 517 00:31:20,600 --> 00:31:21,920 Speaker 1: and there and there, and oh, now we have the 518 00:31:21,960 --> 00:31:23,400 Speaker 1: ability to regenerate limbs. 519 00:31:23,560 --> 00:31:27,120 Speaker 3: So it will require a lot of different scientists coming together, 520 00:31:27,600 --> 00:31:31,760 Speaker 3: which will be like the biomedical people, the molecular biologists, 521 00:31:31,800 --> 00:31:35,719 Speaker 3: people working specifically with Excel models and other organisms as 522 00:31:35,840 --> 00:31:40,240 Speaker 3: model organisms to really understand all the details of the processes. 523 00:31:40,360 --> 00:31:42,920 Speaker 3: So I think in the end, all these lines of 524 00:31:42,960 --> 00:31:46,640 Speaker 3: evidence will come together to know what the process is 525 00:31:46,720 --> 00:31:50,320 Speaker 3: triggered by and how to maybe implemented in humans at 526 00:31:50,360 --> 00:31:51,240 Speaker 3: some point in time. 527 00:31:53,640 --> 00:31:57,120 Speaker 1: All right, So the answer to the question why can 528 00:31:57,240 --> 00:32:01,400 Speaker 1: we regrow limbs seems to be who says we can't? 529 00:32:02,000 --> 00:32:05,080 Speaker 1: That ability might be hidden inside of us and all 530 00:32:05,120 --> 00:32:09,480 Speaker 1: we have to do is regrow it. Thanks for joining us. 531 00:32:09,920 --> 00:32:15,680 Speaker 1: Be sure to subscribe. See you next time you've been 532 00:32:15,680 --> 00:32:20,000 Speaker 1: listening to Science Stuff production of iHeartRadio written and produced 533 00:32:20,000 --> 00:32:24,000 Speaker 1: by Me or Hey Cham candited by Rose Seguda, executive 534 00:32:24,000 --> 00:32:27,720 Speaker 1: producer Jerry Rowland, and audio engineer and mixer Jasey pepperm 535 00:32:27,800 --> 00:32:29,960 Speaker 1: And you can follow me on social media. Just search 536 00:32:30,040 --> 00:32:33,240 Speaker 1: for PhD Comics and the name of your favorite platform. 537 00:32:33,320 --> 00:32:36,280 Speaker 1: Be sure to subscribe to Sign Stuff on the iHeartRadio app, 538 00:32:36,320 --> 00:32:39,520 Speaker 1: Apple Podcasts, or wherever you get your podcasts, and please 539 00:32:39,760 --> 00:32:43,320 Speaker 1: tell your friends we'll be back next Wednesday with another episode.