WEBVTT - The Lesser of Two Crab Claws, Part 1 0:00:03.040 --> 0:00:05.360 Welcome to Stuff to Blow Your Mind production of My 0:00:05.480 --> 0:00:14.920 Heart Radio. Hey you welcome to Stuff to Blow your Mind. 0:00:15.080 --> 0:00:18.239 My name is Robert Lamb and I'm Joe McCormick. And 0:00:18.640 --> 0:00:21.200 for the next few episodes we're going to be doing 0:00:21.320 --> 0:00:25.520 a series on a symmetry. And to introduce this series, 0:00:25.600 --> 0:00:28.400 I wanted to talk a little bit about a favorite 0:00:28.440 --> 0:00:31.639 animal of ours, the nar wall. Yes, the what is it, 0:00:31.680 --> 0:00:34.800 the corpse whale um of of the ocean, the unicorn 0:00:34.840 --> 0:00:37.800 of the sea. Right, yeah, so corpse whale. That's literally 0:00:37.800 --> 0:00:41.360 what its name means, whale of course wall, but nar 0:00:42.479 --> 0:00:45.080 meaning corpse. So yeah, it's like a dead body whale, 0:00:45.440 --> 0:00:48.040 having to do with its gray and modeled appearance as 0:00:48.080 --> 0:00:50.520 it sort of floats around near the top of the water. 0:00:50.800 --> 0:00:53.360 But the more famous feature of this whale, apart from 0:00:53.400 --> 0:00:57.560 looking like a corpse, is its horn or tusk or 0:00:58.080 --> 0:01:00.760 we can dispute what's the best word to use for 0:01:00.840 --> 0:01:02.840 it here, but yeah, as you say, it is the 0:01:02.920 --> 0:01:05.959 unicorn of the polar seas. So the nor wall is 0:01:06.000 --> 0:01:10.120 a medium sized Arctic marine mammal in the suborder of 0:01:10.280 --> 0:01:14.959 toothed whales or Odonto ceti. And it is immediately recognizable 0:01:15.000 --> 0:01:18.560 because most males of the nar walls, and occasionally some 0:01:18.600 --> 0:01:23.000 females as well, possess a giant spike or tusk growing 0:01:23.200 --> 0:01:26.920 straight out of their faces. And this tusk can grow 0:01:26.959 --> 0:01:30.640 absurdly long, up to about three meters or ten feet, 0:01:31.319 --> 0:01:35.880 and the orientation of this tusk looks very unusual compared 0:01:35.880 --> 0:01:38.080 to most other mammals. So you think about other mammals 0:01:38.080 --> 0:01:41.000 with horns or tusks. Uh, you might think about bo 0:01:41.120 --> 0:01:43.440 vines in which the horns rise up off the top 0:01:43.480 --> 0:01:46.240 of the head, or you might think about the rhinoceros 0:01:46.240 --> 0:01:48.400 where it points up from the end of the snouts 0:01:48.680 --> 0:01:51.480 kind of you know, up from the ground. Or you 0:01:51.520 --> 0:01:54.320 might think about the tusks of a bore an elephant 0:01:54.400 --> 0:01:56.360 kind of coming out of the mouth at an angle. 0:01:57.000 --> 0:02:00.160 But but no, in the In the narwhall, you have 0:02:00.400 --> 0:02:03.200 a whales body, which again is a sort of modeled 0:02:03.240 --> 0:02:06.000 gray tube that can grow about four to five meters 0:02:06.160 --> 0:02:10.639 long in adulthood, and then the tusk just juts straight 0:02:10.680 --> 0:02:13.560 out of the face, adding another three ms or so 0:02:13.800 --> 0:02:16.079 or up to another three ms or so in length. 0:02:16.520 --> 0:02:19.240 So when the tusk is present, the animal is sort 0:02:19.280 --> 0:02:22.359 of shaped like a dart. Or like a spear. Now, 0:02:22.400 --> 0:02:24.200 when we've talked about in Our Walls before, I think, 0:02:24.280 --> 0:02:27.800 especially in our episodes on the unicorn legend, uh, we 0:02:27.800 --> 0:02:32.240 we talked a lot about the theories behind the origin 0:02:32.320 --> 0:02:34.880 and the purpose of the tusk. We're not going to 0:02:34.919 --> 0:02:38.200 completely rehash that discussion here, though, I did want to 0:02:38.240 --> 0:02:42.079 note a development which was in a more recent paper 0:02:42.120 --> 0:02:45.080 I came across addressing the biological function of the tusk. 0:02:45.200 --> 0:02:48.720 So a long running question for marine biologists who study 0:02:48.760 --> 0:02:52.400 the nar wall is why this giant tusk it's it 0:02:52.560 --> 0:02:55.519 looks very unwieldy. What is it for? What is the 0:02:55.560 --> 0:02:59.720 evolutionary justification? And this can be difficult to study because 0:02:59.840 --> 0:03:03.160 it is not a trivial task to go out and 0:03:03.200 --> 0:03:06.000 just observed in our walls. In the wild, not only 0:03:06.040 --> 0:03:09.720 do they live underwater, but they live under the Arctic ice. 0:03:10.040 --> 0:03:12.760 So they remain veiled in a great deal of mystery. 0:03:13.160 --> 0:03:16.000 But we're not without some clues. And I guess the 0:03:16.040 --> 0:03:19.120 place to start is that the tusk looks so threatening 0:03:19.160 --> 0:03:22.240 to the naive human brain that we immediately want to 0:03:22.240 --> 0:03:24.079 say it is a weapon, right, you know, it is 0:03:24.120 --> 0:03:26.720 a spear, It is a dark that That's what I 0:03:26.800 --> 0:03:29.920 without even thinking about it compared the animal too, right, right, 0:03:30.000 --> 0:03:32.520 you think of it being some sort of a javelin 0:03:32.639 --> 0:03:36.120 or spear um harpoon on the front of this, uh, 0:03:36.200 --> 0:03:39.040 this whale that it's using to to skewer things, or 0:03:39.080 --> 0:03:42.680 that it's using this to sort of fence with other whales. Yeah, 0:03:42.680 --> 0:03:44.840 so you think it must be for you know, stabbing 0:03:44.880 --> 0:03:48.360 sharks or skewering fish prey or something. Though it's funny 0:03:48.400 --> 0:03:51.160 that people think, oh, yeah, it's for for skewering fish 0:03:51.200 --> 0:03:53.840 that they're going to eat. But if that were true, 0:03:54.040 --> 0:03:56.040 wouldn't that be a little awkward? Like how would it 0:03:56.080 --> 0:03:59.680 get the fish to its mouth after that? Like you 0:03:59.680 --> 0:04:03.760 would normally you don't need a stab and then eat. 0:04:03.880 --> 0:04:06.000 If you're a whale, you just eat, You just bite 0:04:06.000 --> 0:04:09.240 and then swallow. Anyway, there have been some accounts of 0:04:09.240 --> 0:04:12.440 what appeared to be various offensive uses of the tusk, 0:04:13.080 --> 0:04:16.320 but these might be coincidental or secondary behaviors. And then 0:04:16.320 --> 0:04:20.440 there are all other odd proposals, including things like stabbing 0:04:20.480 --> 0:04:23.960 through surface ice to create holes for breathing. Of course, 0:04:24.000 --> 0:04:26.839 remember the nar walls and air breathing mammal, but the 0:04:26.880 --> 0:04:29.760 fact that the tusk is hollow and filled with sensitive 0:04:29.800 --> 0:04:33.480 nerve endings, has led some researchers to believe it is 0:04:33.520 --> 0:04:36.520 a sensory organ and there there is some evidence that 0:04:36.600 --> 0:04:39.039 it can be used for gathering and even potentially for 0:04:39.240 --> 0:04:45.000 sharing information about the characteristics of seawater, maybe things like temperature, salinity, 0:04:45.040 --> 0:04:48.960 and so forth. However, one of the most important clues 0:04:49.000 --> 0:04:52.719 about the primary evolutionary justification of the tusk is the 0:04:52.760 --> 0:04:56.960 fact of sexual dimorphism. So the tusks are almost always 0:04:57.160 --> 0:05:00.760 found in males, and one obvious conclud lusion from this 0:05:00.880 --> 0:05:05.039 is that the tusk can't be necessary for survival, or 0:05:05.080 --> 0:05:07.240 else females would have them as well. Right, so it 0:05:07.279 --> 0:05:12.680 can't provide a major individual survival advantage, or else you'd 0:05:12.680 --> 0:05:15.320 expect all individuals to have them, or we would at 0:05:15.360 --> 0:05:18.680 least observe, uh, you know, the the whales that have 0:05:18.800 --> 0:05:21.960 them out competing the other one the ones that don't 0:05:21.960 --> 0:05:24.760 have them in survival, which is not the case. So 0:05:24.880 --> 0:05:27.159 one of the leading theories then is that it's a 0:05:27.240 --> 0:05:31.000 sexually selected trade. It's a body feature without a major 0:05:31.200 --> 0:05:35.120 role in survival, which grows very prominent in males because 0:05:35.240 --> 0:05:39.520 it increases reproductive success, maybe by being more appealing to 0:05:39.600 --> 0:05:42.720 female in our walls, or maybe by causing rival males 0:05:42.760 --> 0:05:45.560 to stay away and so forth and anyway. As so, 0:05:45.720 --> 0:05:48.800 the recent paper I found was one by Graham at 0:05:48.800 --> 0:05:52.080 All published in Biology Letters called the longer the Better 0:05:52.240 --> 0:05:57.640 evidence that narwhal tusks are sexually selected. This was from 0:05:57.680 --> 0:06:00.479 and of course this paper acknowledges that it's really difficult 0:06:00.520 --> 0:06:02.520 to study nar walls in the wild to figure out 0:06:02.560 --> 0:06:05.520 what the tusk is for, so instead it asks if 0:06:05.560 --> 0:06:09.560 we can infer anything about tusk function from examining the 0:06:09.640 --> 0:06:13.400 natural variation in narwhal tusk measurements that have been taken 0:06:13.440 --> 0:06:16.080 over the course of the last thirty five years. And 0:06:16.160 --> 0:06:21.000 so their sample comprised two D forty five individual adult males, 0:06:21.040 --> 0:06:23.760 and based on these measurements, the authors conclude that the 0:06:23.800 --> 0:06:28.080 evidence does suggest the primary driver of tusk evolution is 0:06:28.120 --> 0:06:32.440 sexual selection. Quote. By combining our results on tusk scaling 0:06:32.839 --> 0:06:36.000 with known material properties of the tusk, we suggest that 0:06:36.000 --> 0:06:38.960 the narwhal tusk is a sexually selected signal that is 0:06:39.040 --> 0:06:43.559 used during male male contests. So how would you conclude this? Well, 0:06:44.080 --> 0:06:48.680 the tusk demonstrates a growth pattern known as hyper alimentary, 0:06:48.760 --> 0:06:52.080 which means a body feature that grows faster than the 0:06:52.080 --> 0:06:56.560 body as a whole. So, for example, most body features 0:06:56.640 --> 0:07:01.040 are roughly alometric. They're linearly allometrics. They grow in size 0:07:01.120 --> 0:07:03.880 proportional to the rest of the body. If your body 0:07:03.960 --> 0:07:07.800 is bigger overall, you probably also have longer shin bones 0:07:07.880 --> 0:07:11.760 and larger hands and so forth. Some features might be 0:07:11.960 --> 0:07:16.760 hypo allometric or you know, sublimetric, they grow less than 0:07:16.800 --> 0:07:21.120 the body as a whole. But narwhal tusks are hyper alometric. 0:07:21.240 --> 0:07:25.480 In the largest individuals, the tusks grow longer than simple 0:07:25.560 --> 0:07:28.760 linear scaling would predict. So they're not just big in 0:07:28.840 --> 0:07:31.800 proportion to the rest of the body, they're way bigger 0:07:31.800 --> 0:07:36.560 than that. There they just they get ridiculously huge. And 0:07:36.640 --> 0:07:39.920 so this is not proof, but it is characteristic of 0:07:40.000 --> 0:07:43.240 traits that are sexually selected. And the authors write in 0:07:43.240 --> 0:07:47.480 their conclusion quote, sexually selected signals used in mail mail 0:07:47.560 --> 0:07:51.800 competition are more likely to exhibit hyper elimetry when compared 0:07:51.840 --> 0:07:56.080 to other sexually selected traits. Because the information being signaled 0:07:56.160 --> 0:08:00.000 is simple, I am bigger than you. To convey this message, 0:08:00.040 --> 0:08:03.280 males exaggerate the size of their signals, which facilitate the 0:08:03.320 --> 0:08:08.520 detection of size discrepancies. Between individuals, reducing the likelihood of 0:08:08.600 --> 0:08:12.960 engaging in potentially dangerous fights, and they note that this 0:08:13.040 --> 0:08:16.720 could explain the so called tusking behavior that's been observed, 0:08:17.080 --> 0:08:20.800 where male narwhales sometimes appear to be crossing tusks are 0:08:20.800 --> 0:08:25.160 almost like dueling with their tusks um, which could actually 0:08:25.160 --> 0:08:27.880 be not a form of fighting, but a way for 0:08:28.000 --> 0:08:31.160 the animals to compare the size of their tusks in 0:08:31.280 --> 0:08:35.680 order to avoid a fight. So, in an interesting twist, 0:08:35.760 --> 0:08:38.520 it could be the case that our naive intuition that 0:08:38.600 --> 0:08:42.520 this tusk is a weapon is true in a sense, 0:08:42.679 --> 0:08:47.839 but it's a weapon designed specifically to look scary because 0:08:48.000 --> 0:08:52.319 it will discourage actual fighting between males and sexual competition 0:08:52.559 --> 0:08:55.800 most of the time. So it's you know, two rival 0:08:55.840 --> 0:08:58.840 males are are competing for a chance to mate, and 0:08:58.920 --> 0:09:01.080 one of them goes, wow, that that other one's tusk 0:09:01.200 --> 0:09:04.199 is absurdly long. No need to fight this out, my mistakes, 0:09:04.240 --> 0:09:07.320 see you later. Now. They say that the existing evidence 0:09:07.320 --> 0:09:10.079 sort of points us in this direction, but it's not conclusive. 0:09:10.120 --> 0:09:13.480 Their alternate explanations. Maybe the large tusk plays a role 0:09:13.520 --> 0:09:18.080 in mate choice itself. Maybe females prefer males with larger tusks, 0:09:19.520 --> 0:09:21.760 but they're in general, there's still just a lot we 0:09:21.760 --> 0:09:23.800 don't know about these animals, so so the book is 0:09:23.840 --> 0:09:27.760 not completely closed on this question. And it's also possible 0:09:27.840 --> 0:09:31.040 that the tusk has multiple secondary functions, for example, as 0:09:31.040 --> 0:09:33.920 a sensory organ like we talked about earlier. Though again, 0:09:33.960 --> 0:09:36.840 as I mentioned earlier, that those secondary functions can't be 0:09:36.960 --> 0:09:40.640 all that crucial for survival or we would see that, 0:09:40.840 --> 0:09:42.360 you know, we would see that playing out in nar 0:09:42.400 --> 0:09:44.840 whale populations, the ones with the tusks would be more 0:09:44.880 --> 0:09:48.160 likely to survive, and that's not what we find now. 0:09:48.200 --> 0:09:50.679 To bring it back to the reason I wanted to 0:09:50.720 --> 0:09:54.560 talk about narwhals in today's episode, you may remember one 0:09:54.640 --> 0:09:58.080 strange fact about the narwhal's tusk from our previous episodes 0:09:58.120 --> 0:10:01.440 where these animals came up, and it's that the normals 0:10:01.520 --> 0:10:05.920 tusk is not an external caratinous horn like that of 0:10:05.960 --> 0:10:11.120 the rhinoceros. Instead, it is a tooth. And I don't 0:10:11.160 --> 0:10:13.520 just mean it is made out of the same stuff 0:10:13.559 --> 0:10:16.560 as a tooth. It is literally a tooth. It is 0:10:16.600 --> 0:10:20.360 a tooth from the upper jaw that has been repurposed 0:10:20.360 --> 0:10:24.400 by evolution to grow into a tusk. By changing the 0:10:24.480 --> 0:10:28.960 orientation of growth so that it grows straight out forward forward, 0:10:29.000 --> 0:10:32.400 out of the jaw and then erupts from the flesh 0:10:32.520 --> 0:10:35.640 of the face. It literally grows through the flesh of 0:10:35.640 --> 0:10:39.120 the upper lip and then continues growing rapidly, and as 0:10:39.160 --> 0:10:43.640 we've seen, even hyper elemetrically. But here's what I've been 0:10:43.679 --> 0:10:46.360 getting hung up on. The nor Wals tusk is not 0:10:46.440 --> 0:10:50.040 only a tooth. In almost all cases, it is the 0:10:50.360 --> 0:10:56.520 left canine, the left maxillary canine tooth having erupted from 0:10:56.600 --> 0:10:59.240 the upper lip. And this is this is certainly something 0:10:59.280 --> 0:11:01.400 when you learn for the first time it does it 0:11:01.440 --> 0:11:03.680 does feel a little bit wrong. I mean, a number 0:11:03.720 --> 0:11:06.559 of these these factoids about the norwell perhaps feel a 0:11:06.600 --> 0:11:09.439 little wrong, you know, because ultimately it's just a far 0:11:09.559 --> 0:11:13.840 weirder and perhaps sillier animal than than most of us assumed. 0:11:14.080 --> 0:11:17.600 It is not silly, is deadly serious, but it does 0:11:17.720 --> 0:11:20.400 have one tooth just poking out of its lip for 0:11:20.640 --> 0:11:23.080 I don't know, ten feet. But you're not allowed to laugh, 0:11:23.559 --> 0:11:27.360 um so, But yeah, anyway, So, to quote from a 0:11:27.400 --> 0:11:33.000 paper from in the Anatomical Record by Nuilla at all quote, 0:11:33.120 --> 0:11:37.360 males usually exhibit an erupted tusk on the left side 0:11:37.920 --> 0:11:41.360 and an unerupted embedded tusk on the right. So it's 0:11:41.360 --> 0:11:43.880 got two of these teeth. It's got, you know, that's symmetrical. 0:11:43.920 --> 0:11:48.079 There's one on each side, except usually one just kind 0:11:48.080 --> 0:11:49.959 of grows a little bit and then stays inside the 0:11:50.040 --> 0:11:52.520 upper jaw and doesn't do anything, while the other one 0:11:53.120 --> 0:11:56.240 breaks through the skin and grows up to ten feet long. 0:11:56.679 --> 0:12:00.520 So that's what you usually see. But then the quote continues, 0:12:00.559 --> 0:12:05.000 whereas females usually have two embedded tusks, neither erupting. Other 0:12:05.120 --> 0:12:09.520 less common expressions of narwhal dentition include males with two tusks, 0:12:09.559 --> 0:12:12.880 males with two embedded tusks so neither one comes out, 0:12:13.320 --> 0:12:17.520 females with one erupted and one embedded tusk, and females 0:12:17.559 --> 0:12:20.520 with two erupted tusks. And I checked. I think there's 0:12:20.559 --> 0:12:23.680 only been one documented case of the ladder of the 0:12:23.760 --> 0:12:27.200 females with two tusks coming out. But the authors of 0:12:27.200 --> 0:12:30.360 this paper do extensive analysis to confirm that these are 0:12:30.400 --> 0:12:33.600 not horns, they are teeth, and they figure out exactly 0:12:33.640 --> 0:12:36.280 what teeth they are. They are the upper canines, and 0:12:36.600 --> 0:12:41.240 in almost all cases, the left upper canine. Now I 0:12:41.280 --> 0:12:42.920 don't know if I'm alone in this, but I am 0:12:43.080 --> 0:12:45.400 just as struck by the fact that the tusk is 0:12:45.400 --> 0:12:48.960 actually the left canine as I am about the fact 0:12:49.000 --> 0:12:52.320 that it's a tooth to begin with. Why the left canine, 0:12:53.200 --> 0:12:57.200 As the paper mentions, narwhal's occasionally have two erupted tusks, 0:12:57.280 --> 0:12:59.840 two tusks of about the same length coming out to 0:13:00.000 --> 0:13:02.839 other It's rare, but you find some like that, And 0:13:02.960 --> 0:13:05.920 if you see pictures of the narwhals with two tusks, 0:13:06.440 --> 0:13:09.760 they look much more appropriate to the preferences of nature. 0:13:09.840 --> 0:13:12.000 You can look up images of this online. In fact, 0:13:12.040 --> 0:13:15.480 even though they're much more rare in the wild. Uh. 0:13:15.520 --> 0:13:18.600 A lot of the images of narwhal skulls have two tusks. 0:13:18.640 --> 0:13:22.000 I guess because the rare ones get photographed more often. Well, 0:13:22.040 --> 0:13:24.400 I mean, I guess. On one hand, the left handed 0:13:24.440 --> 0:13:27.800 side is the sinister side the sinstral side. So if 0:13:28.000 --> 0:13:31.000 you're going to have a crazy, super long tooth emerged 0:13:31.000 --> 0:13:34.839 from your face and maybe the sinister side makes sense, well, 0:13:34.880 --> 0:13:38.319 that's just your twisted mind working. It's it's fancy. I mean, no, 0:13:38.840 --> 0:13:42.800 come on, like the two tusks, they look more like 0:13:42.880 --> 0:13:46.040 something that you would just buy intuition expect to find 0:13:46.080 --> 0:13:49.080 in the ocean, much more so than the common one 0:13:49.160 --> 0:13:51.360 tusk skull, which when I see it, I mean, it 0:13:51.520 --> 0:13:56.760 is beautiful, but it also it looks unbalanced and wrong. Though. 0:13:56.760 --> 0:13:59.080 I will say that the two tusks or wall, if 0:13:59.080 --> 0:14:03.280 you look up images of specimens of this creature like 0:14:03.360 --> 0:14:06.720 this one is perplexing as well because it kind of 0:14:06.760 --> 0:14:11.960 it doesn't form um. They're not perfectly parallel to each other. 0:14:12.200 --> 0:14:15.640 It creates kind of a V shape that is a 0:14:15.640 --> 0:14:19.760 little confusing and certainly makes you lean more into possibilities. Yeah, 0:14:19.760 --> 0:14:23.640 that this is not about stabbing or using these uh 0:14:23.640 --> 0:14:27.200 these tusks for some sort of a a physical practical use, 0:14:27.280 --> 0:14:30.880 but something else like that they look more like communications 0:14:30.960 --> 0:14:33.200 array when you see two of them as opposed to 0:14:33.200 --> 0:14:35.880 just one. Well, yeah, I think having two of them 0:14:35.960 --> 0:14:40.000 even further highlights that these are obviously not practically useful 0:14:40.120 --> 0:14:42.960 for something like like catching prey or eating you know, 0:14:43.040 --> 0:14:44.800 you just you look at that and it's like, how 0:14:44.840 --> 0:14:47.320 how's that going to work? And it's obviously they're not 0:14:47.480 --> 0:14:50.240 using it for that, at least not most of the time. 0:14:50.720 --> 0:14:53.040 I know. There are these little anecdotes of somebody saying 0:14:53.040 --> 0:14:54.920 that you know, they saw a nar wall like tap 0:14:54.920 --> 0:14:57.280 a fish with a tusk or something, so maybe, but 0:14:57.840 --> 0:15:00.000 that that clearly does not appear to be a prime 0:15:00.080 --> 0:15:02.680 very use of them. But I wanted to come back 0:15:02.720 --> 0:15:06.560 to the idea that it looks it looks wrong at 0:15:06.600 --> 0:15:08.440 least even though of course you know this is what 0:15:08.560 --> 0:15:12.320 evolution selected. It is, uh, it is right for something, 0:15:12.600 --> 0:15:16.120 it has a use, but it looks wrong to our brains, 0:15:16.240 --> 0:15:18.880 and so it causes you to ask the question, well, 0:15:18.920 --> 0:15:21.920 first of all, why is it that evolution drove the 0:15:22.000 --> 0:15:25.480 narwhall to be unbalanced in this way? And and second, 0:15:25.640 --> 0:15:29.280 why is it that my intuition tells me incorrectly that 0:15:29.360 --> 0:15:32.440 a long, single tusk should not emerge from the socket 0:15:32.520 --> 0:15:36.800 of the left maxillary canine, like if an animal has 0:15:36.880 --> 0:15:38.920 one tusk, it should come out of a hole right 0:15:38.960 --> 0:15:41.240 in the middle. And so this is going to be 0:15:41.280 --> 0:15:43.280 the beginning of a series of episodes. We're gonna do 0:15:43.320 --> 0:15:45.960 at least two maybe more. What we'll see, uh, but 0:15:46.080 --> 0:15:49.200 there will be on a symmetry in the animal world 0:15:49.280 --> 0:15:53.320 when an animal's left and right do not match. So 0:15:53.360 --> 0:15:56.600 in future episodes we will we will explore some theoretical 0:15:56.720 --> 0:16:02.000 questions about about embryonic developed meant and how animal asymmetry 0:16:02.120 --> 0:16:06.320 comes about. Uh, probably look at some crabs and other crustaceans. 0:16:06.320 --> 0:16:08.560 But today I think we're gonna we're gonna look especially 0:16:08.600 --> 0:16:11.840 at like whales and uh and other swimming creatures of 0:16:11.840 --> 0:16:15.600 the sea, UH, and just generally highlights some interesting examples 0:16:15.640 --> 0:16:24.520 of asymmetry in the natural world. Now, I think it's 0:16:24.560 --> 0:16:27.480 important to acknowledge at the beginning that the kind of 0:16:27.920 --> 0:16:31.680 symmetry or asymmetry we're talking about, the kind of symmetry 0:16:31.840 --> 0:16:35.920 we expect to see in animals is only one specific 0:16:36.040 --> 0:16:40.520 type of symmetry, called bilateral symmetry, and not all animals 0:16:40.520 --> 0:16:44.800 actually possess it, even in an approximate sense. So bilateral 0:16:44.840 --> 0:16:48.160 symmetry is actually a fairly restricted type of symmetry. There 0:16:48.160 --> 0:16:51.200 are three dimensions of space, and if you plot a 0:16:51.280 --> 0:16:53.960 human body on those three dimensions, you'll notice we are 0:16:54.000 --> 0:16:58.600 actually only symmetrical along one of those three axes. So 0:16:58.720 --> 0:17:01.720 on height, our head in our feet, of course, are 0:17:01.760 --> 0:17:05.720 not mirror images of each other. On depth, we're also 0:17:05.800 --> 0:17:08.800 not symmetrical. Our backs do not mirror our fronts. We 0:17:08.840 --> 0:17:12.240 don't have faces or butts on both sides. It's only 0:17:12.280 --> 0:17:16.399 across our width that you find approximate symmetry our left side. 0:17:16.520 --> 0:17:20.959 Roughly mirrors are right side. And in three dimensional space, 0:17:21.119 --> 0:17:25.280 the most perfectly symmetrical form is actually a sphere, since 0:17:25.320 --> 0:17:28.480 if you divide a sphere in half along any plane 0:17:28.480 --> 0:17:32.920 you want, no matter it's orientation, the two sides will match. Uh. 0:17:32.960 --> 0:17:35.320 And I hesitate because I'm about to make a generalization 0:17:35.359 --> 0:17:38.160 about geometry. I'm always afraid I'm gonna say something wrong there. 0:17:38.160 --> 0:17:40.040 But I tried to look this up and confirm it. 0:17:40.560 --> 0:17:44.440 I believe this is unique to the sphere, that all 0:17:44.440 --> 0:17:48.760 other three D shapes can be bisected in ways where 0:17:48.880 --> 0:17:52.160 the two halves may have equal volume but will not 0:17:52.280 --> 0:17:54.840 match an outline. But if you cut a sphere in half, 0:17:55.160 --> 0:17:59.000 it's always two perfect hemispheres, no matter what direction you 0:17:59.040 --> 0:18:02.000 cut from. And this actually connects to a passage in 0:18:02.000 --> 0:18:05.760 a book I came across by the mathematician Herman Vile 0:18:06.320 --> 0:18:09.960 called Symmetry from Princeton University Press in nineteen fifty two, 0:18:10.480 --> 0:18:15.399 and Vile is writing about about the history of association 0:18:15.560 --> 0:18:21.359 between symmetry in the geometric sense and the concept of beauty. Uh. 0:18:21.480 --> 0:18:25.560 You know, moral virtue, and perfection, and he writes quote 0:18:25.600 --> 0:18:29.600 because of their complete rotational symmetry, the circle in the 0:18:29.600 --> 0:18:32.600 plane and the sphere in space were considered by the 0:18:32.640 --> 0:18:38.680 Pythagoreans the most perfect geometric figures, and Aristotle ascribed spherical 0:18:38.760 --> 0:18:43.200 shape to the celestial bodies because any other would detract 0:18:43.400 --> 0:18:47.679 from their heavenly perfection. Now it's interesting, knowing what we 0:18:47.720 --> 0:18:50.520 know now about the cause of spherical objects in space, 0:18:51.000 --> 0:18:53.640 namely gravity, right that as as the mass of an 0:18:53.640 --> 0:18:58.119 object increases, it tends to become more and more perfectly spherical, 0:18:58.520 --> 0:19:00.920 with the I guess the end point of that being 0:19:00.960 --> 0:19:04.280 that a black hole theoretically is pretty much perfectly spherical, 0:19:04.600 --> 0:19:07.960 whereas smaller objects in space, because gravity is not as 0:19:07.960 --> 0:19:11.080 strong a force on the on the smoothing of their 0:19:11.080 --> 0:19:13.639 outer edges, they can have more irregular shapes. This is 0:19:13.640 --> 0:19:17.520 why you get irregular potato shaped comets and asteroids. But 0:19:17.680 --> 0:19:19.680 you know, you start getting up into planet size and 0:19:20.000 --> 0:19:23.399 you move closer and closer to spherical perfection. But anyway, 0:19:23.480 --> 0:19:26.560 Vile goes on to quote a poet named Anna Wickham, 0:19:26.600 --> 0:19:30.000 which was actually the pseudonym of a modernist poet named 0:19:30.119 --> 0:19:35.000 Edith Alice Mary Harper uh in connecting the idea of 0:19:35.240 --> 0:19:40.720 symmetry to God or the divine being, so Wickham rights quote, God, 0:19:40.880 --> 0:19:43.840 thou great symmetry, who put a biting lust in me? 0:19:44.000 --> 0:19:47.399 From whence my sorrow spring for all my frittered days 0:19:47.480 --> 0:19:50.640 that I have spent in shapeless ways, Give me one 0:19:50.720 --> 0:19:54.840 perfect thing, and then vile rights. Symmetry, as wide or 0:19:54.880 --> 0:19:57.760 as narrow as you may define its meaning, is one 0:19:57.800 --> 0:20:00.399 idea by which man, through the ages has tried to 0:20:00.480 --> 0:20:06.200 comprehend and create order. Beauty and perfection. And equating symmetry 0:20:06.240 --> 0:20:09.600 with beauty, goodness and perfection and even divinity can be 0:20:09.680 --> 0:20:13.480 found all throughout literature. I think of Blake's The Tiger. 0:20:13.560 --> 0:20:17.320 You know what immortal hander eye could frame thy fearful symmetry. 0:20:17.480 --> 0:20:19.400 I guess it makes you want to say symmetry there, 0:20:20.119 --> 0:20:23.480 But this clearly is has not just a geometric meaning, 0:20:23.520 --> 0:20:25.639 where you will the two halves of the tiger do 0:20:25.840 --> 0:20:28.280 match one another roughly because it is an animal with 0:20:28.320 --> 0:20:32.119 bilateral symmetry, but that it means something more than that. 0:20:32.240 --> 0:20:36.879 Symmetry here is in some sense synonymous with greatness or divinity. Yeah, 0:20:36.960 --> 0:20:39.600 it's so that the tiger is is a perfect organism 0:20:39.680 --> 0:20:43.720 and Blake's I here, um yeah, And you know, I 0:20:43.760 --> 0:20:48.040 can be said about our obsession with with symmetry to 0:20:48.200 --> 0:20:51.199 the point where it's like a flawed obsession with it. 0:20:51.359 --> 0:20:54.880 Like we think that we want, say, perfectly symmetrical faces, 0:20:55.359 --> 0:20:59.000 when most faces are certainly not a symmetrical And if 0:20:59.040 --> 0:21:02.359 you take even famous and you know, often held up 0:21:02.400 --> 0:21:05.920 his beautiful faces and you do the trick of creating 0:21:05.920 --> 0:21:08.439 a symmetrical symmetrical face out of it, it's going to 0:21:08.480 --> 0:21:10.920 look wrong to your eyes. It may it may look 0:21:11.000 --> 0:21:13.800 very well look unnatural. Well. The the whole quest for 0:21:13.880 --> 0:21:18.000 symmetry in in aesthetic beauty um is one of those 0:21:18.040 --> 0:21:21.720 where it's like there's almost a kind of inverse uncanny valley. 0:21:21.760 --> 0:21:25.000 It seems like people's natural preferences or something that tends 0:21:25.200 --> 0:21:28.400 very close to symmetry. But then if you get right 0:21:28.480 --> 0:21:30.760 up to it and go to actual symmetry, it's like, 0:21:30.760 --> 0:21:33.520 oh no, no, no, that that looks all wrong. So 0:21:33.560 --> 0:21:35.480 you want to be like right in the zone where 0:21:35.480 --> 0:21:40.240 you're approaching symmetry, but not there. Yeah, though there, Certainly 0:21:40.240 --> 0:21:42.280 when you get into design it gets it gets weird 0:21:42.320 --> 0:21:47.720 because take airplanes, for example, airplanes tend to look best 0:21:47.760 --> 0:21:51.000 to our I when they are perfectly symmetrical, and then 0:21:51.119 --> 0:21:53.320 there are various reasons for that. And if you see 0:21:53.840 --> 0:21:56.800 an asymmetrical airplane, and there there have been certainly done 0:21:56.840 --> 0:22:02.600 some some very asymmetrical looking airplane designs uh uh here 0:22:02.600 --> 0:22:05.920 and there throughout aviation history, they do look incredibly wrong 0:22:05.960 --> 0:22:09.439 to the eye. Um, and that shouldn't fly. Yeah, Like 0:22:09.480 --> 0:22:11.720 how how how is that a good idea? But I 0:22:11.720 --> 0:22:15.720 mean it can work, it's just you you generally don't 0:22:15.760 --> 0:22:18.240 see it. Well, there's a different logic at work here. 0:22:18.280 --> 0:22:21.200 But that just sort of reminds me, incidentally of how 0:22:21.240 --> 0:22:23.560 I'm always surprised at the idea that a plane can 0:22:23.600 --> 0:22:25.960 continue to fly with one engine, you know, as like 0:22:26.040 --> 0:22:28.600 two jet engines, Like one engine fails, but it can 0:22:28.680 --> 0:22:31.000 keep flying with the other one, which makes that that 0:22:31.040 --> 0:22:33.240 doesn't seem right. It seems like, well, if only one 0:22:33.320 --> 0:22:35.320 engine is going, then shouldn't it just sort of like 0:22:35.400 --> 0:22:38.320 spin out of control? But no, I mean, as long 0:22:38.359 --> 0:22:42.120 as it's generating forward thrust, it can keep going usually Yeah. 0:22:42.880 --> 0:22:45.679 But anyway, so there's always a strong argument, you know, 0:22:45.720 --> 0:22:49.399 that much of what we find beautiful and good is 0:22:49.680 --> 0:22:53.320 biologically contingent, that it has at least in part to 0:22:53.440 --> 0:22:55.760 do with the kind of animals we are and how 0:22:55.800 --> 0:22:58.600 we relate to our environment. And of course we are 0:22:58.680 --> 0:23:01.520 part of that clade of animal all is known as biolateria. 0:23:01.760 --> 0:23:07.719 These these are the animals featuring bilateral symmetry during embryonic development. Now, 0:23:07.720 --> 0:23:10.240 of course this is always approximate, right, because while you're 0:23:10.320 --> 0:23:12.879 left and you're right in one sense do match. There 0:23:12.880 --> 0:23:14.960 are mirror images of each other, as you were just 0:23:15.000 --> 0:23:18.359