WEBVTT - From the Vault: Hooves, Part 2 0:00:06.320 --> 0:00:09.280 Hey, welcome to Stuff to Blow your Mind. It's Saturday. 0:00:09.360 --> 0:00:11.959 It's time for a vault episode and this is going 0:00:12.000 --> 0:00:15.920 to be Hoof's Part two, which originally published six thirteen, 0:00:16.280 --> 0:00:17.239 twenty twenty three. 0:00:17.720 --> 0:00:23.439 Please enjoy Welcome to Stuff to Blow Your Mind, a 0:00:23.520 --> 0:00:28.280 production of iHeartRadio. 0:00:31.960 --> 0:00:34.279 Hey, welcome to Stuff to Blow your Mind. My name 0:00:34.320 --> 0:00:35.320 is Robert Lamb. 0:00:35.520 --> 0:00:37.880 And I'm Joe McCormick, and we're back with part two 0:00:38.000 --> 0:00:41.200 of our series on the horse hoof. Now. In part one, 0:00:41.720 --> 0:00:45.080 we discussed the anatomical form of the horse hoof, with 0:00:45.120 --> 0:00:48.839 an emphasis on the alarming fact that the hoof is 0:00:48.960 --> 0:00:54.200 essentially a highly specialized form of the tetrapod middle finger. 0:00:54.400 --> 0:00:56.640 So when you see a horse galloping around, yes, it 0:00:56.760 --> 0:01:01.320 is running around on all middle fingers and toes. We 0:01:01.360 --> 0:01:04.640 talked about an ancient legend about the horse ridden by 0:01:04.720 --> 0:01:09.080 Julius Caesar, which some artists have depicted as having dock 0:01:09.160 --> 0:01:12.200 in hair and human feet instead of hoofs, at least 0:01:12.240 --> 0:01:16.240 on the first two legs. Rob's idea, I think was 0:01:16.319 --> 0:01:18.960 that this it's possible that these stories could be based 0:01:19.000 --> 0:01:23.440 on observations of what are called polydactyl horses, horses born 0:01:23.520 --> 0:01:26.800 with extra hooflets on the sides of the primary hoof, 0:01:26.840 --> 0:01:28.120 which do in fact exist. 0:01:28.520 --> 0:01:32.320 Yeah, this seems to be the more sensible interpretation that 0:01:32.360 --> 0:01:35.720 you see taken by folks. And I don't think anyone's 0:01:35.760 --> 0:01:41.240 actually arguing that these horses had like human fore feet, 0:01:41.840 --> 0:01:44.679 but it looks hilarious in the illustrations. 0:01:45.280 --> 0:01:48.440 It does. And we finally talked about the evolution of 0:01:48.440 --> 0:01:51.440 the horse hoof, with the commonly accepted narrative being that 0:01:51.840 --> 0:01:55.560 millions of years ago, the ancestors of modern horses lived 0:01:55.600 --> 0:02:00.000 in more forested environments, maybe warmer, wetter environments. They were 0:02:00.160 --> 0:02:03.280 much smaller, maybe about the size of dogs, and had 0:02:03.400 --> 0:02:08.080 multiple toes per feet. Then, due to climate and habitat changes, 0:02:08.160 --> 0:02:12.560 they became grassland dwellers, which drove them to evolve larger 0:02:12.600 --> 0:02:17.360 body sizes and select for galloping speed, and these changes 0:02:17.400 --> 0:02:21.360 coincided with the loss of peripheral toes until you end 0:02:21.440 --> 0:02:23.720 up with the modern horse and its relatives in the 0:02:23.760 --> 0:02:26.800 genus equis, so that would include the zebra and the 0:02:26.919 --> 0:02:31.320 ass all having only one toe per foot, the columnar hoof. 0:02:32.080 --> 0:02:34.320 Now today, we wanted to continue the series on the 0:02:34.320 --> 0:02:38.119 horse hoof getting into a couple other things, about horsecof 0:02:38.120 --> 0:02:41.320 evolution as well as the invention of the horseshoe. But 0:02:41.440 --> 0:02:44.079 before we do that, I wanted to take a brief 0:02:44.160 --> 0:02:48.760 detour into a metaphorical connection to the hoof, which concerns 0:02:49.080 --> 0:02:54.520 medical diagnostics and more generally, the realm of statistical reasoning. 0:02:55.160 --> 0:02:59.240 So there's a famous aphorism widely used in medical education, 0:02:59.520 --> 0:03:03.160 often invoked by practicing physicians, and it goes like this, 0:03:03.840 --> 0:03:09.200 when you hear hoof beats, look for horses, not zebras. Rob. 0:03:09.240 --> 0:03:10.840 I think this thing may have come up on the 0:03:10.880 --> 0:03:13.840 show in the past that I couldn't remember when, but 0:03:13.880 --> 0:03:15.760 I'm sure you've heard this before, right. 0:03:16.440 --> 0:03:20.399 Yeah, yeah, And it basically is what it sounds like, right, it's, 0:03:20.680 --> 0:03:23.760 you know, whatever the evidence seems to indicate, go for 0:03:23.800 --> 0:03:28.240 the more likely and more statistically reasonable explanation for. 0:03:29.800 --> 0:03:32.400 The evidence, right. So I was looking up the history 0:03:32.400 --> 0:03:35.360 of this quote in a chapter on medical aphorisms in 0:03:35.400 --> 0:03:39.400 a book called White Coat Tails Medicine's Heroes, Heritage and 0:03:39.440 --> 0:03:44.120 Misadventures by Robert B. Taylor published by Springer. So I'll 0:03:44.120 --> 0:03:46.200 refer back to that chapter in a second. But yeah, Rob, 0:03:46.480 --> 0:03:49.120 like you say, the point of this aphorism is that 0:03:49.160 --> 0:03:52.080 when a patient presents with symptoms X, Y, and Z, 0:03:52.760 --> 0:03:56.720 you should start by thinking about the most common conditions 0:03:57.080 --> 0:04:01.680 within the population associated with that club of symptoms, rather 0:04:01.800 --> 0:04:05.560 than jumping to assumptions about rare diseases. So, for example, 0:04:05.840 --> 0:04:09.080 if a patient presents at a US clinic with flu 0:04:09.280 --> 0:04:12.920 like symptoms, it's better to start by investigating the possibility 0:04:13.000 --> 0:04:16.520 that they have the flu or common cold, or now 0:04:16.560 --> 0:04:20.160 maybe COVID, rather than to start by investigating whether they 0:04:20.160 --> 0:04:24.159 have contracted the hindra virus from a flying fox in Australia. 0:04:24.960 --> 0:04:29.039 Taylor traces this saying back to an American medical researcher 0:04:29.160 --> 0:04:32.520 named Theodore E. Woodward who lived nineteen fourteen to two 0:04:32.520 --> 0:04:36.240 thousand and five, who taught at the University of Maryland 0:04:36.279 --> 0:04:39.360 School of Medicine. And it seems actually the common form 0:04:39.400 --> 0:04:42.920 of this aphorism might be a paraphrase, and the more 0:04:43.000 --> 0:04:47.960 accurate original quote may have been don't look for zebras 0:04:48.040 --> 0:04:51.800 on Green Street. That might be a little perplexing, but 0:04:52.240 --> 0:04:55.400 it makes sense in the context because Green Street was 0:04:55.480 --> 0:04:59.279 the location of the University of Maryland hospital in Baltimore, 0:04:59.360 --> 0:05:01.520 and he was teaching at the University of Maryland to 0:05:01.680 --> 0:05:04.000 students there, so of course you can see why it 0:05:04.000 --> 0:05:06.520 would need to be rephrased to make more sense outside 0:05:06.560 --> 0:05:10.360 of its original locality. But I also think the localization 0:05:10.600 --> 0:05:15.080 to Baltimore geography highlights something important, which is that this 0:05:15.240 --> 0:05:18.799 aphorism is only useful when you're talking about a known 0:05:19.040 --> 0:05:23.520 population of patients in which the frequency of certain diseases 0:05:23.600 --> 0:05:27.360 or conditions is fairly well understood. Because if you were 0:05:27.400 --> 0:05:29.720 talking to a group of medical students, maybe in a 0:05:30.200 --> 0:05:33.720 region of southern Africa where zebras are abundant, it might 0:05:33.800 --> 0:05:37.000 make sense to use the aphorism inverted, I guess, depending 0:05:37.000 --> 0:05:39.159 on how many horses there are around as well. But 0:05:39.320 --> 0:05:41.479 in the same sense, you have to know what the 0:05:41.520 --> 0:05:45.160 frequencies are in the population you're looking at before deploying this. 0:05:46.320 --> 0:05:47.279 Yeah, that's true. 0:05:47.600 --> 0:05:50.760 Now, I find this the reasoning behind the saying actually 0:05:50.839 --> 0:05:52.960 kind of interesting, because if you interpret it in the 0:05:53.080 --> 0:05:55.800 usual way, it's a piece of advice that can seem 0:05:55.880 --> 0:05:59.800 rather obvious, like common explanations are more common than rare 0:05:59.839 --> 0:06:03.520 way ones. But I think as a general rule, when 0:06:03.640 --> 0:06:07.479 looking for explanations, we do have to be reminded to 0:06:07.600 --> 0:06:12.200 start by considering what is most likely in terms of frequency, 0:06:12.839 --> 0:06:17.040 because there are all kinds of mental biases that constantly 0:06:17.160 --> 0:06:21.680 tempt us to start looking for highly unusual causes for 0:06:21.839 --> 0:06:26.760 unexplained phenomena before we've exhausted all of the extremely commonplace 0:06:26.839 --> 0:06:32.320 candidates for one thing. Unusual causes and explanations are usually 0:06:32.680 --> 0:06:36.239 more exciting. They kind of stick in the mind because 0:06:36.279 --> 0:06:39.080 of our level of interest in them, and they can 0:06:39.160 --> 0:06:42.520 quite easily then come to mind when we start searching 0:06:42.520 --> 0:06:45.360 around for an explanation. They're sort of at the top 0:06:45.400 --> 0:06:49.240 of the toy box right now. In this section of 0:06:49.240 --> 0:06:52.160 the book I was talking about, Taylor makes an interesting 0:06:52.240 --> 0:06:56.640 point about the zebra aphorism, which I hadn't quite considered. 0:06:56.680 --> 0:06:59.159 I was just thinking at the first order level of 0:06:59.360 --> 0:07:03.320 more common explanations and less common explanations. But Taylor also 0:07:03.400 --> 0:07:08.480 writes quote as a clinical corollary, experienced diagnosticians look first 0:07:08.600 --> 0:07:16.120 for uncommon manifestations of common conditions rather than common manifestations 0:07:16.240 --> 0:07:20.920 of uncommon diseases. Now that seemed really interesting to me. 0:07:21.280 --> 0:07:23.680 I hadn't quite thought about it that way. And of 0:07:23.680 --> 0:07:26.640 course it would depend on exactly how uncommon you mean 0:07:26.680 --> 0:07:28.520 in each clause of that sentence, Like if you were 0:07:28.560 --> 0:07:32.080 to represent them as actual percentage chances and stuff. The 0:07:32.520 --> 0:07:35.040 math might break out in different ways. But if a 0:07:35.080 --> 0:07:37.480 certain set of symptoms appears in I don't know, only 0:07:37.640 --> 0:07:41.640 three percent of cases of an extremely common condition that 0:07:42.080 --> 0:07:45.040 affects you know, millions of people every year, it is 0:07:45.080 --> 0:07:50.360 probably still worth investigating that diagnosis the uncommon manifestation of 0:07:50.400 --> 0:07:54.600 the extremely common condition before you look at the possibility 0:07:54.640 --> 0:07:58.440 of a condition that matches the symptoms very closely. But 0:07:58.640 --> 0:08:00.640 you know, you might only see all a couple of 0:08:00.640 --> 0:08:03.840 cases in the world per year, it's extremely rare. You'd 0:08:03.920 --> 0:08:08.120 still get way more hits of confirmation on the on 0:08:08.240 --> 0:08:11.320 the uncommon version of the common condition. 0:08:11.720 --> 0:08:14.560 It reminds me of various discussions we've had about cryptozoology 0:08:15.040 --> 0:08:20.760 and the interpretations and misinterpretations of dead animals and in 0:08:20.760 --> 0:08:25.520 some cases dead human beings, where you're looking at some 0:08:25.720 --> 0:08:28.200 rate of decay and yeah, are you looking at it 0:08:28.280 --> 0:08:31.040 as the as an uncommon manifestation of a common condition, 0:08:31.200 --> 0:08:32.720 and in other words, are you're looking at as kind 0:08:32.760 --> 0:08:37.280 of like a novel pattern or appearance in decay of 0:08:37.520 --> 0:08:41.079 just a normal, mundane animal, or are you going to 0:08:41.160 --> 0:08:43.920 jump to the to that extreme level and think, well, no, 0:08:44.040 --> 0:08:47.199 this is just how it looks and we've just never 0:08:47.240 --> 0:08:48.600 seen this creature before. 0:08:48.960 --> 0:08:51.520 Yeah. Yeah. However, I want to come back on the 0:08:51.559 --> 0:08:55.400 other end, because if you search for medical case reports 0:08:55.640 --> 0:08:58.880 citing this aphorism, which I was doing a lot of times, 0:08:58.920 --> 0:09:03.520 it will be specific to discuss cases where it was 0:09:03.559 --> 0:09:07.920 a zebra on Green Street, the rare and unexpected diagnosis 0:09:07.960 --> 0:09:11.319 that turned out to be correct. So just one example 0:09:11.360 --> 0:09:14.920 I was looking at this was a case report published 0:09:14.960 --> 0:09:18.120 in Clinical Practice in Cases in Emergency Medicine in twenty 0:09:18.240 --> 0:09:21.920 nineteen by Loupez at All called Beware of the Zebra, 0:09:22.200 --> 0:09:25.640 nine year Old with Fever. I believe this incident took 0:09:25.679 --> 0:09:28.240 place in the US state of North Carolina. So it 0:09:28.280 --> 0:09:32.000 was a nine year old girl whose family spoke only French, 0:09:32.160 --> 0:09:37.280 and they presented at the hospital with the patient having 0:09:37.320 --> 0:09:42.120 an abdominal pain, vomiting, intermittent fevers, fatigue, and headache, and 0:09:42.160 --> 0:09:44.560 because there was a language barrier, everything had to be 0:09:44.640 --> 0:09:46.880 done with the help of an interpreter, and it seems 0:09:46.920 --> 0:09:50.800 that this led to some maybe some original misunderstandings about 0:09:51.080 --> 0:09:54.600 the case history. So the doctors tried to diagnose based 0:09:54.640 --> 0:09:57.920 on all the normal explanations that they would be likely 0:09:57.960 --> 0:10:01.080 to see in their patient population, but none of the 0:10:01.080 --> 0:10:05.160 common diagnoses really fit her case. Her condition continued to 0:10:05.160 --> 0:10:08.400 get worse. It even became life threatening, and the breakthrough 0:10:08.440 --> 0:10:11.160 seemed to come when the doctors began looking outside the 0:10:11.240 --> 0:10:14.160 normal slate of conditions encountered in their practice in the 0:10:14.280 --> 0:10:18.240 United States. Finally, they learned that the girl's family had 0:10:18.280 --> 0:10:21.800 just in the weeks before, arrived from the Congo, where 0:10:21.920 --> 0:10:26.120 malaria is common. The care providers eventually ordered a test 0:10:26.280 --> 0:10:28.600 that would put them on the right track. They write 0:10:28.600 --> 0:10:32.240 in their report, quote, this test was a peripheral blood smear, 0:10:32.320 --> 0:10:37.560 specifically a thick and thin smear, which revealed Plasmodium falciparum, 0:10:37.720 --> 0:10:41.080 and this is one of the protozoa responsible for causing malaria, 0:10:41.800 --> 0:10:45.400 leading to a final diagnosis of cerebral malaria. And then 0:10:45.440 --> 0:10:47.760 they write from here they contacted the twenty four hour 0:10:47.840 --> 0:10:53.720 CDC hotline to immediately get the appropriate anti malarial medication. 0:10:54.320 --> 0:10:57.240 They put the girl on a quinine drip and admitted 0:10:57.280 --> 0:11:00.559 her to the pediatric intensive care unit. And then they say, 0:11:00.640 --> 0:11:03.520 quote remarkably, within four weeks, she made a full recovery 0:11:03.559 --> 0:11:07.400 and returned home with her family. So thankfully, the patient 0:11:07.480 --> 0:11:10.280 was all right in the end, but she potentially could 0:11:10.280 --> 0:11:14.080 have died if doctors hadn't made the locally unusual but 0:11:14.200 --> 0:11:17.440 correct diagnosis and given her the right treatment. And so 0:11:17.520 --> 0:11:20.560 the authors say in their conclusion quote, many of us 0:11:20.600 --> 0:11:23.400 are taught the common aphorism in medical school. When you 0:11:23.440 --> 0:11:27.040 hear hoof beats, think horses, not zebras. When approaching a 0:11:27.120 --> 0:11:29.280 nine year old with fever, we hear the hoof beat 0:11:29.320 --> 0:11:32.480 symptoms and tend to think of the typical diagnoses that 0:11:32.559 --> 0:11:36.160 are commonly seen in our pediatric population. Yet if we 0:11:36.200 --> 0:11:38.560 are not thinking about the zebras, we will miss this 0:11:38.679 --> 0:11:42.160 common presentation of a disease that is uncommon north of 0:11:42.200 --> 0:11:45.200 the equator, which could lead to high morbidity and possibly 0:11:45.240 --> 0:11:48.880 even mortality for patients. So it's very good that they 0:11:48.920 --> 0:11:52.960 were able to discover this intervene and probably save the 0:11:53.000 --> 0:11:56.280 girl's life. But it highlights how there's a difficult balance, 0:11:56.480 --> 0:11:59.880 Like if you go looking for zebras before you look 0:12:00.040 --> 0:12:03.160 for horses on Green Street, you will waste a lot 0:12:03.200 --> 0:12:07.040 of time and resources and potentially cause frequent misdiagnoses that 0:12:07.080 --> 0:12:10.920 could harm people. But if you never consider the possibility 0:12:10.920 --> 0:12:14.160 of zebra's on Green Street. There will be rare but 0:12:14.320 --> 0:12:17.160 very real cases where you could save somebody's life but 0:12:17.240 --> 0:12:17.720 you don't. 0:12:18.240 --> 0:12:21.440 Yeah, that's a great point. Yeah, certainly looking at the 0:12:21.559 --> 0:12:25.040 like the professional end of the scenario, because on the 0:12:25.080 --> 0:12:27.520 other end, like say the user end and the media end, 0:12:28.000 --> 0:12:31.400 I mean, zebra on Green Street. That's a great headline. 0:12:31.840 --> 0:12:34.319 You're gonna that's the headline that's gonna stick in your mind, 0:12:34.679 --> 0:12:36.480 and then when you're going to see the doctor, you're 0:12:36.520 --> 0:12:39.400 gonna be like, hey, doc, is it possible that a 0:12:39.480 --> 0:12:42.520 rare amiba is eating my flesh? Or something to that effect, 0:12:42.520 --> 0:12:45.000 because that's what you saw in the headline, that's what 0:12:45.040 --> 0:12:50.320 you saw on the the documentary series that that that 0:12:50.880 --> 0:12:53.560 sensationalized a rare case, right. 0:12:53.640 --> 0:12:56.800 I Mean. The the difficult thing is like, because of 0:12:56.880 --> 0:13:00.600 the way we emotionally react to stories like this, I 0:13:00.600 --> 0:13:03.000 feel like it kind of tends to have the effect 0:13:03.000 --> 0:13:05.000 of making us think, well, maybe then I should start 0:13:05.040 --> 0:13:10.360 looking for diagnoses of unusual diseases in patient populations. So 0:13:10.520 --> 0:13:14.239 it just highlights like diagnosis in the specific case of medicine, 0:13:14.280 --> 0:13:20.920 and searching for explanations for unknown phenomena generally is really difficult. 0:13:21.000 --> 0:13:26.760 It involves a balance between prioritizing likely explanations, which are 0:13:28.040 --> 0:13:31.040 by very definition almost always going to be correct, but 0:13:31.280 --> 0:13:35.360 also being open minded enough to catch the unusual ones 0:13:35.400 --> 0:13:38.960 when they arise. And obviously, I think a big part 0:13:38.960 --> 0:13:42.240 of the art of medicine is gaining good intuition and 0:13:42.960 --> 0:13:48.880 establishing sound processes to prioritize explanations in a reasonable way 0:13:48.960 --> 0:13:52.120 based on what we know about frequency, but then also 0:13:52.240 --> 0:13:56.040 to be able to catch the cases that are unusual 0:13:56.200 --> 0:14:09.400 and intervene appropriately to help people. All right, you want 0:14:09.400 --> 0:14:11.240 to talk a little bit about the evolution of the 0:14:11.240 --> 0:14:11.760 horse hoof? 0:14:12.160 --> 0:14:13.800 Yeah, yeah, we should probably talk a little bit more 0:14:13.840 --> 0:14:16.880 about how they came to run about in their middle fingers. 0:14:17.440 --> 0:14:20.960 We talked in the last episode about a pretty commonly 0:14:21.000 --> 0:14:25.440 accepted story of how that evolutionary process occurred, but there 0:14:25.480 --> 0:14:30.120 was still some uncertainty about exactly why the one toe 0:14:30.160 --> 0:14:33.280 making contact with the ground is favored over keeping the 0:14:34.160 --> 0:14:37.080 larger number of toes that the ancestors of horses used 0:14:37.080 --> 0:14:39.600 to have, And to some degree I think that question 0:14:39.720 --> 0:14:42.680 is still not fully settled. There are still some questions 0:14:42.680 --> 0:14:45.960 about why exactly the one toe was favored. We do 0:14:46.120 --> 0:14:48.920 know that the ancestors of horses and zebras and asses 0:14:49.120 --> 0:14:53.360 had multiple toes per foot. But what is gained by 0:14:53.400 --> 0:14:57.200 going quad bird? You know, the middle fingers across all 0:14:57.200 --> 0:15:01.320 four feet, So the evolution of is called monodactyly, having 0:15:01.360 --> 0:15:05.480 one toe monodactyly. It has long been assumed that that 0:15:05.800 --> 0:15:09.880 was useful for allowing a large animal like a modern horse, 0:15:09.960 --> 0:15:13.720 to achieve greater running speed. But I came across an 0:15:13.720 --> 0:15:17.440 interesting alternative idea explored in a paper called the Evolution 0:15:17.560 --> 0:15:22.000 of equid monodactyly, a review including a new hypothesis published 0:15:22.000 --> 0:15:26.240 in Frontiers and Ecology and Evolution by Christine M. Janis 0:15:26.320 --> 0:15:30.720 and Raymond Bernor, and basically here the authors asked what 0:15:30.960 --> 0:15:35.000 if the evolution of the modern equine hoof was a 0:15:35.240 --> 0:15:41.120 product of selection for endurance rather than speed, meaning that 0:15:41.240 --> 0:15:45.880 the primary advantage conferred was in the evolution of an 0:15:45.880 --> 0:15:50.880 efficient and energy efficient spring foot that would support long 0:15:50.960 --> 0:15:57.400 distance trots at medium speed to locate better food resources. So, 0:15:58.120 --> 0:16:02.280 under their hypothesis, the law of extra toes may have 0:16:02.360 --> 0:16:06.520 been a coincidental byproduct of the selection for the more 0:16:06.560 --> 0:16:11.840 efficient spring foot, which helps the horse conserve energy while foraging, 0:16:12.920 --> 0:16:17.440 rather than an adaptation for top speed. Running, which again 0:16:17.520 --> 0:16:20.280 is assumed to be primarily for the purpose of escaping 0:16:20.320 --> 0:16:23.760 the jaws of predators. Now I cite this not to 0:16:23.760 --> 0:16:26.920 say that I think their hypothesis is definitely correct. I 0:16:26.920 --> 0:16:30.320 have no expertise to decide between which explanation of the 0:16:30.360 --> 0:16:34.640 horsfof evolution better fits the evidence, but this possibility made 0:16:34.680 --> 0:16:37.120 me think back again to the Zebras on Green Street 0:16:37.240 --> 0:16:41.680 saying about how sometimes certain explanations seem more likely to 0:16:41.800 --> 0:16:46.000 us not because they're actually more common, but because they're 0:16:46.000 --> 0:16:50.000 more mentally salient. It reminds me I've talked before about 0:16:50.040 --> 0:16:52.280 this idea that I have the sort of sex and 0:16:52.360 --> 0:16:56.720 violence principle in evolutionary reasoning, where what I think I've 0:16:56.760 --> 0:17:00.960 observed is that when people without or sometimes even with 0:17:01.240 --> 0:17:06.000 biological training, are trying to think of possible evolutionary explanations 0:17:06.040 --> 0:17:09.119 for a trait in an organism, we are a little 0:17:09.160 --> 0:17:14.920 too quick to resort to explanations involving either predation or mating, 0:17:15.680 --> 0:17:19.720 and we often overlook extremely common mechanisms in nature, like 0:17:20.160 --> 0:17:25.000 temperature regulation and energy efficiency, which play a huge role 0:17:25.160 --> 0:17:28.280 in the success of a life form. But I think 0:17:28.280 --> 0:17:32.119 maybe they're not as interesting to our brains as sex 0:17:32.200 --> 0:17:35.120 or violence, so we're less likely to think of them. 0:17:35.200 --> 0:17:37.879 They do not bleed, so they do not lead in 0:17:37.960 --> 0:17:38.480 the mind. 0:17:38.960 --> 0:17:41.120 Yeah, it kind of reminds me of past discussions we've 0:17:41.119 --> 0:17:45.080 talked about concerning the stegosaurus, for example, you know, and 0:17:45.800 --> 0:17:48.199 memory serves you know that there have been various interpretations 0:17:48.240 --> 0:17:51.199 over the years, for there are those curious plates on 0:17:51.240 --> 0:17:54.880 their back, as well as very interpretations of just how 0:17:54.920 --> 0:17:58.720 they are positioned. But yeah, you can with something like that, 0:17:58.800 --> 0:18:01.520 you can. You're inevitably you're going to find those explanations 0:18:01.520 --> 0:18:06.120 that have to do with mating, or protection from predators, 0:18:06.240 --> 0:18:10.399 or protection when they're in conflict with others of their kind. 0:18:10.880 --> 0:18:14.960 But yeah, I guess sometimes these ideas that they're used 0:18:14.960 --> 0:18:18.800 for temperature regulation or something like that may feel less exciting. 0:18:18.880 --> 0:18:21.879 May it may feel more mundane. Though I guess you 0:18:21.920 --> 0:18:25.680 could also argue that maybe the more exotic or mysterious 0:18:25.760 --> 0:18:30.720 the feature is, like say those backridges on the stegosaurus, 0:18:31.359 --> 0:18:33.159 maybe that cancels it out to some degree. 0:18:33.200 --> 0:18:34.160 I don't know, but. 0:18:34.280 --> 0:18:36.400 It's hard to imagine a like a seven year old 0:18:36.440 --> 0:18:38.360 or an eight year old playing with the toy stegosaurus 0:18:38.440 --> 0:18:41.600 and be like, look, mom and dad, this guy's warming 0:18:41.680 --> 0:18:45.439 up in the sun watching. That's not what bathtub dinosaurs do. 0:18:45.480 --> 0:18:46.200 They bite each other. 0:18:48.200 --> 0:18:49.920 But again I want to make clear I'm not saying 0:18:49.920 --> 0:18:54.800 I think that the trotting foraging spring hook explanation is 0:18:54.880 --> 0:18:58.600 necessarily better than the high speed running explanation for the horse. 0:18:59.200 --> 0:19:01.360 I don't know, but I think it's important to remember 0:19:01.440 --> 0:19:04.879 to consider those types of explanations as well. Now, another 0:19:04.960 --> 0:19:09.199 question that has come up in several things I was 0:19:09.200 --> 0:19:12.919 reading is about should we really say that the horse 0:19:13.000 --> 0:19:15.760 only has one toe? I mean, it really does basically 0:19:15.760 --> 0:19:19.880 have only one toe that makes contact with the ground, 0:19:20.280 --> 0:19:23.679 But in what sense did it really quote lose the 0:19:23.760 --> 0:19:27.359 other toes. One example of this counter narrative I was 0:19:27.400 --> 0:19:30.760 reading is in an article in The New York Times 0:19:30.800 --> 0:19:34.439 by Veronique Greenwood published February eighth, twenty twenty, called a 0:19:34.480 --> 0:19:37.679 horse has five toes and then it doesn't. And this 0:19:37.840 --> 0:19:41.000 article tells the story of a researcher named Catherine Kavanaugh, 0:19:41.200 --> 0:19:45.399 a biologist at the University of Massachusetts Dartmouth, who was 0:19:45.640 --> 0:19:50.280 looking at preserved horse embryos in the lab when she 0:19:50.359 --> 0:19:54.359 discovered something very interesting, which is that during the earliest 0:19:54.480 --> 0:19:58.800 stages of gestation, the area of the embryo that will 0:19:58.840 --> 0:20:03.119 eventually develop to become the foot become the hoof in 0:20:03.200 --> 0:20:08.959 that area. The embryonic horses have five toes, so this 0:20:09.080 --> 0:20:12.119 period during development only lasts for a couple of days 0:20:12.119 --> 0:20:15.480 before the extra toes begin to sort of fuse and vanish. 0:20:15.880 --> 0:20:18.880 But to read from the article briefly quote, the discovery 0:20:18.880 --> 0:20:23.240 implies something profound about how anatomical development works. As an 0:20:23.240 --> 0:20:26.879 embryo puts itself together, growing from a tiny wad of 0:20:26.920 --> 0:20:31.040 cells into multiple specialized tissues, fed by blood vessels and 0:20:31.119 --> 0:20:34.120 linked by the winding threads of nerves, it is following 0:20:34.160 --> 0:20:37.960 a template. That template is subject to evolution, just like 0:20:38.040 --> 0:20:41.119 other things about the animal. But some moments in the 0:20:41.119 --> 0:20:45.080 process or some routes that development takes may not easily 0:20:45.119 --> 0:20:49.280 be altered, And so the researcher here, Catherine Kavanaugh, is 0:20:49.359 --> 0:20:53.399 quoted saying something about the early steps in toe development 0:20:53.560 --> 0:20:57.159 is stabilized. We don't know why, but that's what we 0:20:57.240 --> 0:21:00.880 think is going on. So I found it's also interesting 0:21:00.920 --> 0:21:04.440 because it's an example of how stages in development can 0:21:04.560 --> 0:21:10.399 become evolutionarily fixed even when they differ from the final form. 0:21:10.920 --> 0:21:14.000 So like for some reason, as the horse is growing 0:21:14.320 --> 0:21:19.280 as an embryo, it needs to develop five fingers before 0:21:19.480 --> 0:21:22.840 or five toes before it can lose four of the 0:21:22.880 --> 0:21:26.600 toes per hoof, so you know, eventually it will have 0:21:26.720 --> 0:21:30.040 functionally one toe making contact with the ground, but the 0:21:30.080 --> 0:21:34.240 development process has to go through this other stage first. 0:21:34.359 --> 0:21:37.639 For some reason, it reminds me of something we discussed 0:21:37.680 --> 0:21:40.040 in our whale episodes about the blowhole of the whale 0:21:40.320 --> 0:21:43.680 being seen to, of course, through the fossil record, travel 0:21:43.880 --> 0:21:45.520 up the snout up to the top of the head, 0:21:45.520 --> 0:21:48.359 but we can also observe this movement in the womb 0:21:48.720 --> 0:21:51.480 as the fetal whale is developing. 0:21:52.119 --> 0:21:56.840 Yeah. Another interesting thing about the horse hoof is that 0:21:56.920 --> 0:21:59.840 there are some people who have pointed out how vestiges 0:22:00.119 --> 0:22:03.520 of the missing toes can still sort of be found 0:22:03.560 --> 0:22:07.280 as little sort of ridges on the sides of the hoof. Yeah. 0:22:07.320 --> 0:22:08.879 I ran across this a lot in some of the 0:22:10.480 --> 0:22:12.400 veterinary sources I was looking at. 0:22:12.640 --> 0:22:15.120 But don't let this take away from your mental enjoyment 0:22:15.160 --> 0:22:18.000 of thinking about the horses running around on its middle fingers, 0:22:18.000 --> 0:22:20.560 which it functionally is it is, I. 0:22:20.520 --> 0:22:22.920 Mean to me, it makes it even more weird. It's 0:22:22.960 --> 0:22:24.600 kind of like if you were to It's kind of 0:22:24.600 --> 0:22:27.240 like if you're looking at Kermit the Frog and someone 0:22:27.280 --> 0:22:29.439 were to tell you, Like there's a difference in saying, hey, 0:22:29.480 --> 0:22:33.080 there's somebody's hand in there, and and someone saying, actually, 0:22:33.400 --> 0:22:35.639 all the bones of a human hand are present in 0:22:35.720 --> 0:22:39.240 Kermit the frog, but they have been repurposed and formed 0:22:39.520 --> 0:22:43.679 into the skeletal structure of this bipedal frog creature. Like 0:22:43.720 --> 0:22:46.560 that's even crazier, And I feel like that's more in 0:22:46.640 --> 0:22:48.960 line with what we know about the horses. 0:22:49.560 --> 0:22:53.480 Splendid analogy, Bravo. All right, are we ready to talk 0:22:53.560 --> 0:22:55.320 about the horse shoe? 0:22:55.760 --> 0:22:59.440 Yeah, this is something that originally I didn't think we 0:22:59.440 --> 0:23:01.760 were going to cover, or if we were to cover, 0:23:01.880 --> 0:23:03.880 we might come back, but I felt like it's kind 0:23:03.880 --> 0:23:07.080 of so closely linked to our understanding of the horse 0:23:07.119 --> 0:23:09.800 and the human use of the horse. And at the 0:23:09.880 --> 0:23:11.960 same time, in discussing this, we are going to be 0:23:12.080 --> 0:23:18.000 kind of blowing through the domestication of the horse rather quickly. 0:23:18.600 --> 0:23:21.640 Like this is a topic that has received a lot 0:23:21.640 --> 0:23:25.720 of attention over the years in varying fields. I mean, 0:23:26.160 --> 0:23:31.640 there's genetic research, there's archaeology, there's you know, various cultural inquiries. 0:23:32.920 --> 0:23:34.359 It's kind of all over the place, and there are 0:23:34.359 --> 0:23:36.600 a lot of unanswered questions about, you know, especially when 0:23:36.600 --> 0:23:39.840 you get into you know, the exact who's and wins 0:23:39.840 --> 0:23:43.399 and whares, say, horse domestication and even the development or 0:23:43.440 --> 0:23:47.480 the horseshoe. But I feel like covering the horseshoe also 0:23:47.560 --> 0:23:50.560 helps us understand the hoof a little bit more so, 0:23:50.840 --> 0:23:54.479 briefly talking about the modern horse, the modern horse has 0:23:54.520 --> 0:23:58.480 a long and pivotal history as a human steed. Many 0:23:58.520 --> 0:24:02.560 animals have, of course as mounts for human riders, and 0:24:03.000 --> 0:24:06.479 many have served as a pack and draft animals. I 0:24:06.520 --> 0:24:09.040 know that, at least on the artifact and perhaps elsewhere 0:24:09.080 --> 0:24:11.119 in some core episodes, we've touched on the importance of 0:24:11.119 --> 0:24:14.760 the camel and the donkey. But the horse, the horse 0:24:14.840 --> 0:24:17.560 is just a whole different matter, both in terms of 0:24:17.720 --> 0:24:20.480 the impact that it's had, like I think, the larger 0:24:20.520 --> 0:24:24.240 impact that it's had globally, and also just how it 0:24:24.240 --> 0:24:28.080