WEBVTT - Almost Cannibals 0:00:03.000 --> 0:00:04.960 Welcome Stuff to Blow your Mind, a production of I 0:00:05.000 --> 0:00:13.600 Heart Radios How Stuff Works. Hey, are you welcome to 0:00:13.600 --> 0:00:15.600 Stuff to Blow your Mind? My name is Robert Lamb 0:00:15.760 --> 0:00:18.560 and I'm Joe McCormick. And no, you're beating around the bush. 0:00:18.560 --> 0:00:20.880 It looks like cannibalism is on the roster for today. 0:00:21.200 --> 0:00:23.400 That's right, And I just want to remind everybody that 0:00:23.520 --> 0:00:25.560 we're not going to be talking about a hannibal lecter. 0:00:26.160 --> 0:00:31.600 This is not a show about like modern cannibalism among humans. 0:00:32.320 --> 0:00:34.920 This is not the Dahmer cast exactly. This is mostly 0:00:34.920 --> 0:00:36.800 going to deal with animals, and towards the end of 0:00:36.840 --> 0:00:40.040 the episode, we are going to discuss some some of 0:00:40.040 --> 0:00:46.360 the questions surrounding cannibalism among ancient humans. But again, if 0:00:46.440 --> 0:00:48.800 it don't worry, We're not going to be talking about 0:00:48.840 --> 0:00:52.200 like like true crime cannibalism here. That's your thing. There's 0:00:52.240 --> 0:00:54.000 plenty of that out there, you know where to find it, 0:00:54.200 --> 0:00:57.760 that's right. So we we've frequently discussed predation on the show, 0:00:57.800 --> 0:01:00.640 and we've of course discussed cannibalism as well. You know, 0:01:00.640 --> 0:01:04.919 we've talked about how it factors into any given organism, organisms, life, 0:01:05.000 --> 0:01:08.240 whether it's predator or prey, as well as its role 0:01:08.319 --> 0:01:11.520 in human evolution. And I think we've also tried. I mean, 0:01:11.959 --> 0:01:14.959 obviously it can be fun to talk about, especially grizzly 0:01:15.000 --> 0:01:18.320 predatory practices in the wild, especially among like invertebrates, But 0:01:19.200 --> 0:01:21.400 I feel like we tried to do our best to 0:01:22.400 --> 0:01:25.840 dispel predator hatred, right. We We did a whole episode 0:01:25.840 --> 0:01:29.480 a while back about why predators are so beneficial for 0:01:29.520 --> 0:01:33.480 ecology and even for for human civilization. Absolutely, and you 0:01:33.520 --> 0:01:36.920 can't look at predators just as the villain of any 0:01:36.959 --> 0:01:40.480 given peace, no matter how dramatic the music and a 0:01:40.880 --> 0:01:44.440 given nature documentary might be. That's something I found watching 0:01:44.640 --> 0:01:47.360 just so many nature documentaries with my son, is that 0:01:47.440 --> 0:01:50.080 earlier on he would get a little wigged out by 0:01:50.120 --> 0:01:54.480 scenes of predation or pending predation because they just have 0:01:54.640 --> 0:01:57.600 such overly dramatic music and they're really playing into the 0:01:57.680 --> 0:02:02.000 idea that the predator is the villain. Yeah, but I'm 0:02:02.120 --> 0:02:04.120 I'm happy to say that he is. He's really gotten 0:02:04.120 --> 0:02:06.680 out of that. It's very rare now that at age 0:02:06.720 --> 0:02:10.040 he just turned seven. Uh, it's very rare that he'll 0:02:10.080 --> 0:02:12.400 be wigged out by predation scene. In fact, there will 0:02:12.440 --> 0:02:17.440 be scenes where say, like some young lions or ripping 0:02:17.480 --> 0:02:20.400 apart of water buffalo or something, and I'll be a 0:02:20.400 --> 0:02:22.360 little wigged out. I'm like, this is getting kind of bloody, 0:02:22.400 --> 0:02:24.519 and I'm like, you sure you wanna finish watching this scene. 0:02:24.600 --> 0:02:26.959 He's like, oh, yeah, it's cool that they're hungry. No, no, 0:02:27.120 --> 0:02:29.919 he's not. He's not bloodthirsty for it. But he he 0:02:29.960 --> 0:02:32.919 has he's already has his appreciation that. Yeah, those those 0:02:32.960 --> 0:02:35.399 animals are hungry. They need to eat. This is how 0:02:35.440 --> 0:02:37.960 they eat. This is part of the natural order of things. Yeah, 0:02:38.000 --> 0:02:40.120 that's really cool. I mean it's it's a hard thing 0:02:40.120 --> 0:02:42.840 to appreciate because of course, within a human context, if 0:02:42.840 --> 0:02:45.320 you see like one human chasing after another human trying 0:02:45.320 --> 0:02:48.000 to hurt him, we know that's morally bad. That's something 0:02:48.080 --> 0:02:51.919 to to oppose. When you see a predator chasing prey, Yeah, 0:02:51.960 --> 0:02:53.799 the prey is fighting for its life, but the predators 0:02:53.840 --> 0:02:56.560 also fighting for its life. It's just obeying its instinct. 0:02:56.639 --> 0:02:58.680 That's part of what it does. And if if the 0:02:58.680 --> 0:03:01.679 predator doesn't get some prey, it too will die. Yeah, 0:03:01.720 --> 0:03:03.720 a wrong move on the on the part of a 0:03:04.520 --> 0:03:08.079 predator giving chase could lead to its death as well. 0:03:08.200 --> 0:03:10.760 Via via starvation, if it were to say, in draw leg. 0:03:11.080 --> 0:03:14.240 But of course, one of the strangest forms of predation 0:03:14.320 --> 0:03:17.280 and one that often seems to even when you see 0:03:17.280 --> 0:03:19.680 it among animals, even when you know better. One that 0:03:19.720 --> 0:03:22.680 I think still strikes many people as a kind of 0:03:22.760 --> 0:03:26.840 taboo or a kind of violation is when predation is 0:03:26.880 --> 0:03:31.880 turned inward on one's own kind, when it turns into cannibalism. Yeah, 0:03:31.919 --> 0:03:34.280 and we've and we've again we've discussed cannibalism on the 0:03:34.280 --> 0:03:38.080 show before, especially sexual cannibalism, I think more recently, Yeah, 0:03:38.120 --> 0:03:40.720 we did a whole episode on sexual cannibalism, especially as 0:03:40.760 --> 0:03:43.360 it appears like among arachnids, in which there are some 0:03:43.840 --> 0:03:47.800 fascinating behaviors. It's far more complex and interesting than just 0:03:47.880 --> 0:03:50.880 like well, male spider mates with a female spider and 0:03:50.880 --> 0:03:52.960 then the female eats the male. They're all kinds of 0:03:53.280 --> 0:03:58.000 economic energy dynamics going on different behavioral adaptations to that, 0:03:58.080 --> 0:04:01.640 to that kind of world. It's a really truly complex 0:04:01.640 --> 0:04:04.760 and interesting subject. Yeah, And I think economics is the 0:04:04.960 --> 0:04:07.120 way I always try and and and focus on it, 0:04:07.120 --> 0:04:10.840 you know, just thinking of just the the economy of uh, 0:04:11.040 --> 0:04:15.600 turning sunlight into flesh, which is basically what happens with 0:04:15.640 --> 0:04:17.520 the food chain. And so you're going to reach a 0:04:17.560 --> 0:04:22.159 point where even another member of your own species is energy. 0:04:22.320 --> 0:04:24.760 And what are you to do if you are, say 0:04:24.760 --> 0:04:26.880 a scorpion or something. I mean, especially with the with 0:04:26.920 --> 0:04:29.520 the scorpion, which is you know, UM tends to be 0:04:29.520 --> 0:04:31.880 a solitary organism. Uh, you know you're not going to 0:04:32.040 --> 0:04:34.359 let that energy just go to waste because you have 0:04:34.440 --> 0:04:39.760 some sort of you know, heightened scorpion morality or you know, 0:04:39.760 --> 0:04:41.880 our ethical system in play. No, you're gonna you're gonna 0:04:41.880 --> 0:04:44.960 show down on some cannibal meat. Well, no, again, animals 0:04:45.000 --> 0:04:48.040 are not humans. We with human brains can appreciate reasons 0:04:48.080 --> 0:04:51.720 that one should not eat one's own kind. Yeah, but 0:04:51.800 --> 0:04:54.720 if in the rest of the animal animal world cannibalism 0:04:54.800 --> 0:04:58.640 is widespread. So I today's episode, you know a lot 0:04:58.640 --> 0:05:00.520 of what we're gonna deal with this this idea of 0:05:00.600 --> 0:05:04.120 almost cannibals, which is something I started thinking about while 0:05:04.160 --> 0:05:07.240 I was vacationing in Belize. I was out there with 0:05:07.279 --> 0:05:10.360 the family, snorkeling, and I was slipping through a guide 0:05:10.360 --> 0:05:14.440 book for Caribbean organisms um aquatic organisms, and I came 0:05:14.480 --> 0:05:18.200 across a couple of entries for the head shield slug. Okay, 0:05:18.240 --> 0:05:19.520 this is kind of like a it looks sort of 0:05:19.560 --> 0:05:21.919 like a hammerhead slug. Yeah, it looks like a hammer 0:05:21.920 --> 0:05:25.600 head sea slug. They're also known as bubble snails um 0:05:25.680 --> 0:05:30.400 and and these are members of the clade um Cephalospidia, 0:05:30.600 --> 0:05:35.080 and the these names head shield slugs bubble snails. The 0:05:35.120 --> 0:05:37.640 name refers to their common head shield, as is a 0:05:37.680 --> 0:05:40.680 broad head that's used for burrowing in the sand and 0:05:40.760 --> 0:05:43.760 it helps to keep the sand out of their mantle cavities. 0:05:44.240 --> 0:05:48.440 And most have have shells, but some species have have 0:05:48.320 --> 0:05:50.720 to have a reduced shell and some have what's known 0:05:50.760 --> 0:05:53.000 as a like a bubble shell. Now I never got 0:05:53.040 --> 0:05:55.880 to actually see one while snorkeling, but the two entries 0:05:55.920 --> 0:05:59.599 in the book, I got my my mind working because 0:05:59.640 --> 0:06:03.080 there was leech head shield slug, which was this beautiful 0:06:03.240 --> 0:06:07.560 dark blue indigo creature with bright yellow stripes. This is 0:06:07.600 --> 0:06:10.400 one of the counterintuitive things about nature, is that clearly 0:06:10.440 --> 0:06:12.800 one of the most beautiful types of animal in the 0:06:13.000 --> 0:06:17.960 entire world or sea slugs. Yeah, yeah, absolutely, uh. But 0:06:18.000 --> 0:06:20.039 then there was another one. There was the mysterious head 0:06:20.040 --> 0:06:22.800 shield slug. That's what it's called that was in in 0:06:22.800 --> 0:06:24.680 this in this book, and this may have been an 0:06:24.680 --> 0:06:26.719 older book. There may be updated names for some of 0:06:26.720 --> 0:06:30.360 these now, but this one looked had the color of 0:06:30.520 --> 0:06:34.920 just rotting vegetation swearing camo. And as for their diets, 0:06:35.279 --> 0:06:39.480 the book listed that the mysterious head shield slug feeds 0:06:39.480 --> 0:06:43.320 on other sea slugs, especially the the lettuce sea slug. Okay, 0:06:43.320 --> 0:06:45.120 fair enough, right, there are a lot of sea slugs 0:06:45.160 --> 0:06:50.479 out there, and there's a lot of competition in aquatic environments. Um, 0:06:50.520 --> 0:06:53.120 you know, we're dealing with a very large subclass of 0:06:53.160 --> 0:06:56.720 the gastropod of family here. But the leech head shield 0:06:56.720 --> 0:07:00.520 slug its diet was listed as other head shields, So 0:07:00.520 --> 0:07:02.680 it's getting even closer to home, right, Yeah, so it's 0:07:02.760 --> 0:07:06.600 not cannibalism. You know, they're not the same species. Uh, 0:07:06.640 --> 0:07:08.840 they're in the same family, but I suppose, you know, 0:07:08.880 --> 0:07:11.040 it's it's the name that that gives me pause. The 0:07:11.040 --> 0:07:15.480 fact that they're both classified as headshield slugs. Well, that 0:07:15.600 --> 0:07:18.000 is a kind of interesting question to say, Like, Okay, 0:07:18.160 --> 0:07:21.120 we know cannibalism happens pretty often in the wild, and 0:07:21.120 --> 0:07:24.000 we'll discuss the conditions and just a minute here, there 0:07:24.000 --> 0:07:27.440 are some limitations that are imposed by genetics, by the 0:07:27.560 --> 0:07:32.280 energy economy, and by epidemiology on on how far you 0:07:32.320 --> 0:07:35.960 can go with practicing cannibalism as a lifestyle as an animal. 0:07:36.280 --> 0:07:38.400 Uh So they these limitations are in place. Some of 0:07:38.400 --> 0:07:40.800 those limitations might not be in place if you're preying 0:07:40.800 --> 0:07:43.720 on something that's a lot like you, but is not 0:07:43.880 --> 0:07:46.880 exactly you. Right, So, yeah, that's something we're going to 0:07:46.920 --> 0:07:49.440 talk about here. You know, what are some examples of 0:07:50.040 --> 0:07:53.160 um near cannibalism, Like what are some of the more 0:07:53.200 --> 0:07:57.840 closely related prey predator relationships out there in the animal world? 0:07:57.880 --> 0:07:59.480 And then what does that say about us? What does 0:07:59.480 --> 0:08:02.400 that say about the way that humans think about cannibalism? 0:08:02.560 --> 0:08:05.200 In a weird way, this episode topic even got me 0:08:05.240 --> 0:08:08.520 thinking about some of the strange economic dynamics of digital media. 0:08:09.240 --> 0:08:11.520 I promise that's not as boring as it sounds. We'll 0:08:11.560 --> 0:08:15.120 come back to that later. I don't know, digital media cannibalism. 0:08:15.120 --> 0:08:18.640 That sounds pretty exciting and probably just like spot on 0:08:18.800 --> 0:08:23.120 and just a fact of life. So let's refresh a 0:08:23.160 --> 0:08:26.960 little bit about cannibalism. So, to eat one's own species 0:08:27.080 --> 0:08:31.000 is to commit an act of cannibalism. Now, sometimes especially 0:08:31.040 --> 0:08:33.320 we'll get into a few cases later on. Sometimes this 0:08:33.400 --> 0:08:36.680 word we the word cannibalism is used for things that 0:08:36.720 --> 0:08:39.480 are not quite cannibalism. But that's where we get into 0:08:39.520 --> 0:08:42.920 that gray area of near cannibalism. Yeah, and it's sometimes 0:08:42.960 --> 0:08:45.920 said with the derogatory context, but I mean again, it's 0:08:45.920 --> 0:08:48.240 something that like, obviously, if you kill and eat your 0:08:48.280 --> 0:08:50.920 next door neighbor, that's a bad thing. But animals this 0:08:51.000 --> 0:08:54.440 is just sometimes an adaptation that animals have, that's right. 0:08:54.640 --> 0:08:58.320 And there are many different varieties and classifications we've discussed. 0:08:58.320 --> 0:09:01.440 Somebody's done the show before. Sexual anibalism for instance, which 0:09:01.440 --> 0:09:04.600 like you said, can be can be, you know, rather complex. 0:09:04.640 --> 0:09:06.880 It's not just a situation of well I made it 0:09:06.880 --> 0:09:09.240 with him, I guess now I'll consume his flesh. A 0:09:09.280 --> 0:09:11.400 lot of times it depends on, for example, what the 0:09:11.440 --> 0:09:14.199 male brings to the table in the sexual encounter. There 0:09:14.200 --> 0:09:17.720 are some species of spider where if a male shows 0:09:17.840 --> 0:09:21.320 up with a food gift for the female, for example, 0:09:21.559 --> 0:09:24.360 he can he can be more likely to avoid being 0:09:24.400 --> 0:09:27.280 cannibalized after mating, whereas if he shows up and just 0:09:27.360 --> 0:09:29.920 wants to mate and doesn't bring her anything to snack on. 0:09:30.040 --> 0:09:32.839 He's more likely to be cannibalized. And this sort of 0:09:32.880 --> 0:09:35.760 makes sense, right, like or is he is he contributing 0:09:35.800 --> 0:09:39.400 additional food resources to the development of the offspring? Right? 0:09:39.480 --> 0:09:42.800 And then there are other examples like matrophagi where babies uh, 0:09:43.120 --> 0:09:46.240 where the offspring consume the mother um. You know, they're 0:09:46.320 --> 0:09:50.640 they're examples where um of a mother organism will consume 0:09:50.720 --> 0:09:53.120 the young. And a lot of these cases of cannibalism 0:09:53.120 --> 0:09:55.760 in the while, they're they're going to be influenced by uh, 0:09:55.800 --> 0:10:01.679 you know, economic um uh resource uh deprivation issues like 0:10:01.840 --> 0:10:04.920 are those offspring going to survive? Is something threatening them? 0:10:04.920 --> 0:10:08.080 Should then the energy of those uh of the offering 0:10:08.160 --> 0:10:11.240 be uh brought back into the host or into the 0:10:11.400 --> 0:10:15.320 mother organism. Yeah, Now, I detect among the literature in 0:10:15.320 --> 0:10:19.240 in zoology and behavioral ecology and all that that there 0:10:19.320 --> 0:10:22.880 there's been a shift in consciousness about cannibalism over the 0:10:22.880 --> 0:10:25.360 previous decades where I think it used to be more 0:10:25.440 --> 0:10:29.160 common for scientists to believe that cannibalism would was something 0:10:29.200 --> 0:10:32.600 animals would only do under extreme scenarios, like if they 0:10:32.600 --> 0:10:35.960 were in a starvation scenario, you know, just like the 0:10:36.120 --> 0:10:42.360 absolute limits of survival, and that has increasingly it's increasingly 0:10:42.400 --> 0:10:45.760 become clear that that's not the case. Though animals don't, 0:10:45.800 --> 0:10:48.400 you know, they're not usually going to practice cannibalism as 0:10:48.440 --> 0:10:51.800 some kind of primary mode of living. There are actually 0:10:51.800 --> 0:10:55.440 a pretty wide range of scenarios in which cannibalism occurs, 0:10:55.480 --> 0:10:58.040 and we're we're documenting more and more of those scenarios 0:10:58.040 --> 0:11:00.920 all the time. It's not always just star ovation at 0:11:00.920 --> 0:11:04.400 the very edge of survival and the peaks of stress. Yeah. 0:11:04.600 --> 0:11:06.320 So it's one of these things that is, you know, 0:11:06.440 --> 0:11:08.960 we're learning as ubiquitous in the natural world. It it 0:11:09.040 --> 0:11:12.360 offers some really key advantages, though there are some downsides. 0:11:13.160 --> 0:11:17.280 It remains highly popular without ever becoming like the thing 0:11:17.520 --> 0:11:23.240 right like you made your species might engage in cannibalism 0:11:23.679 --> 0:11:27.160 for a number of different reasons, but you were not 0:11:27.240 --> 0:11:31.000 going to become an obligate cannibal like that is where 0:11:31.040 --> 0:11:33.560 the system would collapse. Yeah, and I think there are 0:11:33.600 --> 0:11:36.000 some reasons that that's sort of impossible. I'll talk about 0:11:36.000 --> 0:11:37.839 that in just a minute. It reminds me a lot 0:11:37.840 --> 0:11:40.360 of some things I've heard about the band Primus. I've 0:11:40.360 --> 0:11:44.040 heard stuff, but okay, well I'm going with you. I'm 0:11:44.080 --> 0:11:46.480 not saying that the members of Primus are cannibals, but 0:11:46.600 --> 0:11:49.920 rather um, I think it was less Claypool himself, who 0:11:49.960 --> 0:11:52.040 at one point pointed out that like they were in 0:11:52.080 --> 0:11:55.000 a good place popularity wise, like they like they never 0:11:55.320 --> 0:11:57.800 completely went out of fashion, but at the same time, 0:11:57.840 --> 0:12:00.320 like they never just really blew up. Like I feel 0:12:00.400 --> 0:12:04.400 like most people, Uh, if you asked them, they might say, oh, yeah, 0:12:04.520 --> 0:12:07.240 Primus is cool. I did Primus. I myself have enjoyed 0:12:07.440 --> 0:12:10.439 a prime Primus in concert before, but I would I 0:12:10.480 --> 0:12:16.040 would never say Primus is necessarily my favorite band. Uh. Likewise, cannibalism, 0:12:16.080 --> 0:12:19.480 It's okay, I'm with you. I see what you're saying. Yeah, 0:12:19.640 --> 0:12:22.400 I mean, yeah, they're Primus has long been By the way, 0:12:22.480 --> 0:12:25.679 my candidate for what I joke about is like the 0:12:25.800 --> 0:12:29.840 least sexy or least romantic possible music. So if you're 0:12:29.840 --> 0:12:31.920 trying to like figure out what to put on for 0:12:31.960 --> 0:12:35.080 a Valentine's Day dinner or something like that, so you 0:12:35.120 --> 0:12:37.040 could go with like your Marvin Gay or you know, 0:12:37.080 --> 0:12:39.640 your classic romantic options, and at the other end of 0:12:39.679 --> 0:12:43.000 the spectrum you've got Primus. Yeah. For me, Primus is 0:12:43.080 --> 0:12:48.160 more like driving around music, you know it nothing will 0:12:48.160 --> 0:12:50.920 scribe if you if you were thirsting for primus, nothing 0:12:50.920 --> 0:12:53.160 else will do. But then there are plenty of other 0:12:53.200 --> 0:12:55.800 cases where it probably is not going to be the 0:12:55.880 --> 0:13:00.360 ideal soundtrack for life. But anyway back back to canalism, 0:13:00.400 --> 0:13:03.439 So yes, there it can be especially useful in certain 0:13:03.559 --> 0:13:06.839 ecological situations. Uh and and there are a lot of 0:13:06.920 --> 0:13:09.400 key benefits to the individual. On the other hand, it 0:13:09.559 --> 0:13:14.000 can impact community dynamics. But the exact shape and scope 0:13:14.040 --> 0:13:19.080 of a species cannibalism it varies greatly. Yeah, exactly. Um So, 0:13:19.080 --> 0:13:21.520 so there are these obvious, like you're talking about, economic 0:13:21.600 --> 0:13:25.559 and evolutionary limits on what forms cannibalism can take, even 0:13:25.600 --> 0:13:28.679 though it can to each individual animal that practices that 0:13:28.840 --> 0:13:31.760 give all kinds of benefits. One example would be that 0:13:31.880 --> 0:13:35.040 you know, when one species regularly eats another species, it 0:13:35.160 --> 0:13:38.040 is common that the prey species is in some way 0:13:38.200 --> 0:13:43.320 more vulnerable, it's smaller or weaker, definitely more numerous than 0:13:43.360 --> 0:13:46.520 the predator species. You can't make a diet out of 0:13:46.559 --> 0:13:50.760 eating mostly or entirely animals that are say as good 0:13:50.800 --> 0:13:53.240 at killing you in self defense as you are at 0:13:53.320 --> 0:13:56.200 killing them in predation or the economics of acquisition. Just 0:13:56.240 --> 0:13:58.600 don't work out, right, You're not gonna go chasing down 0:13:58.640 --> 0:14:00.960 something that's got all the same muscles and teeth and 0:14:01.000 --> 0:14:03.120 claws and all that as you. Right, you have to 0:14:03.160 --> 0:14:05.880 have some sort of an advantage, either a direct biological 0:14:05.920 --> 0:14:09.040 advantage or some sort of behavioral advantage such as pack 0:14:09.160 --> 0:14:11.480 hunting or something like that. But but even in those 0:14:11.520 --> 0:14:15.040 cases it can be exceedingly risky. And and think again, 0:14:15.040 --> 0:14:17.600 how I mean, I think we sometimes because we have 0:14:17.679 --> 0:14:22.480 medical care, we uh downplay the risks to an animal 0:14:22.480 --> 0:14:24.640 in the wild of a mirror like you know, leg 0:14:24.680 --> 0:14:26.800 injury or something like that, which can be fatal to 0:14:26.840 --> 0:14:28.800 an animal in the wild, while you know, you can 0:14:28.840 --> 0:14:30.960 just go to the hospital and get fixed up. So 0:14:31.000 --> 0:14:34.920 if adults of a species focus on other similarly sized 0:14:34.960 --> 0:14:38.840 adults of the same species, hunting probably becomes too dangerous 0:14:38.880 --> 0:14:43.040 to sustain as a regular practice. Also, a species cannot 0:14:43.240 --> 0:14:46.360 make a diet out of eating mostly or entirely animals 0:14:46.360 --> 0:14:48.920 that are less numerous than itself, because it's going to 0:14:49.040 --> 0:14:50.760 run out of food and starve, or it's gonna have 0:14:50.800 --> 0:14:53.200 to switch to a different food source. If an animal 0:14:53.240 --> 0:14:57.800 were to eat primarily or entirely members of its own species, Uh, 0:14:57.880 --> 0:15:00.680 there would immediately be a couple of problems. And number one, 0:15:00.720 --> 0:15:03.480 you would have to think, if it's a sexually reproducing species, 0:15:03.560 --> 0:15:05.880 this behavior is probably going to interfere with mating and 0:15:05.960 --> 0:15:09.960 lead to depletion of mates. Probably more importantly, the species 0:15:09.960 --> 0:15:12.920 couldn't survive. It would sort of eat itself to extinction. 0:15:13.160 --> 0:15:15.640 Like if every member of the species needed to eat 0:15:15.720 --> 0:15:18.280 one other member of the species every month in order 0:15:18.320 --> 0:15:21.600 to not starve to death. Your best case scenario is 0:15:21.680 --> 0:15:25.400 having the number of individuals every month. Now, maybe you 0:15:25.440 --> 0:15:28.120 think you could replace those through rapid reproduction, but where 0:15:28.160 --> 0:15:30.800 does the energy to create and grow those new bodies 0:15:30.840 --> 0:15:33.720 come from unless you're eating even more of your own kind. 0:15:34.640 --> 0:15:37.360 So it seems kind of I was trying to find 0:15:37.400 --> 0:15:39.680 an example of something that comes close, but it seems 0:15:39.720 --> 0:15:42.440 to me you can't really have something like an obligate 0:15:42.560 --> 0:15:46.400 cannibal species, something that only eats its own kind. That 0:15:46.480 --> 0:15:51.000 seems like an an absurdity. So you have that fact, 0:15:51.080 --> 0:15:53.320 but then you also have the fact that we do 0:15:53.400 --> 0:15:57.000 observe lots of in species cannibalistic behavior in the wild 0:15:57.160 --> 0:15:58.800 in the wild, and we know that this can only 0:15:58.840 --> 0:16:01.880 take place in sort of limb did conditions and scenarios, 0:16:02.200 --> 0:16:04.240 and we're discovering more and more of those types of 0:16:04.280 --> 0:16:07.000 scenarios all the time. Here's a common one we know. 0:16:07.400 --> 0:16:10.200 You can't just eat members of your own species for 0:16:10.360 --> 0:16:13.560 your entire diet and have every member of your species 0:16:13.600 --> 0:16:15.960 do this for your entire life, for the species would 0:16:15.960 --> 0:16:20.720 cease to exist. But within certain phases of life, cannibalism 0:16:20.800 --> 0:16:24.080 can be a primary strategy. Consider the larval stage of 0:16:24.080 --> 0:16:28.040 many amphibians. Uh you have like cannibal morph larvae of 0:16:28.120 --> 0:16:30.800 tiger salamanders. We talked about those in our episode on 0:16:30.840 --> 0:16:35.440 salamanders with Mark Mandica. Or think about the cannibalistic tadpoles 0:16:35.440 --> 0:16:38.120 of toad species like the spadefoot toad. And this is 0:16:38.120 --> 0:16:40.760 where the biggest tadpoles in a small body of water 0:16:40.840 --> 0:16:44.240 will eat the smaller ones to survive and grow even bigger. 0:16:44.320 --> 0:16:47.680 It's sort of like a letting letting the strongest of 0:16:47.760 --> 0:16:51.640 the of the litter absorb the energy of all the others. Now, 0:16:51.680 --> 0:16:54.600 obviously this kind of strategy can't be continued for the 0:16:54.640 --> 0:16:57.560 amphibians entire life cycle, but it can work in a 0:16:57.600 --> 0:17:01.800 phase of the life cycle because the other energy inputs 0:17:01.800 --> 0:17:05.119 into that phase. Another great example from another episode we 0:17:05.119 --> 0:17:07.280 had with a with a guest was thinking about intra 0:17:07.440 --> 0:17:10.440 uterine cannibalism in some sharks species, like we talked about 0:17:10.480 --> 0:17:15.200 with Mara Hart, where some unborn sharks will swim over 0:17:15.320 --> 0:17:18.920 and eat their siblings or half siblings before they even 0:17:19.000 --> 0:17:22.240 leave their mother's uterus. Do we talk about cannibalism with 0:17:22.280 --> 0:17:24.920 all of our guests? I don't know. It does seem 0:17:24.920 --> 0:17:27.080 to come up a good fit, but maybe we do. 0:17:27.840 --> 0:17:30.360 I don't think we brought either of these up, did we. 0:17:30.880 --> 0:17:32.840 I mean, I guess they were just an innate part 0:17:32.880 --> 0:17:35.720 of the cut, the conversation and the expertise of the guests. 0:17:35.720 --> 0:17:39.720 Maybe we just invite creepy guests. They're not creepy. Maybe 0:17:39.760 --> 0:17:43.080 we're creepy. We're talking about cannibalism right now. We're definitely creepy. 0:17:43.800 --> 0:17:46.920 So while cannibalism can't be the entire diet of a species, 0:17:46.960 --> 0:17:49.679 it can be an important supplemental part of a diet, 0:17:50.040 --> 0:17:53.600 especially in scenarios of environmental stress, and it can even 0:17:53.640 --> 0:17:57.359 reduce competition when times are tough. One example here is 0:17:57.400 --> 0:18:00.160 that cannibalism, according to what I've read, it's much more 0:18:00.160 --> 0:18:04.000 common if you live life in the water. Oh, yes, definitely. Yeah, 0:18:04.040 --> 0:18:07.560 if you're wet, you're probably involved in cannibalism in some way. 0:18:07.600 --> 0:18:10.600 It just happens a lot more in aquatic environments. For example, 0:18:11.080 --> 0:18:14.959 when fish are foraging for food, one type of energy 0:18:15.000 --> 0:18:18.680 source they will often come across is little sphere ules 0:18:18.680 --> 0:18:22.200 of lipids and energetic materials floating in the water. Other 0:18:22.280 --> 0:18:25.119 fish eggs. Uh. These fill the waters of the ocean 0:18:25.119 --> 0:18:28.280 by the bazillions, and this will include some eggs of 0:18:28.320 --> 0:18:32.000 their own species, which they basically just eat discriminately along 0:18:32.040 --> 0:18:34.720 with the other eggs. We recently did the episode on 0:18:34.760 --> 0:18:37.880 the Christmas Island crabs. Oh, yeah, where they just stuff 0:18:37.960 --> 0:18:40.880 the crabble are right into their mouths. Yeah, I mean, 0:18:40.920 --> 0:18:43.080 how do you know if it's your own offspring. Chances 0:18:43.119 --> 0:18:45.399 are it's not. There's so many out there, it's probably 0:18:45.400 --> 0:18:48.199 somebody else's. Also, I think I accidentally said that they 0:18:48.200 --> 0:18:51.520 will eat them discriminately. Obviously they eat them indiscriminately, is 0:18:51.560 --> 0:18:55.440 what I mean. Fish don't discriminate. But yeah, it works 0:18:55.440 --> 0:18:57.720 out because fish produce a lot of eggs. Under the 0:18:57.760 --> 0:19:00.480 evolutionary assumption that most of the eggs, many of the 0:19:00.480 --> 0:19:03.080 eggs at least, will not survive and the eggs of 0:19:03.119 --> 0:19:05.679 one's own species are only a supplemental part of the 0:19:05.680 --> 0:19:08.600 adult fishes diet, not the whole thing for the whole species, 0:19:08.600 --> 0:19:11.399 which again would be a problem. But the phenomenon of 0:19:11.440 --> 0:19:15.600 adults eating young of their own species actually happens in 0:19:15.680 --> 0:19:18.479 many scenarios outside the water too. Obviously, it would make 0:19:18.520 --> 0:19:20.879 no sense for animals to have instincts to kill and 0:19:20.920 --> 0:19:22.919 eat all of their own young, but there is some 0:19:23.119 --> 0:19:28.120 selective strategic snacking of this kind. Like often rodent mothers 0:19:28.160 --> 0:19:30.800 will eat some of their own litters, especially those that 0:19:30.880 --> 0:19:34.160 are sickly or don't seem like they're gonna thrive. Male 0:19:34.280 --> 0:19:38.720 carnivores like lions, will sometimes eat the cubs sired by 0:19:38.760 --> 0:19:41.879 another male, and this tends to increase the female lions 0:19:41.960 --> 0:19:44.800 receptivity to mating and the pride. Yeah, this is seen 0:19:44.840 --> 0:19:47.679 in bears as well, for sure. Oh yeah, definitely. And 0:19:47.720 --> 0:19:50.600 then there are some really strange cases that were observing 0:19:50.640 --> 0:19:53.879 again more and more all the time, even with animals 0:19:53.920 --> 0:19:58.840 once thought to be herbivores engaging in occasional cannibalism. Here's 0:19:58.840 --> 0:20:02.800 when I came across hip pose what hundred percent herbivores right, Well, 0:20:02.800 --> 0:20:04.680 that this one one I always assumed. I mean you 0:20:04.720 --> 0:20:07.280 hear to hear about like the vast amount of vegetation 0:20:07.280 --> 0:20:09.240 that a given hippo needs to consume, and that is 0:20:09.280 --> 0:20:13.000 their primary diet. They mostly are herbivores, but occasionally they'll 0:20:13.040 --> 0:20:15.560 just be versatile. So we used to think there are 0:20:15.600 --> 0:20:19.120 a hundred percent herbivores. They're mostly herbivores, except now it's 0:20:19.119 --> 0:20:21.720 been observed that sometimes they'll kill and eat an impula, 0:20:22.160 --> 0:20:26.679 or even sometimes they will eat a fellow hippopotamus. Well, 0:20:26.720 --> 0:20:29.120 they are ferocious. I mean, we can't take that away 0:20:29.160 --> 0:20:31.280 from them. So there are just more and more examples 0:20:31.320 --> 0:20:34.639 all the time that science is documenting about ways that 0:20:34.720 --> 0:20:39.480 animals will occasionally or opportunistically or even in some controlled ways, 0:20:39.600 --> 0:20:44.480 regularly engage in direct in species cannibalism. Yeah. I was 0:20:44.920 --> 0:20:49.159 reading the amazingly titled two thousand tin paper Cannibals in Space, 0:20:49.920 --> 0:20:54.960 the Coevolution of Cannibalism and Dispersal in spatially structured Populations 0:20:55.520 --> 0:20:58.119 and U. And in this the authors point out that 0:20:58.160 --> 0:21:01.240 the propensity for cannibalism, you know, it's going to vary 0:21:01.280 --> 0:21:05.320 considerably among even closely related species. And then a lot 0:21:05.320 --> 0:21:09.440 of questions remain concerning exactly what drives variation and the 0:21:09.480 --> 0:21:13.960 evolution of cannibalism across and even within a species, and 0:21:14.040 --> 0:21:15.760 the can and the same can be said for the 0:21:15.840 --> 0:21:20.600 evolutionary consequences of cannibalism. Yeah, a lot about cannibalism remains 0:21:20.600 --> 0:21:22.840 an open question. There's still a ton we don't know. 0:21:23.240 --> 0:21:25.040 But I think one thing that is emerging is what 0:21:25.119 --> 0:21:28.480 we're getting some good ideas of what the major downsides 0:21:28.600 --> 0:21:31.520 to cannibalism are, like, what are the limitations that are 0:21:31.560 --> 0:21:34.600 imposed on it as a practice, And so I want 0:21:34.640 --> 0:21:36.600 to mention I think three major ones that there may 0:21:36.600 --> 0:21:39.199