WEBVTT - From the Vault: Mutational Meltdown 0:00:06.240 --> 0:00:08.440 Hey, you welcome to Stuff to Blow Your Mind. My 0:00:08.520 --> 0:00:09.360 name is Robert. 0:00:09.200 --> 0:00:12.959 Lamb and I am Joe McCormick, and today we are 0:00:13.000 --> 0:00:16.520 bringing you an episode from the vault. This one originally 0:00:16.560 --> 0:00:20.080 published April twentieth, twenty twenty three, and it is called 0:00:20.320 --> 0:00:21.640 Mutational Meltdown. 0:00:22.520 --> 0:00:26.200 Yeah, this is one that I was drawn to initially 0:00:26.280 --> 0:00:30.440 solely because of the title Mutational Meltdown, How can you resist? 0:00:31.040 --> 0:00:33.640 But there's a lot of fascinating content in there as well, 0:00:33.680 --> 0:00:37.160 beyond just sort of the knee jerk feel of imagining 0:00:37.200 --> 0:00:39.720 some sort of mutant melting in some sort of a 0:00:39.800 --> 0:00:42.440 sci fi context. Let's jump right in. 0:00:45.720 --> 0:00:49.479 Welcome to Stuff to Blow Your Mind, production of iHeartRadio. 0:00:55.960 --> 0:00:58.120 Hey you welcome to Stuff to Blow your Mind. My 0:00:58.200 --> 0:00:59.040 name is Robert. 0:00:58.840 --> 0:01:02.200 Lamb and I'm Joe McCormick, and today we're going to 0:01:02.240 --> 0:01:07.600 be talking about a concept in the realm of genetics 0:01:07.640 --> 0:01:14.559 and reproduction, a concept known as mutational meltdown. Very enticing name, Rob. 0:01:14.680 --> 0:01:19.720 I understand you became interested in mutational meltdown earlier this week. 0:01:19.760 --> 0:01:21.039 What got you going on this? 0:01:21.959 --> 0:01:24.600 Well, it actually didn't have anything to do directly with 0:01:25.360 --> 0:01:27.319 any melt movies. We might have been talking about on 0:01:27.360 --> 0:01:30.640 Weird House Cinema. I actually, I think I was on 0:01:30.680 --> 0:01:33.080 a walk with my family and I said, Hey, I 0:01:33.080 --> 0:01:34.840 think we're going to need an episode for Thursday. What 0:01:34.840 --> 0:01:38.120 should we do it on? And there my wife and 0:01:38.120 --> 0:01:39.440 my son are like, Oh, you should do it on 0:01:39.800 --> 0:01:44.400 asexual reproduction. So okay, let's just started looking around a 0:01:44.440 --> 0:01:47.520 little bit. And yeah, this particular term kind of jumped 0:01:47.520 --> 0:01:49.840 out at me. I wasn't familiar with it, and it 0:01:50.960 --> 0:01:53.640 basically gets down into and I think for our purposes 0:01:53.640 --> 0:01:55.040 here on the show, you know, it's a reason to 0:01:55.080 --> 0:01:58.120 sort of provide an overview of sort of asexual reproduction 0:01:58.240 --> 0:02:04.320 versus sexual reproduction as sort of competing ways of going 0:02:04.360 --> 0:02:08.000 about sort of the same thing for an organism, but 0:02:08.240 --> 0:02:12.520 one with more short term benefits versus long term benefits. 0:02:12.560 --> 0:02:14.080 And I don't know, I just found it to be 0:02:14.200 --> 0:02:19.280 kind of a neat way to re examine and think 0:02:19.320 --> 0:02:22.880 about these these concepts that I imagine we've covered on 0:02:22.880 --> 0:02:25.280 the show before, and many of you out there have 0:02:25.280 --> 0:02:29.120 have encountered in varying formats. 0:02:29.720 --> 0:02:32.200 Sure well, I know over the years we have alluded 0:02:32.280 --> 0:02:35.919 to the big question in biology of like where sex 0:02:35.960 --> 0:02:40.040 comes from, the where when and why of sexual reproductions 0:02:40.320 --> 0:02:43.280 as a part of the history of organisms on planet Earth. 0:02:43.360 --> 0:02:47.079 Not going to solve that problem today, but yeah, I 0:02:47.160 --> 0:02:50.839 think maybe this little subtopic could help shed a little 0:02:50.880 --> 0:02:51.560 bit of light there. 0:02:52.040 --> 0:02:56.320 Yeah, so let's let's start with the basics. Though, we're 0:02:56.320 --> 0:02:58.919 going to just approach it as if you know, you're 0:02:58.919 --> 0:03:02.359 not really familiar with any of the topics that we're 0:03:02.360 --> 0:03:07.000 discussing here, So asexual reproduction versus sexual reproduction on a 0:03:07.160 --> 0:03:10.240 very basic level, here's how it all goes down. So, 0:03:10.320 --> 0:03:13.639 with sexual reproduction, you have the offspring of two genetic 0:03:13.720 --> 0:03:18.280 parents inheriting a mix of genes from those parents, genetically 0:03:18.360 --> 0:03:22.320 distinguishing itself from either parent. The resulting genetic variation is 0:03:22.440 --> 0:03:26.120 highly adaptive because it provides individuals with varying traits that 0:03:26.200 --> 0:03:30.040 may prove necessary for survival in an ever changing environment. 0:03:30.680 --> 0:03:34.280 The resulting genetic diversity makes the population more resistant to 0:03:34.360 --> 0:03:35.320 disease as well. 0:03:35.520 --> 0:03:37.720 I think one of the theories we've talked about before 0:03:37.920 --> 0:03:42.680 is that an advantage of sexual reproduction is that it 0:03:42.800 --> 0:03:46.960 helps protect the host organism against various types of parasites 0:03:47.000 --> 0:03:51.280 by introducing genetic variability that makes it harder for the 0:03:51.280 --> 0:03:56.040 parasite to target each successive generation of the host. 0:03:56.400 --> 0:04:00.480 Yeah, this is a clumsy analogy at best, but I 0:04:00.520 --> 0:04:02.200 can't help but think too about like to say that, 0:04:03.000 --> 0:04:06.080 because essentially, when you're talking about asexual reproduction, you're talking 0:04:06.600 --> 0:04:09.760 essentially about making a clone of oneself. And so the 0:04:09.800 --> 0:04:14.840 clone army in the Star Wars prequels highly susceptible to say, 0:04:16.000 --> 0:04:18.320 a single order coming out and telling them to turn 0:04:18.320 --> 0:04:21.159 on the Jedi, that sort of thing. But that's just 0:04:21.200 --> 0:04:23.520 a very very rough idea of how to think about it. 0:04:24.800 --> 0:04:28.720 But more specifically for our purposes here, another key benefit 0:04:29.120 --> 0:04:31.480 that comes up in the literature is looking at is 0:04:31.520 --> 0:04:36.120 that you can think of sex and genetic recombination is 0:04:36.200 --> 0:04:41.000 ultimately a means of purging deletarious mutations. 0:04:41.440 --> 0:04:44.240 Right, so the impact of mutations that might be harmful 0:04:44.279 --> 0:04:49.880 to the organism can be blunted by sexual recombination. Yeah. 0:04:49.960 --> 0:04:52.640 Yeah, So you end up with this, I mean, roughly speaking, 0:04:52.839 --> 0:04:54.599 you know, you have kind of like a randomization of 0:04:54.600 --> 0:04:57.680 these different traits, and the individuals that end up the 0:04:57.680 --> 0:05:01.800 offspring with that end up with the the negative traits, 0:05:01.839 --> 0:05:06.120 the harmful traits. They don't survive the ones that have 0:05:06.200 --> 0:05:09.479 been purged of those mutations do survive, and therefore it 0:05:09.560 --> 0:05:13.240 can purge the mutation from a particular lineage. Okay, all right, 0:05:13.279 --> 0:05:17.320 So moving on to asexual reproduction. This is a case 0:05:17.360 --> 0:05:19.520 in which you have the offspring of a single genetic 0:05:19.600 --> 0:05:22.680 parent inheriting the genes of the parent, making it a 0:05:22.720 --> 0:05:25.720 clone identical to the parent. The advantage here is that 0:05:25.760 --> 0:05:30.279 you can reproduce rapidly without all of the energy expenditure 0:05:30.360 --> 0:05:33.359 of mating. And I mean that's a pretty big statement 0:05:33.480 --> 0:05:37.120 to think about, because so many organisms we end up 0:05:37.160 --> 0:05:40.040 discussing on the podcast. You know, what is the key 0:05:40.080 --> 0:05:42.960 thing that makes them interesting? Well, in some cases, many cases, 0:05:42.960 --> 0:05:45.680 it's how they acquire their food, But in other cases 0:05:45.720 --> 0:05:47.480 it's how do they get a mate? How do they 0:05:47.480 --> 0:05:50.599 attract a maid or pursue a mate, And it ends 0:05:50.680 --> 0:05:53.279 up taking up a whole lot of time, a whole 0:05:53.279 --> 0:05:55.680 lot of energy. And what if you didn't have to 0:05:55.720 --> 0:05:59.560 do that? What if instead you could just essentially clone yourself. 0:06:00.200 --> 0:06:03.200 Convenient and safer in a lot of cases, because I 0:06:03.240 --> 0:06:05.920 mean it varies by organism, but in many cases, yeah, 0:06:05.960 --> 0:06:08.640 if you have to go seeking out a mate, it 0:06:08.760 --> 0:06:12.200 is not only you know, an energy expense to go 0:06:12.320 --> 0:06:15.839 looking around, but you're also often removing yourself from safe 0:06:15.880 --> 0:06:19.000 locations and going into dangerous ones. Yeah. 0:06:19.000 --> 0:06:21.320 I mean it's kind of like when you get some 0:06:21.360 --> 0:06:24.080 sort of new kit to a symbols of Ikia furniture, right, 0:06:24.520 --> 0:06:27.200 and the first thing you notice is that on the 0:06:27.240 --> 0:06:29.359 instructions it says, oh, you have to have two people 0:06:29.400 --> 0:06:32.159 to do this, and you're like, oh, that totally recks 0:06:32.160 --> 0:06:34.800 my day. Now, I've got to get my significant other 0:06:35.040 --> 0:06:36.920 or a friend to help with this. We've got to 0:06:36.960 --> 0:06:39.560 align our schedules, and we have to both work together 0:06:39.680 --> 0:06:43.080 to build this thing, as opposed to one where I 0:06:43.120 --> 0:06:45.680 can just build it myself and put it where it 0:06:45.720 --> 0:06:48.359 needs to go in the house. Now, there are multiple 0:06:48.400 --> 0:06:50.560 types of asexual reproduction, and we're not going to go 0:06:50.600 --> 0:06:52.200 into all of them, but you have all sorts of 0:06:52.240 --> 0:06:56.560 things like asexual budding and so forth. The sources I 0:06:56.560 --> 0:07:00.920 was looking at dealt a lot with parthenogenis, which occurs 0:07:00.960 --> 0:07:04.560 widely and invertebrates. This word stems from the Greek for 0:07:04.680 --> 0:07:08.480 virgin creation parthenos plus genesis. 0:07:08.640 --> 0:07:11.000 Okay, so this would describe, for example, a lot of 0:07:11.080 --> 0:07:15.480 vertebrates like maybe some lizards or fish that can give 0:07:15.680 --> 0:07:18.840 birth without ever having without ever having their game meets 0:07:18.880 --> 0:07:21.000 fertilized by a member of the opposite sex. 0:07:21.440 --> 0:07:26.840 Yeah, yeah, we're talking about lizards, geckos, various insects, particularly 0:07:26.880 --> 0:07:31.520 some sharks. And it's of course very important to note 0:07:31.560 --> 0:07:36.800 that there are obligates sexual reproducers and then they're obligate 0:07:36.920 --> 0:07:40.240 asexual reproducers. But then there are also organisms that can 0:07:40.280 --> 0:07:44.400 do either depending on environmental pressure. So a classic example 0:07:44.560 --> 0:07:48.440 of a sexually reproducing organism engaging in asexual reproduction is, 0:07:48.480 --> 0:07:51.800 of course, when an individual cannot find a mate. It's 0:07:51.880 --> 0:07:53.720 kind of there as I guess you could think of 0:07:53.760 --> 0:07:58.720 it as kind of a backup plan that or some 0:07:58.760 --> 0:08:00.640 sort of a you know, an emergency button that can 0:08:00.640 --> 0:08:03.240 be pushed. And this has been the case with some 0:08:03.320 --> 0:08:06.120 of the famous examples of say sharks or lizards such 0:08:06.120 --> 0:08:11.360 as the Komodo dragon reproducing in captivity, these so called 0:08:11.440 --> 0:08:14.960 virgin births that will suddenly occur in shock zoo keepers. 0:08:15.480 --> 0:08:19.840 So the ideal is to mix and match your genetic 0:08:19.920 --> 0:08:23.520 material with somebody else's, but in a pinch, you could 0:08:23.560 --> 0:08:26.520 just make a copy of yourself if you're. 0:08:26.400 --> 0:08:29.480 The right species correct, Yeah, and if I'm remembering correctly, 0:08:29.560 --> 0:08:31.880 This also pops up in the plot of Jurassic Park, right, 0:08:31.920 --> 0:08:34.800 something to do with the way that they're recreating dinosaur 0:08:34.840 --> 0:08:36.280 DNA using amphibian DNA. 0:08:36.760 --> 0:08:39.439 Well, I don't know if this is parthenogenesis or if 0:08:39.480 --> 0:08:40.880 it would be different. I think what they say, at 0:08:40.960 --> 0:08:42.760 least in the movie, I don't remember what happens in 0:08:42.800 --> 0:08:45.040 the book. In the movie they say that because they 0:08:45.120 --> 0:08:49.920 use some frog DNA to cover up patches in the 0:08:50.000 --> 0:08:53.560 DNA sequence. I'm just recalling from memory what mister DNA 0:08:53.679 --> 0:08:59.600 tells us that some frogs are able to spontaneously change 0:08:59.640 --> 0:09:02.439 sex in a single sex environment, and thus, even though 0:09:02.520 --> 0:09:05.200 all of the dinosaurs in the park were supposed to 0:09:05.200 --> 0:09:09.280 be female, some changed into males, and thus we're sexually reproducing. 0:09:09.800 --> 0:09:12.160 Ah okay, I think that's the main thing. I'm either 0:09:12.200 --> 0:09:15.480 misremembering that, or maybe there's something from one of the 0:09:15.559 --> 0:09:18.959 later like Jurassic World films that I'm only like half 0:09:19.000 --> 0:09:22.080 processing here. All Right, So you have these two basic 0:09:22.120 --> 0:09:24.800 ways of reproducing, then this of course means that there 0:09:24.800 --> 0:09:28.200 are drawbacks to either one. So in sexual reproduction again, 0:09:28.559 --> 0:09:30.120 you got to put a whole lot of energy and 0:09:30.200 --> 0:09:35.480 time into mating behaviors. It necessitates the existence of males, 0:09:35.960 --> 0:09:39.600 which in some cases like do little or nothing else, Like, 0:09:40.040 --> 0:09:44.360 you know, an entire division of the species just for reproduction. 0:09:45.640 --> 0:09:50.040 Mating can prove fatal in and of itself, not necessarily 0:09:50.080 --> 0:09:53.760 in a way that actually has any impact on the species. 0:09:53.760 --> 0:09:56.000 But still it's like the again, you get into these 0:09:56.040 --> 0:09:59.760 situations where the male's whole role is reproduction and then 0:10:00.040 --> 0:10:03.920 afterwards it has no purpose except maybe death. And it 0:10:03.960 --> 0:10:07.240 can of course also can be nutrition, could be nutrition. Yeah, 0:10:07.240 --> 0:10:10.400 so it's not a complete ways. But also just mating 0:10:10.440 --> 0:10:14.000 in general creates opportunities for predators in a number of ways. 0:10:14.280 --> 0:10:16.760 You could it could be something very specific, like well, 0:10:16.800 --> 0:10:19.559 while you're mating, it's possible that something could could prey 0:10:19.600 --> 0:10:23.160 on you. But also again, just think of all the 0:10:23.160 --> 0:10:27.080 the links that creatures end up going to inmate selection 0:10:27.600 --> 0:10:31.559 and so forth. Various examples of this, even if it's 0:10:31.600 --> 0:10:35.719 just say sexual dimorphism could mean that one member of 0:10:35.720 --> 0:10:37.760 the species is more likely to be consumed than the other. 0:10:38.200 --> 0:10:40.400 Yeah, it makes me think about all of the I 0:10:40.440 --> 0:10:45.160 don't know, like birds that essentially where male birds are 0:10:45.160 --> 0:10:51.240 trying to attract mates, specifically by being conspicuous. Yeah, you 0:10:51.320 --> 0:10:53.520 got to think that that also that comes with some 0:10:53.720 --> 0:10:56.120 amount of predation risk, at least in many cases. 0:10:56.600 --> 0:11:00.160 Yeah, another thing could be a particular places you have 0:11:00.200 --> 0:11:03.000 to travel to in order to engage in the mating, 0:11:03.040 --> 0:11:08.080 et cetera. But another drawback to sexual reproduction is that 0:11:08.120 --> 0:11:11.800 if it's your only option, it means that isolated members 0:11:12.040 --> 0:11:16.000 just of a particular species or population just cannot reproduce. 0:11:16.440 --> 0:11:19.600 And it also means that sufficiently reduced populations are just 0:11:19.679 --> 0:11:23.240 already at a dead end. Now in asexual reproduction, there's 0:11:23.280 --> 0:11:26.920 also a potential dead end there as well, because if 0:11:26.960 --> 0:11:31.040 you don't have genetic variation occurring, if you're basically just 0:11:31.080 --> 0:11:33.840 putting out the same model after the same model, after 0:11:33.880 --> 0:11:37.640 the same model, it may well improve, it may well 0:11:37.679 --> 0:11:41.840 prove impossible for the species to adapt or to change. 0:11:42.880 --> 0:11:44.600 So it's you know, if you're just putting out the 0:11:44.600 --> 0:11:48.560 same model after the same model, and like the market 0:11:48.679 --> 0:11:50.840 is the same for that product, then I guess you 0:11:50.840 --> 0:11:52.840 don't have anything to worry about so long as the 0:11:52.840 --> 0:11:56.080 market doesn't change. It's suddenly, if the demand for a 0:11:56.120 --> 0:12:00.360 particular you know, toy or item we were to alter 0:12:00.480 --> 0:12:03.679 in some way and you couldn't alter the product, then 0:12:03.679 --> 0:12:07.000 you'd be in trouble. And the same goes for any 0:12:07.080 --> 0:12:10.560 kind of biological form. What happens when say, things begin 0:12:10.600 --> 0:12:14.240 to dry up, or there's warming or cooling, or whatever 0:12:14.280 --> 0:12:17.920 the case may be. Sexual reproduction is what gives you 0:12:17.960 --> 0:12:23.080 the ability to bust out these different variations on the 0:12:23.080 --> 0:12:27.520 genetic code that could prove adaptive to change. Yeah, it 0:12:27.559 --> 0:12:34.000 gives you options, diversity, Yeah, yeah, diversifies your portfolio. Now, 0:12:34.040 --> 0:12:37.680 we mentioned disease and parasites already, so that's very much 0:12:37.920 --> 0:12:40.960 the case. If you just have a whole bunch of clones, 0:12:41.040 --> 0:12:46.640 then they all have the same susceptibility to illness or parasites. Overall, 0:12:46.720 --> 0:12:49.640 the big drawback is just a lack of genetic diversity, 0:12:50.040 --> 0:12:53.720 which can also result in the accumulation of harmful mutations. 0:12:54.360 --> 0:12:57.240 And another thing about the difference between the two though, 0:12:57.240 --> 0:12:59.480 that I guess I hadn't really thought about too much, 0:12:59.600 --> 0:13:01.960 is that it being a difference between short term and 0:13:02.080 --> 0:13:06.559 long term benefits. So, asexual reproduction is great for rapidly 0:13:06.600 --> 0:13:09.600 growing a population during a time of plenty, but the 0:13:09.640 --> 0:13:13.439 resulting population can run into problems long term. Meanwhile, sexual 0:13:13.520 --> 0:13:17.800 reproduction requires more energy and time, but generates diversity that 0:13:18.200 --> 0:13:20.880 may come in handy in the long term again when 0:13:20.920 --> 0:13:25.000 there are changes and obstacles that arise. Anyway, coming back 0:13:25.000 --> 0:13:29.400 to this idea that via asexual reproduction you can have 0:13:29.480 --> 0:13:35.440 this accumulation of harmful genetic changes. This brings us to 0:13:35.480 --> 0:13:38.880 the topic of Mueller's ratchet, which is not something I 0:13:38.920 --> 0:13:43.080 was familiar with previously. The basic theory here is that 0:13:43.600 --> 0:13:49.160 long term reproduction, particularly a sexual reproduction, but some of 0:13:49.200 --> 0:13:51.079 the studies we're looking at they're also looking at it 0:13:51.960 --> 0:13:56.120 with sexual reproduction. Basically, you see this accumulation of harmful 0:13:56.120 --> 0:14:00.600 genetic mutations, and after thousands of generations pass by, you 0:14:00.640 --> 0:14:05.800 can eventually reach a tipping point, which we refer to 0:14:05.840 --> 0:14:09.480 as mutational meltdown. And we'll get back to mutational meltdown 0:14:09.520 --> 0:14:13.920 in just a second. But interestingly, the namesake for Muller's 0:14:14.000 --> 0:14:17.400 ratchet is Hermann. Joseph Muller, who lived eighteen ninety through 0:14:17.480 --> 0:14:21.800 nineteen sixty seven, an American geneticis mostly known for his 0:14:21.920 --> 0:14:26.600 work on mooda genesis and for being like an outspoken 0:14:27.360 --> 0:14:31.320 critic and just sort of communicator on the dangers of 0:14:31.360 --> 0:14:35.120 radioactive fallout. He won the nineteen forty six Nobel Prize 0:14:35.160 --> 0:14:38.320 in physiology or medicine. And he was also the father 0:14:38.520 --> 0:14:43.560 of mathematician and computer scientist David E. Muller, who also 0:14:43.640 --> 0:14:47.080 has various things named after him. So you'll find a 0:14:47.160 --> 0:14:51.560 number of things in both genetic concepts and what have you, 0:14:51.640 --> 0:14:56.400 in genetics and mathematics that have the Muller name attached 0:14:56.400 --> 0:14:56.920 to them. 0:14:57.000 --> 0:14:59.840 Now, Rob, before you suggested this, I had never heard 0:14:59.840 --> 0:15:02.920 of mutational meltdown or Mueller's ratchet, at least as far 0:15:02.960 --> 0:15:05.120 as I know. But one of the things that I 0:15:05.160 --> 0:15:09.560 got really interested in here is how it violates sort 0:15:09.560 --> 0:15:13.400 of the simple assumptions that you make when you think 0:15:13.400 --> 0:15:16.080 about evolution on a surface level, because, of course it 0:15:16.160 --> 0:15:20.280 makes this reference to the idea of harmful genetic mutations 0:15:20.440 --> 0:15:25.240 accumulating over time in a species, and at a surface level, 0:15:25.240 --> 0:15:28.280 you might think, well, wait a minute, why would harmful 0:15:28.400 --> 0:15:32.960 genetic mutations accumulate? Isn't natural selection supposed to get rid 0:15:32.960 --> 0:15:37.000 of those? And so over time, with enough enough opportunities, yes, 0:15:37.240 --> 0:15:41.200 mutations that bring more harm than benefit to an organism's 0:15:41.440 --> 0:15:45.760 ability to survive and reproduce will tend to disappear. But 0:15:46.080 --> 0:15:50.040 under certain circumstances, bad genes can accumulate. And one of 0:15:49.880 --> 0:15:53.240 the key concepts to understand here is what's known as 0:15:53.360 --> 0:15:58.560 genetic drift. So genetic drift is a change in the 0:15:58.600 --> 0:16:03.280 frequency of a particular gene variant also known as an allele, 0:16:04.120 --> 0:16:08.440 in a population due to random chance rather than to 0:16:08.720 --> 0:16:13.360 natural selection. So random genetic drift is always happening. It's 0:16:13.400 --> 0:16:16.720 always going on in the background in the evolution of species. 0:16:17.040 --> 0:16:19.480 While you might think of natural selection as sort of 0:16:19.960 --> 0:16:25.560 acting in the foreground, amplifying or diminishing alleles because they 0:16:25.680 --> 0:16:29.360 are helpful or harmful. So you might think of, say 0:16:29.480 --> 0:16:33.360 a gene for blue feathers in some kind of bird, 0:16:33.680 --> 0:16:38.920 that gene might increase in the population, not for any 0:16:39.000 --> 0:16:42.600 reason having to do with blue feathers making the bird 0:16:42.680 --> 0:16:47.160 survive or reproduce more. Maybe it's just you know, sheer 0:16:47.280 --> 0:16:50.600 luck one season. Or maybe there might be some kind 0:16:50.640 --> 0:16:53.840 of random thing that happens in the popular lakes, maybe 0:16:53.840 --> 0:16:56.600 a big population of blue feathered individuals come across a 0:16:56.640 --> 0:16:59.400 big cache of food or something, or there is just 0:16:59.760 --> 0:17:03.840 the the standard fluctuations in the sampling rate of the 0:17:03.880 --> 0:17:08.400 different alleles that get recombined in sexual reproduction. The smaller 0:17:08.440 --> 0:17:11.919 a population is, the more likely it is to be 0:17:12.160 --> 0:17:17.960 irreversibly changed by random trends in genetic drift. Now you 0:17:18.080 --> 0:17:20.840 might wonder, how would that work. If the trends in 0:17:20.920 --> 0:17:24.320 genetic drift are just random, it's just chance, how would 0:17:24.359 --> 0:17:28.320 that cause irreversible changes. I think one way you might 0:17:28.320 --> 0:17:31.960 be able to compare this is if you think about gambling. Okay, 0:17:32.040 --> 0:17:36.800 imagine you're making bets on somebody flipping a coin. If 0:17:36.840 --> 0:17:39.880 you have an infinite pot of money to bet with, 0:17:40.160 --> 0:17:42.359 you could just keep doing this forever, right Like, you 0:17:42.440 --> 0:17:44.120 might get a run of good luck. You might get 0:17:44.119 --> 0:17:46.560 a run of bad luck. You might call the coin wrong. 0:17:46.880 --> 0:17:48.760 You know, I don't know how many times it would 0:17:48.800 --> 0:17:51.040 be plausible eight times in a row and lose a 0:17:51.080 --> 0:17:54.760 lot of money. But eventually, on average, you'd have a 0:17:54.760 --> 0:17:57.120 winning streak again, and you'd win your money back as 0:17:57.160 --> 0:18:00.240 long as you can keep gambling, as long as you've 0:18:00.280 --> 0:18:03.040 got like an infinite pot to play from. But if 0:18:03.080 --> 0:18:06.399 you are gambling with a fixed amount of money, you 0:18:06.680 --> 0:18:10.080 eventually will hit a random run of bad luck and 0:18:10.119 --> 0:18:12.720 lose it all. You will play to extinction. 0:18:13.680 --> 0:18:14.800 Very fitting, very fitting. 0:18:15.160 --> 0:18:19.399 So for my analogy here, you could compare the size 0:18:19.400 --> 0:18:21.439 of your purse you're going in to gamble with with 0:18:21.640 --> 0:18:24.760 the size of the population where the random genetic drift 0:18:24.800 --> 0:18:29.680 is happening. Genetic drift in a small population can easily 0:18:29.800 --> 0:18:33.959 drive certain alleles extinct, even though those alleles had no 0:18:34.200 --> 0:18:38.440 negative effect on survival. The other side of the other 0:18:38.480 --> 0:18:41.800 side of that is that in small populations, random genetic 0:18:41.840 --> 0:18:45.080 drift can also do the inverse. It can take an 0:18:45.119 --> 0:18:48.920 allele and make it the only version of that gene 0:18:49.160 --> 0:18:53.200 left in the population, present in one hundred percent of individuals. 0:18:53.600 --> 0:18:57.200 And there's a term for this, The population genetics term 0:18:57.960 --> 0:19:01.719 for when an allele becomes present in the entire population 0:19:01.920 --> 0:19:06.119 is fixation. When that allele is the only version of 0:19:06.119 --> 0:19:09.199 that gene left, it is said to be fixed in 0:19:09.240 --> 0:19:12.439 the population. Everybody's got it. And of course, once a 0:19:12.520 --> 0:19:15.719 gene variant is fixed in a population, of course, that 0:19:15.800 --> 0:19:18.480 means the individuals in that population are stuck with it, 0:19:18.560 --> 0:19:22.679 you know, unless there is new information introduced. Now that 0:19:22.720 --> 0:19:25.840 could be maybe a random mutation causes a new version 0:19:25.880 --> 0:19:28.400 of that gene to appear and then it can maybe compete, 0:19:28.880 --> 0:19:32.720 or there is inflow of new alleles of that gene, 0:19:32.720 --> 0:19:37.119 maybe by interbreeding with another population or something like that. 0:19:37.359 --> 0:19:42.240 But for a closed population, once a gene variant is fixed, 0:19:42.359 --> 0:19:53.960 they're stuck with it. Now, the important thing to realize 0:19:54.000 --> 0:19:58.359 is that alleles don't have to be the best version 0:19:58.400 --> 0:20:00.679 of that gene. They don't have to be helpful to 0:20:00.800 --> 0:20:05.640 survival or reproduction in order to become fixed in a population. 0:20:06.720 --> 0:20:11.560 In big populations, harmful versions of genes will not tend 0:20:11.560 --> 0:20:14.159 to dominate over time. They will tend to get removed 0:20:14.280 --> 0:20:18.160 or remain in the background. But in small populations, because 0:20:18.240 --> 0:20:22.639 you're essentially gambling with a small purse, those deleterious alleles 0:20:22.680 --> 0:20:27.000 can become fixed just through bad luck. So you imagine, 0:20:27.000 --> 0:20:31.560 maybe every season within a population, you pick a randomly 0:20:31.600 --> 0:20:34.960 assorted number of the individuals in that population, You say, 0:20:35.000 --> 0:20:38.760 whichever allele they've got, make another copy of that one, 0:20:39.240 --> 0:20:41.480 and then you just keep doing that over and over. 0:20:42.080 --> 0:20:45.560 You can get random results where suddenly a gene that's 0:20:45.680 --> 0:20:49.160 not very good for the population is suddenly the only 0:20:49.200 --> 0:20:55.520 one left. So that's how genetic drift can cause deleterious, 0:20:55.840 --> 0:21:00.159 harmful genes to become fixed in a population. But I 0:21:00.240 --> 0:21:02.480 was wondering, Okay, so what's the deal with this idea 0:21:02.680 --> 0:21:06.879 of mutational meltdown. What's happening there? Well, I was reading 0:21:06.920 --> 0:21:10.040 about this in a in a biology textbook I found 0:21:10.040 --> 0:21:15.680 called Practical Conservation Biology edited by David Lindenmeyer and Mark Bergmann. 0:21:15.920 --> 0:21:19.320 And you know, one of the things that the authors 0:21:19.359 --> 0:21:22.600 mention is that every population carries some load in the 0:21:22.640 --> 0:21:28.760 background of deleterious recessive genes. But the core theory of 0:21:29.760 --> 0:21:33.879 mutational meltdown again, it's something that really applies in particular 0:21:34.000 --> 0:21:38.160 to small populations. That's where it's really dangerous. The author's 0:21:38.200 --> 0:21:43.040 write quote. In small populations, the dominant genetic process is drift. 0:21:43.520 --> 0:21:46.520 If the size of the breeding population is very small, 0:21:46.640 --> 0:21:50.959 then random drift can overwhelm natural selection and a population 0:21:51.119 --> 0:21:55.800 can accumulate and become fixed for quite deleterious mutations. If 0:21:55.800 --> 0:21:59.280 the decline in fitness that results from the accumulation of 0:21:59.359 --> 0:22:04.560 new mutations reduces fecundity, so it reduces birth rates and 0:22:04.640 --> 0:22:10.640 reduces survival to the extent that the population declines, feedback 0:22:10.760 --> 0:22:15.160 between random genetic drift and mutation is set in motion. 0:22:15.760 --> 0:22:20.760 As the population size decreases, random genetic drift becomes a 0:22:20.920 --> 0:22:25.000 more significant force, and the rate of fixation of deleterious 0:22:25.080 --> 0:22:29.800 mutations increases, further reducing population size. So it is this 0:22:30.359 --> 0:22:36.119 feedback loop between the harmful mutations making the population smaller 0:22:36.640 --> 0:22:40.720 and thus increasing the effects of genetic drift compared to 0:22:40.880 --> 0:22:42.720 the effects of selection forces. 0:22:43.240 --> 0:22:46.520 Yeah, so at first you just have one wrong turn movie, 0:22:46.600 --> 0:22:48.840 and then you have two wrong turn movies, and before 0:22:48.880 --> 0:22:50.840 you know it, there's like twenty of them and you 0:22:50.880 --> 0:22:53.280 haven't seen a single one, but you know that they 0:22:53.320 --> 0:22:56.879 all have something to do with mutated hillbillies. 0:22:57.480 --> 0:23:00.760 Yes, it's a vicious cycle of some kind. And as 0:23:00.800 --> 0:23:02.800 a side note, by the way, this is not relevant 0:23:02.800 --> 0:23:04.919 to most of the species we'd be talking about, but 0:23:05.080 --> 0:23:07.399 just because I thought it was interesting. The authors in 0:23:07.440 --> 0:23:11.040 the context of this conservation biology book also mention how 0:23:11.080 --> 0:23:15.960 this applies in captive populations in a conservation context. So 0:23:17.720 --> 0:23:22.320 because captive populations of animals where you know there's concern 0:23:22.440 --> 0:23:27.280 for the species level survival, because those might those animals 0:23:27.320 --> 0:23:31.679 are not really competing in the wild to survive, It 0:23:31.800 --> 0:23:36.000 is very easy, in fact, for them to accumulate deleterious 0:23:36.080 --> 0:23:40.560 mutations in their genome because you have this genetic drift factor. 0:23:40.680 --> 0:23:44.680 But then also the normal selection pressures are not really 0:23:44.680 --> 0:23:49.160 applying at all, so once the population is reintroduced into 0:23:49.160 --> 0:23:53.080 the wild, the build up of all these deleterious mutations 0:23:53.160 --> 0:23:56.639 acquired through genetic drift can be quite harsh, and they 0:23:56.680 --> 0:24:01.440 say that this could explain some examples of basically poor 0:24:01.520 --> 0:24:06.200 performance of captive bread individuals of endangered species after being 0:24:06.280 --> 0:24:07.440 released into the wild. 0:24:08.640 --> 0:24:11.480 Yeah, there's so many factors to take into account with 0:24:11.800 --> 0:24:14.560 captive populations, because, yeah, on top of everything you just 0:24:14.600 --> 0:24:18.000 talked about, there's also the idea that some species will 0:24:18.080 --> 0:24:23.359 just then spontaneously asexually produce offspring, which of course is 0:24:23.400 --> 0:24:25.320 not going to that particular offspring is not going to 0:24:25.320 --> 0:24:31.080 be genetically diversified either, So yeah, you have this huge 0:24:31.119 --> 0:24:32.080 bottleneck potential. 0:24:32.080 --> 0:24:34.600 There one last thing from that book. The most common 0:24:34.600 --> 0:24:38.760 citations I see for the theoretical work on mutational meltdown 0:24:39.280 --> 0:24:43.840