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Speaker 1: Hey, you welcome to Stuff to Blow Your Mind. My

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Speaker 1: name is Robert.

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Speaker 2: Lamb and I am Joe McCormick, and today we are

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Speaker 2: bringing you an episode from the vault. This one originally

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Speaker 2: published April twentieth, twenty twenty three, and it is called

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Speaker 2: Mutational Meltdown.

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Speaker 1: Yeah, this is one that I was drawn to initially

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Speaker 1: solely because of the title Mutational Meltdown, How can you resist?

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Speaker 1: But there's a lot of fascinating content in there as well,

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Speaker 1: beyond just sort of the knee jerk feel of imagining

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Speaker 1: some sort of mutant melting in some sort of a

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Speaker 1: sci fi context. Let's jump right in.

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Speaker 3: Welcome to Stuff to Blow Your Mind, production of iHeartRadio.

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Speaker 1: Hey you welcome to Stuff to Blow your Mind. My

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Speaker 1: name is Robert.

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Speaker 2: Lamb and I'm Joe McCormick, and today we're going to

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Speaker 2: be talking about a concept in the realm of genetics

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Speaker 2: and reproduction, a concept known as mutational meltdown. Very enticing name, Rob.

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Speaker 2: I understand you became interested in mutational meltdown earlier this week.

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Speaker 2: What got you going on this?

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Speaker 1: Well, it actually didn't have anything to do directly with

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Speaker 1: any melt movies. We might have been talking about on

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Speaker 1: Weird House Cinema. I actually, I think I was on

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Speaker 1: a walk with my family and I said, Hey, I

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Speaker 1: think we're going to need an episode for Thursday. What

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Speaker 1: should we do it on? And there my wife and

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Speaker 1: my son are like, Oh, you should do it on

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Speaker 1: asexual reproduction. So okay, let's just started looking around a

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Speaker 1: little bit. And yeah, this particular term kind of jumped

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Speaker 1: out at me. I wasn't familiar with it, and it

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Speaker 1: basically gets down into and I think for our purposes

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Speaker 1: here on the show, you know, it's a reason to

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Speaker 1: sort of provide an overview of sort of asexual reproduction

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Speaker 1: versus sexual reproduction as sort of competing ways of going

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Speaker 1: about sort of the same thing for an organism, but

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Speaker 1: one with more short term benefits versus long term benefits.

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Speaker 1: And I don't know, I just found it to be

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Speaker 1: kind of a neat way to re examine and think

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Speaker 1: about these these concepts that I imagine we've covered on

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Speaker 1: the show before, and many of you out there have

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Speaker 1: have encountered in varying formats.

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Speaker 2: Sure well, I know over the years we have alluded

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Speaker 2: to the big question in biology of like where sex

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Speaker 2: comes from, the where when and why of sexual reproductions

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Speaker 2: as a part of the history of organisms on planet Earth.

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Speaker 2: Not going to solve that problem today, but yeah, I

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Speaker 2: think maybe this little subtopic could help shed a little

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Speaker 2: bit of light there.

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Speaker 1: Yeah, so let's let's start with the basics. Though, we're

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Speaker 1: going to just approach it as if you know, you're

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Speaker 1: not really familiar with any of the topics that we're

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Speaker 1: discussing here, So asexual reproduction versus sexual reproduction on a

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Speaker 1: very basic level, here's how it all goes down. So,

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Speaker 1: with sexual reproduction, you have the offspring of two genetic

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Speaker 1: parents inheriting a mix of genes from those parents, genetically

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Speaker 1: distinguishing itself from either parent. The resulting genetic variation is

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Speaker 1: highly adaptive because it provides individuals with varying traits that

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Speaker 1: may prove necessary for survival in an ever changing environment.

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Speaker 1: The resulting genetic diversity makes the population more resistant to

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Speaker 1: disease as well.

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Speaker 2: I think one of the theories we've talked about before

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Speaker 2: is that an advantage of sexual reproduction is that it

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Speaker 2: helps protect the host organism against various types of parasites

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Speaker 2: by introducing genetic variability that makes it harder for the

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Speaker 2: parasite to target each successive generation of the host.

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Speaker 1: Yeah, this is a clumsy analogy at best, but I

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Speaker 1: can't help but think too about like to say that,

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Speaker 1: because essentially, when you're talking about asexual reproduction, you're talking

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Speaker 1: essentially about making a clone of oneself. And so the

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Speaker 1: clone army in the Star Wars prequels highly susceptible to say,

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Speaker 1: a single order coming out and telling them to turn

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Speaker 1: on the Jedi, that sort of thing. But that's just

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Speaker 1: a very very rough idea of how to think about it.

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Speaker 1: But more specifically for our purposes here, another key benefit

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Speaker 1: that comes up in the literature is looking at is

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Speaker 1: that you can think of sex and genetic recombination is

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Speaker 1: ultimately a means of purging deletarious mutations.

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Speaker 2: Right, so the impact of mutations that might be harmful

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Speaker 2: to the organism can be blunted by sexual recombination. Yeah.

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Speaker 1: Yeah, So you end up with this, I mean, roughly speaking,

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Speaker 1: you know, you have kind of like a randomization of

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Speaker 1: these different traits, and the individuals that end up the

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Speaker 1: offspring with that end up with the the negative traits,

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Speaker 1: the harmful traits. They don't survive the ones that have

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Speaker 1: been purged of those mutations do survive, and therefore it

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Speaker 1: can purge the mutation from a particular lineage. Okay, all right,

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Speaker 1: So moving on to asexual reproduction. This is a case

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Speaker 1: in which you have the offspring of a single genetic

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Speaker 1: parent inheriting the genes of the parent, making it a

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Speaker 1: clone identical to the parent. The advantage here is that

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Speaker 1: you can reproduce rapidly without all of the energy expenditure

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Speaker 1: of mating. And I mean that's a pretty big statement

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Speaker 1: to think about, because so many organisms we end up

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Speaker 1: discussing on the podcast. You know, what is the key

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Speaker 1: thing that makes them interesting? Well, in some cases, many cases,

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Speaker 1: it's how they acquire their food, But in other cases

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Speaker 1: it's how do they get a mate? How do they

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Speaker 1: attract a maid or pursue a mate, And it ends

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Speaker 1: up taking up a whole lot of time, a whole

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Speaker 1: lot of energy. And what if you didn't have to

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Speaker 1: do that? What if instead you could just essentially clone yourself.

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Speaker 2: Convenient and safer in a lot of cases, because I

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Speaker 2: mean it varies by organism, but in many cases, yeah,

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Speaker 2: if you have to go seeking out a mate, it

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Speaker 2: is not only you know, an energy expense to go

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Speaker 2: looking around, but you're also often removing yourself from safe

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Speaker 2: locations and going into dangerous ones. Yeah.

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Speaker 1: I mean it's kind of like when you get some

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Speaker 1: sort of new kit to a symbols of Ikia furniture, right,

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Speaker 1: and the first thing you notice is that on the

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Speaker 1: instructions it says, oh, you have to have two people

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Speaker 1: to do this, and you're like, oh, that totally recks

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Speaker 1: my day. Now, I've got to get my significant other

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Speaker 1: or a friend to help with this. We've got to

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Speaker 1: align our schedules, and we have to both work together

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Speaker 1: to build this thing, as opposed to one where I

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Speaker 1: can just build it myself and put it where it

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Speaker 1: needs to go in the house. Now, there are multiple

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Speaker 1: types of asexual reproduction, and we're not going to go

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Speaker 1: into all of them, but you have all sorts of

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Speaker 1: things like asexual budding and so forth. The sources I

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Speaker 1: was looking at dealt a lot with parthenogenis, which occurs

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Speaker 1: widely and invertebrates. This word stems from the Greek for

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Speaker 1: virgin creation parthenos plus genesis.

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Speaker 2: Okay, so this would describe, for example, a lot of

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Speaker 2: vertebrates like maybe some lizards or fish that can give

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Speaker 2: birth without ever having without ever having their game meets

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Speaker 2: fertilized by a member of the opposite sex.

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Speaker 1: Yeah, yeah, we're talking about lizards, geckos, various insects, particularly

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Speaker 1: some sharks. And it's of course very important to note

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Speaker 1: that there are obligates sexual reproducers and then they're obligate

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Speaker 1: asexual reproducers. But then there are also organisms that can

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Speaker 1: do either depending on environmental pressure. So a classic example

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Speaker 1: of a sexually reproducing organism engaging in asexual reproduction is,

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Speaker 1: of course, when an individual cannot find a mate. It's

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Speaker 1: kind of there as I guess you could think of

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Speaker 1: it as kind of a backup plan that or some

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Speaker 1: sort of a you know, an emergency button that can

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Speaker 1: be pushed. And this has been the case with some

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Speaker 1: of the famous examples of say sharks or lizards such

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Speaker 1: as the Komodo dragon reproducing in captivity, these so called

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Speaker 1: virgin births that will suddenly occur in shock zoo keepers.

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Speaker 2: So the ideal is to mix and match your genetic

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Speaker 2: material with somebody else's, but in a pinch, you could

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Speaker 2: just make a copy of yourself if you're.

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Speaker 1: The right species correct, Yeah, and if I'm remembering correctly,

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Speaker 1: This also pops up in the plot of Jurassic Park, right,

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Speaker 1: something to do with the way that they're recreating dinosaur

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Speaker 1: DNA using amphibian DNA.

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Speaker 2: Well, I don't know if this is parthenogenesis or if

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Speaker 2: it would be different. I think what they say, at

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Speaker 2: least in the movie, I don't remember what happens in

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Speaker 2: the book. In the movie they say that because they

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Speaker 2: use some frog DNA to cover up patches in the

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Speaker 2: DNA sequence. I'm just recalling from memory what mister DNA

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Speaker 2: tells us that some frogs are able to spontaneously change

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Speaker 2: sex in a single sex environment, and thus, even though

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Speaker 2: all of the dinosaurs in the park were supposed to

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Speaker 2: be female, some changed into males, and thus we're sexually reproducing.

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Speaker 1: Ah okay, I think that's the main thing. I'm either

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Speaker 1: misremembering that, or maybe there's something from one of the

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Speaker 1: later like Jurassic World films that I'm only like half

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Speaker 1: processing here. All Right, So you have these two basic

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Speaker 1: ways of reproducing, then this of course means that there

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Speaker 1: are drawbacks to either one. So in sexual reproduction again,

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Speaker 1: you got to put a whole lot of energy and

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Speaker 1: time into mating behaviors. It necessitates the existence of males,

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Speaker 1: which in some cases like do little or nothing else, Like,

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Speaker 1: you know, an entire division of the species just for reproduction.

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Speaker 1: Mating can prove fatal in and of itself, not necessarily

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Speaker 1: in a way that actually has any impact on the species.

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Speaker 1: But still it's like the again, you get into these

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Speaker 1: situations where the male's whole role is reproduction and then

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Speaker 1: afterwards it has no purpose except maybe death. And it

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Speaker 1: can of course also can be nutrition, could be nutrition. Yeah,

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Speaker 1: so it's not a complete ways. But also just mating

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Speaker 1: in general creates opportunities for predators in a number of ways.

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Speaker 1: You could it could be something very specific, like well,

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Speaker 1: while you're mating, it's possible that something could could prey

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Speaker 1: on you. But also again, just think of all the

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Speaker 1: the links that creatures end up going to inmate selection

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Speaker 1: and so forth. Various examples of this, even if it's

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Speaker 1: just say sexual dimorphism could mean that one member of

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Speaker 1: the species is more likely to be consumed than the other.

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Speaker 2: Yeah, it makes me think about all of the I

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Speaker 2: don't know, like birds that essentially where male birds are

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Speaker 2: trying to attract mates, specifically by being conspicuous. Yeah, you

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Speaker 2: got to think that that also that comes with some

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Speaker 2: amount of predation risk, at least in many cases.

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Speaker 1: Yeah, another thing could be a particular places you have

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Speaker 1: to travel to in order to engage in the mating,

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Speaker 1: et cetera. But another drawback to sexual reproduction is that

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Speaker 1: if it's your only option, it means that isolated members

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Speaker 1: just of a particular species or population just cannot reproduce.

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Speaker 1: And it also means that sufficiently reduced populations are just

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Speaker 1: already at a dead end. Now in asexual reproduction, there's

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Speaker 1: also a potential dead end there as well, because if

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Speaker 1: you don't have genetic variation occurring, if you're basically just

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Speaker 1: putting out the same model after the same model, after

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Speaker 1: the same model, it may well improve, it may well

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Speaker 1: prove impossible for the species to adapt or to change.

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Speaker 1: So it's you know, if you're just putting out the

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Speaker 1: same model after the same model, and like the market

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Speaker 1: is the same for that product, then I guess you

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Speaker 1: don't have anything to worry about so long as the

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Speaker 1: market doesn't change. It's suddenly, if the demand for a

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Speaker 1: particular you know, toy or item we were to alter

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Speaker 1: in some way and you couldn't alter the product, then

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Speaker 1: you'd be in trouble. And the same goes for any

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Speaker 1: kind of biological form. What happens when say, things begin

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Speaker 1: to dry up, or there's warming or cooling, or whatever

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Speaker 1: the case may be. Sexual reproduction is what gives you

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Speaker 1: the ability to bust out these different variations on the

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Speaker 1: genetic code that could prove adaptive to change. Yeah, it

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Speaker 1: gives you options, diversity, Yeah, yeah, diversifies your portfolio. Now,

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Speaker 1: we mentioned disease and parasites already, so that's very much

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Speaker 1: the case. If you just have a whole bunch of clones,

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Speaker 1: then they all have the same susceptibility to illness or parasites. Overall,

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Speaker 1: the big drawback is just a lack of genetic diversity,

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Speaker 1: which can also result in the accumulation of harmful mutations.

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Speaker 1: And another thing about the difference between the two though,

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Speaker 1: that I guess I hadn't really thought about too much,

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Speaker 1: is that it being a difference between short term and

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Speaker 1: long term benefits. So, asexual reproduction is great for rapidly

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Speaker 1: growing a population during a time of plenty, but the

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Speaker 1: resulting population can run into problems long term. Meanwhile, sexual

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Speaker 1: reproduction requires more energy and time, but generates diversity that

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Speaker 1: may come in handy in the long term again when

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Speaker 1: there are changes and obstacles that arise. Anyway, coming back

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Speaker 1: to this idea that via asexual reproduction you can have

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Speaker 1: this accumulation of harmful genetic changes. This brings us to

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Speaker 1: the topic of Mueller's ratchet, which is not something I

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Speaker 1: was familiar with previously. The basic theory here is that

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Speaker 1: long term reproduction, particularly a sexual reproduction, but some of

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Speaker 1: the studies we're looking at they're also looking at it

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Speaker 1: with sexual reproduction. Basically, you see this accumulation of harmful

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Speaker 1: genetic mutations, and after thousands of generations pass by, you

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Speaker 1: can eventually reach a tipping point, which we refer to

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Speaker 1: as mutational meltdown. And we'll get back to mutational meltdown

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Speaker 1: in just a second. But interestingly, the namesake for Muller's

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Speaker 1: ratchet is Hermann. Joseph Muller, who lived eighteen ninety through

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Speaker 1: nineteen sixty seven, an American geneticis mostly known for his

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Speaker 1: work on mooda genesis and for being like an outspoken

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Speaker 1: critic and just sort of communicator on the dangers of

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Speaker 1: radioactive fallout. He won the nineteen forty six Nobel Prize

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Speaker 1: in physiology or medicine. And he was also the father

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Speaker 1: of mathematician and computer scientist David E. Muller, who also

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Speaker 1: has various things named after him. So you'll find a

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Speaker 1: number of things in both genetic concepts and what have you,

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Speaker 1: in genetics and mathematics that have the Muller name attached

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Speaker 1: to them.

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Speaker 2: Now, Rob, before you suggested this, I had never heard

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Speaker 2: of mutational meltdown or Mueller's ratchet, at least as far

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Speaker 2: as I know. But one of the things that I

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Speaker 2: got really interested in here is how it violates sort

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Speaker 2: of the simple assumptions that you make when you think

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Speaker 2: about evolution on a surface level, because, of course it

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Speaker 2: makes this reference to the idea of harmful genetic mutations

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Speaker 2: accumulating over time in a species, and at a surface level,

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Speaker 2: you might think, well, wait a minute, why would harmful

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Speaker 2: genetic mutations accumulate? Isn't natural selection supposed to get rid

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Speaker 2: of those? And so over time, with enough enough opportunities, yes,

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Speaker 2: mutations that bring more harm than benefit to an organism's

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Speaker 2: ability to survive and reproduce will tend to disappear. But

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Speaker 2: under certain circumstances, bad genes can accumulate. And one of

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Speaker 2: the key concepts to understand here is what's known as

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Speaker 2: genetic drift. So genetic drift is a change in the

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Speaker 2: frequency of a particular gene variant also known as an allele,

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Speaker 2: in a population due to random chance rather than to

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Speaker 2: natural selection. So random genetic drift is always happening. It's

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Speaker 2: always going on in the background in the evolution of species.

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Speaker 2: While you might think of natural selection as sort of

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Speaker 2: acting in the foreground, amplifying or diminishing alleles because they

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Speaker 2: are helpful or harmful. So you might think of, say

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Speaker 2: a gene for blue feathers in some kind of bird,

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Speaker 2: that gene might increase in the population, not for any

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Speaker 2: reason having to do with blue feathers making the bird

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Speaker 2: survive or reproduce more. Maybe it's just you know, sheer

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Speaker 2: luck one season. Or maybe there might be some kind

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Speaker 2: of random thing that happens in the popular lakes, maybe

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Speaker 2: a big population of blue feathered individuals come across a

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Speaker 2: big cache of food or something, or there is just

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Speaker 2: the the standard fluctuations in the sampling rate of the

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Speaker 2: different alleles that get recombined in sexual reproduction. The smaller

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Speaker 2: a population is, the more likely it is to be

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Speaker 2: irreversibly changed by random trends in genetic drift. Now you

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Speaker 2: might wonder, how would that work. If the trends in

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Speaker 2: genetic drift are just random, it's just chance, how would

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Speaker 2: that cause irreversible changes. I think one way you might

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Speaker 2: be able to compare this is if you think about gambling. Okay,

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Speaker 2: imagine you're making bets on somebody flipping a coin. If

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Speaker 2: you have an infinite pot of money to bet with,

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Speaker 2: you could just keep doing this forever, right Like, you

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Speaker 2: might get a run of good luck. You might get

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Speaker 2: a run of bad luck. You might call the coin wrong.

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Speaker 2: You know, I don't know how many times it would

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Speaker 2: be plausible eight times in a row and lose a

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Speaker 2: lot of money. But eventually, on average, you'd have a

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Speaker 2: winning streak again, and you'd win your money back as

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Speaker 2: long as you can keep gambling, as long as you've

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Speaker 2: got like an infinite pot to play from. But if

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Speaker 2: you are gambling with a fixed amount of money, you

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Speaker 2: eventually will hit a random run of bad luck and

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Speaker 2: lose it all. You will play to extinction.

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Speaker 1: Very fitting, very fitting.

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Speaker 2: So for my analogy here, you could compare the size

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Speaker 2: of your purse you're going in to gamble with with

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Speaker 2: the size of the population where the random genetic drift

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Speaker 2: is happening. Genetic drift in a small population can easily

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Speaker 2: drive certain alleles extinct, even though those alleles had no

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Speaker 2: negative effect on survival. The other side of the other

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Speaker 2: side of that is that in small populations, random genetic

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Speaker 2: drift can also do the inverse. It can take an

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Speaker 2: allele and make it the only version of that gene

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Speaker 2: left in the population, present in one hundred percent of individuals.

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Speaker 2: And there's a term for this, The population genetics term

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Speaker 2: for when an allele becomes present in the entire population

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Speaker 2: is fixation. When that allele is the only version of

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Speaker 2: that gene left, it is said to be fixed in

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Speaker 2: the population. Everybody's got it. And of course, once a

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Speaker 2: gene variant is fixed in a population, of course, that

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Speaker 2: means the individuals in that population are stuck with it,

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Speaker 2: you know, unless there is new information introduced. Now that

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Speaker 2: could be maybe a random mutation causes a new version

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Speaker 2: of that gene to appear and then it can maybe compete,

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Speaker 2: or there is inflow of new alleles of that gene,

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Speaker 2: maybe by interbreeding with another population or something like that.

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Speaker 2: But for a closed population, once a gene variant is fixed,

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Speaker 2: they're stuck with it. Now, the important thing to realize

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Speaker 2: is that alleles don't have to be the best version

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Speaker 2: of that gene. They don't have to be helpful to

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Speaker 2: survival or reproduction in order to become fixed in a population.

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Speaker 2: In big populations, harmful versions of genes will not tend

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Speaker 2: to dominate over time. They will tend to get removed

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Speaker 2: or remain in the background. But in small populations, because

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Speaker 2: you're essentially gambling with a small purse, those deleterious alleles

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Speaker 2: can become fixed just through bad luck. So you imagine,

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Speaker 2: maybe every season within a population, you pick a randomly

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Speaker 2: assorted number of the individuals in that population, You say,

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Speaker 2: whichever allele they've got, make another copy of that one,

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Speaker 2: and then you just keep doing that over and over.

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Speaker 2: You can get random results where suddenly a gene that's

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Speaker 2: not very good for the population is suddenly the only

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Speaker 2: one left. So that's how genetic drift can cause deleterious,

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Speaker 2: harmful genes to become fixed in a population. But I

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Speaker 2: was wondering, Okay, so what's the deal with this idea

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Speaker 2: of mutational meltdown. What's happening there? Well, I was reading

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Speaker 2: about this in a in a biology textbook I found

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Speaker 2: called Practical Conservation Biology edited by David Lindenmeyer and Mark Bergmann.

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Speaker 2: And you know, one of the things that the authors

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Speaker 2: mention is that every population carries some load in the

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Speaker 2: background of deleterious recessive genes. But the core theory of

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Speaker 2: mutational meltdown again, it's something that really applies in particular

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Speaker 2: to small populations. That's where it's really dangerous. The author's

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Speaker 2: write quote. In small populations, the dominant genetic process is drift.

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Speaker 2: If the size of the breeding population is very small,

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Speaker 2: then random drift can overwhelm natural selection and a population

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Speaker 2: can accumulate and become fixed for quite deleterious mutations. If

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Speaker 2: the decline in fitness that results from the accumulation of

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Speaker 2: new mutations reduces fecundity, so it reduces birth rates and

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Speaker 2: reduces survival to the extent that the population declines, feedback

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Speaker 2: between random genetic drift and mutation is set in motion.

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Speaker 2: As the population size decreases, random genetic drift becomes a

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Speaker 2: more significant force, and the rate of fixation of deleterious

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Speaker 2: mutations increases, further reducing population size. So it is this

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Speaker 2: feedback loop between the harmful mutations making the population smaller

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Speaker 2: and thus increasing the effects of genetic drift compared to

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Speaker 2: the effects of selection forces.

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Speaker 1: Yeah, so at first you just have one wrong turn movie,

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Speaker 1: and then you have two wrong turn movies, and before

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Speaker 1: you know it, there's like twenty of them and you

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Speaker 1: haven't seen a single one, but you know that they

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Speaker 1: all have something to do with mutated hillbillies.

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Speaker 2: Yes, it's a vicious cycle of some kind. And as

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Speaker 2: a side note, by the way, this is not relevant

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Speaker 2: to most of the species we'd be talking about, but

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Speaker 2: just because I thought it was interesting. The authors in

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Speaker 2: the context of this conservation biology book also mention how

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Speaker 2: this applies in captive populations in a conservation context. So

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Speaker 2: because captive populations of animals where you know there's concern

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Speaker 2: for the species level survival, because those might those animals

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Speaker 2: are not really competing in the wild to survive, It

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Speaker 2: is very easy, in fact, for them to accumulate deleterious

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Speaker 2: mutations in their genome because you have this genetic drift factor.

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Speaker 2: But then also the normal selection pressures are not really

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Speaker 2: applying at all, so once the population is reintroduced into

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Speaker 2: the wild, the build up of all these deleterious mutations

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Speaker 2: acquired through genetic drift can be quite harsh, and they

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Speaker 2: say that this could explain some examples of basically poor

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Speaker 2: performance of captive bread individuals of endangered species after being

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Speaker 2: released into the wild.

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Speaker 1: Yeah, there's so many factors to take into account with

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Speaker 1: captive populations, because, yeah, on top of everything you just

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Speaker 1: talked about, there's also the idea that some species will

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Speaker 1: just then spontaneously asexually produce offspring, which of course is

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Speaker 1: not going to that particular offspring is not going to

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Speaker 1: be genetically diversified either, So yeah, you have this huge

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Speaker 1: bottleneck potential.

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Speaker 2: There one last thing from that book. The most common

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Speaker 2: citations I see for the theoretical work on mutational meltdown

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Speaker 2: are attributed to papers by Lynch published in the nineties

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Speaker 2: in the nineteen nineties, but they do note also in

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Speaker 2: this book chapter that there have been some studies that

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Speaker 2: looked for so that's the theoretical work by Lynch, but

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Speaker 2: there were some studies that look to try to find

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Speaker 2: evidence of what they call greater genetic loads accumulations of

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Speaker 2: mutations in small fruit fly populations. This was cited to

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Speaker 2: Gilligan at all in two thousand and five, and they

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Speaker 2: didn't find it. They didn't find evidence of these of

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Speaker 2: these loads they expected. So I guess some questions about

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Speaker 2: how the theory of mutational meltdown actually applies to populations

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Speaker 2: in the wild.

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Speaker 1: Yeah, yeah, it's my understanding that, Yeah, we are dealing

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Speaker 1: with theories here, and there is a continued challenge for

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Speaker 1: evolutionary biologies to find examples and potential examples of all

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Speaker 1: of this and to define these breakthrough examples. It will

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Speaker 1: help us better understand not only this whole question of

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Speaker 1: potential mutational meltdown, but also just sort of a larger

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Speaker 1: question again of like why is sexual reproduction more beneficial

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Speaker 1: or seemingly more beneficial? Like why sexual reproduction at all?

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Speaker 1: But anyway, as I understand it, based on what we're

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Speaker 1: looking at here, yeah, we have Mueller's which is the

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Speaker 1: theoretical process that then could bring us to this end

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Speaker 1: game of mutational meltdown. Mutational meltdown in this regard would

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Speaker 1: be considered a subclass of an extinction vortex. Extinction vortex

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Speaker 1: is a larger classification entailing different environmental, genetic, and demographic factors.

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Speaker 1: It's also worth noting and perhaps inflating the obvious here,

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Speaker 1: and that is that extinction is in the long term inevitable.

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Speaker 1: All species eventually face extinction, and I've read that something

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Speaker 1: like more than ninety nine percent of all species to

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Speaker 1: ever exist have gone extinct. Again, this is stuff that

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Speaker 1: makes perfect sense when you spell it out, but also

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Speaker 1: it can sort of mess with your short term, short,

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Speaker 1: short lived human brain when you start again thinking about

435
00:26:51,680 --> 00:26:56,280
Speaker 1: the really long term history of life on Earth. So,

436
00:26:56,320 --> 00:26:59,840
Speaker 1: of course, one of the big obvious challenges to exploring

437
00:26:59,840 --> 00:27:02,120
Speaker 1: all of this is that humans have only been around

438
00:27:02,560 --> 00:27:05,120
Speaker 1: on Earth and in a position to look for examples

439
00:27:05,359 --> 00:27:08,879
Speaker 1: of things like mutational meltdown for a very short period

440
00:27:08,920 --> 00:27:14,680
Speaker 1: of time. And if most asexual species or populations don't

441
00:27:14,800 --> 00:27:19,240
Speaker 1: last very long, do you know, theoretically to Muller's ratchet

442
00:27:19,359 --> 00:27:23,680
Speaker 1: or to the stability of sexual reproduction outlined and things

443
00:27:23,720 --> 00:27:27,600
Speaker 1: like the red queen hypothesis, then the various examples of

444
00:27:27,760 --> 00:27:31,960
Speaker 1: ancient asexual species that we have that are more easy,

445
00:27:32,160 --> 00:27:33,840
Speaker 1: you know, to look to, those are going to be

446
00:27:33,960 --> 00:27:37,480
Speaker 1: exceptions to the rule. And then this creates additional additional

447
00:27:37,600 --> 00:27:41,919
Speaker 1: questions arise, well, how has this asexual species been able

448
00:27:42,000 --> 00:27:46,199
Speaker 1: to survive these challenges, these rigors that we're identifying in

449
00:27:46,240 --> 00:27:49,439
Speaker 1: the data here. And you know, one of the sources

450
00:27:49,480 --> 00:27:51,960
Speaker 1: I was looking at two thousand and eights quantifying the

451
00:27:51,960 --> 00:27:55,800
Speaker 1: threat of extinction from Mueller's ratchet in the diploid Amazon

452
00:27:55,880 --> 00:27:59,800
Speaker 1: molly This is from Low and Lamach. They point out that, yeah,

453
00:27:59,840 --> 00:28:03,800
Speaker 1: these species are of considerable interest to researchers for these

454
00:28:03,920 --> 00:28:04,680
Speaker 1: very reasons.

455
00:28:05,320 --> 00:28:06,879
Speaker 2: That would be the Amazon molli.

456
00:28:08,320 --> 00:28:11,680
Speaker 1: Well, just in general, these sorts of species species that.

457
00:28:11,920 --> 00:28:14,800
Speaker 2: Oh I see, yeah, ancient asexual species.

458
00:28:14,880 --> 00:28:18,040
Speaker 1: Sorry, right, in this particular paper, this particular paper that

459
00:28:18,160 --> 00:28:21,080
Speaker 1: the main focus the Amazon mollie, though, is also really interesting.

460
00:28:21,160 --> 00:28:25,480
Speaker 1: This is a small asexual fish species that seems just

461
00:28:25,640 --> 00:28:30,200
Speaker 1: prime for mutational meltdown. However, in modeling out the rate

462
00:28:30,240 --> 00:28:34,280
Speaker 1: of harmful mutations in the species, they ran into what

463
00:28:34,320 --> 00:28:37,320
Speaker 1: they referred to in the paper as a genomic decay paradox.

464
00:28:37,800 --> 00:28:41,120
Speaker 1: So in most of the models they ran, the expected

465
00:28:41,200 --> 00:28:45,120
Speaker 1: time to extinction for this species was less than previous

466
00:28:45,240 --> 00:28:48,040
Speaker 1: estimates on the age of the species, So it would

467
00:28:48,080 --> 00:28:53,480
Speaker 1: seem that the species has outlived its genomic expiration date.

468
00:28:54,440 --> 00:29:01,520
Speaker 1: If Mueller's ratchet and mutational meltdown is indeed a factor

469
00:29:01,960 --> 00:29:06,040
Speaker 1: the author's right quote, several biological processes can individually or

470
00:29:06,080 --> 00:29:10,640
Speaker 1: in combination solve this genomic decay paradox, including paternal leakage

471
00:29:10,680 --> 00:29:15,600
Speaker 1: of undamaged DNA from sexual sister species, compensatory mutations, and

472
00:29:15,680 --> 00:29:18,680
Speaker 1: many others, and they, of course conclude that more research

473
00:29:18,760 --> 00:29:22,880
Speaker 1: is ultimately required. Another paper that looks into all this

474
00:29:23,000 --> 00:29:27,360
Speaker 1: that I found quite interesting was Deleterious mutation Accumulation in

475
00:29:27,440 --> 00:29:31,840
Speaker 1: Asexual Tymema stick Insects by Henry at All, published in

476
00:29:31,920 --> 00:29:36,360
Speaker 1: twenty twelve in Molecular Biology and Evolution. In this paper,

477
00:29:36,400 --> 00:29:42,040
Speaker 1: the researchers look at six independently derived asexual lineages and

478
00:29:42,120 --> 00:29:47,360
Speaker 1: related sexual species of the temma stick insects. So we're

479
00:29:47,360 --> 00:29:51,840
Speaker 1: talking about closely related species, some that reproduce sexually and

480
00:29:51,880 --> 00:29:55,320
Speaker 1: others that reproduce asexually. The idea here, of course, is

481
00:29:55,360 --> 00:29:58,800
Speaker 1: the closeness. They're the related closely related to each other,

482
00:29:59,040 --> 00:30:03,400
Speaker 1: so this would make the accumulation of deletarious mutations stand

483
00:30:03,440 --> 00:30:07,880
Speaker 1: out more in the asexual species versus the sexual species,

484
00:30:08,400 --> 00:30:11,480
Speaker 1: and that seems to be what they found. Quote. We

485
00:30:11,560 --> 00:30:15,560
Speaker 1: found signatures of increased coding mutation accumulation in all six

486
00:30:16,000 --> 00:30:20,200
Speaker 1: asexual tymema and for each of the three analyzed genes,

487
00:30:20,720 --> 00:30:23,840
Speaker 1: with three point six to thirteen point four fold higher

488
00:30:23,960 --> 00:30:28,280
Speaker 1: rates in the asexuals as compared with the sexuals. They

489
00:30:28,360 --> 00:30:31,440
Speaker 1: also point out that the coding mutations and the asexuals

490
00:30:31,440 --> 00:30:35,800
Speaker 1: are likely associated with more strongly deletarious effects than the

491
00:30:35,880 --> 00:30:40,120
Speaker 1: sexuals due to some specific molecular reasons that they outline

492
00:30:40,120 --> 00:30:44,800
Speaker 1: in the article. They conclude that quote deletarious mutation accumulation

493
00:30:45,040 --> 00:30:49,920
Speaker 1: can differentially affect sexual and asexual lineages and support the

494
00:30:49,960 --> 00:30:54,280
Speaker 1: idea that deletarious mutation accumulation plays an important role in

495
00:30:54,360 --> 00:30:57,880
Speaker 1: limiting the long term persistence of all female lineages.

496
00:30:58,320 --> 00:31:01,400
Speaker 2: So, according to this, as we were alluding to earlier,

497
00:31:01,640 --> 00:31:06,680
Speaker 2: a species that's mainly reproducing or totally reproducing asexually and

498
00:31:06,720 --> 00:31:11,120
Speaker 2: just making clonal copies will will tend to one of

499
00:31:11,160 --> 00:31:15,000
Speaker 2: the pressures acting against it will be the tendency to

500
00:31:15,200 --> 00:31:19,400
Speaker 2: build up loads of mutations that are not helpful to survival.

501
00:31:19,880 --> 00:31:23,400
Speaker 1: Yeah, so over time, worse mutations accumulate, and the asexual

502
00:31:23,440 --> 00:31:27,160
Speaker 1: species who do not diversify via sexual recombination, they don't

503
00:31:27,160 --> 00:31:32,840
Speaker 1: purify through purging harmful mutations via sexual reproduction either and

504
00:31:33,200 --> 00:31:36,520
Speaker 1: in fact, the authors here specifically mentioned that sexual reproduction

505
00:31:36,760 --> 00:31:41,680
Speaker 1: enhances the efficiency of purifying selection. This is fascinating, It's

506
00:31:41,720 --> 00:31:44,200
Speaker 1: not I mean, certainly the authors are not arguing that

507
00:31:44,200 --> 00:31:45,720
Speaker 1: this is the case, but it's obviously this is not

508
00:31:45,760 --> 00:31:49,040
Speaker 1: like a smoking gun for the whole idea here, but

509
00:31:49,360 --> 00:31:54,440
Speaker 1: it does seem to give us some interesting evidence to

510
00:31:54,760 --> 00:31:57,200
Speaker 1: back up some of these ideas, though of course also

511
00:31:57,320 --> 00:32:10,520
Speaker 1: raising additional questions about you know, what exactly going on. Now.

512
00:32:10,600 --> 00:32:13,320
Speaker 1: There's a I've mentioned ted Ad before. There's a great

513
00:32:13,400 --> 00:32:17,800
Speaker 1: ted ad video titled no Sex, No Problem, and I

514
00:32:17,920 --> 00:32:21,040
Speaker 1: highly recommend checking that out. It has a nice overview

515
00:32:21,200 --> 00:32:24,760
Speaker 1: of sort of the different the different strategies of asexual

516
00:32:24,840 --> 00:32:28,600
Speaker 1: versus sexual reproduction, and and and briefly mentioned some of

517
00:32:28,640 --> 00:32:31,640
Speaker 1: the concepts we're talking about here. Uh. One thing that

518
00:32:31,680 --> 00:32:34,560
Speaker 1: I thought was interesting in this videos it points out

519
00:32:34,560 --> 00:32:38,840
Speaker 1: that pa fits are a great example of an organism

520
00:32:39,160 --> 00:32:44,400
Speaker 1: that utilizes both sexual reproduction and asexual reproduction. Uh Uh.

521
00:32:44,760 --> 00:32:48,560
Speaker 1: But but depending on what the circumstances are, So with

522
00:32:48,640 --> 00:32:54,160
Speaker 1: these particular a fits, when it's springtime, they are asexual reproducers.

523
00:32:54,480 --> 00:32:56,600
Speaker 1: So it's like it's this is the these are the

524
00:32:56,600 --> 00:32:59,680
Speaker 1: fat times, Like it's it's time to feed, it's time

525
00:32:59,720 --> 00:33:02,160
Speaker 1: to red it's not time to worry too much about,

526
00:33:02,520 --> 00:33:06,520
Speaker 1: you know, differentiating your product. It's about just getting product

527
00:33:06,560 --> 00:33:09,920
Speaker 1: on the shelves, and so that's what they do. But

528
00:33:09,960 --> 00:33:13,360
Speaker 1: then when autumn rolls around, then it's time for sexual reproduction.

529
00:33:13,520 --> 00:33:16,000
Speaker 1: So it's like, Okay, this is our time to think

530
00:33:16,040 --> 00:33:19,880
Speaker 1: about the product. This is our time to get experimental

531
00:33:19,920 --> 00:33:22,680
Speaker 1: and see what we can do to change up our

532
00:33:22,760 --> 00:33:26,000
Speaker 1: offering for the next season. So I thought that was

533
00:33:26,080 --> 00:33:31,600
Speaker 1: just a really really interesting, like single species example that

534
00:33:31,760 --> 00:33:34,640
Speaker 1: kind of sums up some of the benefits and some

535
00:33:34,720 --> 00:33:39,040
Speaker 1: of the costs involved with asexual versus sexual reproduction, Like

536
00:33:39,120 --> 00:33:40,880
Speaker 1: this is not the It's kind of like when you

537
00:33:40,880 --> 00:33:43,680
Speaker 1: think about films in a series, for example, when it's

538
00:33:43,680 --> 00:33:47,000
Speaker 1: time to make Wrong Turn two, you're not necessarily thinking about, well,

539
00:33:47,040 --> 00:33:49,040
Speaker 1: how am I going to recreate? No, you don't recreate.

540
00:33:49,080 --> 00:33:52,000
Speaker 1: You just do what worked the first time, accept more

541
00:33:52,040 --> 00:33:55,440
Speaker 1: of it. This is the springtime of the wrong term franchise.

542
00:33:56,000 --> 00:33:58,480
Speaker 1: Much later, when it's run out of gas, that's when

543
00:33:58,520 --> 00:34:00,840
Speaker 1: you can you can sit down and think, yeah, that's

544
00:34:00,840 --> 00:34:03,040
Speaker 1: when you can be like, how do we reanalyze this,

545
00:34:03,080 --> 00:34:06,840
Speaker 1: how do we reconceptualize Wrong Turn for a new audience?

546
00:34:06,880 --> 00:34:09,200
Speaker 1: And maybe we can hire Matthew Modine to be in

547
00:34:09,239 --> 00:34:10,279
Speaker 1: it too, and.

548
00:34:10,200 --> 00:34:13,080
Speaker 2: It makes sense they both be part of your content strategy,

549
00:34:13,120 --> 00:34:15,440
Speaker 2: you know. Sometimes you do reruns, sometimes you do a

550
00:34:15,440 --> 00:34:16,320
Speaker 2: crossover event.

551
00:34:16,880 --> 00:34:20,080
Speaker 1: Yeah. No, I haven't actually seen a Wrong Turn movie,

552
00:34:20,120 --> 00:34:22,840
Speaker 1: So please don't go out and see these movies just

553
00:34:22,840 --> 00:34:24,600
Speaker 1: based on me casually mention them.

554
00:34:24,600 --> 00:34:29,040
Speaker 2: Here Rob wrongly recommends the Wrong Turn franchise. I can't

555
00:34:29,120 --> 00:34:31,040
Speaker 2: remember if I have or not. Is it is that

556
00:34:31,160 --> 00:34:33,359
Speaker 2: the one there's like a guy in a muscle car

557
00:34:33,400 --> 00:34:35,640
Speaker 2: who drives into the woods and then they meet some

558
00:34:36,120 --> 00:34:37,960
Speaker 2: I don't know some people and they get chased by

559
00:34:38,360 --> 00:34:39,280
Speaker 2: dudes with hatchets.

560
00:34:39,880 --> 00:34:42,560
Speaker 1: That sounds likely. I think that it's basically it's the

561
00:34:42,640 --> 00:34:45,239
Speaker 1: hills have Eyes except in the woods. And there's like

562
00:34:45,280 --> 00:34:48,160
Speaker 1: a million of these films. It's one of there's something

563
00:34:48,200 --> 00:34:50,200
Speaker 1: always kind of alarming to me when I realized there's

564
00:34:50,320 --> 00:34:54,319
Speaker 1: like a whole franchise that has been around for years

565
00:34:54,360 --> 00:34:56,719
Speaker 1: and years and I just not only have I not

566
00:34:56,760 --> 00:34:58,640
Speaker 1: seen them, but I just have just a very surface

567
00:34:58,719 --> 00:35:02,000
Speaker 1: level understanding of what they're about, you know, like I've

568
00:35:02,040 --> 00:35:04,920
Speaker 1: maybe never even seen a trailer for one of them.

569
00:35:05,360 --> 00:35:07,200
Speaker 2: Yeah, there are a lot of series like that, and

570
00:35:08,360 --> 00:35:10,799
Speaker 2: I understand what you mean, Like it can be alarming, Like, oh,

571
00:35:10,840 --> 00:35:13,560
Speaker 2: I didn't even see the first Purge. We're on Purged

572
00:35:14,080 --> 00:35:16,799
Speaker 2: nine now, this is Yeah, I don't know what's going on.

573
00:35:18,000 --> 00:35:20,080
Speaker 2: I kind of can't start at this point. I'm not

574
00:35:20,080 --> 00:35:21,160
Speaker 2: going to see these movies.

575
00:35:21,640 --> 00:35:24,920
Speaker 1: Yeah, the Purge franchise, which I haven't seen any of

576
00:35:24,960 --> 00:35:27,839
Speaker 1: those either, but I've read a bit more about them,

577
00:35:27,880 --> 00:35:30,919
Speaker 1: so I'm kind of intrigued by the way it has

578
00:35:31,080 --> 00:35:34,279
Speaker 1: survived thus far. It seems like it is a franchise

579
00:35:34,320 --> 00:35:38,200
Speaker 1: that definitely has its springtime and autumn cycles of how

580
00:35:38,239 --> 00:35:41,000
Speaker 1: it puts out new content, Like some of these seem

581
00:35:41,120 --> 00:35:43,640
Speaker 1: like definite, like Okay, it's time for another Purge, and

582
00:35:43,640 --> 00:35:45,760
Speaker 1: then other times it's like what can we do different

583
00:35:45,840 --> 00:35:48,000
Speaker 1: with the Purge this time? And then it's like cut

584
00:35:48,040 --> 00:35:50,480
Speaker 1: that we're doing a TV series, so just like ten

585
00:35:50,560 --> 00:35:53,839
Speaker 1: the Purges, and then we'll work about innovating after that.

586
00:35:54,560 --> 00:35:58,400
Speaker 2: I like that you have read about the Purge. I

587
00:35:58,400 --> 00:36:02,319
Speaker 2: haven't seen it, but you've on some research. Well, you know, it.

588
00:36:03,000 --> 00:36:05,360
Speaker 1: Feels like it has more of a you know, you

589
00:36:06,120 --> 00:36:07,960
Speaker 1: got to stay on top of culture, so you got

590
00:36:08,000 --> 00:36:10,880
Speaker 1: to read about the Purge, whereas somehow Wrong Turn movies

591
00:36:11,239 --> 00:36:14,799
Speaker 1: maybe were less important culturally, or so it seems to me.

592
00:36:15,200 --> 00:36:17,839
Speaker 2: Wrong Turn movies, i'd say, are less high concept because

593
00:36:17,920 --> 00:36:21,919
Speaker 2: Purge has an elevator pitch right there, unless I misunderstand

594
00:36:22,080 --> 00:36:24,600
Speaker 2: the idea is all crime is legal on one night.

595
00:36:24,960 --> 00:36:28,440
Speaker 1: Yeah, yeah, okay, so, and I think it lends itself

596
00:36:28,680 --> 00:36:31,360
Speaker 1: well to referencing. You can be like, oh, wow, I

597
00:36:31,440 --> 00:36:33,600
Speaker 1: tried to drive across town the other day and it

598
00:36:33,640 --> 00:36:35,879
Speaker 1: was like the Purge out there. You know, that makes sense.

599
00:36:35,880 --> 00:36:38,000
Speaker 1: It's like you're saying something about how bad traffic was.

600
00:36:38,040 --> 00:36:41,120
Speaker 1: But I don't know, Wrong Turn franchises maybe just a

601
00:36:41,160 --> 00:36:44,680
Speaker 1: little harder to you know, bring into your daily life.

602
00:36:45,120 --> 00:36:47,799
Speaker 2: I guess some organisms also have more of an elevator

603
00:36:47,840 --> 00:36:51,560
Speaker 2: pitch quality to them, though, you know, like the platypus.

604
00:36:51,960 --> 00:36:54,440
Speaker 2: It is it is a furry, poisonous duck.

605
00:36:56,000 --> 00:36:57,759
Speaker 1: But it's also kind of high concept.

606
00:36:58,920 --> 00:37:01,440
Speaker 2: Yeah that's what I'm saying. Yeah, it's high concept.

607
00:37:01,840 --> 00:37:04,080
Speaker 1: Yeah, good creature. Have we ever done an episode on

608
00:37:04,160 --> 00:37:07,600
Speaker 1: the Platypus? I can't recall. Of course, it's diversified enough

609
00:37:07,640 --> 00:37:11,600
Speaker 1: that it's inevitably come up at least in passing in

610
00:37:11,640 --> 00:37:12,799
Speaker 1: any number of episodes.

611
00:37:13,080 --> 00:37:14,560
Speaker 2: I don't know if we have. I just really I

612
00:37:15,160 --> 00:37:19,000
Speaker 2: said poisonous, but I think the correct word would be venomous.

613
00:37:20,480 --> 00:37:22,080
Speaker 2: I don't know. We'll have to sort that out later.

614
00:37:22,480 --> 00:37:24,880
Speaker 1: All right, Well, on that note, I think we have

615
00:37:25,280 --> 00:37:30,120
Speaker 1: we have reached mutational meltdown for this episode. But we'd

616
00:37:30,120 --> 00:37:32,240
Speaker 1: love to hear from everyone out there. I mean, especially

617
00:37:32,320 --> 00:37:36,120
Speaker 1: if there's anyone out there who is in the field

618
00:37:36,200 --> 00:37:40,760
Speaker 1: of evolutionary biology. Perhaps you have some additional feedback, additional

619
00:37:40,800 --> 00:37:42,440
Speaker 1: examples you'd like to bring to mind.

620
00:37:43,120 --> 00:37:43,560
Speaker 2: Let us know.

621
00:37:43,640 --> 00:37:47,160
Speaker 1: You know, this is a topic that it caught my attention,

622
00:37:47,440 --> 00:37:50,759
Speaker 1: but I'd love to see some more data on it.

623
00:37:50,760 --> 00:37:53,360
Speaker 1: I'd love to see some more studies of note. In

624
00:37:53,440 --> 00:37:55,839
Speaker 1: the meantime, will remind you that Stuff to Blow Your

625
00:37:55,840 --> 00:37:59,080
Speaker 1: Mind is primarily a science podcast, with core episodes on

626
00:37:59,120 --> 00:38:02,120
Speaker 1: Tuesdays and Thursday Days. On Mondays we do listener mail,

627
00:38:02,160 --> 00:38:05,080
Speaker 1: on Wednesdays we do a short form artifact or monster fact,

628
00:38:05,520 --> 00:38:08,000
Speaker 1: and on Fridays we set aside most serious concerns to

629
00:38:08,080 --> 00:38:10,120
Speaker 1: just talk about a weird film on Weird House Cinema.

630
00:38:10,160 --> 00:38:13,680
Speaker 1: That's usually where our discussions of films about mutants would

631
00:38:13,760 --> 00:38:19,879
Speaker 1: wind up, but sometimes those mutations accumulate in the core

632
00:38:19,960 --> 00:38:20,879
Speaker 1: episodes as well.

633
00:38:21,280 --> 00:38:24,600
Speaker 2: Huge thanks to our audio producer JJ Posway. If you

634
00:38:24,600 --> 00:38:26,719
Speaker 2: would like to get in touch with us with feedback

635
00:38:26,719 --> 00:38:29,000
Speaker 2: on this episode or any other, to suggest a topic

636
00:38:29,040 --> 00:38:30,920
Speaker 2: for the future, or just to say hello, you can

637
00:38:31,000 --> 00:38:34,160
Speaker 2: email us at contact at stuff to Blow your Mind

638
00:38:34,320 --> 00:38:42,239
Speaker 2: dot com.

639
00:38:42,360 --> 00:38:45,279
Speaker 3: Stuff to Blow Your Mind is production of iHeartRadio. For

640
00:38:45,360 --> 00:38:48,160
Speaker 3: more podcasts from my Heart Radio, visit the iHeartRadio app,

641
00:38:48,320 --> 00:39:00,000
Speaker 3: Apple Podcasts, or wherever you listen to your favorite shows.

642
00:39:00,080 --> 00:39:03,360
Speaker 1: Said to wait. We had to write, to write, Tote

643
00:39:03,360 --> 00:39:03,720
Speaker 1: tot