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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 Lamb.

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Speaker 2: And I'm Joe McCormick, and it's Saturday. We are heading

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Speaker 2: down down into the vault for an older episode of

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Speaker 2: the show. This one originally published on July seventh, twenty

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Speaker 2: twenty two, and it's called The Lesser of Two Crab Claws,

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Speaker 2: Part three. This is part three of the series we've

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Speaker 2: been running over the past couple of Saturdays. This is

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Speaker 2: about asymmetry in nature.

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

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

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Speaker 1: is Robert Lamb.

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Speaker 4: And I'm Joe McCormick, and we're back with part three

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Speaker 4: in our series on asymmetry in animals. When the left

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Speaker 4: and the right side do not match. If you have

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Speaker 4: not listened to parts one and two yet, why not

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Speaker 4: go back and do that first, then you'll be all

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Speaker 4: caught up. But in the last episode of this series,

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Speaker 4: we were talking about asymmetrical development in the clause of

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Speaker 4: the American lobster or homarusamericanas and how during larval development,

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Speaker 4: the lobster's previously symmetrical claus differentiate into one real thick boy.

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Speaker 4: It's a crusher claw. It's gigantic, it's got like molar

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Speaker 4: like teeth on it, and it's got slow muscle fiber.

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Speaker 4: And then the other one turns into a sharper cutter

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Speaker 4: or pincher claw that can close very fast because of

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Speaker 4: its fast muscle fiber. And we talked about attempts to

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Speaker 4: pin down exactly why and how this happens at these

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Speaker 4: early stages in lobster development. But there are other crustaceans

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Speaker 4: where the mismatch between left and right is much more

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Speaker 4: extreme than it is even in the American lobster. And

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Speaker 4: I think we should begin this episode by considering the

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Speaker 4: male of the many species of phil crabs, so fiddler

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Speaker 4: crabs comprise. It's not just one species of animal, its

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Speaker 4: many species within a family of crustaceans known as oc

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Speaker 4: pot day And once again, I think we keep saying

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Speaker 4: it during the series, but this is one you should

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Speaker 4: go and look up pictures of because you need to

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Speaker 4: have it in your head. In some species, male fiddler

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Speaker 4: crabs have one claw that grows not just bigger than

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Speaker 4: the other one, not even just significantly bigger than the

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Speaker 4: other one, but hilariously bigger than the other one.

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Speaker 1: Yeah, going back to lobsters for a second, you'd be

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Speaker 1: forgiven if you were just not aware of the fact

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Speaker 1: that lobsters had this different, this difference between one claw

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Speaker 1: and the next. Certainly, many illustrations I'm thinking, like restaurant

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Speaker 1: logos and whatnot, may not even bother to make one

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Speaker 1: claw look different from the other. But with a fiddler crab,

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Speaker 1: it is very pronounced. It is absurdly different one side

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Speaker 1: from the other.

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Speaker 4: Yeah. And for a bit of expert summary on what

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Speaker 4: life is like for your average fiddler crab, I wanted

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Speaker 4: to quote from a New York Times interview I was

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Speaker 4: reading with a researcher named Sophie L. Moles, who is

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Speaker 4: a scientist at Anglioruscan University in Cambridge and has done

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Speaker 4: some research on fiddler crabs, including the use of a

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Speaker 4: robotic fiddler crab claw that I want to come back

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Speaker 4: to later in this episode, but just in summarizing fiddler

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Speaker 4: crab life, she says, they live in burrows and you

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Speaker 4: only see them at low tide. At high tide, they

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Speaker 4: go back into the burrow and they seal it up.

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Speaker 4: They feed on mudflats by sifting the sediment through their

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Speaker 4: mouthparts and eating micro organisms. That's the buffet of life.

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Speaker 4: You just sift the mud in your mouth and get

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Speaker 4: the microbes out, but moles goes on. The female has

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Speaker 4: two little claws, two normal size claws for her which

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Speaker 4: she uses to help that feeding, to help pass the

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Speaker 4: sediment up to her mouth. The male has one that

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Speaker 4: it uses for feeding, and the other is huge. It's

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Speaker 4: greatly enlarged, to the point that it can be approximately

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Speaker 4: half of his body weight. It's often really brightly colored

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Speaker 4: as well. Now, what the males do is they wave

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Speaker 4: this claw in a species specific pattern. So each species

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Speaker 4: of fiddler crab has its own kind of wave, and

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Speaker 4: they do this to maintain a territory but also to

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Speaker 4: attract a female. So for a rough analogy on the

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Speaker 4: size and appearance of a fiddler crab claw, just imagine

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Speaker 4: an adult human that had one normal sized right hand,

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Speaker 4: but then a left hand with a digit span of

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Speaker 4: about four feet, and that hand weighs eighty pounds.

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Speaker 1: Yeah. One example of this was that it was brought

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Speaker 1: in a book I'm going to reference in a bit

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Speaker 1: Animal Weapons by Douglas j Emmlin. He says, if you're Basically,

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Speaker 1: if you're at the store, go pick up the largest

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Speaker 1: bag of dried dog food that you you can find

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Speaker 1: and start carrying it around, and that will give you

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Speaker 1: approximately what we might think of as the male fiddler

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Speaker 1: crab experience.

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Speaker 4: So yeah, so imagine the largest sized bag of dog food.

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Speaker 4: Not just you're carrying it around, but that is one

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Speaker 4: of your hands, yes, and again the other one is

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Speaker 4: regular sized. So what is going on with having a

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Speaker 4: crab claw that big? Well, it turns out that the

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Speaker 4: main theory explaining this asymmetric size difference in fiddler crab

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Speaker 4: claus is much like the main theory for explaining the

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Speaker 4: narwhal tusk, that this hugely asymmetrically exaggerated feature found in

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Speaker 4: males is probably primarily a sexually selected trait, meaning it's

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Speaker 4: more important for maximizing reproductive success than it is for

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Speaker 4: direct survival value, though it may be in part reproductively

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Speaker 4: attractive attractive to mates because of some value it has

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Speaker 4: in helping maximize like burrowing. So, for example, things that

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Speaker 4: have been cited are that a male that has a

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Speaker 4: very big claw can also probably dig a very big burrow,

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Speaker 4: which is better for a female to go into to

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Speaker 4: incubate her eggs and also, like crustaceans, tend to just

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Speaker 4: keep getting bigger they as they grow as they grow older.

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Speaker 4: So a bigger crab with a bigger asymmetric claw is

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Speaker 4: also probably an older male, which is good in crab

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Speaker 4: mating terms, because that probably means he has survived more

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Speaker 4: seasons of life and is just generally fitter, better able

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Speaker 4: to survive, and has good genes.

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Speaker 1: Yeah. Yeah, And I mean part of the obvious display

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Speaker 1: here too is like, look at this thing I have grown.

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Speaker 1: It is so big, and yet I am still alive.

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Speaker 1: I am able to sustain myself. Plus this massive claw,

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Speaker 1: it's like the sports car of the crab anatomy.

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Speaker 4: Yeah, that's another thing that has often been put up.

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Speaker 4: There's sort of a theory in some sexually selected traits

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Speaker 4: in biology that says, well, they may operate on the

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Speaker 4: basis of essentially advertising a handicap. They offer a good

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Speaker 4: faith display that even by working at a disadvantage, you're

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Speaker 4: still fit enough to do well within your environment by

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Speaker 4: having this ridiculous thing attached to you. So a male

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Speaker 4: fiddler crab is running around also basically advertising I mean,

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Speaker 4: this would be true of all the males with the

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Speaker 4: big claw that they have basically have to their capacity

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Speaker 4: to eat.

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Speaker 3: You know.

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Speaker 4: So these crabs eat by shoving mud and debris into

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Speaker 4: their mouths, and that's true for males and females, but

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Speaker 4: of course you can't do that with that gigantic claw.

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Speaker 4: So essentially the male fiddler crabs they got them one

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Speaker 4: good eat in hand, whereas females have two.

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Speaker 1: Yes, absolutely, and this is something that Emlin gets into

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Speaker 1: an animal weapons. Basically you're getting into just the energy

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Speaker 1: costs of having this gigantic claw. So some of this

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Speaker 1: is going to be a repeatd what we just said,

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Speaker 1: but it all kind of builds together. So, first of all,

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Speaker 1: male fiddlers, he says, burn a lot of energy just

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Speaker 1: to have these, just to develop them and carry them

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Speaker 1: around resting. Metabolic rates of males with big claws are

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Speaker 1: almost twenty percent higher than females due to the cost

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Speaker 1: of the claw. And then of course, on top of this,

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Speaker 1: you're going to have to scamper around. We see everyone

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Speaker 1: out there, I think it's probably seen crabs about doing

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Speaker 1: their business on the beach. You've got to scamper around,

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Speaker 1: you've got to run with that giant claw and so

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Speaker 1: this is going to be energetically demanding as well.

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Speaker 4: Yeah, I can how fast can you run holding that

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Speaker 4: dog food bag?

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Speaker 1: Exactly? Yeah, this is where he originally brought up the

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Speaker 1: dog food bag, but he also cites a study. This

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Speaker 1: one was really fun. This is a two thousand and

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Speaker 1: seven study that was published in Functional Ecology by Alan

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Speaker 1: and Levinton, and they were testing this out by putting

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Speaker 1: male fiddler crabs on treadmills, little treadmills inside of air

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Speaker 1: tight box. Now, sadly, I could not find photos of

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Speaker 1: this that I brought up the original paper and there

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Speaker 1: were no photos or illustrations, so I only have my

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Speaker 1: imagination to go on here.

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Speaker 4: This is the shrimp shrimp on a treadmill paper that

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Speaker 4: you promised in previous.

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Speaker 1: Parts, right right, Yeah, shrimp on a treadmill For anyone

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Speaker 1: not familiar, that frequently brought up as there was an

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Speaker 1: actual shrimp on a treadmill study, and it was used

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Speaker 1: as an outrageous example of like, look at what the

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Speaker 1: scientists are doing. They won't cure a cancer, but they'll

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Speaker 1: put a shrimp on a treadmill. And as we've discussed

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Speaker 1: in the show before, that that's kind of ridiculous. I mean,

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Speaker 1: these are not the scientists that would be developing the

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Speaker 1: cure for cancer. These are the ones that would be studying, say,

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Speaker 1: the metabolic rates of shrimp or in this case, crabs.

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Speaker 4: Right, they're not mutually exclusive pursuits to begin with. But

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Speaker 4: then also sometimes you don't even know what benefits that

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Speaker 4: new knowledge about animal life could lead to down the road.

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Speaker 1: Yeah. Absolutely, And so the study put the crabs on

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Speaker 1: the treadmills inside of the air tight boxes. And you

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Speaker 1: might be one, why the air tight box. This sounds

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Speaker 1: like something from a Saw movie. No, it's because it's

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Speaker 1: the crabs exert themselves. They burn through oxygen and they

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Speaker 1: produce CO two. And so the researchers are then able

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Speaker 1: to measure the gas concentrations inside of the little boxes,

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Speaker 1: and they use these readings to calculate the exact metabolic

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Speaker 1: costs of running. As one might expect, the males with

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Speaker 1: big claws burned more energy to run compared to smaller males,

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Speaker 1: males with the smaller claw, or females that of course

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Speaker 1: just have two regularly sized claws. And these big males

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Speaker 1: with the big claws also tired out more quickly. And

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Speaker 1: then there's the impact on feeding, which we have already

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Speaker 1: alluded to. We've all seen crab eat I know, we've

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Speaker 1: talked about it on the show. Crabs disassemble their food.

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Speaker 1: Their claws and mouth bits work very hard to break

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Speaker 1: everything down, or in the case of fiddler crabs, they

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Speaker 1: are often just sifting through and finding those little tiny

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Speaker 1: pieces to eat. Anyway, it's what describes as quote delicate

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Speaker 1: and tedious, and with the females it means. It often

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Speaker 1: means the feeding claws are just working incessantly.

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Speaker 4: Yeah, you can see video of this. So there's just

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Speaker 4: like a conveyor belt. They're just machines kind of shoveling

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Speaker 4: the sediment into the mouth.

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Speaker 1: But the male, on the other hand, like we've said,

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Speaker 1: only has the one claw that's suitable to eat with anymore.

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Speaker 1: He's got that big claw just setting there, and then

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Speaker 1: the other claw, the normal sized claw, is the one

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Speaker 1: that he's using to eat. So this cuts their energy

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Speaker 1: intake in half, just as lugging the giant claw around

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Speaker 1: increases their energy output. So they generally have to feed

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Speaker 1: faster and or more often in order to make up

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Speaker 1: the difference.

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Speaker 4: Right again, because you got it, they've divided their body

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Speaker 4: into eating hand and handsome hand, right.

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Speaker 1: And this complicates things for the crabs even more because

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Speaker 1: remember this is not an apex predator we're talking about here.

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Speaker 1: The crab, the filler crab especially, they have to concern

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Speaker 1: themselves with predators, especially of the avian variety. So if

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Speaker 1: this crab with this big claw that's having to do

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Speaker 1: extra feeding, that means extra exposure to potential predation. In fact,

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Speaker 1: studies have proven out that these males are picked off

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Speaker 1: by birds at an enhanced rate.

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Speaker 4: Right, So you're saying, because it eats slower because it

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Speaker 4: can only eat with one of its claws, it has

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Speaker 4: to spend more time outside the burrow, and that's got

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Speaker 4: to target on its back exactly.

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Speaker 1: Yeah, it's more time out in the open, more time

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Speaker 1: exposed to predators, and the predators in many cases they

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Speaker 1: have advanced tactics for dealing with these These these either

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Speaker 1: tired or distracted or essentially one clawed crab at this

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Speaker 1: point when it comes to the feeding process Inland points

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Speaker 1: to a study from Christy Blackwell and Coga regarding fiddler

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Speaker 1: crabs in Panama getting basically taken out by grap fed

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Speaker 1: on by grackles, who as a type of bird that

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Speaker 1: have devised a diagonal feint attack where they they kind

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Speaker 1: of they come in, they kind of fake the crab out,

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Speaker 1: and apparently this is even more effective on the mail crabs.

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Speaker 4: Now you might think, well, but wait a minute. Having

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Speaker 4: a bigger claw surely also means that that crab can

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Speaker 4: pinch with greater force, which you would think could make

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Speaker 4: it able to defend itself better.

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Speaker 1: Right, yeah, I mean you you might you might think that,

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Speaker 1: but but then you know, as we'll get into like

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Speaker 1: these claws, this big claw anyway, it doesn't seem to

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Speaker 1: be that useful when you're dealing with something like a

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Speaker 1: hungry grackle that's sweeping in at you. So like the

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Speaker 1: end result is that the big clawed mails they're easier

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Speaker 1: to find, they're easier to pick off, they're potentially more tired,

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Speaker 1: and also they're a better there. They're a better kill

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Speaker 1: for the predator because that big old claw has big

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Speaker 1: old meat in it. So there's every reason in the

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Speaker 1: world to kill them and eat them if you were

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Speaker 1: a grackle or some other hungry bird.

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Speaker 4: Now, from what I've read about fiddler crab clause, it

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Speaker 4: seems like what they are most of the time used

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Speaker 4: for is probably visual signaling, but they are on occasion

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Speaker 4: actually used for fighting or actually used as a weapon.

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Speaker 1: Yeah. Yeah. Emlin gets into this in the book as well,

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Speaker 1: highlighting particularly the work of John Christy. I believe he

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Speaker 1: was in the second study that was cited there that

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Speaker 1: we decided. So basically, yeah, they wave them around to

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Speaker 1: communicate their reproductive fitness. They do fight other male fiddler

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Speaker 1: crabs with them, so they do serve as actual weapons

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Speaker 1: in contests for those burrows that we were talking about.

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Speaker 1: But Emlin writes that quote, for every few minutes of

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Speaker 1: outright fighting, male spend dozens of hours waving and other

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Speaker 1: words communicating, showing off that claw, saying look, you know,

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Speaker 1: look at this mighty claw. I imagine what I can

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Speaker 1: do with it. That happened. That's what's going on most

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Speaker 1: of the time. A very small amount of the time

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Speaker 1: they're actually using it. So it's ultimately more of a

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Speaker 1: deterrence than anything. And this is evolutionarily sound because fighting

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Speaker 1: is dangerous. The battle itself is dangerous and can certainly

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Speaker 1: be fatal to an organism, but fights can also just

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Speaker 1: wound you, making you more susceptible to predation, it may

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Speaker 1: distract you and allow the grackle or some other creature

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Speaker 1: to come in and take you out. So even though

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Speaker 1: there are hard disadvantages to developing such a deterrence, and

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Speaker 1: he compares this to other animals as well, like anytime

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Speaker 1: you see something that you might label an elaborate weapon

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Speaker 1: in some sort of an animal's anatomy, there's a huge

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Speaker 1: payoff there. Nothing is free, nothing is cheap. When it

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Speaker 1: comes to the development of these things. There's an energy

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Speaker 1: cost involved. So even though there are all these disadvantages

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Speaker 1: to growing, say a giant crab claw, there are also

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Speaker 1: strong benefits in not having to actually fight all of

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Speaker 1: the time.

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Speaker 4: Yeah, I mean, I think this goes against our intuition

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Speaker 4: because we think of fighting in terms of winning and losing.

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Speaker 4: So like fight it fight has a winner who wins

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Speaker 4: and thus they come out good the effect for them

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Speaker 4: is positive, and a loser who loses, and of course

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Speaker 4: the effect for them is negative. But in fact, in nature,

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Speaker 4: I would argue that most fighting is probably actually lose

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Speaker 4: lose because even the winner is probably somewhat injured or

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Speaker 4: tired out by the fight, putting them at a later

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Speaker 4: disadvantage for survival even if they come out on top

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Speaker 4: in that particular struggle.

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Speaker 1: Yeah, yeah, And all of this makes even more sense

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Speaker 1: when we start looking at the closer to the scenario

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Speaker 1: of these fighting and protecting these burrows and trying to

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Speaker 1: move females. Again, the male setup shop in front of

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Speaker 1: key burrows that are offered as brooding burrows to perspective females,

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Speaker 1: and this is where they make their sh and this

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Speaker 1: is where they fight if it comes to that. And

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Speaker 1: the numbers here are apparently great. They're just tons of

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Speaker 1: crabs out there, and they're just face off after face off.

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Speaker 1: And again, most of these face offs are not going

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Speaker 1: to result in a big, drag out fight. A lot

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Speaker 1: of them are just going to be displays. But still

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Speaker 1: lifting that crab claw in the air and to signal

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Speaker 1: with it, that's going to have an energy cost, and

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Speaker 1: so this is ultimately exhausting too many crabs. Crabs will

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Speaker 1: eventually have to bow out and work their way back

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Speaker 1: up to good burrows. So there's like this whole system

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Speaker 1: of communication. Most of these face offs don't rise to

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Speaker 1: the level of a full intensity battle, and the display

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Speaker 1: of the claw allows the male crabs to easily determine

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Speaker 1: who they have a chance against, so they're able to

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Speaker 1: size each other up, like, Okay, this is a battle

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Speaker 1: that I definitely can win, and he knows I can

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Speaker 1: win it, So we're done. This is a display only situation. Okay,

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Speaker 1: he's a crab that can definitely beat me, so I'm

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Speaker 1: not going to mess with him. We're just going to

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Speaker 1: carry on our ways. This one, however, we're going to

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Speaker 1: have to communicate a little bit and we might have

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Speaker 1: to fight because we seem to be evenly matched.

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Speaker 4: Yeah. That's actually the most dangerous situation is when it's

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Speaker 4: not clear which one is stronger. All right, Well, I

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Speaker 4: wanted to come back to something which was earlier. I

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Speaker 4: mentioned that a New York Times interview with the researcher

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Speaker 4: Sophie Moles, who was one of the authors of a

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Speaker 4: paper published in twenty eighteen in Biology Letters called Robotic Crabs,

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Speaker 4: revealed that female fiddler crabs are sensitive to changes in

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Speaker 4: male display rate. The other authors here were Michael D.

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Speaker 4: Jinions and Patricia ur Why Backwell.

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Speaker 1: Yes, I might have referred to her earlier as Blackwell,

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Speaker 1: my apologies.

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Speaker 4: Oh I didn't catch that.

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Speaker 1: You should apologize, Well, I just want to make sure

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Speaker 1: I get the names right. Yeah, had a type in

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Speaker 1: my notes.

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Speaker 4: There, so, But from the crabs perspective, I think it

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Speaker 4: is important to realize that this really is a study

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Speaker 4: that involved creating crab sex robots, like this is creating

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Speaker 4: the It was an attempt to create the hunkiest male

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Speaker 4: robot crab claws that have ever been put together with

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Speaker 4: the explicit purpose of attracting female fiddler crabs. So I'm

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Speaker 4: just going to read directly from their abstract. They write quote,

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Speaker 4: Males often produce dynamic, repetitive courtship displays that can be

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Speaker 4: demanding to perform and might advertise male quality to females.

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Speaker 4: A key feature of demanding displays is that they can

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Speaker 4: change in intensity, escalating as a male increases his signaling effort,

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Speaker 4: but de escalating as the signaler becomes fatigued. Here we

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Speaker 4: investigated whether female fiddler crabs of the species Uka miyoburgi

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Speaker 4: are sensitive to changes in male courtship wave rate how

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Speaker 4: fast the arm is waving. We performed playback experiments using

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Speaker 4: robotic male crabs that had the same mean wave rate

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Speaker 4: but either escalated, de escalated, or remained constant females demonstrated

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Speaker 4: a strong preference for escalating robots, but showed mixed responses

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Speaker 4: to robots that de escalated fast to slow compared to

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Speaker 4: those that waved at a constant medium rate. These findings

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Speaker 4: demonstrate that females can discern changes in male display rate

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Speaker 4: and prefer males that escalate, but that females are also

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Speaker 4: sensitive to pass display rates indicative of prior vigor. So,

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Speaker 4: if you are a male fiddler crab, it's not just

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Speaker 4: important to have a big claw, but it apparently, at

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Speaker 4: least with this species, is more attractive to females if

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Speaker 4: you start waving it faster and faster as the female

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Speaker 4: comes close to you. And from this New York Times

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Speaker 4: interview with the lead author, their moles, it was there

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Speaker 4: was the question where the females terribly disappointed when they

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Speaker 4: realized they'd been tricked. You know what happened once they

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Speaker 4: finally got up to the waving robot arm that they

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Speaker 4: were so interested in, Well, Mole says quote, once they

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Speaker 4: got to the robot, they would touch the base plate

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Speaker 4: of it and realize there's something wrong here, it's not real,

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Speaker 4: and they would usually at that point stop moving or

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Speaker 4: run away. Some of them actually responded as if he

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Speaker 4: were a real male crab, which is by tickling him.

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Speaker 4: What the females do is go up to the male

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Speaker 4: and use their legs on one side of their body

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Speaker 4: to tickle him. This communicates to him that she's interested

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Speaker 4: in him as a mate and not just trying to

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Speaker 4: steal his home. So this study did indeed implicate female

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Speaker 4: fiddler crabs tickling metal base plates because they thought it

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Speaker 4: just that claw is so huge, it's swinging so fast,

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Speaker 4: I've got to believe it might be a real crab.

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Speaker 1: This sounds like something that could be factored into, I

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Speaker 1: don't know, Battlestar Galactica sort of situation.

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Speaker 4: Yeah, I go the.

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Speaker 1: Replicants, the robots. They look just like us, they behave

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Speaker 1: just like us, except tickling them will reveal their true nature.

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Speaker 4: Anyway, in the spirit of our enthusiasm for the shrimp

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Speaker 4: on the treadmill, the crab on the treadmill, I want

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Speaker 4: more studies with robot crab hunks. We have to build

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Speaker 4: the most attractive male crab that has ever been that

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Speaker 4: has ever existed on Earth, and but I guess we

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Speaker 4: have to be careful with it because we don't want

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Speaker 4: to drive crabs to extinction by like now now the

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Speaker 4: real crabs only desire the robot.

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Speaker 1: It's weird how this does line up with the sort

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Speaker 1: of trope of the muscle man on the beach attracting

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Speaker 1: the women and and the and the nerd that's that's

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00:22:34,840 --> 00:22:36,959
Speaker 1: also inevitably on the beach as well, and may get

402
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Speaker 1: sand kicked in his face or whatnot. But it also

403
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Speaker 1: does bring to mind like even with humans, there's sort

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Speaker 1: of there's there's fitness, and there's like visible fitness, but

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Speaker 1: then there's also like fitness to the level where it's

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Speaker 1: no longer purely functional anymore. Like there's like, for instance,

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Speaker 1: there's the muscle that might aid in the delivery of

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Speaker 1: a punch, and then there's like than the muscle build

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Speaker 1: up that say, makes it harder to move around or

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Speaker 1: makes it more difficult to say, touch portions of your back,

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Speaker 1: that sort of thing.

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Speaker 4: I totally know what you're saying, though, I also that

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Speaker 4: reminds me. I always want to caution people, you know,

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Speaker 4: just don't try to extrapolate too much from animal sex

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Speaker 4: and attractiveness studies to humans, because you know, crabs and

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Speaker 4: humans are pretty different.

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Speaker 1: Right, right, and certainly the reasons that humans do things

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Speaker 1: and the way they react to things, or generally there's

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Speaker 1: a lot more going on. There's this whole level of

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Speaker 1: human complication that's taking place on the surface of whatever

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Speaker 1: else is going on.

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Speaker 4: All Right, after we've talked about all of these examples

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Speaker 4: of animals that broadly have bilateral symmetry but then some

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Speaker 4: major deviation from it, I've been thinking about how symmetry

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Speaker 4: and asymmetry come about at the cellular level, because you know,

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Speaker 4: you can imagine why it would be genetically efficient to

427
00:23:58,119 --> 00:24:01,560
Speaker 4: have bilateral symmetry. You just basically need half of a

428
00:24:01,600 --> 00:24:03,679
Speaker 4: body plan and then you just copy it over on

429
00:24:03,720 --> 00:24:08,520
Speaker 4: the other side. But within that broadly symmetrical framework, you know,

430
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Speaker 4: we get these deviations major and minor. And it's not

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Speaker 4: all narwhal tusks and fiddler crab claws things that are

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Speaker 4: like huge and noticeable. There are plenty of forms of

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Speaker 4: asymmetry that are common but harder to spot, such as

434
00:24:20,920 --> 00:24:25,080
Speaker 4: the orientation of internal organs. You know, your digestive tract

435
00:24:25,280 --> 00:24:30,600
Speaker 4: and its associated organs and your heart and circulatory system

436
00:24:30,640 --> 00:24:35,040
Speaker 4: are all asymmetrical. They have different organs and pathways situated

437
00:24:35,160 --> 00:24:37,919
Speaker 4: on the left and right of the body cavity, and

438
00:24:38,119 --> 00:24:41,800
Speaker 4: there are also minor more invisible variations at the cellular

439
00:24:41,880 --> 00:24:46,480
Speaker 4: level within mostly symmetrical creatures like us. So how do

440
00:24:46,600 --> 00:24:50,560
Speaker 4: these deviations from perfect symmetry come about at the level

441
00:24:50,600 --> 00:24:54,080
Speaker 4: of cell division, which is actually, you know, actively building

442
00:24:54,119 --> 00:24:57,760
Speaker 4: your body's tissues. How do the cells know which side

443
00:24:57,840 --> 00:25:00,520
Speaker 4: is which and how to do something different on the

444
00:25:00,600 --> 00:25:03,120
Speaker 4: left than what they're doing on the right. Well, one

445
00:25:03,200 --> 00:25:06,640
Speaker 4: jumping off point here is I came across an interesting

446
00:25:06,720 --> 00:25:11,040
Speaker 4: article about this in Quantum Magazine from January twenty seventeen

447
00:25:11,200 --> 00:25:16,439
Speaker 4: by Tim Verneman called how Life Turns Asymmetric, which is

448
00:25:16,480 --> 00:25:18,800
Speaker 4: worth a read in its entirety, but I just wanted

449
00:25:18,800 --> 00:25:21,440
Speaker 4: to summarize and jump off from a few things I

450
00:25:21,520 --> 00:25:23,879
Speaker 4: learned from it. And one of the big takeaways is

451
00:25:23,880 --> 00:25:26,879
Speaker 4: that I think we have some good answers about at

452
00:25:27,000 --> 00:25:32,760
Speaker 4: least some strong factors for like mammalian or vertebrate symmetry

453
00:25:32,800 --> 00:25:36,240
Speaker 4: and symmetry breaking something. We know some things about the

454
00:25:36,480 --> 00:25:39,280
Speaker 4: genetic and cellular basis for a symmetry in the body,

455
00:25:39,640 --> 00:25:42,479
Speaker 4: but we still don't know everything yet, and so one

456
00:25:42,520 --> 00:25:44,760
Speaker 4: of the ideas that gets brought up in this article

457
00:25:45,320 --> 00:25:50,560
Speaker 4: is the nodal lefty genetic connection, and it goes like this.

458
00:25:50,640 --> 00:25:54,600
Speaker 4: Since the nineteen nineties, scientists have been studying a gene

459
00:25:54,880 --> 00:26:00,399
Speaker 4: called nodal in ODL, which appears specifically on the left

460
00:26:00,520 --> 00:26:04,399
Speaker 4: side of the developing embryo of At the time this

461
00:26:04,520 --> 00:26:08,320
Speaker 4: article was written, they said every vertebrate animal yet studied

462
00:26:09,040 --> 00:26:14,119
Speaker 4: and associated with this gene is a somewhat confusingly named

463
00:26:14,160 --> 00:26:18,480
Speaker 4: gene called lefty, which appears to work specifically to suppress

464
00:26:18,640 --> 00:26:22,240
Speaker 4: the nodal gene's activity on the right side of the

465
00:26:22,359 --> 00:26:26,640
Speaker 4: vertebrate embryo. So the purpose of lefty, if I understand correctly,

466
00:26:26,640 --> 00:26:29,679
Speaker 4: appears to be something like telling the right side of

467
00:26:29,680 --> 00:26:32,480
Speaker 4: the body not to do left side of the body stuff.

468
00:26:33,600 --> 00:26:37,880
Speaker 4: According to the Harvard biologist Cliff Tabin, the nodal lefty

469
00:26:37,920 --> 00:26:41,760
Speaker 4: gene combination seems to be the main genetic factor guiding

470
00:26:41,880 --> 00:26:46,720
Speaker 4: asymmetry in animals, or at least invertebrates. So how does

471
00:26:46,880 --> 00:26:52,360
Speaker 4: this difference get expressed? Well, another biologist named Nobotaka Hirokawa

472
00:26:52,840 --> 00:26:56,760
Speaker 4: has offered an explanation that has to do with sillia.

473
00:26:57,920 --> 00:27:03,320
Speaker 4: Cillia are little hair like or thread like projections. Technically,

474
00:27:03,359 --> 00:27:07,639
Speaker 4: they're a type of organelle which stick up from cell

475
00:27:07,720 --> 00:27:12,400
Speaker 4: membranes within the cells or of eukaryotes, and they serve

476
00:27:12,480 --> 00:27:17,160
Speaker 4: various functions like gathering sensory information four cells or facilitating

477
00:27:17,200 --> 00:27:21,320
Speaker 4: the movement of cells through fluid. So you might read

478
00:27:21,359 --> 00:27:25,800
Speaker 4: about as sillia motility. These things often move back and forth,

479
00:27:25,800 --> 00:27:30,399
Speaker 4: though actually they're divided into motile and nonmotile cilia. So

480
00:27:30,600 --> 00:27:34,679
Speaker 4: how would tiny hairs sticking up off of cell membranes

481
00:27:34,760 --> 00:27:38,040
Speaker 4: have anything to do with the body of a vertebrate

482
00:27:38,240 --> 00:27:43,240
Speaker 4: splitting from perfect symmetry into a differentiated left and right half. Well.

483
00:27:43,480 --> 00:27:47,960
Speaker 4: One fascinating clue came in the form of a rare

484
00:27:48,200 --> 00:27:53,480
Speaker 4: genetic disorder found in humans known as Cartagener's syndrome. Actually,

485
00:27:53,520 --> 00:27:54,960
Speaker 4: I'm not sure if I'm saying that right, but it's

486
00:27:54,960 --> 00:27:57,520
Speaker 4: spelled k A R T A G E N E

487
00:27:57,680 --> 00:28:04,320
Speaker 4: R Cartagener syndrome, which presents most often in patients as

488
00:28:04,800 --> 00:28:09,800
Speaker 4: patients with continued respiratory problems such as recurrent lung infections

489
00:28:09,800 --> 00:28:15,280
Speaker 4: and sinus problems, and also sometimes infertility. It turns out

490
00:28:15,480 --> 00:28:20,920
Speaker 4: this condition is caused by a congenital defect that prevents

491
00:28:20,960 --> 00:28:25,080
Speaker 4: the body's scillia from functioning as needed, so these little

492
00:28:25,520 --> 00:28:30,680
Speaker 4: hair like projections on cells don't function as they normally would. Now,

493
00:28:30,800 --> 00:28:33,280
Speaker 4: why would that affect respiration? Well, of course, the inside

494
00:28:33,280 --> 00:28:36,720
Speaker 4: of our breathing passages are lined with cilia, and the

495
00:28:36,920 --> 00:28:42,040
Speaker 4: cilia need to move in synchronization for I think multiple purposes,

496
00:28:42,040 --> 00:28:45,160
Speaker 4: but one of them is to help clear breathing passages

497
00:28:45,240 --> 00:28:49,280
Speaker 4: of mucus. And this disorder causes the cilia to have

498
00:28:49,360 --> 00:28:52,840
Speaker 4: trouble again with motility, with movement, and so they can't

499
00:28:52,880 --> 00:28:55,760
Speaker 4: really synchronize. They can't really work together to get the

500
00:28:55,880 --> 00:29:00,320
Speaker 4: mucus out of the lungs and out to the throat

501
00:29:00,440 --> 00:29:05,920
Speaker 4: to prevent infections. Now, strangely, this disorder affecting cilia also

502
00:29:06,240 --> 00:29:12,400
Speaker 4: frequently coincides with a seemingly totally unrelated issue. About half

503
00:29:12,480 --> 00:29:16,720
Speaker 4: of people diagnosed with cartagen or syndrome also have their

504
00:29:16,880 --> 00:29:21,160
Speaker 4: internal organs flipped. Their body is a mirror image of

505
00:29:21,200 --> 00:29:23,680
Speaker 4: what a thoracic surgeon would expect to see if they

506
00:29:23,720 --> 00:29:25,920
Speaker 4: open you up. So you know, the heart on the

507
00:29:26,000 --> 00:29:28,000
Speaker 4: right and the liver on the left and so forth.

508
00:29:28,160 --> 00:29:31,400
Speaker 1: That's right. Yeah, if we're looking to spy literature, of course,

509
00:29:31,440 --> 00:29:34,160
Speaker 1: if we look at Ian Fleming's doctor know we might

510
00:29:34,160 --> 00:29:36,440
Speaker 1: remember doctor No has this where his heart is on

511
00:29:36,440 --> 00:29:39,320
Speaker 1: the other side of his body. Oh, it survives. I

512
00:29:39,360 --> 00:29:42,719
Speaker 1: think he survives an assassination attempt at some point because

513
00:29:42,760 --> 00:29:44,320
Speaker 1: of this anatomical quirk.

514
00:29:44,560 --> 00:29:47,240
Speaker 4: Oh, I say, somebody shoots him on the wrong side. Yeah,

515
00:29:47,560 --> 00:29:57,120
Speaker 4: that's a good twist. Well, anyway, so you have that

516
00:29:57,200 --> 00:30:01,040
Speaker 4: association people who have this, who have this congenital condition

517
00:30:01,160 --> 00:30:06,920
Speaker 4: affecting proteins that in turn affect sillia. They also half

518
00:30:06,920 --> 00:30:09,560
Speaker 4: of the time their organs are flipped opposite of what

519
00:30:09,600 --> 00:30:11,880
Speaker 4: you normally see. On top of that, there was a

520
00:30:11,920 --> 00:30:15,640
Speaker 4: twenty fifteen paper in Nature by Lee at All, which

521
00:30:16,360 --> 00:30:20,840
Speaker 4: Vernemon in the article points to called global Genetic Analysis

522
00:30:20,880 --> 00:30:24,880
Speaker 4: in mice unveils central role for ccilia in congenital heart disease.

523
00:30:25,680 --> 00:30:29,760
Speaker 4: And this paper apparently found multiple instances of genes where

524
00:30:29,960 --> 00:30:33,640
Speaker 4: if the gene was defective, the mouse presented with some

525
00:30:33,720 --> 00:30:37,440
Speaker 4: kind of unusual issue related to symmetry and asymmetry in

526
00:30:37,480 --> 00:30:40,280
Speaker 4: the body, some issue with the haves left and right,

527
00:30:40,840 --> 00:30:44,440
Speaker 4: And in those instances the gene was somehow also related

528
00:30:44,520 --> 00:30:50,840
Speaker 4: to scillia. So these clues indicate that somehow scillia may

529
00:30:50,880 --> 00:30:55,600
Speaker 4: play a role in symmetry breaking during mammalian development. So

530
00:30:55,680 --> 00:30:58,880
Speaker 4: how could this be Well, A leading explanation has to

531
00:30:58,920 --> 00:31:03,640
Speaker 4: do with something called dorsal flow and a little patch

532
00:31:03,760 --> 00:31:09,240
Speaker 4: on the surface of mammalian embryos called the ventral node. So,

533
00:31:09,280 --> 00:31:12,280
Speaker 4: if you're looking at like a mammalian embryo, the ventral

534
00:31:12,360 --> 00:31:16,600
Speaker 4: node is a little pit or depression on the underside

535
00:31:16,720 --> 00:31:20,480
Speaker 4: or the bottom surface, and the pit is ciliated, meaning

536
00:31:20,520 --> 00:31:23,240
Speaker 4: it's covered in cilia, these little hair like or thread

537
00:31:23,360 --> 00:31:27,840
Speaker 4: like projections. And the explanation goes that the waving of

538
00:31:28,080 --> 00:31:32,239
Speaker 4: cilia in this little pit create a consistent direction of

539
00:31:32,440 --> 00:31:36,120
Speaker 4: flow in the fluid around the ventral node. So the

540
00:31:36,160 --> 00:31:39,239
Speaker 4: cilia rotate to get the fluid moving, and then they

541
00:31:39,320 --> 00:31:42,200
Speaker 4: keep it moving in a consistent direction. The fluid is

542
00:31:42,240 --> 00:31:44,920
Speaker 4: always moving to the left along with the with the

543
00:31:44,960 --> 00:31:48,840
Speaker 4: way the cilia are waving, and the direction of this

544
00:31:49,000 --> 00:31:53,560
Speaker 4: flow seems to cause a chain reaction that results in

545
00:31:53,720 --> 00:31:58,960
Speaker 4: changes in gene expression, specifically in the asymmetry genes coming

546
00:31:59,000 --> 00:32:02,880
Speaker 4: back to again no and lefty. So apparently, if the

547
00:32:02,960 --> 00:32:08,560
Speaker 4: cilia are having trouble with motility, the unidirectional leftward current

548
00:32:08,640 --> 00:32:12,560
Speaker 4: of fluid is not established and the symmetry breaking genes

549
00:32:12,640 --> 00:32:15,840
Speaker 4: aren't expressed as they would normally be, which can lead

550
00:32:15,880 --> 00:32:19,960
Speaker 4: to deviations from the type of mammalian asymmetry we would

551
00:32:19,960 --> 00:32:24,320
Speaker 4: see in most members of that species, such as creating

552
00:32:24,560 --> 00:32:27,000
Speaker 4: a condition where the body fifty percent of the time

553
00:32:27,040 --> 00:32:31,360
Speaker 4: can have its internal organs flipped. However, this can't be

554
00:32:31,480 --> 00:32:36,280
Speaker 4: the only factor leading to standard symmetry breaking in animal bodies.

555
00:32:36,600 --> 00:32:41,400
Speaker 4: Vernemon's article also cites a Tufts University biologist named Michael

556
00:32:41,520 --> 00:32:45,000
Speaker 4: Levin who points out that some animals, even some mammals,

557
00:32:45,280 --> 00:32:49,120
Speaker 4: don't have that ciliated dorsal node we were just talking about,

558
00:32:49,840 --> 00:32:53,480
Speaker 4: and Levin believes there's some involvement of a factor called

559
00:32:53,640 --> 00:32:58,120
Speaker 4: the cellular skeleton or the cytoskeleton. Did you know that

560
00:32:58,160 --> 00:33:02,600
Speaker 4: your cells have a skeleton of their own? I don't know.

561
00:33:02,680 --> 00:33:04,960
Speaker 4: I guess i'd heard the word cytoskeleton, but I hadn't

562
00:33:05,040 --> 00:33:08,320
Speaker 4: quite put it together. It's not exactly like your bigger skeleton.

563
00:33:08,360 --> 00:33:11,880
Speaker 4: I mean, it's not like bones. The cytoskeleton is a

564
00:33:12,280 --> 00:33:15,720
Speaker 4: system of protein filaments that are, at least in a

565
00:33:15,760 --> 00:33:18,240
Speaker 4: metaphorical sense, sort of like the bones of a cell.

566
00:33:19,240 --> 00:33:21,200
Speaker 4: To describe them, I own a quote from a twenty

567
00:33:21,240 --> 00:33:25,760
Speaker 4: ten review in nature by Fletcher and Mullins quote. The

568
00:33:25,800 --> 00:33:30,320
Speaker 4: ability of a eukaryotic cell to resist deformation, to transport

569
00:33:30,440 --> 00:33:35,360
Speaker 4: intracellular cargo, and to change shape during movement depends on

570
00:33:35,600 --> 00:33:42,200
Speaker 4: the cytoskeleton, an interconnected network of filamentous polymers and regulatory proteins.

571
00:33:42,880 --> 00:33:46,480
Speaker 4: Recent work has demonstrated that both internal and external physical

572
00:33:46,520 --> 00:33:50,920
Speaker 4: forces can act through the cytoskeleton to affect local mechanical

573
00:33:50,960 --> 00:33:55,240
Speaker 4: properties and cellular behavior. Attention is now focused on how

574
00:33:55,320 --> 00:34:00,600
Speaker 4: cytoskeletal networks generate, transmit, and respond to mechanical cellar over

575
00:34:00,680 --> 00:34:04,440
Speaker 4: both short and long time scales. An important insight emerging

576
00:34:04,480 --> 00:34:08,839
Speaker 4: from this work is that long lived cytoskeletal structures may

577
00:34:08,880 --> 00:34:13,960
Speaker 4: act as epigenetic determinants of cell shape, function, and fate.

578
00:34:14,680 --> 00:34:17,360
Speaker 4: And it's exactly this last comment that I think is

579
00:34:17,400 --> 00:34:20,160
Speaker 4: most relevant here, because in the case of symmetry breaking,

580
00:34:20,920 --> 00:34:24,920
Speaker 4: it may be that features of this cellular skeleton, this

581
00:34:25,040 --> 00:34:29,040
Speaker 4: system of sort of strands of polymers and proteins that

582
00:34:29,120 --> 00:34:32,360
Speaker 4: help give a cell its shape and help it resist

583
00:34:32,480 --> 00:34:36,520
Speaker 4: deformation when it's under pressure and things like that, that

584
00:34:36,600 --> 00:34:41,640
Speaker 4: this system may ultimately epigenetically determine the development of cells

585
00:34:41,680 --> 00:34:45,760
Speaker 4: and ultimately the handedness or asymmetry of the whole body.

586
00:34:46,000 --> 00:34:48,719
Speaker 4: Oh wow, this was so This next part was also

587
00:34:48,719 --> 00:34:50,160
Speaker 4: a surprise to me. I don't think I knew this.

588
00:34:50,239 --> 00:34:55,680
Speaker 4: Apparently cells themselves have a kind of handedness or asymmetry.

589
00:34:56,200 --> 00:34:58,719
Speaker 4: Some cells are sort of left oriented and some are

590
00:34:58,800 --> 00:35:01,600
Speaker 4: right oriented, and you can and see this in their

591
00:35:01,640 --> 00:35:04,759
Speaker 4: behavior when they're moving through fluid and they come up

592
00:35:04,800 --> 00:35:08,000
Speaker 4: against an obstacle. So you can have experiments where you

593
00:35:08,040 --> 00:35:11,280
Speaker 4: show that cells are flowing along in a controlled environment

594
00:35:11,600 --> 00:35:14,440
Speaker 4: and then they bump up against something, bump a surface.

595
00:35:14,840 --> 00:35:17,960
Speaker 4: When that happens, the cell will tend to turn in

596
00:35:18,080 --> 00:35:22,040
Speaker 4: one direction or the other, and that preference for a

597
00:35:22,040 --> 00:35:27,720
Speaker 4: particular way of turning tends to remain consistent for each cell.

598
00:35:27,800 --> 00:35:30,760
Speaker 4: You have sort of left turning cells and right turning cells,

599
00:35:31,800 --> 00:35:36,360
Speaker 4: and experiments in fruit flies demonstrate that these small differences

600
00:35:36,440 --> 00:35:41,400
Speaker 4: at the cellular level can snowball into major morphological differences

601
00:35:41,480 --> 00:35:46,319
Speaker 4: at the body level. Vernamon's article mentions researchers named Leo

602
00:35:46,440 --> 00:35:51,120
Speaker 4: Ian and Kinji Matsuno, who each identify proteins within the

603
00:35:51,160 --> 00:35:56,600
Speaker 4: cellular skeleton, specifically the actin and myosins, as having an

604
00:35:56,600 --> 00:35:59,720
Speaker 4: influence on whether a cell becomes left handed or right handed.

605
00:36:00,440 --> 00:36:03,960
Speaker 4: And there may also be some interplay between proteins in

606
00:36:04,000 --> 00:36:08,680
Speaker 4: the sidoskeleton and the asymmetrical expression of the nodle gene,

607
00:36:09,200 --> 00:36:11,960
Speaker 4: each playing a role. But then there's one more thing

608
00:36:11,960 --> 00:36:14,840
Speaker 4: that gets mentioned toward the end of this article, the

609
00:36:14,920 --> 00:36:17,120
Speaker 4: Quanta article that I thought was interesting, which is that

610
00:36:17,400 --> 00:36:20,400
Speaker 4: other factors leading to asymmetry. Of course, there might be

611
00:36:20,440 --> 00:36:23,799
Speaker 4: some that haven't been discovered yet, but one candidate has

612
00:36:23,840 --> 00:36:28,120
Speaker 4: to do with communication between cells, for instance, based on

613
00:36:28,239 --> 00:36:31,879
Speaker 4: the relative prevalence of proteins on a cell surface, which

614
00:36:31,920 --> 00:36:35,799
Speaker 4: would in turn determine how cells trade electrical charges back

615
00:36:35,800 --> 00:36:39,320
Speaker 4: and forth between each other. And the Quanta article cites

616
00:36:39,520 --> 00:36:43,760
Speaker 4: Michael Levin again saying quote, if we block the communication channels,

617
00:36:43,880 --> 00:36:48,760
Speaker 4: asymmetrical development always goes awry. And by manipulating this system,

618
00:36:48,760 --> 00:36:52,680
Speaker 4: we've been able to guide development in surprising butt predictable directions,

619
00:36:53,080 --> 00:36:58,000
Speaker 4: creating six legged frogs, four headed worms, or froglets with

620
00:36:58,040 --> 00:37:01,680
Speaker 4: an eye for a gut without changing their genomes at all.

621
00:37:02,360 --> 00:37:05,239
Speaker 4: And in a final twist, bringing this back to medicine,

622
00:37:05,880 --> 00:37:08,319
Speaker 4: it's interesting that all of this knowledge might one day

623
00:37:08,320 --> 00:37:13,279
Speaker 4: be useful in finding treatments for pathological growth and development

624
00:37:13,320 --> 00:37:17,200
Speaker 4: patterns and somatic cells by sort of harnessing these systems,

625
00:37:17,200 --> 00:37:23,279
Speaker 4: by harnessing the bodies existing mechanisms for detecting and directing

626
00:37:23,320 --> 00:37:26,040
Speaker 4: its own shape, you know, the way the cells come

627
00:37:26,080 --> 00:37:30,000
Speaker 4: together to form larger structures that might be harnessed for

628
00:37:30,520 --> 00:37:33,960
Speaker 4: treating cases where cell development is going wrong.

629
00:37:34,280 --> 00:37:36,840
Speaker 1: Yeah, that's fascinating, you know, coming back to what you

630
00:37:36,920 --> 00:37:39,480
Speaker 1: said earlier, I don't know if prior to this, if

631
00:37:39,680 --> 00:37:41,759
Speaker 1: someone had just stopped me on the street, like a

632
00:37:41,760 --> 00:37:44,959
Speaker 1: man on the street reporter situation asked me if cells

633
00:37:45,000 --> 00:37:46,759
Speaker 1: have a skeleton, if I would have been able to

634
00:37:47,040 --> 00:37:52,440
Speaker 1: correctly answer regarding the site of skeleton. Here, this is

635
00:37:52,440 --> 00:37:55,840
Speaker 1: pretty fascinating. And then to get into its sort of

636
00:37:55,880 --> 00:37:59,640
Speaker 1: the ramifications of that and how that ends up being

637
00:37:59,680 --> 00:38:04,280
Speaker 1: reflect elected in the left handedness of the overall system

638
00:38:04,800 --> 00:38:07,000
Speaker 1: or the right handedness, whichever the case may be. You know,

639
00:38:07,080 --> 00:38:08,919
Speaker 1: I have to think back once more to the cock

640
00:38:08,920 --> 00:38:13,000
Speaker 1: eyed squid Histiotoothus that we discussed in Oh, this was

641
00:38:13,040 --> 00:38:16,320
Speaker 1: the first episode. Yeah, one of the reasons to marvel

642
00:38:16,440 --> 00:38:19,200
Speaker 1: this amazing creature is that its eyes have evolved to

643
00:38:19,239 --> 00:38:22,080
Speaker 1: look in different directions to different realms of the ocean.

644
00:38:22,239 --> 00:38:26,520
Speaker 1: Light and dark, and this seems understandably strange and alien

645
00:38:26,600 --> 00:38:30,520
Speaker 1: to us, but perhaps less so when we remember things

646
00:38:30,680 --> 00:38:32,759
Speaker 1: like left handed and right handedness. When we think about

647
00:38:32,800 --> 00:38:37,239
Speaker 1: neural asymmetry that defines us on the inside, and of

648
00:38:37,280 --> 00:38:40,000
Speaker 1: course it's not just us. Asymmetries between left and right

649
00:38:40,040 --> 00:38:42,520
Speaker 1: side of the nervous system are present throughout the animal kingdom,

650
00:38:42,560 --> 00:38:46,560
Speaker 1: from invertebrates to mammals. And as one source I was

651
00:38:46,600 --> 00:38:51,040
Speaker 1: looking at this is by Conca, Bianco and Wilson in

652
00:38:51,320 --> 00:38:55,080
Speaker 1: Encoding Asymmetry within Neural Circuits, published in twenty twelve in

653
00:38:55,200 --> 00:38:59,880
Speaker 1: Nature of Views Neuroscience. The theoretical advantages of brain asymmetry

654
00:38:59,880 --> 00:39:04,279
Speaker 1: and include the capacity for parallel processing, the specialization of

655
00:39:04,360 --> 00:39:07,880
Speaker 1: left and right sides for distinct computations, and the restriction

656
00:39:07,920 --> 00:39:12,520
Speaker 1: of information processing within local circuits with short, fast connections.

657
00:39:12,800 --> 00:39:17,120
Speaker 1: But while there are obvious advantages to brain asymmetry, are

658
00:39:17,160 --> 00:39:20,759
Speaker 1: there advantages to brain symmetry. So I was looking into

659
00:39:20,760 --> 00:39:23,480
Speaker 1: this a little bit and I read some thoughts from

660
00:39:23,520 --> 00:39:28,360
Speaker 1: a Marco Data of the University of Padua who experimented

661
00:39:28,440 --> 00:39:32,840
Speaker 1: with the often lateralized fish species the gold belly top

662
00:39:32,920 --> 00:39:37,080
Speaker 1: mino in two thousand and nine. Basically, what this experiment

663
00:39:37,080 --> 00:39:40,719
Speaker 1: consisted of was dividing these top minnows, these gold belly

664
00:39:40,760 --> 00:39:46,719
Speaker 1: top minnows, into groups of left lateralized, right lateralized, and

665
00:39:46,840 --> 00:39:51,839
Speaker 1: non lateralized specimens. So the seeming advantage to the non

666
00:39:51,920 --> 00:39:57,120
Speaker 1: lateralized came when judging stimuli to either side of the

667
00:39:57,120 --> 00:40:03,239
Speaker 1: creature through either eye. Experiments involved judging advantageous shoals of

668
00:40:03,239 --> 00:40:05,839
Speaker 1: fish to join on either side. Remember, you're a small

669
00:40:05,880 --> 00:40:08,840
Speaker 1: fish in the ocean. There's a lot of survival advantage

670
00:40:08,840 --> 00:40:12,000
Speaker 1: of being able to determine which shoal of fish you

671
00:40:12,040 --> 00:40:16,400
Speaker 1: should take refuge in their strength in numbers, and so

672
00:40:16,480 --> 00:40:20,120
Speaker 1: it seems that in these fish having a lateral tendency,

673
00:40:21,400 --> 00:40:24,000
Speaker 1: most often they just joined the shoal that they saw

674
00:40:24,200 --> 00:40:28,279
Speaker 1: with their dominant eye. So I guess the take home

675
00:40:28,320 --> 00:40:31,279
Speaker 1: here is that in some cases, yeah, it's going to

676
00:40:31,600 --> 00:40:34,160
Speaker 1: it may come down to your dominant side is just

677
00:40:34,200 --> 00:40:37,520
Speaker 1: going to be the tendency that you go in, and

678
00:40:37,560 --> 00:40:41,680
Speaker 1: it's maybe going to potentially get in the way of

679
00:40:41,760 --> 00:40:45,239
Speaker 1: properly evaluating in this case, two different shoals of fish.

680
00:40:45,600 --> 00:40:47,279
Speaker 4: I don't have evidence of this in front of me,

681
00:40:47,360 --> 00:40:49,879
Speaker 4: but it makes me think that surely things like this

682
00:40:50,480 --> 00:40:54,600
Speaker 4: must also be true even with you know, brains we

683
00:40:54,640 --> 00:40:56,560
Speaker 4: would think of as more complex. I mean, I'm sure

684
00:40:56,600 --> 00:41:00,480
Speaker 4: even with humans, handedness probably plays a role in like

685
00:41:01,120 --> 00:41:05,360
Speaker 4: directional reactions to fast you know, something pops up and

686
00:41:05,400 --> 00:41:09,279
Speaker 4: scares you, which direction do you bolt in? I would

687
00:41:09,320 --> 00:41:12,920
Speaker 4: be surprised if there is not some kind of tendency

688
00:41:12,920 --> 00:41:16,239
Speaker 4: there that's not purely dictated by where the stimulus is,

689
00:41:16,280 --> 00:41:18,759
Speaker 4: but also has to do with like body side dominance.

690
00:41:19,280 --> 00:41:23,640
Speaker 1: Yeah, and body side dominance and left handedness and right

691
00:41:23,640 --> 00:41:26,520
Speaker 1: handedness and human beings. This is something I think we'll

692
00:41:26,520 --> 00:41:29,479
Speaker 1: have to come back to in a future episode. There's

693
00:41:29,520 --> 00:41:33,040
Speaker 1: a lot of great research out there, particularly when again

694
00:41:33,040 --> 00:41:34,680
Speaker 1: it comes back to what we were saying earlier about

695
00:41:34,680 --> 00:41:37,399
Speaker 1: how you have whatever's going on on the animal level

696
00:41:37,400 --> 00:41:40,480
Speaker 1: and then you have the human complications involved there. Because yeah,

697
00:41:40,480 --> 00:41:43,200
Speaker 1: when you start getting into whole situations of okay, you

698
00:41:43,239 --> 00:41:46,600
Speaker 1: have a right handed dominant society and then you have

699
00:41:46,719 --> 00:41:50,400
Speaker 1: left handed individuals within that society, you know, what is

700
00:41:50,440 --> 00:41:54,799
Speaker 1: the impact? And of course there's a lot of There

701
00:41:54,800 --> 00:41:56,640
Speaker 1: have been a number of interesting studies over the years

702
00:41:56,680 --> 00:41:59,040
Speaker 1: that have looked at this, how it plays into sports,

703
00:41:59,080 --> 00:42:03,640
Speaker 1: how it plays to conflict and combat. How it just

704
00:42:03,640 --> 00:42:06,560
Speaker 1: plays into thinking about the world around you. So that

705
00:42:06,600 --> 00:42:08,440
Speaker 1: would be a fun one to come back and do.

706
00:42:08,560 --> 00:42:10,839
Speaker 1: And I know that the lefties especially will love it.

707
00:42:11,000 --> 00:42:11,960
Speaker 4: Oh yeah, but.

708
00:42:12,120 --> 00:42:14,960
Speaker 1: Righty's your most of our audience, so don't worry. You'll

709
00:42:15,000 --> 00:42:20,919
Speaker 1: like it too, You're just less special. Sorry, Okay, should

710
00:42:20,960 --> 00:42:23,520
Speaker 1: we wrap it up there? I suppose we should. So

711
00:42:23,560 --> 00:42:28,280
Speaker 1: we hope that you've enjoyed this partial journey through asymmetry.

712
00:42:28,640 --> 00:42:30,520
Speaker 1: Like we said, there are plenty of other examples of

713
00:42:30,560 --> 00:42:33,799
Speaker 1: asymmetry in the animal world. We tried to focus on

714
00:42:34,080 --> 00:42:40,920
Speaker 1: some of the examples that illustrated the topic the best.

715
00:42:41,440 --> 00:42:44,319
Speaker 1: But perhaps you're thinking of something we didn't mention that

716
00:42:44,360 --> 00:42:47,719
Speaker 1: bears mentioning, right in, let us know. Let us know

717
00:42:47,760 --> 00:42:50,360
Speaker 1: if you're interested in an episode in the future about

718
00:42:50,680 --> 00:42:55,879
Speaker 1: left handedness and right handedness in humans, anyway you look

719
00:42:55,920 --> 00:42:57,640
Speaker 1: at it, just right in. We'd love to hear from

720
00:42:57,680 --> 00:43:01,560
Speaker 1: you past episodes, future episodes, and episodes. It's all fair game.

721
00:43:02,360 --> 00:43:04,640
Speaker 1: We read those on Mondays on listener Mail and the

722
00:43:04,680 --> 00:43:06,759
Speaker 1: Stuff to Blow your Mind podcast feed. We have our

723
00:43:06,800 --> 00:43:09,880
Speaker 1: core episodes on Tuesdays and Thursdays. Short Form Artifact or

724
00:43:09,880 --> 00:43:13,319
Speaker 1: Monster Fact episode on Wednesdays and on Fridays, we put

725
00:43:13,360 --> 00:43:16,000
Speaker 1: aside most serious concerns and we just watch a weird

726
00:43:16,080 --> 00:43:17,760
Speaker 1: film on Weird House Cinema.

727
00:43:17,880 --> 00:43:20,919
Speaker 4: Huge thanks, as always to our excellent audio producer Seth

728
00:43:21,000 --> 00:43:23,479
Speaker 4: Nicholas Johnson. If you would like to get in touch

729
00:43:23,520 --> 00:43:25,960
Speaker 4: with us with feedback on this episode or any other,

730
00:43:26,080 --> 00:43:28,360
Speaker 4: to suggest a topic for the future, or just to

731
00:43:28,360 --> 00:43:31,080
Speaker 4: say hello, you can email us at contact at stuff

732
00:43:31,120 --> 00:43:32,480
Speaker 4: to Blow your Mind dot com.

733
00:43:40,040 --> 00:43:42,960
Speaker 3: Stuff to Blow Your Mind is production of iHeartRadio. For

734
00:43:43,040 --> 00:43:45,840
Speaker 3: more podcasts from my heart Radio, visit the iHeartRadio app,

735
00:43:46,000 --> 00:43:48,720
Speaker 3: Apple Podcasts, or wherever you listen to your favorite shows

736
00:44:00,080 --> 00:44:02,239
Speaker 1: At the U