Listener Questions #54

0:07 Renovations were meant to make the reflecting pool American flag blue. So what caused the massive algal bloom with its stomach-churning hue?

0:17 Do you have to be aware to have a memory? Or can you mindlessly recall things that are purely sensory?

0:24 I want to learn more about the charismatic banana slug. And I'll throw Kelly a bone. She can give slug parasites a plug.

0:32 Whatever questions are keeping you up at night. You know that Daniel and Kelly's answers will make it all right.

0:38 Listener questions episode number 54.

0:41 54.

0:41 Not a prime.

0:59 Hi, I'm Daniel. I'm a particle physicist. I love thinking about aliens. And I was wrong again about the Nobel Prize.

1:07 Hello, I'm Kelly Wintersmith. I study parasites and space, and I really don't have any predictions when Nobel Prize time comes along. And usually I don't actually even pay attention to the announcement. How were you wrong this year? Oh, was this a project that you could have been involved in?

1:21 No.

1:22 Oh, yeah. That's right. My record is flawless.

1:27 Is that four projects you could have?

1:28 That is four now. Oh, no. So the Nobel Prize was awarded this week to Francis Halzen, an awesome guy who wrote a great textbook and the guy who conceived of the amazing idea of using a cubic kilometer of ice at the South Pole to see neutrinos. This is the project where they drilled a kilometer down and dropped cameras in there and then let it refreeze. Now they have literally an ice cube to see neutrinos. And when I was a grad student... In the 90s at Berkeley, there were folks working on this very early on. And I could have gone in on the ground floor of this Nobel Prize winning experiment. But I thought, that's crazy.

2:06 They'll never get that to work. Which is what I also said about many other experiments that went on to win the Nobel Prize. So, you know, when Daniel thinks your idea is impractical, you're destined for Nobel gold.

2:17 You are on the right track. Do not back down. Double your efforts.

2:24 Daniel's won a Nobel Prize in some alternative universe, but not this one.

2:28 Oh, man, maybe four or five alternative universes, but not this one. But that's okay. You love what you do, and you don't need a prize to feel good about it.

2:36 That's right. Yes, I didn't want the Nobel Prize anyway. No sour grapes here. Absolutely not.

2:41 That's right. Well, that's good.

2:44 But we're not talking about Daniel's lack of curiosity in Nobel Prize-winning experiments. We're talking about the listeners and the questions they have about the nature of the universe. how things work, why things work, and we're here to explain all of it to you.

2:58 And first up today, we have a question from Discord, and I am maintaining my tradition of not getting first names ahead of time. So we have a question from Dernal K from our Discord community.

3:10 Hi, Daniel and Kelly. This is David from Dallas via New Zealand, Australia, and England. Yes, I've lived in lots of places. On Discord, I'm Dernal K, which is Colonel D switched up to be unique. My question might be fun if it's not crossing our currently topical line is, how do we get algal blooms in ponds and how that impacts the aquatic ecosystems in waterways and ponds?

3:36 All right. This is a very topical question. Unusual for us, Kelly.

3:40 It is.

3:40 However, one, I... Let it sit on my list for a while so it's not super topical anymore.

3:46 Trying to stay irrelevant.

3:47 Good.

3:48 That's how we roll. But also, after the 2012 renovations of the reflecting pool, which were, you know, not during a Trump presidency, there were also algal blooms in the reflecting pool. So this is a recurring problem.

4:02 OK.

4:02 And so, you know, that's my attempt at being apolitical. But let's let's jump into the the science here.

4:09 So what is an algal bloom, first of all? Is it just a bunch of algae in a pool?

4:13 It's a bunch of algae or a bunch of cyanobacteria. So these are both organisms that photosynthesize. They are in very different places on the tree of life. And actually, we think that algae and other plants got the ability to photosynthesize because way deep in the past, one of them managed to incorporate a cyanobacteria, which is a bacteria that can do photosynthesis. And that ended up becoming the chloroplast.

4:40 Oh, this is like what we talked about recently on the symbiosis episode.

4:44 Yeah, except you and I are like time travelers. Yes, we've already recorded the symbiosis episode, but I don't think it will have come out by the time this listener question episode comes out. So stay tuned.

4:53 Preview of the symbiosis episode.

4:55 That's right. That's right. Time traveling extraordinaries.

4:58 Awesome.

4:59 Anyway, both algae and cyanobacteria use photosynthesis. And when you say there's an algal bloom, even though cyanobacteria are not algae, people will still... refer to an overgrowth of both cyanobacteria and algae as algal blooms.

5:14 So you're saying common names are not super clear and descriptive sometimes.

5:18 Which is why sometimes it's helpful to use scientific names. Yes, that's right.

5:22 I saw a comic about that from Zach. I was wondering if that's been part of the conversation over there.

5:28 No, but you know, Zach Wienersmith listens to DKEU, and I've been listening to his podcast, Last Humans in the Loop.

5:35 It's good.

5:36 I've been enjoying it. I'm glad you're liking it, too.

5:38 Yeah, yeah.

5:39 OK, so back on track. When do you get massive growths of these photosynthesizing organisms? And some of the things that cause a lot of growth in these organisms are, one, loading of phosphorus. So for a lot of algae in freshwater systems, the thing that limits their growth is the availability of phosphorus in the environment.

6:01 Phosphorus. Why phosphorus?

6:03 Phosphorus. Why phosphorus? So I should know that, but I also am going to point out that that's clearly biochemistry. So let's go ahead and throw to Katrina.

6:16 Well, phosphorus is important for life in general, but what's really interesting about phosphorus is that it doesn't go into the atmosphere. So a lot of the other resources like nitrogen, oxygen, et cetera, have a gas phase in And so you can just sip them out of the air. And microbes are so creative that if you like try to grow them in water that doesn't have any nitrogen, they're like, no problem for me.

6:40 I'll just fix it out of the atmosphere.

6:43 However, for phosphorus, it's a little harder because it has to come out of a solid form, like out of the rocks. So as rain occurs and like the sediment is coming out of the rocks and into the water sources, the cyanobacteria can grab the phosphorus from there. What's really cool about them.

7:03 Is that they can hold on to the phosphorus.

7:05 So if it rains in the spring, it doesn't matter if it's like August, the cells hold on to the phosphorus and it doesn't like run out right away. But if they go long enough without any rain or like perturbation from the solid sources nearby, they will totally run out of their phosphorus. And that concludes my statement about cyanobacteria and phosphorus. I wish I could tell you all about phages and how you could use them to control algal blooms. And I also wish I could tell you about agriculture and how phosphorus is a really important resource that can be limiting for agriculture.

7:40 But humans give algae a leg up because we have phosphorus in our fertilizer because our plants also need phosphorus to grow.

7:48 Mm-hmm.

7:49 And so we apply fertilizer to our yards. We apply fertilizer with phosphorus to our agricultural crops.

7:55 Yeah.

7:56 Our animals, like our cows, defecate out piles with phosphorus in it. And then when it rains, that phosphorus accumulates in the rain and then ends up in our waterways.

8:08 Hmm.

8:09 And so this is what causes eutrophication which is essentially just lots of nutrients in the water which allows the algae to grow like crazy because it's no longer limited by phosphorus anymore and so often you'll get an algal bloom because there's been nutrient loading in that system.

8:24 So the way you described it suggests that like humans and cows are putting more phosphorus into the system than you find naturally, I guess. And that's because of like human civilization or whatever.

8:36 Yeah.

8:37 But like these things are living near humans for a long time. Why isn't there just always more phosphorus? Like why aren't we always in algal bloom?

8:46 We are in algal blooms a lot more now than we were before. And some areas like Lake Erie, the lakes have gone what's called eutrophic, which is to say they almost always have more algae than would be desirable growing in them. And so this does happen a lot. And algal blooms are happening more and more often. And that's a combination of... More phosphorus runoff, but it's also a combination of warming temperatures, which increase the water temperature, which makes it easier for algae to grow. And I should say that, you know, Lake Erie, there was a period where we were doing a really good job of keeping runoff with phosphorus and nitrogen because nitrogen is sometimes also a limiting factor. And our fertilizers have that, too.

9:23 We were doing a good job of keeping that from getting into the waterways. And Lake Erie was looking nicer. And then we started doing more fertilizer. I think the problem in this case was agricultural fertilizer. We started doing more agricultural stuff. And now Lake Erie is starting to have algal bloom problems again.

9:39 And why is it a problem? Like, is it just it doesn't look as nice? This is like a human aesthetic thing? Or is it like, you know, tip off the balance of the ecosystem and everything collapses and pretty soon it's just goo on the planet?

9:51 Oh, good question. OK, so the answer is multifactorial. So one of the problems is that, okay, so algae produce oxygen during the day through the process of photosynthesis, but at night, they actually suck oxygen out of The environment when they were doing respiration. So if you have massive amounts of algae at night, they suck the oxygen out of the water and a big algal mat on the surface will block sunlight to the plants growing below. And so now they're not producing oxygen. And at some point, often these algal blooms die. end and the algae die off in large numbers. And when they die off, they get decomposed by bacteria and those bacteria create low oxygen environments.

10:36 And so one of the problems is these algal blooms are associated with sucking the oxygen out of the water and you often end up with massive fish kills afterwards.

10:44 Oh, yeah.

10:45 So really bad for the environment. But also, if the quote unquote algal bloom is caused by cyanobacteria, cyanobacteria release toxins. And these toxins can either be really bad for your liver. Some of them are neurotoxins. There are lots of different species of cyanobacteria. They produce different kinds of toxins.

11:04 Do the toxins turn you blue?

11:06 You know, that would be interesting.

11:09 I mean, we are on brand for cyanobacteria, right? They should turn you cyan.

11:14 Well, they're also called blue-green algae sometimes, which is, you know, not a good name. It's like a physicist named them or something, you know. But, for example, I grew up in Toledo, and my parents still live there, and Toledo has their water from Lake Erie. And a couple years ago, there was a do-not-drink-the-water warning because there was so much cyanobacteria growing in Lake Erie, and that toxin... that they make, microcystin in this case, was in the water and it would have been like dangerous for your liver to drink the water. And so a lot of money is spent every year on filtering water in very particular ways to remove cyanobacteria and toxins in areas where they're present. So it's a ecological, financial, and human health problem.

11:57 So we're on one hand making it worse by putting phosphorus everywhere. And on the other hand, struggling against it, constantly trying to remove it. Exactly.

12:06 Yep. And and we're also making it worse by warming our planets. And those warmer temperatures also result in more algal growth. Other things that contribute to algal bloom are sunlight. So you're more likely to get algal growth on a sunny day than a cloudy day. And calm water tends to be more conducive to the growth of like algal mats and clumps of algae. And so let's go through our list again. We've got phosphorus, warm water, sunlight, and calm water. The reflecting pool in Washington, D.C. was the perfect storm.

12:42 It's like what you would design if you wanted an algal bloom.

12:45 Yes, that's right. If you wanted an algal bloom, these are the conditions you would create.

12:49 Okay.

12:50 So first of all, it was painted so that it would look American flag blue.

12:54 Right.

12:54 This was a darker shade than was previously covering the bottom of the reflecting pool. And darker shades mean the water was warming up more because that darker paint was, what is it, absorbed? What is the physics answer for why darker paint is bad, Daniel?

13:09 Right. Well, something is lighter because it's reflecting more of the light. And it's darker. It's absorbing more of the light. So it heats up.

13:16 There you go.

13:17 The way that, like, a black car will heat up faster than a white car in the sun. Okay.

13:21 Yep.

13:21 And that water is meant to be still so that you can see the reflection of the Lincoln Memorial and the George Washington Monument. So that's calm water. And it's warm. I think this was, what, June or July when this was happening? Oh, it was meant for the July 4th celebration. So, yes, this was happening in, like, June. So it was warming up.

13:39 And so what they think happens is that there was algae that was still in the hoses, the lines that feed the reflecting pool.

13:47 Okay.

13:48 And so while they were painting it, the algae was growing in the lines. And then they turned the water on, they filled it up, and they essentially injected the algae into the reflecting pool.

13:58 Nice.

13:58 The water either comes from the tidal basin, which is a man-made reservoir outside D.C. that has... Phosphorus from runoff from the area, or sometimes they get it from the city water supply. And if you get it from the city water supply, there's still a chance that there will be phosphorus in it because we use orthophosphates to line the inside of metal pipes. So here's what you need to know. They coat the metal pipes. They change the pH right at the point where like the pipe and the water meet. And that's important because if you have lead pipes, you want to make sure that the water is not causing the lead to leach out of the pipes.

14:38 And so putting orthophosphate in the water source means that the pipes get a little bit coated. They're less likely to leach out the lead. But now there's phosphorus in the water, which promotes the growth of algae. So no matter where the water came from when they refilled the reflecting pool, there's a good chance that phosphorus was added to the reflecting pool as well.

14:58 Even though this is orthophosphates, not just phosphates, are these like that have had their teeth straightened or what's an orthophosphate? I mean, the scientific name is perfectly clear, right? So help us out here.

15:09 Oh, you're being not nice. So I looked at a chemistry website to get the word orthophosphate. I'm so sorry. You're right, you're right. And so it was chemical and engineering news. And so I should have just said a form of phosphate. I am retreating into my ignorance. But anyway.

15:30 Victory against chemistry.

15:32 That's right. That's right. Well, I feel like chemistry won and I'm running away, but.

15:38 No, we have pushed back the chemistry. Go away, chemistry.

15:41 Go away, chemistry.

15:41 I'm running. So what could they have done to combat the algal blooms in the reflecting pool, Kelly?

15:48 Yeah, what could they have done? So they could have, I don't know, maybe put treatments in earlier to kill, try to kill all of the algae. It looks like after the algae grew, they tried to remove it using like mechanical means, like vacuuming it out. And then I think they dumped hydrogen peroxide in there, which I believe is what messed up the lining at the bottom of the reflecting pool because it was still in the process of curing.

16:12 But I saw these pictures of them, like, emptying one-gallon jugs of hydrogen peroxide, which I was like, I don't know what that's really going to do anyway.

16:20 Well, and I think the algal blooms came back after that. So some solutions that I've seen include keeping the water more well aerated because more well aerated water supports bacteria that compete with the algae. So you're less likely to get an algal bloom.

16:37 I heard they were using these machines called nanobubblers, but I never understood what they are and why the bubbles are so nano.

16:44 Yeah, I think they dump in nanobubbles and there's something about like the surface area of the bubble and the bubble is impregnated with a certain kind of gas. I didn't get into that science, but it was meant to be a way to keep the oxygen supply in the reflecting pool up for longer. And I think you can put other things other than oxygen in there, like some chemicals to try to kill the algae. But I'm not an expert on that.

17:07 It's a shame that the scientific term nanobubbler isn't clear. You know, it should just make sense on the surface, you know, but it doesn't somehow.

17:14 Are you throwing shade on me? I can't tell anymore.

17:16 I can't tell anymore either.

17:19 Okay.

17:19 All right. So anyway, this is a long standing problem because if you do have bubblers in there, then your reflecting pool is not going to be perfectly still. And that's kind of the whole point. And so, you know, this thing I think was built in 1922. We've been sort of set up for algal blooms ever since then.

17:35 And they have been a recurring problem. It's just difficult to solve.

17:39 Okay.

17:40 Yeah.

17:40 Yeah.

17:41 Okay, so, Dirt LK. Does that answer your question? Let me know.

17:46 Wow, thanks for the great discussion as always. So the problem with the reflecting pool in Washington comes down to bad chemistry. Hopefully there is a fix for that. This reminded me of an organic chemistry lab where we had to measure dissolved oxygen from different points around a pond in the university park at Sydney University. Collecting samples in bud flasks needed a very specific technique. No one needed to titrate with the Wigler method. I've been a listener since your episode with Ty and Daniel on The Expanse.

18:18 Thanks to the great podcast that keeps me entertained and up to date on the latest science.

18:43 Next up, we have a question from Rosalyn about memory and consciousness.

18:47 Hi, Danielle and Kelly. I have a question for you about the relationship between memory and consciousness. From my understanding, consciousness is a sense of oneself and working memories occur in order for us to make sense of ourself in the world around us, to help learn from past mistakes and to aid in our survival in the future. So my question is, Wouldn't the ability to create working memories require on some level a sort of consciousness? Wouldn't something need to know that it exists in that state and that in order to continue to exist in that state, it needs to retain a certain information about the world and itself in relation to the world so that it can continue to do so?

19:37 Am I like wildly off base here?

19:39 I just have a hard time understanding How one would retain or how anything could retain a memory without having a sense of self. that would necessitate why that particular memory is important for the future thank you i appreciate you.

19:57 Guys daniel you love talking and thinking about consciousness.

20:03 You know, I'm a physicist, which means that I love talking about stuff I have no training in and trying to speak about it confidently. Wow.

20:13 Actually, one of many things I really appreciate you is that you do rein that tendency in. I feel like you are really– You're really good about being like, I'm not a biologist. I don't know. Unlike Feynman, who's like, I'm not a biologist. I don't know. But I'm going to pretend I do.

20:27 Right.

20:27 And I'm smarter than the biologists.

20:28 That's right.

20:29 So, yeah, this is about memory and consciousness and also like a sense of self. So there's a bunch of topics in here. They're all getting sort of bundled together. And Rosalind is asking, you know, which of these things actually require the others? And I'm not a cognitive scientist, nor a biologist, nor a philosopher, but I'm interested in all of these things and like thinking about them. So these are my thoughts, but, you know, that doesn't mean that they are reasonable thoughts. I think this is what Rosalyn wrote in here about, and she knows we're not experts.

20:59 So let's go.

21:01 That's right.

21:02 All right.

21:02 So I think first I'd like to try to, like, untangle memory, consciousness, and sense of self. I feel like those three terms feel like they could be interchangeable.

21:11 Yeah, but the question is basically how they differ and whether one meets the other. So like, what is memory anyway? There's lots of different kinds of memory, right? Like most broadly, you could say memory is like a record of the past, maybe something that affects how you act in the future. But, you know, there's like working memory that holds information temporarily, like a way you can remember what somebody said, like digits of a phone number for a few seconds. You have this like loop in your brain. There's like episodic memories, remembering something that happened to you. There's just semantic memory, like stored knowledge and facts, you know, like things you know in your head. You know, the way Kelly has

21:50 like a huge pile of ridiculous scientific names, just like filling up her noggin and preventing her from knowing other useful stuff.

21:57 Oh my gosh, you are on a roll today. Look, sometimes those Latin names have information in them that's helpful.

22:03 Yeah, sometimes, sometimes. And then there's like procedural memory, you know, like how to ride a bicycle or even implicit memory, things you don't explicitly remember but do change your behavior. And so there's lots of different kinds of memory. And not all of them seem to require you to be like conscious or self-aware because, you know, like the memory that you have doesn't always require you knowing like why the information matters, right? Like, you know, evolution can design a system that responds to history. In that sense, it has a memory, but you might not be like consciously aware of it. Like, for example, your immune system remembers the bits and the pathogens that it's seen, right? It

22:49 has like some catalog inside of it. That is like a memory. It says, oh, we've seen this. We know how to respond to hear all the antibodies. But you don't know that. You don't remember that. Like maybe you remember being sick, but you don't remember the surface of these things, right? And you're not aware of them. And so information can be useful and it can be recorded and it can affect the future without it being like part of your conscious experience.

23:14 I'm going to regret saying this, but I've always thought that immune system memory was a bad use of the word memory, where we should have just come up with a different word because that seems like something very different than implicit memory or procedural memory, for example.

23:29 Well, I would say it's sort of more like semantic memory. It's like stored knowledge and facts, you know, the way like your computer has a memory, right? You put numbers into the computer, they're still there. We call it memory for a reason, right? It can recall it. you can store it and recall it in that same way your immune system has a memory of the pathogens it's seen, even if you're not aware of them. I don't think my computer is aware of the number 17 that I put in this register over there. So yeah, that's an example of like semantic memory that doesn't require you to be aware. So we've been talking about awareness What do we mean by that? Like, what is consciousness anyway? Man, that's like, you know, not a subtopic. That's like such

24:10 a deep question that we can't answer today. It's even harder to define what we mean than memory, which is already tricky and slippery. You know, you could think of it as like subjective experience. What is it like to see something or to feel something or to hear something or smell something? Philosophers use this word qualia. to describe the experience of seeing red or eating chocolate or something.

24:33 And so that's like the basic concept of consciousness. But then there's also this other side of it, which is like a sense of self that Rosalind is talking about. Sort of like a self-consciousness. So consciousness is like, I'm feeling pain. Self-consciousness is like, I am a thing and I am the thing experiencing the pain.

24:55 Okay.

24:55 You're like aware of the existence of yourself, not just like raw, I'm feeling pain or I'm eating chocolate, but like I'm a thing that is eating the chocolate. And beyond that, I think Rosalind is referencing something deeper, which is like an autobiographical identity. This feeling that like Daniel is eating chocolate today is the same Daniel that went for a jog yesterday to balance out that chocolate. You know, like, I'm the same person who existed yesterday and tomorrow, and my memories help define who I am, right? So, you know, there's like actually experiencing things, that's consciousness. There's realizing that you are a thing experiencing, so it's like turning that consciousness inwards. And then there's the autobiographical self, which is

25:37 like telling a story about how you evolved through time. So there's lots of different layers there of consciousness that all have different relationships to the concept of memory.

25:47 Yeah.

25:48 So then is the question, which of those can exist without the others?

25:52 Yeah, exactly. So like, can you be conscious without memory? I think certainly you can, right? There are people, for example, who can form long-term memories, right? But they're still here in the world. They can eat chocolate. They can perceive. They can have conversations. They can solve problems. They can have emotions, right? They can appear conscious in the present even if tomorrow or in five minutes they don't remember it, right?

26:15 So forming lasting memories doesn't appear necessary to be moment-to-moment conscious. So you can have consciousness, you can have self-consciousness without like even a sense of autobiographical identity or long-term memories.

26:29 Amazing, yeah.

26:30 Imagine, for example, like experiencing 10 seconds of the world normally and then forgetting those 10 seconds. doesn't mean you weren't aware. And maybe you were even aware of who you were and your history. The fact that you don't remember it later doesn't mean that the original experience was unconscious.

26:48 Yeah.

26:48 Okay.

26:49 And maybe you've had this experience where you're like driving somewhere, but you're a little distracted. And then you get there and you're like, I don't remember any of those red lights. Boy, I hope I didn't like run over a bunch of pedestrians without noticing.

27:02 I hate those moments.

27:03 Right? Aren't those terrifying?

27:05 How did I get here?

27:06 Yeah.

27:07 Probably your brain was doing it and you might have even been aware of it in the moment, but you weren't paying attention to it in a way that would get recorded so that later you can retrieve it.

27:16 Please don't take away our licenses.

27:18 I know.

27:19 So probably in the moment if somebody said, hey, Kelly, are you paying attention? You'd be like, yes, of course. What are you talking about? And you probably did stop for all those red lights.

27:27 Yeah.

27:27 But it wasn't interesting enough to be recalled. So you were aware, you were conscious, you were self-conscious, but you don't remember it.

27:35 Yes. Scary though that is.

27:37 Yeah. So let's flip it around. Can memory exist without consciousness? Right. Like certainly you can learn stuff without consciously remembering every time you learned it. Like I don't remember when I learned arithmetic, but I can do it. Right. A lot of implicit memory influences later choices, even if you don't recall exactly why you've learned it.

27:59 But did you need to be conscious in the moment to make that memory? Probably not. See, I feel like I don't ever want to lead a discussion on consciousness because every question is a, oh, Kelly needs 10 minutes to think about this. Do I really know what these terms mean? That's what I always go back to.

28:19 I would say that memory by itself is weak evidence for consciousness. I don't know that you need to have been conscious in order to remember something. You're not even always aware of, you know, why you are doing something or how something has influenced your behavior. And so it's like somehow there in your memory, it's changed the way you operate, but you don't remember learning it. And you might not have even been paying attention to the facts that have influenced you. But it does feel like our sense of self, you know, being one person across time, like Daniel said, is not the same person he was a year ago. He knows more chemistry and biology now than he did, but it's still the same person. You know,

29:05 I still feel like I am who I am. And so memory sort of like stitches all those moments together into this like biological narrative. And so this makes me think of like Daniel Dennett's theory of consciousness. He wrote this great book called Consciousness Explained.

29:21 What a Ballsy title.

29:22 Oh, wow. Yeah, I know. I loved it. And the idea he attacks in that book is a sort of intuitive notion of consciousness. I think a lot of people have, which is that there's like a little dude inside your brain watching the world like a movie theater. Right. He calls this the Cartesian thing. like there's some little homunculus in your brain and it's like you can't really experience the world except it just gets the senses and it sits there hearing and seeing and feeling but it's not really an answer to the question of consciousness it just sort of kicks it down the road Right. Because if there's like a little person in your head watching a movie about all of your senses, then like who's watching

30:01 the movie inside that little person's head.

30:04 Right.

30:04 Yeah.

30:04 Where did that do that come from?

30:06 Exactly. And so he's got this kind of bonkers theory of consciousness. It's called the multiple drafts model. And it says in the brain is constantly trying to make sense of what happened and stitch it together into a story about what has just happened to you. And so it's like, it tries this, it tries that, it tries to weave it all together into something that's simplified, that it can tell as a story. But there's no actual moment of consciousness in Dennett's theory. It is just a memory of the story of what just happened. There is no like, I am experiencing this now. It's just like, I'm recalling what just happened like a bill a second ago. It's this interesting theory because in his view, what we call

30:49 consciousness emerges from this like, distributed activity where you're like processing this and processing that and then writing down your like history. And there is no like, I am having this experience now that's writing histories. You're like going back and weaving it together. It's like a journalist telling a story about what happened and forming a consensus among the journalists.

31:11 But there is no like, I'm feeling it right now. And so in relation to Rosalind's question, It tells you that consciousness itself is nothing but recalling the immediate past, which is experiencing memory. And so I think Daniel Dennett, may he rest in peace. would say that memory is absolutely essential for consciousness because that's what consciousness is. It's just the recollection of the immediate past. And like, there's lots of criticisms of Dennett's idea, by far not like a widely held view. My favorite criticism is that his book should have been called Consciousness Explained Away instead of Consciousness Explained. And so, you know, Rosalind, this is really hard.

31:56 Nobody knows the answer. These are just my unqualified thoughts. You know, memory and consciousness are not the same thing. Some kinds of memory you can have without consciousness or a sense of self, right? It also seems like you can be aware without remembering things. But it does seem like memory is crucial to our experience of being a continuous person, part of what defines who you are and your identity. And so I think memory does help define who we are and how that changes over time. And so there's definitely a close relationship between these two concepts.

32:29 And I think it's important to mention, didn't Daniel Dennett say something nice about, do aliens speak physics?

32:35 That's right. I wrote a whole chapter about whether we're smart enough to understand what aliens... think and he's talked about this like the limits of biological intelligence and i sent him the book and i was like when you take a look at this especially the parts where i reference your work and let me know if i got it right and he wrote me back just three words he said this is good i'm so relieved you know that thing where you step outside your field and you write something and then you send it to experts and you're like please tell me if i got this wrong yep and you're terrified you're gonna get like 10 pages of rant yep yep so The shorter the response, the better. Anyway, that was a relief.

33:11 I once wrote a Nobel Prize winner to ask if I could interview them about a topic. And they wrote back and said, you didn't pick the most interesting thing to talk about. And then didn't respond to my emails anymore.

33:22 Oh, no.

33:23 I was like, wow. I guess you have a lot going on. All right. Anyway, so thank you to the people who actually respond to emails.

33:30 That's right. Thank you.

33:51 All right, next up, we have a question from Paul from New Hampshire, who's really into slugs.

33:57 Hey, Daniel and Kelly, since you often mention bananas, How about an episode on banana slugs, plus slugs and snails in general? Seems like a relevant topic given the UC Santa Cruz connection. Though not a UC alumnus, I used to live in Silicon Valley and would often hike in the coastal forests, so I got to see banana slugs in the wild. When I describe them, some people look at me like I've been smoking banana peels, and I'm sure Kelly can find some interesting slug parasites like rat lungworm.

34:25 I'm into slugs too. I'm banana slugs. Yeah. Go UC. Yeah.

34:29 Yeah.

34:30 Right.

34:30 So University of California, Santa Cruz, their mascot are the banana slugs.

34:34 Awesome.

34:35 And I will note that I have been working on answering Paul's very broad question from a number of different angles. A while ago, we did an episode, and this was partly in response to a question from Jane about slugs and snails and whence shells came from and what the purpose of the shells is and how the shells are made.

34:55 And so that was my beginning of the sluggy answers. And then Paul also mentioned rat lungworm. We did a whole episode on rat lungworm, which.

35:05 Terrifying episode.

35:06 I promise we will not talk about rat lungworm in any detail again. I think the message that I am getting is that was maybe the least enjoyed. Our guest was amazing. It was very informative, but it made many people squirm.

35:18 Yeah.

35:19 Which I totally get. And so now I am wrapping up this question by talking about banana slugs. What do you know about the banana slugs, Daniel?

35:28 They're big. They're yellow.

35:30 Sometimes yellow.

35:31 They're sometimes yellow. Okay. Can you lick them and get some sort of interesting experience or is that something else?

35:39 No, I think no. Let's say no. So I believe that there is a thing where sometimes people will go ahead and smooch banana slugs and their lips tingle afterwards.

35:51 Oh, yeah, that's what it is.

35:52 Banana slugs will eat poison oak. They also eat mushrooms that are very toxic to us. You should never pick up a wild banana slug and stick it up to your mouth because you don't know where that thing has been. That's true. I don't know what's going on with the tingliness there. But so, you know, maybe now's a good time to talk about the like slime that they produce.

36:14 Yeah.

36:15 So the slime they produce has these amazing like granules in them that suck up water. And this is part of how banana slugs manage to stay moist is that the slime is constantly like sucking up water. So it's possible that when you put a banana slug on your lips, again, do not do that. The tingling feeling you're feeling is the moisture being sucked out of your lips, maybe. But don't do that.

36:40 But that slime, they also— You're making it sound fun, though.

36:44 Well, that's not my fault. People make bad choices. I am absolving myself of any responsibility.

36:52 Please sign this waiver before listening to this episode. That's right.

36:55 That's right. So this slime, like one, it helps them move around their environment, like it lubricates the environment. It helps them stay moist by sucking the moisture out of the environment to try to keep them moist. But it also is this great anti-predator technique. So when like a salamander or a garter snake or a raccoon tries to eat them, the slime like essentially starts multiplying as the saliva inside the predator's mouth starts like getting sucked into the slime to grow the size of the slime.

37:24 Wow.

37:25 And so there have been like videos of snakes that are just their mouths are like full of slime and like they're spitting the slugs out like, no, just forget it. This was a mistake. I quit. I guess raccoons have been observed to be very cleverly rolling the slug in the dirt. And I think what it's doing is rolling off the slime so that then it can eat it.

37:45 You know, I guess it could also just like. squeeze it out like a paper towel or something. But anyway, so this slime is kind of an amazing material that helps them both stick to things and slide along their environment and protects them from predators. Way to go, banana slugs.

38:03 Yeah.

38:03 But I think what these slugs are probably most well-known for is their reproduction. And so if y'all have kids around and you don't want them to hear about slug reproduction, this is just a heads up that here it comes.

38:16 Uh.

38:17 So the slugs are hermaphrodites. They have really big wieners in a lot of cases. And they have vaginas because they're hermaphrodites. So they've got both sets of equipment. They are able to self-fertilize. But what they usually do is find a mate. When they find a mate, they begin like fertilizing each other essentially at the same time. Although sometimes you can observe slugs where just one of them is using their penis and the other one is not.

38:44 All right, I got to ask, because you mentioned it twice now. Yep. You say the slug has a really big wiener. In relation to the slug, what does the slug wiener look like? Like, give me a visual here.

38:55 Let's go to Google.

38:56 I'm glad this is not in my search history.

39:02 Oh my God, this is not the worst of... Okay, so I would say it's about... Looking at the one photo that I'm seeing right now, the wiener is about the size of their head.

39:11 Okay, all right.

39:12 Yeah, I mean, that's pretty... Impressive.

39:17 Kelly is impressed.

39:18 Relative to the size of their body. Although these guys can get really big. So like I was looking at one of the measurements and like a big banana slug can get from like my wrist to the crook of my elbow. So like the length of my forearms. That's a pretty big slug, right?

39:33 That's a huge slug.

39:34 Yeah, huge slug.

39:35 Okay.

39:35 But so what they're known for is they will go ahead and have sex. And when sex is done, one will go to pull their wiener out, but it seems to get stuck. And so in these cases where it seems to get stuck, it seems like for a while they attempt to detach. But if detaching doesn't work, then one of them will chew the wiener off.

39:55 Okay. We should have more warnings, Kelly. Why? I'm... Sorry? All right, go ahead. What happens next?

40:04 That's called apophylation.

40:06 Uh-huh.

40:07 And so there's this big debate about why do they do that? Is it like, for example, to make sure that the mate who just lost the penis invests in protecting the eggs that just got fertilized by the other individual? I think at the end of the day, we don't know why this happens. We all just know that it kind of makes us uncomfortable to hear about, particularly the male of the species.

40:31 I don't know how I feel about the theory that it brings the family together. Oh, no, no, no.

40:35 That's not that's not at all what I'm saying. And so, OK, so both individuals get their eggs fertilized in this interaction.

40:42 Yeah.

40:42 And so now they both have eggs that require a little bit more like energy to finish like growing up or whatever. If you don't have A penis. You can't go find another partner and invest in it doesn't make sense to invest in making more sperm because you don't have a penis anymore. Yeah. And so you better invest in making the set of eggs that you're growing like really great.

41:03 Exactly.

41:04 Yeah.

41:04 No, that's what I understood completely. But it's like it makes the parents invest in the kids. Right.

41:09 Oh, I thought you said invest in the family. And I thought you were. I don't know. That's that was a. More touchy-feely way of saying it than I– I don't think anybody necessarily buys that. That's just a idea that's floated out there. But I think at the end of the day, we throw our hands up in the air and we're like, why are you guys eating each other's wieners?

41:26 We don't know. That's a weird thing to do.

41:29 Glad we agree on that. All right.

41:32 Yeah, yeah, yeah. So there was this idea for a long time that you'll go to some populations– And it will be hard, if not impossible, to find a banana slug with a wiener. And so the question was like, oh, my gosh, did this population just like go to town on the apophyllation situation? And it looks like actually in some populations, the hermaphrodites are born without penises. And so they can still fertilize themselves by like, you know, they've got like an internal tube system where they can mix the sperm and the eggs on their own. And they can still accept sperm if they're able to find another individual that has a penis. And in that way, they can mate naturally. You know, with someone other than themselves.

42:14 But like why you see this diversity amongst populations in some species of banana slugs where some of them have penises and some of them don't. That's another open question. And so there's lots of questions about the sex lives of banana slugs that keep scientists.

42:29 Up at night.

42:30 Wow, that's a whole PhD topic right there.

42:32 That could be a couple PhD topics. There's some interesting questions there about, like, sexual selection and... Anyway, that'll... Yeah. We just need money, you know?

42:41 I hope some student doesn't bite off more than they can chew, you know?

42:45 That was too much. Too much.

42:48 But.

42:49 Paul gave me an opening to talk about parasites. And we're not going to talk about rat lungworm.

42:54 Yeah.

42:56 But we're going to talk real quick about biocontrol. So slugs, if you are a gardener, slugs are like the bane of your existence. So we bought six ducks to try to control the slug population in Zach's garden. And it turns out the ducks were more work than the slugs.

43:13 Yeah. Of course. And now you have ducks to take care of.

43:16 Well, you know, they got taken care of by a predator, unfortunately. But yeah, it was really sad. Betty White, her passing was the hardest to deal with. But anyway, so OK, so another option for getting rid of slugs in an agricultural setting is. is to release nematodes, which are a kind of like, you know, hard tube-ish shaped parasite. You release these slug attacking nematodes into your garden. And when a slug walks over them, the nematodes, which are parasites in this case, are like, there's a host. And they go ahead and they attack the slugs and they kill the slugs. But the problem is these nematodes don't only go after slugs that are bad for your garden. They go after like whatever slug they find. And so on

44:01 three different continents, there is a product you can buy called NEMA slug or NEMA slug 2.0. And these are two different species of nematodes that can kill slugs. And so there was a paper in BioRxiv in 2026 where they wanted to know if we bring this into the United States, because right now you're not allowed to use it in the United States because we don't know what it would do to like native slug populations. If we brought it into the United States and started using it in the Pacific Northwest where you find banana slugs, would this kill banana slugs, too? And the answer does seem to be yes. These nematodes will kill banana slugs. So now the question is, will banana slugs, which tend to live in like moist forest environments, which is to say

44:43 not really agricultural fields. Like, is there a risk of these nematodes getting into those environments and killing the banana slugs? That's something that we need to think about. But there is some evidence that if we start using this agricultural pest control method, there could be some implications for these most charismatic of slugs.

45:04 All right. Thank you very much. Let's send that question back to Paul and let him chew on it.

45:09 Or see if he wants to slug me after talking about apophylations.

45:14 Hey, Kelly and Daniel. Thanks for answering my questions about slugs and banana slugs in particular. I knew something of the banana slug reproductive cycle, but not all the, uh, details. I think they are a great example of creatures that seem strange at first, but when you dig past appearances, they're even more interesting than expected. We don't have banana slugs here in New Hampshire, but at least I could look at the banana slug plushie on my bookcase shelf.

45:40 Right next to my Cthulhu idol.

45:42 Thanks again.

45:43 All right. Thank you very much, everybody who's curious about the universe and listens to the podcast. If you have a question you'd like us to tackle, don't be shy. Send it to us. We would love to hear from you. Thanks, everybody, for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us.

46:07 Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman.

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