Of lice and men

25:03We have what are called like molecular clocks where essentially you can look at the rate at which different genes tend to pick up mutations and then back calculate how long it must have been. All right. So we look at gorilla lice and we compare it to human pubic lice and we see these are pretty similar. and that's why we think this jump happened. We also see there are differences. And by the number of differences, we can guess when this happened because we know how long it takes to make these differences on average. Beautiful. Yep, that's right. Wow, that's really fascinating. So we have head lice from our common ancestor from chimps and then pubic lice jumped over three or four million years ago.

25:41And do we think that before that, the head lice were just not in the pubic region because they were not adapted to it? or were they all over the body and then they got out-competed in the pubic region? For those of us who, like our common ancestors, are basically covered in hair, do we have lice everywhere or is it only on the head and in the pubic region? Like, does anybody have back hair lice? As sexy as that sounds. Oh, yum. So, okay, so body lice are lice that tend to live in like your clothes. And so the point is that there are lice that can be like up against your back. But I think lice do well in areas where the hair is very thick.

26:20Yeah. And well, there are some of us who have a dense land bridge between the head and the lower parts of our bodies. I had a roommate from New Jersey once who looked like he was wearing a sweater when he didn't have a shirt on. I don't know if you had to specify that he was from New Jersey. He liked saying, New Jersey, only the strong survive. And I just imagined it was a veritable jungle out there. Okay. All right. Well, I think the answer is that for most people, the hair on the rest of our body is not as thick as the hair on our heads or in our pubic region. And so you do tend to have separation.

26:57But I don't know if head lice were in the pubic region and then they were outcompeted by lice that could hang on better. Yeah, that's a great question. That's a great question. I don't know who's spending their life on that one, but I didn't find their papers. Well, here's another question maybe you don't know the answer to. Okay. Is on a gorilla, is it the same lice all over the body? Or like human head lice jump over to the gorilla pubic region or something crazy? No, I think gorilla just have a species of lice that you find all over their body. Okay. Okay. And so then there's this other thing that maybe you've heard.

27:30I know I've heard it a couple times, but maybe it's not as common a misconception as I thought. But I feel like every once in a while, the pop-sci press will say, pubic lice at risk of extinction because of rise in bikini waxing. What? Have you heard this? No. But I love it. Are Brazilians going to put pubic lice out of business? That's hilarious. That's hilarious. And I think the answer is quite clearly no, because it would have to be a global – Ouch. Exactly. We would all have to have Brazilians all at once and make sure that all of our bed linens had been dried at like 130 degrees Fahrenheit to kill any pubic lice that happened to be off, although they don't live very long off the human body.

28:13But anyway, I don't think they're at risk of extinction. I just really don't buy that. And I'm always amazed when it makes it in the press again. I'm like, come on, man. It's not like everyone is doing this. Take them off the endangered species list. They can survive on their own. Yes, right. Right. And I know that's like a big relief for some people. OK. All right. So now let's jump into body lice and head lice. OK. OK. So head lice and body lice have very different ways that they go about their life. So head lice tend to take lots of small meals and they tend to be smaller on average and they just live in the hair and they cling to the hairs.

28:53body lice spend a lot of their time living in the nooks and crannies of your clothes, and they jump onto your body to take a small number of big blood meals a day, and they also tend to be bigger, and then they retreat back into your clothes where they lay their eggs. All right, so body lice are a different species from head lice? We thought so. Oh. And so for a long time, we thought body lice and head lice are different. Like they look different. They have different behaviors. And so we were like, OK, they're different. And now here is another like story you may have heard about lice. Because they're different, dating that divergence must tell you about when humans started to wear clothes.

29:39That would be cool. That would be cool, right? And so what we know from archaeological sites is that something like 780 ,000 years ago, we were scraping hides. 780 ,000 years ago? We're talking almost a million years ago. Yeah, yeah. People started preparing leather clothing. So almost a million years ago, ancient humans were scraping hides, which could have been used as blankets. Maybe they weren't being used as clothes. We just know they were scraping hides. Maybe they were being used in bullfights or something, right? Yeah, right. Who the heck knows what they were being used for? Maybe they were umbrellas.

30:15Maybe they had parades. That's right. Who knows? Right, and floats. And I remember that humans have been using tools for more than a million years. And so we're talking about like stone tools here being scraped against the skin kind of thing. Probably, yes. All right. Yeah. And then we have evidence of eyed needles. So needles that you could put a thread through from about 40 ,000 years ago. That is mind-blowing. I know. 40 ,000-year-old eyed needles. That's amazing. So cool, right? They're made out of bone or antler or something? I don't know what they're made out of. But that suggests that we were making pretty complicated clothes at that point.

30:52We weren't just like cutting a hole and sticking our arms through and it was like toga style. We were like, you know, doing something a little bit fancier at that point. All right. Yeah. OK, so that's a pretty big gap. But we think that somewhere between 1.2 and 3 million years ago is when we started to lose our hair. And so, okay, so then the question is, can the split between body lice and head lice tell us anything, right? And so for a while, this paper came out that was going all over the place that said, it looks like the split happened about 83 ,000 to 170 ,000 years ago. Between body and head lice.

31:30Between body and head lice. And so that could be when we started wearing clothes. Because wearing clothes creates this new environment for body lice to live their own way. Right, because now they can live in our clothes. But OK, so I have seen this like set a bunch of places and I've probably repeated it, but we don't think that these are separate species anymore. Maybe this was a confusion looking at the different clades. So, you know, remember how we were talking about how we got body lice from a lot of different places. But now we've done experiments where if you let head lice get to super high concentrations, some of them start to change their body shape and move into clothes.

32:10And so it looks like actually this is like a way that lice bodies respond to overcrowding. They move into a different environment. And so it's not different species. It's like in ecology, we'd call this phenotypic plasticity, which is to say something early in your environment tells you, hey, you need to prepare for this kind of situation. And bodies can go on like a different trajectory. That's cool. There are little aquatic organisms where if they can sense that there are fish in the area, they'll develop like spikes on their heads and they can't get rid of those spikes. They'll have those spikes for the rest of their lives, but they're energetically expensive.

32:44So they only develop them when they get cues early in life that like this is the kind of environment you live in. So human head lice in the right situation, when the head is already overcrowded, the babies will develop a different form that's better suited to living in the clothing on the body. It does seem like that is what's happening. And do chimp lice do that also? Or do we think this is a feature human lice evolved because humans were wearing clothing? I would not expect that chimp lice would have something similar because they've got fur all over their bodies. It's not like they have somewhere else to switch to.

33:19And so I think we think that this is something that has to do with living in clothes. And so if we could tell when human lice developed this capability, then we could date when this environment became available to the lice and learn about when humans started wearing clothing. But that doesn't seem possible. Is that possible? Right. I wouldn't know how to start there. I mean, because they're all interbreeding. Right. And so, I mean, I think what's happening is that they are using genes that they already have and they're just expressing them differently. You could maybe date it if this ability came from some gene that got added to the population, and you could try to time when that gene got in there.

34:02But as far as I know, you really can't time this. And this is just like, so now we call them two different kinds of ecomorphs. And I want to be clear, we really don't understand what's happening here very well, but we no longer think of them as separate species. It looks like head lice can become body lice, and they're interbreeding. Interesting. All right. And so then head lice really are whole body lice except for the pubic region. Yeah. Yeah. Except they, so your kids, you take them to, I was going to say lice upon a time. I cannot remember the name of this place. Once upon a lice time. Once upon a lice time.

34:40That's not what it's called, is it? Sorry. Once in a lice time. Yes. Once in a lice time. Okay. Right. So you took your kids immediately to once in a lice time, which means the density of head lice didn't get very high. And so they didn't jump to close. And so in the United States, you know, children of wealthy families like our children, the lice doesn't get that bad. But if you are someone who's unhoused and doesn't have the opportunity to change or wash their clothes for long periods of time or shower for long periods of time, it can build up and then body lice become a problem. But what has really become a problem is body lice during periods in our history where we have had concentration camps or war.

35:28And in those situations, you get a lot of body lice. And one of the things that differentiates body lice from head lice is how their immune system responds to pathogens. Oh. So when we get back, we're going to talk about how body lice have killed millions of people throughout history, whereas head lice pretty much don't. Wow. Fascinating. All right. Let's take a break. When we come back, we'll hear all about the lice wars.

36:14And we're back. And we've talked about how head lice and body lice are very closely related. And our best guess at the moment is that body lice are just head lice that in a high competition environment have sort of changed the way their body is shaped. And now they're living in your clothes. And so here Kelly is nitpicking the science for all of you. That's right. That's right. And again, I want to clarify, there's a lot that we don't know. This is like the story, literally, as I've been reading, like every five or 10 years worth of like literature chunks, they've been like, oh, we've kind of changed our mind about this.

36:48And so this is an evolving story. But part of why we think that body lice can transmit disease is that one of the things that differs between head and body lice is how they respond when they get infected with a pathogen and the volume of their blood meals changes. So a disease that's transmitted by body lice that has been absolutely horrible for humans in the past is called epidemic typhus. Sounds bad. I hate the word typhus because there are three different kinds of typhuses. They're all very different. And it's different than typhoid fever. So just keep in mind that there's a lot of other things that you might have heard about that are not the thing we're about to talk about right now.

37:32But epidemic typhus is what we're talking about. And it is caused by a bacteria called Rickettsia prowizekii. And Daniel's like, why did you have to say the scientific name? And Daniel, I had to say the scientific name because that is the way you can be sure that you are talking about the disease that I'm about to tell you about. Look, I've succeeded. I don't even need to make my objection anymore. It's already in your brain. And now I just have you questioning yourself, which is good because this means you only give us the Latin name when we actually need it. So I can retire. Well, I look forward to when you stop telling us about all the different particles and you call them particle one, two, and three.

38:09But anyway, all right. All right. So what does this bacterium do? So this is a nasty bacteria. So the lice get infected by taking a blood meal from a human who already has the bacteria in their body. Okay. The bacteria replicates inside of the lice and eventually is going to kill the lice also. And so when we talk about malaria, we talk about how the mosquito gives it to people when they bite you. Right. And it essentially like comes out in the saliva into our body. That's not what happens here. What happens here is that the lice poop on your body or die on your body. And all of those bites are itchy.

38:46So you scratch. And when you scratch, you scratch the bacteria, which is still present in the poop and the body parts of the lice. You scratch that into your body. Or maybe you get it on your hands and then you rub your eyes and it gets in through the mucous membranes. This is if I don't have the bacterium in my blood yet, but I've gotten a louse from somebody who does have it, then it can cross back into my body through an itch I've scratched. Yeah, exactly right. So if you borrow the coat of somebody who has lice and they gave their lice epidemic typhus and then that lice dies on you or poops on you and you scratch, now you've got it.

39:22Oh, boy. And so what it does is it lives in the cells that line your blood vessels. And in particular, it tends to line the blood vessels when they get really thin. And this includes the blood vessels in your brain. So the root for typhus is a Greek word, I think, that means hazy or foggy. And that refers to the fact that it has a lot of neurological symptoms that make you sort of – I know. I know. It's the worst. And so what it's doing is it like – it's living in your blood vessels, including the ones in your brain. and it replicates and replicates and replicates until it bursts open those blood vessels.

39:58And now you've got these leaky blood vessels. That sounds bad. Super bad. And then your body responds by trying to clot and stop that leaking. And so now you've also got blood clots in your brain or in these other parts of your body. And so there tend to be a lot of neurological symptoms in the past. This parasite was associated with death rates up to 60%. If you survived, that was great. but a lot of people, you know, would not survive it. Wow. And so have there been big outbreaks of this? Is this why it's called epidemic? Yes. Yes. You shouldn't say yes so enthusiastically, Kelly. Yes. We're talking about a lot of suffering here.

40:37Why am I laughing? I'm not, right, yeah, right. I'm not excited about the suffering. I'm interested in the fact that pretty much none of us have heard of epidemic typhus. Right. Because this is like a problem that doesn't bother most of us in our day-to-day lives anymore. Yay. Yay. But for example, during World War I, the Bolshevik Revolution happened. And so Lenin and the rest of his Bolsheviks were essentially starting a civil war within Russia. They didn't want to be part of World War I anymore. So they tried to pull out. The Germans sort of kept coming anyway. And so you had this civil war happening in Russia at the same time as World War I.

41:16And things were just an absolute disaster. Epidemic typhus started sweeping through, people couldn't like wash their clothes or shower regularly enough. And something like 20 to 30 million people got infected by epidemic typhus and like two to three million people died. Oh, man. Right. During World War I. So that was obviously not good. Another thing that's kind of a bummer from the perspective of humans having this disease is that it seems to be able to like live sort of quietly in our body for a long time. So you can be fine. And then something stressful happens and now you have a less intense version of epidemic typhus, but you have epidemic typhus again.

41:58It used to be called, I think, bereavement syndrome because this would like people who would be absolutely stressed out and devastated because someone they love died would end up having epidemic typhus essentially wake back up again and make them feel miserable all over again. What's the connection between stress and the disease waking up? Ah, so like diseases, even like shingles. So shingles is when the chickenpox virus wakes back up again. Which is really bad, right? Yeah. Oh my gosh, Zach had it and he felt like he was having a heart attack. It was absolutely horrible. And so there are viruses and bacteria that can infect you when you're young.

42:32And then years later, when you get super stressed out, that can suppress your immune system. And when your immune system is suppressed, these organisms wake back up again is a very anthropomorphic way of saying it. But they take advantage of your immune system's weakened state to essentially give you the disease all over again or a slightly different version of the disease. Oh, my gosh. So shingles is like the adult version of chickenpox. And that's for people who had chickenpox as a kid, right? So chickenpox parties, bad idea. Well, yeah, right. Bad idea. Vaccinations for chickenpox, great idea.

43:03I don't expect that my children are ever going to have to suffer through shingles like my husband did. Or like I might have to. Who knows what awaits the future? Yay. A chicken pox roulette. So in this case, we're talking about a disease that's in your blood, but can lay dormant. But then when you get stressed out or you have a terrible life event, it can rear its ugly head. That's terrible. Take advantage of you when you're down. Totally terrible. Totally terrible. But, you know, for most of us in the United States, we haven't been exposed to epidemic typhus. We haven't been in like war or refugee situations because we're very lucky in that regard.

43:39But why is that exactly? is that because we just don't have very many lice or because the lice we do have are not infected or both? Both. So the big thing is that your head lice don't become body lice unless you are not showering or washing your clothes regularly. Right. And that happens more often in situations where you're a refugee or you're unhomed or it's a war. Got it. So, for example, lice diseases, this one and others, including one called trench fever, was a really big problem in World War I when they were in the trenches and they, like, couldn't get out to shower regularly. And so the lice built up to very high numbers.

44:22The head lice became body lice. And now they're transmitting disease and you're in close quarters. So it's jumping from one person to another. Got it. I see. But in the United States, there's a reservoir for the bacteria, which I won't say again so that Daniel doesn't get upset with me. And the reservoir are little flying squirrels. What? Yeah. So people who interact with flying squirrels or their nests where the lice can get left behind for a little while are some of the rare cases of epidemic typhus that you see in the United States. And when you say reservoir, you don't mean like a lake out there with water we can drink.

44:59You mean someplace where the disease is like hiding out and hanging out and waiting to strike. Quite so. Yes, that's right. That's right. So for the most part, we don't worry about epidemic typhus. If somebody does happen to get epidemic typhus, you can treat it with doxycycline, which is an antibiotic. Thank you, Big Pharma. That's right. Yeah. Yep. So being in the United States is pretty great when you are able to regularly shower and wash your clothes. Great. Hans Zinser, who's like famous for writing Rats, Lice, and History, which is like a book on epidemic typhus. I've been itching to read that book.

45:32Honestly, I don't recommend it. He goes on long tirades about like art and science, and they're not particularly insightful. And like, you got to get at least like 25 % of the way through the book before he starts talking about typhus. And you're like, get to the point. And he starts each chapter with, I'm sorry about the digression. And you're like, you should be. Get to typhus. Sounds like the book needed an editor. I know, right? So anyway, he has this great quote, Typhus will continue to break into the open whenever human stupidity and brutality give it a chance. So anyway, it happens to come along with war and refugee situations.

46:08That is a pretty great quote. That is a pretty great quote. He's got a lot of great quotes in the book. He's got another quote about how you should feel bad because the lice give up their little ghost when they die from typhus. And so maybe you should like not feel so bad about the lice. And if anybody wants a lot more detail on these diseases, they should check out the typhus episode on this podcast will kill you. Anyway, lots of additional great quotes in that podcast. I didn't mean to brush off the suffering of the lice. Yeah, that's right. I don't feel as bad for lice as I do for people. Okay.

46:41Anyway, there's also louse-borne relapsing fever. This is caused by a different kind of bacteria. It gives you fevers that kind of come and go. There's estimates that around World War I, about 5 million people died from this fever as well. And this was happening like in the trenches and stuff. And then there's trench fever, which we talked about a little bit earlier, which was a problem for the people living in trenches, but is still a problem now in some parts of the world where lice can kind of reach high numbers. But so we talked about how, you know, millions of people died during World War I from diseases transmitted by lice.

47:17There's another figure that goes around a lot when you're reading through the lice literature, as some of us do. And there is a cemetery where some of Napoleon's soldiers from the Grand Army were buried. And this was after they went to Moscow and were defeated by the Russian winter. Yeah. And about a third of the dental pulp that they went through. So sometimes you can find like evidence of bacterial infections in dental pulp in skeletons. About a third of them. Sorry, dental pulp. This is like the inner part of a tooth or something. Yeah. Yeah. The inner part of the tooth. If you can like extract that and do like genetic sequencing on it, which they were able to.

48:00They dug up all these graves? Yeah, they dug up all these graves. What? I mean, this kind of stuff happens a lot. Oh, man. For historic when you're trying to study history. Right. But anyway, they found that a third of the soldiers that were in those graves were carrying diseases transmitted by lice. And so it looks like lice might have played a role in defeating Napoleon's army in addition to the horrible Russian winters. Wow. Amazing. Yeah. But like just to really emphasize how many people died there, Napoleon went to Moscow with half a million people, came back. You want to guess how many he came back with?

48:34Let's see, 20 % died from lice, so I'm going to go, I don't know, maybe 100 ,000? 3 ,000. 3 ,000? 3 ,000. Don't sound so excited, Kelly. You're talking about human death here. Right, okay. 3 ,000. Now it sounds like you're pretending to care. Well, okay, I care, but like - It's dramatic, yeah, I agree. Yes, my voice is trying to convey like just the like mind blowing this of like, holy cow, that is so many lives. This is like, what was Napoleon doing? Anyway, history. OK, so let's wrap things up. There have been a lot of different instances throughout history where lice transmitted diseases have killed millions of humans.

49:18Lucky for us today, especially if you live in a place like the United States, when you get lice, which happens to six to 12 million kids every year. Wow. What you think is, oh, I have to go to once in a lice time again. You don't think, I hope I don't get epidemic typhus. But now I'm going to think that. Okay, well, your kids are old enough that hopefully they're not bringing home head lice anymore. No, no longer. Yeah. Yeah. And so now we treat this with like, you know, with combs and specialized shampoos. There's an interesting new treatment that people are trying out. So lice have an endosymbiotic bacteria, so a bacteria that lives inside of them.

49:56and that bacteria is critical for providing the lice with B vitamins, which are not present in human blood. And so people are trying to explore whether or not you can use antibiotics to kill the bacteria that live inside of the lice and if that will then kill the lice because they need those bacteria. Or the lice just get like the lice version of scurvy or something? Yeah, arrr, this be a bad head.

50:25All right. All right. All right. Well, this is a fascinating dive into history. It is tragic, of course, that lice terrorize people and kill so many people. But it's also fascinating that it can tell us so much about our ancient, ancient history. Or that it can confirm what we already think is happening with our ancient, ancient history. As I said, I have to be a wet blanket. But still, there's lots of interesting stuff going on here. So yes, more money to study lice. But they do tell us about this gorilla-human crossover event. Yeah, yeah. That we didn't know about before. I mean, I guess you, like, how interesting is it to know that humans interacted with gorillas in the past?

51:03Like, I would have guessed that we were killing and eating gorillas. You'd kill and eat whatever you need to when you're an ancient human. I don't know. Kelly's ancestors killed and ate gorillas all the time, it sounds like. Come on down for a gorilla barbecue at Kelly's ancestors' house. That's right. Okay, all right. Well, you're all invited. Did you say you grew up in New Jersey? Not surprised. Oh, oh. My ancestors are largely, I guess, French and Irish. And so, you know, a bunch of us might have died, you know, hiking back from Moscow with Napoleon's Grand Armée or whatever. And then during the Great Irish Famine, the potato famine around like 1845, 1848, there was also a lot of deaths because of disease at that time.

51:47Like if you are starving, you probably don't have the energy to change your clothes or shower. So epidemic typhus killed a bunch of Irish people there as well. So ancestors on both sides of my family were dying from typhus, maybe. She says gleefully. This is just the tone of voice at which I approach everything in my life. You might consider having different tones for different topics, you know. Or folks out there who want a really bright eulogy, write to Kelly. She will come to your funeral and talk gleefully about your death. Yes. If your funeral is a celebration of life, then invite me. If it is a - Celebration of lice.

52:25All right. We need to knock this off. It's time for us to go. Thanks, everybody, for taking this journey with us. Until next time.

52:39Thanks, 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. Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman. He really is a wizard. You can also find us online on Blue Sky, Instagram, and XDNKUniverse. Come engage with us. You can email us at questions at danielandkelly.org. We really do want to hear from you. And you can find our website, www.danielandkelly.org, where you'll also find an invitation to join our Discord where everybody comes and talks about the amazing universe.

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