SciShow Tangents - Cities

Episode Date: August 23, 2022

Tall buildings, subways, bodegas, rats. These are just some of the things you'll find in cities. Another thing you'll find? Science! From the smelly yet impressive sewers to the smelly yet impressive pigeons, we're covering big city science this week, baby!SciShow Tangents is on YouTube! Go to www.youtube.com/scishowtangents to check out this episode with the added bonus of seeing our faces! Head to www.patreon.com/SciShowTangentsto find out how you can help support SciShow Tangents, and see all the cool perks you’ll get in return, like bonus episodes and a monthly newsletter!And go to https://store.dftba.com/collections/scishow-tangents to buy your very own, genuine SciShow Tangents sticker!A big thank you to Patreon subscribers Garth Riley, Tom Mosner, Daisy Whitfield, and Allison Owen for helping to make the show possible!Follow us on Twitter @SciShowTangents, where we’ll tweet out topics for upcoming episodes and you can ask the science couch questions! While you're at it, check out the Tangents crew on Twitter: Ceri: @ceriley Sam: @im_sam_schultz Hank: @hankgreen

Hello and welcome to SciShow Tangents, the lightly competitive science knowledge showcase. I'm your host Hank Green and joining me this week as always is science expert sari riley hello and our resident everyman sam schultz hello if there could be an animal that doesn't exist that you wish it could exist what would it be i will answer first okay okay i thought it would be a pelican which is a pelican that's a unicorn that sounds scary yeah but i not very useful well yeah well it turns out what happened was i was i don't know if this is gonna be out yet when this podcast comes out but i keep a lookout for it i was just on uh drawfee this morning like we recorded an episode drawfee is a show where you that's very get weird prompts and then they draw the prompts and I gave them animals I wished existed. And the first one was not the pelicorn, but the second one was a pelicorn.

And it turned out not as glorious and magical and mystical as I would have liked. It was terrifying and I don't want it to exist. So pelicorn is right out. uh i don't want it to exist so pelicorn is right out but the thing that turned out really great was the tyrodosaurus rex which is a giant otter that is also a reptile and it really loves coffee and it goes hard uh and um it could totally tear you apart and kill you but it wouldn't because it's adorable and lovely and happy that's what i want to exist a happy kind thoughtful giant otter dinosaur good more happy and thoughtful animals would be nice that could yeah that's the vein i was thinking too before even learning about the tire tire how do you say it tiratus tyrod tyrod tyrod or source um i was

thinking like so a glass frog which are those tiny little guys that you can see through see their little organs they're sometimes greenish sometimes clearish but the size of a volkswagen beetle and they're very friendly very friendly that's part of the description uh and i don't know you could like ride on their backs sometimes they'd like carry you across the water they'd be a little slimy but very lovable and i don't know that's just yoshi yeah you can just hang out yeah maybe maybe what we want is yoshi and now that you've said it i would like yoshi it'd be weird to go on Drawfee and be like, can you draw a Yoshi for me?

I'm thinking of a dinosaur. Yoshi, but I want to see his heart. Yes, that's what I want then. Yoshi, but transparent so I can learn a thing. You can see his great big heart. Yeah, see his great big heart. See his little guts. That's the biggest part.

And when he eats you, you can see yourself inside. Yeah, you can see the apple-shaped blob like, go in and then squish into poop. You gotta be able to see the poop. It's important, it's vital. How else will you know he needs to poop? An animal that I wish existed was a... um... talking...

um... bird. How about that? Those exist. Those exist, Sam. Okay. Okay. Dream a little bigger. Okay.

A little bigger. Imagine, yeah. Hmm. The animal that I wish existed was a, one of them like in the Flintstones where they have the vacuum, that's an elephant. And he would vacuum your floor for you, that's great all of those animals would be great

actually if we wanted that just for some reason instead of having scissors they had like a daredevil yeah somehow yeah yeah you want that elephant that likes every kind of fuss up its nose yeah it's their favorite thing to do is just go around suck it up and say it's still living and i have to pay him every week i guess too everybody we're at size show tangents on twitter tell us which animal you wish existed and then we'll all like each other and have a good time that sounds like a great conversation for twitter i need more good i would love to do fake animals. Just hide from the other stuff. Yeah, please don't show me anything that doesn't make me happy at this point. I'm tired.

Every week here on Tangents, we get together to try to one-up, amaze, and delight each other with science facts. While also trying to stay on topic and failing. Our panelists are playing for glory, but they're also playing for Hank Bucks, which I'll be awarding as we play. And at the end of the episode, one of them is going to win. They're going to win the episode and they're going to go home feeling that particular rare joy. Now, as always, we introduced this week's topic with the traditional science poem. This week is going to be from me. A collection of people, just a few, is definitely not anything new. And a few more than that, and then again, that's a very old trend. Multiply that by a dozen and see it's starting to look a bit weird to me,

and multiply that again by 10,002. That's something that's entirely new. It can be pretty or gritty, but not itty-bitty. You can pack us together and you get a city. A city that clings to the side of a hill, a city that's home to a lumber mill, a city that clings to the side of a hill a city that's home to a lumber mill a city that needs a giant landfill a city that's just jacksonville a city that millions of people a city that's millions of people reaching for something they can't describe for thousands of years we've done this but still we do not know why that's my city poem it was a beautiful city the city is probably not a thing that's particularly easy to define, except that it is definitely a large gathering of people who all live in one place. Yep. But the lines between it, I often am not sure whether I live in a city, for example.

They're very blurry. Everyone, it seems, takes the I'll know when I see it definition approach which you know we've done for plenty of episodes here because it's easy you can say here's the line well it's almost not hard because everybody agrees that nobody knows what a city is because like it's not like like one more person moved to town we officially are a city though i think in some places it's it is legally designated um but that's just the law that That's where it gets complicated, where people have to define a city for quantitative studies. Because you know us scientists, we've got to be like, we've got to set a threshold, even if it's arbitrary. And then a bunch of people set different thresholds for laws and for studies and for, I don't know, mostly laws. And then things get complicated.

So, for example, using different countries, everyone has a different minimum population size to define an urban area or a city. So, it can be like 200 in Denmark, 2,000 in Argentina, 5,000 in India, 50,000 in Japan, even 100,000 in China, which are still like relatively small. Yeah. Well, I mean, Missoula is 70,000 and sometimes I straight call it a town. Yeah. Yeah. Yeah.

Usually it seems like from what I found across the internet, and by that I mean a couple papers that I had time to look at, is that statisticians generally have settled around at least 50,000 inhabitants, but then also a certain density of that. Yeah, you can draw a line that it has 50,000 people in it. In any place with 50,000 people. But it has to be around 1,500 inhabitants per square kilometer. Just not too, too densely packed. I don't have a comparison for that.

But it seems like the definition of city versus town versus village or whatever is people, the density of the people. or whatever is people the density of the people and then you can start layering on other sociological and other concepts like building structure cultural behavioral approach like the the diversity and languages that you find in an area are you going to classify it as a city but numbers are the easiest one to but then there's also like the reality that that's a lot of cities were used to be like a bunch of smaller towns and they just got sort of like smushed into one yeah and you know you like la is this way where it's los angeles but then it's like lots they used to be lots of different pockets that just all got connected together and and now at what point does it is it not los angeles anymore like is it and and there are even places like there's in holdings in la like i feel i think i don't know which one it is but there are little places that are like nope we're not la

we're entirely surrounded by la but we're not the vatican situation yes a vatican situation but it's burbank yeah instead of the pope it's retin link the leaders of burbank everyone knows yeah so i don't know when when that comes so a lot of languages only have a couple words for cities too it's like you got the big one you got the small one and english has three like city town. I would have guessed we had more. We have more. I guess you start subdividing Hamlet. Yeah, Hamlet.

Okay, borough. Sari, do you know anything about etymology of these words? You know, the etymology of city is just as complicated as our definition of city in that we just used a lot of words to describe places that people lived so yeah city comes from uh latin civitas or civetem um which is more applied to like citizenship or a member of a community so it's like and came from the word civis which means like a townsperson and then there was a companion word that meant a city in latin which was herbs which is a great word i don't know why we don't have words like herbs anymore uh and then it seems like historically as rome fell

and lost its prestige then herbs was out and civitas was in and then we were like we're not calling them herbs anymore we're calling them cities but they can still be urban but they can still be urban yes but the the the idea of urbanness carried on throughout history but we just don't call them urbans we call them urban centers i guess because city now yeah and we can sometimes the suburbs are the burbs which is very close to herbs but not quite there the the herbs and the burbs is the the name of every hallmark christmas special um i guess i guess it's rural usually so the herbs and the herbs and the burbs the herbs the herbs and the burbs coming together for love on christmas day always that christmas tree farm isn't gonna do its own books i think

it's on social media postings a hot shot from the herbs to come here. To the rrrrrbs. All right, before we get too deep, it's time for us to move on to the quiz portion of our show. Are you ready to be quizzed? Yes! It's going to be a city's true-to-fail. Life can be tough in the big city, and it can require lots of changes and adaptations

for humans, but also for animals. So scientists have been studying city animals, leading to some very educated hypotheses and conclusions about how our habits and buildings have changed our animal neighbors. The following are three possible tales of city-based animal evolution, but only one of them is rooted in actual scientific fact. You're going to have to tell me which one. Story number one, summers can make city streets unbearably hot, of course. But alas, animals still find themselves needing to hit that pavement. So in San Juan, the Puerto Rican crested anole or anole has been adapting its lizard body to deal with that heat by growing an additional layer of skin on its feet that shields it from all that heat on the pavement.

Hot foot. But that might not be the true fact. It might be story number two. One of the first things about going to a new city is that you got to find some new places to eat. But all that food can be overwhelming to both our choices and our bellies. To make good use of discarded takeout food throughout New York City. White footed mice have upgraded their metabolism with genetic changes that make them better able to digest fatty foods.

But that also might be a lie. And it might be this one. Story number three. In a city full of crowds and noise, it can be hard to stand out. But everybody is still looking for love, which means that everybody is also looking for clever strategies to get a date, even if they are birds. In the city of Leiden, great tits make their songs stick out to potential mates by developing new melodies that are actually copied from popular hits that can be heard on radios throughout the city. So, is it story number one, lizards developing pavement protective paws? Story number two, pizza mice?

Or story number three, great tits cover human songs to stand out in the crowd? For the first one, lizards developing little hot feet. Hot feet. That makes sense, I think. It does make sense. Yeah, it does get hot. You can't have shoes. They can't buy lizard shoes.

In this economy, no way. No. But you can walk around and just get thicker skin. I can't think of any compelling reason that wouldn't be it. Well, there are two other options. Yeah. Oh, okay. So that's the main one.

What about pizza mice, Sam? I feel like you have, you would have good thoughts. Their genome has changed to allow them to better digest fatty foods. So like mice might traditionally eat grain, but now they eat a lot of cheese.

And etc. Just like fettuccine Alfredo. Bacon. Little prosciutto. All those big city foods. They're hanging out at the Olive Garden. Well, my first thought was that white-footed mice aren't real. Is that? Are they?

No, they're real. Oh, okay. Well, that blows out of the water. Great tits are also real. I know that one. And anole lizards are also real. Anole lizards? I don't know how to say it.

I like anole better. So, I'd like to motion it be anole. Oh, Jay says anole. Anole. Oh. That don't know how to say it. I like anole better, so I'd like to motion it be anole. Oh, Jay says anole. Anole. That sounds like a pasta, though. Pizza, Maisa, eating the anole. The anole Alfredo. That was my Italian accent.

Yeah, I think, shockingly, mine was a little better than yours. The anole Alfredo. Shockingly, mine was a little better than yours. So do you, Maddox. You're the only Alfredo. Okay, well, then the third one, the tits. The tits singing the pop songs. I would say, I don't think they're known to be one of the birds that talk of Sam's mythical dreams. I don't know if they have enough mimicry, and I guess with enough urban exposure. exposure the question is do y'all know enough about great tits to know whether they're

good at mimicry i don't even know what they look like and i'm too afraid to google it no they're just like a little normal little bird they look kind of yeah they look like normal little birds like a like if you pictured a quintessential bird in a picture book they look like that i think yeah they look a little like that that's a great tit yeah no and i googled great tit just now and it is all birds those little guys ain't mimicking anything they're just going do do do do do do their heads are too small to keep all that stuff in their brain to mimic it i'm gonna go with pizza mice because i think i like the little ratatouille it's ratatouille in real life he He eats the pizza.

While you were talking, I came around on the pizza mouse thing. I think that is the one it is. Because you said the thing about they were eating grain and now they're eating cheese. I feel like that makes sense to me. And they probably can change really quickly, their genomes, right? Isn't that something mice can do? I think it's something that

happens too. It's evolution. It's natural selection. And it is a thing they probably do all species like that they're like i need to eat this cheese right away it does seem to be some indication that certain animals can evolve faster than others which is very interesting and something that maybe should also go on my scishow list if cheese is on the line you're evolving to eat also just fast generations they make a lot of babies really fast. That's true. That's one of the ways. So I will second. But lizards also make a lot of babies.

That's true. Nobody's buying your lizard story, Hank. Come on. We're going with Pizza Rat. Well, researchers have found that the Puerto Rican crested in all has been adapting its feet to city life by making them better able to climb buildings. So not. You're right. That's the pizza rats.

It turns out that like buildings are smoother than the stuff that those anoles would or anoles would normally climb in nature. And so they have adapted their feet to be better able at climbing smooth buildings. But pizza rat or pizza mouse is true. A paper published in 2017 compared white-footed mice living in parks inside New York City to white-footed mice living in parks outside the city, and the research sequenced their genetic material, and they found that in general, the city mice had changes in genes that help digest and metabolize lipids and carbohydrates. The interesting thing here is that scientists working on this paper disagree about what could be driving the changes at least

as of 2017 when the paper was published one of them thought the changes might be due to the types of plants and insects available in the city versus uh not city parks whereas the other went with the cheeseburger hypothesis where the idea is that the mice are adapting to fatty foods that are in the trash which honestly that makes a lot more sense yeah but uh figuring out the actual reason it's gonna require a little more study you got a bug in front of you and a chicken strip or whatever i mean god there's so much food inside of uh just a quarter of a hamburger yeah but the great tits this is actually really interesting too they were not mimicking songs but they did adjust their songs in different

parts of the city based on the way that noise travels so there's places where there are a lot of ambient noise which is lower frequency and in those places the tits sang higher frequency songs to be heard over that noise than in places where uh there wasn't as much of that rumbly bumbly noise they were doing some sound engineering just like our friend tuna made by frequencies pop than in places where there wasn't as much of that rumbly bumbly noise. They were doing some sound engineering, just like our friend Tuna. Make my frequencies pop, Tuna. Yeah, you great tit. Oh boy.

All right. So that means that Sam and Sari both get the point. We're going to take a short break now, and then it'll be time for the fact off. All right, everybody, get ready for the fact off. Our panelists have brought in science facts to present to me in an attempt to blow my mind. And after they've presented their facts, I will judge them and award Hank Bucks any way I see fit, with an emphasis on which one of these is going to make the best TikTok. There's a trivia question, though, to decide who goes first. In the 18th century, the city of Paris had a problem.

They had too many dead bodies lying around in mass graves in their cemeteries, creating unsanitary conditions for the city's residents. It's a problem for the city of Paris. It's not a problem for the dead people anymore. They're fine. So they decided to handle this problem by throwing those corpses into pits that the Romans had dug up long before to mine limestone. The final result is known as the Paris Catacombs, a network of tunnels under the city that are filled with the skeletal remains that have been deposited there. Approximately how many bodies were moved from those cemeteries to the Paris Catacombs?

Did you say what year it was? I said that it was the 18th century. Okay, that's a long time. I feel like for France to have been there. But I don't know when that started. You're a Halloween expert, Sam. I feel like you're going to be good at this question. What's the spookiest number?

Yeah. How many bodies is too many? How many bodies is like, it goes from being cool to, and then you start shoving them somewhere else. Skeletons are different. Bodies is one. Skeletons. Skeletons though is 700,000 skeletons. If it's 700,001 skeletons, you got to get me out of there.

Okay. Okay. I'm going to say 400,000. Six million. Oh, my God. I knew it was going to be way more than that. I did not. I have no sense of scale of big numbers.

How long would that take? Well, I think it happened over a fairly long period of time and initially the catacombs which are around 20 meters under the ground so pretty far down there uh uh it was just like sort of the bones just were kind of piled and dumped inside and then later this guy uh henry car day three that's my french accent for you just started decided i don't know if he decided or if he was sort of hired for this i assumed that somebody was paying him he started to arrange the bones into something more artful and now you can go and see these very kind of intense human remains structures that are built down in the catacombs i hope somebody somebody asked them to do that. Yeah. It's not just like,

I don't know. I didn't really know what else to do with my time. There are about 300 kilometers worth of tunnels down there. Only 1.5 kilometers are open to the public. So, 300 kilometers of tunnels will fit 6 million skeletons. Jesus. I had no idea.

I thought that that was like a religious thing. But no. The catacombs. Well, it was consecrated. They did like, sort of and skeletons jesus i had no idea i thought that that was like a religious thing but no the cat well it was consecrated they did like sort of like say this is a religious this is fine what we're doing is fine yeah put the bones there we promise it's we promise it's great god said it was cool if we did this all right sam that means that you get to go decide who goes first i think i'll go first i like to go first now i'm'm being brave. Like I said before, I'm brave. You're a monster. A monster?

Yeah. Professional. You're going after it. You're a champion. I like that. Hit the pavement. Nobody ever says anything nice about me. A lot of birds are not great at regulating heat.

They can't sweat, so they pant to cool down. But panting requires a lot of muscle movement, which also generates heat. So it's not the most efficient cool-down method. And birds' insulating feathers can also work against them by trapping lots of heat close to their bodies. So it just kind of sounds like it sucks to be a hot bird. And baby birds are babies. And much like babies are worse at everything than adults are,

baby birds are worse at heat regulation than adult birds. They mostly just have to depend on their parents sitting on them to keep them in okay temperature, which also doesn't sound like the best way to do it. But, well, they've been around for a while, so what do we know? And these bird temperature issues are exacerbated by global climate change. So I found several reports from organizations about baby birds dying in their nests or dying from trying to leave their nests too early to like find

somewhere cooler to go which is just grim and horrible and you would think that since cities are heat sinks meaning that due to what they're made out of uh cities tend to be hotter than like the area around them. Baby birds that live in cities would be doing way worse than baby birds that live in the woods. However, a recently published study looked at 760 broods of great tits. I was scared to say it, but you said it for me. From 2013 to 2018, half of which lived in cities

and half of which were in forests, and found that as the number of hot days in a given year increased, the mortality rate of city-based chicks did not increase and, in fact, seemed to decrease, I think is what the paper was saying, as opposed to forest-dwelling chicks who died more often as the amount of hot days increased, even though cities were indeed hotter than the woods that these other great tits were living in. They find the air conditioning. They go and

say go to Barnes and Noble like the rest of us. Yeah. They go into Starbucks and they get a cup of water and they just stand there for a while. A few other things that they noticed. Urban great tits usually laid fewer eggs, and their chicks had less feathers and were smaller. And these adaptations most likely come from their city slicking lifestyle so since cities were already

warmer these birds were possibly laying less eggs because less babies equals less body heat and their chicks maybe got a leg up by growing less feathers to keep cool and city birds were generally smaller which could be attributed to less food availability in cities. But the researchers also cited previous studies of city-dwelling animals like birds and insects that found that it's common for city animals to be smaller than rural ones. The rubens. Yeah, the rubens. Ruben birds. And also common for smaller animals to be more resistant to extreme temperatures.

Meanwhile, rural birds didn't have to adapt to such an extreme change, and they haven't caught up adaptation-wise as the world heats up. So, in conclusion, sorry, birds, for global warming. That's our bad. But also, they should be thanking us for building the harsh, unnaturally warm asphalt hellscapes that have prepared some of them to live in the global hellscape to come. Oh, birds are in trouble.

But those urban birds. Move to the city, birds. The urban birds are going to do great. That's weird. I want to see little pictures of these tiny little hairless baby birds. Oh, man. These tiny hairless baby tits. And I'm scared to Google great tits, more scared to Google great tit chick.

I can't look that up. Just look up baby. My parental alert will go off. Yeah. Yeah, this is my work computer. So, this seems to be another, like like could have been in the truth or fail animals adjusting to cities yeah which of course they do and um and and in lots of ways i always thought that squirrels should evolve a sort of brighter color scheme so that i they're less

likely to get hit by the car they're exactly road colored i know don't do that yeah be like bright pink all right sari what do you got So much infrastructural engineering goes into cities, like getting electricity to people safely and efficiently. An important piece of that puzzle is substations, where there are incoming power lines, outgoing lines, and a bunch of machinery in the middle that helps process the electricity in some way. That's great. I'll list some examples in case you want That's great. I'll list some examples

in case you want some electricity words. For example, some can change the voltage of electricity to make it easier to go long distance, or safe for consumers to use, so raising it or lowering it, switch from AC to DC current, or lots of other important transition-y things from big system

to personal use. And in many areas, these substations look very industrial, with steel structures supporting on the metal machinery, surrounded by a chain-link fence, and big warning signs. But that's not the case in some parts of Toronto, Canada. So the city of Toronto started to have electric power around the 1880s, supplied by private companies. But in 1911, the municipal electricity company Toronto Hydro was established, helping funnel electricity from generators at Niagara Falls, among other places, to residents. And as part of this, they needed to build more

substations in neighborhoods, especially as the urban area grew post-World War II. But instead of sticking with the classic industrial structure with keep out signs, Toronto Hydro hired a bunch of architects to disguise neighborhood substations in whatever building style the neighborhood called for. So basically, during the 1950s and 1960s, Toronto Hydro built a bunch of fake film set houses and office building shaped boxes with circuit breakers and voltage dials and heavy equipment inside them, instead of, you know, living spaces for humans. These houses still had decorative windows, landscaping, and working doors for engineers to go inside,

and if you look at pictures, they look pretty darn normal, besides the occasional chain across a driveway, or a warning high-voltage sign plastered on a door. I really looked for this, but there aren't a wealth of city planning texts online, but a 2016 conference proceeding from an architectural historian named Amy Clark describes how this sort of architectural camouflage was a big trend throughout the 20th century, not just with electrical transformers, but with public transit ventilation or other city utilities that needed to be sprinkled amongst homes. And while these buildings maybe didn't reflect an industrial strength or what was going on inside, she writes that they, quote, contributed to an experience of suburban life

that matched the aesthetic expectations of the communities, unquote, which basically means people don't like ugly things and want to pretend that they're in a little quiet little community humdrumming along, so hide all the big machines. I don't want to think about power plants. Yeah, this is also done with pump stations, which like sewage pump stations where you're like, most sewage just sort of travels downhill,

but eventually there is no more downhill to travel, so you have to pump it back up. And there's a bunch of pump stations that just look like houses. Yeah. But like literally, if you look, the windows aren't, like, you can't see through them. They're just glass in front of wood. Dark. Or, like, painted wood.

Mm-hmm. But apparently the modern electrical grid doesn't require Toronto to build these kinds of small neighborhood substations anymore, so they're gradually going out of commission. I don't know about other public utilities, how they're going. But mostly, this was weird because I didn't know that these existed. And all this makes me wonder what the next movement will be in urban planning and infrastructure. Will we still want to hide our public works or do we want to draw more attention to them so that people can know how much work and cool things like cool science is going on in our neighborhoods i don't know i wish people looked at the substation and were like wow look at what look at what we do together but the missoula we've got a substation downtown that

is right now being redone and they're you know they're putting like a big art wall around it so you can't see it and it's going to be murals and stuff, which is also cool. But I'm also like, you know, there's a lot of... Like, it's pretty amazing. You gotta go start standing down there. Giving people some talks. So I can go with Sam with the city-dwelling baby birds that might have a leg up in coping with global warming. Or Sari's old Toronto electric substations designed as houses.

And you're tied. So I really have to pick which one of these is good and better. They're both good. I'm going to go with the baby birds. Cause I was aware of the substations before. It's not a new fact to me, but it'd be a good tick tock though, but I'm going to go with the baby birds.

Now you can never do a tick tock about the other one though. It's a little, it's kind of a little bit of good news, you know, it's a little bit good news. it's like uh it's like look we can like animals can handle things if we give them the time to handle the things yeah all the animals just have to move to the city yeah everybody they'll don't worry they'll figure it out that's the good news we're good on global warming the tits have figured it out now it's time to ask the science couch we've got a listener question for our couch of finely honed scientific minds at crystal r99

and at ryan laser ask does living in a city change your physiology how about your immunity changes those birds physiology and then uh does. Lizards and mice. You know, all I can say about this before Sari goes is I feel like somebody's done some research and it's found something interesting, but I have no idea what it is. Am I right? Yeah, you're right. that that tackles this topic was published in 2010 in the journal evolution and specifically studied genetics from ancient humans or older populations of humans compared to modern and it's like a very difficult thing to study human evolution over time for a lot of reasons, but they specifically looked at 17 different human populations living across Europe, Asia, and Africa and analyzed DNA samples and found that

populations that lived in more urban settlements had higher frequencies of a gene allele that was resistant to tuberculosis and leprosy. So big diseases that spread through urban areas. And so that in itself, a lot of the clickbait articles about it, I'll be nicer to the journalists, a lot of the popular science articles about this uh equate that to well cities mean that you build up your genetic resistance to diseases no that's not individuals yeah not individuals populations populations and so you have to think of the number of people that died of those diseases and then the survivors are the ones that passed down the genetic resistance throughout generations um and so really what the study

concluded was uh generally that infectious disease loads are higher in urban environments and like seriously affect human populations to the point where genetic markers can be passed down through generations. Like it affects human evolution to that level. water, air can lead to health impacts, whether it's increased rates of asthma or cognitive disparities or all other kinds of physical illnesses, cancers, whatnot. So then there's like that portion of it, which is the different places in society for a variety of reasons affect your health in different ways and then there's the the whole idea of like should i raise my kids in a city or in the country because i don't want them to be allergic to things and that revolves around the idea of like the hygiene

hypothesis um which is the idea that in overly sanitized spaces, people worry that children are not being exposed to enough microbes or like different allergens. And so then they build up these intense immune responses to things that would otherwise be normal. There does seem to be some people who just get sick a lot less than me, particularly. And immune systems are definitely different and some appear to be better than others. Yeah.

Mine sucks. Mine's pretty good. I think I lucked out in whatever genetic lottery. I can't really smell, but everything else, I'm pretty fine. That's not ideal, but also there's some perks there. If you want to ask the Science Couch your question, you can follow us on Twitter at SciShow Tangents, where we'll tweet out topics for upcoming episodes every week. Or you can join our Patreon and get access to our Discord and ask us there. Thank you to at Cowboy Crab on Discord, at Cammy J. Boy and everybody else who asked us your questions for this episode.

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And remember, the mind is not a vessel to be filled, but a fire to be lighted. But one more thing. City sewer systems are engineering marvels. And we have a variety of ways to unclog pipes that have too much poop and other junk inside, including spraying high pressure water or scraping out buckets of waste. In addition to those modern methods though the city of paris uses an innovation that was first showcased at the

paris world's fair in 1878 giant balls these iron or wooden balls are custom fit to the diameter of various sewer pipes the biggest of them being around eight feet in diameter and they work exactly like how you'd think they would work the balls get shoved through the pipes and scrape away all the poop on the side and they push the sludge out the other side they're doing some weird stuff underground in Paris

is what we're learning today