7 Scientific Urban Legends Debunked! |Urban|Legends|debunked 7 Wissenschaftliche Urban Legends entlarvt! 7 leyendas urbanas científicas desmentidas 7가지 과학적 도시 전설이 밝혀졌습니다! 7 Wetenschappelijke Urban Legends Ontkracht! 7 lendas urbanas científicas desmascaradas! 7 научных городских легенд развенчаны! 7 個科學都市傳說被揭穿！

Hey smart people Joe here - stay tuned for a special announcement after the video. ||||||||||announcement|||

So I used to have this shirt.

I know at least one of you was watching back in 2013…

Hey Kyle.

For the rest of you are probably wondering the same thing as me. El resto de ustedes probablemente se pregunten lo mismo que yo.

What's up with the hair?

What this shirt means is that the microbes in and on our bodies outnumber our own cells. |||||||microbes||||||outnumber|||

Most common figure is by 10 to 1.

Except… that's not true. Excepto que... eso no es verdad.

It's a scientific urban legend. ||||legend

Yet this factoid continues to be shared and recited as fact. ||fact||||||repeated|| Toch wordt dit feit nog steeds gedeeld en als feit gereciteerd.

I'm guilty of it too, I mean, my old video is called “You're Mainly Microbe” and ||||||||||||||Microbe|

it's literally centered around this erroneous factoid. |||||erroneous| se centra literalmente en este hecho erróneo. het is letterlijk gecentreerd rond dit foutieve feit.

It turns out that urban legends like this are surprisingly common, even in science,

and how they begin and the reasons why they persist can teach us a lot about how science |||begin||||||persist||teach||||||

works, and when it doesn't.

At some point the 10-to-1 bacterial to human cell ratio became “common knowledge”. |||||bacterial|||cell||||

Common knowledge is information that the average, educated person in some group–the general ||||||average|educated||||||

public, scientists, whoever–accepts as reliable without having to look it up, like how we |||accepts||reliable|||||||||

all know that water freezes at 0˚C. ||||freezes||

We all know that, right?

Somewhere along the line, people stopped asking where this “common knowledge” came from.

There are countless facts in science that have become common knowledge. ||countless|facts|||||||

I mean, if research papers cited an original source for every single fact they presented, |||||cited||original|||||||

it would be an absolute mess.

Say you wrote a paper about synthesizing some new chemical? ||||||synthesizing||| Supongamos que escribes un artículo sobre la síntesis de una nueva sustancia química.

Do you have to cite a paper that proves chemicals are arrangements of different atoms? ||||cite|a||||chemicals||arrangements|||atoms

Ok, then do you need to cite something to prove that atoms exist?

Maybe Einstein's 1905 paper on Brownian motion? |Einstein's|||Brownian| ¿Quizá el artículo de 1905 de Einstein sobre el movimiento browniano?

Or do you have to go back to John Dalton in the early 1800s? |||||||||Dalton||||

You can see things get ridiculous pretty fast. |||||ridiculous||

But!

Sometimes things that aren't true become common knowledge, or they're corrected later, ||||||||||corrected|

but the new information fails to replace the old idea. ||||||replace|||

Here's an example: I wouldn't be surprised if at some point in your life, you probably ||||||surprised|||||||||

heard that spinach was a particularly excellent source of iron. ||spinach|||||||iron

I certainly remember being taught that, I can't even remember where. ||||taught||||||

And–you can probably guess where I'm going with this–it's not true.

In 1981, a biologist named Terry Hamblin studied historical science papers and realized the ||||Terry|Hamblin||historical|||||

iron content in spinach was misreported, thanks to a misplaced decimal point, way back in |content||||misreported||||misplaced|decimal|||| El contenido de hierro en las espinacas se comunicó erróneamente, gracias a un punto decimal mal colocado, hace ya mucho tiempo.

the early 1900s.

Except he didn't cite a source for the misplaced decimal point story either. Excepto que tampoco citó una fuente para la historia del punto decimal mal colocado.

And it turns out that THAT's a myth too. |||||||myth|

Turns out the earliest old-school measures of iron in spinach were waaaay too high, ||||||||||||way|| Resulta que las primeras medidas de hierro en las espinacas eran demasiado altas,

and wrong, but because of contamination, not a misplaced decimal point.

It's science! Details matter! ||details|

Spinach actually does contain large amounts of iron, as much as red meat in some cases,

but it also contains compounds that make the iron it does have harder for us to absorb. |||contains|compounds||||||||||||

So it's not an exceptionally great source of iron. ||||exceptionally||||

Incidentally, it turns out "Popeye" creator E.C. Segar chose spinach as the sailor man's food by the way||||Popeye|creator|||Segar|chose||||sailor|| Por cierto, resulta que el creador de "Popeye", E.C. Segar, eligió las espinacas como alimento del marinero.

of choice for its high vitamin A content, not because of iron.

It's another case where the correction never seems to spread as wide as the lie, and it's |||||correction|||||||||lie||

a good reminder that a good story is not necessarily a true story. ||reminder|||||||necessarily|||

And I'm willing to bet that at some point in your life, you've taken vitamin C to

help cure or prevent a cold. |cure||||

Yeah, that's not true either.

That myth traces to legendary scientist Linus Pauling. ||traces||legendary||Linus|Pauling Ese mito se remonta al legendario científico Linus Pauling.

In 1966 Pauling was convinced by a random dude named Irwin Stone that taking large doses |||||||guy||Irwin|Stone||||doses

of Vitamin C would help him live longer, and Pauling started taking doses equivalent to |||||||||||||equivalent|

1800 glasses of orange juice every day, and wrote books and articles claiming that the ||||||||books||articles|claiming|| 1800 vasos de zumo de naranja cada día, y escribió libros y artículos afirmando que la

colds he had suffered from his whole life “no longer occurred”. |||suffered|||||||occurred resfriados que había padecido toda su vida "ya no se producían".

Even though Linus Pauling won not one but two solo Nobel Prizes in his life, dozens |||||||||solo||Prizes||||dozens

of studies since have proven he was wrong, about vitamin C. It doesn't significantly ||||proven|||||||||significantly de estudios desde entonces han demostrado que estaba equivocado, sobre la vitamina C. No significativamente

affect colds, and the only disease it definitively prevents is scurvy. affect|||||disease||definitely|prevents||

Yet somehow the cold myth still continues today.

Or maybe you've heard that you lose most body heat through your head?

That urban legend goes back to one military study in the 1950s where people were left

out in the cold with no hats on. ||||||hats|

I mean, you're gonna lose most of your body heat through your head if that's all that's Quiero decir, vas a perder la mayor parte de tu calor corporal a través de la cabeza si eso es todo lo que es

exposed.

Today scientists know the amount of body heat you lose depends on the total surface area

exposed, but parents everywhere are still making sure you don't leave home without ||parents||||||||||

a hat. |hat

You also don't need to drink 8 glasses of water a day.

That urban legend probably goes back to one set of dietary recommendations for water intake ||||||||||dietary|recommendations|||intake Die stedelijke legende gaat waarschijnlijk terug op één reeks voedingsaanbevelingen voor waterinname

from 1945.

Except many people who cited that number ignored the part where it said most people get a majority |||||||ignored||||||||||majority

of the water they need from food.

It's important to stay hydrated, but 8 glasses… ||||hydrated||

I mean, like what size of glasses even?!

And one of the most famous is that sugar causes hyperactivity in children. ||||||||||hyperactivity||

This one seems totally logical, but more than a dozen randomized controlled trials have ||||logical||||||randomized||trials| Esto parece totalmente lógico, pero más de una docena de ensayos controlados aleatorios han

failed to detect different behavior between kids given large doses of sugar and kids who failed||detect||||children||||||||

weren't.

That's right, the cake is actually a lie! |||cake|is||| Así es, ¡la tarta es en realidad una mentira!

Turns out when parents even think their children have been given a drink containing sugar (even |||||||||||||containing||

if it's actually sugar-free), they tend to think their kids are being hyperactive. |||||||||||||hyperactive

This particular urban legend traces its origin back to California allergy doctor Benjamin ||||||origin||||allergy|doctor|Benjamin El origen de esta leyenda urbana se remonta al médico californiano especializado en alergias Benjamin

Feingold in 1973, who with little to no evidence, recommended removing artificial colors and Feingold||||||||recommended|removing|||

flavors from the diets of hyperactive children, and I guess people were like “why not sugar

too!”

I mean, kids are just kids, and they're gonna go nuts some times. ||||||||||crazy||

Let's go back to that 10-to-1 mainly microbe cell number from the beginning. ||||||||||||beginning Volvamos a ese número de células microbianas principalmente de 10 a 1 del principio.

In 2010 a couple of researchers went on a deep dive to find the original source, and |||||||||dive||||||

the paper cited most often was this one, from 1977.

It states the human body contains 100 trillion microbial cells and 10 trillion of its own |states||||||microbial||||||

cells.

Ten to one. ten||

Scroll down to reference #70 and we find the source of the 100 trillion microbial cell Scroll|||reference||||||||||

number is this 1970 paper by Thomas Luckey, which, when we read the paper, turns out was |||||Thomas|Luckey|||||||||

just a back of the envelope estimate, and wasn't based on any actual experiments. |||||envelope||||||||experiments лише приблизною оцінкою, яка не ґрунтувалася на жодних реальних експериментах.

This has nothing to do with the rest of the video, but I just have to mention Dr.

Luckey was literally an honorary samurai, which is awesome ||||honorary|samurai|||

And going back to the original 1977 paper, the human cell number comes from reference

#27, a 1970 textbook by biologist Theodosius Dobzhansky. |textbook|||Theodosius|Dobzhansky

I dug through the internet to find a copy of it, and right there in chapter 1, with |dug|||||||||||||||

absolutely zero supporting evidence, is the claim that a human body contains ten trillion

cells.

And there you have it.

A back of the envelope estimate combined with a totally unsupported approximation to create ||||||||||unsupported|approximation||

the very wrong and very widely shared fact that human cells are outnumbered by microbes |||||widely|||||||outnumbered||

10-to-1.

Right about now you're probably wondering what the real numbers are.

First, the original estimate for microbes living inside us was calculated using the

volume of the entire lower intestine.

But the vast majority of your body's microbes live in your colon, which is only a portion

of that volume.

And yes, that's where your poop is made.

Using a more accurate volume of the average colon–409 milliliters–and the number of

bacteria we typically find per volume of poop, in 2016 researchers calculated that your inner ||||per|||||||||inner

microbial population is… drumroll please… |||drumroll|

39 trillion.

Not 100 trillion.

And as for the number of cells in the human body?

This is a seemingly simple question that you might assume we biologists have known for |||seemingly|||||||||||

a long time.

But the truth is, until very recently, no one really knew.

Over the past couple centuries, estimates have ranged from 5 billion to more than a |||||||ranged||||||

quadrillion cells in our body. quadrillion|||| quadriljoen cellen in ons lichaam.

What makes it so difficult is that cells in our body vary hugely in size and how tightly |||||||||||vary|greatly|||||tightly

packed they are, so the only way to get a good count is to estimate each organ individually. ||||||||||||||||organ|individually

And that's what a group of researchers did in 2013.

Based on actual evidence, their new number is… 37.2 trillion cells in the average human

body.

That makes the ratio of microbe to you more like 1 to 1… pretty much even stevens. ||||||||||||||stevens

Amazingly, although most of your mass comes from muscle and bone cells, by sheer number, Amazingly|although|||||||muscle|||||sheer|

red blood cells make up more than 80% of the cells in your body.

bit more in favor of the microbes. трохи більше на користь мікробів.

But remember how I said almost all of your inner microbes live in your colon?

Well, you lose almost a third of them every time you have a bowel movement, so every time |||||||||||||bowel|movement|||

you poop, the ratio swings in your favor, at least for a few hours until they get their ||||swings|||||||||||||

numbers back up.

Doesn't make as catchy a shirt though… |||catchy||| Але це не робить сорочку такою ж помітною...

Things we consider common knowledge can be based on bad information, and despite the ||||||||||||despite|

amazing power of science to correct its own mistakes and uncover better and better knowledge ||||||||mistakes||uncover||||

over time… that good knowledge doesn't always spread out and replace the bad knowledge.

So how do these scientific urban legends continue to persist?

More scientific journals exist today than ever before, and we're doing more science ||journals||||||||||

today than ever before.

Most of that science is peer-reviewed, but peer-reviewed doesn't always mean something |||||peer|reviewed||||||| Більшість цих наукових досліджень рецензуються, але рецензування не завжди щось означає

is true.

If one false citation makes it into the system, it can set up a domino effect as other people ||false|citation|||||||||||domino|effect|||

cite that bad fact instead of verifying the original. ||||||verifying||

The solution?

Well, for you out there in the “general public” at least, wherever you can, even |||||||||||wherever|||

if you think something is common knowledge, try to learn where it came from.

You might be surprised by what you find.

But that's easier said than done, because most published science today isn't freely ||||||||published||||freely

available, at least not legally. ||||legally

Most scientific research today sits behind paywalls, so even if you wanted to check a ||||||paywalls|||||||| Het meeste wetenschappelijk onderzoek zit tegenwoordig achter betaalmuren, dus zelfs als je een

source, you couldn't.

Then what about this?

Now, it's easy to dump on Wikipedia. ||||post||Wikipedia

Anyone can edit it, and I mean, they have en entire page titled “Wikipedia is not ||edit|||||||an|||titled|||

a reliable source”.

It's a paradooooox… wait, why don't I have a wikipedia page? ||paradox|||||||| Het is een paradox... wacht, waarom heb ik geen wikipedia-pagina?

Come on Kyle.

But Wikipedia represents a collection of our common knowledge. ||||collection||||

It's the most widely read and widely accessible information source on Earth. |||||||accessible||||

And at least one study has shown that Wikipedia pages are more likely to cite scientific sources ||||||shown|||pages|||||||

that are freely available.

This isn't an ad for Wikipedia, it just seems like if you want to get good science

out to the broadest audience, making it freely available is not a bad place to start. |||broadest|audience||||||||||| |||mais ampla||||||||||||

The point, to me at least, is pretty clear.

If you want common knowledge to be true, you have to let true knowledge be common.

Every one of us carries quite a few pieces of incorrect knowledge in our heads. ||||||||||incorrect||||minds

That is nothing to feel bad about.

What matters is being comfortable enough with the idea of not knowing everything that you're ||||comfortable||||||||||

able to replace bad knowledge when you find better knowledge.

Stay curious.