7 Scientific Urban Legends Debunked!

7 Scientific Urban Legends Debunked!

Hey smart people Joe here – stay tuned for a special announcement after the video. 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. What’s up with the hair? What this shirt means is that the microbes
in and on our bodies outnumber our own cells. Most common figure is by 10 to 1. Except… that’s not true. It’s a scientific urban legend. Yet this factoid continues to be shared and
recited as fact. I’m guilty of it too, I mean, my old video
is called “You’re Mainly Microbe” and it’s literally centered around this erroneous
factoid. 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 works, and when it doesn’t. At some point the 10-to-1 bacterial to human
cell ratio became “common knowledge”. Common knowledge is information that the average,
educated person in some group–the general public, scientists, whoever–accepts as reliable
without having to look it up, like how we all know that water freezes at 0˚C. 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. I mean, if research papers cited an original
source for every single fact they presented, it would be an absolute mess. Say you wrote a paper about synthesizing some
new chemical? Do you have to cite a paper that proves chemicals
are arrangements of different atoms? Ok, then do you need to cite something to
prove that atoms exist? Maybe Einstein’s 1905 paper on Brownian
motion? Or do you have to go back to John Dalton in
the early 1800s? You can see things get ridiculous pretty fast. But! Sometimes things that aren’t true become
common knowledge, or they’re corrected later, but the new information fails to replace the
old idea. Here’s an example: I wouldn’t be surprised
if at some point in your life, you probably heard that spinach was a particularly excellent
source of iron. I certainly remember being taught that, I
can’t even remember where. 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 iron content in spinach was misreported, thanks
to a misplaced decimal point, way back in the early 1900s. Except he didn’t cite a source for the misplaced
decimal point story either. And it turns out that THAT’s a myth too. Turns out the earliest old-school measures of iron in spinach were waaaay too high, and wrong, but because of contamination, not a misplaced decimal point. It’s science! Details matter! 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. So it’s not an exceptionally great source
of iron. Incidentally, it turns out “Popeye” creator E.C. Segar chose spinach as the sailor man’s food 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 a good reminder that a good story is not necessarily
a true story. 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. Yeah, that’s not true either. That myth traces to legendary scientist Linus
Pauling. In 1966 Pauling was convinced by a random
dude named Irwin Stone that taking large doses of Vitamin C would help him live longer, and
Pauling started taking doses equivalent to 1800 glasses of orange juice every day, and
wrote books and articles claiming that the colds he had suffered from his whole life
“no longer occurred”. Even though Linus Pauling won not one but
two solo Nobel Prizes in his life, dozens of studies since have proven he was wrong,
about vitamin C. It doesn’t significantly affect colds, and the only disease it definitively
prevents is scurvy. 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. I mean, you’re gonna lose most of your body
heat through your head if that’s all that’s 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 a 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 from 1945. Except many people who cited that number ignored
the part where it said most people get a majority of the water they need from food. It’s important to stay hydrated, but 8 glasses… I mean, like what size of glasses even?! And one of the most famous is that sugar causes
hyperactivity in children. This one seems totally logical, but more than
a dozen randomized controlled trials have failed to detect different behavior between
kids given large doses of sugar and kids who weren’t. That’s right, the cake is actually a lie! Turns out when parents even think their children
have been given a drink containing sugar (even if it’s actually sugar-free), they tend
to think their kids are being hyperactive. This particular urban legend traces its origin
back to California allergy doctor Benjamin Feingold in 1973, who with little to no evidence,
recommended removing artificial colors and 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. Let’s go back to that 10-to-1 mainly microbe
cell number from the beginning. In 2010 a couple of researchers went on a
deep dive to find the original source, and 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 cells. Ten to one. Scroll down to reference #70 and we find the
source of the 100 trillion microbial cell number is this 1970 paper by Thomas Luckey,
which, when we read the paper, turns out was just a back of the envelope estimate, and
wasn’t based on any actual experiments. 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 And going back to the original 1977 paper,
the human cell number comes from reference #27, a 1970 textbook by biologist Theodosius
Dobzhansky. I dug through the internet to find a copy
of it, and right there in chapter 1, with 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 the very wrong and very widely shared fact
that human cells are outnumbered by microbes 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 microbial population is… drumroll please… 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 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 quadrillion cells in our body. What makes it so difficult is that cells in
our body vary hugely in size and how tightly packed they are, so the only way to get a
good count is to estimate each 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. Amazingly, although most of your mass comes
from muscle and bone cells, by sheer number, red blood cells make up more than 80% of the
cells in your body. bit more in favor of the microbes. 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 you poop, the ratio swings in your favor,
at least for a few hours until they get their numbers back up. Doesn’t make as catchy a shirt though… Things we consider common knowledge can be
based on bad information, and despite the amazing power of science to correct its own
mistakes and uncover better and better knowledge 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 today than ever before. Most of that science is peer-reviewed, but
peer-reviewed doesn’t always mean something is true. If one false citation makes it into the system,
it can set up a domino effect as other people cite that bad fact instead of verifying the
original. The solution? Well, for you out there in the “general
public” at least, wherever you can, even 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 available, at least not legally. Most scientific research today sits behind
paywalls, so even if you wanted to check a source, you couldn’t. Then what about this? Now, it’s easy to dump on Wikipedia. Anyone can edit it, and I mean, they have
en entire page titled “Wikipedia is not a reliable source”. It’s a paradooooox… wait, why don’t
I have a wikipedia page? Come on Kyle. But Wikipedia represents a collection of our
common knowledge. It’s the most widely read and widely accessible
information source on Earth. And at least one study has shown that Wikipedia
pages are more likely to cite scientific sources 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. 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. That is nothing to feel bad about. What matters is being comfortable enough with
the idea of not knowing everything that you’re able to replace bad knowledge when you find
better knowledge. Stay curious.

100 thoughts on “7 Scientific Urban Legends Debunked!”

  1. It's Okay To Be Smart

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  2. One I hate – the myth that glass is a liquid at room temperature. It's not. Telescopes wouldn't work if glass flowed. People don't believe it when you say it's a solid, but it is. People will respond to this comment with an incorrect definition of liquids or solids, or examples that don't actually happen.

    Glass is a solid. And you don't only use 10% of your brain. Or maybe you do, which is why you think glass is a liquid.

  3. I've been arguing about the water intake myth for a long time but it is like talking to a wall with the water police out there, "Only clear water to counts!" (_8(|) D`oh!

  4. indeed. being humble and engaging respectfully with people who don’t agree is always a good approach. Building ivory towers is never good.

  5. Props to this man for going back and correcting himself just like a real scientist would, in the case that he was wrong, which he proved again by himself.

  6. I think everyone needs to know this! "Facts" can also vary from country to country. There's been a few times when I've argued so called facts with people from the US because we're taught different facts in school.

  7. I don't practice the metric system so I don't validate the notion of 0 degrees C. My water only freezes in farenhites 32 or fewer generally speaking.

  8. The stones from Stonehenge actually came from a nearby quarry and not hundreds of miles away like some papers and documentaries have said.

    The pyramids in Egypt are next to the coasts or large rivers. It wouldn't have been hard to cut out a ditch so that the ships could unload the stones right there at the work site. There was no need to haul the stones any great distance on land.

    That electroshock therapy was painful quack science. It is still being used though and what looks like pain are induced seizures.

    That other dimensions that we cannot observe exist. The idea these other dimensions exist are much closer to religion than science.

    That an asteroid killed off the dinosaurs except that some dinosaurs survived and evolved into birds.

    That when it comes to climate change, past data can show future results.

    The idea of sea level as a tangible height. Not only do the moon and sun cause bulges and dips in the oceans, the gravity from the continents also pulls the water towards them.

  9. I thought the microbiome existed internally and externally. If they only counted the gut biome then I misunderstood the extent of our microbial family.

  10. Suggesting to a college student that everything they're being taught isn't necessarily true is a waisted effort and will get you called a "mouth breather".

  11. At 3:19, "It's another case where the correction never seems to spread as wide as the lie."
    The examples seem more like mistakes rather than lies.

  12. If we had microbes on us 10 to 1 I think we would have a clearly visible layer of microbes on our skin. Don't get me wrong, we have a LOT of cells, but 10 times that is REDICULOUS! Especially since our insides are mostly filled. Where would all of those microbes even be at??

  13. I have a love-hate for science; it's what I call an organized mess. I hate it every time I do research and find an article that I have to pay to read (right up there with microtransactions), then I have to go to the library and wait weeks for them to get it for me. Whoever said knowledge is free has never used Google.

  14. The urban legend I hear the most is about how daddy long legs are the most venomous spiders on earth buy they can't bite through our skin

  15. Hmm… my dad and I have this thing where just before we start feeling flu symptoms, we get a craving for oranges and apples. I'm curious, If vitamin C doesn't actually help, why do we have that craving? Is it for something else in oranges in apples, or is it just placebo?

  16. Joe, you perpetuated yet another myth about research paper availability.

    First and foremost, "most research is hidden behind paywalls" is completely wrong. In fact, you can easily access just about any research paper at a university library, especially one dedicated to that subject. Also, websites charging money for research papers are strictly profiteering schemes, the authors get nothing. But you can contact the author and they are usually more than happy to send you a copy for free–it benefits them to do so.

    So, you know, you really should do a lot more research into the things you pass off as "common knowledge". 🙂

  17. On the whole sugar + kids = ? debate I weigh in on the side of sugar making kids hyper, not because sugar energizes them but because it causes a release of endorphins which causes hyperactivity.

    I've spent a lot of time around kids in my day and even if there is no sugar in a treat they will get hyper.
    If you know your science then you know that the same effect can be observed in adults…
    In the brain, not outward behavior.

  18. Just wanted to say, I have come back to people I have given false "common knowledge" to, after doing some research, and they are always either, "meh", or are appreciative that I taught them something new.

  19. The lessons here applied to science can also be applied to politics. People still believe untrue things that are demonstrably false, but widely spread as common knowledge because it confirm a bias or conforms to a popular opinion. So fact checking is just a good habit.

  20. Growing up i HATED writing research papers. We did them every year in jr high, highschool, and college in every class. The main point being to cite sources. I HATED it. But now i understand why and appreciate it very much.

  21. Allan Bruno Petersen

    Your ability to absorb iron from such a food as spinach largely depend on your microbiome + your iron status + what else you ate. Lots of science on this topic can be found on nutritionfacts.org website.

  22. Phew! I was worried there!
    Luckily for me, I never cited the 10-1 ratio in favour of microbes, just that they had a straight majority, so it looks like I'm still good.

  23. Something I recently realized about Wikipedia, for the most part they seem to just translate it 1 for 1, but depending on the subject and the language you can get different information.

  24. This is getting expensive though, I said I wouldn’t be able to go more than £30 a month which is quite a lot for me, so every time I join a new Patreon I’ve now got to delete another. However you are worth it Joe, I've enjoyed every video you’ve done!

  25. The microbe count doesn’t take into account surface microbes on the skin, or inside other…um…internal volumes. Nor does it account for mitochondria. I think if you want to include those, it’s probably still OK to say we’re “mostly” microbe 😉

  26. Interestingly, people will still vigorously defend the Vitamin C myth…with personal anecdote, rather than with scientific research or any scientific approach at all. For them, facts don’t matter; only experience matters. They should look into the phenomenon of The Placebo Effect 😂

  27. how do scientific urban legends persist today?
    well, I'd say they're to science what meme are to "pop culture"… most peoples don't even know where they originate from but they use them

  28. There is another false factoid in science. It is such common knowledge that angular momentum is conserved that people instantly ignore any contrary suggestion … but it isn’t. www.baur-research.com/Physics

  29. Use simple logic. Heat rises. Humans are bipeds. The idea that we lose most our body heat through our heads (I fact I have personally witnessed through thermal imaging) is because of these two facts. Same as pigs lose most of their body heat through their backs.

  30. So I'm about half microbe to half human. Pooping removes about 1/3 of my microbes. Therefore, pooping removes 1/6 of my body. If I am about 150 lbs (68 kg) then according to math my poop is then 25 lbs (11 kg). Flawless logic.

  31. The idea is that vitamin c is a necessary vitamin that your body can't make and can easily get rid of it in excess. So when your sick you have all your necessary nutrients. Good health isn bad when you're sick.

  32. Calling debunked information a lie might be a bit of a falsehood as well. A lie requires intent to spread a falsehood. Many of these were just simply wrong information, not necessary lies.

  33. I call bullshit on "sugar not making kids go super sonic".. I've worked as a teacher for years and without a doubt it does affect them, whether it's endorphins being released due to getting a glass of lemonade att school or a piece of cake at recess it DOES affect them.

  34. I laughed at the 8 glasses of water. What size of glass? EXACTLY. This is the problem with the murican unit system… whose foot is a foot? 😀 Oh and don't even get me started on recipes calling for 2 spoonfuls of something…

  35. There are a few times in life I have noticed somethings don't work like we've been taught or that knowledge in a certain subject has been updated without notice.
    That occurance has made my life difficult at the times I have to stop and say to myself "but I always thought…" Now I've become the person who gives out advice on many things and I am really good at trivia because I read a lot, often. Sometimes when things are discovered that change what we once knew and the knowledge doesn't spread, it can cost you an entire game of Trivial Pursuit. So sad.

  36. Hey! From a pedagogic point of view: there are allot of distractions in your video, and sometimes a little pause to think about some cool fact would be nice. Like your videos!

  37. Regarding #1, how could you even fall for that myth? If your microbes would outnumber your cells 10 to 1 it means your weight and volume would be from 50 to 90% microbes… and that's of course absurd. It takes a minimum of logic to realize it is wrong.

  38. It's so refreshing to see someone admit they were wrong about something and are willing to not only change their opinion but also try to spread the correct info. Thank you so much for this. It help me correct some of my own miss information

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