7 Scientific Urban Legends Debunked!
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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. BIG EXCITING ANNOUNCEMENT!! We are now on Patreon! Come join our family: https://www.patreon.com/itsokaytobesmart
    For a while, you've been asking if there's another way you can support our show besides just watching and sharing the videos. The answer is now YES!!! Head over to our Patreon page to check out all the different perks, and thank you for your support… however you show it

  2. For those who actually are looking for free papers in physics, you should know that pretty much all physics papers that are published in journals are also posted on arXiv.org, where anyone can access them. Its pretty awesome and it'd be great if all fields could do that kind of thing.

  3. Supposedly if you encounter a scientific article behind a paywall, all you have to do is email the author for a copy of it

  4. When I was a kid, they told us there were 6 trillion cells in the human body. Heaven only knows where that number came from!


  5. Joe you continue to amaze. Speaking of untrue, I hear the flat earth folks are looking for a few good men ? Remember, your PUBLIC BLOG assertion they made the Giza pyramid using string, now even for a correspondence Ph.d that's a real top ten hoot. Yeah, Joe their now lining up everywhere to try your insights. String , shadows, water, how about birds (?) always 'pyramid to code' essentials. Good luck Joe, I mean who knew pseudo intellect snob appeal worked ? You are funny.

  6. I'm surprised you didn't mention the "glass is a liquid" myth. I know it's thoroughly debunked, but I've still heard people say it's a liquid semi-recently

  7. Idk bruh, i agree with you on everything except the sugar. When i give my kids cake, they strip naked and run around tearing up the house while screaming and cackling hysterically. Pretty much every single time lol

  8. Why don't I have a Wikipedia page?

    Wikipedia: You haven't been convicted of a crime, elected or appointed to a significant governmental position, and/or don't have enough money. Submission deleted.

  9. Thank you. ~ 2:2 Ratio. ~ 1 is a prime variable. Ratios do not use the unit of 1, Brains Crash.

    (Yes i know most recipes say 1table=3tea of this or that. ~ Ounce or Oz is both volume and weight, yet not in agreement, except if pure water, so call it "water volume" instead of o'u'n Contemporary Errors? Ratios with the unit of 1 get more errors, so Milli-Liters started being placed on Imperial Units which are more theme-based than mathematicals.)

  10. dude does water really freeze at 0 degrees ?? , there is super cooled water that stays liquid until disturbed , ie tap or flick , THEN it freezes

  11. I will not do business with patron. Get a pobox. I do not have much to donate and I am not about to share it with a censorship organization.

  12. I did a science today. I put it into a white and brown plastic jar and dropped it off at a path lab. I’ll get the results in two days. If I do more and don’t collect it, am I still doing sciences?

  13. 39 trillion > 37.2 trillion. The shirt isn't wrong. And won't the extra sugar give kids bodies the energy needed to stay awake when without the extra sugar or carbs, they would probably fall asleep? Like getting gas for your car. If you don't get gas when your tank is low, you'll have to stop. Once you refill your car with sugar, you can drive more.

  14. Wait, some clickbait video on YouTube is NOT where I should be getting my knowledge? Next you’re going to tell me not to listen to Buzzfeed news.

  15. One of the biggest problems are people quoting non-peer reviews science journals. One guy did a study to see how fake information could be passed on as true scientific information. One step was to publish his fake information in a non-peer reviewed journal, then it got picked up by “reporters” that don’t bother checking sources and it got passed along social media as true so much so that some tv stations picked up the story.

  16. I am a teacher and I can vouch that kids don't get hyper because of sugar intake, it's more that they get hyper and excited if a party is going on. HOWEVER– they DO get more aggressive/ impatient. Playing large motor activities can help. That is why Valentine parties are harder to cope with than Halloween, because kids are normally more able to go to the playground in October than in February due to inclement weather. But it's true, a kid will get just as 'hyper' at a party with only fruit, veggies, cheese and crackers as one with cookies and cupcakes. You just get more conflict later on with the latter.

  17. Apparently, it's only 5 debunks, plus or minus depending on which of the non-main ones you count or which ones you divide into two. If you count the one about Popeye, and separate the human and microbe cellcount from the ratio count, you get 7 debunks. If you separate the human cell count from the microbe cell count, 8 debunks.

  18. I just replaced old wrong knowledge with correct knowledge. I was military. I have always since my military days known that most of my heat escapes thru my head. Well, now I know that is not so. The answer is so obvious that it's a wonder I never realized it before. I know how layering works to keep warm, or do I?

  19. I thought the claim was that there is more microbial DNA in your body than your own, which is still true, given than a huge number of our cells – e.g. red blood cells – have no DNA.

  20. I would LOVE to know about the source to the scientific myth that glass is a liquid that flows very, very slowly. This was told to me by numerous teachers throughout my youth! They even showed us, on a field trip, an old shack out in the woods, where the glass in the window appeared to have "flowed" out of its frame.

  21. Ok… so how does cooking your spinach affect the bio-available Fe?… I was taught that spinach ONLY became an iron 'superfood' once cooked and that made it an oddity in the world of green-veggies as most green-leaf veggies don't have their iron locked-up behind the 'Rhubarb-Defense' of Oxalic-Acid-Sequestration… and to state parrot-fashion—any of YOUR comments will be (required, expected and) welcomed in the comments section.
    Regards and best wishes, Mark.

  22. Sadly most of our science is not scientific anymore. Anything with the prefix "theoretical" is subject to being completely nonsense given future experimental results. Science has become a religion that defends its weak foundations as ferociously as any other religion.

  23. What you said about vitamin C is not true. There have been many studies demonstrating that high doses of vitamin c can prevent and help with many deseases…to be honest It seems like the majority of you 'science guys' at least here on the web don't really think your own thoughts and never spend time looking at the actual evidence from both sides… I suspect that just like you published that video about microbes becouse you had read somewhere about it, you are publishing this video now with absolute no independent double checking of your sources because you have read another article somewhere else. and that being said guys, do look into the evidence advocating the use of megadoses of vitamin c… they are pretty amazing. And if you come across studies that claim to disprove its efficacy please, look at the dosage used…youll see that 90% of times they are using less than a gram of vit c.

  24. "enlightenment is a destructive process." to be enlightened you must remove all misconceptions, assumptions, and deceptions.

  25. If your children are hyperactive, it's due to a lack of park.

    Fact. Taking children to the park for over an hour and putting them to bed before 7pm with a consistent bedtime process that includes book reading, results in awesome children. Prove me wrong!

  26. How is 8 glasses of water per day a myth? Beside a "glass" being an idiotic unit of measurement, an average glass holds ~250ml so that equals 2 liters. That is about right (even a little low) for a moderately active adult living in mild climate, provided you get some additional water from food. Of course it doesn't need to be pure water, any drink counts with few exceptions (caffeinated drinks, alcohol, …).



  27. Wikipedia is the only organization I regularly donate to. It may not be perfect, but there's really nothing else like it. If wikipedia were to disappear than even more knowledge would disappear behind paywalls. I believe information and knowledge belongs to no one.

  28. D.A.R.P.A. will police the Internet to identify all the fake news so that Google, Facebook and YouTube can bury* popular alt news search results.
    You'll conveniently find what corporations only want you to know. It's driven by power and money, not about science or truth. [lol, global warming!]

    *like with a shovel.

  29. Oh my! I'm way behind! I've been watching old SciShows with you on it! Hmm…flu=binge watching. I don't think I need to find the source of that fact!

  30. So…. what about all the microbes outside of your colon? Also technically, mitochondria are microbes (they have their own DNA) and they're found in each of your cells. So at the very least, that would mean 2/3 of you is microbes.

  31. The problem is that people don’t THINK critically about what they hear other people say. I mean, one should be immediately skeptical of a claim as ridiculous as microbes in and on our bodies outnumbering our own cells by 10 to 1. I mean, how would that even work?

    If you hear something and think, “That’s incredible,” well, it probably IS. Question it.

    What have you got to lose?

  32. Dr.Luckey is A) wearing his obi(belt) incorrectly. The obi is meant to hold the kimono closed, but under the hakama (pants); B) wearing his katana upside down.
    Seems his papers aren't the only thing to suffer under-researching.😒😒

  33. 7:22 We also have microbes on our skin, nasopharynx, nasal cavity, sputum (otherwise you wouldn't holes in your teeth), hair, urinary tract and the appendix.
    Just using the colon for a calculation is like just using the brain to calculate how many nerves a human body has.

  34. You know, I really appreciate when u guys(youtubers) admit that you gave us bad information in previous videos and admit that you were wrong.

  35. Cool! When I was writing a paper, I tracked the multiple references to a paper that "proved birds do not have language". I read the original study. It was horribly designed and their conclusions reached way further than the "evidence" should have allowed.

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