Why Scurvy Shouldn’t Exist
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Why Scurvy Shouldn’t Exist


Thanks to Brilliant for supporting this whole
week of SciShow. Go to Brilliant.org/SciShow to learn more. [♪ INTRO] When you hear the word “scurvy,” you probably
think of jokes about pirates, but this disease can actually be really serious. Its symptoms include bleeding gums; bumpy, rashy skin; and joint pain, and if it’s not treated, it can be deadly. It’s not just a thing of the past, either. Scurvy still shows up in developing nations, and dozens of cases were reported in the United States in the last decade. Thankfully, it is relatively easy to treat
— all you need is a high dose of Vitamin C. But here’s the thing: If it weren’t for a quirk of evolution, nobody would have ever gotten scurvy in the
first place. The reason Vitamin C cures scurvy is because the disease is actually caused by a Vitamin
C deficiency. Without this vitamin, the body can’t properly
form collagen. Collagen is the protein that makes up the vast majority of our connective tissues, so without enough of it, things can go seriously
wrong. For example, scurvy patients can develop skin that’s thin and fragile, where any wounds
they get stay open and can’t heal. That can make them more likely to contract a life-threatening infection. Scurvy can also cause the collagen supporting blood vessels to fall apart, which can lead to hemorrhages. So this protein is a pretty big deal — and by extension, so is Vitamin C. To be clear, this vitamin isn’t the only
thing we need to make collagen. But it is the only component of the collagen synthesis process our bodies can’t naturally
produce. We need to consume it somehow. That’s why a lack of it leads to scurvy, and why a high dose of it can cure the disease. But what’s interesting is that most of nature doesn’t have to deal with this. Lots of animals can make their own Vitamin
C without consuming it in their diets. And here’s the kicker: Our very distant primate ancestors could do
this, too. More than 60 million years ago, the branch of primates that now includes humans did have the ability to make Vitamin C. But then we lost it. More specifically, we lost the ability to make an enzyme called GULO. Just like with collagen, the process of making Vitamin C is… a process. But for this story, all you need to know is that the last step depends on GULO. When you look at different animals’ genomes, you’ll see that most animals have the gene that codes for this enzyme. And those that do can tweak how much or how little Vitamin C they produce. Like, rabbits pump out way more GULO enzymes during the winter months when Vitamin C-rich
foods are in short supply, and goats can really
crank it out when they’re sick or stressed. Even animals toward the bottom of the evolutionary
tree, like sponges and jellyfish, have the gene responsible for GULO, which means it’s existed for a very long time. The only members of the no-GULO club are guinea pigs, some bats and birds, most fish… and many primates, including humans. So in our evolutionary past, our very distant
ancestors had the ability to make GULO and therefore
Vitamin C. But somewhere in primate evolution, a random mutation broke it. This might seem more than a little unfair, but you have to remember, mutations are random. Most of the time, they’re harmless and unnoticeable, but sometimes they affect an important gene. And when they do… well, it just kind of
stinks. We can tell this happened to GULO because its gene is actually still in our
genetic code — although these days, it’s just something called a pseudogene. That’s a copy of a DNA sequence that accumulated enough mutations that it
can’t perform its original job — or in the case
of the GULO gene, accumulated enough that it’s totally nonfunctional. Pseudogenes actually crop up all the time, and the GULO gene is one of about 20,000 others in our genome. For reference, we have about 27,000 genes that actually make what they’re supposed
to. So, you know… our genomes are kind of a
mess. But that’s a little beside the point here. The real question is, why did the nonfunctional GULO gene get passed down in the first place? After all, we can literally die without Vitamin
C. So it seems like the first primates to get
this broken gene should have died before they could pass it along to their offspring. Well, scientists have looked into it, and they’ve come up with a hypothesis about what happened. A part of it could be that there is some benefit to ditching the GULO gene. GULO can create hydrogen peroxide as a byproduct of its reaction, which can form
particles called free radicals when it breaks down. These are little free-floating electrons that have the potential to harm cells and make certain diseases more likely. So it seems helpful to produce as few of them
as possible. But then again… that’s a marginal benefit
at best, considering what happens without Vitamin C. So the better explanation seems to be that the GULO pseudogene wasn’t eliminated because there just wasn’t enough selective
pressure. Not making GULO is easy to compensate for if you’re an animal that consumes plenty of Vitamin C in your diet. And at the point in our ancestry where primates lost the GULO gene, they lived mostly in tropical environments, so their diets contained plenty of fruits
and vegetables. So we probably never noticed the ability to synthesize this vitamin was gone because, well, we got it pretty easily in our diets. Today, that seems pretty rough, considering that scurvy is still a problem. But unfortunately, that’s just how evolution plays out sometimes. The best we can do now is try and make sure everyone gets what they need. Scurvy isn’t anything to joke about, but there are plenty of other great jokes
you can make about storybook pirates. Like, anything about booty is a good time. Pirates are always collecting it, counting
it, and divvying it up among their crew. And if you want to experience some of that for yourself, you can check out the Logic course from Brilliant. It features a quiz that’s all about pirates, where you use your new logic skills to figure out who’s cheating whom out of the
most booty. It’s fun a time, and Brilliant also has
a bunch of other courses that can help you cultivate your math and scientific thinking skills. They’re also available offline using Brilliants iOS and Android app. So whether you’re stuck on the subway or sailing the seven seas, you’ll be able
to keep learning. If you’re one of the first 200 people to
sign up at Brilliant.org/SciShow, you’ll also get
20% off an annual Premium subscription. And you’ll be helping SciShow make more
content, too! [♪ OUTRO]

100 Comments

  • SciShow

    Go to http://Brilliant.org/SciShow to try their Logic course. The first 200 subscribers get 20% off an annual Premium subscription.

  • Aquilux R.

    "free floating electrons" something seems off about that, especially considering the graphics associated with the sentence. Are you sure it's not ions, with oxygen atoms that are down an electron pulling them from potentially important molecules around them?

  • Draeas

    At 2:00, in the diagram, what is HO? I know OH is hydroxyl and a Quora answer said they were the same thing but sometimes written differently, but why would you do that in the same diagram of a molecule? Is the HO just meant to represent H2O without the 2? Are the HO(s) (sorry, accidental pun there, although HOs do tend to be radical but they're not exactly free what with the pimps and all) the free radicals?

    I digress, it's doing my head in, Google does not give relevant results for anything these days.

  • Draeas

    If our genomes are such a mess, I think we need to petition our leaders to switch humanity to gedwarves or gehobbits and see if they work out better.

  • bel pet

    I'm willing to bet that the gene was harmless because their diets were high in vitamin c so it didn't matter at the time.

  • Alex Morrison

    Collagen is important? Tell that to my EDS. Also does this mean I'm immune to scurvy? Did I just discover that I'm a pirate god?

  • Well, I'll be damned.

    Starvation shouldn't exist either, in today's world;
    At least we're spending billions on bombs, so we can… oh…

  • Vin Chavez Castro

    "Any thing about booty is a good time"-
    "And if you wanna experience some of that for yourself"
    I honestly thought we were getting a Sci Show hookup app.

  • Hiker Bro

    Vitamin C and carbohydrates compete for use of the same metabolic pathways. If you don't consume carbohydrates, you will have plenty of Vitamin C. Increase carbohydrate consumption and you have to increase Vitamin C intake. Human blood chemistry is also much more efficient than that of other mammalian species at using available Vitamin C, using uric acid to perform antioxidant functions and converting DHA to ascorbic acid within red blood cells (https://www.sciencedaily.com/releases/2008/03/080320120726.htm?fbclid=IwAR2gz_ZiOPPNlOdBh_BwomSof-IMaJxEKVOC0lnDA-gD8Glm-VNOjndVyVA). Stop consuming carbohydrates and you won't get scurvy. It's not a defect. We are poisoning ourselves.

  • michael browne

    Why it shouldnt exist what a stupid thing to say.
    It exists so it exists moron.
    evolution morons. they say a planet shouldnt exist so it shouldnt exist with your theory so that proves evolution wrong moron. Evolutionists will never 2nd think there religion. Lol
    They found a fish from millions of years ago and says woah it survived all this time lol such morons. It shouldnt survive if evolution is true cause it should have evolved moron lol

  • unepommeverte17

    I supposedly knew someone who got scurvy in college. I say "supposedly" because they never told us who it actually was, just that someone in the organization i was in got it by living on froot loops and instant ramen. don't do that, kids!

  • adam dubin

    Cap'n says to eat your limes and kraut and stop complaining to the cook for putting it on the table! Next person to complain about it gets flogged.

  • Aumann04

    Next time put Sauerkraut in the thumbnail. That saved almost every man who had to sail over a week from getting scurvy. Without Sauerkraut America could not have been colonized. Hail the Sauerkraut!

  • WJohnM

    This explains why we call a test subject a "guinea pig". Guinea pigs are way more expensive than mice or rats–but they need vitamin C, and could be used in what were then some pretty highly publicized experiments. This is not as much fun as being a pet, but it's a step up from being a menu item, which is what the Incas used them for. Why they're called guinea pigs when they're not from Guinea and they're not pigs is a whole other question. Turkey sandwich, anyone?

  • Audrey Winter

    The way I was brought up, I couldn't even imagine, humans could live without fruit and vegetables. But scurvy in a developed country seems to indicate that people actively avoid fresh foods. Vitamin C is the most readily available vitamin in natural foods after all…

  • Blalack77

    I had to pause and address something real quick (he may answer me later in the video, but:) Could CRISPR fix the mutated pseudo gene that regulates our vitamin C? Or maybe other "deactivated" genes for that matter? Seems like that would be yet another groundbreaking use for CRISPR..

  • Neil Wilson

    Mmm, I love a keto diet. It makes me a BIG man, I can destroy the environment with beef farming, and I don't get vitamins, fiber, and other nutrients. I will lose a bit of weight, quickly, and be a fat, lethargic, miserable man at age 50.

  • fireyf

    I could not convince some idiot I know that ascorbic acid added to foods was not poison and that it's just vitamin C that we need anyways.

  • Mekratrig

    So why cant the GenMod folk come up with a "fixed" GULO? Zap the precious little zygotes with the fix and 'force correction' of the mistake evolution made.

  • Lisa Broody

    People posting scurvy isn't a big deal. I got it from arthritis meds! Believe me it's PAINFUL!! Made my gums receed permanently. Left me all f'd up. Imagine a migraine through your whole body 24/7 for a month and 1/2! Methotrexate did it to me. ( John B.)

  • SpiritWolf2K

    Vitamin C cures scurvy because the disease is caused by vitamin c deficiency

    The reason eating food helps starvation because starvation is caused by not eating food

  • DavidFMayerPhD

    Scurvy killed more sailors and ship passengers than all other causes combined (including war, storms, shipwrecks, etc) until Captain Cook discovered the preventative.

  • Happy Fox

    great, humans are genetic rejects, we get higher cognitive function but keel over when we don't have a freaking orange

  • 4111g

    So wait… Not enough pressure to select against it because the environment provides for unfit individuals? I’m glad I’ll be dead before the world looks like an only slightly less exaggerated version of that movie idiocracy.

  • Daniel Jensen

    I don't really know why we associate citrus fruits with vitamin C, it's in basically all fresh fruits and vegetables. And peppers (like jalapenos) actually have way more vitamin C.

  • Ian Foote

    Pirates were rapists, thieves and murderers. Actually not really fit subject matter for joking about in most cultures. Just learned that recently.

  • wyvern723

    When I was in college, there was a scurvy awareness day, and volunteers were handing out oranges. A friend of mine missed what was going on, and kept bring handed oranges. He broke down, was like "how did you know?" He'd just gotten over the illness.

  • Not Quite

    A friend of mine had scurvy for a bit. He ate 2 things ever : frozen chicken nuggets and lemons. He liked the lemons cuz they tingled. Doctor says to stop eating it because hes allergic and eat different things, but he stayed with eating only chicken nuggets. Then he goes to the doctor cuz hes bleeding a lot and he feels bad all the time and he keeps getting cuts.

  • Nyleve A. Vanger

    🎶What do you do with a scurvy pirate?
    What do you do with a scurvy pirate?
    What do you do with a scurvy pirate?🎶
    Just give them vitamin Sea!

  • Naomi Weneck

    This episode FEELS a lot like an episode of Mushi-Shi. (I know this is way out of left field) But, it DOES… Same energy…

  • Kieran Nurmi

    If the inability to form vitamin c us prevalent throughout all humanity doesnt that imply that the genes that replaced it provided some evolutionary advantage?

    It seems unlikely that random mutation led to the removal of that from the entire population, but I guess it was far enough in the past…

  • Vio Venda

    It blows my mind that people living in developed countries still get scurvy. You really have to try to not get enough vitamin C because it’s in everything. People really must be choosing to live off of ramen and hot cheetos

  • Mete Can Karahasan

    This evolutionist pov is killing me. Species 'branch out' when food is abundant. There are no gain of function mutations. You cannot mutate a 140kD protein. There is no evolution, there is inheritance.

  • Alex Mercer

    Strangely, evolution happens based on what we need to adapt to and based on how/where we live, it doesn't happen based on what we need to survive/live.

  • Fred Bach

    Free radicals are NOT just free floating electrons. They include the naked proton and the OH- radical, just for starters. Some of these free radicals, especially in the case of radiation, can also be thermally energetic (hot) which can cause further cellular damage.

  • Stephen Atwood

    Dozens of cases a year? In the US? Let's cheat and say 100 cases a year. With the population of the US at 325+ million (2017 numbers)…. That's 0.0000308%? It's statistically been made nonexistent, right?

  • Chris Herrick

    Given humans would only need to repair/replace the gene (instead of brand-new grafting), how difficult would this be to address using gene-therapy?

  • Engin Yeğnidemir

    Eating fresh vegetables is awful. We have to find a genetic treatment to this giant problem. Future of humankind depends on this. Lets start a global funding campaign for this issue.

  • Goog Tube

    It has been sugested with evidence that vitamin B17 helps prevent and may cure some forms of cancer. Just like vitamin C prevents scurvy. Although it is safe to use it is outlawed by the FDA. Another victory for big pharmaceuticals. The public health is the big loser.

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