Articles, Blog

The Viral Origins of the Placenta

December 21, 2019


This is the placenta. And without it, you would never have been born. This amazing organ is a lifeline connecting mother and baby, as well as a defensive barrier between them. The placenta provides the baby with oxygen and nutrients, carries away waste, filters out harmful microbes, and pumps out hormones– all while keeping maternal and fetal blood supplies completely separate. But we might never have evolved a placenta like this if it wasn’t thanks to an infection… with a virus. Viruses are excellent at making more copies of themselves. Some viruses do this by inserting their own genes into the host’s DNA. This tricks the infected host into doing the virus’ dirty work: producing viral proteins to build more viruses to infect more cells. Very rarely, one of these viruses will infect a sperm or an egg cell. And as the the new organism grows, these viral genes are also copied into every single one of its cells, ready to be passed down to future generations. In other words, changing the whole genome of the host forever. In fact, if we looked into your entire genome, around 8% of it originally came from viruses. So, you could say that we’re all part virus. Most of these viral genes no longer work. They’re like dead viral fossils in our DNA. However, some of them have been resurrected, including one gene that’s fundamental in the formation of the placenta. The human placenta is a blend of maternal and fetal tissue. And the way it forms is incredibly invasive. After the embryo implants into the womb, finger-like projections burrow into the maternal tissue and alter its blood vessels so that they become bathed in a constant supply of the mother’s blood. This interface, which has a surface area of twelve square meters, is what allows mother and fetus to exchange nutrients and waste. And yet, such close contact means that the mother’s immune system could attack the developing embryo, which it sees as a foreign invader. And in a way, it kind of is. As a first line of defense, the fetal cells along this boundary fuse together, using a protein called syncytin. This removes any gaps where maternal white blood cells could squeeze through and launch an immune attack. It’s a clever strategy, but we didn’t come up with it entirely on our own. That’s because syncytin was originally a viral protein. That virus used syncytin to fuse with cells so it could infect them. And sometime in the past, during one of those ancient viral infections, a virus inserted the gene for syncytin into the genome of its host. Once it was inherited, that gene may have lain dormant for generations. But eventually it was repurposed by evolution to fuse cells together in the placenta. The interesting thing is that in some ways, a developing fetus is a little bit like a virus, in that it exists inside the body of another organism where it tries to avoid detection by the immune system. So perhaps it’s fitting that syncytin, which helps the placenta to invade the womb, originally helped a virus to invade its host.

89 Comments

  • Reply Ethan December 10, 2019 at 6:03 pm

    You mean it came from a MEME?!?!

  • Reply Sam Harper December 10, 2019 at 6:06 pm

    Had absolutely no idea. Thank you so much.

  • Reply voctier December 10, 2019 at 6:08 pm

    Very interesting and informative content! Although the animations were less than helpful as the weirdness kept distracting me from the narration. Next time, please choose something less psychodelic.

  • Reply frits germs December 10, 2019 at 6:12 pm

    fantastic. quality production. the placenta was crucial as an advantage for mammals.

  • Reply MappaCrappa December 10, 2019 at 6:13 pm

    All the more reason to liken humans to viruses… nice.

  • Reply نور الإلحاد December 10, 2019 at 6:17 pm

    Interesting topic but horrible graphic presentation. The topic is too complex and the graphics is played too fast. Hard to understand anything. Or perhaps I am just too dumb for this.

  • Reply piranha031091 December 10, 2019 at 6:20 pm

    The subject discussed is fascinating, but the animation is really unhelpful. It's just weird and confusing.

  • Reply Jimmy Ezra December 10, 2019 at 6:20 pm

    MMMMMagical…….!!!! Loved it …thanks

  • Reply Constantina Mylona December 10, 2019 at 6:26 pm

    The animations are not really helpful but the info is mind blowing.

  • Reply jesse dampare December 10, 2019 at 6:26 pm

    Am i the only one trying to understand the animation? Cause it didn’t help at all. Great content though

  • Reply Opin-Eon December 10, 2019 at 6:32 pm

    Interesting and informative.
    I wouldn't be surprised if it went viral.?

  • Reply superj1e2z6 December 10, 2019 at 6:32 pm

    The animations are amazing but it's too overpowering

    Edit: although if there was a song about the placenta, this would like a sick music vid

  • Reply Adymn Sani December 10, 2019 at 6:33 pm

    love this line of thinking, but could the protein just as easily been developed by the human species too, much in the same way of thinking that we say the eyes have been separately developed by different species?

  • Reply Sandcastle • December 10, 2019 at 6:33 pm

    First it was mitochondria, now its placentas. When will these foreign immigrants stop!

  • Reply Damian Reloaded December 10, 2019 at 6:42 pm

    Agent Smith was totally right

  • Reply CarthagoMike December 10, 2019 at 6:44 pm

    Now if only this video would go viral

  • Reply Andrew Bond December 10, 2019 at 6:46 pm

    Agent Smith likes this video.

  • Reply Dragon Slayer Ornstein December 10, 2019 at 6:47 pm

    Actually no, we still invading our parents by being their borned children. Basement anyone?

  • Reply Jesse H. December 10, 2019 at 6:50 pm

    That animation was wicked cool. Reminds me of something Felix Colgrave would do.

  • Reply Photonic Pizza December 10, 2019 at 6:52 pm

    Good topic, and the narration is nice, but the animation is unhelpful, and at points just confusing and disorienting.

  • Reply Alec Hill December 10, 2019 at 6:55 pm

    My opinion is…the visuals complemented the audio. Overall I had a great time.

  • Reply Sara Murphy December 10, 2019 at 7:00 pm

    Too bad we couldn't have actual footage of placenta and/or viruses instead of the weird animation which, I agree was terrible. Otherwise it was interesting.

  • Reply Therese Assar December 10, 2019 at 7:12 pm

    awesome information but the animations was distracting. beautiful but distracting. i had to try to listen rwther then watch to follow the story

  • Reply OutOfSight123 December 10, 2019 at 7:16 pm

    Only 4 minutes? =(

  • Reply john December 10, 2019 at 7:21 pm

    One thing missing is when approximately the virus invaded a non-placental species – I’m guessing several hundred million years ago?

  • Reply Abhinav Tripathi December 10, 2019 at 7:31 pm

    Glad to see the Monty Python back.

  • Reply Atlas WalkedAway December 10, 2019 at 7:34 pm

    Cool explanation, but the visuals were an incoherent trip that contributed nothing functionally and possibly detracted from the understanding of those with less of a knowledge base in the subject.

  • Reply Rafael Feldner December 10, 2019 at 7:42 pm

    Remarkable strange animations?

  • Reply StaringCompetition December 10, 2019 at 7:45 pm

    There is nothing wrong with the animation per se, only that I struggled to connect any of what was represented with what was being said. Abstract indeed. The auditory information was complex enough grasp that I had to pause or go back many times, due to conflicting visual content.

  • Reply James Moss December 10, 2019 at 7:53 pm

    Nice animations, but I found them very unhelpful in terms of understanding the content.

  • Reply Oracojisan December 10, 2019 at 7:54 pm

    This video makes more sense if you keep your eyes closed

  • Reply John Lonergan December 10, 2019 at 7:57 pm

    Irrelevant and distracting animations.

  • Reply PedoDorf December 10, 2019 at 8:02 pm

    Agh, I have been bamboozled again, please remind me that placenta is not a placebo.

  • Reply b. griffin December 10, 2019 at 8:04 pm

    nice. so we're going to see more of these RI nuggets?

  • Reply b. griffin December 10, 2019 at 8:04 pm

    I gather from this immunity evolved before the placenta.

  • Reply b. griffin December 10, 2019 at 8:04 pm

    any idea of when this cinciten (sp?) infection originally took place?

  • Reply b. griffin December 10, 2019 at 8:11 pm

    RI nuggets, so tasty!

  • Reply LUCE December 10, 2019 at 8:33 pm

    Does this mean mammals in a whole were inventd by viruses?

  • Reply Nandodando December 10, 2019 at 8:40 pm

    WTF was with that animation? 🙂

  • Reply vortex42studios December 10, 2019 at 8:48 pm

    Fascinating!

  • Reply Tony Blakeney December 10, 2019 at 9:04 pm

    In other words, the root "cause" of placental mammals.

  • Reply Milos Marinkovic December 10, 2019 at 9:30 pm

    This was way more creepy than it should have been!

    (impressed&confused slow clapping)

  • Reply Natural D’Vaughn December 10, 2019 at 9:45 pm

    That was weird as f*ck, but so cool. Thanks for sharing!

  • Reply cybermbebe December 10, 2019 at 9:57 pm

    Does it mean the motherhood is a form of a stockholm syndrome?

  • Reply Micke Nordin December 10, 2019 at 9:58 pm

    I really liked the animations, nice job.

  • Reply The Trevor December 10, 2019 at 10:23 pm

    I agree, the animations could have been scrambled, shown in any order, and/or reversed, without adding to, or detracting from their meaning. If anything, they were a distraction, obscuring the meaning of the narration.

  • Reply xBris December 10, 2019 at 10:38 pm

    The animations in this video are terrible. I've got a PhD in biochemistry and understood maybe half of them (the script was good though). The animations are both too detailed and too artistic. They're more or less useless.

  • Reply Dominic Roseland December 10, 2019 at 10:38 pm

    Who knew Pink Floyd did Placenta vids?!

  • Reply NARODIAZ December 10, 2019 at 10:40 pm

    Subtitles please!

  • Reply Kate S December 10, 2019 at 11:05 pm

    I have always found a mode of reproduction of placental mammals to be rather disgusting. Thanks for making me even more convinced that birds (and other theropods) are a superior life form LoL

  • Reply Jérôme Vuarand December 10, 2019 at 11:25 pm

    Both the title and description are gross exaggerations. It's one single protein among many many others that make up a functioning placenta, and I'd bet there were proto-placentas before that protein became a part of it. And it wasn't embedded in the human genome: it wasn't human when the viral DNA got into the genome, and it still wasn't human when the gene got reactivated.

  • Reply DNTME December 10, 2019 at 11:45 pm

    I don't know why everyone is going on about the animation. I found it entertaining. And, no, I was not smoking anything at the time.
    There is even more on this general topic as well. Such as how the mother's and father's contribution are actually at odds with each other on a genetic level. Each doing their own thing towards their own self-centered ends. It is not a perfect cellular union. The male wants his offspring (be it either male or female) to get the maximum possible amount of nutrients from the mother. This, even to her detriment. The mother, on the other hand, wishes to pass on her genes but , of course, wants to live to produce more offspring. This reproductive tug-of-war has led to what is termed genetic imprinting. That is to say, paternally supplied genes tend to promote growth while maternal ones tend to reduce it. For example, in the placenta, the fathers allele for the Insulin Growth Factor 2 is expressed while the receptor for Igf2 is controlled by the allele of the mother. Our genes are compatible for the sake of reproduction, but, even on the cellular level, we are at odds with our final objectives. To say our genes are compatible is not really saying much. Most of the genes for all mammals are compatible. It is only in small ways they differ, making producing offspring unlikely or impossible. Thus, men and women can be thought of as different as humans and cats at the genetic level.

  • Reply DNTME December 10, 2019 at 11:46 pm

    I don't know why everyone is going on about the animation. I found it entertaining. And, no, I was not smoking anything at the time.
    There is even more on this general topic as well. Such as how the mother's and father's contribution are actually at odds with each other on a genetic level. Each doing their own thing towards their own self-centered ends. It is not a perfect cellular union. The male wants his offspring (be it either male or female) to get the maximum possible amount of nutrients from the mother. This, even to her detriment. The mother, on the other hand, wishes to pass on her genes but , of course, wants to live to produce more offspring. This reproductive tug-of-war has led to what is termed genetic imprinting. That is to say, paternally supplied genes tend to promote growth while maternal ones tend to reduce it. For example, in the placenta, the fathers allele for the Insulin Growth Factor 2 is expressed while the receptor for Igf2 is controlled by the allele of the mother. Our genes are compatible for the sake of reproduction, but, even on the cellular level, we are at odds with our final objectives. To say our genes are compatible is not really saying much. Most of the genes for all mammals are compatible. It is only in small ways they differ, making producing offspring unlikely or impossible. Thus, men and women can be thought of as different as humans and cats at the genetic level.

  • Reply dzhiurgis December 11, 2019 at 12:05 am

    Damn this is way too psychedellic

  • Reply aLOOF gOALS December 11, 2019 at 12:22 am

    I spent the majority of the time trying to work out what the animations were trying to represent.

  • Reply Drew Fisher December 11, 2019 at 1:10 am

    Simply mindblowing

  • Reply Karlo Montano December 11, 2019 at 1:56 am

    I liked this; my brain was scrambling to make a sense of the artistic alongside the scientific narrative, then at some point I was just like 'ahh this is a trip', cool.

  • Reply Jesse Krizik December 11, 2019 at 2:09 am

    It's the Legendary Black Beast of Aaaaarrrrrrggghhh

  • Reply Henry December 11, 2019 at 2:11 am

    i think the narrator could sound even more creepier to scare off more people, and turn this into a horror genre.

  • Reply Foolish&Afraid December 11, 2019 at 2:20 am

    Great info, terrible animations

  • Reply Don Jabra December 11, 2019 at 2:55 am

    Nice!

  • Reply Benjamin December 11, 2019 at 3:08 am

    Varg Vikernes wants to know your location

  • Reply PalimpsestProd December 11, 2019 at 3:56 am

    I like this format, people complaining about the animation probably think that a Rutherford Bohr model is "realistic". I would have liked a bit more info as to when the the viral DNA got there. Before all placental mammals but how far before? Before all sexual reproduction?

  • Reply Random Dude December 11, 2019 at 4:35 am

    Was the animations done by felix Colgrave?

  • Reply sean mortaz December 11, 2019 at 9:57 am

    Excellent essay and graphics!

  • Reply Giulia Bonino December 11, 2019 at 12:12 pm

    Very interesting. But the animations were totally unhelpful

  • Reply anrade86 December 11, 2019 at 1:35 pm

    animation and sounds are useless, distracting and disturbing

  • Reply TurningSeasonWithin December 11, 2019 at 3:46 pm

    Love the art style, not at all what I was expecting!

  • Reply etyrnal December 11, 2019 at 3:46 pm

    These are the worst graphics I have ever seen and are not representative of anything obvious. And this is a video full of assertions after assertion after a surgeon after assertion was absolutely no discussion whatsoever of how any of these conclusions were arrived at. Not even the most basic concepts are mentioned.

  • Reply Jaime Espinoza December 11, 2019 at 4:10 pm

    Man that animator was high

  • Reply ozdergecko December 11, 2019 at 4:12 pm

    Back in '91, we called our daughter 'the endoparasite' during the first few months of pregnancy. Well, actually, until the delivery. oh, and… we both worked in molecular biology research back then.

  • Reply khhnator December 11, 2019 at 4:25 pm

    this is like something out a 80's british documentary, i love it 😀

  • Reply The Eternal Bruh December 11, 2019 at 7:03 pm

    An artistic masterpiece

  • Reply digiryde December 11, 2019 at 9:28 pm

    So, as a follow on question, what is the biological history of the placenta as we understand it now. It looks like it is research time!

  • Reply ATR December 11, 2019 at 10:13 pm

    The animations are like some awful French conceptual artwork, but the information is interesting

  • Reply enotdetcelfer December 12, 2019 at 2:47 am

    Meh, I actually liked the animation! 😀

  • Reply amresh yadav December 12, 2019 at 4:03 am

    what a hopeless animations.

    try better next time.

  • Reply I may Be Q December 12, 2019 at 4:17 am

    hey guys … can you justt make like a tooth repair pill from shark cells or shark dna ?cuz they have tooth repair ?

  • Reply guy December 12, 2019 at 6:19 am

    Animation reminds me of felix colgrave

  • Reply Scott M December 12, 2019 at 12:33 pm

    All I can say is wow.

  • Reply Scott M December 12, 2019 at 12:34 pm

    Lots of comments about the animations being a bit much, but I actually really like them. Thanks!

  • Reply Scott M December 12, 2019 at 12:34 pm

    The animations were an art piece of their own. Love it!

  • Reply dirac bracket December 12, 2019 at 11:40 pm

    Brilliant.

  • Reply Stan B December 13, 2019 at 7:42 am

    The animation is really confusing and detrimental to the value of the content presented at the same moment.

  • Reply KayJay Parko December 13, 2019 at 7:52 am

    Courtesy of Mr Aesop………….

  • Reply freedommascot December 15, 2019 at 4:02 am

    I’ve never seen such horribly confusing video imagery before! How did this ever pass inspection?

  • Reply Erik 567 December 20, 2019 at 8:15 pm

    Nice story telling. I like the graphics.

  • Reply Sergey Po December 20, 2019 at 8:22 pm

    Animations is really bad!

  • Reply Mighty MOSA December 21, 2019 at 1:19 pm

    Very interesting ??????

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