Ep 6 - The Great Split

 LUCA had kids. And like all kids, they went their separate ways. Today we're covering the first great split in the tree of life - when LUCA's descendants branched into Bacteria and Archaea. Same genetic code, completely different everything else. Plus: viruses (where have THEY been this whole time?), horizontal gene transfer (strangers sharing genes), and why bacteria sharing resistance genes is now one of the biggest threats to modern medicine. Also, I make a lot of puns. You've been warned. 

Transcript

Jackie 0:02

Hello, I'm your host Jackie Mullins and a welcome to From Cells to Us How the podcast where we figure out how life went from a single cell to complex creatures like us. So, wow, here we are still in the Archon Eon at about 3.5 to 3.8 billion years ago. But big things have happened, like huge. Huge. Like something will will always be talking about since it's still around. I want to do just a quick where we came from to where we are in episode one. We imagine we were a scared little RNA strand, if you remember shivering scared little RNA strand floating in the primorial seas, watching organic molecule carnage all around us. Then we drifted into a fatty acid membrane or a spherical Oreo. From there, we became more comfortable, more protected. We learned how to do our own chemistry, fold in on ourselves, grab amino acids and have them work for us. Then some of us lost in oxygen, paired up with some similar strands, and became DNA. Way more stable, a lot less mobile. Not to be outdone. We as RNA, decided we're splitting three ways. We'll be the messenger for DNA, we'll do the chemistry in the ribosome, and we'll bring over amino acids to be made into our workers, the proteins. This has been a long journey, a few billion years in fact. But the transformation is nothing short of amazing. Now here you are, the once scared RNA strand all split up and running the cell with precision in Luca. How could it get any better? Well, what if Luca had kids? Last episode, we watched the genetic code get refined. Tina got her anti-codon ID badge. Rick got his protein crew and became a full ribosome. The wobble hypothesis gave evolution room to experiment, and Luca emerged the last universal common ancestor, the population of cells that would give rise to every living thing on Earth. But here's the thing about Luca. Luca didn't stay. Luca. Luca had kids and like all kids, they went their separate ways. They moved out, they got different jobs, developed different lifestyles, and eventually some stopped calling home. Today we're talking about the first great split in the Tree of life. But before we dive in, let me give you a quick roadmap because there are some new words coming and I don't want you to get lost from Luca. To us there have only been two major splits. That's it. Two forks in the road that created all the diversity of life we see today. Split one. Luca's descendants branched into bacteria and ArcHa. That's what we're covering today. Split two, about a billion or two years later, eukaryotes branch off from the ArcHa line. That's us for a future episode. So that gives us three types of cells, bacteria, ArcHa, and eukaryotes. I feel like these three are kind of like the Hemsworth Brothers. A lot of people have heard of a bacteria and eukaryotes just like Chris and Liam, but not many have heard of ArcHa much like Luke, which is unfortunate because both are still fairly prominent. Luke, I'm sure you're listening. I thought you were great in Westworld. Now here's one more word, pro karaoke. Pro Caros are simple cells. They don't have a nucleus. If you don't know what that is, don't worry, we'll get there. They don't have membrane bound organelles, basically no little organs inside their cell. It's just the basics. DNA ribosome and a membrane. Both bacteria and ArcHa are prokaryote. They're simple cells. The OGs, the ones that ran the planet for over a billion years before anything more complex showed up. Eukaryotes, that's us. We come later. We're the fancy cells with all the extras. Future episode. So Pro Caros are like a studio apartment. Everything's in that one room. Your bed, your kitchen, your stuff. It works. It's efficient. There's no separation. U caros are like a mansion. Separate rooms for everything. Bedroom, kitchen, office, gym, walls and doors are everywhere. More complex, more specialized, more space to do different things at once. The mansion comes later. Today we're talking about the studio apartments. Procars, the simple but wildly successful cells. But if bacteria and ArcHa are both procars, why do we call them different things? What makes them so different that scientists said, uh, no. We need these in separate categories. Oh, and we need to talk about viruses because they've been here the whole time watching, waiting, infecting. And honestly, they might be older than all of this. Let's get into it. So Luca had everything figured out, right? DNA for storage, RNA for messaging, ribosomes for building proteins, the genetic code, the central dogma, all the basics. But Luca wasn't just one cell sitting there being perfect. Luca was a population, probably a messy, diverse population of similar cells all doing roughly the same thing. And within that population variations existed. Some cells did things slightly differently, different membranes, different ways of handling energy, different strategies for survival, but one thing stayed the same. The universal language, the genetic code that never changed, and that's going to matter a lot in a few minutes. But over time, these variations accumulated. The population started to diverge and eventually Luca's descendants split into two major groups. We call them bacteria and arch. Now if you're thinking, wait, I've heard of bacteria, but what the heck is ArcHa? You're not alone. As we earlier discussed, We actually didn't even know Aiaa existed until 1977. A scientist named Carl Woes was comparing ribosomal, RNA, the RNA inside ribosomes, our friend Rick, across different microbes, and he noticed something. Odd, some of these so-called bacteria had RRNA sequences that were wildly different from actual bacteria, like not even close, it was like opening a book and expecting Spanish, but finding Mandarin both argued that these weren't bacteria at all, that there were something entirely different. A third domain of life hiding in plain sight. People kind of thought he was nuts. It took 20 years for science to catch up to Carl Woes. Now it's in every textbook. Also, no one really talks too much about Archaea because none of them cause disease in humans. We've just been living peacefully with each other. How about that? Unlike bacteria where it's been an evolutionary arms race since day one, they evolve. We evolve antibiotics resistance, on and on. The stakes just keep getting higher. so what actually makes bacteria and ArcHa different? Well, they're both prokaryote. They both have the genetic code. They both use ribosomes. What's the big deal? Let's break it down. The biggest difference is their cell membrane. Remember that spherical Oreo in episode one? You know the bouncer that was bad at his job? Both bacteria and ArcHa have membranes, but they build them completely different. It's like two people building a house. Same concept walls, roof. Keep the weather out, but one uses brick and the other one uses concrete. From the outside it's similar, but under the hood, completely different. It's fatty acids versus isoprene chains, blah, blah. The point is different materials but the AO membrane, it's tougher. More stable handles heat acid and extreme conditions like a champ. That's why ArcHa dominate the extreme environments. Boiling hot springs, super salty lakes, acidic volcanic vents. Many ArcHa are extreme of viles. They can live almost. Anywhere due to their tough membranes, it'll be them cockroaches and twinkies. After the nuclear fallout. So the second thing that bacteria and ArcHa have different is cell walls. rigid structures outside the membrane that give the cell shape and protection, and those two are made of completely different stuff. And perhaps you're like, wait, what? Didn't we just talk about this and close? But what we are talking about is the cell membrane. The cell wall is something different. The membrane is like the bouncer deciding who gets in. The cell wall is like the brick wall of the building itself. The bouncer works the door, but the wall keeps the whole club from collapsing. Bacteria and ArcHa have both bouncer and brick wall. Your cells, eukaryotes. Just have the bouncer, just the membrane. We are more flexible, but less armored. So bacterial cell walls contain pep glycan, a mesh of sugar and amino acids. Think chain mail, armor, flexible interlocking links all woven together. AR cell walls, no peptic glycan at all. They use different proteins and sugars depending on the species. That's more like plate armor. Solid pieces, completely different construction. Same job, different build bacteria's. Got chain mail flexible. Gets the job done. Arch's got plate armor heavier, tougher. Good luck getting through that. This is actually why antibiotics work on bacteria, but not ArcHa many antibiotics. Target Pepto Glycan synthesis. No pog, glycan, you know, no target. And you might be wondering, why do we even know this if ArcHa doesn't make us sick? Well, back before we knew AIA were their own thing. Scientists tested antibiotics on everything. When some, you know, so-called bacteria didn't respond, that was actually a clue that something weird was going on. One more piece of evidence that ArcHa wasn't bacteria at all. And here's where it gets interesting. When you look at how bacteria and ArcHa handle DNA replication, transcription, translation, ArcHa actually look more like eukaryotes. That's us. The cells with the nucleus than bacteria, Archie's ribosomes were more similar to ours. There are DNA handling enzymes are more similar to ours. It's like bacteria went one direction. ArcHa started walking toward what would eventually become complex life. So ArcHa are not just weird bacteria. They're a completely separate branch of life, and they might actually be more closely related to us than bacteria are. It's like finding out, uh, Liam Hemsworth, the bacteria was actually adopted and Luke and Chris are the blood brothers. Even though Liam and Chris look more similar, the blood relation is between Luke and Chris or ArcHa and eukaryotes. Wild. Right. Okay, so why did Luca's descendants split into bacteria and ArcHa? Why not just one type of pro cario? Well, honestly, we're not entirely sure, but you know, just think about humans. We started in Africa, spread across the globe, encountered different environments and adapted different climates, different food sources, different challenges, given enough time, isolated populations diverge. Same idea here. Luca's descendants spread out, encountered different conditions, found different ways to survive. Some went one direction, you know, some went the other. Over hundreds of millions of years, those differences add up. And now they're two completely separate domains. And honestly, we're still trying to figure out the details. The split happened around 3.5 to 3.8 billion years ago. So we're doing forensic science on a crime scene older than most rocks on earth. But what we do know is it happened and both branches have been wildly successful ever since. So before we move on, let's talk about what life was like for those early Procars, both bacteria and ArcHa. Like what was their deal? Pro Caros are tiny. We're talking one to 10 micrometers for most bacteria. For reference, a single strand of human hair is about 70 micrometers wide. You could line up seven to 70 bacteria across the width of one single hair. That's crazy. And they're simple. No nucleus. The DNA just floats around the cell in a region called the Nucleoid. No membrane bound organelles, no mitochondria, no fancy internal structures. Just membrane, cytoplasm. DNA, ribosomes. And that's about it. But don't let simple fool you. Simple does not mean ineffective. Prokaryotes have been running this planet for billions of years. They were here first, and they'll probably be here last. One thing that pro Caros are really good at is making more of themselves. Some bacteria can divide every 20 minutes under the ideal conditions. That means one cell becomes two, two cells become four. Four cells become eight. Do the math. Over a day and you've got astronomical numbers. This is why bacterial infections can get out of control so fast, and it's why pro caros can evolve so quickly. More generations mean more chances for beneficial mutations. Now I know what you're thinking. Tons of kids, without getting intimate, sign me up. Well slow down there. You anti Casanova, you. There is a downside. They're all clones. When you reproduce a sexually, you are just copying yourself. No mixing, no variation. Every daughter cell is genetically identical to the parent. That's great. When times are good, you found a strategy that works. Copy it a million times, take over. Done. But when something bad comes along, a new threat, a change in the environment, a disease, everyone's vulnerable because everyone's the same. Did you ever hear of the Irish potato famine in the 1840s Ireland was growing mostly one variety of potato. The lumper farmers kept planting clones of clones of clones, genetically identical. Then a pathogen called the potato blight showed up, and because every potato was the same, every potato was vulnerable. The blight spread like wildfire crops. Failed a million people died a million more fled the country. That's the danger of no genetic diversity. What kills one? Kills all procars face this same risk. If they only reproduce asexually, one bad virus or environmental change could wipe out the entire population. But at first, it's great, right? You're multiplying every 20 minutes to an hour. If you're a successful bacterium, you know, let's call you Brad, the bacteria. You've got good genes for surviving in your hot little thermal vent. You can make a whole colony of Brad's Brad, Jr. Bread, the third bread, the revenge bread forever. You, you get it. But here's where it gets dicey. The environment isn't stable. Earth 3.4 billion years ago is kind of a drama queen. Temperatures fluctuate. Chemical compositions change, new minerals appear UV radiation is absolutely brutal because there's no ozone layer. The sun is literally trying to murder everything. And poor Brad and all his identical Brad clones, they're all equally screwed when the conditions change. But don't worry, they found a workaround. Keep this in the back of your mind. Here's where pro Caros also shine. They can eat anything, and I mean anything. Some eat sugars like us. Some eat sulfur, some eat iron, some eat methane. Some eat literal rocks. Some don't eat at all. They photosynthesize capturing light energy like plants would eventually do. Procars, figure it out every possible way to extract energy from the environment they colonized. Every niche on earth, hot, cold, acidic, alkaline, salty, deep. Underground high in the atmosphere. Pro caros are there. This metabolic creativity is part of why life survived on earth. Conditions were harsh and constantly changing. Having a diverse toolkit of ways to make energy meant something would survive no matter what. Alright, so that was a lot of information. Let's do a quick checkpoint here. See what we got. All right. Luca had kids and those kids split into two groups. Bacteria and ArcHa. The first great fork in the Tree of Life, both are Procars Studio apartments, simple cells, no nucleus, no fancy organelles, just DNA, ribosomes and a membrane. But under the hood, they're completely different. Different membranes. They're brick versus concrete. Arch's are tougher, which is why they dominate extreme environments, different cell walls, chain mail versus plate armor. This is why antibiotics work on bacteria but not ArcHa, different machinery. And here's, you know, the plot twist. Arch's machinery looks more like ours. Then like bacterias, Luke and Chris are blood brothers. Liam's adopted. We don't know exactly why they split. The same reasons humans spread across the globe and diverged different environments, different challenges, enough time, evolution doesn't need a master plan, and both branches well, they were wildly successful They're still here. They're still thriving billions of years later. Now we need to talk about something that's been lurking in the background this whole time. Something that's not bacteria, not ArcHa, not even a cell. Something that might not even be alive. Viruses. So when you hear virus, I'm sure most of you think of COVID flu, that annoying thing, you just have to let run its course because antibiotics don't work on it. But viruses aren't just a modern inconvenience. They are ancient, like ancient, ancient, possibly older than the bacteria. ArcHa split possibly. Older than Luca possibly hanging around since the RNA world and they've been messing with cells for billions of years. But why we haven't talked about them yet. Well, because viruses might not be alive. Might not even technically be a cell. So, so what are they, how, where do, where do viruses fit in all of this? Are they pro caros? Are they u caros? Well, they're, neither viruses are weird. A virus is basically just genetic material, either DNA or RNA. Wrapped in a protein coat. That's it. That's the whole thing. No membrane doing its own thing. No ribosomes, no rick, no metabolisms, no way to reproduce on their own. If pro coyotes are studio apartments and U Coyotes are mansions, viruses are that stray dog that hangs around outside. He's not part of the house. He doesn't have his own place, but he keeps showing up and he's wearing a sweater that grandma knitted for him. That's his protein coat. You know, mom thinks he's part of the family. He shows up every day. He responds to his name. He's basically ours. That's, you know, some people think viruses are alive. Dad thinks he's just another mouth to feed, right? No, he doesn't pay rent. He can't survive on his own. He just takes our stuff and leaves. You know, that's, the viruses are not alive. Camp the truth. Viruses exist in this weird gray zone. They've got genetic material. They can evolve, they can make copies of themselves, but they can't do any of that without breaking into your house and using your kitchen. They're not alive, but they're not. Not alive. They're the freeloaders of biology and they've been freeloading for billions of years. So in essence, viruses hijack your cells, machinery, your ribosomes, your energy, your nucleotides, and use it to make copies of the cells. Hundreds of copies, thousands until your cell either dies, explodes, or gets. So overwhelmed it can't function crazy, to think that when you are infected, that's exactly what's happening inside of you. Silently invisibly, your body is fighting off infiltrators of the highest magnitude and you have no clue besides a runny nose. It blows my mind. Speaking of viruses and that blurry line between alive and not. Remember Agent Smith in the Matrix, he calls humans a virus. You know, human beings are a disease, a cancer of this planet. You're a plague, and we are the cure. I am bringing back imitations. Let's give it a whirl. But here's the delicious irony. Smith is the real virus. He can't exist on his own. He needs to hijack human bodies and minds to replicate. He spreads by infecting one host after another, turning them into copies of himself. No metabolism, no independent life, just endless copying until the system crashes. Sound familiar. Humans might multiply and mess things up, but at least we build, create, and adapt. Smith pure parasite, freeloaders, supreme. So next time someone quotes that line at you, you know you can flip it actually. Agent, you are the virus. We're just the messy, wonderful host trying to wake up. So how old are viruses? We used to think viruses were relatively recent, like maybe they evolved after cells as escaped bits of genetic material. You know, like one day a piece of DNA just looked around and was like, I don't need you. People packed its handkerchief on a stick and walked out the door. You know, no goodbye party, just vibes in a protein coat. But the more we study them, the more ancient they look and that changes everything about where they fit in the story of life. And here's the evidence. Viruses, infect everything. Bacteria, ArcHa, plants, animals, fungi. If it's alive, there's a virus that infects it. This kind of universal presence suggests that they've been around for a long time. Bacterial phs and AR viruses are very different. Bacterial phs are viruses that infect bacteria. There are also viruses that infect ArcHa, and these two groups of viruses Are quite different from each other. Different structures, different strategies. This suggests viruses were already diversifying before the bacteria ArcHa split, which means viruses might predate the split, which means viruses might be older than 3.5 billion years. Now, some viral proteins are incredibly ancient. Certain proteins found in viruses appear in viruses across all domains of life. These proteins are so old and so conserved that some scientists think that they may trace back to the RNA world. So when did viruses actually originate? Honestly, we don't know where viruses came from. There are three theories. One, they came first hijacking, RNA, back in the RNA world, two, their escaped genes, you know, that went rogue. Three, they're lazy cells that stripped themselves down until all that was left was genetic material and a coat. And the real answer is it's probably all of these different viruses, different origins. What we do know is they're ancient. They were here when bacteria and AIA split, and they've been shaping evolution ever since. Now, remember when I talked about the downside of asexual reproduction, how pro coyotes are all clones and one bad virus or environmental change could wipe out everyone I told you, they found a workaround. I told you to keep it in the back of your mind. And here's the answer, horizontal gene transfer. Instead of just passing genes from parent to child vertical like a family tree pro, Caros figured out a way to pass genes sideways, neighbor to neighbor, stranger to stranger, completely unrelated cells swapping genetic material. And that'd be like if we as humans had horizontal gene transfer and someone would be like, I love your hair. And instead of saying it's genetic and unattainable, you would say, thanks, I got it from a stranger I met yesterday on the sidewalk. Imagine how different our lives would be. And guess what was one of the main drivers of that? Viruses. When a virus infects a cell, it hijacks the machinery and makes copies of itself, but sometimes accidentally the virus packages some of the host cell's, DNA, into the new virus particles. Then when the virus infects a new cell, it delivers not only its own genes, but the genes from that previous host. So it's basically like a molecular pollinator, a bee flying from flower to flower, accidentally carrying bits of pollen from one to the next. That's what viruses are doing, except with genes. Now this is called transduction. It's one of the major ways Genes move between bacteria, between ArcHa and even between bacteria and ArcHa. And the only reason that could happen is because they have the same universal code. Viruses don't mean to help evolution, obviously, they're just trying to make copies of themselves. But in the process, they shuffle genes around. They spread innovation. They connect the branches of the tree of life in ways that wouldn't have happened otherwise. Weird bits of genetic material, just trying to, well stay, not, not alive. Who accidentally changed the course of evolution? And before I move on from viruses, I need to tell you this tidbit. About 8% of your DNA is viral, not DNA, that fights viruses viral, D-N-A-D-N-A. That came from viruses. These viruses infected our ancestors millions of years ago inserted their DNA into ours, and some of those genes turned out to be useful, so we kept them. One of these viral genes is essential for pregnancy. I am not making this up. A gene that originally came from a virus is necessary for the placenta to form properly without an ancient viral infection. Mammals might not exist as we know them. So the next time you see a pregnant person, remember that baby bump is brought to you in part by horizontal gene transfer. Locate an ancient virus near you, So you are 8% virus, ancient viral sequences, just sitting in your genome, mostly doing nothing, but oh wow, if that sci-fi book doesn't just write itself. Okay, so let's get a little bit more into horizontal gene transfer because horizontal gene transfer is actually the reason we are all here. Without it, life would've ended right here in the Archon Eon. If Pro Caros had only used asexual reproduction, just making identical copies of themselves over and over, there'd be no variety, no backup plan, one bad day, one small environmental change. And that's it. Everybody dies End of story. Roll credits. Now when You think about inheritance, you probably think it's going in one direction, right? Parent to child. I got my grandma's eyes, my father's height, my mother's eczema. Thanks for that one, ma. You get half your genes from your mom, half from your dad. They get half their genes from their parents, so on and so forth. Back their time. This is vertical gene transfer genes flowing down the family tree. Normal stuff. But pro caros. Pro caros, were like, no, no, we don't have time for that. I'm not buying anyone flowers. No one milkshake with two straws. Thank you very much. They're stuck in the fifties apparently. And with that declaration, they invented something entirely different. The horizontal gene transfer. This is Completely unrelated cells swapping genetic material like they're trading snacks at lunch. Imagine you could walk up to a stranger on the street and just absorb their ability to play piano or speak French or digest lactose. That's basically what pro caros do, except instead of skills, it's genes and instead of strangers on the street, it's other cells floating nearby. This is wild and it changes everything about early evolution. So how does this actually happen? How do cells swap genes with random strangers? It's not like they're sitting around a microscopic poker table with microscopic visors on and microscopic chips in the middle dealing with their genes. I may have taken that joke a microscopic step too far. But I do like to picture cells playing poker, much like dogs. So there are three main methods of horizontal gene transfer method one transformation. This is the simplest. When a cell dies, it breaks open. Its DNA spills out into the environment and it just floats around naked, DNA in the water or soil or whatever, and some cells can absorb that floating DNA. They just, you don't slurp it up, incorporate it into their own genome. Oh, you don't need this gene anymore because you're dead, you know? Cool. It's mine. Now Now, can you imagine how different wills would be if humans worked this way, like actual legal documents? Witnessed and notarized and to my husband. I leave you my ability to remember every movie line I've ever heard. May you finally see what a gift it actually is. Oh, that would be fun. I. But alas, we do not work like that. However, a scientist found out, how procars were working like that in 1928. this was actually how we first discovered horizontal gene transfer Frederick Griffith was working with streptococcus pneumoniae. The bacteria that causes pneumonia and had two strains. One was smooth and deadly. One was rough and harmless. Griffith killed the deadly ones, just chopped them up Griffith with a knife in the conservatory, but actually he used heat. The point is these pneumonia causing bacteria are dead now. He took these dead pneumonia causing bacteria and dumped them in. With the living harmless ones, and lo and behold, the harmless ones became deadly. They stole the gene that made the deadly one deadly and incorporated it into their DNA. Griffith was like, uh, excuse me, what the scientific community was like, uh, excuse me, what? That can't be right. But it was right. Bacteria were out here eating their dead friend's, DNA, and incorporating it into themselves, like some microscopic zombie apocalypse, but with genes instead of brains. Just insane. Now method two is transduction. This is the one we discussed. Viruses acting like bees pollinating the molecular world with mini gifs of new genes. You know, Brees, I'm on a roll this episode. Okay. And just to note, the viruses are usually bacteria, phages viruses that infect bacteria and let me tell you, these things look crazy. They literally look like an alien spaceship. Google them later. They're terrifying and awesome. And just to use a. A previous analogy, a virus infects. You know, Brad, the bacterium uses Brad's cellular machinery to make copies of itself and then bursts out like, you know, a scene from Alien, but sometimes the virus accidentally packages some of Brad's DNA along with its own. Then it infects another bacterium. Let's call her Brenda, and it injects Brad's DNA into Brenda. Now Brenda has some of Brad's genes they've never met. They might not even be the same. Species, but thanks to a clumsy virus delivery service. Brenda is now part Brad. But wait, you might say to yourself like, cool, the virus is gifting genes to others, but didn't you just say that the virus hijacks the cells machinery and then leaves it to die? How will they be able to pass on these supposed gifts? If they're dead, and yes, that is correct. That does happen most of the time. However, if that virus picked up some bacterial DNA by accident, it often can't complete a full infection. Why? Because that bacterial DNA took up some space where essential viral genes should be genes the virus needed to complete its hostile takeover now has bacterial DNA there instead. Now, instead of infecting and killing the cell, the virus just delivers some new DNA and leaves. It's like a Trojan horse, but you know, they forgot to put the soldiers inside. It's just an empty wooden horse, you know, maybe with a gift. It's a little Monty Python and the Holy Grail energy right there. The third one is conjunction. This one is the most sci fiy two cells physically connect through a little bridge called a pils. One cell extends this, Pils attaches to another cell and transfers DNA directly. Scientists sometimes call this bacterial sex, but that's not really accurate. It's more like bacterial file sharing. One cell has a useful gene, builds a bridge to a neighbor and copies the file over, you know, no romance involved. No flowers, no milkshake with two straws, just pure utilitarian gene transfer. Okay. If you like me are like, um, what? With this one, I got you. The other two I get, I was like, okay, that makes sense. But then we have this portal just popping up and one cell's like, gimme your genes. Like how and why? Well, some cells have these little extra circles of DNA called plasmids. Separate from their main DNA and some plasmids contain instructions that basically say, build a bridge, find a neighbor, copy me, send me over. The plasmid is the selfish one. It just wants to be spread. It has a separate drive from the cell, and the cell is just following directions that the plasmid gives it. And sometimes that plasmid comes with gifts. Like genes for antibiotic resistance or the ability to eat something new so the receiving cell gets an upgrade. It never asked for. The plasmid is also kind of like Han Solo in Star Wars, A new hope. You know, he's just in it for the money. I'm not here to save anyone. He's looking out for number one, but he does do some good, you know, he saves a princess, what have you. The plasmid is the same. He's just looking to spread, looking out for number one, but sometimes accidentally delivers gifts. And here's the real world kicker. In 1959 when Japanese scientists figured out why antibiotic resistance was spreading so fast, it wasn't just evolution through mutation, bacteria were actively sharing resistance genes. A bacterium in a hospital in Tokyo could share its antibiotic resistance with a completely different species, and that bacterium could share it with another, and suddenly you've got a super bug situation. Antibiotic resistance is now one of the biggest threats to modern medicine. The ancient past isn't so ancient after all. Now, quick, PSA here. This is why it's so important to take all the antibiotics your doctor gives you, every single one. Here's what happens if you don't. Day one, you take the antibiotic, it kills most of the bacteria. Day three, you feel better. Day four, you think I'm fine. Why would I keep taking these? But most is not all the bacteria still alive. They're the tough ones. They're the survivors. Maybe they had a gene that helped them hold on a little longer. Maybe they got a gift from a dying neighbor. A little resistance, cheat code passed right over Now those survivors multiply. And they pass that resistance to their kids and their kids, and suddenly you've got a whole population that knows how to survive that antibiotic next time you're sick. Same medicine doesn't work. And here's the real nightmare. Those resistant bacteria can share that cheat code with completely different species through horizontal gene transfer, your resistant bacteria meets a stranger, builds a little bridge, copies the file over. They're all swapping genes like it's a genetic flea market. Now, it's not just one species that's resistant. It's spreading. That is how superbugs happen. This is why your doctors beg you to finish your antibiotics, so take the whole bottle. Do not share with a friend or family member because you have the same thing. Kill them all. No survivors don't give them any help from us. Believe me, they don't need it. All right, so why should you care about horizontal gene transfer? Well, because it completely changed how evolution worked in the early world. Think about it with only vertical gene transfer, a beneficial mutation has to arise in your lineage. Then it spreads to your descendants, then their descendants. Then slowly over generations that might spread through the population, but with horizontal gene transfer, if any cell anywhere figures out something useful, how to eat new food, how to survive a toxin, how to resist heat, that innovation can spread immediately to unrelated cells. It's the difference between one person inventing the wheel and teaching it to their kids versus inventing the wheel and immediately uploading the blueprints to the entire internet. Or like the matrix. When Trinity needs to fly a helicopter and they just upload the skill directly into a brain done instant pilot. I would absolutely love if humans could horizontal gene transfer like that. But a less we're stuck with our slow, clumsy way of doing things. But for bacteria, evolution went from slow and steady to fast and chaotic. This is why the universal genetic code matters so much. Remember how I said it evolved once and got locked in. This is why that was so important. If every cell speaks the same genetic language, then any gene can work in any cell. A gene from a bacterium can function in an archon, a useful innovation in one branch of life can spread to another. The universal code made horizontal gene transfer possible and horizontal gene transfer made early evolution fast. And just a quick jump into the future, you know, our present. Scientists are using horizontal gene transfer to our benefit right now. We may not get to download the ability to pilot a helicopter or no kung fu instantly, but genetic engineering, that's basically us doing horizontal gene transfer on purpose. We take genes from one organism and put them in another bacteria that produce human insulin for diabetics, horizontal gene transfer crops that resist pests. You guessed it. Horizontal gene transfer. Crispr, the gene editing tool that's revolutionizing medicine. We stole that from bacteria too. This is pretty cool stuff. So when you picture evolution, you probably picture a tree. You know, one trunk and that's Luca that branches into two limbs, bacteria, ArcHa. Then those branches split into more branches. No crossover, just up and out, right? Everything neat and tidy. But horizontal gene transfer means that branches are connected. Genes jumping from one branch to another, the tree of life. Isn't really a tree, it's more like a tangled web or you know, a tree where the branches occasionally fuse back together. This makes drawing evolutionary relationships really complicated for scientists. You can't just say this species descended from that species when they're both trading genes with random strangers for billions of years. It's like trying to draw a family tree for a family where everyone's adopted each other's children, but also kept theirs and remarried each other's spouses. You know, technically you could probably trace the lineages, but it's gonna be messy. And honestly, the messiness is beautiful, right? Life isn't neat. Life is chaotic, creative, and constantly borrowing good ideas from wherever it can find them. So here we are. Luca has split into bacteria and ArcHa. They've spread across the planet. They've colonized every environment. They're swapping genes like they're in a genetic commune. Karl Marx may have studied bacteria and thought, well, if it works for them, pro caros are evolving at breakneck speed, and this is the state of life on earth for a long time. A a really long time, like thousands of times longer than humans have existed. Pro Caros had the planet to themselves for over a billion years, maybe closer to 2 billion. The first complex cells, U carry outs, cells with nuclei. The cells that make us plants animals, they don't show up until around 2 billion years ago, maybe 1.5 billion depending on which evidence you believe. That means for more than half, for more than half of life's history on earth, it was just bacteria and ArcHa. Small, simple, everywhere. We tend to think of procars as primitive as stepping stones on the way to real life, like plants and animals, but that's backwards. Procars aren't primitive. They're refined, optimized, incredibly successful at what they do. Your gut alone contains trillions of bacteria on the same order of magnitude as the number of human cells in your body. There are more bacteria cells on earth than there are stars in the observable universe. Pro caros aren't the opening act. They're kind of the main event. Everything else, including us, is just kind of a side project that happened later. Alright, so let's do a checkpoint. Let's make sure we've got this. There was a split. Luca's descendants diverged into two domains, bacteria and ArcHa. Same basic genetic code, completely different, everything else, different membranes, different cell walls, different ways of handling DNA. Prokaryote life. Small, simple, fast reproduction. Metabolically diverse, no nucleus, no organelles, just the essentials. And it works. It works really well. Viruses, they're not cells, they're not really alive. Just genetic material in a protein coat. You know, the stray dog in grandma's sweater, they've been here the whole time. Infecting, replicating and accidentally shuffling genes between your cells. Freeloaders who accidentally shaped evolution, and 8% of your DNA is proof. They were there. Horizontal gene transfer genes don't just flow from parent to child. They flow sideways. Neighbor to neighbor, stranger to stranger through dead cell. DNA transformation through viruses, transduction, and through direct sell to sell bridges. You know, Han Solo Conjugation Evolution on Fast Forward because horizontal gene transfer. Beneficial innovations could spread across unrelated lineages. The Universal genetic code made this possible evolution was fast and chaotic. The Web of Life, the Tree of Life, is more of a tangled web. Branches are connected. Genes jump. It's messy and that's okay. It works. So here's our conclusion. This is the age of Procars. Luca gave rise to two great lineages, bacteria, and ArcHa. Different strategies, different structures, same fundamental code. And for over a billion years, they ruled. They spread across the planet. They colonized every environment imaginable. They swapped genes freely involving, faster than anything that came before or since. This was the age of prokaryote simple cells doing extraordinary things. But something was brewing. Oxygen was starting to accumulate in the atmosphere, a deadly poison to most life at that time. Wild, right? Oxygen was poison. The world was about to change next time on from cells to us cyanobacteria, invent, photosynthesis, and accidentally poison the entire planet. The Great Oxygenation event, the first mass extinction, and how life survived by learning to breathe the very thing that was killing it. Thank you for joining me on this biological journey. I'm Jackie Mullins, and this has been from Cells to Us. How I'll see you next time. I.