12 tiny worlds

If you went back 500 million years and re-ran evolution, would life be totally different today? Guests: Richard Lenski and Zachary Blount, evolutionary biologists at Michigan State University For show transcripts, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unxtranscripts⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ For more, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unexplainable⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ And please email us! ⁠⁠⁠[email protected]⁠⁠⁠ We read every email. Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/members⁠⁠⁠⁠⁠⁠⁠ Thank you! Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Noam Hassenfeld?

  Anyone who listens to Unexplainable knows that music is really important to me. So I want an amazing sound system. But I also want something that's easy, that just works. Sonos delivers on all fronts. The sound is incredible, and my Sonos system follows me wherever I go. I can mix and match speakers in any room in my apartment, louder in the living room, quieter in the kitchen. And the Sonos app makes it all super easy. Visit sonos.com and build your system. Sonos: Love the sound, feel the system.

• 0:38Speaker 01

  What if managing company spend took less managing? Introducing AMEX Corporate, one intelligent platform connecting cards, expenses, and payments so you can keep work moving. Built to simplify, designed to scale. This is AMEX Corporate. Get started at go.amex/ammexcorporate. Terms apply.

• 1:05Speaker 02

  Imagine for a moment that we have the ability to rewind time,

• 1:11Speaker 02

  that we're able to press a button and slide back through the last centuries' worth of history, through millennia of music and culture, back through tens and then hundreds of thousands of years of human existence. Imagine that we keep going. We go back through the age of the dinosaurs and the age of the giant insects,

• 1:39Speaker 02

  all the way back to around 500 million years ago, when our ancestors, ancestors, ancestors were crawling around in the muck along with other animals.

• 1:50Speaker 02

  Creatures like Hallucigenia, which does in fact look like something out of a hallucination, full of strange spikes and weird legs, or Opabinia, which has five eyes and a trunk-like appendage with a claw at the end. These are animals that only exist as fossils now because they don't seem to have direct descendants today. Other animals, like the ones that became our ancestors, they won the evolutionary contest and spread far and wide across the globe instead.

• 2:24Speaker 02

  But if we did travel back to that time, back to when all these animals coexisted in the oceans, and if we started over from that point, would we end up with the same world that we have today? Or could things evolve completely differently? Evolution is a process of random mutations interacting with chance happenings, right? So what if some random roll of the mutational dice went differently? What if a mudslide wiped out the ancestors of some animals that were key to life as we now know it? Could some other option, some hallucigenia or opabinia or something else,

• 3:07Speaker 02

  could they have won the evolutionary lottery and spread far and wide instead of our ancestors? This is, basically, the question that a paleontologist named Stephen J. Gold asked in his book Wonderful Life back in 1989. In that book, he argued that the world as we know it is the result of a series of amazing accidents. And if you reran things, you might get some very different results. Other scientists disagreed. One pointed out that, over and over and over again, life has gravitated towards certain solutions to being on this planet. Stuff like eyes, for example, have developed many times in otherwise very different animals.

• 3:48Speaker 02

  And so it's not unreasonable to think that things maybe wouldn't look exactly the same, but that there are some strategies that are just like a good idea if you want to thrive on Earth. And given enough time, natural selection will eventually kind of steer life towards those options. All evolutionary roads lead to a kind of evolutionary Rome. Now, as Gold acknowledged in his book, there's no way to definitively settle this question. We do not have a time machine or the ability to watch multiple Planet Earths unfold across hundreds of millions of years to see if they all end up in the same place. But what we do have is an experiment that started even before Gold's book came

• 4:33Speaker 02

  out. This experiment that kind of has the potential to maybe not answer this question, but at least explore it. It is an attempt to make something like 12 tiny, parallel universes and do a sort of speedrun of evolution. So this is unexplainable. I'm Bert Pinkerton. And today on the show, the long-term evolution experiment.

• 5:20Speaker 02

  The first seeds of the long-term evolution experiment started forming decades ago in the mind of one man.

• 5:28Speaker 03

  I'm Richard Lensky, and I'm a professor of microbiology here at Michigan State University.

• 5:34Speaker 02

  Now, long before Richard became a professor, he was a young scientist, less focused on tiny microbes.

• 5:42Speaker 03

  Microbiology seemed kind of complicated, and I was more interested in big-picture sorts of questions.

• 5:48Speaker 02

  Questions about how evolution worked, how populations changed over time, how quickly or how slowly they changed. And he was especially interested in a question that was kind of similar to the one that Stephen J. Gold ended up asking. Basically, how predictable is evolution?

• 6:06Speaker 03

  I think it's a really interesting question, which is to examine the tension between randomness and predictability in evolution. How does that play out?

• 6:16Speaker 02

  As he progressed through his career, He started to wonder if he might be able to explore these big questions.

• 6:23Speaker 03

  I got really interested in sort of the idea that you might be able to watch evolution as an ongoing process.

• 6:29Speaker 02

  The problem was that watching evolution at work is very hard to do.

• 6:34Speaker 03

  Because environments in nature are constantly changing. There's not just two species, but hundreds of species potentially interacting. So seeing it as an ongoing process is very challenging.

• 6:45Speaker 02

  Richard, in fact, experienced firsthand how challenging it could be.

• 6:50Speaker 03

  For my PhD, I worked at University of North Carolina on beetle populations in forests and in clear-cut areas, trying to understand the competition between species and the growth of populations and that sort of thing. And the project went pretty well, but it was also very frustrating to me. The weather didn't always cooperate. The beetles didn't always cooperate. And it was a lot of work.

• 7:17Speaker 02

  What does an uncooperative beetle look like?

• 7:20Speaker 03

  Well, among other things, they can squirt some nasty stuff at you. At least these particular ones.

• 7:28Speaker 03

  So you have to handle them a little bit gingerly.

• 7:30Speaker 02

  If Richard wanted to get answers to his questions about evolution, he realized that he needed to strip things down to get rid of the literal mess of squirting beetles, but also the figurative messiness of them. All the other things that they might encounter during their little beetle lives, like bad weather or good weather, or lots of food or not enough of it. Richard needed to create an experiment so simple, basically, that he had a realistic chance of keeping track of everything in it, of watching evolution play out without distractions.

• 8:05Speaker 03

  I wanted to strip evolution down to its bare bones.

• 8:09Speaker 02

  And to do that, he moved away from beetles, away from animals entirely, and he landed instead on bacteria, and specifically E. coli.

• 8:19Speaker 03

  E. coli is the lab rat of bacteria. Many people have sort of a visceral reaction to E. coli, saying, oh, that's a nasty bug. Don't get near me. But in fact, every one of us, every human on the planet, has roughly a billion E. coli in their lower digestive tract.

• 8:38Speaker 02

  Most strains of E. coli are not harmful. In general, it's just a little bacteria with a big, sweet tooth, right? It gobbles up sugar and then just kind of minds its own business. And it's very easy to work with in a lab, not just because it's not squirting stuff at you, but also because it's easy to look after and it reproduces really fast. It can go through six generations in a day, which would be like if you could produce great, great, great, great grandchildren in 24 hours. That's pretty perfect for someone who's trying to figure out how things evolve over time. So it's pretty perfect for Richard. He couldn't go back and see how the Earth might have evolved differently if you reran it in different ways.

• 9:21Speaker 02

  But he could create 12 almost identical situations and then watch each of them play out, like making 12 parallel universes if those universes were in laboratory flasks.

• 9:35Speaker 03

  Little flasks, little tiny flasks that hold up to 50 milliliters. They're only a couple of inches tall, little glass flasks that have little beakers sitting on top of them.

• 9:47Speaker 02

  And so 37 years ago, Richard took 12 little piles of E. coli, each of which had grown from a single cell. And on February 24th, 1988, he put one pile into each of 12 flasks. And inside each flask, there was a mixture of water and sugar and some other ingredients that you can think of kind of like a broth or a soup, I guess. It was a tweaked version of a historical recipe that lots of other microbiologists had used to raise E. coli. And this broth mixture, again, was pretty much identical in each flask or is as close to identical as possible. And then after the E. coli were added, each flask was put into an incubator,

• 10:32Speaker 02

  this big box kept at 37 degrees Celsius that shakes very slightly to keep everything kind of moving around a bit.

• 10:39Speaker 03

  And when the flasks are sitting in the incubator with their little glass beakers on top, they make a very delightful little jingling sound, very quiet to the ear. Too bad I don't have any here. I could shake one for the recording. But it's a very pleasant sound.

• 10:54Speaker 02

  Inside each flask on that first day in 1988, E. coli basically did their thing. They ate glucose, they reproduced. They reproduced some more. And by the next day, they'd eaten the glucose in their flasks. So Richard took 12 new flasks, put fresh broth in each of them, and then took some of the E. coli from the first flask and transferred it carefully into a new one. Then he did the same with the second flask.

• 11:23Speaker 03

  And you do that for all the populations. Takes a few minutes, once you're good at it at least, and you pop those back into the incubator.

• 11:32Speaker 02

  And there, the E. coli continued eating, and reproducing, and eating, and reproducing some more. And the next day, he transferred the E. coli again, and again. Eventually, other people in his lab were doing the transfers too, but it was always the same routine. Each day, they would transfer the E. coli to new flasks, and then the next day, they do it again. And the next day, again. And again, the next day. And then again. Again, again, and again, again. Weekends and holidays, and as close to 365 days a year as possible for first weeks, and then months, and then years.

• 12:16Speaker 02

  And with each day and each round of reproduction, the populations in each flask started to peel away from each other. Because in each flask population, even though everything else was almost the same, different random mutations were happening, tiny changes to the E. coli genes. Some of those mutations did not help the E. coli, maybe even harmed them. But some mutations were helpful, and those E. coli were more likely to reproduce and pass their mutations on. And so even though the E. coli in each flask started with an almost identical ancestor, and close to identical food, and close to identical conditions, as they mutated, they started to differ from each other just a little tiny bit.

• 13:02Speaker 02

  So this is how Richard and his colleagues set up essentially a miniature model of evolution. These 12 tiny doll's house worlds full of bacteria.

• 13:12Speaker 02

  But in order to figure out how those worlds were changing over time, they also needed a record, right? Snapshots of the doll's houses across the generations. So they also made a doll's house version of a fossil record. Every 75 days after they moved a small fraction of E. coli from last day's flask into a new one, they took some of the leftover E. coli from the old flasks, and they froze it. Because E. coli have one more superpower that makes them especially good research subjects.

• 13:47Speaker 03

  We can freeze the bacteria, and they are still alive.

• 13:51Speaker 02

  You can think of them like they're in suspended animation, almost. So if you thaw them out again down the line, they come right back to life.

• 13:59Speaker 03

  And that allows us to do what I like to call time travel. We can directly compare strains of our bacteria that lived at different times in the past.

• 14:09Speaker 02

  A paleontologist who's studying the normal fossil record, they have to look at stuff like old skeletons, right? Those skeletons are often incomplete, sometimes just single bones. They're creatures we don't have any bones from at all. And also, bones are obviously fossilized, so they've turned to rock. All to say, our fossil record is a puzzle with a lot of pieces missing. But in Richard's lab, the record of E. coli past is beautifully thorough.

• 14:41Speaker 03

  Yeah, we call it the frozen fossil record. So not only do we have images of the cells, not only do we have their DNA preserved, but we can actually bring them back to life. And so, as I said, we can compare things that lived at different times, directly compete them head to head. Well, I guess bacteria don't have heads, but cell to cell.

• 15:02Speaker 02

  If they froze bacteria one day, then 75 days later, or 150 days later, or 3,000 days later, they could pull out that first frozen sample, thaw out those bacteria, and then compare them to current bacteria. It'd be a little bit like if we could thaw out cryogenically frozen but somehow living humans from 10,000 years ago or something, right? And then... See what would happen if we compared ourselves to them directly.

• 15:34Speaker 03

  What if we played football with them? What if we played chess? Or what if we had to hunt for food?

• 15:40Speaker 02

  Who would win in a hot dog eating contest? Me or my 500th great grandmother? In Richard's lab, they can meaningfully ask a version of that question. It's just, who would win in a glucose eating contest? This bacterium or its 500th great ancestor? And doing work like this gave them some really fascinating insight into some of Richard's questions about how evolution actually works. Over the years, they've been able to track how beneficial mutations spread through a population. And they even saw that some E. coli seemed to increase their mutation rate, as though to increase their odds of hitting on a lucky mutation that could help them out. It is all really fascinating work. But a few years in, after the E. coli evolved and evolved and evolved some more, Richard

• 16:25Speaker 02

  and his colleagues were also able to start answering the big question that they'd had about what the effects of random chance mutations might be. They could compare the 12 parallel populations, the doll's house universes, if you will, and see, did all the bacteria take sort of different evolutionary routes to wind up in essentially the same place or not? When he set up the experiment, Richard assumed that the answer was going to be not.

• 16:54Speaker 03

  I was imagining that if I set up these replicate populations in the laboratory under identical conditions and with the exact same ancestor, I was thinking they'd kind of all go off in very different directions. And what we found, a little bit to my consternation, was that all roads seemed to lead to pretty similar improvements in fitness. Basically, the common solution seemed to be to eat as much glucose as you can and as fast as you can and get really big, fast-growing cells.

• 17:26Speaker 02

  With DNA analysis tools, Richard and various collaborators could peek under the hood of the E. coli cells, too. And there, they also saw that the bacteria in the different populations were taking different approaches, and there were definitely some significant differences between them. But they were, overall, landing in pretty similar places.

• 17:46Speaker 03

  And moreover, not only were they doing things remarkably similar, not identical, but it was really hard to sort of see the differences. They were also slowing down.

• 17:57Speaker 02

  It seemed like all roads led to maybe different suburbs of Rome, but still Rome-ish.

• 18:06Speaker 02

  Now, that doesn't mean that Stephen J. Gold was wrong to say that the past matters and things that happened millions of years ago shaped the future, right? Our Earth is a lot more complex than a little box of flasks.

• 18:20Speaker 02

  It contains a lot of different species, all interacting with each other, not just one species of E. coli. And it also changes over time. In Gold's thought experiment, part of what created different paths for different universes was random chance stuff beyond just mutations, right? Like a lake drying up or an asteroid hitting the Earth. That stuff is not happening in this experiment. Still, by about 15 years in, it did seem like, at this small, super simple scale, the question was somewhat settled.

• 18:54Speaker 03

  I kind of imagined that the experiment had run its course. And I even talked to some colleagues.

• 19:04Speaker 03

  You know, maybe, maybe we should end this experiment.

• 19:09Speaker 02

  And then, one of the 12 flask populations stopped looking like all the other populations. It stopped going to Rome.

• 19:17Speaker 03

  One of them went on a, you know, transpacific flight and did something completely different.

• 19:25Speaker 02

  That's after the break.

• 19:30Noam Hassenfeld?

  Support for the show comes from Sonos. Hey, Sonos, give me some music.

• 19:36Noam Hassenfeld?

  All right, one of life's great mysteries. You're listening to music in the living room, but you gotta grab something from the kitchen. You don't want to take the speaker with you, but you also don't want to miss that beat drop. And this is where I introduce you to the magic of Sonos. Sonos sent me a couple of speakers to try out, so I've got to move two here in the living room. And then, I walk down the hall.

• 20:01Noam Hassenfeld?

  I get in here to the kitchen, and I got a brand new Sonos Play right here on the counter. I can open the fridge, grab a seltzer.

• 20:19Noam Hassenfeld?

  And yeah, I didn't miss a second. And I can make each speaker louder or softer in the Sonos app, or if I'm using AirPlay, so I can make it louder in the kitchen without blasting whoever is still in the living room. It's all just easy and it sounds amazing. These speakers are crisp. They've got great bass. And I'm especially impressed with the new Sonos Play. It packs this like truly awesome sound in a much smaller size. So I don't know if I want to

• 20:52Noam Hassenfeld?

  head outside for a minute.

• 20:55Noam Hassenfeld?

  It's super easy and yeah, pretty nice out. Visit sonos.com and build your system. Sonos, love the sound, feel the system.

• 21:10Speaker 02

  Support for the show comes from Quince. Fall is my absolute favorite season. I love fall colors. I love fall leather. I love the specific light you sometimes get on a fall afternoon. And I really love fall clothes, which Quince has. This fall, Quince is offering pieces with premium materials like 100% Mongolian cashmere, organic cotton and merino wool. The styles are timeless, versatile, and designed to become the dependable pieces you reach for day after day. Their 100% Mongolian cashmere sweaters start at just $60, giving you the softness and quality you'd expect from a luxury brand without the luxury price tag.

• 21:53Speaker 02

  I think my favorite thing about Quince clothes is that they're just good wardrobe staples. I got three black shirts from them, each in a slightly different style, and they are just correct. They fit the way they are supposed to. They look nice. They feel nice and they go well with the rest of my closet. Find your next fall favorites at Quince. Download the Quince app for app exclusive offers or go to quince.com. Get free shipping on your order and 365 day returns, now available in Canada and the UK too. And when Quince asks you where you heard about them, please let them know it was unexplainable. It's a great way to support the show.

• 22:35Speaker 04

  This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome? That's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense? There's no place like Chrome. Check responses set up required. Compatibility and availability varies 18 plus.

• 23:05Speaker 05

  Wait, I think we've established that caca, caca, and tuky, tuky don't work.

• 23:11Speaker 02

  Richard actually almost missed one of the most exciting discoveries of the long-term evolution experiment.

• 23:16Speaker 03

  Yeah, it's kind of a complicated story and one that I almost blew. And history gives us do-overs in some cases.

• 23:24Speaker 02

  It all started one day in January of 2003. A researcher in Richard's lab was going through the usual process of pulling out the 12 flasks to transfer the E. coli in them into new flasks when he noticed something odd.

• 23:38Speaker 03

  So the person who first noticed this increased turbidity was, or increased cloudiness of the culture, was a postdoc. And this happened to be on a weekend. So I was just looking back at the lab notebook. I have it right here beside me, in fact. So it was a weekend. And on Saturday, he said, hmm, something seems off. One of these cultures is more turbid than it should be.

• 24:04Speaker 02

  Cloudiness like this, it means that so much stuff is growing in the flask that it started to lock out the light. E. coli multiply as they eat glucose and reproduce, but there wasn't enough glucose in the flask for E. coli to grow to light-blocking numbers, which suggested that there might be a contaminant in the flask, right? Or that something had gone wrong somehow.

• 24:26Speaker 03

  And on Sunday, same thing. It was still too turbid. So on Monday, the transfers were being done by Nirja Hajela, a former technician in my lab. Who actually has done more transfers than anybody else. She worked with me for over 20 years. And Nirja showed it to me. And I said, something's wrong. We got a contaminant in there. Let's go back into the freezer and restart that population.

• 24:52Speaker 02

  Basically, they did the equivalent of going to your last saved place in a video game and starting again. They went back into the freezer, grabbed their last frozen population. And that let them start from a freezer save point, essentially, and continue on.

• 25:07Speaker 03

  And do I remember that only vaguely? What I remember much more is, so the first discovery of the turbidity, the cloudiness, was in January.

• 25:22Speaker 02

  And then in April.

• 25:24Speaker 03

  The same population that had been restarted by going back into the freezer, suddenly got very cloudy again. And I said, whoa. And I started doing things like looking more closely at the colonies, doing literally a little bit of a smell test, how they smelled and how they looked on plates, and checking some genetic markers. We knew certain things that would tell us these were really E. coli doing this.

• 25:50Speaker 02

  His analysis of the bacteria that were in this cloudy flask ultimately showed that they were, in fact, E. coli and descendants of that first ancestor. There were just a lot more of them than there should be. And the explanation had to do with the broth that Richard had been putting in these flasks. This broth, again, was basically just a recipe that Richard had pulled from other historical experiments on E. coli. Right, a mixture of water with some glucose.

• 26:18Speaker 03

  But there was another thing that I left in the recipe, which is something called citrate, which is a compound that gives lemons and oranges and citrus fruits their sort of tart, sour taste. And that was in the recipe for historical reasons. And I just left it in. I had sort of played around over the years with getting rid of it, but I just left it in. But I didn't reduce the amount of it. So there was a lot of citrate. But it didn't really matter because E. coli. Can't grow on citrate.

• 26:51Speaker 02

  At least not in these conditions. In these conditions.

• 26:55Speaker 03

  It eats the glucose and then goes to bed every night until we transfer it, not knowing that there's this delicious lemony substance, this citrate, this lemony dessert that was sitting there to be had. And for 15 years, none of them figured it out. And then suddenly, one of the populations figured it out.

• 27:14Speaker 02

  This one flask full of E. coli had figured out a way to eat this lemony citrate stuff. That's not totally unheard of. There are other examples in the world of E. coli that have developed the ability to eat citrate. But Richard and his colleagues were really interested to see that even though there was a lot of citrate around in this broth to eat, and even though the E. coli had had over a decade to evolve and had gone through many thousands of generations of evolution at this point, only one of the flask populations of E. coli had made this leap. It seems strange that if it was possible, it would have taken so long and only happened one time.

• 27:55Speaker 03

  Something weird was going on, and we wanted to get to the bottom of that weirdness.

• 28:03Speaker 02

  Which is kind of an exciting task to have as a bunch of scientists.

• 28:07Speaker 06

  I'm still really excited about it. So yeah, yay. Yeah, actually, I still get almost silly with excitement whenever I give talks about this, which is unusual because I'm, I'm actually a very shy person, but I don't seem that way when I'm talking about this.

• 28:24Speaker 02

  Zach Blount was not actually there for the discovery of the lemony citrate eating behavior in this E. coli because he joined Richard Lenski's lab as a PhD student a little later on. But through a series of lucky breaks, he wound up directly involved in studying the citrate eaters.

• 28:40Speaker 06

  And the entire project fell into my lab.

• 28:42Speaker 02

  Zach wound up spending the next few years of his life trying to figure out what exactly had happened with these E. coli, how they had developed the ability to eat this lemony citrate stuff. And to do that, he went back into the freezer to unfreeze some of the past generations of E. coli, to then see if he could get them to do this again, essentially.

• 29:04Speaker 06

  There was a lot of waiting and worrying, is this going to work?

• 29:08Speaker 02

  There's actually a picture of him sitting next to more than 13,000 little trays that he used to grow. Just a whole lot of E. coli, which he then kept careful track of in a bunch of notebooks and spreadsheets, waiting to see if the E. coli would re-evolve the ability to eat this lemony dessert.

• 29:28Speaker 06

  I'd have to look back my calculation, but I think I went through something like 10 trillion cells and found 13 independent re-evolutions of the citrate-using bacteria.

• 29:41Speaker 02

  At what point did you finally feel like, okay, this is real? I did, like, this is real, I'm gonna have a pretty good PhD on my hands.

• 29:51Speaker 06

  Well, I'm a worry wart, so I kept thinking, maybe I should go a little bit further. Maybe I should go a little bit further. And finally, Rich said, Zach, it's time to move on. There are other questions to answer. I think you got this one.

• 30:08Speaker 02

  Zach was, ultimately, able to work out that this newfound citrate-eating ability didn't happen all at once in a single mutation, but instead came from a series of mutations that built on top of each other.

• 30:23Speaker 06

  Becoming able to use the citrate required multiple steps, multiple mutations. And over the course of this one population's history, it just happened to pick up a number of the mutations that were needed, so it only needed one or two more mutations to finally be able to do it.

• 30:45Speaker 02

  Basically, in order to wind up not in Rome, these E. coli took a bunch of turns along the way. They had to take one fork in the path of potential mutations, and then another fork on that evolutionary path, and then a few more fork choices until they eventually landed on the path that led them away from Rome and any of its suburbs and towards somewhere else, their evolutionary Tokyo.

• 31:17Speaker 02

  All this left me wondering what this might mean for the the big question that Stephen Jay Gould asked, right? The question of would our world look different if we reran it again? Or would it look the same? Or to put it another way, how much does history matter? Right? If you take one fork in the road versus another at some point early on, does that affect anything? Or will things eventually loop back to such a similar place that your historical choices are kind of unimportant? In this extremely simplified, experimental version of evolution,

• 32:00Speaker 02

  it seems like in most of the tiny populations of bacteria, history kind of didn't matter, right? They didn't wind up in exactly the same place, but they are still eating glucose 37 years in. And yet, in one population, history did matter. So what does that mean?

• 32:25Speaker 06

  I think, I think the answer I have come up with is history doesn't matter, except for when it really does. The natural selection largely is going to drive evolution to a certain set of outcomes. But sometimes history is going to lead it down a different path, and there's going to be something radically different.

• 32:50Speaker 02

  In some ways, this reminded me of the experiment itself, because it's also full of a lot of historical accidents, right? Some feel like they didn't necessarily change the outcome, like Richard dismissing that first cloudy flask as contaminated. But others, like Richard using that old recipe that happened to have citrate in it, those seem to have had a big effect. So it feels like kind of the same thing. History didn't matter, except when it really did. But before we draw some grand, sweeping conclusions about the nature of history or of evolution, I think it's important to remember that we don't know the final outcome here,

• 33:34Speaker 02

  because the experiment isn't over yet. It's still running.

• 33:39Speaker 02

  And maybe, given enough time, some of the other 11 blast populations will develop the ability to eat citrate, too. Maybe all of them will. Maybe all roads will actually lead to citrate eating if we wait long enough. How can we know?

• 33:56Speaker 03

  We don't know. That's one reason I want this experiment to continue into perpetuity. You could imagine that as difficult and background-dependent and rare mutation-dependent as it is, that none of them will get there over any, whatever timescale you want to imagine. Or perhaps, well, one every 35 years is our best estimate. So maybe it will happen in some of the others. And I'd love to know the answer to that.

• 34:26Speaker 02

  A few years ago, Richard decided to pass the experiment on. So it's entering its second scientific generation with a new director. He is committed to continue the experiment, to keep watching and waiting and seeing what happens next with these bacteria. When I spoke to him, he told me that he liked the fact that every day with this experiment was kind of like pulling a slot machine, waiting to see if, by some random chance, today might be the day that we get some answers to our questions or learn something interesting. And I guess if not today, then maybe tomorrow, or the day after that, or the day after that, or after that,

• 35:09Speaker 02

  or the next day, or the day after that, the day after that, or after that, or the next day, the day after that, or the day after that. There is so much more to read about the long-term evolution experiment. And I really encourage you to look up their research website and dig in. We will link to that in the transcript. And we will also link to a great review paper in Nature written by James Stroud and William Ratcliffe. It gives an overview of what long-term studies have taught us about evolution so far. This episode was produced by me, Bert Pinkerton.

• 35:49Speaker 02

  It was edited by Julia Longoria with help from Jorge Just and Paige Vega. Meredith Hodnot runs our show. Noam Hassenfeld makes our music. Christian Ayala did the mixing and the sound design. Melissa Hirsch checked the facts. And I am always, always grateful to Brian Resnick for co-creating the show. I'm also grateful this week to the many people who gave me their time to help me better understand some of the science here. Thanks so much to Jeff Barrick, the new director of the Long-Term Evolution Experiment, to William Radcliffe, James Stroud, Joe Wolfe, and Jean Bernard Caron.

• 36:29Speaker 02

  An extra huge shout out to Zach Blount as well for all his time. If this episode made you think, or if you have something you'd like to share with us, write in or send us a recording. We are at [email protected]. I love hearing from you all so much. Please write in. If you want to support the show and help us keep making it, please join our membership program. It is at vox.com/members and you get ad-free podcasts, unlimited access to Vox journalism. What more could you want? If you sign up because you love Unexplainable, please tell our bosses. It makes a big difference.

• 37:11Speaker 02

  You can also support us by leaving a nice rating or a review perhaps, or just by telling the people in your life to listen. Thank you for listening. And Unexplainable is part of the Vox Media Podcast Network. We will be back in your ears next week.

• 37:45Speaker 07

  This episode is brought to you by State Farm. Football has a play for just about everything. You can go deep, keep it on the ground, or draw up something nobody sees coming. And whether you want to run a flea flicker or the tush push, you need a plan to fit your unique situation. That's why State Farm takes the time to get to know you, so they can help personalize coverage for your life and budget. Now that's a solid game plan. Like a good neighbor, State Farm is there.

• 38:13Speaker 08

  When you shop Kroger Delivery, you can expect the savings you love and fresh groceries delivered right to your door. From delicious produce to everyday essentials, enjoy the convenience of delivery and the trusted selection you've come to know from Kroger. Because bringing you fresh, quality groceries is what we do best. Right now, enjoy free delivery on orders of $50 or more with your digital coupon. Restrictions apply. See site for details. Kroger. Fresh for everyone.