In short
“12 tiny worlds” explores how predictable evolution is by describing the Long-Term Evolution Experiment (LTEE): 12 replicate E. coli populations started from single cells in 1988 and have been transferred daily, with “frozen fossil record” samples enabling direct comparisons across time.
Guest backgrounds
Richard Lenski is a Michigan State microbiology professor who designed the LTEE to study randomness vs predictability in evolution. Zach Blount studied the LTEE’s “citrate-eater” breakthrough as a PhD student in Lenski’s lab. (Host: Bird Pinkerton.)
Key claims
Most replicate populations converge on similar fitness improvements (“eat glucose fast, grow big”), suggesting many evolutionary outcomes are repeatable. But history can matter: one population evolved the ability to use citrate after decades, via multiple-step mutations.
Notable examples
hallucinogenia and opabinia fossils as Gould’s “rerun history” inspiration; the LTEE citrate-eating event triggered by citrate left in the broth recipe; 13+ independent citrate re-evolutions observed in later replays.
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOImagining Time Travel Through Evolution
0:00 to 0:30
Explore the concept of rewinding time to examine evolutionary paths.
“Support for the show comes from Google Gemini.”
Imagining Time Travel Through Evolution
0:42 to 4:55
Explore the concept of rewinding time to examine evolutionary paths.
“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.”
Introduction to the Long-Term Evolution Experiment
4:55 to 5:21
Learn about Richard Lenski's groundbreaking evolution experiment.
“And today on the show, the long-term evolution experiment.”
From Beetles to Bacteria: Simplifying Evolution Study
5:21 to 8:06
Understand the challenges of studying evolution and how Lenski tackled them.
“I'm Richard Lenski, and I'm a professor of microbiology here at Michigan State University.”
Setting Up Parallel Universes in the Lab
8:06 to 14:00
Discover how Lenski created a controlled environment for bacteria evolution.
“And to do that, he moved away from beetles, away from animals entirely, and he landed instead on bacteria, and specifically E.”
Exploring the Frozen Fossil Record of E. coli
14:00 to 16:20
Learn about the detailed experimental setup of studying E. coli evolution over time.
“We can directly compare strains of our bacteria that lived at different times in the past.”
Unexpected Findings in Evolutionary Paths
16:20 to 19:20
Discover the surprising results of parallel E. coli populations evolving under identical conditions.
“coli evolved and evolved and evolved some more, Richard 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.”
The Turbidity Discovery
19:20 to 23:00
Learn about the crucial moment when increased turbidity was observed in one E. coli flask, indicating an anomaly.
“Like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks.”
The Citrate-Eating Breakthrough
23:47 to 28:00
Explore the groundbreaking discovery of E. coli's ability to metabolize citrate after years of evolution.
“This broth, again, was basically just a recipe that Richard had pulled from other historical experiments on E.”
Exploring Evolution and History's Role
28:00 to 31:28
Discover how mutations in bacteria illustrate the unpredictability of evolution.
“but instead came from a series of mutations that built on top of each other.”
Show all 13 chapters
The Ongoing Evolution Experiment
31:28 to 32:36
Learn about the long-term evolution experiment and its implications for future discoveries.
“Maybe all roads will actually lead to citrate eating if we wait long enough.”
The Ongoing Evolution Experiment
35:10 to 35:45
Learn about the long-term evolution experiment and its implications for future discoveries.
“This is the love story of real hinge couple Isabella and Rebecca, written and read by me, Temi Denton-Hurst.”
The Ongoing Evolution Experiment
35:49 to 36:11
Learn about the long-term evolution experiment and its implications for future discoveries.
“officially here, and Deedee's has everything on your list.”
Transcript
Automatic transcript. May contain errors.0:00Richard Lenski:Support for the show comes from Google Gemini. You know that moment when curiosity strikes? You're exploring a new city with a family and a sculpture catches your daughter's eye. What is that? Who made it? With Gemini, you can snap a picture and get a fully interactive breakdown of its history, architecture, and even hidden secrets. Gemini is built for moments like that. Whether you're learning something new, solving a problem, or looking for your next favorite thing, Google Gemini is here to help. Download Gemini, Google's AI app, or visit gemini.google.com to learn more.
0:39Zachary Blount: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+.
1:05Richard Lenski:Imagine for a moment that we have the ability to rewind time. That we're able to press a button and slide back through the last century's 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. 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. Creatures like hallucinogenia, which does in fact look like something out of a hallucination.
1:57Richard Lenski: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. 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?
2:44Richard Lenski: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 hallucinogenia or opabinia or something else, 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 Jay Gould 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.
3:29Richard Lenski:And if you re-ran 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. 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.
4:11Richard Lenski: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 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 speed run of evolution. So, this is Unexplainable. I'm Bird Pinkerton.
4:58Richard Lenski:And today on the show, the long-term evolution experiment.
5:20Richard Lenski:The first seeds of the long-term evolution experiment started forming decades ago in the mind of one man.
5:28Zachary Blount:I'm Richard Lenski, and I'm a professor of microbiology here at Michigan State University.
5:34Richard Lenski:Now, long before Richard became a professor, he was a young scientist, less focused on tiny microbes.
5:43Zachary Blount:Microbiology seemed kind of complicated, and I was more interested in big picture sorts of questions.
5:49Richard Lenski: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 Jay Gould ended up asking. Basically, how predictable is evolution?
6:06Zachary Blount: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?
6:17Richard Lenski:As he progressed through his career, he started to wonder if he might be able to explore these big questions.
6:24Zachary Blount:I got really interested in sort of the idea that you might be able to watch evolution as an ongoing process.
6:29Richard Lenski:The problem was that watching evolution at work is very hard to do.
6:34Zachary Blount: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.
6:46Richard Lenski:Richard, in fact, experienced firsthand how challenging it could be.
6:50Zachary Blount:For my Ph.D., 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.
7:18Richard Lenski:What does an uncooperative beetle look like?
7:21Zachary Blount:Well, among other things, they can squirt some nasty stuff at you, at least these particular ones. So you have to handle them a little bit gingerly. 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.
7:44Richard Lenski: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.
8:05Zachary Blount:I wanted to strip evolution down to its bare bones. And to do that, he moved away from beetles, away from animals entirely, and he landed instead on bacteria, and specifically E. coli. 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.
8:39Richard Lenski: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 was pretty perfect for Richard.
9:15Richard Lenski:He couldn't go back and see how the Earth might have evolved differently if you re-ran it in different ways, 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.
9:36Zachary Blount: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.
9:47Richard Lenski: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 as close to identical as possible. And then after the E. coli were added, each flask was put into an incubator.
10:33Richard Lenski:This big box kept at 37 degrees Celsius that shakes very slightly to keep everything kind of moving around a bit.
10:40Zachary Blount: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.
10:55Richard Lenski:Inside each flask on that first day in 1988, the 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.
11:23Zachary Blount: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.
11:32Richard Lenski: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 and again and again and again and again and again and again weekends and holidays and as close to 365 days a year as possible for first weeks and then months and then years 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.
12:31Richard Lenski:coli genes. Some of those mutations did not help the E. coli, maybe even harm 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. 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. But in order to figure out how those worlds were changing over time, they also needed a record, right?
13:20Richard Lenski:Snapshots of the doll's houses across the generations. So they also made a doll's version of a fossil record. Every 75 days after they moved the small fraction of E. coli from last day's flasks 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.
13:47Zachary Blount:We can freeze the bacteria and they are still alive.
13:51Richard Lenski: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.
13:59Zachary Blount: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.
14:10Richard Lenski: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.
14:41Zachary Blount: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.
Read the full transcript
15:03Richard Lenski: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.
15:35Zachary Blount:What if we played football with them? What if we played chess? Or what if we had to hunt for food?
15:40Richard Lenski: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.
16:17Richard Lenski:It is all really fascinating work. But a few years in, after the E. coli evolved and evolved and evolved some more, Richard 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.
16:54Zachary Blount: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 seem 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.
17:26Richard Lenski: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.
17:47Zachary Blount: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.
17:58Richard Lenski:It seemed like all roads led to maybe different suburbs of Rome, but still Rome-ish. Now, that doesn't mean that Stephen Jay Gould 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. 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.
18:41Richard Lenski: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.
18:54Zachary Blount:I kind of imagined that the experiment had run its course. And I even talked to some colleagues, you know, maybe we should end this experiment.
19:09Richard Lenski:And then one of the 12 flask populations stopped looking like all the other populations. It stopped going to Rome.
19:17Zachary Blount:One of them went on a, you know, trans-Pacific flight and did something completely different.
19:25Richard Lenski:That's after the break.
19:39Zachary Blount: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+.
19:57Richard Lenski:This episode is brought to you by Accenture. When your advertising operations fall out of sync, everything else follows. Spotify and Accenture are working together to reinvent the rhythm of ad sales, using automation, analytics, and smarter workflows to simplify campaign delivery and access better data across the business. The result? Less time spent on operations, more time connecting brands with the moments and fandoms that matter most. Learn more at Accenture.com slash Spotify. I didn't like what you said, Odin pauses, about the future. This is the love story of real hinge couple Odin and Edward, written and read by me, Curtis Garner.
20:39Zachary Blount:Listen to the free audiobook now.
20:54Richard Lenski:Richard actually almost missed one of the most exciting discoveries of the long-term evolution experiment.
20:59Zachary Blount:Yeah, it's kind of a complicated story and one that I almost blew. And history gives us do-overs in some cases.
21:07Richard Lenski: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.
21:21Zachary Blount:So the person who first noticed this increased turbidity was our 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.
21:48Richard Lenski:Cloudiness like this, it means that so much stuff is growing in the flask that it started to block 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.
22:10Zachary Blount:And on Sunday, same thing. It was tilled too turbid. So on Monday, the transfers were being done by Nirja Hajala, 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.
22:35Richard Lenski: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 safe point, essentially, and continue on.
22:50Zachary Blount: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. And then in April. 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.
23:34Richard Lenski: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.
24:02Zachary Blount: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.
24:35Richard Lenski:At least not in these conditions. In these conditions?
24:38Zachary Blount: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.
24:57Richard Lenski: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.
25:39Zachary Blount:Something weird was going on, and we wanted to get to the bottom of that weirdness.
25:46Richard Lenski:Which is kind of an exciting task to have as a bunch of scientists.
25:50Zachary Blount: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 actually a very shy person, but I don't seem that way when I'm talking about this.
26:08Richard Lenski:Zach Blount was not actually there for the discovery of the lemony citrate-eating behavior in this E. coli because he joined Richard Lensky'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. And the entire project fell into my lap. 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.
26:42Richard Lenski:coli to then see if he could get them to do this again, essentially.
26:47Zachary Blount:There was a lot of waiting and worrying, is this going to work?
26:51Richard Lenski: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.
27:12Zachary Blount: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-ucine bacteria.
27:25Richard Lenski:At what point did you finally feel like, okay, this is real? I did, like, this is real. I'm going to have a pretty good PhD on my hands.
27:38Zachary Blount:Well, I'm a worrywart. 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.
27:52Richard Lenski: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.
28:07Zachary Blount: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.
28:29Richard Lenski: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.
29:00Richard Lenski:All this left me wondering what this might mean for 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, it seems like in most of the tiny populations of bacteria, history kind of didn't matter, right?
29:52Richard Lenski: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? I think the answer I've come up with is
30:15Zachary Blount: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.
30:33Richard Lenski: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 because the experiment isn't over yet.
31:20Richard Lenski:It's still running. And maybe, given enough time, some of the other 11 flask 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.
31:38Zachary Blount:How can we know? 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.
32:09Richard Lenski: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.
32:51Richard Lenski:Or after that. 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. Or the next day. 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.
33:33Richard Lenski:It was edited by Julia Longoria with help from Jorge Just and Paige Vega. Meredith Hodnott runs our show. Noam Hasenfeld 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 Beric, the new director of the Long-Term Evolution Experiment, to William Radcliffe, James Stroud, Joe Wolfe, and Jean-Bernard Caron. An extra huge shout out to Zach Blount as well for all his time.
34:18Richard Lenski: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 unexplainableatvox.com. 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 slash 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. 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.
35:03Richard Lenski:Thank you for listening. And Unexplainable is part of the Vox Media Podcast Network. We will be back in your ears next week.
35:27Zachary Blount:I don't think I can be your friend. Isabella said.
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From the publisher
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
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