Jonathan Losos, biology professor at Harvard and curator of herpetology at the university’s Museum of Comparative Zoology, talks about his latest book,Improbable Destinies: Fate, Chance and the Future of Evolution. Stephen Jay Gould famously argued that evolution should not repeat itself. But the work of many biologists, including Losos himself, found evolution recapitulating itself in certain situations. So how does evolution work?
Steve Mirsky: [Music] Welcome to Scientific American’s Science Talk, posted on September 27th, 2017. I’m Steve Mirsky. On this episode….
Jonathan Losos: And we now realize that there is plenty of convergence around us. Well that has led some people to argue, in fact, that evolution is very deterministic, that the environment poses certain problems for organisms, and that there are best solutions that natural selection finds repeatedly.
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Mirsky: That’s Jonathan Losos, spelled L-O-S-O-S. He’s a biology professor at Harvard, and curator of herpetology at the university’s Museum of Comparative Zoology. And his latest book is Improbable Destinies: Fate, Chance, and the Future of Evolution, in which he addresses a question that’s been the subject of debate in evolution circles for decades. Given the same starting point, does evolution happen the same way over and over again, or will each unspooling of the tape give rise to a different set of outcomes?
Stephen Jay Gould argued that evolution should not repeat itself, and that’s where we begin. Losos sat down with me at the Scientific American office. Be advised that almost three minutes into the interview, I utter a vulgar expression, which has been used repeatedly over the years by Scientific American columnist John Horgan to sum up Gould’s overarching view of evolution. So, consider yourself warned.
Maybe a good place to start is by talking about Stephen Jay Gould.
Losos: Great.
Mirsky: And the outsized effect his musings, really, sometimes have had on the whole field of evolutionary biology.
Losos: Well, Gould had an enormous impact, and he really invigorated the entire field of paleontology for one thing, from sort of a scientific backwater, where it was in the 1970s, to now at the forefront of evolutionary biology. Because he came up with ideas about how evolution occurs that really required fossils to test them. And he got people thinking about these ideas in new and completely interesting and novel ways. And so, he had a huge impact on the field.
And in many – I have to say, he also was a highly controversial figure for two reasons. One is that he liked to make arguments at their extreme. He liked to make the extreme argument. He said, “Well, maybe what I’m saying occurs half the time, but if I said this phenomenon occurs 47 percent of the time, no one would pay attention. But if I say this is the dominant mode of evolution, well, then people will engage and discuss.”
And so, he took extreme positions to be a lightning rod, and it worked, but a lot of people reacted against that. His ideas were also very unorthodox in many respects relative to the standard views of how evolution proceeds. And, lastly, he had an oversized ego, and he was extremely successful. And so, people don’t like arrogant people who are successful. And so, he generated a lot of – people didn’t like him, and took a lot of cheap shots as a result.
Mirsky: I saw that at numerous talks of his that I went to, just a prickly interaction with members of the audience.
Losos: Yes, I mean, there was – his famous theory of punctuated equilibrium, which argued that evolution – that a species stayed the same for a long period of time, and then changed rapidly over a short period. He called that punctuated equilibrium. Someone else called it evolution by jerks.
Mirsky: And the response to them was evolution by creeps, I believe.
Losos: I didn’t hear that one. But, yes.
Mirsky: I think Gould and Eldridge came back with, “Yeah, well, yours is an evolution by creeps.”
Losos: I hadn’t hear that one. The thing about Gould is it turns out that a lot of his ideas probably were not correct. But nonetheless, he deserves a huge amount of credit for getting people to think about ideas in completely new ways, and really revolutionizing how we think about evolutionary history. So, even if the exact ideas were wrong, he was a major figure in the field.
Mirsky: And one of the issues I know that some evolutionary biologists had with him was that they summarized his viewpoint as “shit happens.”
Losos: Yes, in a sense, I could see that. And, well, his book, Wonderful Life, which is the jumping off point to my book, his basic idea is that things happen that affect evolution, and will send evolution down one road and not another. And these events are not predictable beforehand. You can’t predict that an asteroid will slam into the earth, or even more minor events, but they happen, and as a result, evolution can go in very different ways that would not be predicted beforehand.
Mirsky: And he famously called this contingency.
Losos: Yes.
Mirsky: And your book is a book that a lot of us have been waiting for for a long time to discuss this issue of how predictable is evolution, in fact.
Losos: Well, and so, what Gould said in 1989, he basically said that if we could somehow replay the tape of life, go back 50 million years, or 500 million years, and let it all happen again, he said the outcome would be – he said you could re-run the tape a million times and humans would never evolve again, because just random events would come along and send evolution down another alley.
But, this argument, there were no data. It was all conjecture, thought experiments, theory, philosophy. There were no data behind it. But the idea was so influential that now, 30 years later, there are a lot of data from several different approaches that speak to the predictability of evolution, the extent to which contingency really does make evolution unpredictable.
Mirsky: And toward the end of the book, you even go into a lot of detail about the notion of contingency itself, and a philosopher of science, Bede, was it –
Losos: Yes, John Bede.
Mirsky: who talks about how even Gould didn’t quite make it clear what he might have meant by that. But let’s get to that in a minute.
Losos: Okay.
Mirsky: Because first I want to talk about the two opposing ideas. Kangaroos evolved once. There’s nothing like a kangaroo anywhere outside of Australia. Wallaby is a little bit like a kangaroos, but –
Losos: But it’s a type of kangaroo.
Mirsky: yeah, it’s a type of kangaroo, right We’re splitting hairs, which Australia has its own problem with. But anyway, meanwhile, your own research on anole lizards finds this unbelievable duplication series of events among the islands in the Caribbean.
Losos: Yes, well I – so that’s perhaps the irony of my book is that my research is on a type of lizard called an anoles lizard. People who’ve been to Florida or the American Southeast, or certainly the Caribbean have seen these lizards, because they’re running all around on the ground and on the trees and so on. They have a little flap of skin under their throat called a dewlap that they stick out that is very colorful and entertaining.
Mirsky: It looks like a watermelon slice in the ones you see in Florida.
Losos: That’s exactly right. And so, but it turns out there are 400 species of this type of lizard throughout the Caribbean and in Central and South America. And the interesting thing about these lizards is that on the big islands of the Caribbean, that is, Hispaniola, Puerto Rico, Jamaica, and Cuba, on each one of those islands, the lizards have had an independent evolutionary radiation that all the lizards on that island are descendant from one or a few species, and they’ve evolved independently of the lizards on the other islands.
And on each of those islands, they have diversified widely. So, for example, in Puerto Rico, if you went into the rainforest in the _____ Mountains, and you sat quietly for a few minutes, the lizards would forget you were there and they would come out.
And you would see that there are different species in different parts of the forest adapted for where they’re living. One species living on the tree trunks and running down to the ground with long legs to run fast and jump far, another species on twigs with very short legs to creep very carefully, another species high in the tree with big toe pads to hang on, and green in color so it blends in to the vegetation, and so on.
Well, if you then went to, say, Jamaica, you would see the same set of habitat specialists, another twig – another species living on twigs with short legs and very camouflaged. You might think it’s the same species on Puerto Rico, but it’s not. The same set of species as evolved independently on [crosstalk]
Mirsky: An analogous set of species.
Losos: An analogous set, exactly. This is the phenomenon that we call convergent evolution. It’s when species unrelated – well, when species independently evolve to be very similar in their appearance. And this is a particularly good example of convergence because it’s not a single type of species that has evolved multiple times, like the twig anoles, but an entire suite of species, each one parallel on each of the islands. So, it’s a remarkable case of convergent evolution.
Mirsky: And then, you guys actually start doing experimental evolution in these tiny – you can’t even call some of them islands they’re so small.
Losos: Yes, they’re very small, very small little rocks, really, in the Bahamas. They’re officially called rocks. Sometimes you call them keys, but some of them as small as a baseball diamond. And what we did was we found some of these islands that didn’t have any lizards on them at all and we put lizards on them, but we put them from surrounding areas. The reason they don’t have any lizards is that hurricanes come through and wash all the lizards off as probably just happened.
And then over time the lizards manage to find their way back, and re-establish a population, and then they get washed off again, and so on. And so, we were mimicking a natural process by putting the lizards on the islands, and then seeing how they evolve. And in this particular case, we were taking lizards from a bigger island nearby where they live on big trees.
And so, so they had long legs. And we were putting them on these islands where there was only very scrubby, scraggly vegetation. So, they had to hang on to very narrow vegetation. And so, our hypothesis was that if the species are adapting to the surfaces they use, then they should evolve shorter legs to use the narrower surfaces. And, sure enough, that’s exactly what happened.
Mirsky: And, we should say, these are not, you know, I don’t want to insult anybody’s intelligence, but the way this works is these organisms, these lizards in this case, they don’t – their legs don’t get shorter. There is a variation in the population, and the ones with the shorter legs have a higher survival rate.
Losos: Yes. It’s actually a little more complicated than that, but that’s the – what you said is the basic idea of evolution by natural selection, that you can imagine that you put lizards on an island, and lizards vary in their anatomy, just like humans do. If you look around, some people are taller, some people are shorter, some have longer legs, different hair color, and so on.
Mirsky: Right, like if mating was – in humans was purely predicated on basketball ability, I probably wouldn’t be here, but you’d be okay.
Losos: Well, perhaps. You haven’t seen me do a free throw. But that’s the idea. There is variation in a population, and it’s based on genetic differences. And if that variation actually matters to how well you survive and reproduce, then the genes of the successful individuals will be passed on to the next generation. And so, the population will more and more have those attributes.
And so, when we put the lizards on the islands, they varied in how long their legs are. And in this case, the ones with the shorter legs do better, they survive better. And so, the genes for short legs get passed on to the next generation. But there is a complication to that, because it turns out, we’ve discovered that if you raise a lizard – if you take two – say take identical twin lizards, if you could, and you put one and let it grow up using very narrow little surfaces, very narrow twigs, and you put the other one on very broad surfaces, it turns out that the lizard on the broader surface will – will not evolve, will grow longer legs, which was completely surprising to us.
This is a phenomenon called phenotypic plasticity. It’s the ability of genetically identical individuals to produce different anatomies based on their circumstances. And the easiest way to think about that is think about having two identical plants and putting one – watering one a lot and the other not very much.
Mirsky: Or, as you say in the book, the tennis players, and their own experiments.
Losos: Well, all right, let me tell you about the tennis players. It turns out that tennis players, their serving arms are longer than their non-serving arms. And the reason is that professional tennis players, of course, have been hitting tennis balls all their life, including their formative growth years. And it turns out that these pressures, the stresses put on their bones from smacking a ball for hours on end every day actually causes the bone to grow longer.
And so, that’s why their serving arms are longer. And so, this is not a genetic change. This is just the flexibility that any genotype – that any genetics has to produce variation.
Mirsky: But, in the book you point out that it’s still – that phenotypical plasticity only accounts for a small percentage of the difference that you see in the change over time.
Losos: That’s exactly right. So, we put the lizards on the islands. We come back 15 years later, and they had different leg lengths. And it turns out that a little bit of that might be this inherent plasticity based on circumstances, but most of it is due to genetic difference.
Mirsky: Right, so that’s the situation there. And then you also talk about the guppies in –
Losos: Yes, in Trinidad.
Mirsky: Trinidad, right.
Losos: Yeah, and this is the classic story of doing evolution experiments in nature. And the story is this. We all know guppies. You’ve seen them in pet stores, and they’re very colorful. Few people know where guppies come from. Well, they come from streams in the mountains of Trinidad and Venezuela. And, many of those guppy populations are very colorful. The males are colorful. But not all of them. In some populations, the males are quite bland.
And scientists, back in the 1930s, I think it was, noticed that there was a correlation, that the bland ones occurred in pools that also had larger predatory fish, whereas the colorful ones occurred in pools where there were no predatory fish. And so, the hypothesis was that the presence of predators selected for bland individuals, because the predators saw the flashy ones and picked them off.
Now, a corollary of this is it turns out that female guppies really like colorful males. And that’s why in the absence of predators, colorful males – color evolves in the males. Why the females like that we still don’t know. It’s an active area of research. But, be that as it may, so that’s the hypothesis. And so, a researcher named John Emler had this experiment, well let’s do an experiment to see if we can test this hypothesis.
And he did the simplest possible experiment. He took guppies from a pool that had predators in it, and moved them to another pool without predators. And sure enough, within two years, they had evolved to be much more colorful – clear evidence that it was, in fact, the predators that were driving color evolution in these fish.
Mirsky: One of the things I really appreciated about your book was that you do spend a little time talking about the ethical considerations of doing these kinds of experiments where you’re influencing the – you’re violating the Star Trek prime directive.
Losos: Well, this is an important question. And both in the question of the lizards and the guppies, researchers were simply mimicking a process that goes on all the time. And in the case of the lizards, they colonize these little islands, then a hurricane comes through and washes them clean. And so, it’s really just doing what occurs naturally. In the case of the guppies, there’s something comparable. Periodically, there’s a flash flood that basically washes everything out of the upper reaches of a stream, and then the fish get back up.
And the cool thing about this is that the predatory fish get stopped by waterfalls. And so, that’s why the higher reaches of the stream don’t have the predators. But the guppies apparently can get around the waterfalls. And we’re not quite sure how, but it seems that what happens is on a really big thunderstorm, water just goes rushing down the hill, and the fish can actually swim up in the leaf litter, if you will, and get around the waterfall and colonize new pools.
Mirsky: Like tiny little salmon.
Losos: Exactly, exactly.
Mirsky: You have other examples of these kinds of predictable outcomes. You talk about the sticklebacks, which are now a famous case.
Losos: Yes. Well, so, let me step back for a second, and talk more broadly about the idea of doing evolution experiments. Because few people realize it, but Charles Darwin was a great experimenter. And this is going back to the 1850s, before the experiment was the standard way of doing science. But even back then, he did all kinds of cool experiments. He was trying to figure out – how is it, why do plants grow towards light. And so, he exposed different parts of the plant to see what part of the plant was key for them moving that direction.
Or, how do – can seeds survive being in salt water to colonize islands? And so, he put seeds in salt water and saw what happened, and then planted them. Or even kind of comically can earthworms hear? And so, he put earthworms on a piano and he played the piano for them, he yelled at them, and so on, and found that they pretty much are deaf, but they could feel sensations. If you hit a piano, they could respond.
Anyway, he was a great experimenter. And yet, his most famous idea, evolution by natural selection, it never even occurred to him to do an experiment. And the reason is that he thought that evolution was so glacially slow that you could never do an experiment. It would be thousands of years before you could detect any response. So, Darwin thought that evolution was a very slow process, but we can’t really blame him. There weren’t any data around at the time.
And so, it was really his intuition, it was guided really by Victorian sensibilities about the proper pace of change, and analogy with geology, and how we thought everything occurred gradually. So, he thought evolution occurred very slowly, and basically, because he said that, and because he was right about so many things, really for about a century, the field of evolutionary biology followed his lead and assumed that evolution only occurred very slowly.
And then about the middle of the last century, we began to see that evolution actually can occur quickly. And we saw it in ways that really affected us, as microbes were evolving resistance to our drugs, and pests were evolving resistance to our antibiotics, and moths were evolving to adapt to trees covered with soot. And just around us, we were changing the environment, and sure enough, populations were adapting very quickly.
Mirsky: And then there are the Grants who really bring this home.
Losos: And exactly the first really detailed field study in natural conditions, Peter and Rosemary Grant in the Galapagos, who studied Darwin’s finches for 40 years. And they showed that when conditions change dramatically, when there’s immense amounts of rainfall, or immense droughts, the finches’ populations would change extremely quickly.
Mirsky: And there’s an excellent book by Jonathan Weiner, is it?
Losos: Yeah.
Mirsky: Beak of the Finch.
Losos: Yeah, Jonathan Weiner’s Beak of the Finch, a great story about the Grants and their research, and you know, not only what they found, but how evolutionary biologists do their work. And more recently, the Grants, themselves, have written a wonderful book, a little more scientific at a little bit of a higher level called Forty Years of Evolution, talking about this amazing study on the Darwin’s finches.
Mirsky: And then the sticklebacks are really interesting.
Losos: Yeah, so the sticklebacks. So, so now that we knew evolution could go quickly, we realized, well, that means we can do an experiment. The gold standard of science, which we thought was out of reach, we can do that. And so, people have started doing that, and the sticklebacks are another great study system. They are fish that occur in – around the world, actually, but they’re particularly notable on the West Coast of Canada and British Columbia, where they occur in lakes, lakes near the sea.
And the particularly interesting thing – there’s two things interesting about them. One is that there are a number of lakes that have not one species of three-spine stickleback. And how that has happened is that they, from the ancestral starting point, similar to a marine stickleback, that has invaded from the sea, they have diverged, one adapting to live on the bottom of the lakes, or on the mucky parts low down, and the other in the open water catching little things in the water column itself.
And they’ve evolved differences in their size and the shape of their mouth, and in a variety of other traits. The interesting thing about this is just like the lizards I study, in all six lakes, they have evolved the same differences. You have one called a Benthic one that lives near the bottom, and they all look alike from one lake to another. And the another one that lives in the open water.
Mirsky: And if you do the genomic analysis, you see that the same gene has been affected. Is that right?
Losos: Yes, well this is ongoing work, but they’ve actually sequenced the genome of the stickleback now, the three-spine stickleback, and they’re able to see what genes are actually changing to produce these differences. And there’s a lot of parallel evolution from the convergent types in the different lakes.
Mirsky: And then you have a long chapter on the famous Lenksi experiment, the 64,000 and counting generations of E. coli evolution.
Losos: Yes, a spectacular experiment, and I have to say, one of the really great things about reading this book is I really had to dive in deeply into the work that they’ve done. I thought I understood their research program, but it turns out I had barely skimmed the surface of the breadth of this study. This is a very cool study. What they did is they took E. coli – we know E. coli as the microbe responsible for outbreaks of food poisoning.
But, actually, there’s lots of different varieties of E. coli. And the researchers took a variety that’s harmless to people. And what they did was they actually took Stephen Jay Gould at his word, and did exactly what he said, in some respects. They took an identical population of E. coli microbes, and they started 12 new populations, taking individuals from this one population. So, the 12 populations started out completely identical.
So, you’re replaying the tape of life, not by going back through time, but by starting 12 populations completely identically, and they’re all under identical conditions. And these are conditions to which they’re not well adapted. They gave them a particular mix of nutrients to feed on that they were not adapted to eating.
And the question was would these E. coli be able to adapt to the new mix of nutrients, and would they adapt in the same way. And to make a very fascinating and complicated study very simple, the answer is that for the first 30,000 years –
Mirsky: 30,000 generations.
Losos: Oh yes, thank you. For the first 30,000 generations – and, I should explain that they have six generations per day. So, basically, what they do is they’re given their food for the day, and they can multiply for six generations, until the population has eaten up all the food. And then the microbes just sit there and then they get put into a new flask with a new round of provisions for the next day. And so, every day, six generations go by.
Mirsky: It’s still taking decades to do this.
Losos: Yes. This is a project now close to three decades old. So, for the first 30,000 generations, you could say that they evolved to a large extent in very similar ways. There certainly were some differences. It’s a little bit of a glass half empty, glass half full, whether you look at them as evolving in the same way or not, but there are a lot of similarities in what the 12 populations do.
And then, one day, in January of 2004, I think, the researcher whose job it was that day to put them in the new flasks observed that one flask was much cloudier than all the others. And the reason it’s cloudy means that there are a lot of microbial cells in that flash, making it not – so the light doesn’t pass through.
Mirsky: The population has exploded.
Losos: The population has exploded. And there’s only two possible explanations for that. The first explanation, which they suspected, was that there was contamination, that some other microbe had managed to get into the flask, despite all their controls. Something better adapted to this solution, and it had proliferated. And so, they did a bunch of tests, and it turns out that was not it. It was the E. coli that were supposed to be in the flask were in the flask.
And so, what that meant is that this one population had found a way to use the nutrients in a completely different way that allowed them to have a much larger population size than any of the others, a way that in the previous 30,000 generations, none of the 12 populations had been able to do.
And, in fact, in these subsequent almost 40,000 more generations, none of the 11 still have been able to find this way of adapting. And so, it was a major evolutionary advance, if you will, that has occurred only one time out of 12, showing that, in fact, the result isn’t that you could have – the result is not predictable. You can occasionally get something randomly going in a different direction.
Mirsky: Within the timespan that we have so far observed.
Losos: That’s correct. Now, the question is give them another 300,000 generations, will they all eventually find their way. And that’s what Lenski would like to write that grant for a 500 year grant to follow them and see. Or, I guess it would be 50 – it would be a grant, anyway.
Mirsky: It would be a long time.
Losos: Right.
Mirsky: So, just for completeness, the E. coli are feeding on glucose, but this one strain has figured out a way to live on citrate.
Losos: Yes, all right. So, this is – I have to get a little bit into the microbial weeds for this, but basically, they were feeding on glucose, but the nutrients put in included citrate for arcane reasons. E. coli cannot use citrate in the presence of oxygen. And this is such a defining characteristic of E. coli that that’s how you recognize – that’s a defining characteristic. If it can’t use citrate in the oxygen, it’s E. coli.
So, no E. coli in nature apparently ever has been able to evolve this capability. But someone this one population managed to do so, which is such an extraordinary adaptation that the researchers are considering describing it as a completely new species it’s so different. And how it was able to do that turns out to be the sort of contingent events of evolution that are completely happenstance, that a particular gene duplicated itself.
Well, these sorts of things happen all the time, but the gene that duplicated itself happened to put itself next to another gene that turned on in the presence of oxygen. And so, the gene that duplicated is used in using citrate when there is no oxygen, but it just happened to get hooked up next to the what’s called a promoter that turns on in the presence of oxygen.
That was then the second mutation. And then it duplicated itself many more times, providing enough capacity to actually start using the citrate. And so, it was at least three mutations that occurred that allowed this to happen. And if they hadn’t occurred in the right order, then, it wouldn’t have worked. And it was just happenstance that those mutations came along in the right way.
Mirsky: So, we read your book, and we have all these amazing examples of what seem to be convergent evolution, predictability in evolution, and then we reach the part where we get back to this idea of contingency, and the issues with the very definition of contingency that Bede brings up.
Losos: Well, so, Gould’s Book, Wonderful Life, it’s just a masterful book. And I had to – I read it several times as I was writing my own book, and it’s very intimidating, because you read – Gould’s prose is so beautiful and it’s very – I feel very inadequate reading that. I can’t write like that. So, he was a great writer. But it turns out that when you look at what he wrote carefully, as John Bede did, and no one had pointed this out beforehand, Gould was contradictory in what he said.
He said two different things. He said if we go back and replay the tape of life, see if the outcome is the same. And so, that implies that you start with conditions exactly the same, which is pretty much what the Lenski experiment did. Start with the conditions exactly the same and see if life plays out in the same way. Elsewhere in the book, however, he said something somewhat differently. He said, suppose we went back in time and changed something in an apparently insignificant way, changed some insignificant jot or tittle, he said, and see if that affects it. Or, as another scientist once remarked, if you went back to the Cambrian period, 500 million years ago, and moved a trilobite two feet to the left, would that make any difference.
And so, the important difference was not that you’re just going back and starting again, but you’re changing some condition and seeing whether the same end result ensues anyway. Those are two slightly different perspectives, but it actually makes a difference in how you would design an experiment to test his idea.
Mirsky: And what we then find out is that we have all these examples of convergence and what would feel like predictability and the experimental evolution experiments that bear those out. And then we have the stuff that really does appear to be a one-off. And I don’t want to say who did it, the butler in the parlor. But, ultimately, it’s a little of this and a little of that.
Losos: Yeah, so Gould writes his book, incredibly influential, and I think a lot of people were swayed by his argument that contingency really matters, the course of history has a strong effect on the ultimate outcome. Then along comes a group of scientists led by Simon Conway Morris, a paleontologist at the University of Cambridge, who start documenting just how widespread convergent evolution is.
Now, we had always known that convergence occurs. Darwin wrote about it in On the Origin of Species. But we’d also often considered it to be very rare, that unusual phenomenon that so clearly shows the power of natural selection. What Conway Morris did is he wrote two enormous books that are just compendia of convergent evolution, showing that it’s actually quite common.
And there was another book by someone named George McGee with even more examples. And we now realize that there is plenty of convergence around us. Well, that has led some people, again, led by Conway Morris to argue, in fact, that evolution is very deterministic, that the environment poses certain problems for organisms, and that there are best solutions that natural selection finds repeatedly.
And so, the implication of that is that contingency really doesn’t matter, that history doesn’t matter, because natural selection is so powerful, it will get to the same end result time and time again, regardless of particular circumstances. And so, Conway Morris and colleagues have posed this as a strong counter-argument to Gould, arguing that evolution isn’t that quite deterministic, quite inevitable, if you will, and that contingency, history don’t matter.
I think that they’ve done a great service, and they’ve made a very strong argument. But you can make an equally long list of what are called evolutionary singletons, or evolutionary one-offs – organisms that have evolved and have no parallel. And my favorite is the duckbilled platypus, this animal that comes in for a lot of ridicule, but it’s actually a brilliantly adapted species in the streams of Australia.
It’s got many characteristics – lush fur to live in cold water, webbed feet for swimming, a powerful tale, and it’s duck bill, which actually looks like a duck bill, but doesn’t feel like a duck’s bill, because it’s very leathery, covered with receptors, _______ receptors, that can detect slight ripples of water, helping it to find its prey, and even more importantly, electroreceptors that can detect the electric discharge of a crayfish moving its muscles.
And so, even though when it’s underwater, its eyes are shut, its mouth is shut, its nose is shut, its ears are shut, it finds its prey by the receptors on its bill. Exquisitely adapted to the environment in which it lives, but that environment is nothing special. There are streams with crayfish just like that in my backyard in St. Louis. They’re all around the world. Where is my duckbilled platypus? It’s never evolved anywhere else in the world. It’s an evolutionary one-off.
And, in fact, there are a lot of other examples. The elephant that turned its nose into a long, grasping object, giraffes, chameleons, many types of plants. These very well adapted species really have not been paralleled elsewhere in the world. Or more, at a broader scale, look at New Zealand. An island dominated by birds, well the species that have evolved there look nothing like their parallels in Australia or Africa or anywhere else.
So, there are many examples of a failure of convergent evolution, of a species to evolve adaptively and nothing like that has evolved anywhere else.
Mirsky: What do I go to bed with tonight in my mind? How do I think evolution works?
Losos: Well, so, what we now know is that convergence does happen a lot, but it often also doesn’t happen a lot. And they both occur. And at some level it’s not worth making, see whose list is longer, because there are lots of examples of both. The question is why does it occur sometimes and not others. And what seems – this is what people are working on now. And there is one generality, with many exceptions, that we have, and that is closely-related species, or even populations of the same species, when exposed to the same environmental conditions, often evolve in the same way.
And that makes sense, because they have the very same starting point. They’ve got the same genes, sometimes the same mutations in those genes, they live in the same way, so it makes sense that natural selection would steer them in the same direction.
Mirsky: There may be constraints that really govern just how far off the beaten path they can go.
Losos: Yes. They have the same limits, if you will. It’s easier for them to evolve in certain directions and not others, because of all their shared similarities. Conversely, distantly related species, because they are so different – their genetics are different, their lifestyles are different – they tend to adapt in different ways to the same circumstances. They find different solutions for problems. And so, although there are exceptions, of course, convergent evolution seems to be more likely the more closely related two species are.
Mirsky: It’s a fascinating book. There’s a lot of great stuff toward the end that we don’t have time to get into about human medicine and the bacteria that infect people, especially one great example is the cystic fibrosis stuff. What the heck? Let’s talk about that for just a couple of minutes.
Losos: Well, all right. So, question, who cares whether convergence? And here’s who cares, we do. And the reason is that we’re – that evolution is going on all around us, and it’s challenging us in many ways. We have all these organisms that are evolving to our detriment. Microbes and pests evolving resistance to our drugs and our pesticides; microorganisms evolving to attack us. All these new diseases you hear about.
Those are different organisms adapting to us. And so, on the one hand we would really like to combat this evolution, to stop it, to counteract it in some way. On the other hand, many species are in real trouble today because we’ve changed their environment, and the question is can they adapt or will they go extinct. And, again, we, in this case, we would like to be able to help evolution help them evolve and adapt.
And so, the question is if we can understand in which cases evolution is likely to occur in the same way, then we can devise general solutions, that if microbes adapt to some drug repeatedly doing the same trick, well then we can counteract that with one countermeasure, whatever that might be. Conversely, if each microbe finds a different way to adapt to a particular drug we come up with, well, then we’re going to have to study every case individually to come up with a counter measure.
So, if we can understand where we can have a one size fits all result answer, and where we have to focus specific efforts, that will really help a lot in designing new drugs, in helping species adapt to global warming, and so on.
Mirsky: But the specific cystic fibrosis thing that you talk about in the book is really fascinating because here we’re using evolutionary principles to actually treat cystic fibrosis patients in a different way.
Losos: Yes. So, the story with the cystic fibrosis is that the – well, one of the major causes of mortality of individuals with cystic fibrosis is they get infections from a particular microbe called pseudomonas aeruginosa. And that microbe infects the lungs of the individual. Cystic fibrosis, the individuals get very thick mucus, and they can’t clear their throats. And it turns out there’s a niche that is exploited by these microbes.
Well, it turns out that when the microbe actually infects an individual, it actually evolves within that individual to adapt to the environment in the lungs, to evolve resistance to drugs, and so on. And so, in trying to treat these infections, biomedical scientists were trying to figure out what are the genes responsible for the adaptation of pseudomonas, and then how can we design something to counter them. But the question was how do they identify what genes are important in adapting to a human lung.
Because they don’t understand the genome of that organism very well. And they had this great idea – well, step back one step. One thing about people with cystic fibrosis is that they are monitored regularly in cystic fibrosis clinics. And so, they give sputum samples in some places once a month. And those samples are stored. And so, what the researchers realized is that they could detect when individuals were infected and they could chart the course of evolution of the microbes in an individual, and see what genetic changes occurred.
And then, by comparing the genetic changes on multiple individuals, they could look for the same mutation occurring multiple times. And if many individuals had the same mutation, that would suggest that that was a mutation adapting to attack humans. And in that way, they found a number of genes that seem responsible for the adaptation of the microorganism. So, they’ve bene able to find the genes and now they can try to figure out how to combat those changes.
Mirsky: Is evolution not the most unbelievably compelling concept and story? I am just constantly fascinated and amazed by the things, especially now when we can join macroscopic evolutionary findings to genomics, and understand how the genes are affecting the phenotypes. And it’s just unbelievable.
Losos: Well, I agree. It’s an incredibly exciting time with the tools that we have now. And one of the cool things about biodiversity, about the evolutionary world, is that organisms, almost anything that you can imagine happening has evolved some time. It’s not like physics or chemistry where you can just go to a chalkboard and derive general principles. There are no inviolate rules, because as Jeff Goldblum said in Jurassic Park, nature finds a way.
And so, what we need to understand is what happens most often, and then what are those crazy exceptions that buck the rule. And you’re always surprised by how some organism has been able to adapt in a way you never would have thought possible.
Mirsky: Or as Kramer says on Seinfeld, “Mother Nature’s a mad scientist!”
Losos: Yes, exactly.
Mirsky: Yeah, the book has Seinfeld references, a lot of good pop culture references that bring it home. It’s a very accessible book. It’s not dumbed down in any way, but it’s highly readable. [music starts] So, I thoroughly enjoyed it, and I highly recommend it.
Losos: Well, thank you very much.
Mirsky: That’s it for this episode. Get your science news at our website, www.ScientificAmerican.com, where you can also find the various previous uses by Scientific American Writer John Horgan of the vulgar expression I quoted early in the podcast, and where you can read about the giant coconut eating rat just discovered in the Solomon Islands. That’s a giant rat that eats coconuts, not a giant coconut eaten by a regular rat. And follow us on Twitter, where you’ll get a tweet whenever a new item hits the website. Our Twitter name is @SciAm. For Scientific American’s Science Talk, I’m Steve Mirsky. Thanks for clicking on us. [music continues]
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