08/18/2017

Inevitable Or Accident? Tackling The Big Questions Of Evolution

26:38 minutes

bird
A pair of blue-footed boobies on Isabela Island in the Galapagos. Credit: Shutterstock

Jonathan Losos, a professor of organismic and evolutionary biology at Harvard University, writes of the advances in evolutionary understanding in his new book, Improbable Destinies. In it, he seeks to address a longstanding debate in the field: Is evolution of certain traits inevitable, or random? If we “ran the tape” of Earth’s history again, would the same animals — and even ourselves — still emerge?

[This woman teaches evolution in the South.]

Thanks to new advances in DNA sequencing and the rise of experimental evolutionary science, Losos says, it’s not just an exciting time to study evolution — we may also be able to answer that question and resolve that debate. He shares what we’ve learned about the traits that seem to crop up again and again, and the organisms that remain decidedly unique.   

[Read an excerpt from Jonathan Losos new book, Improbable Destinies: Fate, Chance, and the Future of Evolution.]

Segment Guests

Jonathan Losos

Jonathan Losos is a biology professor and director of the Losos Laboratory at Harvard University and Curator of Herpetology at Harvard’s Museum of Comparative Zoology.

Segment Transcript

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky, Ira Flatow is away. So let’s say we started over on evolution. We just rebooted the earth and ran the whole experiment of life as we know it. Once again, what would happen? Would it be the same? Would we see starfish, elephants, the duckbilled platypus, even ourselves? Or is everything we see today some kind of accident, something that could have turned out very, very differently with just the toss of the dice?

That is a debate that evolutionary theorists like the late great Stephen Jay Gould among them have been considering for a very long time, but the science of evolution has advanced some in recent years. We can sequence animals DNA with some surprises about who is related to who, and we can do something Charles Darwin never really thought was possible. We can experiment with evolution.

Both of these together are making it an exciting time to be an evolutionary biologist. Here to explain everything we’re learning plus help us with that thought experiment is my guest. Jonathan Losos is professor of organismic and evolutionary biology at Harvard University and author of a new book called, Improbable Destinies: Fate, Chance, and the Future of Evolution. Dr. Losos, welcome to our program.

DR. JOHNATHAN LOSOS: Thank you so much. It’s a pleasure to be here.

JOHN DANKOSKY: You can read an excerpt of this book on our website at sciencefriday.com/evolution. And if you’ve got a big question about how evolution works, maybe what you learn in school or what we’re talking about today, our number’s 844-724-8255. That’s 844-SCI-TALK. You can also tweet us @scifri, and there’s a lot to talk about.

So you kick off the book with a pretty provocative question. Could dinosaurs have eventually evolved into something with our kind of brain and maybe look a bit like us? A bipedal lizard that looks like something from a science fiction movie, where did this idea come from?

JONATHAN LOSOS: Well, think first about velociraptor, the villain of the Jurassic Park movies, and of course, suddenly the hero of Jurassic World. If you think about that animal as portrayed in the movies, it was pretty smart. It outwitted the safari hunter. It was able to open doors. And if you think about it a little bit more, it walked on two legs, had grasping hands, forward facing eyes, a relatively big brain. Sort of sounds like someone you might know.

Well, 30 years ago a Canadian paleontologist, Dale Russell, was studying a relative of a velociraptor called, troodon. And troodon it turns out had the largest brain for its body size of any dinosaur. And Russell got to thinking. He realized that over the course of evolution’s long history there has been a general trend towards increasing brain size, and that was true of the dinosaurs as well.

The largest brained ones occurred at the end of their tenure, and so Russell began to wonder what if that asteroid had not hit Earth? How might the dinosaurs have kept on evolving? How specifically might troodon have kept evolving if natural selection continued to favor larger and larger brains?

And his argument was that eventually their heads would get much bigger, and as a result, he argued the best way to balance a big head over your body is to have an erect upright posture. In turn, they would lose their tails because they no longer need a tail to balance the front of their body and voila. You’d have a green scaly dinosauroid that pretty much looked like a human. And so that was Russell’s argument that dinosaurs might have evolved into something very similar to ourselves.

JOHN DANKOSKY: So does it seem to you that the way we turned out were more or less inevitable in Earth’s evolutionary history that something at kind of the top of the food chain would look an awful lot like humans?

JONATHAN LOSOS: Well, that’s what Russell argued, and that’s what some other scientists have argued as well. They’ve argued that the human body form and lifestyle is uniquely adapted to the Earth’s environment and that something like us inevitably would have evolved by natural selection. Now I don’t agree with that, but that is what has been argued. I think, in fact, that evolution is much more contingent upon what happens in Earth’s past. If events had happened differently, they might have sent life down a different course. So I think it’s very unlikely that something like us actually would have evolved if circumstances had been different.

JOHN DANKOSKY: Yeah, maybe we will talk about it later that there’s a drawing at the end of your book of what another alternative life form might look like, nothing like a human or humanoid from a science fiction movie. We mentioned this earlier though whether there’s a best way to fill any particular niche or if everything could have just turned out differently if we started evolution all over again. It’s fate versus chance in your book title, so what’s the evidence on each side of this?

JONATHAN LOSOS: Sure, let me give you two examples. On the one hand, think about a dolphin or a shark. These are two distantly related animals. One’s a mammal, animal with hair like ourselves. The other is a fish, and yet they look really very similar, highly identical. A streamlined body form, a powerful tail for propulsion, flippers for steering, and a fin for stability. They’ve evolved to look very similar, and that’s because that body shape is particularly good for moving fast through water.

In fact, if engineers we’re going to design an animal, that’s pretty much what they would design. Submarines, for example, are fairly similar in body shape, and so the idea is that there are particular demands that the environment sets for which there are optimal solutions. And natural selection repeatedly sculpts those solutions out of different organisms. In other words, if an animal is going to adapt to living in the water and swimming fast, this is how they will do it.

And there are many examples of this what is called, convergent evolution, in which species evolve to become similar. Often because they’re adapting to the same ecological niche in the same way. On the other hand, this is not inevitable, and to me, the best example of that is a woodpecker. Everybody knows woodpeckers tapping on trees or maybe on your house, but people don’t really know what woodpeckers are doing.

What the woodpecker is doing is it’s tapping listening for a hollow sound because they eat grubs that live in dead wood, and those grubs build tunnels. So they’re tapping listening for the echo of a tunnel. When they find that, they start tapping very hard. Tap, tap, tap, tap, tap, 15 or 20 times a second. Basically, jackhammering their way through the wood to the tunnel.

Once they get there they stick out a long bristly tongue so long that the tongue actually wraps around their brain. They stick out their tongue to snag the insect and pull it out. And so that’s how they adapt to eating this resource. Well, woodpeckers live on many continents around the world, but they don’t get to islands.

And so on islands, other species fill this ecological niche, and they often do it in different ways. And the best example of this of a different way of doing the exact same thing is an animal on the island of Madagascar called an Aye-aye. Now an Aye-aye is a cat sized lemur, a type of primate, and it eats the same thing as the woodpecker. It eats little grubs that are living in dead wood, and it catches them in the same way.

It taps the wood looking for hollow sounds, then digs through the wood, and then it extracts the grub. But instead of having a long bill and a bristly tongue like the woodpecker, it has a completely different set of adaptations. They have a very long skeletal like third finger that they use to tap on the wood and with big ears that they cup their ears to listen for the sound of the echo.

When they find that, they then have enormous incisor teeth that are very good at digging through wood digging down to the tunnel. And then they use that long skeletal finger with a little nail on the end to hook out the grub and pull it out. So in other words, they and the woodpecker are doing the exact same thing, but they’ve evolved very different adaptations to do so. And so I think this is a very common explanation for why evolution is not inevitable.

That it depends on how you evolved in the past makes it easier to evolve one way or another. Birds don’t have teeth. They couldn’t chew through the wood like the Aye-aye. Conversely, the Aye-aye doesn’t have a bill, so it couldn’t do the jackhammering. So based on their evolutionary heritage, they adapt in different ways to do the same thing, and that’s why evolution often leads to different outcomes, even to species adapting to the same ecological niche.

JOHN DANKOSKY: If you’ve got some evolution questions, 844-724-8255, 844-SCI-TALK. We’re talking with Jonathan Losos, and his book, Improbable Destinies: Fate, Chance, and the Future of Evolution. You’re about Charles Darwin, who was, of course, right about in many things, but he got one really important thing wrong. He said that we can’t observe or experiment with evolution in real time, but we’re starting to find a little differently, right?

JONATHAN LOSOS: Absolutely, now we shouldn’t be so hard about Darwin because there were no data on evolution back in the 1850s. His notion that evolution occurred at a glacially slow pace was basically an intuition. It was based on Victorian sensibilities about the proper pace of change in the world, and so he thought that evolution probably was very slow.

We now know, however, that that is very wrong that when conditions change, when natural selection is strong, species can adapt very quickly. Sometimes over the course of just a couple of years. So quickly that we can observe it with our own eyes, and in fact, it turns out that evolution is all around us. We are changing the world in many different ways, and we are watching species adapt to those changes often to our detriment.

JOHN DANKOSKY: While we’re on this topic of observing natural selection in real time, one of your former graduate students conducted a pretty well timed study in Texas. We’re going to bring him on, Dr. Shane Campbell-Staton, is a post-doctoral fellow at both the University of Illinois Champaign-Urbana and the University of Montana at Missoula. Shane, welcome to Science Friday.

DR. SHANE CAMPBELL-STATON: Thank you kindly. It’s great to be here.

JOHN DANKOSKY: So why don’t you tell us what you were studying and what you found.

SHANE CAMPBELL-STATON Yes, so I did my dissertation work on the evolution of cold tolerance in one particular species of lizard called an anole, the green anole. The green anole is actually the only species of this genus of about 400 species of lizards that’s native to North America. And the ancestors of this particular species come from the island of Cuba where it’s pretty warm and thermally stable pretty much all year round.

But this particular species migrated from Cuba to Florida some time during like the Miocene or Pliocene and then gradually spread northward into more temperate environments in Tennessee, North Carolina, Oklahoma, where it gets very cold in the winter. And so I spent most of my dissertation trying to understand the physiological and genetic processes are involved in this cold adaptation associated with this migration farther north.

And then during the course of this study after what was supposed to be my last field season, these extreme winter events swept through my collecting sites in Texas and Oklahoma and caused extremely cold winter storms. And so I decided to go back out to these storms after these storms to ask if the populations that I had just recently collected data on– if they had somehow responded to this really extreme weather event on a rapid time scale.

JOHN DANKOSKY: What did you find? What happened with these lizards?

SHANE CAMPBELL-STATON Yes, so I found that in the south like in Brownsville, Texas– so this is the southernmost site that we looked at. This is right at the border of Mexico. We found that the survivors of the extreme winter incidents were significantly more [INAUDIBLE] than the population was beforehand. So they were able to maintain function at about a degree and a half colder temperature than the population on average was before those storms hit.

It may not seem like a lot just a degree and a half celsius, but this is equivalent to lizards that live about 350 miles farther north than Austin, Texas. So geographically speaking, that’s a pretty significant shift. And not only that, but we found that patterns of gene expression that we see in the survivors of the storm, they’re much more similar to patterns of expression that we see in populations that occur much farther north.

And then we also found that there were specific genes that are associated with nervous system function. So processes like synoptic function and neuroinhibitor transport that both change in gene expression and lie in regions of the genome that show specific signatures of natural selection.

JOHN DANKOSKY: OK, what are some of your findings out of all this? I mean what does this really tell us about our larger understanding of natural selection and the way it works?

SHANE CAMPBELL-STATON Well, it tells us that the process of natural selection and it happens very rapidly. So this entire study was done over the course of a single calendar year. And we find that there are significant changes not only in terms of organisms performance, but also changes in gene expression and changes that the genetic sequence level that we observe in these populations within the course of a single calendar year. So this is just within a single generation.

JOHN DANKOSKY: I’m John Dankosky. This is Science Friday from PRI, Public Radio International. We’re talking with Shane Campbell-Staton, who’s a post-doctoral fellow who’s been studying lizards. What it tells us a little bit about rapid evolution, and also with us is Jonathan Losos. So Jonathan Losos, what do we need to know before we can say that evolution has actually occurred in a case like this?

JONATHAN LOSOS: Well, we need to know that there has been genetic change in the population– that the population has changed as it has adapted to new circumstances.

JOHN DANKOSKY: And that can take in the case of what Shane’s talking about not very long. How does this change our overall view of Darwin’s theories that this is a very long time indeed to actually say that evolution has happened?

JONATHAN LOSOS: Well, it changes it radically. I think we now realize that Darwin got this one wrong. He was amazing about how many things he got right, both about evolution and other things. But his intuition was wrong here. That as Shane has demonstrated, natural selection can be very strong in nature sometimes, and as a result, the genetic constitution of a population can change very markedly from one generation to the next.

JOHN DANKOSKY: Now you’re also researching anoles around various tropical islands. What are you looking for there?

JONATHAN LOSOS: Well, it’s a two pronged research program that animals are remarkably diverse lizards. These aren’t the ones that you would have seen in Florida running around on the ground sticking out a little flap of skin under their neck or on Caribbean islands. And there are 400 different species of them throughout the Caribbean and Central and South America, so they’re a great evolutionary success story.

And we have been focusing particularly on the large islands of the Caribbean, the islands of Cuba, Hispaniola, Puerto Rico, and Jamaica where a quite unusual phenomenon has occurred that these lizards have diversified independently on each island. That is that from one or very few ancestral species they have produced a wide variety of different species on each island, but each island has been a separate evolutionary theater. That they’ve diversified independently on each island, and yet the outcome has been very much the same.

That on each island a series of habitat specialists has evolved. Each one adapted to using different parts of the environment. One species up at the top of the tree with big toe pads to hang on, another species at the bottom of the tree with long legs to run on big tree trunks and on the ground. Another type on twigs with short legs and so on.

These habitat specials have evolved independently on each island, an example of convergent evolution. So that’s part of our research program has been documenting this what we call a replicated adaptive radiation. However, more recently we’ve also been asking can we actually test the hypothesis that living on different surfaces causes them to adapt in different ways? We see this correlation with species with long legs on broad surfaces and so on. But can we actually test that? Can we use the gold standard of science these days, the experiment to test these ideas?

And one of the consequences of the realization that evolution can occur very rapidly is that we can actually do experiments. Now until a few years ago, no one would have thought of doing an evolution experiment because we thought they took so long. In fact, Darwin was a great experimenter in his other scientific pursuits, but it never occurred to him to do an experiment on evolution. But we now know that evolution experiments are possible, and so we’ve done some experiments with anolis lizards.

We’ve taken them from islands where they live on broad surfaces and long legs and put them on nearby tiny little islands that have only scrubby vegetation. So they have to use the narrow vegetation, and our prediction was that they would evolve shorter legs as they adapt to these surfaces. And sure enough, just after very quickly that’s what they did.

JOHN DANKOSKY: Well, let’s find out more about some of these experiments with Jonathan Losos. I just want to thank Shane Campbell-Staton for some of his work. You can join us at 844-724-8255 with your questions as we continue our conversation about evolution here on Science Friday from PRI.

This is Science Friday. I’m John Dankosky, and we’re continuing our conversation about evolution in the age of DNA sequencing and real time experiments. Our guest is Jonathan Losos, a professor of organismic and evolutionary biology at Harvard University and the author of a new book called, Improbable Destinies: Fate, Chance, and the Future of Evolution. If you want to join us, 844-724-8255.

Let’s go to the phones. Nathaniel is calling from Fairfield, California. Hi, there Nathaniel. You’re on Science Friday.

NATHANIEL: Hi.

JOHN DANKOSKY: Hi, what’s your question?

NATHANIEL: Well, if you’ll forgive the sensationalism, I was curious what’s the extent to which these tendencies of evolution that you’ve been talking about would be expected to hold true if we found extraterrestrial life on a planet with Earth like conditions?

JOHN DANKOSKY: Well, there’s a big question. What do you think Jonathan Losos?

JONATHAN LOSOS: Well, that’s a great question. We now know that there are many earth like planets in the universe, perhaps even millions of them in our own Milky Way galaxy. And so with that many planets out there it seems to many like it’s almost inevitable that life would have evolved on some of them, perhaps even intelligent life. And so the question is can we take any lesson from life on Earth? Would life on other planets be very similar?

Well, we can immediately go to one source for the answer to that question, and that’s Hollywood. And Hollywood very clearly thinks that life on other planets would look a lot like it does here. We always see the intelligent life forms being bipedal and looking like us perhaps with pointy green ears, scaly skin, or so on. Surprisingly, there are scientists who pretty much agree with that. They argue that just as here on Earth that there are certain demands that the environment sets and that there are optimal solutions that natural selection will find time and time again.

And so they argue that if a planet was truly earth-like with a similar atmospheric composition, and so on, temperatures, that life if it evolved would adapt in the same way to conditions there as it does here. And so some people have gone as far to say that something like a humanoid is almost inevitable on such a planet, so there is a contingent of scientists who extrapolate from what they see here on Earth to argue that we would see a very similar life on another planet.

I and many others however, do not agree with this. One thing that we have learned from our study of evolution on Earth is that distantly related species often adapt to similar conditions in different ways, like the example of the woodpecker and the Aye-aye. And of course, you couldn’t be more distantly related than life on another planet that was not even based on DNA probably. And so most people tend to think that life on other planets would find another way and would be very unrecognizable, unfamiliar to us here.

JOHN DANKOSKY: What about us though? Do you think that humans at this point are still subject to natural selection? I mean we can alter our own environment so much to adapt to hardship, unlike these animals that you study. We don’t have to physically adapt so much because we can build a new enclosure for ourselves or take a new medicine. I mean is natural selection for humans over?

JONATHAN LOSOS: I think to a large extent evolution by natural selection is no longer relevant to humans, at least to humans living in developed countries. And the reason is that for evolution by natural selection to occur you need three things to happen. You need to have variation in a population, say blue eyes and brown eyes or big thumbs and little thumbs.

Secondly, that variation must have consequences in terms of your survival and reproductive success. And finally, third, the trait needs to be genetically based so that the genes for that trait get passed to the next generation. The problem is that in modern life, at least in developed countries, the link between a trait, and survival, and reproduction probably no longer exists.

Someone asked me the other day, will we evolve big thumbs because we’re texting so much? Well, the fact is that someone who texts better probably isn’t going to survive longer nor have more children. And so even if bigger thumbs are useful for texting, it probably won’t evolve by natural selection.

JOHN DANKOSKY: So certainly, not if they’re texting while walking down a busy street.

SHANE CAMPBELL-STATON That’s true.

JOHN DANKOSKY: Let’s go to the phones again. Zack is calling from Hershey, PA. Zack, are you still there?

ZACK: Yeah, can you hear me?

JOHN DANKOSKY: Yeah, it sounds like you’re in a wind tunnel, Zach. What’s up?

ZACK: I’m sorry. It’s stormy where I’m at in Hershey right now.

JOHN DANKOSKY: OK, what’s your question?

ZACK: Real quick question in regards to human evolution. I was just curious to know if humans were to start to live in space for a long period of time, how might humans evolve living in space?

JOHN DANKOSKY: There’s a good question. OK, thanks so much, Zack. Get back to that rain storm. Be careful. What are your thoughts, Jonathan?

JONATHAN LOSOS: Well, it gets back to the same thing we talked about with the last question. If there were variation among the astronauts or whoever that were up there. And if that variation actually determined how many offspring were produced, then you might see evolutionary change. But my guess is that things would be much too regulated for that, that we would fix the environment if you will. And that the changes that occur would not be the result of evolution by natural selection. We would just change in the environment.

JOHN DANKOSKY: What about our own environment here on earth? The thing that we’re changing so rapidly. A lot of people want to know the answer to this question. I mean as our own environment change, as climate changes, is it speeding up the process of evolution for I guess all the beings that aren’t humans?

JONATHAN LOSOS: Absolutely. We are changing the world in very radical ways, and organisms have three possible responses. One is that they migrate, and many species are moving northward to stay in conditions that are a similar temperature. The second option is to adapt to evolve ways of living in hotter places or however that the climate will change. And the third option, of course, is to go extinct. Certainly, we are changing the world, and species are adapting as a result.

JOHN DANKOSKY: So how did a lizard guy end up with the platypus as his favorite animal?

JONATHAN LOSOS: Well, the duckbilled platypus is the most remarkable animal of all time. I think that’s indisputable. My particular love of platypuses came when I was seven years old, and my parents went to Australia. I was very unhappy about that. But when they came back with a stuffed animal platypus, I forgave them and fell in love with the platypus. And I have loved them ever since.

And I must say the platypus gets a bad rap. We think it’s kind of a joke, mishmash of parts that’s not well adapted to the environment. But actually, it is extraordinarily well adapted to its environment in streams in Australia.

JOHN DANKOSKY: So what is the lesson that the platypus can teach us about evolution?

JONATHAN LOSOS: Well, the platypus teaches us a very important lesson, and that is– so the platypus, the most remarkable feature of this animal is its duck bill. We just think, well, it has a bill like a duck but no. It’s so much more than that. The bill of a platypus is covered with thousands of touch receptors that can detect the most minute little ripple in the water. So if one of its prey moves a little bit, it can detect that ripple.

But even more remarkable, the bill also is covered with thousands of electroreceptors. So when crayfish moves its leg a little bit, there’s an electrical discharge, and the platypus can detect that with its bill. So even though it forages is underwater, it swims with his eyes closed, its ears closed, and its nose closed. It can still find its prey thanks to the receptors on its bill, so it’s remarkably adapted to living in streams.

Well, those streams are nothing special. In my own backyard we have a similar stream here in North America, but no duckbilled platypus equivalent has evolved in North America nor in similar streams anywhere else in the world. They’ve only evolved in Australia, so it’s a clear example that evolution does go its own way and that outcomes are not inevitable. If the outcomes were inevitable, we would see platypuses evolving all over the world, but they’re only in Australia.

JOHN DANKOSKY: Hey, I just have 30 seconds. I have to ask you. What is it you think that the dinosaur would look like? Maybe not a bipedal humanoid, what’s your theory about this?

JONATHAN LOSOS: They would look like a super sized big brained chicken. We now know that dinosaurs were covered with feathers. There is no reason that they would have lost their legs. They already moved on two legs. If they evolved a bigger head, they would have evolved a bigger tail just like t-rex did, and so they would be super sized heads covered with feathers. We now know that’s how dinosaurs are. They would look like a big brainy bird.

JOHN DANKOSKY: I hope you’re listening Hollywood. Jonathan Losos is evolutionary biologist at Harvard University, author of a new book, Improbable Destinies: Fate, Chance, and the Future of Evolution. Thanks so much for talking with us. I really appreciate it.

JONATHAN LOSOS: Thank you.

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