Daniel and Kelly’s Extraordinary Universe - What is a species? (featuring Dr. Scott Egan)

Episode Date: June 9, 2026

Daniel and Kelly talk to Prof. Scott Egan about the meaning of species in modern biology.See omnystudio.com/listener for privacy information.

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What do you want to say? Documentary is all by your ear. What do you hear? I feel like my job is listening really, really hard. Listen to Here's the Thing on the I Heart Radio app Apple Podcasts, or wherever you get your podcasts. Some questions that seem straightforward at first become devilishly hard once you start to dig in. For example, what is a species? In our day-to-day lives, the answers are pretty obvious.

A cat is clearly not a dog. When you call your children by your dog's name, it's not because you're confused. used at the species level. It's because your children kept you up last night and your brain isn't working anymore. But then you go to the grocery store. And you look at the cabbage, the broccoli, the cauliflower, kale, colerabi, and Brussels sprouts. Those are all actually the same species. But they look super different.

And don't get me started on dogs. How is it possible that Great Danes and teacup chihuahuas are the same species? All right, now Brussels sprouts and domestic dogs are examples where human intervention has resulted in a lot of the variation in appearance. But for a lot of scientific history, we relied on things like appearance to figure out what a species is. And clearly, nature can produce a lot of variability at the species level. So this makes things hard.

But we also rely on other criteria. For example, many of us have heard that species can be defined as organisms that breed together and produce offspring. So dogs and cats don't make cogs or... Dats, so they're definitely different species. But what about polar bears and grizzly bears? They split evolutionarily not very long ago, so not only do they look pretty genetically similar, but if you get them together, they can produce offspring.

So are polar bears and grizzly bears actually just one species? Or does it matter that they're specialized in very different environments? And if you picked up a grizzly bear and dropped it in the middle of polar bear habitat, it's not likely to survive. And what do you do about fossils? You can't ask fossils to interbreed, so how can you figure out if there are a species or not? What do you do here?

Well, to answer this deceptively complicated question, today we have my friend, collaborator, and perhaps most importantly, evolutionary biologist, Dr. Scott Egan on the show. He has discovered and scientifically described many species, and he's going to help us answer this question, what is a species? Welcome to Daniel and Kelly's complicated universe.

Daniel, I study particles and aliens, and we now only have two species in the Whiteson family. You only have two species in the Whiteson family. What happened? We used to have a horse, but the horse moved on to other owners. Oh, I'm sorry. How is Hazel holding up? She's okay with it.

It was time. Okay. The horse was getting quite old and needed more attention than she could provide, and we found somebody who really loves him and is taking great care of him. And so she gets a text every day with a picture from the new owner of the very happy horse. That's good. All right.

Well, I'm Kelly Weenersmith. I study parasites and space. And I have been a collaborator on two projects that have described new species. And today we've got the collaborator that I worked with on those projects on the show. And I am like when I was a kid, one of my dreams was to describe a species. Amazing. And I didn't really do it. But I was adjacent to.

to the work, and that was very exciting. Well, you're dodging the obvious question. How many species are there on the Wienersmith Farm? Let's see. We've got dogs, cats, humans. I should have mentioned that first, but they're third. Geese, ducks, chickens, sheep, and goats. And those are, you know, the ones that I take care of.

But, you know, we live on a farm with many amazing species. that I think of as part of my extended family. And we, you know, try to do the best we can to take care of them as well. But we did just come home with four sheep in the back of a minivan this weekend. And that was a bit crazy. As one does. As one does. As one does.

Yes. Yeah. That was a little nuts. But we had fun. All right. Well, today we're going to be hearing all about species and speciesation. So we'll be learning about whether or not any of those varied species on Kelly's farm will eventually hybridize and give us new animals.

animals with crazy names. Oh, yeah. What would you call a human and a sheep? Oh, a human and a sheep. That's sheeple, of course. What about a human and a goose? A guman? Manus?

A hoose. A hoose? Okay. Get that hoose out of my house. Oh, love it. It sounds like a Dr. Seuss book, right? There are hooses in my houses. It does.

And I'm going to reveal that you were texting me this weekend with sheep-related puns. That was. That's right. And I woke up one morning to a sheep. sheep-related pun, and I read it out loud and my daughter said, mom, it is way too early for sheep puns. And I was like, well, I think the moment I wake up is the right time for a sheep puns. It's never too early for sheep puns. That's right.

All right. You can't stop me. Oh, no, I wish I could sometimes. And so, on today's show, we're talking about how do you define species? What even is a species? This is a question that's come up on the show a lot and a question that we've had from listeners a lot. And so let's give you a sample of the questions that we've received related to what is a species. Hi, Daniel and Kelly, Joe here. I've been wondering for years what makes

speciation so different between, well, species. They often read about marine expeditions where they're delighted to discover a new species of deep sea fish, for example. They'll describe that it looks basically identical to the known species, but the black bars on this one radiate out at 15 degrees instead of 22 degrees, so it's definitely different. Okay, that's awesome, and I love that kind of discovery. But then you have dogs. A Maltese and a husky are the same species? That's ludicrous, and there must be something wild going on in the genetics to allow that.

So, what's going on? How can we have separate species of fish that are effectively identical to any layperson, while Lika, Lassie, and Balto are all the same? interested in better understanding this, if possible. Thanks a lot, guys. I've had this question in the back of my mind a few times, but have felt a little silly about not really knowing the answer. What is a species exactly?

I thought it was something about being able to mate and produce viable offspring, but hybrids seem to break that. It's starting to seem kind of hand-wavy. Is it the biology equivalent of planet? Like, I think you talked about bacteria-trading DNA at some point, but that's not mating. Does it make sense to talk about species? that reproduce asexually.

Thank you very much. Really looking forward to your answer. Okay, great questions. And I know just the guy to answer these questions for you. We're going to bring my friend Scott Egan on the show, who has described a bunch of different insect species, and he's going to give us some really great answers. Because he comes from a state that doesn't have some weird lady in a toga

standing on the neck of some other guy in their flag. He's got, like, a really nice, simple flag. We like Liberty, and we're in charge, man. That's the message you should get. Virginia. Dr. Scott Egan is an evolutionary biologist and scientific naturalist at Rice University in Houston, Texas. Between academic degrees, he worked as a seventh grade public science teacher. Thank you so much, Scott, for being on the front lines there.

Scott was recently elected as a fellow with the Royal Entomological Society and a teaching fellow with the Rice Center for Teaching Excellence. He's published over 130 papers, including the discretion. of 20 new insect species. His discoveries have been featured in the New York Times, The Atlantic, the Wall Street Journal, National Geographic, Scientific American, and the game show Jeopardy, which is a like stretch life goal of mind to somehow tangentially end up on Jeopardy. Welcome to the show, Scott. Thanks. Thanks for having me, Kelly and Daniel. We're excited you're here. Tell us about your question on Jeopardy. What was it about? Well, first off, I might have never known about it, but I had an undergrad working in the summer.

And she told her grandfather what she was doing that summer. And then grandpa went back to whatever grandpa's do. And he chimes her back like a week later and said, I think I heard about what you're doing on Jeopardy. And so we all just attacked and Googled and found out. And lo and behold, one of our recent discoveries, a discovery where a parasitic vine was attacking one of, one of the little insects we study that is also a parasite on their shared host, a plant,

was one of the features. And so we were able to, yeah, so yeah, we ended up as a cool little clue on Jeopardy. Interestingly enough, I was just contacted by a game show in Germany about another discovery we made. So we're going to be featured on a German game show in a couple weeks here, which I'm also excited about. That's amazing. Any way we can connect folks to science, I'm in favor. Yeah, right.

Same. Okay, well, so let's jump right in. And so we've got a bunch of questions from our listeners about how you define the word species. But I think it helps first to talk about the process by which you get species before we start talking about definitions. So can you tell us a bit about what speciation is in some examples of how it happens? I love this question. And I love that you're immediately linking up those two somewhat separate things, how we define species and then the study of the evolution of species or speciation. because they are intrinsically linked. How you define species, then tells you how you are going to study that process of the evolution of species. So very important. So let's start off with speciation.

It's an evolutionary process where one lineage evolves into two or more lineages through time, simply stated. But then how you measure it depends on that definition of the species that's so important. An important thing about both of them is that it's an evolutionary process, so it's a continuum. You have some lineage and it evolves into two, but that takes time. And so by definition, you should find things halfway along the way or partly along the way or close to being a species, but not really. And so that gets at the definition part that if you find things all along this continuum, it can be really challenging to define what a species is. So then you also ask like, you know, how speciation can happen or some examples of it. We have many examples. Most take time, right? We think about. evolutionary processes taking you know millennia millions of years and that's that's the general way in which biodiversity has evolved but what's really interesting is scientists can actually study it sometimes in real time when we get kind of special

experiments happening unintended or intended where scientists can actually watch lineages move environments and begin adapting to new environments and and then look at how those potential changes result in you know the trajectory evolving towards two very very, very different things. I'm confused about the continuum issue because if you define the species in one way, like can these two organisms have fertile offspring, then the answer is binary, right? It's either yes or it's no. Does the continuum come in when you talk about the communities of species? Like if you have, you know, these elk and those antelope, maybe some fraction of them could have fertile offspring, but some fraction of them could not? Where is the continuum there? Right. Absolutely. So,

So it's not binary. You can actually find things with what we call partial reproductive isolation where some barrier like the fertility or viability of offspring, some are fertile and viable and some are not. Sometimes that depends on potentially the direction of the cross, whether it's a male from species one and a female of species two or vice versa that can completely change the story. You know, even the well-documented cases where we talk about like infertile or inviolable. hybrids, there's always exceptions even to those rules where you can actually find that every once in a while a viable and fertile hybrid can be formed. So yeah. So it's a continuum. You see things all along that power. Wow. Without getting political, it seems like maybe nothing in biology is binary. It depends. It depends. So, Scott, if somebody were to say to you, I don't believe species. happens, what concrete example would you give them to be like, no, look, here's all the data we have.

This is a very clear example. What would you cite? Yeah, I love that question. That's one of the first three lectures I give in the evolution class, which is we talk about just the massive amount of evidence of evolution. And one of those pieces of evidence is speciation in action, meaning we can actually observe speciation happen in the laboratory or in nature. And I'll start off with a really cool example from the laboratory because it's just so complete. There was this wonderful experiment done by Dr. Chobon Duffy. She studied these little RNA viruses that attacked bacteria.

And she was observing her population of these RNA viruses. And at some point, they got a mutation. And it allowed that virus that attacked a bacteria to expand its host range. So it could attack many more bacteria. And then she got really interested in that lineage, which she gave kind of a different name to that strain. And then the new virus then had a second mutation. And it allowed it to live in a better way. It basically adapted to this new environment, but it then allowed it not to be able to expand back to the original host. So the virus basically

had two mutations that led to it attacking and surviving well in a new host. And it now would never even run into the original ancestor. So now you have these two RNA viruses that are completely isolated from each other. And that was observed in the laboratory over, you know, 100 generations, was there's like the blink of an eye, how fast viruses have generations. So that's a lab experiment where you've seen two species evolve. And then in nature, we see the same thing. So a great example comes from these wonderfully interesting fruit feeding flies called Ragalides. They've lived in North America for, you know, millions of years, living on these plants called Cretagis or hawthorns. And then 400 years ago, Europeans start settling the northeastern part of North America and bringing

apples with them from Eurasia. Well, it just so happens that apples are really closely related to Hawthorne's, only they're much bigger. Apples are not native to America. You're telling me that all those like New England apple orchards are invasive species. Yeah. Oh, my gosh. Yeah.

So the genus malice, which is what apples are, comes from Eurasia. but these hawthorn flies that are from North America saw this wonderful new resource. They're growing right on the fence lines of all of these orchards even to this day, and they shifted onto the apple crops. And in the course of about 160 years, they have evolved very, very strong differences in the timing. They come out during the year. They come out now when the apples come out rather than when the hawthorn fruits come out. And they've also evolved some differences in their habitat choices, their preferences that are very, very strong. so they only choose to go to one of these gruding trees versus the other.

The combination of the evolution of timing differences and habitat choice differences has led to very distinct lineages living right in the same farm or orchard across the northeastern United States. And we know when it happened. We know when it started because it was an agricultural crop. We know this shift happened somewhere in upstate New York. In the Hudson River Valley, USDA scientists were monitoring the apples and observed this shift happening. And so in 150, 160 years, which is also the same number of generations these flies

have had, they've evolved very, very strong differences that you can observe in a laboratory or in nature. And so now there's a hawthorn, would you call it a hawthorne species of fly and an apple species of fly? Or are they just, you use the word lineage, which seems like a smart way to avoid saying species. What do you think? Are they lineages or species? Yeah. So I think it'd be good if we jump into the species definition part because it's intrinsically tied to talking about any of these stories. So for the Ragolides fruit flies, they have had a strong reduction in the degree of gene flow between these lineages. That puts them very close to what one might define as a species depending on your definition. So for the most part, in my lab, and I think a generally accepted

term for how you define species is some kind of group of individuals and populations. that actually interbreed or potentially can interbreed and that can make viable infertile offspring, which we've already talked about to some degree. Under that definition, bees, ragdaletes, fruit flies are, for all intensive purposes, on that path to being distinct lineages, although they still hybridized to some degree. When you say gene flow, that means essentially having sex with each other, right?

Just for exchanging DNA. Okay. Hmm. And can I back up and ask you sort of a meta question about this? The definition you gave sounds sort of ornate and elaborate, almost as if it's meant to describe something we sort of understand intuitively and historically, but didn't exactly derive from first principles, kind of like the way we describe planetary definitions. Is that because species are a thing the humans do? Like this is us categorizing some just validations. continuum of life? Or can you make an argument that like, hey, this is a real thing. It's an actual emergent phenomena in biology that deserves like a name. Or is it just us trying to give post facto a scientific basis for something we've just been saying a lot? Yeah, that's a really good question. And a question that evolutionary biologists debate and discuss to this day. Oh, okay. I think if you take it at a very basic level, if we were all to walk on a trail together

in a park and look at things. We would see things and we would call them by different names. We would see differences in nature. And so when you look at even a group of closely related organisms that maybe harbors multiple species or types within it, we see discontinuities. We see differences that are pretty strong. So while that evolutionary process of the continuum might show some continuous nature in the beginning, ultimately, some sort of barrier to that genetic exchange occurs so that those things

are now distinctly evolving differently. And you can see that. You can see that in the behavior or the DNA or the morphology. So yes and no. There is a continuous nature to it, but there's also some strong, consistent discontinuities that you observe. And, you know, if you were to take us and we were to go into a different forest, somewhere far away, and met people that had no scientific training, like maybe our backgrounds, they would see differences and see types of things and want to give them names. So I do think species does mean something and it is a real biological entity, even though there's a lot of exceptions to the rules and gray area and fuzziness, which is part of the excitement of studying biology. I should probably anticipate the answer to the question

would be yes and no. Let me ask you this one more question about the nature of species, which is, is the definition transitive? Like if A can have babies with B and B can have babies with C, does that mean A can have babies with C? Ah, very good question. Well, there are examples, the exact thing you just talked about

does exist in nature where A cannot have babies with C. And we call those things a ring species. So you can think about a population of organisms that can't exchange DNA and they are commonly moving, adapting, and evolving around some barrier, usually like a geographic barrier, like, let's say, the Himalayas. Okay.

There's a very famous bird species called the Greenish warbler that started down. I'm sorry, the Greenish? It's called the Greenish Warbler. Don't kill the messenger. Here's the moment I'm like, wow, we need a precise Latin name for this thing because it does. It does, but I can never remember that. You'll have to ask an ornithologist about its real scientific name.

So who does the Greenish Warbler like to have a big? babies with. Yeah, so every population it's right next to. So as the Greenish Warbler adapted and moved along both sides of the Tibetan Plateau, it adapted to those unique conditions on the east and the west. Ultimately, those lineages met on the north side of the Tibetan Plateau. By the time they got there, they had evolved different bird songs and slightly different bars, wing bars, which are very species diagnostic for some bird lineages. So each of those populations interbreeds with the other until the last ones, they don't recognize each other's song or what they look like anymore and do not interbreed. We call that a ring species, and it's a wonderful example of this continuous nature of evolution and speciation.

Were you trying to set up ring species? Because I had that in my notes. That was great. Oh, no, I was just curious. I mean, because I'm wondering, like, if this really is a continuum, you know, where do you draw the lines? And if you don't have the transit of property, then, boy, it becomes really complicated. Yeah, right. So if you were to think about what a species is with the greenish warbler and you were to study any of those populations along the ring, you would say, no, they're the same thing, except when you got to the very top. Now you have these two lineages that don't recognize each other's songs. So you have a decrease in gene flow, which we call reproductive isolation. If you look at their DNA, you also see genetic differences.

They are very, very distinct from each other than all the other continuous parts of that. And then morphologically, they look different. One has one wing bar. One has two. That's important to the greenish warbler. That actually covers a lot of the ways in which people define species, morphology, genetics, behavior. And based on any of those definitions, those top two populations that don't recognize each other would be defined as potentially distinct lineages.

Well, that's mind-blowing and fascinating to me because it suggests that there really is a continuum here, and yet you can also crisply define a species, except that the definition isn't unique, because you can choose some window in that continuum and keep expanding it until birds at the edge of the window can no longer mate with each other, and that's your species window, but you could also slide it around the ring, right? Like move at 30 kilometers, and that window also satisfies the constraints and as a species, but has different overlapping members to it. So that's just like, there really is something discrete there, and yet the whole spectrum is continuous. Wow. Yeah, it's a hard field. And so what is the answer then with the

ring species, Scott? When you describe that, would you say you have two different species at the, you know, top of the Himalayas? Or you're just like, this is a process and that's where we are. Okay. I mean, to me, the reason I bring it up is because it's a wonderful illustration of the nature of it. That southern group of lineages, you know, one might think is the ancestor, and you can see each of these stages as you move along that have evolved over, you know, tens of thousands of years to hundreds of thousands of years. But when you get to the top, they don't recognize each other.

So that's why I use it. I use it to illustrate. Yeah. But what's it like for those guys to meet each other? They must be like, you seem sort of, hmm, I mean, I wish we could, but I guess we can't. Or, you know, there's got to be some recognition there. Yeah. Birds are wonderful systems to study species because bird song is something we can hear.

And it's really, really important to the birds. So it's something where human perception and the biology we're watching actually can kind of match up. There's wonderful stories, for example, from the Darwin's finches as well, where they have evolutionary changes that changes their beak shape for maybe an ecological region to eat seeds. And then, you know, that's also the way in which they sting. And so the birds start recognizing each other as well similarly. Well, a running joke we have on the show is that anytime Daniel asks me a straightforward question about biology, I always say, well, it depends. And so we're keeping that going here. You're playing right in my hands here, Scott.

That's right. And he does the same thing to me when I ask him about relativity and stuff. So anyway, it's all right. Oh, no, but in relativity, it depends, but the answers are all correct, even if they contradict each other. Oh, whatever. All right. So Scott agrees with Kelly that it depends when we're talking about biology. We are going to take a break.

And when we get back, we're going to talk about if speciation ever unhappens. And probably it depends. Pride is like love. You feel it in your heart. IR. Radio. Canada's number one streaming app

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podcast. I agree with both of you that it depends is the answer in biology. I'm just not sure I agree with you whether you should say it's shamefaced or not. Oh, I see. All right. Well, we're back. And without shame, we're going to now talk about biology. All right, Scott.

So you get the process of speciation happening. does it ever unhappen? Yes. I mean, so first off, evolution has no direction to it. It just describes change through time. So in the same way that species or populations can evolve along that continuum in one direction, they can also evolve in the other direction. That's just evolution.

That's the same thing. When thinking about measuring reproductive isolation and finding populations kind of along that continuum that exhibit partial reproductive isolation, but not complete reproductive isolation, we absolutely have observed populations retreating back to something more panmictic where they're exchanging genes more regularly. So there's an example. There's a wonderful group of fishes up in the northwestern United States and Canada called the three spine stickleback. And they're really cool little tiny fishes and they live in all different parts of these rivers and lakes across the northwest. Is it three or is it three-ish?

It's exactly three. This one's three because there's also a nine spine stickleback as well. So the three spined stickleback has recolonized all these lakes that just, you know, 15,000, 17,000 years ago were covered in glaciers. So we know when time equals zero. Amazing. And they've recolonized these lakes. And very quickly they commonly will adapt to different parts of the habitat. So when you go to some of these lakes, you'll see kind of an open water form that's swimming and feeding in the open water, and you'll find one that's more a bottom dweller that's feeding along the bottom. They have different environments. There's a different potential body shape that's better. So they start kind of diverging very quickly. In some of those lakes, scientists have been watching them, observing them. And in one lake, Paxton Lake, there were these distinct lineages that then started hybridizing and formed back into a single species.

And that was likely because of human changes to that singular lake. They made the lake a little more turbid so you couldn't see as well. The fish couldn't identify the lineages very well. And they just merged back into one distinct lineage. How does that happen? I'm confused because it feels like to speciate means to move in different directions. And there's lots and lots of ways that can happen. And so it makes sense that like two species going to two random directions, that's fine.

Right. But to come back together, they have to like. both evolve in the same direction, don't they? Isn't that totally improbable? Yeah, so the way in which things come back together is due to this genetic exchange, the exchange of DNA. And that homogenizes to some degree the differences between them and pulls them back together. But if they were different species, how do they exchange DNA? That's a great question. So the change in this specific lake was turbidity. And so one of the ways these two fishes stayed separate is they were identifying each other by what they look like.

And I think the males have different colorations between the two lineages. And so at some point, the females and the males couldn't see that anymore. And they were very, very closely related still. I'm terrified where this is going. Are you saying that they accidentally made it with the wrong people because they couldn't see because the lake was too murky? Yes. Yes. Yes. Yes. Wow. So they could actually exchange DNA. They just didn't because they preferred not to because they could see what they were doing. Yeah. Wow.

And if you take the story and go to another place where there's amazing fish diversity, like the Rift Valley Lakes in Africa, like Lake Victoria has some insane number of cichlid fishes that have also evolved in the last 15,000 years, some estimated as a 500 different species. Same story there. There's turbidity issues with humans being around and stirring up the water a little bit. And there's some fishes that live at two different depths. Oh, here we go. We can start talking about physics.

I don't even understand the physics of it, but like red light and blue light go at different depths. And so the fishes have evolved to use that signal based on what depth they live at. And when it becomes a little more turbid, they actually can't see each other's differences anymore. And the males and females will mate more often. And so you can actually see that continuum. In turbid waters, these two distinct species are a. back not. And when you get into the clearer parts of Lake Victoria, they are still distinct. And you can see that continuum as well. Do you think it got really foggy for a while in our past? And that's why

homo sapiens and Neanderthals started breeding. We were just confused. I don't touch human stories. I don't get anywhere close to those. We had Scott Solomon on to touch those stories. So we're perfect. And when those fish wake up in the morning and see what they've done, are they like, oh, No. How am I going to tell my family? The physics there is interesting because, you know, water absorbs light at certain wavelengths, but the efficiency of it to absorb light depends on the wavelength, which is why you get like red and blue light at different depths. Yeah. Yay, physics.

So speciation can unhappen or you can go backwards in the process. And most of what we've talked about has involved, like, being able to, you know, recognize based on patterns or color. or song, what do you do when you don't have any of those clues as a scientist and you're like digging up fossils and you're trying to figure out species for dinosaurs? Like, what do we rely on then? That's right. That's right. So the working definition that my lab uses where we study diploid, sexually reproducing insects, is going to be different than someone who studies a fossil or an asexual species or some other, you know, thing that doesn't quite fit in those definitions. And So that's a good example.

Scientists will use a definition that's appropriate to the organism or group they're studying. And so obviously fossils, you can still think about things that I think about with living, sexually reproducing lineages. So you can study some degrees of reproductive isolation. So one thing is just geography. If they live in two different areas, they're not going to have the opportunity to exchange genes. That's in some level a measure of reproductive isolation. And then even more specifically, if you think about males and females exchanging DNA, there is a mechanical nature to that exchange. And so mechanical isolation is actually something that's really important for extant living species.

It's also important for fossil species. So if there's some mechanical difference, you could actually measure reproductive isolation as well. But then you are more likely to use something like a morphological species definition where the morphology is what, This is the only thing you have. And so you'll have to use that to define that lineage. And that's absolutely appropriate and also important for our living species as well. We use morphology as well. So Daniel has a dog that's a mixed between a German shepherd and a chihuahua. And so does the mechanic, can you get confused when you're imagining the mechanics? He does. Yeah. Is it true? This is true. We did DNA testing. He's a rescue from Ensonatus. We were not there that epic night when this happened. Nobody knows. There's some

sort of physics and biology mysteries there. So I feel like mechanics can lead you astray. And so I guess you just do the best you can, because I can't imagine how that worked. But he's really cute. He's sort of like a smaller German shepherd with sad eyes. Aw. Okay. I have no idea about how that could work.

There are so many reproductive barriers I'm thinking about here. There's the mechanical things that happen before copulation. There's also these things that can happen after copulation. right that are related to like inviable or infertile hybrids and one of them is with this strange combination is how a potential female chihuahua could even have a baby of that size so there's that degree of you know maybe uh the female dies during the birth of the hybrid offspring as another barrier because even though genetic change occurs and even though that hybrid offspring is potentially viable if the female dies during pregnancy, that's also gene flow has stopped.

Because dogs usually have multiple puppies, right? Yeah, this is getting wild really quickly. Yeah. Okay. All right, all right. Let's move on to safer ground. Wait, but on this question of like the definition of species again, now we have like multiple different definitions of species, morphological, genotypical, ecological. I'm confused because like which do we use? Is there no actual arbiter? Or are we just like saying, look, this is kind of fuzzy in a different context. We have different definitions. Yeah, I mean, I think depending on the group of organisms you study, you have to define species within that natural system. The most commonly used definition, I would say, is this biological species definition or biological species concept,

which is all about the degree to exchange DNA with individuals within other populations. So it's this reproduction that seems to be core, whether you decide to exchange genes, whether you run into those individuals, those are all different ways in which you can measure the chance that you would reproduce. If you study asexual bacteria that are living in the soil, you're going to have a very different way of defining species. So, you know, a microbiologists will define the genetic components that are part of that bacteria and maybe even a little bit about the ecological. environment they live in and combine that information to define that species of bacteria. So it just, it does depend. But you talked about like an arbiter. The U.S. Endangered Species Act, of course, has to have a definition of species in it.

And it, for the most part, uses this biological species concept. It uses measures of reproductive isolation as a way to measure what is and what is not a species. So that actually has a legal definition and is applied in courts within the U.S. and other countries have their own definitions. And when you have any protection for an endangered or a threatened species, you need to define what that is. So can I ask you a question about the animal appears on the flag of the best state in the United States? Boo, California. I don't recall there being a bear on the state of Texas flag. Oh, slice. There's just a big star. We have an animal on our flag, and I think that's better, obviously, because we're pro-biology here.

I love it. But in any case, I want to ask about grizzlies and polar bears. Tell us about the history here. Are they different species? Can they interbreed? Why don't they? And is that even more outrageous than chihuahuas and German shepherds? Yeah.

No, it's a great question. And it's really getting back to some of the things we've already talked about. So you have the grizzly, you have the polar. They are, in all intents and purposes, living. historically in different environments adapting to different conditions, but those conditions have changed just like the turbidity in a lake. And it's causing these individuals to run into each other more often. And so some of those barriers have been observed to break down to some degree. After a crazy night out, the polar bear wakes up next to a grizzly, you're telling me.

It doesn't mean that those two species will collapse. It just means that those two species will collapse. It just means that there's some degree of hybridization, but some degree of gene flow is allowed, even under a biological species concept. It just means that you can allow so much hybridization, but as long as those differences can still be maintained, that is an allowable amount of hybridization. So this process is ongoing. Environmental change is ongoing, especially for the polar bearer. And so we don't know what's going to happen with these two lineages, but you are seeing a little bit of a breakdown in those barriers that is happening in real time. So there really are bears out there that have like one polar bear parent and one grizzly

bear parent. And what do they look like? They are, as most will show, there are intermediates. Wow. Incredible. So you talked about RNA viruses and you talked about asexually reproducing bacteria. And so all of these things have genetic sequences in them. So why can't we just say, you know, if you're 5% different at the sequence level,

than another population, you're a different species. And then everybody could agree. Why can't we do something like that? I'm sorry. I have to interrupt because I googled grizzly polar bear hybrid and discovered that they're called Grover Bears or Pizzley Bears. Pizzly bears pretty cute. I like that.

And they look pretty awesome. All right, back to your regularly scheduled question. Sorry. Yes. Okay. Yeah. So the genetic thing is a good question. And genetics is an important way of measuring difference.

So it is incorporated into a lot of studies of speciation, and it is incorporated into sometimes how we are defining what is a new species. It's one piece of information. The challenging part is depending on what group of animals or plants or bacteria are you studying, that magic, let's say, 5% is going to be different for every group. So, you know, there are insects that are living, you know, almost cosmopolitan across the globe, one single species. So there is genetic differences that are pretty strong between them, but they, for the most part, are still one singular species just linked by, you know, a very widely distributed population. That might be very different than a small little endemic plant that just lives in a couple different canyons in, let's say, California, where they don't exchange genes very often, so they have a pretty strong differences. So you have a global population with little differences. You have a very close geographic lineage that has pretty distinct genetic differences.

And so it's really hard to find a magic number that fits everything. And then if you bring in things like asexual reproduction or the weird thing that bees, wasps and ants do, the haplodiploid thing, that creates genetic differences between lineages that are very, very strong. And so there's just no one-size-fit-all for the genetics. And then even if you look within the genetics, you look at one gene, they might be completely the same. You look at another one and they're almost completely different. And so it's hard to capture that with just one magic metric of DNA. It depends.

It depends. Sorry to be so boring. No, no. I love it depends. To me, that means ecology and evolutionary biology is always interesting. There's always some fun reason to dig into a system, bit deeper because it's probably different than what you were doing last week, even though you thought it would be the same.

Yeah. And I don't know. I love that. Same. All right. We're going to take another break. And when we get back, Scott is going to actually walk us through the process he went through to identify one of the over 20 insect species that he has named.

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And so we've talked about a bunch of different ways that you can go about making the argument that two different lineages are actually different species. And so Scott, as somebody who has identified tens of species, which is super awesome. Amazing. Can you give us an example of, you know, here's the species you identified and here is the multiple different pieces of evidence you brought to bear to make that argument? Sure. Yeah, happy to do it.

Certainly historically, the way in which species have been identified for millennia is based on what they look like. So that's their morphology, their physical features. That is still very, very important to this day. But my lab tends to do something called this whole area. naming species and classifying species, we call this taxonomy. And my lab tends to adopt something called integrative taxonomy, where we take as many pieces of information from disparate areas of biology to come together to make a conclusion about whether something's a new species or not. And so that obviously is going to involve their morphology. That's going to evolve their, potentially their DNA,

so looking at genetics, behavior, ecology, geography. So those are all the things. we're thinking about when we're trying to define a new species. But then let me walk you through one of ours because strangely enough, even though I have described our lab as a team has described many new species, I am not a trained entomologist. I'm an evolutionary biologist that studies a very intricate system of trees and the weird herbivores that live on them and the predators that attack those herbivores. So just like a food chain you learned about in elementary school, plant, herbivore, predator. to interrupt real quick. They must be very confused in the United Kingdom because they named you a

fellow of the Royal Entomological Society. So I think you get to say you're an entomologist. Not after to hear this podcast. All right. Okay. So anyway, go on. I call you an entomologist as well as other hats. But anyway, go on. But you have to say it in a British accent if you do it, Kelly. Thank you. I really appreciate that. Okay. So I'll actually take you through the very first insect we discovered. And that can help you kind of understand. the way in which we approach this process because I really didn't know how to do it either. So it starts off, as Kelly alluded to earlier when I was on vacation with my family,

I was walking around some sand dunes on the coast of Florida with my daughter when she was about four years old. And we observed this unique pattern, discovered something kind of unique, which I can get into the biology of this critter later. But ultimately, it was weird enough that I brought it back to the lab. Something crazy crawled out of the samples I took. And so I had something that I'd never seen before, and that started this process of is this new, or did someone else observe this in the past? What was it doing that caught your attention? Okay, we could do that too. So it was a beautiful, iridescent, green, almost purplish, tiny wasp, about a miller meter or two that was attacking a group of herbivores that my lab studies called

gall wasps. Now, gall wasps in and of themselves are really interesting because they are little tiny wasps that attack oak trees and induce the oak to grow a little tiny tumor or home, and the insect, the juvenile insects live inside that tumor where they feed, they're protected from the environment, and ultimately emerges an adult unless they're attacked by a predator. And so this is one of the predators. This predator also happens to do something really interesting, though because it manipulates the behavior of the gall wasp. So the gall wasp feeds and grows to an adult. It starts cutting a little tunnel out of the wood, but ultimately stops during that process and cuts a hole only about 25% smaller than normal size. So the head gets stuck. Oh my gosh. And so this is what we found in the field and brought back to laboratory. And then weeks to months past and another little wasp was living in those same little.

galls. It burrows its way through the body of the gall wasp and emerges through its face. Oh, my God. So cool. Wow. Even for people who've listened to lots of parasite life cycles, that's pretty shocking. Yes. And so lucky for me, my colleague, Dr. Kelly Weiner-Smith, was right down the hall at the time, and I showed her all of this stuff and said, you know, I know you study parasites and how they manipulate the behavior of their hosts. Could anything like that be happening here? What is going to? on. And so she and I dived into this for years and published some cool papers about this work, including some really nice experiments to see why this manipulation was important. Basically, these measly little predators can't cut themselves out of the wood on their own. So they really need

the host to burrow its way first, and then they just emerge through the body and cut a hole straight through the face and emerge right through it. So, wow. And now I can see why Kelly got that look of expectant bemusement when I asked this question. She knew what was coming. I didn't know what example he was going to pick. Well, I like this one, Kelly, because it's the first one. So it caused me to really ask this question myself of, so we get this crazy biology. Kelly helps with all the cool work and she leads this really cool research project that we publish.

But then ultimately we're left with this critter and asking, okay, we observe these differences, but is this something that's new? Yeah. And that's where, you know, this kind of how do you even define and decide what is it species. And so, you know, the first step for us was finding out even within the courses scale, what is this? So we knew it was an insect. We knew it was a wasp. We knew it was likely a group of parasitoid wastes in this group called the calcidoid. So we got a little bit farther down the taxonomic nomenclature. But at that point, we were struggling. So we reached out

to some experts. We reached out to some folks that are trained in that group. They said, yeah, it's probably in this family. It might be in this genus. And then we started digging a little deeper. Ultimately, we did find some morphological features of this very tiny was that led us to this one group. And luckily for us, there was a specialist in that group that had written a nice dichotomous key. And these are wonderful. They're kind of like choose your own adventure, but for what kind of critter you're looking at. So it gives you choices. Does it have, are its antennae on the top of its side or on the side of its head. Does it have seven hairs on its back legs?

Is it green? Does it have this or that? Choose go to step three. Or greenish. If it's greenish. Go to step four. If it has this, go to step seven if it has this. And so we, even as non-specialists, were able to kind of follow this path.

But what was really exciting is every time we followed this dichotomous key to its ultimate end, it never resulted in the thing we were looking at under the microscope. It just didn't fit. We would get to one end of the dichotomous key and would say, you have found species X from Nova Scotia. And we were sitting in the middle of Texas. Or you have had species Y and it's from Costa Rica. I see.

So each time it didn't actually pan out. So somebody had written a guide to figuring out which kind of wasp you have. Every time you went through it, you ended up on the different wrong wasp. Yes. Right. Right. So that was one step. So then we complemented that morphological work with.

some genetic work. We sequenced a short region of the DNA and tried to compare it to all the other sequences of the same region of DNA that have been sequenced across the world. And again, we found something that sort of matched, but wasn't exactly the same. So each time, kind of the same answer. If you combine that with then this very interesting behavior, so we could call this generally their ecology, their living environment, that also didn't match with anything that had been described from this genus before. So collectively, all of these pieces of information, geography, ecology, behavior, genetics, and morphology led us to the conclusion that we had, in fact, found something that we thought was new. We wrote this up in a paper, and then there's the

ultimate arbiter, which is peer review. The scientific review process is wonderful. This is sent off to a journal that specializes. It's wonderful. Well, for this, because I didn't know what I was doing. Have you only had positive experiences with peer review? It's important. Okay. Yeah, yeah. Okay. Yes.

I get all that and it's not perfect. But for this process, we were treading in waters and we were just trying to find our way. We needed a little bit of oversight. Yeah. And so we sent it to a journal that specializes in this area of taxonomy. And it went to some specialists anonymously. They reviewed our work. It definitely said it seems like.

like we were amateurs in the review process, which they were right. Fair, fair. But they agreed that our version of the story, which I wrote the scientific paper, almost like I'm talking to you right now, it was kind of like, we did this, then we did this, then we did this, and we determined it was new, but they agreed. And so they gave us some feedback. We modified our documents to be a little bit more in that realm of taxonomy. And that paper was published and we were able to name a new species.

And it was really fun. And Kelly and I even got to choose the name. Yeah. Okay. And Scott picked the coolest name. And so, Scott, go ahead. What did you name the species? So it's in the genus Eudaris, which we mispronounced for the first year we were describing the thing.

And it's specific epithet. So the species part is Eudaris Set. And set is named for the Egyptian god of evil and chaos, who also happened to, to cut up its brother Osiris and put it in a crypt and cut it into many pieces, which is exactly what this little tiny wasp does within the crypt it lives in, within these oak trees. It cuts up the gall wasp into its itty-bitty pieces. It's very, very similar.

So Udaris set is the name of our new species. That was when Scott was like, oh, you know, I've got an idea. I was thinking, what if we name it after the Egyptian god set and trapped his brother into crypt and scattered his body parts? And I was like, my mind was blown. I was like, we don't have to think about this anymore. That is absolutely the name that we're picking. And anyway, yes, props to Scott. That was amazing.

Well, that is an incredible story. So does this mean that you have particularly keen eyes for identifying new insects or that we are surrounded by undiscovered insect species or both? It's definitely more of the latter. We don't know even the species within some major U.S. We're discovering species within the city limits of Houston, which is the third or fourth largest city in the United States. We're discovering them on the oak tree just outside the front door of the biology building at Rice University. So we're finding them everywhere. And so that's the main part, especially when you start thinking about things that are very, very small.

And then flipping to the first part, we rely on specialists to really get down to the nitty gritty of some of these new species, whether it be a gauwass for one of these periods. or I even work a little bit in a group of beetles. Specialists are so important to this. My role is that my lab, undergraduate, graduate students, postdocs, we study a system, a system that involves an oak tree, a group of peculiar herbivores that I've always found interesting called gall was that induced this weird tumor that they live inside. And then because they live in this kind of predictable thing in space and time, this gall, this resource, they've attracted a huge, diverse community of natural enemies, of predators that eat them during different times of the year.

So this little system, we are specialists in that system, and we're good to get to the point where, hey, have we ever seen this before? Maybe not. We should reach out to someone. And so then we link up with specialists in whatever group, whether it be a parasitoid wasp or a gall wasp or even a plant. You know, sometimes we find weird parasitic plants attacking our galls. And all of those are, you know, a combination of our natural history observations in nature, which we work hard at and linking those observations up with specialists. And then we also do the DNA sequencing, which really helps seal the deal. I also want to put a little plug in for museums here because, like, when I was a kid and I went to the Smithsonian, I was like, oh, they've got dinosaur bones.

And I guess I assumed that, like, you know, most of the stuff they had was out there for you to see. but actually they have loads of experts that are like watching over massive collections behind closed doors where, you know, only other experts get to see. And they've got like, drawer after drawer after drawer of insects where you can go and be like, I'm pretty sure my insect is different than this other insect. And so you go and you bring pictures of your insect and then you can compare it to the actual insect that was used to describe, you know, another species a while ago. And I probably should have just passed this over to Scott because he knows much more about this. But I got very excited. And there's loads of stuff behind those doors that are like massively useful for scientists when we're trying to describe biodiversity. Yes, 100% like right here in the U.S.

The Smithsonian in the American Museum of Natural History. Those two museums have been so important to our research. And then even regionally, a huge university just to our north, Texas Am has a huge entomology collection, insect collection. And all of those are such great resources for us to compare and to link up with these specialists that work on these groups. day in and day out. Yeah, extremely helpful and important. Yeah. So we got this amazing question from a listener named Boris, and let's go ahead and listen to it now.

Hey, Kelly and Daniel. I recently watched a video about something called K9 transmissible venerot tumor or CTVT, and it was presented as, I quote, a single-celled, brainless, boneless, asexually reproducing species in the genus canis, that is dogs. I think that's really fascinating. Its genome split off from dogs about 11,000 years ago,

and in this short time, has changed dramatically. So my questions are, do you biologists normally consider this a species of dog? Could it continue to evolve in the long term and eventually give rise to a whole branch of new species? Do we know of other similar cases where evolution happened with a sudden dramatic change? And is something like this were to happen a long time ago in the history of a species, would we even know? Yeah. Wow. that's a great one. Yeah. So very briefly, as some background, because I think these transmissible

tumors are fascinating, but also like absolute nightmare fuel. So the idea here is that there's a cell in the host body that has mutated, and it started to become cancerous. It's reproducing like crazy. And usually cancer sticks with the person who got the cancer. You know, you can't usually pass a liver tumor onto your husband. But in a very few cases, there have been self-cells. like Tasmanian devil cells that have become cancerous and have picked up the ability to jump from one Tasmanian devil to another. And so when Tasmanian devils fight with each other, they bite, there's a lot of blood that's passed back and forth,

a lot of saliva that's passed back and forth, and I know more about the Tasmanian devil facial tumors than the other example, so I'm sticking there. But anyway, this tumor is passing between Tasmanian devils, and it's a Tasmanian devil cell that now produces tumors on all of these other individuals and makes it hard for them to breathe and eat and stuff and so they die.

And so I guess the question is these cancerous cells, and this is the same thing with CTVT, that jump and can now do something totally different than normal dogs do, but it's a dog cell. Yeah, what would you call that?

Is that a different species? Well, that's a fun exercise. And it certainly illustrates this whole important thing about defining a species. Right? and how one defines a species, then would frame how you would view CTVT or any of these, what I will say are probably, you know, rare gray area exception to the rule type things.

But as long as you follow the definition, you should be able to determine whether this entity, whatever it is, is a species or not. It makes me wonder, though, because it doesn't have the ability to survive and reproduce if it's not in its host. So it seems to fill that same area as like a virus, which we have a discussion in our evolution class. You know, what is life? How do you define life? And one of those, you know, prerequisites that many of the students come up with is you should be able to reproduce on your own. Viruses can't do that, right? They require the reproductive machinery of their host to do it. So I will not stay one way or the other. Well, I think, but I will say that that is an interesting example of something that's in that gray area and challenges what how we do. to find species. Yeah, I think we always, we're always doing the best that we can, but nature

doesn't care that humans would really like to have nice boxes to put things in. And I don't know, that's like 90% of the fun, I think, of being an ecology is trying to figure out what nature did and what's the best framework for understanding it. Yeah. I mean, I think we have the answer at hand. It's clearly dog-ish, right? Yes. So, Scott, I want to ask you if we find life on other planets, and we meet alien biologists that are studying their own variety of life, do you think those alien biologists are going to have something in analogy to the concept of a species, that they're going to have your same sort of thought experience walking through the park and noticing like trees are different from cats, except now they're alien trees and alien cats?

Or do you think that this is possibly a function of life on Earth and that life on other planets could be fundamentally different in ways that make the whole concept of a species on Earth bound idea. That's a wonderful question. I don't know what they would do. I certainly think, you know, if you were to, you know, just forget all the knowledge as biologists that we have accumulated on planet Earth. And if you were asked us to restart evolutionary biology, I think we would again come across the definitions of species and why they're important for this understanding evolution as a whole and the evolution of biodiversity. So I think if you were to replay the learning of humans and our understanding of planet Earth, I think we would again come up

with species again. If we were to go to another planet and ask if some other intelligent life form would define species and find them in the same way we would, my answer would probably be yes. I think the first thing we'd want to know is what are the relationships between the life on Earth and the life on this other planet, they may share themselves a common ancestor. We still don't know exactly where life started on planet Earth. And one of the potential hypotheses that I love is panspermia, where it actually came from somewhere else and seeded life on planet Earth. We're all descended from a tumor on the face of an alien dog.

Oh, no. Yes. Wouldn't that be beautiful? It would be something. Yeah. And even, you know, take a step back earlier than that, you know, there's all these wonderful experiments exploring how biomolecules may actually form through natural processes right here on planet Earth. And that same process could happen on a moon around Saturn or on

another planet in another solar system. Those are all possibilities. And so if they formed in similar ways, then I also think these discontinuities that evolve seem to be a natural outcome of evolutionary biology. And so under all those conditions, I do think an alien life form would would find species and be excited about variation and see that. But there is a really big universe and a lot of opportunities there. So I will only say that's my guess. Well, I hope we get to find alien life and then we get to discover what happens when you put like alien fish and earthfish together in a lake and then make it too murky for them to make good decisions. Yes. I do too. Maybe one day. All right. Thanks so much, Scott, for being on.

on the show. We hope to have you back in the future, and this was a lot of fun. Thanks, Scott. Yes, fun for me too. Thank you all. Thank you for that wonderful interview, which highlights the great truism of biology. It depends. In the case of dogs, it seems we adopted the concept of breeds, rather than declaring every very good boy and girl, a different species, since genetically they're still close enough for horseshoes, as it were.

If there's ever an opportunity for extended discussion on the genetics part, I'd be curious to understand what it is or what selective breeding from humans over the ages is done to allow dogs such a wide variation in appearance, behavior, size, while remaining reproductively compatible, or, in the vein of Daniel, if we discovered an alien planet filled with space corgis, poodles, and boxers, besides it being a very cuddly place, how would astrobiologists classify these extra solar canines? Oh, gosh, that went places. I knew it was going to be a complex answer, but that was fascinating. Ring species, dogish nightmare fuel

and an absolutely gorgeous wasp with an amazing name. Next time I walk in the park and admire the discontinuities, I'll have a much greater appreciation for all the twists and turns of how they got that way. Daniel, please pet your baffling dog for me. And thank you so much, all of you, for a fascinating episode. Thank you for tackling this unusual question. The discussion about the meaning of species,

was very interesting and all these edge cases that stretch the definition are fascinating. So thanks again, Kelly and Daniel and also Scott. Thanks everybody for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us. Daniel and Kelly's extraordinary universe is edited by the amazing Matt Kesselman. He really is a wizard. You can also find us online on Blue Sky, Instagram, and X, D&K Universe.

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