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The Edge Episode 13: Should We Bring Back Woolly Mammoths?

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Passenger pigeons. Woolly mammoths. Neanderthals. They’re all extinct. But what if we could bring them back? And if we could, should we? Geneticists are exploring de-extincting extinct and near-extinct species, but ethical and logistical problems abound. Laura and Leah sit down with a genetic engineer and an ecologist to understand how de-extinction works and the unintended consequences of playing god. Life, uh, finds a way.

Show Notes:

This episode was written and hosted by Laura Smith and Leah Worthington and produced by Coby McDonald.

Special thanks to Pat Joseph, Nathalia Alcantara, Katherine Blesie, and Wyatte Grantham-Philips. Special thanks to Ed Green and Doug McCauley. Art by Michiko Toki and original music by Mogli Maureal.


LEAH WORTHINGTON: Laura, I want to tell you about something that happened in Columbus, Ohio in 1855, so go back a few years, a sort of extreme and terrifying natural phenomenon.

LAURA SMITH: Ok Leah, I’m all ears.

LEAH: Ok so, it was just a normal day when, out of nowhere, the sky began to darken. And this darkening was accompanied by an incredibly loud, otherworldly noise. Some accounts have described it as sounding like a powerfully approaching storm, or a stampede of horses, or a roaring steamboat, or a train passing through a tunnel. The point is, it was loud. So loud, you couldn’t talk to the person next to you. And people were terrified. Children ran home, adults dropped to their knees and prayed.

LAURA: Whoa. Ok, so what was it?

LEAH: Pigeons.

LAURA: What?? That is not what I expected you to say at all.

LEAH: I know. I’ve been really looking forward to telling you that. Well, more specifically, it was passenger pigeons. The famous conservationist, Aldo Leopold, called it “a feathered tempest.” Which is a pretty awesome name for a bird storm.

LAURA: Or a band.

LEAH: Or a band! But unlike the pigeons we see every day around town, passenger pigeons flew in enormous, almost biblical, masses that were known to topple trees under their collective weight, leaving a path of destruction in their wake. And this was happening year after year, all across the continental United States.

ED GREEN: This species was a huge part of the natural environment of North America. There were flocks of birds that were in the billions. That it would take long amounts of time for these flocks to pass overhead. They would block out the sun, make it night during the day, there were so many of them.

LEAH: That’s genetic engineer and UCSC professor, Ed Green, who got his PhD in molecular biology from Cal. And as crazy as it might sound that a flock of birds could block out the sun, there’s a ton of historical documentation from the time that backs it up. Listen to this 19th century account from famous ornithologist Alexander Wilson. He said, “Happening to go ashore one charming afternoon, to purchase some milk at a house that stood near the river, and while talking with the people within doors, I was suddenly struck with astonishment at a loud rushing roar, succeeded by instant darkness, which, on the first moment I took for a tornado about to overwhelm the house and everything around in destruction. The people, observing my surprise, coolly said: ‘It is only the pigeons.’” That’s how I imagine they said it. But not everyone was afraid of these enormous pigeon flocks. Some considered it beautiful. Here’s a Potawatomi tribal leader named Simon Pokagon who saw a passenger pigeon flock doing a mass dive in the 1850s: “Never have my astonishment, wonder, and admiration been so stirred as when I have witnessed these birds drop from their course like meteors from heaven.”

LAURA: Woah, I mean, yeah that sounds really cool…but why doesn’t this happen anymore?

LEAH: Well…it’s a sad story actually. Passenger pigeons don’t exist anymore. In a matter of decades they went from billions to nonexistent. In the 19th century, by some estimates, they accounted for a quarter of the birds in North America and may have been the most abundant bird species…in the entire world. And then they were just gone.

ED: No one is alive anymore who remembers this bird.

LAURA: I’m just confused about how that could be if there were so many. It feels a little like saying that chickens could go extinct.

LEAH: Yeah, I mean that was actually part of the problem. Because they flew in these huge flocks, some up to a mile wide, which in theory protected them from predators, they were really easy to hunt because, well, you couldn’t miss them. So people would just stand below the flock and shoot into it. Or catch them with nets. You could even swing a pole in the air and just kill a bunch by hitting them. And so people did. They did it because they were scared, they did it because they could, and they also did it because they were hungry and apparently passenger pigeons taste pretty good. White settlers on the frontier who would have to preserve food for the winter would be running low on supplies and then low and behold, a flock descends and you are SET. By the late 1800s, hunting passenger pigeons had become a booming business that was aided by two new technologies: the telegraph and the railroad.

ED: I'm told that one of the earliest uses of the telegraph, when it was being deployed across the eastern part of the U.S. was to alert folks that the passenger pigeon flocks were coming so that they could set up their giant nets to catch these birds.

LAURA: And how did the trains figure into all of this?

LEAH: Yeah, so once the pigeon hunters and trappers were alerted to the presence of a large flock over, say, Columbus, Ohio, they’d hop on a train and arrive en masse to slaughter the birds in the tens of thousands. And their catch was then packed into barrels, loaded onto trains, and shipped all over the country.

LAURA: Ok so clearly they were being over-hunted. But it still seems somehow hard to imagine that they could kill ALL of them. I mean they were darkening the sky, right?

LEAH: There is still some mystery about just how this could have happened so fast. But there are a few features that likely made passenger pigeons particularly vulnerable. For one thing, they didn’t lay a lot of eggs. Another thing that some recent genome analysis from UC Santa Cruz’s Paleogenomics Lab has shown is that, despite their huge numbers, they had relatively low genetic diversity and low rates of mutations, which would have made it difficult for them to, say, adapt to new environmental pressures, like really hungry humans. And then there’s also the possibility that their population had gotten so large it simply couldn’t be sustained. And ultimately, by the end of the 19th century the passenger pigeon population had plummeted, and by 1900, there were no more. At least not in the wild. They went from millions, if not billions, to one in a matter of three decades.


LEAH: Oh yes. If you’re ever feeling lonely, try being the last passenger pigeon, the only one of your kind, on earth. That was Martha’s plight. In 1914, after outliving the last male, George, and not producing a single fertile egg over the course of her life, Martha died in a zoo in Cincinnati at the age of 28. Which is my age.

LAURA: Oh my god, that is so tragic.

LEAH: I know, it’s sort of amazing and terrible. But it’s actually not the end. Now, more than 100 years later, we’re on the brink of a really incredible and kind of shocking new frontier. Some recent leaps in genetic engineering have made it increasingly possible, not just to edit existing genomes, but to restore long-lost, even ancient ones. In other words: de-extinction.

LAURA: Just like Jurassic Park. I mean, what could go wrong?


LAURA: This is The Edge, a podcast produced by California magazine and the Cal Alumni Association. I’m your host, Laura Smith.

LEAH: And I’m your other host, Leah Worthington.

LAURA: Today we’re talking about how close we are to reviving endangered or extinct species. Which ones should we bring back? And who gets to decide?


LEAH: So, the story of the passenger pigeon may be an especially dramatic story of human beings driving a species to extinction, but of course it’s far from the only one. It’s believed that we’ve been extincting species from our earliest days. And we’ve never stopped. So there’s obvious appeal to the idea that we could reverse some of the damage we’ve done, that we could bring some of these species back from oblivion.

LAURA: Yeah that sounds great. But it also sounds really really complicated. Or maybe even impossible.

LEAH: Technically it’s been done once successfully—but even that is kind of debatable. In 2003, an extinct Pyrenean ibex was cloned, but she died just ten minutes after birth because of a lung abnormality. So yeah, it’s definitely not easy to resurrect a species. But there is an instruction manual of sorts. The same instructions that determine every aspect of our being, and that of every living thing on earth.

LAURA: I’m not a scientist but are you referring to DNA?

LEAH: You guessed it. It wasn’t until the early 2000s when we’d sequenced the human genome that some people started thinking that maybe, just maybe, we could use this profound new knowledge to bring extinct species back.

ED: One of the big observations after the human and the mouse genomes came out was that we basically have the same genes—20,000 of the same Lego pieces—we just kind of use them differently. And the pieces are subtly different in ways that we're still trying to understand, but basically, it's the same toolkit, the same set of genes there.

LEAH: And so people started to wonder…if the structure is basically the same across different species, how can we manipulate and recombine known genomes to reconstruct unknown ones? Like…cave bears and mammoths and Neanderthals.

LAURA: Oh my!

LEAH: Oh my! In 2005, Ed joined Svante Pääbo at the Max Planck Institute in Leipzig, Germany. Pääbo, who did his postdoc at Berkeley, is pretty much the big cheese in evolutionary genetics and one of the founders of the field of paleogenetics, which is exactly what it sounds like: old genes.

ED: And we were directly sequencing DNA from these bones that were tens of thousands of years old and had the first kind of complete look at what DNA you get out of this very old material.

LEAH: Long story short, Ed was able to use some new technology to sequence ancient DNA samples, ultimately becoming part of the team to piece together the first, full Neanderthal genome. 

ED: And that kind of put me down a path of doing technology development for genomics and for ancient DNA—this field of getting DNA out of really old things and doing analysis of it.

LEAH: Of course, we’re all of us—plants, animals, bacteria—the product of our DNA. So, if you have the genetic code for a particular species, then you basically have its programming manual.

LAURA: It’s like an Ikea construction guide…but for woolly mammoths.

LEAH: Or something like that. So, with the invention of CRISPR and other genetic engineering tools, not to mention growing concerns about species loss and habitat destruction, scientists around the world are exploring the possibility of reviving endangered or extinct animals from just their DNA. Pretty much. Animals like woolly mammoths, black-footed ferrets, northern white rhinos, and, our favorite, the passenger pigeon, which is a project that Ed has contributed to. So, here’s what happened: A few years later, at his new home in UCSC’s Paleogenomics Lab, Ed used the same techniques he helped pioneer in Germany to reconstruct the passenger pigeon genome.

ED: There's a specialized facility that we have here and do a lot of work getting DNA out of old things.

LEAH: Including a cleanroom, specialized suits, and positive air pressure, all to prevent contamination of the highly sensitive DNA samples.

LAURA: So…how exactly do you go about bringing back an extinct species? Can you just type the genetic code into a computer and print out a pigeon?

LEAH: Not quite. So, in 2012 the Paleogenomics Lab in Santa Cruz partnered with the Bay Area-based biotech non-profit, called Revive & Restore, on “The Great Passenger Pigeon Comeback,” which they’ve described as a “model de-extinction project.” So, step one, as Ed put it…

ED: —is learning genetically, what is a passenger pigeon? And that we can kind of check the box there. We have genomes of several passenger pigeons now. 

LEAH: How did we do that? 

ED: We have museum samples. We can get toe pads and other things directly out of museums for birds that are less than a few 100 years old. The preservation for the biological material we get is very, very good, because they're so young. So part of this is just extracting the DNA out of, usually a toe pad sample is what we had. And converting that into a form that can be sequenced.

LEAH: But, as I mentioned, there’s a high chance of contamination, from both the environment where the samples were collected and from the humans handling them. So you have to be able to distinguish between pigeon and non-pigeon DNA.

ED: And in order to facilitate that, we also sequenced the genome of the closest living relative of the passenger pigeon, which is a bird called a band-tailed pigeon. And then we use that as a scaffold to put together the genome of the passenger pigeon. It’s like the picture on the front of the puzzle box. It kind of tells you where everything goes. And then these little tiny, nasty degraded fragments of DNA that are still hanging around in the passenger pigeon, we can put them in the right place in the puzzle because we see how the big picture of this goes. That works great—it gives you exactly the right answer everywhere, except for where a passenger pigeon may actually differ structurally from a band tailed pigeon. We've got all the genes right of the passenger pigeon, and more or less the order of them, right. But it's likely that there are some regions where the order of the genomes may have changed. And we would be blind to that.

LEAH: And would that be a big deal?

ED: We'll know when we make a passenger pigeon.


LEAH: That’s true!

LEAH: Ok, but to be clear, we’re not quite there yet. Researchers have extracted these degraded little scraps of passenger pigeon DNA—so that’s a check box. And then they’ve used a reference band-tail pigeon genome to figure out where all those passenger pigeon genes go, like in what sequential order—so that’s another check box. But then…how do we actually, physically put them all together? How do we check that next box?

ED: Well, the next box is hard. Much harder. However, go back 10 or 15 years, and people would say that that first box is impossibly hard. So all of this requires a little bit of hope and faith in future technology development, which, you know, seems to never let us down. The general approach is that there exists technology, this CRISPR genome editing technology, and this is a technology that is more or less a way to do cut-and-paste in a genome. So the big idea concept is that we take the genome of the band-tailed pigeon, or some close relative, and we edit this. As it stands today, this is a time-consuming, painstaking, very hands-on process to make even a few edits. It needs to be made more efficient by many orders of magnitude to make it feasible that we would swap out enough positions so that what we have is less of a band-tailed pigeon and more of a passenger pigeon.

LEAH: My understanding is that in the same way that people have said with mammoths, we're not really just putting a whole mammoth genome into an Asian elephant and popping out a baby mammoth. We're combining the two and giving ourselves a really hairier looking Asian elephant. Is that sort of the same idea with the passenger pigeon, where we're not exactly reproducing what once was, but making a more passenger pigeon-leaning band-tailed pigeon?

ED: There are a few technical paths one can imagine, one involving this gene editing technology, CRISPR technology, to take a bird that we know that is as similar as possible and bit by bit, turn by turn tweak this into a passenger pigeon. It would be like taking your Toyota and swapping out parts until you have a Honda or whatever. If Hondas were extinct.

LEAH: And this whole process of taking an existing species and swapping out parts until you have a different species, raises a very interesting question. 

ED: You know, at what point do we have a new species? And at what point do cross that line. Species is one of these weird concepts that the more one tries to define it, the more it slips through your fingers. You know, any definition that you could come with, there are obvious exceptions to that definition that you would agree are actually species but violate your species concept. And this is new ground. If one starts deliberately walking away genetically from one species toward another species…at what point have you walked far enough that you have a new species? In a way It's kind of an academic argument: As long as the walk is interesting, and you're getting somewhere, then who cares?


LEAH: Ok so at this point we’ve talked about drafting the genetic instructions for a passenger pigeon, and we’ve talked about how CRISPR can be used to take band-tail pigeon DNA and cut and paste in the passenger pigeon genes. But then the question is, how do we get from genome to bird? And that’s a sort of pigeon-or-the-egg kind of question. First of all, the passenger pigeon-to be needs a surrogate parent. So scientists are doing this CRISPR gene-editing outside of the birds themselves, in isolated germ cells, which contain the DNA that’s passed along to future generations. And then they can take those edited stem cells and inject them into the embryo of a different pigeon called a rock pigeon. 

LAURA: What! Why?

LEAH: I don’t know. Don’t ask me that. But regardless, those cells develop into sperm and egg cells, so that rock pigeon embryo now contains the genome for a passenger pigeon. And when it’s born, this embryo, which is called a chimera, can then mate with another chimera, and produce full blown passenger-pigeon-y babies.   

LAURA: Whoa. Yeah, it’s a lot. So this takes a couple generations. You can’t just get a passenger pigeon.

LEAH: Yeah. But we should be clear that this is still theoretical. Where things stand now is that in 2019, Revive & Restore produced their first successful chimera, but it didn’t have enough passenger pigeon sperm to be able to go to the next step. Right now they’re working on making better chimeras, with the goal being to hatch the first passenger pigeon chicks by 2025. And those babies will be raised by their rock and band-tailed surrogate parents in what’s called a “simulated forest habitat.”

LAURA: But will they eventually be released back into the wild?

LEAH: Yes, so first they’ll do a “soft-release” in sort of controlled forest environments around the country where they’ll be able to help condition the new passenger pigeons back into their normal behaviors, like proper migration and that sort of thing. AND if all goes well, it’s possible, theoretically, that they could darken the skies again. Which, let’s be real, would be awesome. Or at least survive and reproduce as a viable species again. 

LAURA: I don’t know, Leah, this idea of making some cross-species frankenstein birds makes me a little uncomfortable. We can’t say for sure what would happen if we reintroduced passenger pigeons into the environment, let alone some new hybrid species.

LEAH: Yeah, I know. On the other hand, we’re doing this all the time. Even dog breeding, which we’ve been doing for thousands of years, is messing with evolution. I mean I can tell you for damn sure that my mom’s new Bernedoodle is not a naturally occurring species. And these scientists make the argument that hybridization for the sake of conservation is theoretically doing some good for the planet. Which we’ll get more into later.

LAURA: Ok, so theoretically, even if you are able to engineer a passenger-pigeon-ish bird, then what? What do you do with it?

ED: The natural environment of the passenger pigeon is long gone, and how is it that we might expect that there would be a habitat for a species that is extinct now? Would this even make sense? What would be a necessary precondition for establishing a suitable habitat for this bird whose ecology was clearly that it was a social animal? It flocked in giant flocks and required enormous uninterrupted stands of tree canopy. Do we have that now? And if not, what would we need to do to make that available? And if we couldn't do that, would it even make sense to bring these things back? You know, we can do a whole lot of genetic rescue and de-extinction and whatever. If there's no place for animals to live, then what's the point?

LEAH: What do you think about those questions that you just posed about, you know, where we put them…do they still fit in?

ED: Well, like many things in science, we kind of continue to bumble down the road, oftentimes riding on the back of technology development that is being driven by other goals. But bringing back extinct species, there needs to be a reason for that beyond just proving that we could do it. And that reason needs to be something that we all agree is a good reason.

LAURA: Yeah, I think doing something because we have a good reason seems like a good idea. So then, what’s a good reason for bringing a species like the passenger pigeon back?

LEAH: Well, so many of these species played important roles in the ecosystems they once lived in, and without them things were thrown out of balance. Like, in the case of the passenger pigeon, those huge flocks we talked about played an important role in their forest ecosystem by providing regular disturbances to the canopies that helped maintain a diverse and constantly regenerating habitat. The idea being that bringing them back would help restore some of the normal forest cycles, which in turn would help revive the plant and animal species that have been in decline. But, you’re right, that question of what’s a good reason for de-extinction is one that experts in this field are currently grappling with. In fact, some people have recently been trying to draw up some guidelines for deciding which species might be good candidates. And one of those people is Doug McCauley, a Berkeley grad and expert in ecology and marine biology, who also happens to be the author of what I like to call—to be clear this is my words not his—“Doug’s Rules for De-extinction.” 

DOUG MCCAULEY: To put it in a more clean nutshell, I'm looking for better tools to do a better job with conservation. And so I was really curious about what the promise was in this toolkit at de-extinction.

LEAH: So when you first heard about the concept of de-extinction, like, when was that and was your first impression, “Oh, what a cool tool!” or like, “Oh, god, what are we doing?”

DOUG: Yeah. Both. So, extinction is a natural part of the biology of our planet. The planet has been experiencing extinction for its entire, you know, 100-million-year-plus experience with life on the planet. But what is different about what people call the sixth mass extinction, this brand-new resurgence of extinction, is one, the rate. So it's moving faster than ever. And then another novelty is agency; so humans are involved here, which is brand new. We're the driver of this extinction to think about what role we can play in solving this, and so yeah, we should be using our intellect to try to pull in some of these new tools. We also can't forget our culpability in driving these extinctions in the first place. So one of the things that I think is a little bit scary or concerning about this new toolkit is just that it can sometimes be in the shininess of these new tools, a little bit of a distraction from the gravity of the serious impacts we're having on extinction. We need to realize that, for example, if you take the case of the northern white rhino, one of the species that's been a model species for trying out new techniques in de-extinction science, we need to think about the drivers that we’ve created, how we can undo some of those drivers. There would be a lot of peril in hanging our hopes on these new tools such that we don’t feel that sense of responsibility or culpability for driving extinction in the first place. We, you know, shot and killed, cut off the horns of rhinos, ground them up, and exported them with false hopes, completely erroneous hopes of trying to cure cancer. We can, you know, create test-tube rhinos, we can create, you know, GMO ferrets. But unless we actually think about what was it that caused the rhinos and the ferrets to get close to extinction in the first place, these things coming out of our lab are not going to stand a chance for survival, and we're going to see more species be pushed to the brink of extinction.

LEAH: The best example of this, Doug says, is our friend the passenger pigeon. Like Ed, Doug emphasizes the fact that the biggest threats to the passenger pigeon—environmental destruction and humans—are still here. So even if we did bring them back, what kind of world would we be bringing them back to? One they could survive in? I don’t know…

DOUG: We need to acknowledge that sort of interconnectedness as we think about how this will work or not.

LEAH: So, how accurately can you understand how a species behaves when it is completely removed from its ecological context? You know, how much of its essence is preserved in the DNA versus is a product of its interaction with its long-lost ecosystem?

DOUG: Right. No, that's a great point. You know, as we're talking about species, are, what they are not by virtue of their genomes by virtue of their genomes, plus their interactions with one another—their social biology—plus their interactions with their environment—their ecology—plus their interactions with all of the microorganisms that help them do what they do—their microbiome. So you're bringing back just a tiny slice, and even at best a corrupted tiny slice, of what that species is like.

LEAH: In other words, species don’t exist in a vacuum. They’re a product of their environment, the species with which they cohabitate, not to mention their culture…you know, social etiquette, mating behaviors, tool usage, all those things that evolve and pass through generations over time.

LAURA: So if you release a newborn passenger pigeon into the Berkeley Hills it’s not necessarily going to know how to be a passenger pigeon. 

LEAH: Or, even if it does, it might have a hard time figuring out what to eat, or adjusting its body to modern-day microbes and such.

LAURA: And that’s what Doug is trying to understand, right?

LEAH: Yeah, so in 2016, he and a couple of colleagues published a set of guidelines for making de-extinction efforts more ecologically informed and responsible.

DOUG: We had some reservations about these tools, but we decided, well, let's lay those aside and say the sky's the limit. So it was really just conservation biologists sitting together, having coffee, thinking about, ok, how could we do the most, in the same way that we're trying to do more with other conservation tools, how could we use these tools here? The rules that we suggest are: One, think about trying to bring back species that either are not dead yet, or not reaching so far back in time. 

LEAH: What would be an example of a species in that category?

DOUG: Well, I think the work that's being done right now, black-footed ferrets is really interesting. So they're not extinct. They're highly endangered. And very recently, there was some really interesting innovation to try to clone, four weeks ago or so, successfully clone, a black-footed ferret. The reason they’re doing that is because black footed ferrets, they're down to a very small number of individuals, which means they have very low genetic diversity. So as they breed them in these captive breeding facilities, they just don't have that historic genetic diversity to be able to succeed, to be healthy, to overcome environmental challenges. So by using germlines that have been frozen from dead ferrets and cloning those dead ferrets, they're introducing more diversity into this population of a not-yet-dead species, thus, overcoming some of the bottlenecks that are real for trying to do these captive breeding programs. So it’s a mix of old and new. Captive breeding programs is one of the oldest things we do. They’re using these cloning techniques to try to help increase more genetic diversity in there. So that’s a great example of being thoughtful of supplementing some of these traditional conservation techniques with new de-extinction science.

LEAH: In fact, as we record this, the first black-footed ferret clone has just celebrated her 6-month birthday! Happy birthday Elizabeth Ann!

LAURA: Happy birthday!

LEAH: Elizabeth Ann, the first U.S. endangered species to be cloned, was delivered via c-section on December 10, 2020. She’s the very adorable product of a yearslong collaboration between several organizations including the U.S. Fish and Wildlife Service and the biotech nonprofit that we mentioned earlier, Revive & Restore.

LAURA: I didn’t even realize ferrets were endangered. Or that they got c-sections.

LEAH: Well, so black-footed ferrets are actually one of the most rare land mammals in North America. In fact, scientists thought the species was completely extinct until they came across a group of them in Wyoming in 1981. Only seven of those—which I’ve heard described as the seven founding ferrets—passed on their genes, which means that every black-footed ferret born since is the descendant of those seven founding ferrets. Except for Elizabeth Ann.

LAURA: Oh my gosh. Another great band name, “The Seven Founding Ferrets.” Ok, so where did she come from then?

LEAH: Since the 80s, the San Diego Frozen Zoo, which is like a very, very cold storage facility containing thousands of living cell cultures, has been preserving genetic samples from species, including black-footed ferrets. And, in 2013, the Fish and Wildlife Service went to Revive & Restore, and they were like, “hey, you’re using biotech to de-extinct species—think you can help us with this ferret problem?” And Revive & Restore, which was co-founded by Berkeley grad Ryan Phelan and her pretty well-known husband, you may have heard of him, Stewart Brand—

LAURA: The Whole Earth Catalogue guy??

LEAH: Yeah, that’s the one! So Revive & Restore was like, “sure!” And to make a long story short: they sequenced the ferret genome, got government approval to clone an endangered species, created some embryos, and implanted them into a surrogate. And Elizabeth Ann was born.

LAURA: So, are they going to release her into the wild?

LEAH: No, so she’s going to grow up on the farm, also known as the conservation center, where, hopefully, she’ll breed with other clones and eventually with other wild ferrets too. And then her descendents will go back to living on the prairie and doing important things like eating prairie dogs and being eaten by other bigger predators. So yeah, they serve a critical role in their ecosystem. Which brings us to Doug’s next rule, which is that the species should be what’s called functionally unique.

DOUG: So not all species are created equal in the world of ecology. You have some redundancy—you can have species A doing things that are similar to species B and C, or you can have A doing a job that's totally unique. And so if you're going to apply limited resources to choose a focal species to work with, we think it's smart, from an ecological point of view, to try to think about these functionally unique species. You know, if somebody stole a part from your car, you would be less concerned that there's one less part in your car, you'd be concerned that your car doesn't run anymore, right? And some of these parts are more important than others. And so choosing species that are unique, bringing those functions back, restoring those functions, I mean, it's obviously concerning to have less diversity, a smaller portfolio of species on the planet. But what keeps me up at night is a loss of function, the jobs that these species do.

LEAH: Take, for example, hippos, which Doug calls “a truly unique species.” Apparently they used to live all over the place, like even up in Europe and the Mediterranean, but now they’re pretty much contained to Sub-Saharan Africa where they do things that no other species in the ecosystem do.

LAURA: Like…

LEAH: Like eat on land and poop in the water, which I guess is a very important thing. From the perspective of their ecosystem, hippos are pumps that help get vital nutrients from the savannahs where they graze to the rivers where they bathe.

LAURA: So, let me guess—we’ve hunted them to near extinction?

LEAH: I think they’re currently listed as “vulnerable.” But yeah, hunting and habitat destruction have caused their populations to decline significantly. They’re not on their way out yet, but it’s enough to keep poor Doug up at night. 

LAURA: Speaking of Doug, what’s the next rule?

DOUG: The last of the three rules is a little bit more self-evident. It's just a numbers game. So some of these functions and some of the things that species do are achieved by virtue of having large numbers—billions of passenger pigeons. When you’re choosing candidates for de-extinction, you need to think about, can you actually recover them to meaningful levels that they were at before? If you can't, perhaps you shouldn't start. Otherwise, you're just creating novelties in zoos. And that's not going to help us solve this great, grand global challenge of stopping extinction.

LEAH: Do you think there are reasons besides ecological benefit to bringing back any kind of species? Like I'm thinking about, I know there are paleogeneticists who are interested in regrowing, for example, Neanderthal brain organoids just to study how they function.

DOUG: I think there's a lot of potential pure science that could happen here. Of course, here is sort of limited by how far you can go back and get viable DNA. So you have a hard stop. You can't bring back dinosaurs simply because, as far as we know, there are some biological limits for the preservation of DNA. But there's a lot of stuff in the last million years that would be interesting to look at. You know, one thing I think I should point out is that when you're reaching far back in time, most often you're thinking about editing pieces of a genome and not being able to carbon copy. You can't clone a species unless you have a frozen germline, right? So you're editing back in some of those essences.

LEAH: So Doug is pretty much throwing cold water on the idea of bringing back a Brontosaurus or something like that. But there are some not-so-recent species that are being studied as candidates for genetic revival…like woolly mammoths, for example. In fact, Revive & Restore is collaborating with a team at Harvard on what’s called the Woolly Mammoth Revival Project, whose goal, according to their website, is to “bring back this extinct species so that healthy herds may one-day re-populate vast tracts of tundra and boreal forest in Eurasia and North America.” And I mentioned earlier, like passenger pigeons, these revived mammoths won’t be perfect genetic replicas of what they once were—they’ll be more like Asian elephants that are engineered to be extra hairy and better-adapted to cold. Of course, one of the challenges of reviving a species that hasn’t been around for ten thousand years, is the fact that the planet has changed a lot since they were last here.

DOUG: So in North America, you know, when mammoths were running around, we were in the last glacial period, right?North America looks a little bit different these days. And so it'd be difficult, impossible, to try to release a genetically engineered mammoth back into landscape. So mammoths would be very surprised to try to figure out how to make their way across this ecosystem. And in the middle of the United States, imagine what people would think of mammoths that are released and back into their historic range. It would not make the top of my list for constructive projects, if you're trying to face off against this grand global extinction crisis.

LEAH: I should add that proponents of the idea say that bringing back big grazers like mammoths would restore some of the natural grasslands that used to grow in the tundra which, apparently, support biodiversity and slow climate change by sequestering carbon in the earth. But, as this is still theoretical, some ecologists like Doug are a little skeptical of the benefit of focusing de-extinction efforts on species like mammoths.

DOUG: I don't get very excited about having some franken-species in front of me in a zoo aren't allowed to look at and poke. To me it is a distraction, and it's a use of smart people's talent in a non-constructive way, when we need those folks thinking about actually how to apply their toolkits, how to apply their IQ and their talent, for actually taking on perhaps the biggest planetary challenge we have ever faced.

LEAH: To be completely honest, hearing you describe all of the challenges and what you think of as reasonable regulations, it seems nearly impossible. I mean, like, how realistic is this really?

DOUG: I think we need to be frank about how extremely hard the science is. And it becomes harder and harder when you start thinking about these ecological complexities, which are fundamental to species survival. I just think we need to be very, very thoughtful about how to apply them using the same principles for using for thinking about how to guide other kinds of conservation work. And importantly, also thinking about the gravity of this. If we relieve ourselves from this, you know, sense that this is a grave situation for ourselves and our planet, and I have a lot of concern that we won't take it seriously. If you know, developers, hunters and national park managers think that somewhere sitting in a lab, people can undo damage that they've done, and they have, you know, carte blanche to continue to do this damage. That's very, very dangerous. And so we need to have a little more dialogue between people that are doing conservation biology and have a sense of what we want to achieve, or problems we want to fix, with people that are really good scientists developing these tools. Otherwise, we could make some serious messes.

LAURA: Speaking of making a mess, how is this being regulated?

LEAH: Ah yes, enter Laura, the innovation police. You’re right though, you’re right. This is kind of the big question right now. As with so many other areas of cutting-edge biotech, there aren’t super clear rules about de-extinction and the broader field of genetic rescue—which includes things like selective breeding and reintroduction of species. Doug mentioned that you do have to get clearance from the Fish & Wildlife service to clone an endangered species. In 2014, the Species Survival Commission established a “De-extinction Task Force” made up of conservationists, geneticists, bioethicists, and lawyers. A couple of years later, in 2016, they published a 22-page document called the “Guiding Principles on Creating Proxies of Extinct Species for Conservation Benefit.”

LAURA: And what’s the TLDR?

LEAH: Pretty similar to what Doug said. That things like conservation benefit, viability, habitat maintenance, and other factors should be considered before deciding to de-extinct a species. You know, it outlines the risks, ethical questions, and the importance of defining what success even looks like.

LAURA: So it seems like people are really trying to do this right. But I’m not sure whether any of this answers the question of whether we should be messing around with de-extinction in the first place…

LEAH: I had the same thought. You know, the idea that we would think we have the right to destroy a species and then bring it back raises so many philosophical and ethical questions for us. We’re in this human-dominated, Anthropocene era, where we get to say who lives and who dies and who dies and then is resurrected, and it’s like, who gave us that right?

DOUG: I do think we have an obligation to, if we are driving species extinct, to try to slow that, to stop that, and prevent more. But yes, it just gets messier and weirder, and you know, and doesn't do what we want to do when we start trying to move that godliness into, with imperfection, into other domains—choosing what slice of a species we want to bring back and bringing them back just for, you know, entertainment purposes or research purposes. I think, again, there is some culpability and some responsibility associated with that which has to do all with us having too much power as a species or too much ecological power of force on our planet. But if we do it intelligently, as in, you know, if we use the same kinds of design thinking and logic that we use to problem solve, or historically used to problem solve in conservation science, and we apply that to using these tools, I think we can leverage their power to do good things for conservation.

LEAH: Since Ed is part of The Great Passenger Pigeon Comeback project, I’m going to give him the last word on the fate of this magnificent species.

LEAH: So where do things stand now? When might we be able to expect a flock of passenger pigeons thundering overhead?

ED: Probably not this year. I wouldn't venture to guess about this. Someone told me once that science always overestimates what it can do in five years and underestimates what it can do in 50 years. Somewhere between five and 50 years, then.


ED: Today's science fiction is tomorrow's boring science, I would, I would be shocked if it didn't come to fruition. It is far too late to start, you know, worrying about whether we are playing God or not, we've already done this. And one thing we definitely need to do differently is acknowledge what we're doing and start taking responsibility for what we are doing.

LAURA: So the takeaway from all this is that de-extinction could possibly help with conservation.

LEAH: Right, but also, de-extinction is a lot of work. 

LAURA: So it’s better just to save animals in the first place rather than to frankenstein new ones.

LEAH: But if they’re already gone, de-extinction is, at the least, a promising option.

LAURA: Yeah, that sounds about right. Can’t wait to see what happens.

LEAH: Me too.


LAURA: This is The Edge, brought to you by California magazine and the Cal Alumni Association. I’m Laura Smith.

LEAH: And I’m Leah Worthington.

LAURA: This episode was produced by Coby McDonald, with support from Pat Joseph Nathalia Alcantara, Katherine Blesie, and Wyatte Grantham-Philips. Special thanks to Ed Green and Doug McCauley. Original music by Mogli Maureal.


LEAH: With great power, comes great flocks of de-extincted pigeons.

LAURA: It’s a bird, it’s a plane, it’s Super—oh no, it’s a bird. Was that right?

LEAH: Yeah, that’s how it goes.

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