Scientists Think Cloning Could Help Save Endangered Species

17:24 minutes

A short, cream-colored stocky horse in a field of tall grass.
The endangered Przewalski’s horse. Credit: Jessie Cohen, Smithsonian’s National Zoo

Earlier this year, a baby Przewalski’s horse was born at the San Diego Zoo. But this foal isn’t any ordinary foal, he’s a clone. He’s the product of scientists aiming to save his dwindling species using genetics. This endangered horse species once roamed Europe and Asia, but by the 1960, threats like poaching, capture, and military presence drove the horses to extinction in the wild.

Two little ferrets on the ground with their mouths agape at the camera.
The black-footed ferret is another endangered species that has been successfully cloned. Credit: Smithsonian’s National Zoo

Conservationists raced to save this wild horse through captive breeding programs, but with a population so small, there just wasn’t enough genetic diversity to grow a healthy herd. But with careful genetic management, the Przewalski’s horse’s population is now nearly 2,000 horses strong, and this new foal will one day help boost his species’ genetic diversity even more. 

Producer Kathleen Davis talks with Dr. Oliver Ryder, conservation geneticist at the San Diego Zoo Wildlife Alliance, about cloning Przewalski’s horse, and how doing so will infuse genetic diversity into the small population. 

Then Davis talks with Dr. Sam Wisely, professor of wildlife ecology and conservation at the University of Florida, about how cloning can help other endangered species, like the black-footed ferret, and the ethics involved in cloning.

Further Reading

Segment Guests

Oliver Ryder

Oliver Ryder is a conservation geneticist with the San Diego Zoo Wildlife Alliance in San Diego, California.

Sam Wisely

Sam Wisely is a professor of Wildlife Ecology and Conservation at the University of Florida in Gainesville, Florida.

Segment Transcript

KATHLEEN DAVIS: This is Science Friday. I’m Kathleen Davis.

Earlier this year, a baby Przewalski’s horse was born. But this foal isn’t an ordinary foal. He’s a clone. He’s the product of scientists aiming to save his species using genetics.

Let’s go back in time for a moment. This endangered horse once roamed Europe and Asia but, by the 1960s, threats like poaching capture and military presence drove the horses to extinction in the wild. Conservationists raced to save this horse through captive breeding programs. But with a population so small, the horses experienced inbreeding, and there just wasn’t enough genetic diversity to grow a healthy herd.

But with careful genetic management, the Przewalski’s horse population is now nearly 2,000 horses strong. So how does cloning fit into all of this? Here to talk us through it is my guest Dr. Oliver Ryder, conservation geneticist at the San Diego Zoo Wildlife Alliance. He works on Przewalski’s horses.

Welcome to Science Friday. Thank you so much for joining us.

OLIVER RYDER: Nice to be with you.

KATHLEEN DAVIS: So you’ve helped clone two Przewalski’s horses. Can you walk me through the ABCs of how you do that?

OLIVER RYDER: Our big contribution has been to bank cells. The San Diego Zoo Wildlife Alliance has a biodiversity bank that includes the Frozen Zoo, which contains reproductive cells and cells that are established from skin biopsies from birds, reptiles, amphibians, and mammals, including from Przewalski’s horses.

So we start from frozen cells and thaw them. And then those cells are fused with a domestic horse egg that has had its genetic material removed. This work, which was done by ViaGen Pets & Equine, and in collaboration with Revive & Restore, involved our sending cells to their facility– their having the domestic horse eggs on hand– and then removing the genetic information from the domestic horse egg and fusing a cell that we provided from the Frozen Zoo with the horse eggs so that, quite remarkably– quite in a fascinating way– that is sufficient to allow the development of an embryo that can grow into a foal and be born and produce a normal horse.

This has been done with domestic horses. It has never been done with Przewalski’s horses.

KATHLEEN DAVIS: This baby horse that was born– this foal that was born recently– is a clone of an animal that was alive when?

OLIVER RYDER: The animal who was cloned was originally given the name Kuporovic. And he was born in 1975, in the United Kingdom.


OLIVER RYDER: In 1980, we obtained a cell culture from him and grew it up and banked it, determined he had the normal number of chromosomes for Przewalski’s horses, which is 66. And by the way, it’s a different number. All domestic horses have 64. And those cells sat in the liquid nitrogen freezer at 290 degrees below 0 for 40 years before they were brought out and produced the first successful clone of a Przewalski’s horse.

KATHLEEN DAVIS: So why clone these horses in the first place? I mean, what can cloning accomplish that other genetic techniques can’t?

OLIVER RYDER: Well, because in small populations– and all Przewalski’s horses trace their ancestry to only 12 animals that came out of the wild– and there’s been over 100 years of breeding in managed facilities, and the decline of populations, for example, during the Second World War– a substantial proportion of the genetic diversity that was available from the dozen Przewalski’s horses has been lost. And that is not something that can be reversed by just breeding more animals that are descended through the pedigree.

But if one can go back into the pedigree and, if you will, say, bring an animal back that was alive a long time ago, it would have the genetic diversity of the population at that previous time, which was larger than it is today. So it’s actually a way to restore genetic variation that’s been lost. And that’s a really new opportunity. That’s a really new paradigm.

KATHLEEN DAVIS: I would imagine it’s very exciting to be working on cloning a species and to see it actually work. I mean, can you tell me what your reaction has been to successfully cloning these horses?

OLIVER RYDER: Well, it just takes my breath away when I think about it. Because conservation geneticists have been dealing with the challenges of preserving genetic diversity in small populations. And in efforts to prevent extinctions, human society typically doesn’t intervene until the populations are already small. So we’ve been trying to minimize the loss of genetic variation.

But now that we can restore lost genetic variation, we can ameliorate, or mitigate, the process of loss that was otherwise a fact of life. Gene pools can only shrink over time unless you can use a technology like this. So it’s very exciting in that regard.

KATHLEEN DAVIS: So these horse clones that we’ve been talking about are living at a zoo. How are they going to help reestablish this population of Przewalski’s horses in the wild?

OLIVER RYDER: Well, at the San Diego Zoo’s Safari Park, we have a herd of Przewalski’s horses. And the cloned individuals will have a chance to reproduce when they are fully matured, both in terms of stature and in terms of their sexual maturity, and in terms of their behavioral maturity. They will be introduced into a herd of females– a band of females– and then they can reproduce normally.

And when we have those foals, they will be very special animals because they will have one parent who’s a Przewalski’s horse mare who is living now, and they will have as the sire a Przewalski’s horse who was a clone of an animal that lived 40 years ago.

KATHLEEN DAVIS: Dr. Oliver Ryder is a conservation geneticist at the San Diego Zoo Wildlife Alliance, based in San Diego, California. Thanks so much for joining us.

OLIVER RYDER: It’s my pleasure. Thank you.

KATHLEEN DAVIS: Cloning for conservation is complicated, not just the science of it, but the ethics involved, too. Scientists have to consider the goals of cloning, how it’s done, and if all of this time, energy, and money actually pays off. Ultimately, it begs the question– just because we can do something, does that mean that we should?

My next guest is Dr. Sam Wisely, professor of wildlife ecology and conservation at the University of Florida. She’s based in Gainesville, Florida. She’s been involved with the cloning of the endangered black-footed ferret. And she also penned an ethical analysis asking, is this justifiable?

Sam, welcome to Science Friday.

SAM WISELY: Thank you so much for having me.

KATHLEEN DAVIS: So tell me a little bit about this black-footed ferret. Why are they getting this special cloning treatment?

SAM WISELY: Black-footed ferrets are an iconic endangered species. They were the first species to be put on the Endangered Species List. They were the first species to be brought entirely into captivity in order to rescue them to reintroduce them back into the wild. And throughout their conservation history, they’ve really been a key species in applying new biotechnologies for the conservation of a species.

KATHLEEN DAVIS: So what can cloning do that other, more traditional conservation methods can’t?

SAM WISELY: In the case of the black-footed ferret, we’re cloning this species in order to conduct what we would call genetic rescue. And genetic rescue is actually not a new term or a new management technique. It’s using the cloning to enable genetic rescue that’s new.

So in a traditional genetic rescue, you might physically transplant an individual from one population that has genetic uniqueness and physically transport it– meaning fly it in a helicopter and put it in the population that needs genetic rescuing. So that unique individual would breed with individuals in the population that needs rescuing, and that’s how genetic rescue would ensue.

This has happened before in species like the Florida panther. But we don’t have the luxury at this point of live, unique individual black-footed ferrets. We do, however, have cryopreserved cells of unique individuals.

KATHLEEN DAVIS: So this seems like a really intensive process. Is cloning always a last-ditch effort?

SAM WISELY: I would say it is. And you’re absolutely right. It is incredibly technically complicated. It’s complicated from multiple perspectives, in sort of regulatory perspectives as well as ethical perspectives. And if we had unique individuals, live black-footed ferrets that could provide additional genetic diversity, absolutely, those would have been the individuals we would have chosen rather than conducting cloning.

KATHLEEN DAVIS: So I’m wondering in this case of the black-footed ferret, has cloning helped restore the species? And has it been worth it?

SAM WISELY: Well, we certainly hope so. We have produced one black-footed ferret that’s a clone. Her name is Elizabeth Ann. She was born in December 2020. And she’s currently being assessed for her health and her ability to reproduce on her own. And the goal would be to create a lineage of her descendants that could then be incorporated into the captive population of black-footed ferrets to enhance their genetic diversity.

KATHLEEN DAVIS: Elizabeth Ann is a very dignified name for a ferret.


So give us a sense of numbers here. I mean, how many black-footed ferrets are actually left now?

SAM WISELY: So in the captive population, there’s more than 200, but less than 300. In the wild, estimates can range anywhere from 600 to 900 individuals in the wild. And that is spread over a very large geographic range, from Canada to Mexico, in dozens of reintroduction sites.

KATHLEEN DAVIS: And how many genetic ancestors do they actually have?

SAM WISELY: So all black-footed ferrets are descended from seven biological founders.


SAM WISELY: So when they pulled all of those individuals from the wild into captivity– they were able to capture the last 18 individuals that were on Earth– they were only able to get seven of them to breed. Then, as soon as they did, that captive population flourished. But it still means that all of the genetic diversity that’s available to that species, the maximum amount is represented in seven individuals. That’s why adding an additional founder, which is essentially what Elizabeth Ann and her descendants could be, would be so valuable.

KATHLEEN DAVIS: Yeah. I mean, just thinking, I would assume that inbreeding would be a huge issue here, right?

SAM WISELY: It is very much an issue. And the captive breeding program works very hard to minimize that inbreeding, but it’s inevitable. And so all black-footed ferrets today are about second cousins. And we do see indications of what we would call inbreeding depression, meaning physiological changes that are likely due to inbreeding. That’s why it’s so important to add an influx of genetic diversity.

KATHLEEN DAVIS: This is Science Friday, from WNYC Studios. I’m speaking with Dr. Sam Wisely about cloning for conservation.

From an ethical perspective, is cloning these ferrets justifiable?

SAM WISELY: That was exactly the question that we set out to answer. And ultimately, we came up in our analysis that we did think so. And part of that is because the goals of this, like I said, are actually pretty traditional– pretty traditional conservation reasons– and that being genetic rescue for conducting this. So it’s using a new technology to do what we would consider a traditional conservation management action. That’s very different from using cloning for, say, a new application of technology– say, gene editing, for instance. That’s not what is happening here.

KATHLEEN DAVIS: There’s this argument out there that cloning is a waste of resources. I mean, we’ve talked about how it’s very expensive– it takes a lot of resources to do this– and that we could be saving a species that has a better shot of surviving. How do you pick that argument apart?

SAM WISELY: So you’re absolutely right. And we did analyze that. In this specific case, there are a lot of donors that are outside of the federal system. So US Fish and Wildlife Service has not picked up the cost for a lot of this. There are a lot of not-for-profits that are interested in incorporating biotechnology into conservation. So the research and development end of it has not had a significant cost to US Fish and Wildlife Service.

Now, that doesn’t mean that there won’t be costs in the future associated with managing these cloned species, trying to reintegrate them– or integrate them– into the captive population. However, I think that US Fish and Wildlife Service and the technical team that supports US Fish and Wildlife Service in making these decisions– that’s the Black-Footed Ferret Recovery Implementation Team– all agree that the future of black-footed ferrets is much more certain because of this cloning effort.

KATHLEEN DAVIS: And why do you care so much about saving the black-footed ferret?

SAM WISELY: For me personally, I think the prairie ecosystem which these guys come from is really one of the most changed ecosystems in North America. And it was humans that changed it. And I think, as a conservation biologist, I feel like I have a moral obligation to try and restore these prairies because it was people who changed these prairies in the first place.

KATHLEEN DAVIS: There’s been some buzz around resurrecting long-gone species. There are some biotech companies that want to bring back the woolly mammoth, for example, using cloning. Ethically speaking, do you evaluate cloning differently when it comes to an extinct species versus one that is still alive?

SAM WISELY: Well, I think you use the same bioethical principles– and your very first question at the beginning of this segment asks it– you can do it, but should you do it? And what are the goals that you have for doing it? Why do you want to resurrect a woolly mammoth? Do you want to restore the prairies to a Pleistocene or Holocene environment– restoring the environments to 50,000 years ago or 20,000 years ago? Are you doing it to make a splash? Are you doing it to make money?

I think those need to be evaluated. So I think it is incumbent on people who are trying to resurrect dead animals and extinct animals to go through this bioethical process.

KATHLEEN DAVIS: Dr. Sam Wisely is a professor of wildlife ecology and conservation at the University of Florida. That’s based in Gainesville, Florida. Thank you so much for joining me.

SAM WISELY: Thank you.

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