Crispr has produced disease-resistant chickens and hornless dairy cattle. Crispr-edited pigs contain kidneys that scientists hope to test as transplants in humans.
Crispr has been discussed as a de-extinction tool since its earliest days. At the conference, George Church, a Crispr pioneer and geneticist at Harvard Medical School, laid out a scientific roadmap for reviving a species. Church focused not on the passenger pigeon but on his own pet project, the woolly mammoth. Through genetic cutting and pasting, physical and behavioral traits of the mammoth—its namesake coat and ability to withstand subzero temperatures—could be added to living elephant cells.
The idea that woolly mammoths might once again roam the Earth made headlines around the world. With enough mammoth DNA, Church explained, a Crispr-edited Asian elephant would become something else entirely: a modern hybrid that looked and behaved like a mammoth but shared DNA with a living species.
For many in the audience that day, an idea straight out of science fiction suddenly seemed plausible. Of the 1, stuffed passenger pigeons in museums and private collections, he has personally viewed He understands that his obsession is difficult for most people to understand. He has a hard time explaining it himself. Novak grew up in a town of people in North Dakota. Long before he could read, he was fascinated by the idea of extinction, digging unsuccessfully for fossils in his backyard.
Male passenger pigeons were particularly colorful, with red breasts, feet and legs and iridescent pink patches that glistened on the sides of their throats. The birds traveled in flocks that could number three billion, and were known for their grace and speed, flying at up to 60 miles per hour. Novak read histories that described passenger pigeon flocks so large, they darkened the skies for days as they passed overhead.
These massive flocks played an important ecological role, breaking branches to allow sunlight to rejuvenate forests and enriching the soil with their excrement. The birds were prized for their meat; hunters could see the flocks approaching from miles away. The population went into steep decline in the late s and never recovered. The last known passenger pigeon—a bird named Martha—died in captivity at a Cincinnati zoo in Her demise sparked the passing of modern conservation laws to protect other endangered species in the U.
Shortly after her death, Martha was frozen and shipped to the Smithsonian Institution in Washington, D. The first step was to sequence the passenger pigeon genome. For the passenger pigeon project, Shapiro and her team took tissue samples from the toe pads of stuffed birds in museum collections. DNA in the dead tissue left them with tantalizing clues but an incomplete picture. By comparing the genomes of the two birds, researchers began to understand which traits distinguished the passenger pigeon.
Some of these allowed the birds to withstand stress and disease, essential traits for a species that lived in large flocks. They found no genes that might have led to extinction. In , Shapiro taught a graduate class on de-extinction and asked each student to make a case for bringing one animal back from the dead. But, you know, what do we mean by de-extinction? Is it really to have a mammoth that we can look at and hug and maybe put in a zoo and maybe have kid rides on and stuff like that?
Is there some ecological rationale for wanting to bring them back? I think for some recently extinct species whose extinction might have thrown their community that they lived in out of balance, then maybe there is a reason to try to bring them back and to reestablish ecological connections that that existed prior to their disappearance.
But then you have to ask yourself, do you really need that exact species, or could you use something in its iplace? They want mammoths to be back in Pleistocene Park because they think mammoths play a really critical role in establishing this ecosystem just by wandering around and knocking down shrubs, just like elephants do. But do they actually need a mammoth, or could they use an elephant that maybe has been modified using gene editing technologies to be able to survive and even thrive in the cold habitat up in Siberia?
But if we could identify mutations in their DNA that would make them better able to survive in that environment, then maybe we could just create a cold adapted elephant. So if they were to succeed, maybe they would create a cold adapted elephant. So you have an elephant cell, mostly elephant, that has a bit of mammoth DNA in it. Does that count as a de-extinction? To me, no, I guess. What do you think, Marshall? Is that a de-extinction? Marshall Poe: I would call it speciation or something like that.
It reminds me of the process of speciation, where a new species emerges in a kind of natural way. I have to stop and ask you this question. What do you think of the metaphor of DNA as the blueprint for life?
In fact, a lot of what we look like is really based on that. If you want to know how important the DNA letters are in determining what somebody looks like, then just see identical twins. They look identical. They have the same DNA, but extend that a little bit and no identical twins as they get older, as they live different lives, and experience different things and have different illnesses and different stressors and different joys, they diverge in the way that they look and the way that they act.
This is because we are a combination of what is coded by our DNA and the environment in which we live. The same would be true for any clone. A clone is just an identical twin that happens not to be born at the same time. Technological hurdle, number whatever. Would it be a mammoth or will it be an elephant? And mom in this case is one hundred percent elephant. Scientists are only just beginning to understand how important that community of microbes is to making us look and act the way that we do.
So there are lots of differences that come into creating an individual that have nothing to do with the sequence of the letters in their DNA code. What do you mean by that? Beth Shapiro: By that, I just mean if there is a good ecological reason or evolutionary reason to bring something back, we might not necessarily need to bring the whole organism back, but just some traits that allow an organism to fill whatever niche is at the moment not occupied by something.
You also have to remember that ecosystems are not in stasis. Everything is constantly in flux. When a species disappears, the ecosystem will change. New species will come in, other species might go extinct. Everything is changing. That might again destabilize that ecosystem and send it off in some other direction.
This is just our role as humans, and we need to embrace that this is our role as humans. Marshall Poe: But that new animal, the one with the different traits that actually has its roots in another species that is not on the verge of extinction, that species would be invasive then. Beth Shapiro: Invasive. Maybe, but we are constantly introducing other species. And if every time a new species is introduced into a new habitat, perhaps by walking there or by flying there on its own accord, we call it an invasive species.
We like it exactly as it is in December So why do we pick December ? Why do we pick pre-European colonization of North America as some perfect time? Why not the peak of the last Ice Age or the last interglacial right before that? We have to keep in mind when we think about invasive species or other loaded terms that consider the appearance of new communities of organisms as necessarily bad things, that everything is constantly changing. By not allowing things to change, we are making a decisive action.
By allowing things to change, we are making a decisive action. Marshall Poe: So you talk about two methods for cloning. Can you describe back breeding? I found this just fascinating. But the aurochs was bigger and better and meaner than the cattle breeds that we have today.
Because they were the big, bad, mean Nazis, they wanted to be able to have these guys that they could go fight them with swords and things. So they decided they were going to recreate the aurochs by taking the breeds that we had today and looking for ones that had traits that they thought looked like aurochs and then making offspring by breeding those guys together.
So they were taking the individuals that we have right now and then breeding them to each other in order to create some traits that used to exist. Now, this was a silly idea. They had no idea what aurochs looked like anyway. But people are using back breeding now to try to do similar things.
So they are using this approach, back breeding, just looking at traits and trying to bring traits together that they think are optimal to create some target offspring. Marshall Poe: But to really do it, if I understand this correctly, you would need to recreate the selection environment in which that species emerged so you had selection on the traits that you wanted. Beth Shapiro: Yeah, we do everything with artificial selection now, too, though, right?
So if we can imagine that what we want is something with longer horns, then maybe we can do it just by picking individuals that have longer horns and forcing them to breed together rather than creating a habitat that would favor individuals with longer horns and therefore make them the most likely to breed and produce.
So we create selective environments for everything now. How do you know which traits to include? I know the phenotypic ones are probably obvious. You say those phenotypic traits are probably easy. How many genes are associated with that and what genes are associated with that? No idea. So what genes are associated with that? And how do we even know? This miraculous reproductive feat gave the frogs their common names: the northern Rheobatrachus vitellinus and southern Rheobatrachus silus gastric brooding frogs.
Unfortunately, not long after researchers began to study the species, they vanished. To bring the frogs back, the project scientists are using state-of-the-art cloning methods to introduce gastric brooding frog nuclei into eggs of living Australian marsh frogs and barred frogs that have had their own genetic material removed.
The scientists need fresh eggs, which the frogs produce only once a year, during their short breeding season. But does that mean we should bring them back? Would the world be that much richer for having female frogs that grow little frogs in their stomachs? There are tangible benefits, French argues, such as the insights the frogs might be able to provide about reproduction—insights that might someday lead to treatments for pregnant women who have trouble carrying babies to term. But for many scientists, de-extinction is a distraction from the pressing work required to stave off mass extinctions.
Why invest millions of dollars in bringing a handful of species back from the dead, when there are millions still waiting to be discovered, described, and protected? But what would we be willing to call salvation?
Even if Church and his colleagues manage to retrofit every passenger pigeon—specific trait into a rock pigeon, would the resulting creature truly be a passenger pigeon or just an engineered curiosity? Would it be enough to keep a population of the frogs in a lab or perhaps in a zoo, where people could gawk at it? Or would it need to be introduced back into the wild to be truly de-extinct? A huge effort went into restoring the Arabian oryx to the wild, for example.
But after the animals were returned to a refuge in central Oman in , almost all were wiped out by poachers. Hunting is not the only threat that would face recovered species. The Chinese river dolphin became extinct due to pollution and other pressures from the human population on the Yangtze River. Things are just as bad there today. Around the world frogs are getting decimated by a human-spread pathogen called the chytrid fungus.
If Australian biologists someday release gastric brooding frogs into their old mountain streams, they could promptly become extinct again. Even if de-extinction proved a complete logistical success, the questions would not end. Passenger pigeons might find the rebounding forests of the eastern United States a welcoming home. Could passenger pigeons become a reservoir for a virus that might wipe out another bird species?
De-extinction advocates are pondering these questions, and most believe they need to be resolved before any major project moves forward.
Hank Greely, a leading bioethicist at Stanford University, has taken a keen interest in investigating the ethical and legal implications of de-extinction. And yet for Greely, as for many others, the very fact that science has advanced to the point that such a spectacular feat is possible is a compelling reason to embrace de-extinction, not to shun it.
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