Bringing back extinct species is no longer purely science fiction, but it hasn’t fully become science fact either. Scientists have already cloned one extinct animal, a Pyrenean ibex, though the clone survived only minutes after birth. Several well-funded projects are now working to produce living proxies of woolly mammoths, passenger pigeons, and dire wolves, with the first mammoth calves predicted within the next few years. The technology is advancing rapidly, but enormous biological, ecological, and legal hurdles remain.
Three Methods Scientists Are Using
De-extinction relies on three core strategies: back-breeding, cross-species cloning, and genetic engineering. Back-breeding is the simplest concept. You selectively breed living animals that carry ancestral traits, gradually steering the population back toward the extinct form. This works only when closely related species still exist and share enough of the original genetics.
Cross-species cloning takes preserved cells from an extinct animal, extracts the nucleus, and transfers it into an egg cell from a living relative. The resulting embryo is implanted in a surrogate mother from that related species. A woolly mammoth, for example, would be grown inside an Asian elephant using an elephant egg cell, then born from an elephant surrogate.
Genetic engineering, particularly using CRISPR gene-editing tools, is the most flexible approach. Scientists compare the genome of an extinct species to its closest living relative, identify the key genetic differences, and edit those changes into the living species’ cells. The goal isn’t a perfect genetic replica. It’s a proxy animal that carries enough of the extinct species’ defining traits to look, behave, and function like the original.
What Happened With the Pyrenean Ibex
The only extinct animal ever born through cloning was a Pyrenean ibex, a subspecies of Spanish wild goat that went extinct in 2000. In 2003, researchers used frozen skin cells from the last known individual to create cloned embryos and implanted them in domestic goat surrogates. One morphologically normal female was delivered by cesarean section, but she died within minutes of birth due to a severe lung defect. The experiment proved that cloning an extinct subspecies was technically possible, but it also demonstrated how fragile the process is.
The Mammoth and the Dire Wolf
Colossal Biosciences, the most prominent company in the de-extinction space, is working on woolly mammoths, dire wolves, and the dodo. Their mammoth project starts with skin cells from Asian elephants. Scientists edit in mammoth genes responsible for traits like thick woolly coats, cold-adapted blood, and fat storage. The edited cells are then used to create cloned embryos that would be implanted in elephant surrogates for a 22-month pregnancy.
To validate their gene editing, Colossal created “woolly mice,” lab mice engineered with the same coat genes found in mammoth DNA. The mice grew distinctly woolly fur, confirming the team was targeting the right genes. The company predicts the first mammoth calf could be born within roughly two years, though timelines in this field have a history of slipping.
Colossal made headlines more recently by announcing three living dire wolves, named Romulus, Remus, and Khaleesi. Dire wolves were larger and more heavily built than modern gray wolves, with broader skulls and more powerful teeth. The animals are being kept on a private preserve, and details about the genetic engineering involved remain limited.
Why Birds Are Harder
Bird de-extinction faces a unique problem: you can’t clone birds the same way you clone mammals. Bird eggs are structured differently, and the standard cloning technique of transferring a cell nucleus into an emptied egg doesn’t translate well to avian biology. The passenger pigeon project, led by researcher Ben Novak, has taken a different route. The team first sequenced the full passenger pigeon genome, led by Beth Shapiro at UC Santa Cruz. Novak then began breeding rock pigeons injected with the Cas9 gene-editing protein, building a research flock from which to study how pigeon genetics can be modified.
The ultimate plan is to edit the band-tailed pigeon, the passenger pigeon’s closest living relative, inserting as many of the extinct bird’s defining traits as possible. The result would be a hybrid creature that looks and behaves like a passenger pigeon but still carries band-tailed pigeon DNA. It wouldn’t be raised by passenger pigeon parents, so any learned behaviors from the original species would be lost.
The DNA Problem
DNA begins breaking down the moment an organism dies. Microbes attack it first, followed by a slow chemical process called hydrolytic depurination that snaps DNA strands into smaller and smaller fragments. Another chemical reaction converts one of DNA’s four base letters into a different one, introducing errors that accumulate over time.
Despite this degradation, scientists have recovered usable DNA from remains over a million years old. The oldest reconstructed genome comes from a permafrost-preserved mammoth dating to 1 to 2 million years ago, and the oldest isolated DNA fragments come from roughly 2-million-year-old sediment in northern Greenland. Cold environments and caves are the best preservation sites. Clay minerals in soil can bind 200 times more DNA than quartz, helping protect fragments in sediment over geological timescales.
For most remains, DNA is reliably recoverable within the last 100,000 years. Beyond 50,000 years, even standard radiocarbon dating stops working, making it harder to determine exactly how old a sample is. The practical upshot: species that went extinct in the last few thousand years, like the woolly mammoth, passenger pigeon, or dodo, have the best-preserved DNA. Dinosaurs, which disappeared 66 million years ago, are far beyond any foreseeable recovery.
Cloning Success Rates Are Still Low
Even with living species, cloning is remarkably inefficient. Published success rates across all animals average 1 to 3 percent, meaning that for every 100 cloned embryos transferred to surrogates, only one to three result in a live birth. Conservation cloning, which often involves cross-species surrogacy, ranges from under 1 percent to a maximum of 18 percent. That highest figure came from Przewalski’s horse, an endangered wild horse cloned using domestic horse surrogates.
Cross-species surrogacy adds complications. The surrogate mother’s immune system may reject the embryo, the pregnancy hormones may not match what the developing fetus needs, and the birth itself can be dangerous for both mother and offspring. For woolly mammoth embryos carried by Asian elephants, a 22-month pregnancy represents a significant welfare concern for the surrogate, especially given how few attempts are likely to succeed.
What Happens After Birth
Creating a single living animal is only the beginning. A viable population needs genetic diversity, which means producing many individuals from varied genetic backgrounds. A single clone, or even a handful, does not constitute a recovered species. Back-breeding over multiple generations would be needed to strengthen the desired traits and build a self-sustaining population.
Releasing these animals into the wild introduces a separate set of risks. The ecological concerns mirror those of introducing any non-native species: the proxy animal could become invasive, outcompete native wildlife, spread diseases, or disrupt ecosystems through grazing, predation, or changes to water flow and fire patterns. The habitat that originally supported the extinct species may no longer exist in a recognizable form. Woolly mammoths evolved for ice age tundra. The Arctic today is warming faster than anywhere else on Earth.
Legal Gray Zones
No existing legal framework was designed to handle resurrected species. According to IUCN guidelines, proxy species created through cloning or genetic engineering qualify as genetically modified organisms under the Cartagena Protocol on Biosafety. That classification triggers specific national and international regulations that could restrict moving these animals across borders or releasing them into the wild.
Many countries prohibit releasing non-native species, and proxy animals could easily fall under that definition since they aren’t genetically identical to the original species. It’s also unclear how these animals would be treated under wildlife trade agreements like CITES or biodiversity targets under the Convention on Biological Diversity. Each proxy species would need to be evaluated individually against every relevant piece of legislation, a process that doesn’t yet have a clear precedent.
The Ethical Trade-Offs
The ethics of de-extinction involve real costs to real animals. Surrogate mothers endure repeated failed pregnancies. Cloned offspring frequently have developmental abnormalities, as the Pyrenean ibex lung defect illustrated. The first generations of any de-extinction project will likely involve significant animal suffering in the process of refining techniques.
There’s also an opportunity cost. Conservation funding is limited, and money spent resurrecting extinct species could instead protect the thousands of currently endangered species sliding toward extinction right now. Proponents argue that de-extinction technologies, particularly advances in cloning and genetic engineering, will benefit living endangered species too. Critics counter that the headline-grabbing nature of mammoth resurrection diverts attention and resources from less glamorous but more urgent conservation work.
The honest answer to whether we can bring back extinct species is: partially, and not yet reliably. We can create hybrid animals that carry many traits of extinct species, using closely related living animals as the biological foundation. What we cannot do, at least for now, is recreate an exact genetic copy, raise it with the behaviors of its extinct ancestors, or guarantee it a functioning ecosystem to live in.