De-extinction, or “resurrection biology,” is a rapidly developing scientific field focused on recovering the genetic blueprints of lost animals. Scientists use advanced biotechnologies to overcome the challenges of degraded ancient DNA and reproductive hurdles associated with long-extinct organisms. The goal is to recreate a functional proxy that can interact with modern ecosystems. This work aims to develop a new conservation tool to reverse human-caused biodiversity loss, driving breakthroughs in genetic science while raising complex questions about conservation.
The Science of Resurrection
The primary method for de-extinction involves gene editing, using technology like CRISPR/Cas9 to modify the DNA of a closely related living species. Researchers insert specific genetic sequences recovered from an extinct animal’s remains into the genome of its modern relative. This process creates a hybrid organism, not an exact copy, that possesses the defining traits of the extinct species, such as cold resistance or unique physical characteristics. Gene editing is necessary because ancient DNA is often too fragmented for traditional cloning techniques.
Cloning is generally less viable for species extinct for a long period because it requires an intact, non-degraded cell nucleus. This technique involves implanting the nucleus of an extinct animal’s cell into the egg of a surrogate mother from a related species. In 2003, scientists briefly revived a recently extinct bucardo, a type of Pyrenean ibex, using somatic cell nuclear transfer, though the cloned animal died minutes after birth. For most high-profile targets, the lack of viable tissue means cloning is restricted to recently extinct species or those whose remains were exceptionally well-preserved.
Selective back-breeding is a third, more traditional technique that restores ancestral traits lost through domestication or evolution. This method involves cross-breeding living animals that display certain features of an extinct ancestor to gradually restore the desired phenotype over multiple generations. While back-breeding can restore the appearance and some behaviors of a lost species, such as creating a proxy for the extinct aurochs from modern cattle, it does not use ancient DNA or modern genetic engineering.
Priority Species and Their Status
The Woolly Mammoth is the most recognized target for de-extinction, chosen because of the well-preserved DNA found in Arctic permafrost specimens. Researchers are working to insert traits like the dense coat and small ears of the mammoth into the genome of the Asian elephant, its closest living relative. The goal is to produce the first mammoth-like calf, an elephant-mammoth hybrid, by late 2028, using an Asian elephant as a surrogate mother. This project has successfully demonstrated engineering mammoth-inspired traits into cells.
The Thylacine, or Tasmanian Tiger, is a high-priority species, extinct since 1936. Its recent disappearance and role as Australia’s only modern marsupial apex predator make it a prime candidate for ecological restoration. Scientists have generated a nearly complete, high-quality thylacine genome, estimated to be over 99.9% accurate.
The project uses the fat-tailed dunnart, a small, related marsupial, as the genetic scaffold for the thylacine’s edited DNA. Researchers have successfully edited hundreds of unique genetic changes into dunnart cells, moving closer to developing a functional embryo. The team is now focusing on the complex challenges of marsupial reproductive biology, with a timeline suggesting a return to the Tasmanian ecosystem within approximately eight years.
The Passenger Pigeon, once the most abundant bird in North America, is the focus of a project by Revive & Restore. Its extinction in 1914 was rapid, making its revival a symbolic effort for modern conservation. Since cloning is not feasible in birds, the plan uses gene-editing techniques to introduce the pigeon’s defining traits into the genome of its closest living relative, the band-tailed pigeon.
Scientists aim to create a hybrid bird that exhibits the passenger pigeon’s traits, such as its flocking behavior and unique physical characteristics. The project involves generating a line of band-tailed pigeons that can produce eggs and sperm carrying the edited genes. Current projections anticipate hatching the first new pigeons in controlled facilities between 2029 and 2032.
Ecological Justifications for Revival
De-extinction efforts primarily aim to restore ecological functions lost when a species disappeared. Many target species are keystone species or ecosystem engineers, meaning their presence had a disproportionately large effect on the structure and health of their environment. Bringing back a functional proxy could trigger a positive ecological change, often called a trophic cascade.
The Woolly Mammoth is theorized to be a natural solution to climate change in the Arctic, a concept sometimes called “Pleistocene Park.” As large herbivores, mammoths would graze on shrubbery and trample snow, helping restore the ancient Arctic grasslands. This restoration is important because open grasslands reflect more sunlight and allow cold air to penetrate the soil, potentially preserving the carbon-rich permafrost from melting and releasing greenhouse gases.
The Passenger Pigeon played a similar role in the deciduous forests of Eastern North America through immense flocking behavior. Their massive numbers caused significant, cyclical disturbances; their collective weight broke tree branches and their droppings enriched the soil. This created light gaps in the forest canopy, promoting the growth of new plants and ensuring the continuous regeneration and biodiversity of the woodland ecosystem.
Reviving the Thylacine, an apex predator, is justified by the need to re-establish a natural balance in the Tasmanian ecosystem. Apex predators regulate the populations of smaller herbivores and mesopredators, whose overabundance can cause environmental damage. Reintroducing a functional thylacine proxy could help manage the current balance of species, increasing the ecosystem’s overall resilience and stability.
The Legal and Regulatory Landscape
Scientific progress in de-extinction has moved faster than the legal and regulatory frameworks needed to manage the resulting organisms and their reintroduction. A fundamental challenge is determining the legal classification of a de-extinct animal, especially those created through genetic engineering. It is uncertain whether a mammoth-elephant hybrid, for example, would be categorized as a genetically modified organism (GMO), which carries significant regulatory hurdles, or as a protected endangered species.
Existing laws, such as the Endangered Species Act in the United States, were not written to contemplate the revival of an extinct species, leading to ambiguity about their protection or management. The question of where these animals will live, and who is responsible for their care and environmental impacts, presents immediate practical challenges. Scientists must navigate complex permitting and land-use issues for eventual reintroduction.
The work also involves international law, concerning the cross-border movement of genetic material and the potential for patenting the genetic sequences or the resulting animals. The lack of a clear, global legal framework means projects must proceed cautiously, often relying on the precautionary principle to ensure reintroduction does not cause unforeseen environmental harm. The international community is still debating how to regulate and protect these novel organisms.