De-extinction, also known as resurrection biology or species revivalism, is the process of generating an organism that either closely resembles or is an exact genetic copy of an extinct species. This emerging field of science aims to bring extinct species back to life through various biotechnological methods. While de-extinction raises exciting possibilities, it also surfaces ethical, ecological and biological concerns that warrant careful consideration.

The Roots of De-extinction

Interest in de-extinction gained momentum in the late 20th century, as breakthroughs in reproductive technologies, genomics and synthetic biology enabled scientists to deliberately engineer and modify organisms. The idea of resurrecting lost species was popularized by novels like Jurassic Park and motivated real scientific inquiry into whether such feats could be achieved in actuality.

In 2003, scientists produced the first cloned endangered wild ox or gaour through interspecies nuclear transfer between domestic cattle eggs and gaour cell nuclei. This demonstrated the potential of cloning for restoring highly endangered or extinct species. In 2008, a cloned pyrogenic goat was birthed at the Centre for Cellular and Molecular Biology in India using a similar interspecies nuclear transfer approach. These early cloning experiments laid the groundwork for using reproductive technology in de-extinction.

De-extinction aims to bring back extinct species like the woolly mammoth, passenger pigeon, Pyrenean ibex and thylacine. While seemingly far-fetched, scientists are making real progress, with projects underway to revive the woolly mammoth in Russia and the passenger pigeon in the US.

Methods of De-extinction

There are three main approaches to realize de-extinction:

1. Back-breeding

2. Cloning

3. Genome editing

Back-breeding involves selectively breeding animals that contain traces of extinct genetic lineages to reconstitute lost traits over generations. For example, researchers identified that the quagga, a subspecies of zebra that went extinct in 1883, had residual genes in plains zebra populations. Through selective breeding of zebras with quagga-like traits, scientists have been able to reproduce quagga phenotypes like reduced striping.

Cloning entails transferring the nucleus of a somatic cell from the extinct species into an enucleated egg cell of its closest living relative, stimulating cell division to form an embryo containing the extinct animal’s nuclear DNA. The reconstituted embryo is then implanted into a surrogate parent of the related extant species to be carried to term. Cloning presents the most direct path to de-extinction, though it remains hampered by biological challenges.

Genome editing alters the genome of a modern surrogate species to incorporate distinct traits of the extinct species. Advanced gene editing tools like CRISPR enable direct manipulation of an organism’s genetic code. For example, genome editing could transform Asian elephants to contain mammoth genes that encode for long fur and thick layers of subcutaneous fat, conferring adaptations to cold.

Major De-extinction Projects

Here are some major ongoing projects that demonstrate the potential of de-extinction:

• Woolly Mammoth – Geneticist George Church leads the Harvard Woolly Mammoth Revival project which is using CRISPR to insert mammoth genes for small ears, subcutaneous fat and shaggy long fur into elephant DNA. The aim is to grow mammoth-elephant hybrid embryos and achieve the birth of the first mammoth in over 4000 years.

• Passenger Pigeon – The Long Now Foundation is genetically engineering band-tailed pigeons to carry passenger pigeon genes associated with flocking behavior and swift long-distance flights, to recreate passenger pigeon phenotypes capable of thriving in the wild.

• Aurochs – Breeders in Germany are using ancient genetic material from bovine species that went extinct in 1627 to breed back cattle with aurochs-like features through multiple generations of selective cross-breeding. The aim is to release these cattle into wilderness reserves to reestablish wild aurochs populations.

• Pyrenean Ibex – Scientists temporarily revived the Pyrenean ibex, a wild mountain goat extinct since 2000, through cloning in 2009. However, the resurrected ibex clone died shortly after birth due to abnormal lung development. Work is ongoing to attempt a successful de-extinction of the Pyrenean ibex using improved cloning techniques.

• Thylacine – Researchers have sequenced the thylacine genome from preserved specimens and are using gene editing in marsupial cell cultures to experimentally reproduce thylacine organ systems. This could eventually enable cloning and gestation of thylacine embryos by related marsupial species like the numbat.

• Xerces Blue Butterfly – The Xerces Society is using gene editing to introduce genetic mutations conferring the distinctive blue coloration of the Xerces blue butterfly, which has been extinct since the 1940s, into the genomes of closely related butterfly species. This may produce hybrid butterflies with Xerces blue traits.

Ethical Concerns

De-extinction raises several ethical concerns that are important to address:

• Redirecting conservation resources – De-extinction efforts are hugely expensive, costing tens of millions of dollars. Investing resources into de-extinction may divert funding away from conserving threatened extant species and vulnerable ecosystems.

• Animal welfare – The experimental procedures involved in de-extinction like gene editing, cloning and interspecies breeding could potentially cause harm and suffering to animals. There are ethical obligations to ensure the welfare of animals used for de-extinction.

• Playing God – Some view de-extinction as unnaturally interfering with nature, „playing God,“ and overstepping appropriate human boundaries. Others counter that humans have long influenced evolution through selective breeding.

• Commercial exploitation – De-extinction could enable exploitative commercial opportunities like recreating extinct species as exotic pets, zoo exhibits or hunting targets. Clear regulations are needed to prevent misuse.

• Unanticipated impacts – Reintroducing extinct species could have unintended and unpredictable ecological ripple effects. We cannot presume they will integrate harmoniously into modern ecosystems. Caution is warranted.

Ecological Considerations

The ecological impacts of de-extinction are complex and require careful evaluation before the release of any resurrected species into the wild.

• Habitat loss – Many factors that caused a species‘ original extinction like habitat destruction have not been resolved. Releasing revived populations without adequate habitat could doom them to fail again.

• Pathogens – Species have been exposed to hundreds of new infectious diseases since their extinction. Without immunity, resurrected populations may be decimated by disease.

• Genetic diversity – Small founding populations created by de-extinction will lack sufficient genetic diversity for long-term viability. Building genetic health requires incremental additions over generations.

• Synthetic ecosystems – Ecosystems have adapted since the extinction. Introducing an extinct species could create imbalances and competition within delicately balanced food webs and ecological niches.

• Invasive tendencies – Some species were hunted to extinction because they caused problems like destroying crops, preying on livestock or threatening human populations. Releasing them again may provoke renewed conflicts.

Despite these risks, de-extinction may offer ecological benefits in some contexts like helping restore grazers that maintain habitat conditions for other species or bolstering declining populations to enhance genetic diversity.

The Future of De-extinction

While de-extinction is still an emerging field, it has already stimulated critical advances in evolutionary biology, reproductive science, genomics, bioinformatics and conservation genetics. The tools refined through de-extinction initiatives could help strengthen endangered species preservation. Moving forward, interdisciplinary discussion among scientists, ethicists, policy-makers and the public will be key to steering de-extinction science responsibly.

If done carefully and selectively, de-extinction could provide an opportunity to reclaim unique biodiversity lost within recent human history. However, integrating revived species successfully into modern ecosystems while avoiding unintended harms will be an immense challenge requiring precaution. The species we help resurrect will also need indefinite human assistance to survive. Ultimately, preventing extinctions in the first place should remain the priority. But where extinction has regrettably already occurred, de-extinction may offer a chance at partial reparation and ecological enrichment – if pursued wisely.

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