De-extinction, also known as resurrection biology, involves generating an organism that closely resembles or is genetically similar to an extinct species. While once a subject of science fiction, advances in biotechnology have made the possibility of reviving lost species a topic of active research and development.
Understanding De-Extinction
De-extinction efforts do not typically create exact genetic replicas of original animals. Instead, they focus on developing proxies or hybrids by introducing traits of an extinct species into a living, closely related one. This differs from reintroduction, which moves existing populations to areas where they were previously extinct. The genetic material of extinct animals is often degraded, making perfect recreation challenging.
Animals Targeted for Revival Efforts
The Pyrenean ibex, a wild goat subspecies extinct since 2000, was the subject of a de-extinction attempt. Scientists used preserved tissue samples from its last individual, Celia, in a cloning experiment. In 2003, a cloned ibex was successfully born using somatic cell nuclear transfer. Unfortunately, the clone survived for only a few minutes due to a severe lung defect, highlighting the complexities and challenges of the process.
The gastric brooding frog, an Australian amphibian extinct since the 1980s, was also targeted for revival. This species was remarkable for brooding its young in its stomach and giving birth through its mouth. In “Project Lazarus,” scientists used preserved tissue from the 1970s to create early-stage embryos via somatic cell nuclear transfer. None survived beyond a few days.
The Science of Bringing Back Species
De-extinction efforts employ several scientific methodologies, each with distinct principles and applications. Cloning, specifically somatic cell nuclear transfer (SCNT), involves transferring the nucleus from an extinct animal’s somatic cell into an enucleated egg cell from a living relative. The reconstructed egg develops into an embryo, which can be implanted into a surrogate mother. This method was famously used to clone Dolly the sheep.
Selective breeding, also known as back-breeding, involves breeding living animals to emphasize ancestral characteristics. This method can recreate physical traits of an extinct species, but the resulting animal has a different genome than the original. Examples include attempts to breed cattle resembling the aurochs and the ongoing Quagga Project, which aims to breed zebras resembling the extinct quagga.
Gene editing, using tools like CRISPR, introduces specific traits from an extinct species into a living relative’s genome. Scientists compare the extinct animal’s DNA with its closest living counterpart, then use CRISPR to edit the differences. This creates a hybrid organism exhibiting characteristics of the extinct species, typically a genetically modified version rather than an exact replica.
Species Under Consideration for Future De-Extinction
The woolly mammoth is a target for future de-extinction. Projects aim to create a cold-resistant elephant with key traits of its extinct relative. Scientists plan to use CRISPR gene editing to insert mammoth genes into the Asian elephant’s genome, its closest living relative. Efforts are underway to produce mammoth-like calves by 2028.
The passenger pigeon, extinct since the early 20th century, is also under consideration. Researchers are exploring gene editing, using the band-tailed pigeon as a living proxy. The goal is to introduce passenger pigeon traits into the band-tailed pigeon’s genome, aiming to restore its ecological role in forest ecosystems.