De-extinction (also known as resurrection biology, or species revivalism) is the process of human intervention to generate an organism that either resembles or is an extinct organism. There are several ways to carry out the process of de-extinction. Cloning is the most widely proposed method, although genome editing and selective breeding have also been considered. Similar techniques have been applied to certain endangered species, in hopes of boosting their genetic diversity. The only method of the three that would provide an animal with the same genetic identity is cloning. There are benefits and drawbacks to the process of de-extinction ranging from technological advancements to ethical issues.
History of the term De-extinction as a concept involving genetics traces back to the Nazi-era eco-fascist efforts "integral to recreating the mythical German landscape of ancient times, when the Aryan race was pure and unthreatened", but the term itself arose in the twentieth century "in response to a series of breakthroughs in resurrection biology".
One example of this was the work done by Berlin zoo director Lutz Heck, in collaboration with his brother and Munich zoo director Heinz Heck, to bring aurochs back from extinction through a process of selective breeding. Their work was condemned by the Union of German Zoo Directors in 1951, when they stated "that their organization would offer no financial or other support for breeding back extinct species since it was not only a scientific impossibility but took away resources from the pressing issue of preserving threatened animals."
Methods Cloning
Cloning is a commonly suggested method for the potential restoration of an extinct species. It can be done by extracting the nucleus from a preserved cell from the extinct species and swapping it into an egg, without a nucleus, of that species' nearest living relative. The egg can then be inserted into a host from the extinct species' nearest living relative. This method can only be used when a preserved cell is available, meaning it would be most feasible for recently extinct species. Cloning offers the most direct route to an organism with the original species' nuclear genome, but it requires well-preserved viable donor cells. Cloning has been used by scientists since the 1950s. One of the most well known clones is Dolly the sheep. Dolly was born in the mid-1990s and lived normally until the abrupt midlife onset of health complications resembling premature aging, that led to her death. Other known cloned animal species include domestic cats, dogs, pigs, and horses.
Genome editing Genome editing has been rapidly advancing with the help of the CRISPR/Cas systems, particularly CRISPR/Cas9. The CRISPR/Cas9 system was originally discovered as part of the bacterial immune system. Viral DNA that was injected into the bacterium became incorporated into the bacterial chromosome at specific regions. These regions are called clustered regularly interspaced short palindromic repeats, otherwise known as CRISPR. Since the viral DNA is within the chromosome, it gets transcribed into RNA. Once this occurs, the Cas9 binds to the RNA. Cas9 can recognize the foreign insert and cleave it. This discovery was very crucial because the Cas protein can now be viewed as a scissor in the genome editing process.
By using cells from a closely related species to the extinct species, genome editing can play a role in the de-extinction process. Germ cells may be edited directly, so that the egg and sperm produced by the extant parent species will produce offspring of the extinct species, or somatic cells may be edited and transferred via somatic cell nuclear transfer. The result is an animal which is not completely the extinct species, but rather a hybrid of the extinct species and the closely related, non-extinct species. Because it is possible to sequence and assemble the genome of extinct organisms from highly degraded tissues, this technique enables scientists to pursue de-extinction in a wider array of species, including those for which no well-preserved remains exist. However, the more degraded and old the tissue from the extinct species is, the more fragmented the resulting DNA will be, making genome assembly more challenging. Genome editing does not require living cells from the exact same species and can target specific adaptive traits, but an organism created via this method can only ever be a proxy/hybrid.
Back-breeding
Back breeding is a form of selective breeding. As opposed to breeding animals for a trait to advance the species in selective breeding, back breeding involves breeding animals for an ancestral characteristic that may not be seen throughout the species as frequently. This method can recreate the traits of an extinct species, but the genome will differ from the original species. Back breeding, however, is contingent on the ancestral trait of the species still being in the population in any frequency. Back breeding is also a form of artificial selection by the deliberate selective breeding of domestic animals, in an attempt to achieve an animal breed with a phenotype that resembles a wild type ancestor, usually one that has gone extinct. Because back-breeding uses standard breeding techniques, no genetic reconstruction or preserved cells are required. The resulting offspring are phenotypic look-alikes, meaning that they are often lacking in behavioral, physiological, and ecological traits of the original species.
Recurrent evolution
A natural process somewhat resembling de-extinction is recurrent evolution. This occurs when a species becomes extinct, but then after some time a different species evolves into an almost identical creature. For example, the Aldabra rail was a flightless bird that lived on the island of Aldabra. It had evolved some time in the past from the flighted white-throated rail, but became extinct about 136,000 years ago due to an unknown event that caused sea levels to rise. About 100,000 years ago, sea levels dropped and the island reappeared, with no fauna. The white-throated rail recolonized the island, but soon evolved into a flightless species physically identical to the extinct species.
Herbarium specimens for de-extincting plants
Not all extinct plants have herbarium specimens that contain seeds. Of those that do, there is ongoing discussion on how to coax barely alive embryos back to life. Generally, plant material is better conserved than animal tissue. This means that if seeds are preserved, germination can produce living offspring that are identical to the historical specimen. However, many herbarium specimens do not contain viable seeds which complicate reintroduction.
In-vitro fertilisation and artificial insemination
In-vitro fertilisation and artificial insemination are assisted reproduction technology commonly used to treat infertility in humans. However, it has usage as a viable option for de-extinction in cases of functional extinction where all remaining individuals are of the same sex, incapable of naturally reproducing, or suffer from low genetic diversity such as the northern white rhinoceros, Yangtze giant softshell turtle, Hyophorbe amaricaulis, baiji, and vaquita. For example, viable embryos are created from preserved sperm from deceased males and ova from living females are implemented into a surrogate species. In-vitro fertillisation and artificial insemination can help preserve and restore genetic diversity to applicable near-extinct species where fresh gametes and tissues exist. However, cross-species surrogacy and embryo transfer present great biological and ethical challenges.
Ethics of de-extinction
The concept of de-extinction is often met with skepticism, as it presents both significant advantages and disadvantages. Some may believe that extinction is a natural evolutionary process, but the 21st century has been marked as the sixth major extinction event in Earth's history. We have reached unprecedented speed and scale at which species are disappearing. Up to half of the species on Earth are predicted to disappear this century. The scale at which we are losing species is important to the ethical stakes de-extinction presents. This is overwhelmingly caused by human activity (habitat destruction, pollution, invasive species, climate change), not natural processes like previous extinctions. Since humans are the primary cause of this modern extinction, it can be argued that humans now have the moral obligation to repair it. The loss in species variation (biodiversity) is not a result of survival of the fittest, but the negative consequences of human interference with the planet.
With this in mind, reviving species lost through human actions may help restore biodiversity and address harms humans have caused to the planet. De-extinction can be viewed as an unnatural interference, while also showing potential as a tool for ecological restoration. Reviving species could be part of ecological restoration and ethically defensible.
Advantages of de-extinction
The technologies being developed for de-extinction could lead to large advances in various fields: An advance in genetic technologies that are used to improve the cloning process for de-extinction could be used to prevent endangered species from becoming extinct. By studying revived previously extinct animals, cures to diseases could be discovered. Revived species may support conservation initiatives by acting as "flagship species" to generate public enthusiasm and funds for conserving entire ecosystems.
Prioritising de-extinction could lead to the improvement of current conservation strategies. Conservation measures would initially be necessary in order to reintroduce a species into the ecosystem, until the revived population can sustain itself in the wild. Reintroduction of an extinct species could also help improve ecosystems that had been destroyed by human development. It may also be argued that reviving species driven to extinction by humans is an ethical obligation.
Disadvantages of de-extinction The reintroduction of extinct species could have a negative impact on existing species and their ecosystem. The extinct species' ecological niche may have been filled in its former habitat, thus making them an invasive species. This could lead to the extinction of other species due to competition for food or other competitive exclusion. It could also lead to the extinction of prey species if they have more predators in an environment that had few predators before the reintroduction of an extinct species. If a species has been extinct for a long period of time the environment they are introduced to could be wildly different from the one that they can survive in. The changes in the environment due to human development could mean that the species may not survive if reintroduced into that ecosystem. A species could also become extinct again after de-extinction if the reasons for its extinction are still a threat. The woolly mammoth might be hunted by poachers just like elephants for their ivory and could go extinct again if this were to happen. Or, if a species is reintroduced into an environment with disease for which it has no immunity, the reintroduced species could be wiped out by a disease that current species can survive.