De-Extinction

De-extinction, or resurrection biology, or species revivalism is the process of creating an organism, which is either a member of, or resembles an extinct species, or breeding population of such organisms. Cloning is the most widely proposed method, although selective breeding has also been proposed. Similar techniques have been applied to endangered species.

There is significant controversy over de-extinction, and critics assert that efforts would be better spent conserving existing species, and that the habitat necessary for formerly extinct species to survive is too limited to warrant de-extinction. All modern species, along with the "resurrected" species, will be alive when the humans leave (and that means extinct animals cannot replace their relatives).

Cloning
Cloning is one method discussed as an option for bringing extinct species back. Proponents include author Stewart Brand, and proposed species include the passenger pigeon and the woolly mammoth. De-extinction efforts are now underway to revive the passenger pigeon by extracting DNA fragments and taking skin samples from preserved specimens and, later, using band-tailed pigeons or rock pigeons as surrogate parents.

A team of Russian and South Korean scientists are, as of April 2013, in the planning stages of cloning a woolly mammoth using an Asian elephant as a surrogate mother. Large amounts of well-preserved mammoth tissue have been found in Siberia. If the process can be completed, there are plans to introduce the mammoths to Pleistocene Park, a wildlife reserve in Siberia. (Evolutionary biologist Beth Shapiro points out that "cloning" is a specific technique which cannot be accomplished without a living cell, none of which are available for mammoths, but suggests genome editing might be feasible).

Although de-extinction efforts have not yet succeeded in producing viable offspring of a previously extinct species, the same process has been applied successfully to endangered species. The banteng is the second endangered species to be successfully cloned, and the first to survive for more than a week (the first was a gaur that died two days after being born). Scientists at Advanced Cell Technology in Worcester, Massachusetts, United States extracted DNA from banteng cells kept in the San Diego Zoo's "Frozen Zoo" facility, and transferred it into eggs from domestic cattle, a process called somatic cell nuclear transfer. Thirty hybrid embryos were created and sent to Trans Ova Genetics, which implanted the fertilized eggs in domestic cattle. Two were carried to term and delivered by Caesarian section. The first hybrid was born on April 1, 2003, and the second two days later. The second was euthanized, but the first survived and, as of September 2006, remained in good health at the San Diego Zoo.

Scientists from the University of Newcastle and the University of New South Wales reported in May 2013 the successful cloning of the extinct frog Rheobatrachus silus using the process of somatic cell nuclear transfer. The embryos developed for several days but died. In an important development the scientists from Newcastle reported associated technologies that provide a "proof of concept" for the proposal that frozen zoos (also referred to as genome banks and seed banks) are an effective mechanism to provide an insurance against species extinction and the loss of population genetic diversity. They connected the circle between de-extinction and the prevention of extinction for threatened animal species. The important advances were the capacity to successfully recover live frozen embryonic cells from animals that produce large yolky eggs (anamniotes such as fishes and amphibians). When this development is combined with somatic cell nuclear transfer (SCNT) it enables the genome to be recovered. The scientists point out that many embryonic cells can be frozen and when combined with frozen sperm storage enables the genetic diversity of populations to be stored. With groups of vertebrates such as the amphibians facing an extinction crisis they propose this as an effective means to prevent extinction while the causes of declines can be identified and remedied. The technical difference between frozen tissue samples commonly used for genetic studies (e.g. phylogenetic reconstruction) and those in a frozen zoo is the use of cryoprotectants and special freezing rates at the time of freezing and thawing.

Selective breeding
The aurochs, which became extinct in 1627, could possibly be brought back by taking DNA samples from bone and teeth fragments in museums in order to obtain genetic material to recreate its DNA. Researchers would then compare the DNA to that of modern European cattle to determine which breeds still carry the creature's genes, and then undertake a selective breeding program to reverse the evolutionary process. The intention would be that with every passing generation, the cattle would more closely resemble the ancient aurochs.

The quagga, a subspecies of zebra which has been extinct since the 1880s, has been revived using selective breeding of zebras. Since the new animal is not genetically identical to the extinct subspecies, the new animal is called the Rau quagga.

Opposition
Opponents of de-extinction have claimed that efforts, and resources, to resurrect extinct species could have been better used trying to conserve endangered species that might themselves become extinct.

It has also been noted that a resurrected species, while being genetically the same as previously living specimens, will not have the same behaviour as its predecessors. The first animal to be brought back will be raised by parents of a different species (the fetus's host), not the one that died out and thus have differing mothering techniques and other behaviors.

Scientific American, in an editorial condemning de-extinction, pointed out that the technologies involved could have secondary applications, specifically to help species on the verge of extinction regain their genetic diversity, for example the black-footed ferret or the northern white rhinoceros. It noted, however, that such research "should be conducted under the mantle of preserving modern biodiversity rather than conjuring extinct species from the grave."

Other scholars have published ethical concerns regarding de-extinction. In Conservation Biology, Robert Sandler argues that introducing extinct species to environments may produce harm to modern species, as invasive species. Issues regarding scientific hubris, human and animal health, and the ecology of sensitive environments have been raised by the scientific community. Further research must be performed regarding de-extinction to investigate advantages and disadvantages to the technology. New technological practices must be examined to prevent environmental hazards.

Birds

 * Passenger pigeon – This species numbered in the billions before being wiped out due to commercial hunting and habitat loss. Using DNA found in museum specimens and skins, the non-profit organization Revive and Restore aims to recreate the passenger pigeon using its closest living relative, the band-tailed pigeon.
 * Moa – This group of large (up to 4 m [12 ft.] tall and 110 kg [250 lb.]), flightless birds became extinct in approximately 1400 AD following the arrival and proliferation of the Maori people on New Zealand; however, intact DNA from both preserved specimens and eggshells makes the moa a candidate for resurrection. New Zealand politician Trevor Mallard has suggested bringing back a medium-sized species.
 * Heath hen – This can be possible by using prairie chickens as surrogate mothers.
 * Dodo – This may be possible by injecting dodo DNA from specimens into its close relative, the Nicobar pigeon.
 * Carolina Parakeet - Can be possible to bring Carolina parakeets back by using a species of parakeet as surrogate mothers.

Mammals

 * Woolly mammoth – It is possible to recreate woolly mammoths by extracting DNA of dead woolly mammoths and use Asian elephants as surrogate mothers.
 * Pyrenean ibex – It is possible to recreate Pyrenean ibexes by extracting its DNA and use a related ibex species as a surrogate mother.
 * Aurochs – It is possible to recreate aurochs by breeding certain cattle breeds until they become auroch-like. They will be introduced to North America.
 * Quagga – It is possible to recreate quaggas by breeding zebras to have quagga-like stripe-less fur and brown colorations.
 * Thylacine - It is possible to recreate thylacines by extracting its DNA and use a Tasmanian devil as a surrogate mother.
 * Cave lion – The discovery of two preserved cubs in the Sakha Republic ignited a project to clone the animal. However, the scientists will inject the DNA into modern lionesses.
 * Steppe bison – The discovery of the mummified steppe bison of 9,000 years ago could help people clone the ancient bison species back, even though the steppe bison won't be the first to be "resurrected".
 * Toxodon – In 2015, a group of palaeontologists discovered the DNA of Toxodon and discovered that Toxodons were most closely related to today's horses and rhinos. Some people are planning to bring back Toxodons from extinction using a white rhinoceros as a surrogate mother.
 * Irish elk – It is possible to recreate the Irish elk by extracting DNA from a dead Irish elk and use a red deer as a surrogate mother.
 * Woolly Rhinoceros - It is possible to recreate the woolly rhinoceros by extracting woolly rhinoceros DNA and use a Sumatran rhinoceros (its closest living relative) as a surrogate mother.
 * Saber-Toothed Cats - Scientists have talked about bringing back saber-toothed cats such as Smilodon. In the mid-2020s, they extract DNA from fossils from the La Brea Tar Pits into lynxes since they have similar traits to smilodons (e.g. short tail).
 * Dire Wolf - Possible to recreate dire wolves by breeding different dog breeds that resemble it.
 * Giant Wombat - Might be possible by injecting modern wombat DNA into bears.

Reptiles

 * Pinta Island tortoise - May be possible by using modern Galapagos tortoises as surrogate mothers.
 * Megalania - Also known as the Australian Giant Lizard, they will be brought back by breeding its closest living relatives such as Komodo dragons and perentines to make a real megalania.

Amphibians
COMING SOON

Rules

 * Please don't use animals that aren't from the Pleistocene or Holocene time periods.