De-extinction, resurrection biology, or species revivalism is the controversial process of creating an organism, which is a member of or resembles an extinct species, or a 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 (including dinosaurs) to survive is too limited to warrant de-extinction.
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 species by extracting DNA fragments from preserved specimens, and later, using Band-tailed Pigeons as surrogate parents.
Ongoing technological advances have encouraged the hypothesis that by using DNA from the remains of an extinct species, through the process of cloning, the species may be "brought back to life". Proposed targets for cloning include the mammoth, thylacine, and Pyrenean Ibex. For such a program to succeed, a sufficient number of individuals would have to be cloned, from the DNA of different individuals (in the case of sexually reproducing organisms) to create a viable population. Though bioethical and philosophical objections have been raised,[not in citation given] proponents argue that the cloning of extinct creatures is a viable outcome of the continuing advances in science and technology.
In 2003, scientists attempted to clone the extinct Pyrenean Ibex (Capra pyrenaica pyrenaica). This attempt failed: of the 285 embryos reconstructed, 54 were transferred to 12 mountain goats and mountain goat-domestic goat hybrids, but only two survived the initial two months of gestation before they too died. In 2009, a second attempt was made to clone the Pyrenean Ibex: one clone was born alive, but died seven minutes later, due to physical defects in the lungs.
A team of Russian and South Korean scientists are, as of April 2013, attempting to clone a Woolly mammoth using an Elephant as a surrogate mother. Large amounts of well-preserved mammoth tissue have been found in Siberia, but, as of April 2013, the cloning process is still in the planning stages. Once the process is completed, there are plans to introduce the mammoths to Pleistocene Park, a wildlife reserve in Siberia.
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.
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.
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 go 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 rhino. It noted, however, that such research "should be conducted under the mantle of preserving modern biodiversity rather than conjuring extinct species from the grave."
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- Breeding Ancient Cattle Back from Extinction
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