For that reason, the Christmas Island rat ( Rattus macleari) was an obvious choice for analysis for the scientists. It diverged from a close relative, the Norway brown rat ( Rattus norvegicus), only around 2.6 million years ago. With an intact copy of the original book, someone could theoretically reconstruct the book perfectly. When identifying a reference genome, researchers look for a species that diverged evolutionarily from the extinct species fairly recently —in other words, a very similar book. The genomes will match closely, but not perfectly. With the advent of gene-editing technology such as CRISPR, scientists have shifted from cloning to genetic engineering as the most promising method for “de-extinction,” or the resurrection of species that have died out ( SN: 10/7/20). But unlike cloning, genetic engineering wouldn’t create an exact replica of an extinct species. Instead, the technique would edit an existing animal’s genome so that it resembles that of the desired extinct animal. The challenge is making that proxy as similar to the extinct species as possible. To get the extinct rat’s genome, Gilbert and his colleagues took ancient DNA from two preserved skin samples of the Christmas Island rat. Ancient DNA, extracted from specimens that died anywhere from a few decades to thousands of years ago, is far from perfect ( SN: 5/19/08). Gilbert describes an extinct species’ genome as a book that has been shredded. One way to reconstruct this shredded book is to scan the fragments and compare them with a reference. The reference assembly problem will always be a barrier to de-extinction,” Novak says. “Anyone pursuing de-extinction has to settle on the fact that we want to get as close as we can to something that fools the environment.”

Wyatt KB, Campos PF, Gilbert MT, Kolokotronis SO, Hynes WH, etal. (2008). "Historical mammal extinction on Christmas Island (Indian Ocean) correlates with introduced infectious disease". PLOS ONE. 3 (11): e3602. Bibcode: 2008PLoSO...3.3602W. doi: 10.1371/journal.pone.0003602. PMC 2572834. PMID 18985148. a b Harper, Francis (1945). Extinct and vanishing mammals of the Old World. New York: American Committee for International Wild Life Protection. pp.206–208. The team used brown rats, commonly used in lab experiments, as the modern reference species, and found they could reconstruct 95 percent of the Christmas Island rat genome. As a science, it’s awesome,” Gilbert says. But “is this the best use of the money in a world where we can’t keep our rhinos alive?”SAMN05425704 (NZ2), SAMN05425705 (SG1) SAMN05425706 (SG2), SAMN05425709 (NZ1), SAMN05425641 (WH1), SAMN05425642 (WH2), and SAMN05425643 (WH3). Mammoths have roughly the same evolutionary distance from modern elephants as brown rats and Christmas Island rats. Before the early 1900s, if it walked like a Christmas Island rat and talked like a Christmas Island rat, it probably was a Christmas Island rat. But if one of these now-extinct rats ever walks the Earth again, it will most likely be a genetically modified Norway brown rat. And the rodent won’t be as similar to the Christmas Island rat as some would hope, a new study finds. Flannery, Tim & Schouten, Peter (2001). A Gap in Nature: Discovering the World's Extinct Animals. Atlantic Monthly Press, New York. ISBN 978-0-87113-797-5. Teams in Australia meanwhile are looking at reviving the Tasmanian tiger, or thylacine, whose last surviving member died in captivity in 1936.

The rat is named after Captain John Maclear (1838–1907) of the British survey-ship HMS Flying-Fish, who collected the specimen from Christmas Island in 1886. It was described as a new species by Oldfield Thomas the next year, although it was originally described under the genus Mus. [2] [7] Maclear was earlier commander on HMS Challenger for the Challenger Expedition of 1872–1876 under its commission captain, Sir George Nares. By doing these kinds of analyses, which is not hard to do, you can at least come up with the what will you get, what will you not get, and you can use that to decide is it worth doing,” Gilbert says. a b Thomas, Oldfield (1887). "Report on a Zoological Collection made by the Officers of HMS Flying-Fish at Christmas Island, Indian Ocean. Communicated by Dr. A. Gunther, VPZS, Keeper of the Zoological Department, British Museum". Proceedings of the Zoological Society of London: 513–514. The team found that the Christmas Island rat genome mapped to about 95 percent of the Norway brown rat genome. Further analyses showed that the roughly 5 percent that was missing could not be explained solely by a flaw in the technique or an inadequate reference genome. Rather, because of evolutionary divergence between the two species, most of that genetic information was simply lost.In other words, a de-extinct mammoth created using gene editing, if such a thing ever comes to be, won’t exactly be a mammoth; it will be closer to a hairy Asian elephant adapted to live in the cold. And the new analysis suggests that the proxy animal version will probably have enough differences that would make it difficult for the creature to refill its previous ecological niche. For some, that might be enough to defeat the purpose of the exercise. I am not doing de-extinction, but I think it's a really interesting idea, and technically it's really exciting," senior author Tom Gilbert, an evolutionary geneticist at the University of Copenhagen, told AFP. A DNA study found Maclear's rat to be the sister species of Hainald's rat native to the island of Flores, with the clade containing the two being sister to the clade containing Nesokia and Bandicota; this clade, in turn, is sister to the Australasian Rattus radiation, making Rattus as currently defined paraphyletic. [8] See also [ edit ]