Clone Wolf

The following is from "Raising the Dead" by Scott Weidensaul, which was originally published in the May 2002 issue of Audubon magazine. It was republished in The Best American Science and Nature Writing 2003.

The small animal is wrinkled and gray, its forelegs curled against its chest in an unintentionally protective position and a long, open incision running the length of its stomach. Stored in a clear jar of alcohol, it hardly looks like the stuff of high-tech science and acrimonious debate. This young thylacine, the marsupial "tiger" of Tasmania, was taken from its mother's pouch in 1866--at first a curiosity from a weird and newly settled land, and later a pitiable relic of a species recklessly driven to extinction.

But now, 136 years after its death and 66 years after its species was declared extinct, the preserved baby sits at the junction of molecular biology, conservation ethics, and endangered-species politics--and also at the locus of humanity's guilt and hopes in dealing with the natural world. That's a lot to pin to a dead creature you could easily cup in two hands, but ever since 1999, when the Australian Museum in Sydney announced its intention to clone a living thylacine from this pickled specimen, the reaction, both pro and con, has been surprisingly fierce. Critics have lambasted it as science fiction that will drain money from more important work; proponents see it as a way to mitigate a grievous wrong committed against the planet, while burnishing Australia's languishing scientific reputation.

The man at the center of the storm is Don Colgan, a soft-spoken evolutionary biologist who heads the museum's cloning team. He admits the odds of ever producing a live thylacine are long, but his group has already managed to extract unusually good-quality DNA from the preserved baby. Several other cloning projects around the world have focused on long-extinct species, but only the thylacine team has posted any significant success to date (see "Born Again?"). If Colgan succeeds where so many have predicted failure, he will not only have beaten his own odds but restored--at least in facsimile--one of the natural world's most unusual masterpieces.

To understand why the museum's project has attracted such attention, it's important to understand the significance of the thylacine from both a biological and a cultural perspective. Australia's unique, marsupial-dominated fauna has long been a textbook example of convergent evolution, and in this the thylacine is Exhibit A. Though more closely related to kangaroos and opossums, it was molded by the demands of its predatory lifestyle into a close analog of the wolf--a lean hunter with a short brownish coat, a stiff tail, and more than a dozen dark stripes along its back and hindquarters. At roughly 65 pounds, the thylacine was the largest of the carnivorous marsupials and an accomplished hunter of wallabies and other grazing species in the coastal scrublands, eucalyptus forests, and alpine meadows of Tasmania--"Tassie" to most Australians.

English settlers in the early 19th century--the first Europeans to have any close dealings with the thylacine--variously dubbed it the marsupial wolf, a native cat, or even a hyena. But the name that stuck was Tasmanian tiger, even though there was nothing remotely feline about the animal. (The name thylacine, coined by scientists, comes from the Greek words for "pouched dog.") Regardless of what they called it, sheep farmers accused the thylacine of attacking their flocks, and after a century of trapping, shooting, and poisoning, the last known thylacine died in a zoo in 1936--ironically, less than two months after the Tasmanian government extended legal protection to the species.

But Tassie has been reluctant to let go of its tiger. The beast has become an icon--stylized on automobile license plates, gracing the label of the state's best-selling beer, adopted as the symbol of everything from a regional television network to local sports teams. Of the animal itself, though, there is nothing but specimens locked up in museum cases or gathering dust on shelves. Most consist of stuffed skins or skeletal material, but a fair number are pouch babies, the nearly hairless neonates too young to be out on their own. The usual method for preserving such soft-tissue specimens is to submerge them in formaldehyde, but the Australian Museum's now-famous baby is embalmed in alcohol. That makes all the difference, Don Colgan explained, as he guided me through the warren of narrow corridors and cluttered labs in the museum's research wing.

Formaldehyde is hard on DNA's double helix of amino acids, Colgan said, but alcohol is much gentler--meaning that it has been possible to extract relatively high-quality DNA from several tiny samples of the thylacine's heart, liver, and muscle. Colgan pulled a large X ray from a file and held it up to the light, showing me five lines a couple of inches long and heavily crossbarred with light and dark bands--the DNA, treated with radioactive nucleotides and photographed. With his index finger, he indicated one of the blurry streaks.

"The DNA represented on this line would be about 40 copies of every gene in the thylacine genome," Colgan said. "That doesn't sound a lot, but it was extracted from probably a match-head-size piece of tissue." Scientists measure DNA fragments by the number of base pairs they contain--the rungs that form the twisted ladder of a DNA molecule. This thylacine's DNA contains 1,200 to 2,000 base pairs per section--badly fragmented when compared with samples from living organisms but 10 times better than is normal with ancient DNA.

Given the surprisingly good results, the museum's team is preparing to create a bacterial genomic library by inserting the thylacine genes into bacteria, which will allow the scientists to grow as much of the genetic material as they need. Beyond that, they hope to have the Tasmanian tiger genes sequenced--their genomic code "read" in its proper order. "It's like putting a jigsaw puzzle together; if you have large pieces covering the same area as a number of very small pieces, obviously it's a lot easier with the large pieces," Colgan said.

In the near term, genomic sequencing promises several scientific payoffs, he said, including genetic comparisons with other marsupials. But it is the prospect of cloning--creating a living, breathing thylacine--that raises the greatest expectations and presents the most serious challenges. In normal cloning, the nucleus of a host egg cell is removed and another living cell, containing the DNA blueprint for the organism being cloned, is inserted. (Because each clone is an exact genetic copy of the parent specimen, one must have multiple specimens of both sexes and a variety of family lineages to create a reproducing population. Colgan noted that there are hundreds of thylacine specimens in the world's museums, many of which may provide equally usable DNA.)

The trouble is that with ancient DNA, there is no living cell nucleus to serve as a starting point, so unless someone invents a way to tease a dead cell back to life, Colgan and his team must use what he calls "the brute force approach." This entails reading what they can of the thylacine genome and filling in any gaps with DNA from other marsupials, then creating artificial chromosomes, packaging them in artificial membranes, and inserting them into an egg from a closely related species. The Tasmanian devil and the numbat, the latter a small termite-hunter, are prime candidates for supplying both missing DNA and a host egg.


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Learn more about the thylacine here.