Science and Technology
With a Tiger in the Tank
It was a frigid winter night in 1936. A lone Tasmanian tiger huddled in his—or her—open enclosure at Hobart Zoo. With nowhere to shelter from the cold and no keepers to care, the delicately striped animal died. When this solitary animal—whose sex was not even recorded because of lack of interest—died, so did an entire species. What’s more, with the passing into extinction of the Tasmanian tiger, Thylacinus cynocephalus, it was the end of the line for an entire family of marsupials that had lived in Australia for millions of years.
The dog-sized thylacine was once widespread on the Australian mainland, Papua New Guinea, and Tasmania. Evidence is abundant: fossils, skeletal remains, Aboriginal rock paintings, and a mummified thylacine found inside a cave on the Nullarbor Plain in 1965. Thylacines roamed continentwide until about 4,000 years ago when dingoes arrived. Two thousand years later, thylacines survived only on the dingo-free refuge of Tasmania.
But 1830 was the beginning of the end. European settlers incorrectly blamed thylacines for killing their sheep, not dogs which were the likely culprit. To rid the island of the alleged sheep-eaters, the Tasmanian government put a bounty on thylacines. Between 1888 and 1909, officials paid more than 2,000 bounties. By 1936 it was all over. The last captive thylacine died, and not a single confirmed sighting of one in the wild has been made since then. Extinction was complete.
But is extinction forever? Perhaps not, say researchers at Sydney’s Australian Museum. In an audacious project to clone a thylacine, they are attempting to reverse the fate of an animal that fell foul of the ultimate predator, Homo sapiens.
With the cloning project up, running, and making significant progress, another question arises: Will the project, like the thylacine itself, head down the slippery slope to scientific extinction? Certainly, the odds are against the team: project leader Don Colgan, conservation geneticist Karen Firestone, and head of the Australian Museum Michael Archer. No ancient animal has ever been resurrected, and the scientific hurdles are immense. At nearly every step, the team must overcome complex technical hurdles, most of which have never before been faced.
Nonetheless, the long journey has begun. The team has extracted DNA, copied selected pieces manyfold, and confirmed that what they have really is thylacine DNA and not a contaminant, as many feared. These accomplishments are crucial, but they are, in fact, the easiest part of a process that could take decades.
Nor is this early work unique. Michael Westerman of Melbourne’s La Trobe University and Carey Krajewski of Southern Illinois University in Carbondale, Ill., also have extracted small DNA fragments. But for Westerman and Krajewski that was enough. They had what they needed to determine that the thylacine was the sole survivor of a group of carnivorous marsupials that appeared after the land mass Gondwana broke up, between 65 million and 100 million years ago. But it takes more to clone an animal than scraps of DNA. It takes the entire genetic blueprint, the “genome.” And obtaining that, as Westerman observes, is tough. “They’ve got one hell of a job to do, and I don’t know how they’ll attack it,” he says.
Firestone does know. Right now, she’s dipping into uncharted scientific waters to devise a method of inserting damaged thylacine DNA into bacteria. The tiny organisms will serve as a DNA library in which the team can store its precious fragments for future reference, duplication, and genome reassembly. Firestone is about to test a procedure for linking the DNA to the bacterium using designer oligomers, synthetic bits of DNA.
If that sounds complex, it is. And it’s just the beginning. The task of re-creating a thylacine is so daunting that many researchers suspect it can’t be done. For instance, Steve Cooper, an evolutionary biologist at the South Australian Museum in Adelaide, has said the project is “the stuff of science fiction.”
It’s no surprise, though, that the man who initiated the big gamble, Michael Archer, is not deterred. “Already we’ve overcome obstacles that critics tossed up in front of us, saying these couldn’t be overcome,” he says. He’s not alone in his optimism. John Shine, executive director of Sydney’s Garvan Institute of Medical Research, agrees—so much so that he has offered the institute’s expertise in molecular genetics and DNA techniques to assist Colgan and Firestone.
Still, criticism remains. Respected researchers, such as Monash Univer-sity’s reproductive biologist Alan Trounson, charge that the cloning project is a waste of money, given the slim chance of success and today’s scarcity of research dollars.
Archer bridles at the suggestion. He responds that “good science” will be done, even if there is no bouncing baby thylacine at the end. Besides, he says, the project runs on “a wing and a prayer,” with donations from government and private sources adding up to just under US$170,000 since 1999.
True. But that hasn’t prevented some religious fundamentalists picketing the Australian Museum. They fear the scientists are playing God. “My response is that people played God when we exterminated the animal in the first place,” counters Archer. Still, is it unethical or immoral to bring an extinct species back from the dead? For now, the question is hypothetical, although Archer, for one, says no: “It would be immoral not to try.”