True or false? Extinction is forever: researchers' efforts to clone the vanished Tasmanian tiger highlight the quandary of reviving long-gone creatures. (Phenomena & Curiosities).

"Danger," says the sign on the door of a laboratory at the Australian Museum in Sydney: "Tasmanian Tiger, Trespassers will be eaten!" The joke is that the Tasmanian tiger--a beloved symbol of the island state that appears on its license plate--has been extinct for nearly seven decades. But researchers behind that door are working to bring the animal back to life by cloning it, using DNA extracted from specimens preserved decades ago. Among other things, the work raises questions about the nature of extinction itself.

The Tasmanian tiger's Latin designation, Thylacinus cynocephalus, or "dog-headed pouched-dog," makes it redundantly clear that the marsupial's feline nickname is a misnomer. It comes from the dark striping on its back that runs nearly shoulder to tail. The animal had large, powerful jaws, which secured the predator a place atop the local food chain. Females carried their young in backward-facing pouches.

Thylacines, once spread throughout mainland Australia and as far north as New Guinea, were probably outcompeted for food by the dingoes that humans introduced to the area some 4,000 years ago, says Australian Museum director Mike Archer, founder of the cloning project. Eventually, thylacines remained only on the dingo-free island of Tasmania, south of the mainland. But with the arrival of European settlers in the 1800s, the marsupial's days were numbered. Blamed (often wrongly) for killing livestock, the animals were hunted indiscriminately. The government made thylacines a protected species in 1936, but it was too late; the last specimen reportedly died in captivity the same year.

The Australian researchers set out to bring the animal back partly to atone for humanity's role in its extinction, Archer says. The idea took root 15 years ago when he saw a pickled thylacine pup in the museum's collection. "It jarred me and started me thinking," recalls the 58-year-old paleontologist and zoologist, who received his undergraduate degree from Princeton University and his doctorate from the University of Western Australia. "DNA is the recipe for making a creature. So if there is DNA preserved in the specimen, why shouldn't we begin to use technology to read that information, and then in some way use that information to reconstruct the animal? I raised the issue with a geneticist. The response was derisive laughter."

Then, in 1996, Dolly the sheep burst onto the scene and, suddenly, Archer says, "cloning wasn't just a madman's dream." Dolly proved that DNA from an ordinary animal cell--in her case, a ewe's udder--could generate a virtually identical copy, or clone, of the animal after the DNA was inserted into a treated egg, which was implanted in a womb and carried to term. Archer's goal is even more ambitious: cloning an animal with DNA from long-dead cells, reminiscent of the sci-fi novel and movie Jurassic Park. The challenge? The DNA that makes up the chromosomes in which genes are bundled falls apart after a cell dies.

Researchers working with Don Colgan, head of the museum's evolutionary biology department, extracted DNA from a thylacine pup preserved in alcohol in 1866, and biologist Karen Firestone obtained additional thylacine DNA from a tooth and a bone. Then, using a technique called polymerase chain reaction, the researchers found that the thylacine DNA fragments could be copied. The scientists next have to collect millions of DNA bits and pieces and create a "library" of the possibly tens of thousands of thylacine genes--a gargantuan task, they concede. Still, an even greater obstacle looms, that of stitching all those DNA fragments together properly into ...