The idea of cloning a mammoth is just a fantasy,” says biologist Ross MacPhee, an expert on the giant fauna of the last ice age and chairman of the American Museum of Natural History’s mammalogy department. Alex Greenwood, a molecular biologist who studies ice age extinctions (and a colleague of MacPhee’s in New York), agrees: “I am really stunned,” he says, “that there are scientists still pushing this idea.” MacPhee, who has worked extensively with the Jarkov mammoth in Siberia, and Greenwood say that making an exact copy of a species that died off 10,000 years ago is possible only in science fiction movies.
The main reason is simple: To have any chance at a successful cloning, scientists must start with pristine, complete DNA. But even in cold environments, cells quickly break down after an organism dies; entropy occurs, and bacteria and certain enzymes latch onto or destroy cellular material. All the DNA found from long-extinct animals (even those remains found in the Siberian permafrost) has been incomplete and fragmented.
“If freezing is done under special conditions, such as in a modern laboratory, cells with their genetic material can be preserved indefinitely,” explains Russian scientist Alexei Tikhonov. “But conditions out in the permafrost are far from perfect.” Tikhonov has worked with the best-preserved mammoth ever found, a baby mammoth carcass pulled from a construction site in 1977. Nicknamed “Dima,” the small calf still had its skin and looked like it could have died just days earlier. But it probably fell into a mud pit and died quickly 44,000 years ago. Dima now rests in Tikhonov’s institute in St. Petersburg. Studies have shown that proteins in Dima’s cells were seriously modified after death, and that other substances common in living tissues (such as phosphorous) disappeared entirely.
Cloning is only possible when the nucleus taken from a living cell (such as with Dolly the sheep) is placed into an egg from which the original nucleus has been removed. This substitute nucleus, with its DNA, proteins and other crucial material completely intact, was what controlled the development of Dolly. Injecting fragments of DNA into a cell without a nuclear transfer would not result in a clone. Greenwood explains it this way: “If I throw all the parts needed to make a car down the stairs of a building, I will not have a Porsche 911 in the stairwell when they land.”
Ryuzo Yanagimachi, a scientist in Hawaii who has successfully cloned mice and other small mammals, says he would like to clone a mammoth. But he agrees that this could happen only if intact DNA is ever recovered from a long-dead mammoth. In recent years, a Japanese team has mounted several expeditions into Russia’s far north with the expressed aim of trying to bring a mammoth back to life. The team’s main intent is to recover frozen sperm from a mammoth and then use it to impregnate a female elephant, the mammoth’s closest living relative. But Greenwood and MacPhee say this is equally problematic, even on the off-chance that intact sperm DNA from a mammoth could ever be found. “Mammoths and elephants have been separated by about 4 (million) to 6 million years of evolution,” says Greenwood. “This would be like crossbreeding a human and a chimp and expecting to have a successful generation of a hybrid.”
Is it possible that in the march of time and scientific advance, technologies may be developed that will allow extinct creatures to be cloned? Or, someday, may a perfectly intact chain of mammoth DNA be found? According to MacPhee, such questions remain too tough to answer. “There isn’t even a direction we can point to,” he says, “which would indicate whether cloning extinct animals will ever be possible.”
© 2005 Discovery Communications Inc.
Baby Mammoth discovered in Siberia in 2007
Cloning a Better Tomorrow