How Did the Mammoths Go Extinct?
One of the potential culprits has been ruled out, but the debate rages over what killed off the last mammoths.
The last known population of woolly mammoths, roaming a remote Arctic island long after humans invented writing, were wiped out quickly, reports a study released Wednesday.
The culprit might have been disease, humans or a catastrophic weather event, but was almost certainly not climate change, suggests the study, published in the Proceedings of the Royal Society B.
Exactly why a majority of the huge tuskers that once strode in large herds across Eurasia and north America died out toward the end of the last ice age has generated fiery debate.
Some experts hold that mammoths were hunted to extinction beginning some 10,000 years ago by the species that was to become the planet's dominant predator -- humans.
Others argue that climate change was more to blame, leaving a species adapted for frigid climes ill-equipped to cope with a warming world.
It has long been known that a colony of woolly mammoths survived up until about four thousand years ago on what is today Russia's Wrangel Island, north of Siberia in the Arctic Ocean.
Radiocarbon dating shows that at least a few hardy individuals were still hanging on as late as 1700 B.C.
To better understand their demise, researchers led by Anders Angerbjorn of Stockholm University analyzed bits of mitochondrial DNA -- genetic material inherited through females -- extracted from bone and tusk.
"It could be that the island was simply too small to support a long-term viable mammoth population," the authors speculated.
About 7,600 square kilometers (2,900 square miles) in area, Wrangel Island is a bit smaller than Corsica or Puerto Rico.
Once connected to the mainland by an ice bridge, Wrangel was gradually cut off by water 12,000 to 9,000 years ago.
A loss of genetic variation could also have resulted from the shift in climate as Earth entered the so-called interglacial period, a boon for many animals, but not for the giant tuskers, the study said.
To their surprise, however, the researchers found that genetic diversity remained stable, and even increased slightly, right up to the bitter end.
"This suggests that the final extinction was caused by a relatively sudden, rather than gradual, change in the mammoths' environment," the study said.
Humans appear to have arrived on the island about 100 years after the huge mammals had vanished, according to archeological data.
This would exculpate Homo sapiens from killing off the last mammoths, though it is possible humans arrived earlier but left no trace.
That leaves climate or disease, the researchers hypothesize, noting that a sudden event -- a mega-storm, for example -- or a novel bacteria or virus could have wiped out the remaining population.
The fate of mammoths on Wrangel Island, they caution, is not necessarily a microcosm for the species as a whole because islands exert unique evolutionary pressures on animal species.
One theory is that expanding forests in Europe and parts of Asia robbed the grass-eating mammoths of their preferred habitat, gradually starving them to death.
The fate of mammoths on Wrangel Island is not necessarily a microcosm for the species as a whole.
New technologies could make it possible to bring extinct species back to life, concludes a paper published on April 4 in the journal Science. These advances include back-breeding (assembling or reassembling an extinct species' genes), cloning and genetic engineering.
A leading candidate for de-extinction is the woolly mammoth. Russian scientist Semyon Grigoriev, of the Sakha Republic's mammoth museum, plans to replace the nuclei of an elephant egg with nuclei extracted from woolly mammoth bone marrow. The elephant would theoretically become a surrogate mother to a baby mammoth.
Tasmanian tigers died out in 1936, in part because they had little genetic diversity which translates to "bad news for a species," said Katherine Belov, professor of comparative genomics at the University of Sydney. "Species are less able to adapt to change." Even if Tasmanian tigers -- or other animals -- are resurrected, it will take some time to build up diversity again.
Experts believe billions of these birds populated the Americas when Europeans arrived. Loss of habitat and commercial exploitation of the birds for their meat are thought to have killed them all off.
Efforts are now underway to revive the species by extracting DNA fragments from preserved specimens, and later, using band-tailed pigeons as surrogate parents.
The Pyrenean ibex, a horned mammal once common in Europe, was one of the first subspecies targeted for de-extinction. Scientists began the attempts in late 1990s, when the last female Pyrenean ibex was still alive. Even if researchers could successfully clone that individual, there would be no males for her to breed with. Instead, genetic engineering might be required.
Since saber-toothed cat bodies are sometimes found frozen, it might be possible to extract preserved DNA and clone the animal. About 5 years ago, scientists did just that with a mouse that was dead and frozen for 16 years. Woolly mammoth remains are also sometimes found in a well-preserved, frozen state.
The dodo, a flightless bird, proved to be a tasty meal for humans and other predators. In 2007, scientists found a remarkably well-preserved dodo in a cave. Dodo DNA could be used to resurrect this avian species.
Ground sloths, relatively slow, lumbering animals, were easy targets for prehistoric big-game hunters. Scientists have found remains that still bear soft tissue. As with woolly mammoths, there's a chance extracted DNA could be used to back-breed or clone the large sloths.
The Irish elk has been extinct for 11,000 years. Like the woolly mammoth, it inhabited colder regions. As a result, bodies are sometimes found frozen and in relatively good condition, making them candidates for DNA extraction.
Earlier this year, Harvard geneticist George Church -- with tongue in cheek -- said that he was seeing an "adventurous female human" to be a surrogate mother to a cloned Neanderthal. While Church was really just theorizing about what it would take to bring a Neanderthal back to life, the possibility could be a reality, should any scientist undertake such a controversial project.
Paleontologist Jack Horner is leading a project to create a dinosaur out of a chicken -- a "dinochicken." He told Discovery News that birds "are dinosaurs, so technically we're making a dinosaur out of a dinosaur." He and his colleagues have been genetically engineering chickens to reactivate ancestral traits, such as long tails, which are more associated with non-avian dinosaurs.