What, or who, killed the last mammoths?

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 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. Radiocarbon dating shows that at least a few hardy individuals were still hanging on as late as 1700 BC.

To better understand their demise, researchers led by Anders Angerbjorn of Stockholm University analysed bits of mitochondrial DNA -- genetic material inherited through females -- extracted from bone and tusk. They reasoned that signs of dwindling genetic diversity would mean that too much inbreeding among a small population could have partially caused the animals to die out.

The study said a loss of genetic variation could also have resulted from the shift in climate as Earth entered the interglacial period, a boon for many animals, but mammoths. 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 archaeological 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 -- a mega-storm, for example -- or a novel bacteria or virus could have wiped out the remaining population. 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.