Credit: Wikimedia
Named after a Russian word meaning 'earth horn', mammoths are a group of prehistoric mammals that belong to the same family as modern elephants. Arguably the most famous of all the mammoth species, the woolly mammoth has turned up in fossilised form on nearly every continent on Earth.
While the majority of woolly mammoths became extinct about 7,600 years ago, a small population remained alive on the small Russian Wrengel Island until about 3,800 years ago. The reason behind the extinction of the woolly mammoths has been fiercely debated for years, and only in the last year have scientists settled on one theory over all the others.
Now, scientists in Japan and Russia are attempting to resurrect the woolly mammoth by implanting elephant egg cells containing mammoth cells into an elephant surrogate, in the hopes that a hybrid clone will be born.
Extinction theories
Meteor strike
In 2007, a team of scientists led by Arizona-based independent geophysicist Allen West suggested that a huge meteor 4 km in diameter exploded just above the Earth's surface over what is now Canada roughly 12,900 years ago. This supposedly sparked a massive shockwave and fire that caused abrupt climate changes and widespread fires in the Northern Hemisphere, killing off the Earth's woolly mammoth population, among many other species.
West based his theory on the discovery of tiny nanodiamonds, or carbon crystals, in the 12,900-year-old sediments, which he said was evidence of a devastating impact. But in 2010, an analysis by researchers at Washington University in Missouri and the Royal Hollway University of London, revealed that these carbon crystals were not diamonds, but clumps of graphene, a material that is commonly found in sediments. "Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the Younger-Dryas (a time of severe climate change around 12,900 years ago) impact hypothesis," the researchers reported in Proceedings of the National Academy of Sciences.
Human impact:
Perhaps even more controversial than the impact theory is the idea that early humans could have overhunted woolly mammoths to exinction. Originally the theory was that, as the mammoths had survived many temperature fluctuations before the one that coincided with their extinction, it was more likely that a different factor killed them off, namely overzealous hunting. In 2008, a study published in PLoS Biology and led by David Nogués-Bravo of the Museo Nacional Ciencias Naturales in Madrid, toned down the responsibility of humans, using mathematical modelling to suggest that after climate change hit the mammoth population hard, human hunting tipped the survivors over the edge.
Climate change
In 2011, a study published in Nature gave a new perspective on what wiped out many of the large mammal species of the Ice Age period, including woolly mammoths, reindeer, horses and woolly rhinos. Combining analyses of 846 radiocarbon-dated mitochondrial DNA sequences, 1,439 megafaunal bones, and 6,291 radiocarbon dated remains associated with Upper Palaeolithic human sites in Eurasia, researchers led by Eline Lorenzen, from the Centre for GeoGenetics at the University of Copenhagen in Denmark said that most of the animals were wholly affected by a shift in climate.
However, they did suggest that humans did have a hand in the extinction of the Eurasian steppe bison and the wild horse. "People, with flint arrows and spears, dependent on hunting, are always likely to have been limited by availability of their prey, and unlikely to have limited them, let alone exterminated them. So the idea of multiple causes, complex mixtures of climate and habitat change, always seemed more likely," commented Derek Yalden, a zoologist from the University of Manchester in Britain. "Any involvement of humans is probably coincidental, but without some measure of relative densities, I can't see how one would make a convincing argument."
WOOLLY MAMMOTH STATS
Scientific name: Mammuthus primigenius
Range: Africa, Asia, North America, Central America and Europe.
Height: 3 to 4 m
Weight: 8 tonnes
Life span: 60 to 80 years
Diet: Mammoths were herbivores, so their diet mostly consisted of grasses, shrubs and trees. They occasionally fed on fruits, wood and cacti.
Distinguishing features: Three to 5-m-long curved tusks, a shaggy coat of hair up to 1 m in length and relatively small ears.
Can we resurrect one?
In December last year, a team of scientists including Semyon Grigoriev from the Sakha Republic's mammoth museum in Russia and colleagues from Japan's Kinki University announced the launch of a joint research project that will this year try to bring the woolly mammoth back to life.
The key to cloning an extinct animal is to take some egg cells of a similar, living species, extract the nuclei and replace them with cells from the extinct mammal. The altered egg cells are then implanted into the womb of a surrogate and will ideally result in embryos with the DNA of the extinct species. As elephants are closely related to mammoths (their DNA differs by just 0.6%), the researchers hope to use the egg cells of an elephant to impregnate an elephant with a mammoth baby. The baby technically won't be a 'purebred' mammoth, but an elephant-mammoth hybrid.
Of course, finding a perfectly preserved mammoth nucleus with all of its genes intact is no small feat, but after 20 years of searching, the researchers have found bone marrow cells in a woolly mammoth thighbone that they think could do the trick. The cells were found in a specimen from Siberia, thanks to recent warmer temperatures in eastern Russia that have thawed the permafrost ground to reveal the icy mammoths within.
The cloning process is predicted to take five years and has a 1 to 5% chance of success, according to researchers from the Roslin Institute at the University of Edinburgh in Scotland, who cloned Dolly the sheep in 1996.
It's a long shot, and not everyone is convinced it will work. Genomicist Webb Miller from Penn State University in the U.S., who has worked on deciphering woolly mammoth DNA in the past told MSNBC that "it'll never happen", adding, "DNA from a woolly mammoth is a mess. It's fractured into very short pieces, and there's a lot of postmortem DNA damage other than just breakage. The code gets damaged a lot."
In 2003, researchers in Spain tried to resurrect the Pyrenean ibex, a species of Spanish goat that died out in 1999 when the last one was crushed by a fallen tree. Using skin samples from this specimen, the researchers successfully produced a clone named Celia in 2008, but she died just moments after her birth due to lung defects. So even if the Japanese and Russian team does manage to successfully produce this baby mammoth hybrid, there's no guarantee it will be robust or healthy enough to survive.
