In a world first, German scientists say they have reconstructed a key sequence in the genome of the woolly mammoth, enabling them to show that the extinct beast's closest modern relative is the Asian elephant.
Using miniscule bone fragments, scientists can trace the mammoth
Reporting online Sunday in Nature, the British science journal, the researchers say they devised a new technique for the feat, teasing out DNA from just 200 milligrams (0.007 of an ounce) of bone found at a mammoths' graveyard in the Siberian permafrost.
Their technique, called multiplex polymerase chain reaction, copied 46 chunks of sequence, which were rearranged to give a picture of the creature's mitochondrial DNA.
The mitochondria are an internal part of a cell that is the cell's power supply. Mitochondrial DNA is handed down through the maternal line, and is a relatively stable genetic sequence -- it changes little from generation to generation, and at a measurable rhythm. This makes mitochondrial DNA a useful "molecular clock" that can be wound backwards into time, to see how a species evolved. By comparing the sequence with that of modern animals, scientists can spot when and where species diverged from their common ancestor.
In this case, the closest relative today to Mammuthus primigenius is the Asian elephant rather than the African elephant, the researchers say. The difference, though, is not great.
The scientists say the African elephant is a descendent of the woolly mammoth
African elephants branched away from the mammoth's evolutionary tree around six million years ago. Asian elephants followed suit around only 440,000 years later. That timeline of divergence is intriguingly close to that of gorillas, chimps and humans in how they branched out from the primates' family tree.
The mammoth team was led by Michael Hofreiter of the Max Planck Institute for Evolutionary Anthropology in Leipzig.
Previous efforts to recover pre-Ice Age species have run into the predictable problem of retrieving material that has not rotted after 10,000 years or more in the permafrost.
Until now, little more than 1,000 base pairs -- the "letters" on the DNA code which make up the chemical recipe for making and sustaining life -- have been coaxed out of these frozen samples. The previous maximum was 1,600 base pairs.
But by using their new approach to gently amplify the ancient DNA, Hofreiter's team were able to get 5,000 base pairs, even though their sample, too, was degraded.
Drawing of a mammoth and a horse in a cave near Combe d'Arc, France
Woolly mammoths once roamed far and wide across the northern reaches of Eurasia and North America, but no trace of them survives beyond the end of the last Ice Age, some 11,000 years ago. Their heavy layers of fat, their long brown top hair and thick woolly undercoat were superb for bitter cold but left them ill-equipped for a warmer climate and the rise of Homo sapiens.
They are among the best-researched animals of the Ice Age, thanks to the preservation of carcasses in frozen ground and the pictures of the creatures made by Stone Age artists in European caves.
The bone used in the latest research came from the banks of the Berelekh River in Yakutia, where thousands of bones, belonging to some 160 mammoths, have been recovered.