Researchers discover DNA from extinct species in soils

WASHINGTON -- Ancient plant and animal DNA found in undisturbed soil sediment can be used to unlock secrets about life hundreds of thousands of years ago, researchers say.

Scientists analyzing soil from Siberian permafrost and from caves in New Zealand said they found evidence of DNA from animals that died out thousands of years ago and from plants that lived about 400,000 years ago.

Eske Willerslev of the University of Copenhagen, a co-author of the study appearing in the journal Science, said the study found that soil fragments the size of a sugar cube can contain large amounts of DNA from those ancient life forms.

"You can obtain a lot of information about that extinct biota from just two grams of material," Willerslev said.

Permafrost is excellent at preserving the ancient DNA, the researchers said, because it is constantly cold. The scientists identified DNA from 19 categories of plants and from eight kinds of animals, including the extinct mammoth and steppe bison. The animal DNA was thought to be up to about 30,000 years old.

Willerslev said that attempts to look further back in history, beyond 400,000 years, was unsuccessful.

"We tried to look for DNA in sediments dated one and a half to two million years, but those tests came up negative," he said. "There may be some sort of barrier that makes that impossible."

Age of the specimens was based on dating of the sediment layers, the authors said.

In sediments drilled from the floor of a dry cave in New Zealand, Willerslev and his co-authors found DNA from an extinct animal and from plants that lived before humans colonized that island about 3,000 years ago.

Much of the animal DNA found at the sites apparently is from feces and urine deposited by the creatures in ancient times. DNA from herbivorous animals is more common because that diet produces more feces, researchers said.

Analyzing the plant DNA, said Willerslev, gives insight into the types of plants that dominated ancient times and could indirectly give clues to the climate that then existed.

For instance, the plant DNA from Siberia suggests that tundra was once an area rich in plants that would have been able to support large herds of mammoths and other big animals. But about 11,000 years ago, the once plentiful grasses began to disappear, perhaps helping to cause the extinction of some of the large plant eaters that once roamed parts of Siberia and Alaska.

Linking the soil DNA with specific times in the past may "have major implications for many fields," including the study of ancient peoples, the authors said in the study.

Co-author Alan Cooper of Oxford University, England, said in Science that the study shows that DNA can be preserved for long periods of time and could free researchers "from the shackles of needing fossils to be able to look into the past."

Other experts said that the technique needs to be proven in further study, but that it could lead to a better understanding of the plants that lived during the ice ages or during the era that humans first crossed from Asia into North America.

"This technique truly will revolutionize our ability to reconstruct past flora and fauna," Glen MacDonald, an ancient life researcher at UCLA, said in Science.

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Science: www.sciencemag.org