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Pennsylvania State University geneticists said their finding is particularly interesting because it rules out human hunting as a contributing factor for the mammoth's disappearance, leaving climate change and disease as the most probable causes of extinction.

"The population was split into two groups, then one of the groups died out 45,000 years ago, long before the first humans began to appear in the region", said Associate Professor Stephan Schuster, who led the research with Professor Webb Miller.

He said the study marks the first time scientists have dissected the structure of an entire population of extinct mammals by using the complete mitochondrial genome -- all the DNA that makes up all the genes found in the mitochondria structures within cells.

The study included experts in genome evolution, ancient DNA, mammoth paleontology and curators from natural history museums in Denmark, Australia, Belgium, France, Italy, Russia, Spain, Sweden, the United Kingdom and the United States.

The findings are reported in the early online edition of the Proceedings of the National Academy of Sciences.

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