FRIDAY, Sept. 5 (HealthDay News) -- The last woolly mammoths had exclusively North American genetic roots, according to Canadian researchers who say their finding challenges conventional wisdom and could generate controversy.

Woolly mammoths lived between 40,000 and 4,000 years ago.

"Scientists have always thought that because mammoths roamed such a huge territory -- from Western Europe to Central North America -- that North American wooly mammoths were a sideshow of no particular significance to the evolution of the species," Hendrik Poinar, an associate professor in the departments of anthropology, and pathology and molecular medicine at McMaster University in Hamilton, Ontario, said in a university news release.

Poinar and colleague Regis Debruyne collected and analyzed DNA samples from mammoth remains found in Siberia and in North America.

About 5 million to 6 million years ago, an early mammoth species migrated north into China, Siberia and, eventually, North America, which gave rise to a new mammoth known as the Columbian mammoth, Poinar explained. Much later, a cold-adapted form called the woolly mammoth evolved in Siberia and eventually crossed over into North America. The Siberian genetic forms then began to disappear and were replaced by North American migrants.

"Migrations over Beringia [the land bridge that once spanned the Bering Strait] were rare; it served as a filter to keep eastern and western groups or populations of woollies apart," Poinar said. "However, it now appears that mammoths established themselves in North America much earlier than presumed, then migrated back to Siberia, and eventually replaced all pre-existing haplotypes of mammoths."

"Like paleontologists, molecular biologists have long been operating under a geographic bias," Debruyne said in the McMaster University news release. "For more than a century, any discussion on the woolly mammoth has primarily focused on the well-studied Eurasian mammoths. Little attention was dedicated to the North American samples, and it was generally assumed their contribution to the evolutionary history of the species was negligible. This study certainly proves otherwise."

The study was published in the September issue of Current Biology.

More information

The Academy of Natural Sciences has more about the woolly mammoth.