Dropping hints: The fossilised human faeces were found in a cave in the Oregan desert, in a pit that may have served as a toilet.

Credit: Dennis LeRoy Jenkins

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LOS ANGELES: Analysis of ancient human faeces suggests that people inhabited North America more than 14,300 years ago - roughly 1,000 years earlier than was previously thought.

Researchers from the University of Oregon in the U.S. and the University of Copenhagen in Denmark made the discovery after examining DNA found in fossilised human excrement.

The fossils were recovered from an ancient cave system, known as the Paisley Caves, about 350 kilometres southeast of Eugene in the Oregon desert.

The oldest of the droppings - or coprolites - was carbon-dated and found to be approximately 14,340 years old, said Eske Willerslev, director of the Centre for Ancient Genetics at Denmark's University of Copenhagen, who helped analyse the DNA.

The faeces samples contained two main genetic types of Asian origin that are unique to present-day Native Americans, offering proof that immigration took place more than 1,000 years earlier than was previously believed. The researchers reported their findings today in the U.S. journal Science.

Into the Americas

The findings challenge conventional wisdom based on analysis of stone tools from the so-called Clovis culture of southwestern USA. These tools have been dated to about 13,000 BC, and until now, have led scientists to theorise that the first North Americans migrated across a land bridge that once connected Siberia to the region.

These early migrants were believed to have passed through a corridor that opened up in a glacier that covered the continent. However, Willerslev said the tests on the coprolites found in Oregon suggested "there were people south of the ice cap several hundred years before the ice-free corridor developed."

"The first humans either had to walk or sail along the American west coast to get around the ice cap," he said. "That is, unless they arrived so long before the last ice age that the land passage wasn't yet blocked by ice."

The fossilised excrement samples were mixed with sinew and plant fibre threads, hide, basketry, cords, rope and wooden pegs. The Paisley caves also hold many ice-age animal bones, but the faeces are the only human remains that have so far been uncovered at the site.

According to the researchers, the dry conditions in the cave preserved the coprolites, which were found a few metres below the surface in a pit that may have served as a toilet.