Published online 3 April 2008 | Nature | doi:10.1038/news.2008.734

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Fossil faeces pinpoint earliest North Americans

Evidence confirms humans were in the Americas more than 14,000 years ago.

Signs that someone was there: fossilised faeces have been confirmed as human from their DNA.D. L. JENKINS

Some 14,300-year-old fossilized human faeces have been found in Oregon, offering the oldest firm evidence yet of humans in North America, and the oldest human DNA in all the Americas.

The material establishes a new benchmark for when founding groups could have roamed into North America, and helps to confirm previous studies showing people living in South America around this time.

There are various theories about how the first people arrived in the Americas, the main two being crossing from Siberia to Alaska or from Europe. Once in the Americas, the trek south was complicated by ice sheets. Most archaeological evidence in the Americas dates no further back than 10,000 years ago, although there is evidence that the Clovis people populated much of North America from 13,200 to 12,900 years ago. The oldest human site found in the continents thus far is far south at Monte Verde in Chile, dating to 14,500 years ago. Some think this means that there should be evidence of humans further north even longer ago.

In a new report published online this week in Science1, a team led by researchers from the University of Oregon in Eugene report on six specimens of ancient faeces — called coprolites — unearthed from cave sediments. Carbon dating and genetic analysis confirm their date and identity.

“The evidence looks very good,” says Tom Dillehay, an archaeologist at Vanderbilt University in Nashville, Tennessee, who identified Monte Verde 30 years ago. “The genetic analysis is exhaustive.”

On the cave floor

The excavations that produced the coprolites began in 2002, when Oregon archaeologist Dennis Jenkins set out to investigate the story behind some artefacts previously found at the site. Jenkins’s team dug in some shelters known as the Paisley Caves, which were carved out by lake water long ago. Today the region, on the east side of the Cascade Range mountains, is a high desert, with dry conditions that help to preserve buried specimens.

Jenkins says that they recovered about 700 coprolites from the caves: many were fossilized animal faeces, but they suspected some were of human origin.

To confirm this, Jenkins sent 60 samples to researchers at the University of Copenhagen in Denmark for further analysis. They narrowed this group down to 14 possibilities based on shape and other physical characteristics, and used genetic analysis to confirm that at least 6 were of human origin.

The DNA they found is mitochondrial DNA, which is inherited maternally and tends to be better preserved in archaeological samples. The DNA shows that the depositors were from at least two groups. Their genetic types — called A2 and B2 — are two of the four main genetic lineages found today in Native American peoples, with genetic links to Siberia and Asia.

Danger of contamination

Such studies of ancient DNA collection and analysis are known to be prone to contamination by field researchers or laboratory personnel. This was especially possible in this case, because precautions weren’t taken in initial digs to prevent contamination.

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To ensure that the DNA found was truly ancient, and not contamination, genetics study-leader Eske Willerslev, at the University of Copenhagen, had all 55 personnel known to have been near the samples provide specimens for DNA comparison, as did all 13 associated researchers. “All were ruled out” as a source of the DNA, including at least one Native American student who worked in a cave, says Jenkins. He additionally had his Copenhagen lab’s results confirmed by two separate facilities in Sweden and Germany.

The team also found some artefacts from various later periods in the caves, but no human bones relating to the coprolites have been discovered.

Jenkins says that he hopes to secure funding to further analyse the coprolites for a full genetic picture, and to fully excavate cave sediments in hopes of finding bones and artefacts from people of that time. 

  • References

    1. Gilbert M. T. P. et al. Science advanced online publication, doi:10.1126/science.1154116 (2008).
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