Discovered in Washington state in 1996, the skeleton quickly became the subject of a legal battle between a group of scientists who wanted to study it, and the US government, which was prepared to hand the remains over to Native American groups for reburial under a repatriation act.
The case was finally settled in 2004: the courts ruled that the Native Americans could not prove that Kennewick Man was their ancestor, and so repatriation laws did not apply. The scientific study of the remains resumed.
Last year the fruits of those studies were published in a book that seemed to vindicate the 2004 ruling. Among many findings, the studies concluded that the shape of Kennewick Man's skull showed similarities with indigenous communities found today in Polynesia and Japan, from where the ancestors of Kennewick Man were thought to have migrated independently of the forebears of Native Americans.
In other words, Kennewick Man was unlikely to be genetically close to living Native American populations. But new genetic evidence calls that conclusion into question.
Eske Willerslev at the University of Copenhagen, Denmark, and his colleagues have managed to extract and sequence DNA from one of Kennewick Man's hand bones. And despite many Native American groups in the US harbouring suspicions about archaeological research, Willerslev's team was able to work with the Confederated Tribes of the Colville Reservation in Washington state, who provided DNA samples.
The team found that of all the modern genomes available – including sequences from Europeans, Polynesians, East Asians and South Americans – the Colville DNA is the most similar to the Kennewick DNA. The two are so similar that Kennewick Man must be closely related to the modern Colville population, say the researchers. This suggests it's simply a coincidence that the Kennewick skull shape resembles those from indigenous Polynesian and Japanese groups.
In fact, the DNA sequences were so similar that the forebears of Kennewick Man and the Colville tribes may have diverged from a shared ancestor about 9200 years ago, just 700 years before Kennewick Man was born.
There is an alternative explanation for the similarities: that Kennewick is actually a direct ancestor of the modern Colville population, and that any genetic differences are down to gene flow into the Colville population from other human groups over the last few thousand years.
"We could not distinguish between those two hypotheses," Rasmus Nielsen of the University of California in Berkeley told a press conference yesterday. "But since it seems likely that the Colville in fact have received some gene flow from other populations, we think the evidence is in favour of the second hypothesis perhaps more than the first hypothesis."
If that's confirmed, then the Native American cause has ultimately been helped by science despite their opposition to earlier investigations. Science might have belatedly produced the proof that could lead to a successful bid to have Kennewick Man repatriated for reburial. "There's some kind of irony there," said Willerslev at the press conference.
Ideally, genome regions are each read several times independently so that any chance errors in a single read can be identified and corrected. Because the Kennewick DNA was damaged, the results are based on a rather patchy and low-resolution genome sequence, with the genome read only once: as geneticists say, the "coverage" is low. But Willerslev says we can be confident that the ancestry result is sound even at low coverage.
Iosif Lazaridis at the Harvard Medical School, who was not involved in the work, agrees the coverage is sufficient. "It is very exciting to get even such coverage from a skeleton of this age," Lazaridis says. But while Willerslev and his colleagues are talking about Kennewick Man's past with some certainty, they are less clear about his future.
"We are just putting out the results of our analyses," said Willerslev. It's for others to argue about the ultimate fate of Kennewick Man's remains, he added.
Barras, Colin. 2015. “DNA study backs Native American claim to Kennewick Man remains”. New Scientist. Posted: June 18, 2015. Available online: http://www.newscientist.com/article/dn27750-dna-study-backs-native-american-claim-to-kennewick-man-remains.html