Rat Remains Suggest Humans Came Late to New Zealand

Dave Hansford in Wellington, New Zealand
for National Geographic News

June 3, 2008

Ancient, rat-gnawed seeds have confirmed that humans arrived in New Zealand in A.D. 1280, about a thousand years later than previously thought, a new radiocarbon-dating analysis has found.

The Pacific rat, or kiore, could not have swum the vast distances from the nearest islands, so the rodent must have come to New Zealand either as a stowaway on canoes or as a deliberate introduction, scientists say. (See a New Zealand map.)

"Therefore the earliest evidence of the Pacific rat in New Zealand must indicate the arrival of people," said study lead author Janet Wilmshurst, a paleoecologist at the environmental research group Landcare Research in Lincoln, New Zealand.

The finding settles a long debate about when Polynesian voyagers first arrived on the Pacific island.

Controversy began in 1996 when an analysis of rat bones said that Polynesian explorers from western Pacific archipelagos had arrived as early as 200 B.C.

(Related: "Rat DNA Offers Clues to Pacific Colonization, Study Says" [June 9, 2004].)

That suggested New Zealand's indigenous Maori people were neither the discoverers nor the first colonizers of the country.

However, Wilmshurst said that theory did not fit with any archaeological evidence, nor did it correspond with historical records of deforestation and species loss that frequently follow human arrival.

Greater Accuracy

By reexamining some of the bones used in the 1996 study, Wilmshurst and colleagues pegged the humans' arrival date at A.D. 1280. The researchers then used the same technique to reinforce their findings by dating the rat-gnawed seeds.

Newer and improved techniques allowed for greater dating accuracy, she said, adding that the 1996 results may have been distorted by contamination of the samples.

"The oldest evidence we [now] have for the Pacific rat in New Zealand is in very close agreement with the oldest dated … archaeological sites," she said.

"It's also in agreement with the first wave of [animal] extinctions in New Zealand, and with the first evidence of widespread lowland deforestation."

The new date also conforms with Maori genealogy, she added.

(Read: "Rat Invasions Causing Seabird Decline Worldwide" [February 21, 2008].)

The study appeared today in the journal Proceedings of the National Academy of Sciences.

Rapid Dispersal

Seeds preserved in peat bogs and swamps all over New Zealand bore distinctive bite marks.

(See photos of New Zealand's land and people.)

Similar studies on other islands, Wilmshurst said, would "start to piece together the last major migration of people from West Polynesia to East Polynesia with a greater degree of confidence and accuracy."

David Lowe of Waikato University in Hamilton, New Zealand, was not involved in the new study.

He said it confirmed previous findings based on pollen samples, tree-ring growth, and soil layers.

"There are lots of lines of evidence, direct and indirect," Lowe said.

Polynesian explorers may well have used the Kermadec Islands, which is 466 miles (750 kilometers) northeast of New Zealand, as a stepping-stone, he said.

The explorers, he added, "could have rapidly checked out what else was beyond New Zealand: Norfolk Island, the Auckland Islands, and later, the Chatham Islands."