Monday, June 2, 2008

Rats redate Aotearoa (New Zealand) occupation

Rats are helping scientists rethink the first appearance of humans in New Zealand, and that work is causing them to rethink Polynesian migrations.

The new work looks at evidence of Polynesian rats—radiocarbon dating both rat bones and gnawed seeds. It suggests that the first population—at least by rats—of both North Island and South Island New Zealand occurred from 1280 to 1300 AD.

(Photo: A rat-gnawed seed--in this case a macadamia nut eaten by a black rat.)

New Zealand has long been considered the most recently inhabited major island group of Polynesia, but most dates have placed that initial habitation several hundred years earlier.

One problem with those earliest estimates for human habitation has been that there was little archaeological evidence for them. The assumption of archaeologists was that this was because it took a few hundred years for human populations to build up to the point at which they would be “visible” to archaeological investigation.

It has long been known that Polynesian voyaging canoes carried rats. Theories differ as to whether they were carried accidentally, for food or for some other purpose, but it is clear that everywhere Polynesians arrived, rats arrived as well. Furthermore, rats reproduce must faster than humans, and quickly make impacts on the environment.

The new work was published today (June 2, 2008) in the Proceedings of the National Academy of Sciences, researchers Janet Wilmshurst of Landcare Research in New Zealand, Atholl Anderson of Australian National University, Thomas Higham of Oxford University in the United Kingdom and Trevor Worthy of the University of Adelaide in Australia.

They note that many early dates—of rat bones and other evidence of human activity—have been based on flawed radiocarbon dates. In the latest work, the researchers redated previous rat bone samples, and also compared their results with other evidence—notably seed cases that contain the clear imprints of rat teeth in gnawing patterns.

And the new rat information coincides well with other evidence of human presence.

“There is now excellent agreement between the ages of the earliest archaeological sites and the earliest-dated evidence for widespread deforestation, massive megafaunal extinctions,the decline of marine mammal populations and rat predation of seeds and invertebrates,” the paper says.

Rat evidence in the past couple of years has also been used to redate other islands' habitation—notably Rapa Nui or Easter Island. University of Hawai'i archaeologist Terry Hunt found that gnawed seeds and other data suggest the initial occupation of Rapa Nui was about 1200 AD—also several hundred years later than was earlier believed.

“Everything is turning out later than we thought,” Hunt said.

He said both Rapa Nui and Aotearoa (New Zealand) were at the margins of Polynesia and appear to have been occupied near the end of the period of active Polynesian migration. Hunt said there appears to have been a very active period of open-ocean voyaging and discovery starting around about a millenium ago.

“Around 1000 AD people are moving rapidly through eastern Polynesia and out to the margins,” he said. The islands of Rapa and Mangareva appear to have been populated about 1100, and may have been springboard to the occupation of Rapa Nui.

New Zealand's later population appears also to have come from somewhere in eastern Polynesia, but it is difficult to say exactly whence its settlers came. Perhaps Tahiti or the southern Cook Islands, Hunt said.

By contrast with these areas, Hawai'i, although it is extremely isolated, appears to have been populated quite early in the eastern Polynesian migrations.

“Hawai'i is actively settled quite early—as if it was in the locale of Tahiti” rather than more than 2,000 miles away, Hunt said. Modern occupation dates for Hawai'i fall in the neighborhood of 800 or 900 AD.

© 2008 Jan W. TenBruggencate