By the time European explorers reached the islands scattered across the vast expanses of the Pacific Ocean, most of the Polynesians’ travels were between local island groups. But the locals seemed to know of places far beyond their shores, suggesting that their ancestors not only colonized distant islands, but returned to share knowledge about them. It eventually became clear that trade had spread goods to Polynesian communities that later became isolated.
In recent years, modern techniques have revealed the dizzying geographic scope of this trade, including a visit to South America for some takeaway sweet potatoes, later grown on Pacific islands. But the temporal extent of the trade remained the subject of debate, with some arguing for a short burst of exchange and others suggesting that extensive trade networks continued for some time to come. Now, a paper published in PNAS the use of another modern form of analysis argues for at least four centuries of trade.
The work is based on a site in the Cook Islands, which yielded a rare archaeological resource: an extensive array of deposits containing enough material for researchers to date several layers. Also included were some traditional Polynesian stone adzes, tools made from a specific type of volcanic rock. The researchers behind the new paper obtained small samples of these tools and used them in another type of modern analysis called mass spectrometry.
Mass spectrometry involves breaking a sample into its constituent chemicals, ionizing them, and then separating them based on their mass. For rock samples, this process allows researchers to identify all the elements present and even the isotopes of these elements. It is possible to use the presence of trace elements and isotope ratios to match samples to the quarry in which they originated, as they will all share the same idiosyncrasies.
Not surprisingly, most of the tools came from quarries in the Cook Islands, many from the island where the tools were uncovered (called Mangaia). But more than a third had been brought there from other island groups. The closest of these were the Austral Islands, where the quarry is only 400 miles away. But there were also tools from Samoa (1,700 km) and the Marquesas, where the quarry was more than 2,400 km from where the tools were discovered.
Trade began before AD 1300, when the earliest tools were discovered. And while the most remote location in the Marquesas will disappear within 200 years, trade with Samoa seems to have continued almost to the point of discovery by Europeans. However, the authors note that the longer trade routes fell into relative disuse from the 1500s, something also evidenced by the non-stone tools, such as fishing hooks, also found at the site.
The big caveat, or course, is how long a tool was used before it was lost or discarded and buried at the site. The only argument against tool use bias is that the steady flow of tools from almost all sites probably indicates that there are no specific biases about when tools got on the site.
The authors argue that the volume of trade makes it clear that the colonization of new islands was not a process of exchanging goods and people only long enough for a human presence to be established in the new location. Instead, the trade continued over an extended period of time during which it would have “supported socially mediated imperatives such as acquiring high-status goods, nurturing and maintaining strategic alliances, and establishing individual and group prowess or ‘mana’. “
PNAS2016. DOI: 10.1073/pnas.1608130113 (About DOIs).