Left undisturbed by brushing and flossing, the bacteria in your mouth will form a sticky film called plaque. Left further undisturbed, plaque will turn hard and yellow, calcifying on teeth as dental calculus, also known as tartar.
At this point, the tartar is very durable. Just ask these Neanderthals, whose 40,000-year-old tartar scientists recently analyzed to figure out the real paleo diet. Tartar grows in layers—almost like tree rings—entombing DNA from tiny bits of food as well as bacteria in the mouth. Forty thousand years later, scientists can analyze that DNA to reconstruct what was going on in the mouths of long-dead Neanderthals.
Having traveled so far back in time using ancient tartar, some of the same scientists have embarked on a more ambitious project: using the DNA from the bacteria in tartar to figure out how humans settled the 10 million square miles of Polynesia.
Polynesia has confounded the traditional ways of tracing human migration—archaeology, linguistic analyses, even human DNA—because large parts of it were settled so fast. Humans first reached the Society Islands, in the center of the Polynesian Triangle, perhaps around 1,000 AD. Then in the span of just a couple hundred years, they took canoes across vast tracts of open ocean to find specks of inhabitable rock as far-flung as Hawaii, New Zealand, and Easter Island. How Polynesians navigated these waters in the 11th century is a subject of considerable fascination. But even more basically, archaeologists are not sure exactly when the islands were settled and in what order. That’s where the tartar comes in.