英语时差：史前的牙签

If asked to imagine the first prehistoric tools, crafted and used by our early, hominid ancestors, you'd probably think of crude knives or spear heads, chipped from stone. You probably aren't aware of another human innovation that might be just as old. Today we'll learn about the two million year history of the toothpick, possibly one of humanity's oldest tools.

Early stone tools, like knives and scrapers, are easy for anthropologists to learn about because these items are still around. Even after two million years, a chipped stone tool is still going to be there when you dig it up. Toothpicks, however, are another story. Made from splinters of wood, thorns, or bone fragments, these can rot and crumble away over time, leaving no recognizable trace. If this is so, how can an anthropologist look at a two million year old fossil site and claim that these early pre-humans picked their teeth?

It's certain that no toothpick will ever last two million years, but this isn't the case with teeth. In fact, fossil teeth are the most durable remnants that anthropologists work with, and some of these ancient teeth display a curious set of grooves. Although these might have been caused by tooth decay, a close examination of the marks seems to indicate that the grooves were worn by repeated toothpicking--probably to alleviate the pain of gum disease. Indeed, these fossil grooves match the toothpick grooves in the teeth of several modern aboriginal populations.

It's enough to warm every dentist's heart: The first tools weren't just for preparing food, hunting, or fighting. They might have been used for dental hygiene as well.