In the Stone Age, the most important tool was, yes, the stone. But what was second? Well, we’ll spin a yarn about that on this EarthDate, because it was … yarn, or string.

String is just plant fibers like cotton or hemp, or animal hair like sheep or llama wool, twisted together.

This simple invention allowed early humans to turn short fibers into long cords with many uses.

String tied stone points to spears and arrows. It strung a bow to shoot those arrows. It tied fishhooks made of shell to fishing poles. Or could be tied into fishnets.

Early humans wove string together to create rope for lashing things to their backs or slinging them over a shoulder, making life more mobile and freeing arms for collecting or climbing.

And they wove yarn into cloth—for clothing, carrying, bedding, shelter, and even sails.

String, and the things made from it, are perishable fibers, so not many ancient examples survived.

Still, we’ve found remnants in Paleolithic sites around the world, dating back more than 40,000 years. And from a Neanderthal site going back even farther.

Today, we use string and yarn every day, most commonly in our clothes, which are woven of the same old fibers, cotton and wool, along with a new generation of synthetics, made from oil.

So let’s all be glad we invented string. Without it, we might still be wearing animal skins—or less.