“But the Stone Age was not a distinct period or age at all, since it includes the entire evolutionary history of the hominids, from their earliest appearance several million years ago to the fully modern humans of today’s world. This immense period of time encompasses many of the technologies described in this book, including the domestication of fire, the invention of clothing and dwellings, the development of symbolism, the adoption of agriculture, and the beginnings of urban civilization. In fact, the Stone Age technically began to end only when the techniques of metallurgy were first developed a few thousand years ago.”