We have described the Earth before humans set foot upon it. We have tried to understand something about our ancestors, using as our guide the fossil record and the gorgeous panorama of life that now graces our planet. While there are still vast numbers of missing pages in our orphan’s file, the progress of science has enabled us to glimpse a few of the lost or forgotten entries—perhaps even many of the important items. But we have explored only the early chapters of the file. Its key central section—chronicling the dawn of our species and its evolution up to the invention of civilization—is the subject of the next book in this series.