It is just the latest of many climate phases of the Quaternary Period. The 103rd major shift in climate-driven global oxygen isotope values, to be precise, since the official-designated beginning of the Quaternary Period, 2.58 million years ago. And, many of those major phases, as we have seen, include dozens of climate oscillations far greater in scale than humans have witnessed since written records began. Nevertheless, it is our warm phase, that within which our civilization has grown, and hence it has been separated as a distinct epoch, the Holocene, a little over 0.01 of a million years long. Its counterpart is the Pleistocene Epoch, in which reside those other 2.57 million years of Quaternary time, and those other 102 major climate oscillations. Thus, we live—at least as far as formal geological nomenclature goes—in a privileged time. When this epoch began, Homo sapiens had already existed for some 150,000 years. As a species its prospects might not have seemed bright: this creature lacked anything terribly impressive in the way of claws or teeth or thick fur or armour. But by being ingenious at developing what one might describe as artificial claws and teeth—axes and spears and arrows—it could kill and eat mammals considerably larger than itself. In those early days, it might not have prospered, exactly, but it clung to existence, seemingly weathering at least one very bad patch, several tens of thousands of years ago, when its numbers dropped almost to extinction levels. It survived the climate oscillations of the late Pleistocene—the droughts and floods and episodes of bitter cold and killing heat—by adapting its behaviour or migrating as best it could. Its migrations from its place of origin, Africa, were on an epic scale. The many thousands of individual and collective stories of hope, fear, endurance, courage, tragedy, and (less commonly) triumph are all lost. What remains is the evidence that humans, by the beginning of the Holocene, had spread widely over Europe and Asia, ousting (it seems) their kindred hominin species, Homo neanderthalensis and Homo erectus.
Homo sapiens, Homo neanderthalensis and the Denisova specimen: new insights on their evolutionary histories using whole-genome comparisons