The term “Paleolithic” (Old Stone Age) refers to both a time period—from roughly 1.5 million years ago to roughly 10,000 years ago—and a cultural phase, in which subsistence is based on hunting and gathering. The period is subdivided into three stages: the Lower Paleolithic, during which Homo erectus lived; the Middle Paleolithic, which is characterized by Neandertal culture; and the Upper Paleolithic, the time of the first modern humans. Dates for these stages vary depending on the part of the world being studied.