Paleolithic period or Old Stone Age, the earliest period of human development and the longest phase of mankind's history. It is approximately coextensive with the Pleistocene geologic epoch, beginning about 2 million years ago and ending in various places between 40,000 and 10,000 years ago, when it was succeeded by the Mesolithic period. By far the most outstanding feature of the Paleolithic period was the evolution of the human species from an apelike creature, or near human, to true Homo sapiens (see human evolution). This development was exceedingly slow and continued through the three successive divisions of the period, the Lower, Middle, and Upper Paleolithic. The most abundant remains of Paleolithic cultures are a variety of stone tools whose distinct characteristics provide the basis for a system of classification containing several tool making traditions or industries.