This has not yet been definitely established. The ancestors of the great apes and the ancestor of Man probably diverged from one another as early as the Miocene period, and Man acquired certain essentially human characteristics probably in the Pliocene period.\
The earliest known skeletal remains that are accepted as human are believed to date from the early or middle part of the Pleistocene period. For the purposes of the prehistorian, who has to rely largely on archaeological evidence, the record of Man may be said to begin at the moment when he was able to fashion the first stone tools which can be unmistakably recognized to be of human workmanship. This was early in the Pleistocene, or possibly in the very late Pliocene.