Homo is the genus that includes modern humans and species closely related to them. The genus is estimated to be about 2.3 to 2.4 million years old, evolving from australopithecine ancestors with the appearance of Homo habilis. The advent of Homo coincides with the first evidence of stone tools (the Oldowan industry), and thus by definition with the beginning of the Lower Paleolithic. The emergence of Homo also coincides roughly with the onset of Quaternary glaciation, the beginning of the current ice age.