Final answer:
Homo habilis is one of the earliest species in the genus Homo, characterized by increased cranial capacity, bipedalism, and tool use. Criteria for classifying species in this genus include a brain size over 600 cc, reduced prognathism, and hands capable of making tools. The genus also includes Homo erectus, and there is debate about the ancestry within the genus.
Step-by-step explanation:
The genus Homo first appeared between 2.5 and three million years ago, with Homo habilis being one of the earliest species within this genus. This species, living from about 2.5 to 1.4 million years ago, exhibited significant advancements such as increased cranial capacity, bipedal locomotion, and the use of Oldowan stone tools. Beyond bipedalism, other criteria for the classification under genus Homo include a brain size larger than 600 cc, reduced prognathism, a jaw that is less protrusive compared to the australopithecines, and hands capable of dexterity for tool-making. Homo habilis, meaning 'handyman,' was long thought to be the first toolmaker, although it is now understood that tool use predates this species.
In addition to Homo habilis, the genus Homo includes other species such as Homo erectus, which evolved about 2.8 million years ago and were nearly as efficient at bipedal walking as modern humans. Their anatomy displayed a broader pelvis and longer legs suited for bipedalism, despite retaining a relatively small brain and larger jaws compared to Homo sapiens. The determination of a species' inclusion in the genus Homo is complex, given the diversity of traits and how they interconnect. Homo habilis has been at the core of debates, with some scientists proposing Homo rudolfensis as a potential ancestor to later species like Homo erectus. The recognition of stone tool use as a criterion for the genus Homo has also evolved, recognizing that such tools were used by earlier hominins like Australopithecus.