The origin of the genus Homo has been traced to Africa. It is associated with brain enlargement, the acquisition of culture, a reduction in the emphasis of mastication as a means of food preparation, and the development of a bipedal gait. Species of the genus include H. habilis, H. erectus, and H. sapiens. The earliest fossil evidence of these hominids has been found in East Africa; namely, in and around the Olduvai Gorge, Tanzania.
The most primitive species of the genus, Homo habilis, differentiated itself from the Austalopithecus hominid lineage during a major cladogenetic event which occurred about 2.5 to 2.3 million years ago. This event involved an explosive period evolution coinciding with an episode of significant global climatic change. As ice sheets in Antarctica and the Northern Hemisphere underwent an expansion, cooler and drier conditions in Africa led to a reduction of wooded areas and the return of widespread open grasslands. South Africa's fossil record shows that these major changes in fauna resulted in widespread extinctions and the development of many new species.
For example, the musk ox group suddenly disappeared, only to be replaced by about 20 new species of antelope. Similar changes occurred in the species that gave rise to man. At some time before 2.0 million years ago, Homo habilis appeared. Then, at a later date, H. habilis was followed by, yet another evolutionary advance, the species, Homo erectus. Although the extent to which the two hominid species' behavior differed is not known, they both shared increased brain power. This enabled not only the beginnings of speech, but also the ability to use stone tools.
In addition, in Africa's grassland environment, both species developed the capacity for bipedal travel. The more primitive Homo habilis retained its powerful forelimbs. This may have contributed to the fact that it only persists in the East African fossil record for a ...