Many changes in the physical environment contributed to the evolution of these early humans.
Australopithecines comprise a genus of primitive hominids that resided in Eastern Africa about 4.2 million years ago. Many scientists think that some of the australopithecine species are direct ancestors to humans. Others believe that the Australopithecines represent a branch of hominids from which humans evolved, but are not directly related to humans. There several established taxonomic methods for classifying the australopithecines, but the four most frequently acknowledged species are Australopithecus afarensis, Australopithecus africanus, Australopithecus robustus, and Australopithecus boisei (Chardin). The species can be differentiated, because A. robustus and A. boisei have bigger bones and are more "robust" than A. afarensis and A.africanus (O'Neill).
Most species of the Australopithecus were not any more adept at using tools than modern primates. But, Australopithecus garhi seems to have been the most sophisticated, because its remnants have been discovered near tools and slaughtered animal carcasses, which suggests the advent of a highly antediluvian tool conception. This caused many scientists to infer that A. garhi must be the predecessor of the Homo genus, even though recent deductions held that A. garhi was merely competition to the ancestral Homo species.
The brains of most Australopithecus species were barely 35% the size of the modern human brain (Foley). Most species of Australopithecus were small and gracile in nature, often standing no more than 1.2 meters in height (Wikipedia). Fossil records seem to indicate that Australopithecus is the ancestor of a specific classification of hominids, known as Paranthropus, but are not direct ancestors of the genus Homo, which encompasses modern humans. Both the Paranthropus and Homo genera have proven to be more progressed in behavior and customs than the Australopithecus, which were hardly more than bipedal chimps. It is still widely accepted that only the descedants of Homo would go on to generate language and learn how to use fire.
Though opinions certainly vary in regards to whether the species aethiopicus, boisei and robustus should be placed within the genus Australopithecus, the scientific community currently places them in the genus differ as to whether the species aethiopicus, boisei and robustus should be included within the genus Paranthropus. Paranthropus is thought to have originated from the Australopithecus lineage. Until recently, many scientists classified all Australopithecus species within a single genus. Paranthropus, because it was larger and more robust, was physically different from Australopithecus, and its superior anatomy implied that its behaviors might have been very different from that of its ancestor. The more diminutive and gracile forms such as Australopithecus africanus and Australopithecus afarensis are commonly assumed to be the closest relatives to humans. But, some studies have shown that Australopithecus africanus had a body shape more similar to that of the modern apes than to the members of the genus Homo.
Still, the gracile australopithecines are considered to be the earliest known true hominids, because australopithecines and humans are biologically similar enough to be classified in the family Hominidae (Nickels). Australopithecines