We can see the modification of the pelvis and hip joint necessary for bi-pedalism in the image on the right, which contrasts "Lucy," the 3.5million year old Australopithicus afarensis, with a chimp. Lucy was fully bi-pedal and had an erect, human-like posture, although she is classified as an ape.
It is interesting to note in this regard that the complex changes associated with bi-pedalism are already present in a recently discovered Hominid species (A. ramidus), which is even older than A. afarensis and dated at 4.4 million years before the present. Bi-pedalism and erect posture are thus characteristics of all Hominids, not of humans alone. Australopithicus ramidus, the earliest known Hominid species, apparently lived in a forest environment in Ethiopia. The development of bi-pedalism was thus a "pre-adaptation" which enabled their Hominid descendents to survive and flourish in the drier climate which prevailed after 5 million years ago and which converted forest environments into bush or open grasslands. On the basis of present evidence, then, erect posture and bi-pedalism precede the emergence of human species, and therefore human behavior and culture, by several million years.
The young Homo erectus boy to the right, a member of an early human species 1.65 million years old, is gracefully and athletically bi-pedal, suggesting a complete adaptation of early human anatomy to its challenging African habitat. By this point in the fossil record, the freeing of the hands for other tasks, which is a by-product of bi-pedal anatomy, was beginning to have consequences in the emergence of a distinctly human way of life, which includes tool making according to prescribed patterns or concepts.
We can see the modification of the pelvis and hip joint necessary for bi-pedalism in the image on the right, which contrasts "Lucy," the 3.5million year old Australopithicus afarensis, with a chimp. Lucy was fully bi-pedal and had an erect, human-like posture, although she is classified as an ape.