Inhabiting eastern Africa between four and three million years ago, Australopithecus afarensis was a long-lived species that may have given rise to the several lineages of early human that appeared in both eastern and southern Africa between two and three million years ago. For its antiquity, A. afarensis is one of the better known species of early human, with specimens collected from over 300 individuals. It is a species that exhibits many cranial features which are reminiscent of our ape ancestry, such as a forward protruding (prognathic) face, a "U-shaped" palate (with the cheek teeth parallel in rows to each other similar to an ape) and not the parabolic shape of a modern human, and a small neurocranium (brain case) that averages only 430cc in size (not significantly larger than a modern chimpanzee).

The specimens recovered have given representative examples of almost all of the bones of the A. afarensis skeleton. From this, it is clear that there are many significant difference between A. afarensis and its ape predecessors, one of which is crucial to later human evolution, bipedality.

The position of A. afarensis in the phylogeny of early humans is under debate. Many feel that it is ancestral to the east African "robust" early humans, and possibly to all robust forms. Additionally, A. afarensis is proposed as the ancestor to later Homo. Yet, research now suggests that A. africanus might be ancestral to later Homo.