This time-line summarizes present knowledge of the life-spans of these hominid species. The color blue indicates ape and the color red indicates human species (members of the genus Homo). The human species presumably descend from one to another over time; the relationships among the australopithicines and their connections to humans are, however, not clear. For example, this chart positions A. africanus as though it were ancestral to Homo habilis; many would dispute that relationship and place A. Africanus as a descendant of A. afarensis and the progenitor of the robust australopithicines, but only a cousin to humans. Some would also dispute that A. afarensis is ancestral to human species. In 1994-95, two new australopithence species were discovered, A. ramidus, in the Hadar region of Ethiopa, which appears ancestral to afarensis and dates to 4.4 million years ago, and an east African species discovered near Lake Turkana by the Leakeys. The later find provides the earliest direct evidence of bi-pedalism over 4 million years ago.
There is plenty of room for argument and informed speculation about the implications of fossil finds. Even the best fossil record provides largely random snapshots of points in time rather than a complete record. Much of what we would urgently like to know is simply not preserved in the fossil record. However, the broad outlines of human descent are remarkably well established and, in a sense, the arguments are about details.
