Hominids In Time

FOSSIL RECORD OF HOMINIDS shows that multiple species existed alongside one another during the later stages of human evolution. Whether the same can be said for the first half of our family's existence is a matter of great debate among paleoanthropologists, however. Some believe that all the fossils from between seven million and three million years ago fit comfortably into the same evolutionary lineage. Others view these specimens not only as members of mostly different lineages but also as representatives of a tremendous early hominid diversity yet to be discovered. (Adherents to the latter scenario tend to parse the known hominid remains into more taxa than shown here.)

The branching diagrams (inset) illustrate two competing hypotheses of how the recently discovered Sahelanthropus, Orrorin and Ardipithecus ramidus kadabba are related to humans. In the tree on the left, all the new finds reside on the line leading to humans, with Sahelanthropus being the oldest known hominid. In the tree on the right, in contrast, only Orrorin is a human ancestor. Ardipithecus is a chimpanzee ancestor and Sahelanthropus a gorilla forebear in this view.

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