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Why is the ancestry of Australopithecus sediba disputed?

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Side view illustration of Australopithecus afarensis, an early human ancestor, shown walking upright with a hairy body and ape-like facial features. A scale beside the figure marks 12 inches and 40 centimeters. — Australopithecus Artist's rendering of *Australopithecus afarensis*, which lived from 3.8 to 2.9 million years ago.

The ancestry of Australopithecus sediba is a subject of debate among paleoanthropologists due to the species' unique "mosaic" of primitive and humanlike characteristics.12

Some researchers argue that A. sediba is a direct ancestor of the genus Homo—specifically Homo erectus—pointing to shared features in the skull, pelvis, and hand that appear more advanced than those found in other candidates like Homo habilis or Homo rudolfensis. Proponents of this view suggest that the hand structure of A. sediba was better suited for early toolmaking than that of H. habilis.12

Conversely, other paleoanthropologists dispute this evolutionary placement. They contend that A. sediba may simply be a variation of Australopithecus africanus or that it existed concurrently with the true direct ancestors of Homo found in eastern Africa. These critics suggest that the species does not necessarily occupy a central position in the direct lineage leading to modern humans.12