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Why might Homo rudolfensis be considered separate from Homo habilis?

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An illustration of Homo habilis, an early human ancestor, shown walking upright with a hairy body and ape-like features. A scale beside the figure indicates height in inches and centimeters. — Homo habilis Artist's rendering of *Homo habilis*, which lived from 2 to 1.5 million years ago.

The classification of Homo rudolfensis as a species separate from Homo habilis is a subject of ongoing debate in paleoanthropology, primarily centered on the significant anatomical variation observed among early Homo fossil assemblages in East Africa.1

While some researchers suggest that these variations—such as differences in cranial capacity and skull shape—simply reflect sexual dimorphism within a single species, others argue that the differences are too distinct to be explained by sex alone. Specifically, some smaller craniums depart from the morphology of large-brained H. habilis in ways that are not clearly related to sex, and certain specimens exhibit facial features more reminiscent of Australopithecus.1

Consequently, many scholars propose that the fossil record actually represents two distinct species, H. habilis and H. rudolfensis, which may have lived contemporaneously between 2.0 and 1.5 million years ago. In this view, the two groups represent a more diverse early human population than previously recognized, rather than a single, sexually dimorphic group.12