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Why do some paleoanthropologists think Homo habilis fossils represent more than one species?

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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.

Some paleoanthropologists argue that Homo habilis fossils represent more than one species due to significant anatomical variation among the discovered specimens. While some researchers suggest this variation is simply the result of sexual dimorphism—with larger skulls representing males and smaller ones representing females—others point to inconsistencies that cannot be explained by sex alone.1

Key reasons for this debate include:

Morphological Differences: Beyond differences in size, there are distinct variations in the shape of the skulls and facial structures. Some smaller skulls deviate from the morphology of large-brained H. habilis in ways not typically associated with sexual dimorphism.1
Australopith-like Features: Certain specimens exhibit facial similarities to Australopithecus, such as flattened nasal regions or specific cheekbone structures, which contrast with the more modern features seen in other H. habilis fossils.12
Species Classification: Due to these discrepancies, some scientists propose that the fossils actually represent two distinct species: H. habilis and H. rudolfensis.13

This ongoing controversy highlights the difficulty of classifying fragmentary early hominin remains.13