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Why do some scientists classify African Homo erectus as Homo ergaster?

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Side-view illustration of a Homo erectus individual, depicted with a robust, upright body covered in hair, walking with one arm bent. A scale bar beside the figure shows measurements in inches and centimeters. — Homo erectus Artist's rendering of *Homo erectus*, which lived from approximately 1,700,000 to 200,000 years ago.

Some paleontologists classify early African specimens of Homo erectus as a separate species, Homo ergaster, because they believe these fossils represent a more probable ancestral form of modern humans than the Asian H. erectus populations.1

The reasoning behind this classification includes:

Morphological Differences: Unlike Asian H. erectus, which often exhibits a thick cranium and large cranial adornments, the African specimens are considered more "gracile" or slender.12
Evolutionary Lineage: Some scientists argue that the specialized, robust features of Asian H. erectus suggest it could not have been on a direct evolutionary line to Homo sapiens. In contrast, they view H. ergaster as an intermediate form that evolved toward modern humans, potentially through H. heidelbergensis.1

However, this classification is not universally accepted. Other researchers argue that there is insufficient evidence regarding the variability of cranial features within populations to justify splitting the species, and they maintain that African and Asian fossils can be grouped into a reasonable ancestor-to-descendant sequence.12