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By 1.9 million years ago, another lineage
of the genus Homo emerged in Africa. This species was Homo ergaster.
Traditionally, scientists have referred to this species as Homo erectus
and linked this species name with a proliferation of populations across
Africa, Europe, and Asia. Yet, since the first discoveries of Homo erectus,
it had been noted that there were differences between the early populations
of "Homo erectus" in Africa, and the later populations
of Europe, Africa and Asia. Many researchers now separate the two into distinct
species Homo ergaster for early African "Homo erectus",
and Homo erectus for later populations mainly in Asia. Since modern
humans share the same differences as H. ergaster with the Asian H.
erectus, scientist consider H. ergaster as the probable ancestor
of later Homo populations.
H. ergaster had a rounded cranium and a prominent browridge. Its teeth were much reduced in size, especially when compared to Australopithecus. Several features that distinguish H. ergaster from H. erectus are thinner bones of the skull and the lack of an obvious sulcus, or depression, just behind the browridge. By 1.6 million years ago, an advance in stone tool technology is identified with H. ergaster. Known as the Achulean stone tool industry, it consisted of large cutting tools, primarily hand axes and cleavers. Originally thought to be responsible for the spread of early humans beyond Africa, it is now known that the migration out of Africa predates this tool industry. At the top-left is the amazingly well preserved KNM ER 3733 cranium. Second from the top is the type specimen of the Homo ergaster species, the KNM ER 992 mandible. At the bottom is the famous Turkana Boy KNM WT 15000, a nearly complete skeleton dating back to 1.6 million years. |
