HOMO ERGASTER

Comments: The Homo ergaster skull known as KNM ER 3733 was discovered by fossil hunter Bernard Ngeneo in 1975. Its remarkable preservation (the best of its historical time period) is the result of nearly complete burial when found - only the upper portion of the eye orbits were protruding from the ground when discovered.

The skull is of a mature female of the early human species now identified as Homo ergaster. The gender identification comes from a comparison of the anatomical features of her face with another Koobi Fora cranium KNM ER 3883, and the male KNM WT 15000 specimen, discovered on the opposite side of Lake Turkana. The features of KNM ER 3733 are considerably less robust. The fully closed cranial sutures, the degree of dental wear and the eruption of the third molars before the individual's death tells us that KNM ER 3733 was an adult.

Features of all Homo erectus (variants included) are the presence of robust mandible and large molars (although dentition of Homo erectus is nearly identical to modern humans), a non-protruding chin, a heavy brow ridge and a long, low skull similar to modern Homo sapiens. The skeleton of Homo erectus is of heavier and more robust design when compared to the average modern human skeleton but body proportions vary greatly from individual to individual.

By 1.6 million years ago, an advance in stone tool technology is identified with Homo ergaster. Known as the Acheulean 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.

A new lineage of the genus Homo emerged in Africa around 1.9 million years ago known as Homo ergaster. Traditionally, scientists have referred to this species as Homo erectus and attributed this species name with a proliferation of H. erectus populations across Africa, Europe, and Asia. Since that time, it has 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 H. erectus and H. ergaster into two distinct species - Homo ergaster for early African "Homo erectus", and Homo erectus for later populations mainly in Asia. Because modern humans and Homo ergaster share the same differences with the Asian Homo erectus, scientist consider H. ergaster as the probable ancestor of later Homo populations.

H. ergaster has a rounded cranium and a prominent browridge. It possesses a reduced dentition 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 (depression just behind the browridge).