Temporal range: Pleistocene, 1.8–1.3Ma
|Skull KNM-ER 3733 discovered by Bernard Ngeneo in 1975 (Kenya)|
Groves and Mazák, 1975
Homo ergaster (meaning "working man") or African Homo erectus is an extinct chronospecies of Homo that lived in eastern and southern Africa during the early Pleistocene, between 1.8 million and 1.3 million years ago.
There is still disagreement on the subject of the classification, ancestry, and progeny of H. ergaster, but it is now widely accepted to be the direct ancestor of later hominids, such as Homo heidelbergensis, Homo sapiens, and Homo neanderthalensis and Asian Homo erectus.
It is one of the earliest members of the genus Homo, possibly ancestral to, or sharing a common ancestor with, Homo erectus. Some paleoanthropologists consider H. ergaster to be simply the African variety of H. erectus; this leads to the use of the term "Homo erectus sensu stricto" for the Asian H. erectus, and "Homo erectus sensu lato" for the larger species comprising both the early African populations (H. ergaster) and the Asian populations. The latest discoveries go even further claiming that all five contemporary species of early Homo in Africa, including Homo habilis, H. rudolfensis, H. ergaster, and H. erectus, are representatives from the same species, best named H. erectus, which evolved about 2 million years ago in Africa and expanded through Eurasia, as far as China and Java, where it was first documented from about 1.2 million years ago. The binomial name was published in 1975 by Groves and Mazák. The specific epithet, "ergaster", is derived from the Ancient Greek ἐργαστήρ "workman", in reference to the comparatively advanced lithic technology developed by the species, introducing the Acheulean industry.
Discovery and representative fossils
The South African palaeontologist John T. Robinson discovered a mandible of a new hominid in southern Africa in 1949; he named the species Telanthropus capensis, though it is now recognised as a member of H. ergaster. The name was first applied by Colin Groves and Vratislav Mazák to KNM-ER 992, a mandible discovered near Lake Rudolf (now Lake Turkana), Kenya in 1975, which became the type-specimen of the species. The most complete skeleton of H. ergaster (and one of the most complete extinct hominids to date), KNM-WT 15000, was discovered at Lake Turkana, Kenya, in 1984 by paleoanthropologists Kamoya Kimeu and Alan Walker. They nicknamed the 1.6-million-year-old specimen "Turkana Boy".
Classification and special distinction
Many paleoanthropologists still debate the definition of H. ergaster with H. erectus as separate species. Some call H. ergaster the direct African ancestor at H. erectus, proposing that H. ergaster emigrated out of Africa and into Asia, branching into a distinct species. Most dispense with the specific epithet ergaster, making no distinction between such fossils as the Turkana Boy and Peking Man. Though "Homo ergaster" has gained some acceptance as a valid taxon, H. ergaster and H. erectus are still usually defined as distinct African and Asian populations of larger species H. erectus. (For the remainder of this article, the name "Homo ergaster" will be used to describe a distinct species for the convenience of continuity in reading.)
H. ergaster may be distinguished from H. erectus by its thinner skull-bones and lack of an obvious supraorbital foramen. It may be distinguished from H. heidelbergensis by its thinner bones, more protrusive face, and lower forehead. Derived features separating it from earlier species include reduced sexual dimorphism, a smaller, more orthognathous (less protrusive) face, a smaller dental arcade, and a larger cranial capacity (700–900 cm³ in earlier H. ergaster-specimens, and 900-1100 in later specimens). Remains have been found in Tanzania, Ethiopia, Kenya, and South Africa.
Homo habilis is generally accepted as the putative ancestor of the genus Homo, and often of H. ergaster most directly. This taxon's status as a legitimate species within "Homo", however, is particularly contentious. H. habilis and H. ergaster coexisted for 200,000-300,000 years, possibly indicating that these species diverged from a common ancestor. It is unclear what genetic influence H. ergaster had on later hominids. Recent genetic analysis has generally supported the Out-of-Africa hypothesis, and this may designate to H. ergaster the role of ancestor to all later hominids.
Origin and extinction
H. ergaster is believed to have diverged from the lineage of H. habilis between 1.9 and 1.8 million years ago; the lineage that emigrated from Africa and fathered H. erectus diverged from the lineage of H. ergaster almost immediately after this. These early descendants of H. habilis may have been discovered in Dmanisi, Georgia. H. ergaster remained stable for ca. 500,000 years in Africa before disappearing from the fossil record around 1.4 million years ago. No identifiable cause has been attributed to this disappearance; the later evolution of the similar H. heidelbergensis in Africa may indicate that this is simply a hole in the record, or that some intermediate species has not yet been discovered.
Use of tools
H. ergaster used more diverse and sophisticated stone tools than its predecessor, H. habilis. H. ergaster refined the inherited Oldowan, developing the first Acheulean bifacial axes: while the use of Acheulean tools began ca. 1.6 million years ago, the line of H. erectus diverged some 200,000 years before the general innovation of Acheulean technology.
Sexual dimorphism in H. ergaster is greatly reduced from its australopithecine ancestors (around 20%), but still greater than the dimorphism in modern humans. This diminished dimorphism is speculated to be a sign of reduced competition for mates between males.
Not only was H. ergaster like modern humans in body, but also more in organisation and sociality than any earlier species. It is conceivable that H. ergaster was the first hominin to harness fire: whether as the containment of natural fire, or as the lighting of artificial fire, is still a matter of contention. It is now assumed, however, that H. erectus did have control of fire, as well as each other hominin sharing a common ancestor with H. ergaster.
It was thought for a long time that H. ergaster was restricted in the physical ability to regulate breathing and produce complex sounds. This was based on Turkana Boy's cervical vertebrae, which were far narrower than in later humans. However, later discoveries of cervical vertebrae in Dmanisi, Georgia, which were some 300,000 years older than those of Turkana Boy, were well within the normal range of human vertebrae range. It has been established, furthermore, that the Turkana Boy probably suffered from a disease of the spinal column that resulted in narrower cervical vertebrae than in modern humans (as well as the older Dmanisi finds). While the Dmanisi finds have not been established definitively as H. ergaster, they are older than Turkana Boy (the only definite H. ergaster vertebrae on record), and thereby suggest kinship to H. ergaster.
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|Wikimedia Commons has media related to Homo ergaster.|
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