| Homo ergaster Temporal range: Pleistocene |
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|---|---|
| Skull KNM-ER 3733 discovered by Bernard Ngeneo in 1975 (Kenya) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Family: | Hominidae |
| Genus: | Homo |
| Species: | H. ergaster |
| Binomial name | |
| †Homo ergaster Groves and Mazák, 1975 |
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Homo ergaster 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.[1] 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 rather than Asian Homo erectus.[2] It is one of the earliest members of the genus Homo, possibly descended from, or sharing a common ancestor with, Homo erectus.[3]
The binomial name was published in 1975 by Groves and Mazák. The second part, "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.
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The South African palaeontologist John T. Robinson first 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 Homo ergaster.[4] 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".
Many paleoanthropologists still debate the definition of H. ergaster and H. erectus as separate species. Some call H. ergaster the direct African ancestor of H. erectus, proposing that H. ergaster emigrated out of Africa and into Asia, branching into a distinct species.[5] Most dispense with the species-name 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 the 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 Homo heidelbergensis by its thinner bones, more protrusive face, and lower forehead. Derived features separating it from earlier species include reduced sexual dimorphism,[6] a smaller, more orthognathous (less protrusive) face, a smaller dental arcade, and a larger cranial capacity (700-900cm³ in earlier ergaster-specimens, and 900-1100 in later specimens).[1] It is estimated that male H. ergaster stood 1.89 meters (6 ft 2 in) tall. Remains have been found in Tanzania, Ethiopia, Kenya, and South Africa.
Homo habilis is generally accepted as the putative ancestor of the genus Homo,[4] 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.[7] 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 H. ergaster the role of ancestor to all later hominids.[1]
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 Africa and fathered H. erectus diverged from the lineage of H. ergaster almost immediately after this. These early descendants of H. ergaster may have been discovered in Dmanisi, Georgia.[8] 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.
Homo ergaster used more diverse and sophisticated stone tools than its predecessor, Homo habilis. H. ergaster refined the inherited Oldowan developing the first Acheulean bifacial axes:[9] 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. Thus the Asian migratory descendants of H. ergaster made no use of any Acheulean technology.
Sexual dimorphism in H. ergaster is greatly reduced from its australopithecine ancestors (around 20%[6]), but still greater than dimorphism in modern humans. This diminished dimorphism is speculated to be a sign of reduced competition for mates between males , which may also correspond to the more modern social practices of ergaster . 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 erectus did have control of fire,[10] as well as each other hominin sharing a common ancestor with ergaster. The social organisation of H. ergaster probably resembled that of modern hunter-gatherer societies. Unlike australopithecines, ergaster males presumably did not compete at all for females, which had themselves increased in size greatly in proportion to males. This reduced competition and dimorphism also coincided with an increase in brain size and efficiency of stone tools.
Homo ergaster was probably the first hominid to "use a human voice", though its symbolic cognition was probably somewhat limited compared to modern humans. 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. Discoveries of cervical vertebrae in Dmanisi, Georgia some 300,000 years older than those of Turkana Boy are well within the normal human range.[11] 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[12] (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 ergaster vertebrae on record), and thereby suggest kinship to ergaster. Turkana Boy, therefore, may be an anomaly.
There is no archaeological evidence that Homo ergaster made use of symbolic thought (such as figurative art), but the well-evolved brain and physical capabilities (along with reconfiguration of ergaster's breathing-apparatus) suggest some form of linguistic or symbolic communication.
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