add site
services
publishers
database
health videos
toolbar
stats
live show
health store
more stuff
JOIN/LOGIN
| advertise add site services publishers database health videos
| | about toolbar stats live show health store more stuff JOIN/LOGIN |
BrainMaps.org -> Nissl, Homo sapiens brain-maps.org |
Homo ergaster[1] is an extinct hominid species that lived in eastern and southern Africa beginning about 1.9 million years ago during the late Pliocene epoch. Long-standing debate about the classification of H. ergaster has categorised it as a subspecies of Homo erectus, a separate species of African erectus, a broader-defined species (including H. erectus and H. heidelbergensis), or in strict species definition as temporal form of Homo sapiens. Thus dates for its extinction are often subjective to the definition of the species.[2] H. erectus and H. heidelbergensis are probably the migratory descendants of H. ergaster. H. ergaster may be distinguished from H. erectus by its thinner skull bones and lack of an obvious supraorbital sulcus. It may be distinguished from H. heidelbergensis by its thinner bones, more protruding face, and lower forehead. Derived features separating it from earlier species include reduced sexual dimorphism (around 25%), a smaller, more orthognathic (less protruding) face, a smaller dental arcade, and a larger cranial capacity (700 - 850 cm³). It is estimated that H. ergaster stood at 1.9 metres (6.2 ft) tall[citation needed]. Remains have been found in Tanzania, Ethiopia, Kenya, and South Africa.
[edit] Classification and EvolutionHomo ergaster is a species name used to indicate fossils which are also often referred to as Homo erectus[3] or Homo heidelbergensis.[4] Generally, when the name is applied, it refers specifically to the ancestors of H. erectus, H. heidelbergensis, and H. sapiens that lived in Africa. When H. ergaster is referred to, then H. erectus designates the Asian population.[5] H. heidelbergensis is now normally considered a separate, descendant species of H. ergaster [6] due to its brain-size and somewhat robuster features. Many palaeoanthropologists still debate the definition of H. erectus and H. ergaster as separate species. Some, such as Ian Tattersall, distinguish H. ergaster as a separate species on the basis of cranial features and geographical distribution. He calls H. ergaster the direct African ancestor of H. erectus, proposing that H. ergaster emigrated out of Africa and into Asia, where it had already become distinct enough from its African ancestors as to be classified as H. erectus.[7] Others, such as Richard Leakey, make no distinction. Other possibilities have been opened up by the discovery of Homo georgicus in the Republic of Georgia. This species is apparently intermediate between H. habilis and H. erectus, and it had apparently already left Africa before the evolution of H. erectus and H. ergaster. [edit] DivergenceThe relation of H. ergaster to other hominids is extremely uncertain and highly contentious. Because it is anatomically so similar to H. heidelbergensis, H. erectus, H. neanderthalensis, and H. sapiens, such contention is natural. The general division of the palaeontological community between the Out of Africa and Multiregional hypotheses also contributes to the debate, yet most now agree that H. ergaster is not a dead branch of the evolutionary tree, and that later hominids could (and can) trace their genes back to it.[8] Some genes may have been contributed to the modern gene-pool by separate populations of H. erectus and H. ergaster in Africa and Asia;[9] or Asian erectus may not have contributed at all, and H. ergaster evolved in a nearly direct line into H. heidelbergensis and thence into H. neanderthalensis and H. sapiens.[10] In short, supporters of a Recent African Origin generally recognise H. ergaster as a direct ancestor of H. sapiens; those who support a multiregional origin usually consider H. ergaster a major contributor to the modern genome.[11] [edit] ExtinctionDistinguishing the end of H. erectus and H. ergaster is difficult for the reasons discussed above, but both disappear from the fossil record in Africa about 600,000 years ago, when descendants which were distinct become the norm. H. heidelbergensis, sometimes considered a sub-species, disappears from the fossil record some 400,000 years ago in Europe. Homo floresiensis, discovered in 2003, lived until about 12,000 years ago in Indonesia. [edit] Discovery and Representative FossilsSouth African palaeontologist John T. Robinson first discovered an Homo ergaster mandible in 1949 in southern Africa; the species was at the time recognised as Telanthropus capensis, though now as H. ergaster. The name was first applied in 1975 by Colin Groves and Vratislav Mazák to Richard Leakey's find, mandible KNM-ER 992[12], which is now the type specimen of the species. The most complete Homo ergaster skeleton, KNM-WT 15000, was discovered at Lake Turkana, Kenya, in 1984. Palaeoanthropologists Richard Leakey, Kamoya Kimeu, and Alan Walker dubbed the 1.6-million-year-old specimen "Turkana Boy". [edit] Special DistinctionThe name of the species is derived from the Greek ΕΡΓΩ, work, and refers to the discovery of various tools such as hand-axes and cleavers among skeletal remains. Such tools are often more elaborate than are found with H. erectus in Asia. This is one of the reasons it is sometimes set apart distinctly from other human ancestors. The use of advanced Acheulean tools was special to this species; H. ergaster first began using these tools ca. 1.6 million years ago, some 300,000 years after its punctuated divergence from the lineage of Homo habilis (see Homo georgicus). Charred animal bones in fossil deposits and traces of camps suggest that the species made creative use of fire. It is obvious from simple visual analysis of KNM-WT 15000 that the species it represents had almost the same bodily proportions as H. sapiens. The nose is long and efficient for moistening the air; inferred loss of body-hair on H. ergaster implies the evolution of melanin and sweat glands (these guesses are also complemented by the disappearance of muscles needed for panting in H. ergaster). But the arms are slightly longer, the face slightly more projected, and the pelvis displays an efficiency of bipedalism somewhat greater than in H. sapiens: the most efficient locomotion of any known ape. [edit] Language Homo ergaster (or either of the two species generally classified collectively as Homo erectus, H. erectus and H. heidelbergensis) was conceivably the first of the hominins to use articulate language. For a time, this capability was thought to be restricted to fairly primitive language because of the narrowness of the cervical vertebrae. Such a conclusion was reached from the study of the cervical vertebrae in the Turkana Boy. These specific vertebrae later revealed that KNM-WT 15000 suffered from a stunted vertebral growth, which restricted its breathing (and therefore, the ability to produce speech). A recent find in Dmanisi, Georgia of a normal H. ergaster vertebra has been compared to that of Turkana Boy's. Sound-production would not have been restricted in this vertebra, which is within the normal range of correspondent modern human vertebrae.[13][14] It is certainly recognised by endocasts that H. habilis had a significant mode of communication (though its hyoid and construction of the ear do not support spoken language), and that H. ergaster had a more advanced form of this communicative neurology. It is therefore certainly conceivable that H. ergaster had the ability to use what could be called language.[15] [edit] Notable fossils
[edit] See also
[edit] Footnotes
[edit] References
[edit] External links
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ↑ top of page ↑ | about thumbshots |
