Homo ergaster

Homo ergaster Fossil range: Pleistocene
Skull KNM-ER 3733 discovered by Bernard Ngeneo in 1975 (Kenya)
Scientific classification
Domain:	Eukarya
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Phylum:	Chordata
Subphylum:	Vertebrata
Infraphylum:	Gnathostomata
Superclass:	Tetrapoda
Class:	Mammalia
Subclass:	Theria
Infraclass:	Eutheria
Order:	Primates
Suborder:	Haplorrhini
Infraorder:	Simiiformes
Parvorder:	Catarrhini
Superfamily:	Hominoidea
Family:	Hominidae
Subfamily:	Homininae
Tribe:	Hominini
Subtribe:	Hominina
Genus:	Homo
Species:	ergaster
Binomial name
†Homo ergaster Groves and Mazák, 1975

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. Remains have been found in Tanzania, Ethiopia, Kenya, and South Africa.

Classification and Evolution

Homo 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 homo habilis and homo erectus, and it had apparently already left Africa before the evolution of homo erectus and homo ergaster.

Divergence

The 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].

Extinction

Distinguishing 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, lived until about 12,000 years ago in Indonesia.

Discovery and Representative Fossils

South 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".

Special Distinction

The 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.

Language

Homo ergaster skull reconstruction of the Nariokotome Boy from Lake Turkana, Kenya. Museum of Man, San Diego.

Homo ergaster (or either of the two species generally classified collectively as Homo erectus, Homo erectus and Homo 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 vertebræ. Such a conclusion was reached from the study of the cervical vertebræ in the Turkana Boy. These specific vertebræ 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 vertebræ.^[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]

Notable fossils

• KNM ER 3733
• Turkana Boy - also classified as Homo erectus
• KNM ER 992

See also

• Homo erectus
• Homo georgicus
• Homo habilis
• List of fossil sites
• List of human evolution fossils
• Telanthropus capensis

Footnotes

References

• Leakey, Richard. Origins Reconsidered. ISBN 0385412649. http://books.google.com/books?id=rGo8AAAACAAJ&dq=origins+reconsidered&ei=gY_QSJmpPIPWtgOD8eTbAw. 
• Ruhlen, Merritt (1994). The origin of language: tracing the evolution of the mother tongue. New York: Wiley. ISBN 0471584266. 
• Shreeve, James (1995). The Neandertal Enigma: Solving the Mystery of Modern Human Origins. Harper Perennial. 
• Tattersall, Ian; Jeffrey Schwartz (2000). Extinct Humans. Boulder and Cumnor Hill: Westview Press. ISBN 0-8133-3482-9. 
• Deacon, Terrence (1997). The Symbolic Species: The Coevolution of Language and the Brain. New York, NY: W.W. Norton & Company. ISBN 0-393-31754-4. 

External links

• Archaeology Info
• Smithsonian