Homo ergaster

Homo ergaster Temporal 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 is an extinct hominin species (or subspecies, according to some authorities) that lived throughout eastern and southern Africa between 1.9 to 1.4 million years ago as a separate subspecies with the advent of the lower Pleistocene and the cooling of the global climate. H. ergaster is sometimes categorized as a subspecies of Homo erectus (and occasionally H. erectus as an Asian subspecies of H. ergaster). H. erectus and Homo 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. Derived features separating it from earlier species include reduced sexual dimorphism, a smaller, more orthognathic (flat) 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.

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 recognised as H. ergaster. The name was first applied in 1975 by Colin Groves and Vratislav Mazák to Richard Leakey's find (KNM-ER 992), which is now the type specimen of the species. The most complete Homo ergaster skeleton was discovered at Lake Turkana, Kenya, in 1984. Paleoanthropologists Richard Leakey, Kamoya Kimeu, and Alan Walker dubbed the 1.6 million year old specimen as KNM-WT 15000 (nicknamed "Turkana Boy").

Special Distinction

The specific name of H. ergaster is derived from the Greek ΕΡΓΩ, work, and refers to the discovery of various tools such as hand-axes and cleavers among skeletal remains. This is one of the reasons it is sometimes set apart distinctly from other human ancestors. The use of advanced Acheulean tools was especial 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 quite obvious from visual analysis of Turkana Boy that the species he represents had almost the same bodily proportions as H. sapiens. The nose is long and efficient for moistening the air; the 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.

Classification

Homo ergaster is the name least commonly used to represent the species referred to often as Homo erectus and (less commonly) Homo heidelbergensis. Generally, when applied, the name refers specifically to the ancestors of H. erectus, H. heidelbergensis, and H. sapiens living in Africa (while H. erectus refers to the Asian population). In colloquial language and introductory terminology, a distinction will often be made between H. erectus and H. heidelbergensis, but not H. ergaster. H. heidelbergensis is now often considered a separate, descendant species of H. ergaster due to its brain-size and somewhat robuster features.

The line between H. ergaster, H. erectus, H. heidelbergensis, H. sapiens, and H. neanderthalensis has become somewhat blurred with the discovery of recent finds (Bodo skull, Dali skull, H. sapiens idàltu, Petralona 1, Arago 21, H. antecessor), but the general consensus leaves H. ergaster and H. erectus as two populations of one species, and H. heidelbergensis as a descendant of H. ergaster that may represent a distinct species.

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. This was, at the beginning, probably a rather primitive language, showing little resemblance to today's languages in terms of complexity. H. habilis probably had a significantly complex system of communication, but the location of the hyoid bone, the contours of its brain, and the lesser complexity of its ear make it unlikely that H. habilis used anything recognised as speech.

The linguistic abilities of H. ergaster were probably confined to a primitive symbolic language phonetically less complex than modern language. It is not clear when this incomplete language began to resemble the language of H. sapiens, whether later in the life of H. ergaster, in H. heidelbergensis, or in H. sapiens. It is now generally agreed that Neanderthals made use of some kind of language; it is not known, however, how complex this language was, leaving the development of modern language still with either H. ergaster, H. heidelbergensis, or H. sapiens.

Divergent Evolution

It is agreed now that H. ergaster is the direct ancestor of both H. sapiens and H. neanderthalensis.

Homo erectus

Homo erectus (here defined as the Asian migratory descendants of H. ergaster) migrated out of Africa fairly quickly in its evolution (around 1.8 million years ago): shortly after it appeared in Africa as a separate species. This is possibly represented in the new species H. georgicus, resembling H. habilis in terms of brain-size, and H. ergaster in the characteristics of the face.

Homo heidelbergensis

It is generally assumed that H. heidelbergensis evolved in Africa and migrated out into Europe and the Middle-East. The two separated populations became nearly isolated and diverged independently into H. sapiens (in Africa) and H. neanderthalensis (in Europe). It is only recently that H. heidelbergensis has been widely accepted as a separate species, though some still argue for it as, like H. erectus, a subspecies of H. ergaster.

Extinction

H. ergaster became extinct some 400,000 years ago in Europe, usually described as the subspecies heidelbergensis. Considering H. heidelbergensis a separate species, the ergaster-line disappeared ca. 600,000 years ago. H. erectus persisted until about 400,000 years ago in Asia; its descendant subspecies, Homo floresiensis, lived until about 12,000 years ago in Indonesia.

Notable fossils

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

See also

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

References

• Leakey, Richard. Origins Reconsidered. ISBN 0385412649.
• 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 (2000). Extinct Humans. Boulder and Cumnor Hill: Westview Press. ISBN 0-8133-3482-9. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links

• Archaeology Info
• Smithsonian