Homo ergaster

Homo ergaster Fossil range: Pleistocene
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Subfamily: Homininae Tribe: Hominini Subtribe: Hominina Genus: Homo Species: H. ergaster
Binomial name
Homo ergaster Colin Groves & Vratja Mazak, 1975

Homo ergaster (Greek derivation: working man), an early hominid (refer also to hominim), may either have been a predecessor of Homo erectus or an early group of Homo erectus. H. ergaster’s presence has been dated variously and may have ranged over a period of 1.9 to 1.5 million years ago. Remains of H. ergaster have been discovered in Kenya and Dmanisi in the Republic of Georgia.

Description

H. ergaster had a rounded cranium and a prominent browridge. Compared to Australopithecus, its teeth were significantly smaller. Features that distinguish H. ergaster from H. erectus were thinner bones of the skull and the lack of an obvious sulcus, or depression, immediately posterior of the browridge.

Taxonomic status

The genus Homo currently includes a possible six extinct species and the one remaining modern human species, Homo sapiens. H. rudolfensis and H. habilis were contemporaries. Prior to the emergence of later species of the genus, the fossil record indicates that H. ergaster was without contemporaries of the same genus. This may simply be due to an incomplete fossil record however. H. erectus appeared well before the remaining members of the genus and were contemporaries within the last one million years with H. heidelbergensis, H. neaderthalensis and H. sapiens. The last of these to become extinct was H. neanderthalensis.

Homo habilis

Originally described by Louis Leakey, John Napier, and Philip Tobias from finds at Olduvai Gorge, Tanzania, in 1964, H. habilis fossils have been found in eastern and possibly southern Africa. Dated to sometime between about 1.9 million and 1.6 million years ago and possibly as early as 2.4 million years ago, H. hablis fossils resemble those of australopiths, but had smaller and narrower molar teeth, premolar teeth, and jaws than possible predecessors and contemporary species.

Homo rudolfensis

H. rudolfensis are named after the initial discovery of fossils near Lake Rudolf (now Lake Turkana), northern Kenya. Existing fossils date from about 1.9 million years ago but the time range of this species has not been determined. H. rudolfensis would have been a contemporary of H. habilis but any interaction between them is unknown.

Homo ergaster

Possibly an early form of H. erectus.

Homo erectus

Discovered first in Java by Dutch physician Eugene Dubois in 1891. Dubois named hia find Pithecanthropus erectus, or "erect ape-man". H. erectus may or may not be a later group of Homo ergaster, but did then spread to Asia between 1.8 million and 1.5 million years ago. The most recent fossils discovered are from the Solo River in Java, and have been dated to about 50,000 years old. Having survived for more than 1.5 million years, it was particularly successful.

H. erectus had a low and rounded braincase, elongated from front to back, a pronounced brow ridge, and a cranial capacity of 800 to 1,250 cc in adults.

Homo heidelbergensis

Currently there is evidence that early humans migrated into Europe by 800,000 years ago. These populations evidently were not Homo erectus. Predating both H. neanderthalensis and H. sapiens in the region, they are designated as H. heidelbergensis, named for a 500,000-year-old jaw found near Heidelberg, Germany. Stockier that H. ergaster and H. habilis, their fossils have been found in Bodo, Ethiopia; Saldanha (also known as Elandsfontein), South Africa; Ndutu, Tanzania; and Kabwe, Zimbabwe.

They may have been a distinct species or they may have been the predecessors of Neanderthals (in Europe) and H. sapiens (in Africa). Their place in the progress of evolution is unclear.

Homo neanderthalensis

Neanderthal fossils have been found in western Europe through central Asia. Neanderthals were extent between about 200,000 and 36,000 years ago and may have persisted as late as 28-24,000 years ago. Neanderthal (sometimes spelled Neandertal) are named for fossils found in 1856 in the Feldhofer Cave of the Neander Valley in Germany (thal is the old spelling of the word meaning "valley" in German). Fossils found earlier at Engis, Belgium, in 1829 and at Forbes Quarry, Gibraltar, in 1848 (the first early Homo fossils ever found) are now believed to be Neanderthals.

Homo sapiens

Modern humans, the oldest known fossils with skeletal features typical of modern humans date from between 130,000 and 90,000 years ago. Fossils of modern Homo sapiens have been found Singha, Sudan; Omo, Ethiopia; Klasies River Mouth, South Africa; and Skhãl Cave, Israel.

Occurrences/Sites

Koobi Fora, Kenya

On the east shore of Lake Turkana which lies in Kenya and Ethiopia, Koobi Fora is one of the richest fossil sites on earth, Other hominids found at Koobi Fora include Australopithecus afarensis, A. africanus, A. boisei, Homo erectus, and H. habilis.

Associated artifacts

Tool making and use

H. ergaster evidently used large cutting tools of stone, primarily hand axes and cleavers. These tools represent an advanced stage of stone tool technology known as the Achulean stone tool industry now believed to have developed after hominid migration out of the region of eastern Africa.

Important fossils

KNM ER 3733 cranium

Discovered by Bernard Ngeneo in Koobi Fora, Kenya in 1975, ER 3733 is a mature female that may have lived about 1.75 million years ago.

KNM ER 3883 cranium

Discovered in 1976 by Richard Leakey, the ER 3883 is a skull cap which retains an intact right orbit. ER 3883 has no sulcus or depression behind its large browridges.

Found in Koobi Fora, Kenya, ER 3883 was originally thought to be species Homo erectus but has been reclassified as Homo ergaster. ER 3883 may have belonged to a male that lived about 1.5 million years ago.

KNM ER 992 mandible

ER 992 was discovered in 1971 by Richard Leakey in Koobi Fora, Kenya. It is dated to about 1.5 million years ago. The ER 992 mandible shows a lighter build and smaller teeth than Homo erectus.

KNM WT 15000 (Turkana Boy)

Turkana Boy is a nearly complete skeleton discovered in West Turkana, Kenya, August 22, 1984 by Kamoya Kimeu. It is one of the most significant finds in paleoanthropology. TW15000 is the skeleton of an immature boy, about 9-12 years of age, already more than 5 feet in height at the time of death Its height is a significant increase in size over earlier hominids which were about the size of modern chimpanzees. At maturity it might have attained a height of about 6 feet and approximately 150 lbs. WT 15000 lived about 1.6 million years ago. Cause of death is unknown.

WT 15000 cranial capacity is measured at 880cc and might have attained an adult cranial capacity of 909cc.

WT 15000 had slender hips that were better adapted to walking and running over long distances than other hominids. Arm and leg bones were proportioned more like those of modern humans, rather than the shorter legs and longer arms (or more ape-like proportions) of Homo habilis and Africanus afarensis. The long and slender, body was likely more adapted to a tropical environment, an inference drawn from the fact that most modern humans that live in the tropical areas are similarly built.