Difference between revisions of "Homo ergaster" - New World Encyclopedia

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| binomial_authority = [[Colin Groves|Groves]] and [[Vratislav Mazák|Mazák]], 1975
 
| binomial_authority = [[Colin Groves|Groves]] and [[Vratislav Mazák|Mazák]], 1975
 
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'''''Homo ergaster''''' is an [[extinction|extinct]] species or subspecies of [[hominin]] that lived in eastern and southern [[Africa]] from about 1.8 million years ago (mya) to about 1.3 mya.  It is variously considered to be (1) a separate species that is ancestral to ''Homo erectus''; (2) a subspecies of ''H. erectus'', ''H. erectus ergaster''; (3) another name for ''H. erectus''; and (4) the African variety of ''H. erectus'', with "Homo erectus sensu stricto" for the Asian H. erectus, and "Homo erectus sensu lato" for the larger species comprising both the early African populations (H. ergaster) and the Asian populations
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'''''Homo ergaster''''' is an [[extinction|extinct]] [[hominin]] that lived in eastern and southern [[Africa]] from about 1.8 million years ago (mya) to about 1.3 mya.  It is variously considered to be (1) a distinct [[species]], perhaps ancestral to the Asian ''[[Homo erectus]]''; (2) a subspecies of ''H. erectus'', ''H. erectus ergaster''; or (3) the African variety of ''H. erectus'', with "Homo erectus sensu stricto" for the Asian ''H. erectus'', and "Homo erectus sensu lato" for the larger species comprising both the early African populations and the Asian populations. It is one of the earliest known members of the [[genus]] ''Homo'' and, although it is unclear what genetic influence ''H. ergaster'' had on later hominids, it is widely proposed to be the direct ancestor of such later hominids as ''Homo heidelbergensis'', ''Homo sapiens'', ''Homo neanderthalensis'', and Asian ''Homo erectus''.
  
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The binomial name was published in 1975 by [[Colin Groves|Groves]] and [[Vratislav Mazák|Mazák]]. The second part, "ergaster", is derived from the Ancient Greek {{lang|grc|''ἐργαστήρ''}} "workman", in reference to the comparatively advanced [[lithic technology]] developed by the species, introducing the [[Acheulean]] industry.
  
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separate species, Homo ergaster, or it is seen as a subspecies of H. erectus, Homo erectus ergaster (Mayr 2001).
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Just as various periods are recognized in the geological history of the Earth (eg., [[Cambrian]], [[Ordovician]], and other stages), and in the history of an individual ([[egg]], [[birth]], [[child]], youth, adult, [[death]]), various stages are recognized in the [[evolution]]ary history of humanity, with primitive humans being the foundation for later stages. However, despite the considerable skulls and partial skeletons of ''H. ergaster'' and ''H. erectus'' that have been unearthed in [[Africa]], [[Asia]], and eastern [[Europe]], researchers remain uncertain the place these [[Hominidae|hominids]] are exactly aligned in the human evolutionary lineage and even whether later findings in Asia are the same species as those attributed to earlier specimens in Africa.
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Asian species distinct from African ergaster
 
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It is one of the earliest members of the genus Homo
 
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ancestral to, or sharing a common ancestor with, Homo erectus
 
  
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. ergaster and H. erectus are still usually defined as distinct African and Asian populations of larger species H. erectus.
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==Overview==
  
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lived in eastern and southern Africa during the early Pleistocene, between 1.8 million and 1.3 million years ago
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The earliest delineated member of the genus ''Homo'' is ''[[Homo habilis|H. habilis]]'',  which lived from 2.33 to 1.44 million years ago, although some authorities do not consider it should be included in  ''Homo'', considering it more worthy, for example, to be retained in ''[[Australopithecus]]'' (Wood and Richmond 2000). ''[[Homo habilis]]'' is generally accepted as the putative ancestor of the genus ''[[Homo]]'' (Wood and Collard 2001) and often of ''H. ergaster'' most directly.  ''H. habilis'' and ''H. ergaster'' coexisted for 200,000-300,000 years, possibly indicating that these species diverged from a common ancestor (Urquhard 2007). ''H. ergaster'' is believed to have diverged from the lineage of ''H. habilis'' between 1.9 and 1.8 million years ago.
  
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Some call H. ergaster the direct African ancestor at H. erectus, proposing that H. ergaster emigrated out of Africa and into Asia, branching into a distinct species.[6] 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 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.)
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''Homo ergaster'' (or ''[[Homo erectus]]'') first appears in the fossil record from around 1.8 million years ago. Fossils identified as ''H. ergaster'' disappeared from the fossil record about 1.3 to 1.4 million years ago. However, ''Home erectus'', either as synonymous with ''H. ergaster'' or as a distinct Asian population or species, survived until about 143,000 years ago. ''Homo erectus'' was apparently very successful, considering that fossils of the species have been found in [[Asia]] ([[Indonesia]], [[India]], [[Sri Lanka]], and [[China]]), and [[Georgia]] (Caucasus region of Europe), as well as in Africa as ''H. ergaster''.  
  
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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 and Asian Homo erectus
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There is also support for the idea that that the numerous distinct species being recognized in the fossil record, such as ''H. erectus'' and ''H. habilis'', are actually just morphological variation among members of a single evolving lineage among early members of the ''Homo'' genus, and that perhaps even only one species with a lot of variability emerged from Africa (Wilford 2013; Watson 2013; Lordkipanidze et al. 2013).
  
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[[File:Homo ergaster2.jpg|thumb|250px|''Homo ergaster ''skull reconstruction of the ''[[Turkana Boy|Turkana Boy/Nariokotome Boy]]'' from Lake Turkana, Kenya.  Museum of Man, [[San Diego, California|San Diego]].]]
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It is unclear what genetic influence ''H. ergaster'' had on later hominids. Recent genetic analysis has generally supported the [[Recent African origin of modern humans|Out-of-Africa hypothesis]], and this may designate ''H. ergaster'' the role of ancestor to all later hominids (Hazarika 2007). In general, ''H. ergaster'' is widely considered to be the direct ancestor of later hominids such as ''[[Homo heidelbergensis]]'', ''Homo sapiens'', [[Neanderthal]]s, [[Denisovan]]s, and even Asian ''Homo erectus''.  
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''[[Homo habilis]]'' is generally accepted as the putative ancestor of the genus ''[[Homo]]'',<ref name="Wood2001" /> 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.<ref>{{cite book|last=Urquhart|first=James|title=Finds Test Human Origins Theory|website=news.bbc.co.uk|date=8 August 2007}}</ref>
 
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It is unclear what genetic influence ''H. ergaster'' had on later hominids. Recent genetic analysis has generally supported the [[Recent African origin of modern humans|Out-of-Africa hypothesis]], and this may designate ''H. ergaster'' the role of ancestor to all later hominids.<ref name="Hazarika2007" />
 
  
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===Origin and extinction===
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Modern human beings, Neanderthals, and Denisovans are believed to have shared a common ancestor about 400,000 to 500,000 years ago (Marshall 2013; Green et al. 2010). One theory is that these three groups all descended from ''Homo heidelbergenesis'', which lived between 600,000 to 250,000 years ago (Marshall 2013) (other species suggested as ancestral are ''H. rhodesiensis'' and ''H. antecessor''). One branch of ''H. heidelbergenesis'' are theorized to have left Africa about 400,000 years ago and split shortly thereafter to become Neanderthals, which settled in West Asia and Europe, and Denisovans, which settled farther to the east (NG 2013).  
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''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 from Africa and fathered ''H. erectus'' diverged from the lineage of ''H. ergaster'' almost immediately after this. These early descendants of ''H. habilis'' may have been discovered in [[Homo georgicus|Dmanisi]], [[Georgia (country)|Georgia]].<ref>{{cite news|last=Tattersall|first=Ian|title=An Evolutionary Frameworks for the Acquisition of Symbolic Cognition by ''Homo sapiens''|year=2008}}</ref> ''H. ergaster'' remained [[punctuated equilibrium|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.
 
  
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or it is seen as a subspecies of ''H. erectus,'' ''Homo erectus ergaster'' (Mayr 2001). Although ''H. erectus'' was originally believed to have disappeared roughly 400,000 years ago, the dating of deposits thought to contain ''H. erectus'' [[fossil]]s in Java were placed at only 50,000 years ago, meaning that at least one population would have been a contemporary of modern [[human]]s (Smithsonian 2007a).
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Neanderthals are considered to have lived from perhaps 400,000 years ago, with their appearance in the European fossil record variously put at 200,000 (Zimmer 2013) to 400,000 years ago (Green et al. 2010). Neanderthals disappeared from the fossil record about 30,000 years ago. Based on the DNA sequences for the nuclear genome of Neanderthals and modern humans, the population split between Neanderthals and modern humans took place 270,000 to 440,000 years ago (Reich et al. 2010).
  
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*There is still disagreement on the subject of the classification, ancestry, and progeny of ''H. erectus'', with two major alternative classifications: ''erectus'' may be another name for ''[[Homo ergaster]]'', and therefore the direct ancestor of later hominids such as ''[[Homo heidelbergensis]]'', ''[[Homo neanderthalensis]]'', and ''[[Homo sapiens]]''; or it may be an [[Asia]]n species distinct from African ''ergaster''.<ref name="Hazarika"/><ref>See overview of theories on [[human evolution]].</ref><ref>Klein, R. (1999). ''The Human Career: Human Biological and Cultural Origins''. Chicago: University of Chicago Press, ISBN 0226439631.</ref>
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Archaic ''Homo sapiens'', the forerunner of anatomically modern humans, appeared between 400,000 and 250,000 years ago (O'Neil 2013). Anatomically modern humans are believed to have evolved from archaic ''Homo sapiens'' in the Middle Paleolithic, about 200,000 to 130,000 years ago (SA 2005; NG 2013), then migrated out of Africa some 50,000 to 100,000 years ago (Recent African Ancestory Theory) and replaced local populations of ''H. erectus'', ''H. floresiensis'', ''H. heidelbergenesis'', and the Denisovan and Neanderthal populations.
  
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* Some palaeoanthropologists consider ''H. ergaster'' to be simply the African variety of ''H. erectus''.  This leads to the use of the term "''Homo erectus [[sensu stricto]]''" for the Asian ''H. erectus'', and "''Homo erectus [[sensu lato]]''" for the larger species comprising both the early African populations (''H. ergaster'') and the Asian populations. (see numerous references)
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==Discovery and fossil record==
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The [[South Africa]]n [[paleontologist|palaeontologist]] [[John T. Robinson]] first discovered a mandible of a new hominid in southern Africa in 1949; he named the species ''[[Telanthropus capensis]]'', although it is now recognized as a member of ''Homo ergaster'' (Wood and Collard 2001). The name was first applied by [[Colin Groves]] and [[Vratislav Mazák]] to [[KNM ER 992|KNM-ER 992]], a mandible discovered near Lake Rudolf (now Lake Turkana), [[Kenya]] in 1975, which became the [[type specimen|type-specimen]] of the species.  
  
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It is one of the earliest members of the genus ''[[Homo]]'', possibly ancestral to, or sharing a common ancestor with, ''[[Homo erectus]]''.<ref>{{cite journal | title = Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya | author = F. Spoor, M. G. Leakey, P. N. Gathogo, F. H. Brown, S. C. Antón, I. McDougall, C. Kiarie, F. K. Manthi & L. N. Leakey | journal = Nature | issue = 7154| pages = 688–691 | date = 9 August 2007 | doi = 10.1038/nature05986 | volume = 448 | pmid = 17687323|bibcode = 2007Natur.448..688S }}</ref> Some paleoanthropologists consider ''H. ergaster'' to be simply the African variety of ''H. erectus''; this leads to the use of the term "''Homo erectus [[sensu stricto]]''" for the Asian ''H. erectus'', and "''Homo erectus [[sensu lato]]''" for the larger species comprising both the early African populations (''H. ergaster'') and the Asian populations.<ref>Antón, S. C. (2003), Natural history of ''Homo erectus''. Am. J. Phys. Anthropol., 122: 126–170. {{doi|10.1002/ajpa.10399}} "By the 1980s, the growing numbers of ''H. erectus'' specimens, particularly in Africa, led to the realization that Asian ''H. erectus'' (''H. erectus sensu stricto''), once thought so primitive, was in fact more derived than its African counterparts. These morphological differences were interpreted by some as evidence that more than one species might be included in ''H. erectus sensu lato'' (e.g., Stringer, 1984; Andrews, 1984; Tattersall, 1986; Wood, 1984, 1991a, b; Schwartz and Tattersall, 2000)." ... "Unlike the European lineage, in my opinion, the taxonomic issues surrounding Asian vs. African ''H. erectus'' are more intractable. The issue was most pointedly addressed with the naming of ''H. ergaster'' on the basis of the type mandible KNM-ER 992, but also including the partial skeleton and isolated teeth of KNM-ER 803 among other Koobi Fora remains (Groves and Mazak, 1975). Recently, this specific name was applied to most early African and Georgian ''H. erectus'' in recognition of the less-derived nature of these remains vis à vis conditions in Asian ''H. erectus'' (see Wood, 1991a, p. 268; Gabunia et al., 2000a). It should be noted, however, that at least portions of the paratype of ''H. ergaster'' (e.g., KNM-ER 1805) are not included in most current conceptions of that taxon. The ''H. ergaster'' question remains famously unresolved (e.g., Stringer, 1984; Tattersall, 1986; Wood, 1991a, 1994; Rightmire, 1998b; Gabunia et al., 2000a; Schwartz and Tattersall, 2000), in no small part because the original diagnosis provided no comparison with the Asian fossil record."</ref>
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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 [[paleoanthropologist]]s [[Kamoya Kimeu]] and [[Alan Walker (anthropologist)|Alan Walker]]. They nicknamed the 1.6-million-year-old specimen "Turkana Boy."
  
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The binomial name was published in 1975 by [[Colin Groves|Groves]] and [[Vratislav Mazák|Mazák]]. The second part, "ergaster", is derived from the Ancient Greek {{lang|grc|''ἐργαστήρ''}} "workman", in reference to the comparatively advanced [[lithic technology]] developed by the species, introducing the [[Acheulean]] industry.
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Remains have been found in [[Tanzania]], [[Ethiopia]], [[Kenya]], and [[South Africa]].
  
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Notes:
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''H. ergaster'' remained [[punctuated equilibrium|stable]] for about 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.
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*'''''Homo erectus''''' ("upright man") is an [[extinction|extinct]] species of the genus ''Homo.'' It lived from about 1.8 million years ago (mya) to 50-70,000 years ago. However, often the early phase, from 1.8 to 1.25 (or 1.6) mya, is considered to be a separate species, ''[[Homo ergaster]],'' or it is seen as a subspecies of ''H. erectus,'' ''Homo erectus ergaster'' (Mayr 2001). Although ''H. erectus'' was originally believed to have disappeared roughly 400,000 years ago, the dating of deposits thought to contain ''H. erectus'' [[fossil]]s in Java were placed at only 50,000 years ago, meaning that at least one population would have been a contemporary of modern [[human]]s (Smithsonian 2007a).
 
  
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There is still disagreement on the subject of the classification, ancestry, and progeny of ''H. erectus'', with two major alternative classifications: ''erectus'' may be another name for ''[[Homo ergaster]]'', and therefore the direct ancestor of later hominids such as ''[[Homo heidelbergensis]]'', ''[[Homo neanderthalensis]]'', and ''[[Homo sapiens]]''; or it may be an [[Asia]]n species distinct from African ''ergaster''.<ref name="Hazarika"/><ref>See overview of theories on [[human evolution]].</ref><ref>Klein, R. (1999). ''The Human Career: Human Biological and Cultural Origins''. Chicago: University of Chicago Press, ISBN 0226439631.</ref>
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==Description and classification ==
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[[File:Homo ergaster2.jpg|thumb|250px|''Homo ergaster ''skull reconstruction of the ''[[Turkana Boy|Turkana Boy/Nariokotome Boy]]'' from Lake Turkana, Kenya.  Museum of Man, [[San Diego, California|San Diego]].]]
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The differences between the early populations of ''H. erectus''/''H. ergaster'' in Africa and the later populations found in Asia, Europe, and Africa are substantial enough for the separation by many researchers into the early African ''H. ergaster'' and the mainly Asian populations ''H. erectus'' (Smithsonian 2014).
  
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Some palaeoanthropologists consider ''H. ergaster'' to be simply the African variety of ''H. erectus''.  This leads to the use of the term "''Homo erectus [[sensu stricto]]''" for the Asian ''H. erectus'', and "''Homo erectus [[sensu lato]]''" for the larger species comprising both the early African populations (''H. ergaster'') and the Asian populations.<ref>{{cite journal|author=Antón, S. C. |year=2003|title=Natural history of Homo erectus|journal= Am. J. Phys. Anthropol.|volume=122|pages=126–170|doi=10.1002/ajpa.10399|quote=By the 1980s, the growing numbers of H. erectus specimens, particularly in Africa, led to the realization that Asian H. erectus (H. erectus sensu stricto), once thought so primitive, was in fact more derived than its African counterparts. These morphological differences were interpreted by some as evidence that more than one species might be included in H. erectus sensu lato (e.g., Stringer, 1984; Andrews, 1984; Tattersall, 1986; Wood, 1984, 1991a, b; Schwartz and Tattersall, 2000) ... Unlike the European lineage, in my opinion, the taxonomic issues surrounding Asian vs. African H. erectus are more intractable. The issue was most pointedly addressed with the naming of H. ergaster on the basis of the type mandible KNM-ER 992, but also including the partial skeleton and isolated teeth of KNM-ER 803 among other Koobi Fora remains (Groves and Mazak, 1975). Recently, this specific name was applied to most early African and Georgian H. erectus in recognition of the less-derived nature of these remains vis à vis conditions in Asian H. erectus (see Wood, 1991a, p. 268; Gabunia et al., 2000a). It should be noted, however, that at least portions of the paratype of H. ergaster (e.g., KNM-ER 1805) are not included in most current conceptions of that taxon. The H. ergaster question remains famously unresolved (e.g., Stringer, 1984; Tattersall, 1986; Wood, 1991a, 1994; Rightmire, 1998b; Gabunia et al., 2000a; Schwartz and Tattersall, 2000), in no small part because the original diagnosis provided no comparison with the Asian fossil record}}</ref><ref>{{cite doi|10.1537/ase.061203}}</ref>
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''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]] (McHenry 1994), a smaller, more orthognathous(less protrusive) face, a smaller dental arcade, and a larger [[cranial capacity]] (700–900&nbsp;cm³ in earlier ''ergaster''-[[Biological specimen|specimen]]s, and 900-1100 in later specimens) (Hazarika 2007).
  
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*Fossil findings of early hominids is often fragmentary and inferences speculative, and although fossils of ''Homo erectus'' are much more common and complete than those of ''[[Homo habilis]],'' researchers are not even sure into how many species the fossils can be placed. Nonetheless, it is clear that ''Homo erectus'' was a major stage in the history of [[human evolution]]. Just as in the stage-by-stage development of individuals (egg, baby, child, adolescent, adult) and the history of life on Earth ([[Precambrian]], [[Cambrian]], [[Ordovician]], etc.), ''Homo erectus'' served as a foundation for subsequent stages, and it is considered to have given rise to [[Neandertal]]s and [[Homo sapiens]] (Mayr 2001). ''H. erectus'' is thought to have been the first human ancestor to walk truly upright.
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Many [[paleoanthropologist]]s still debate the definition of ''H. ergaster'' with ''H. erectus'' as separate species. Some call ''H. ergaster'' the direct African ancestor at ''H. erectus'', proposing that ''H. ergaster'' emigrated out of Africa and into [[Asia]], branching into a distinct species (Tattersall and Schwartz 2001). Mayr (2001) notes ''Homo ergaster'' can be seen as a separate species or as a subspecies of ''H. erectus'', ''Homo erectus ergaster''. 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 [[Asia]]n populations of  larger species ''H. erectus''. The view of palaeoanthropologists who consider ''H. ergaster'' to be simply the African variety of ''H. erectus'' has led to the use of the term "''Homo erectus [[sensu stricto]]''" for the Asian ''H. erectus'', and "''Homo erectus [[sensu lato]]''" for the larger species comprising both the early African populations (''H. ergaster'') and the Asian populations (Antón 2003).
  
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*''Homo erectus'' was apparently very successful, considering that fossils of the species have been found in [[Africa]], [[Asia]] ([[Indonesia]] and [[China]]), and [[Georgia]] (Caucasus region of Europe)(Mayr 2001). It is considered to be the first hominid to spread out of Africa. The differences between the early populations of ''H. erectus'' in Africa and the later populations found in Asia, Europe, and Africa are substantial enough for the separation by many researchers into the early African ''H. ergaster'' and the mainly Asian populations ''H. erectus'' (Smithsonian 2007b).
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==Social/cultural aspects==
  
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* The first fossils of ''Homo erectus'' were discovered by Dutch physician [[Eugene Dubois]] in
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===Use of tools===
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1891 on the [[Indonesia]]n island of [[Java]]. He originally gave the material the name ''Pithecanthropus erectus'' based on its morphology that he considered to be intermediate between that of humans and apes. A famous example of ''Homo erectus'' is [[Peking Man]], unearthed in China.  
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''Homo ergaster'' appears to have used more diverse and sophisticated [[stone tool]]s than its predecessor, ''[[Homo habilis]]''.
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''H. ergaster'' refined the inherited [[Oldowan]],  developing the first [[Acheulean]] bifacial axes (Beck et al. 1999). While the use of Acheulean tools began around 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.
  
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* Mayr (2001) notes that ''H. erectus'' existed without major change for at least one million years.
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===Sociality===
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Sexual dimorphism in ''H. ergaster'' is greatly reduced from its Australopithecine ancestors (around 20% according to McHenry 1994), but still greater than dimorphism in modern humans. This diminished dimorphism is speculated to be a sign of reduced competition for mates between males (Gray 2010), which also may correspond to the more modern social practices of ''ergaster''.
  
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==Overview==
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Not only was ''H. ergaster'' like modern humans in body, but also more in organization 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 (Goren-Inbar et al. 2004), as well as every other hominin sharing a common ancestor with ''ergaster''. The social organization of ''H. ergaster'' probably resembled that of modern [[hunter-gatherer]] societies. The reduced competition among males and dimorphism also coincided with an increase in brain size and efficiency of stone tools.
  
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The earliest delineated member of the genus ''Homo'' is ''[[Homo habilis|H. habilis]]'', which lived from 2.33 to 1.44 million years ago, although some authorities do not consider it should be included in  ''Homo'', considering it more worthy, for example, to be retained in ''[[Australopithecus]]'' (Wood and Richmond 2000). ''[[Homo erectus]]'' is considered to have arrived around 1.8 million years ago, with fossils supporting its existence to 143,000 years ago. ''Homo ergaster'' is another early ''Homo'' species that has been delineated, and traced to about 1.8 to 1.3 million years ago. ''H. ergaster'' is possibly ancestral to or shares a common ancestor with ''H. erectus''; it is widely considered to be the direct ancestor of later hominids such as ''[[Homo heidelbergensis]]'', ''Homo sapiens'', [[Neanderthal]]s, [[Denisovan]]s, and even Asian ''Homo erectus''.  ''Homo erectus'' and ''H. ergaster'' were the first of the hominina known to leave [[Africa]]. For example, ''H. erectus'' is known to have spread as far as Georgia, India, Sri Lanka, China and Java.
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===Linguistic use===
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According to the BBC series ''[[Walking With Cavemen]]'', ''Homo ergaster'' was probably the first [[hominid]] to use "what we would recognize as a human voice," though its symbolic cognition was probably somewhat limited compared to modern humans.
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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 (country)|Georgia]] some 300,000 years older than those of Turkana Boy are well within the normal human range (Bower 2006). 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 (Wong 2003). 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.
  
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There is also support for the idea that that the numerous distinct species being recognized in the fossil record, such as ''H. erectus'' and ''H. habilis'', are actually just morphological variation among members of a single evolving lineage among early members of the ''Homo'' genus, and that perhaps even only one species with a lot of variability emerged from Africa (Wilford 2013; Watson 2013; Lordkipanidze et al. 2013).
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==References==
  
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Modern human beings, Neanderthals, and Denisovans are believed to have shared a common ancestor about 400,000 years ago (Marshall 2013). One theory is that these three groups all descended from ''Homo heidelbergenesis'', which lived between 600,000 to 250,000 years ago (Marshall 2013) (other species suggested as ancestral are ''H. rhodesiensis'' and ''H. antecessor''). One branch of ''H. heidelbergenesis'' are theorized to have left Africa about 300,000 to 400,000 years ago and split shortly thereafter to become Neanderthals, which settled in West Asia and Europe, and Denisovans, which settled farther to the east (NG 2013).  
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* Antón, S. C. 2003. Natural history of ''Homo erectus''. ''Am. J. Phys. Anthropol.'' 122: 126–170.
  
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Neanderthals are considered to have lived from at least 230,000 years ago. Neanderthals disappeared from the fossil record about 30,000 years ago. Based on the DNA sequences for the nuclear genome of Neanderthals and modern humans, the population split between Neanderthals and modern humans took place 270,000 to 440,000 years ago (Reich et al. 2010).
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* Beck, R. B., L. Black, L. S. Krieger, P. C. Naylor, and D. Ibo Shabaka. 1999. ''World History: Patterns of Interaction''. Evanston, IL: McDougal Littell. ISBN 039587274X.
  
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Archaic ''Homo sapiens'', the forerunner of anatomically modern humans, appeared between 400,000 and 250,000 years ago (O'Neil 2013). Anatomically modern humans are believed to have evolved from archaic ''Homo sapiens'' in the Middle Paleolithic, about 200,000 to 130,000 years ago (SA 2005; NG 2013), then migrated out of Africa some 50,000 to 100,000 years ago (Recent African Ancestory Theory) and replaced local populations of ''H. erectus'', ''H. floresiensis'', ''H. heidelbergenesis'', and the Denisovan and Neanderthal populations.  
+
* Bower, B. 2006. Evolutionary back story: Thoroughly modern spine supported human ancestor. ''Science News Online'' 169(18): 275.  
  
−
The transition to behavioral modernity for ''Homo sapiens'' with the development of symbolic culture, language, and specialized lithic technology happened around 50,000 years ago according to many anthropologists (Mellars 2006), although some suggest a gradual change in behavior over a longer time span (Mcbrearty and Brooks 2000). Until about 50,000 to 40,000 years ago, the use of stone tools seems to have progressed stepwise: Each phase (''habilis'', ''ergaster'', and neanderthal) started at a higher level than the previous one, but once that phase had started, further development was slow. After 50,000 years ago, in what Jared Diamond, author of ''The Third Chimpanzee'', and other anthropologists characterize as a "Great Leap Forward," human culture apparently started to change at much greater speed: "Modern" humans started to bury their dead carefully, made clothing out of hides, developed sophisticated hunting techniques (such as pitfall traps, or driving animals to fall off cliffs), and made cave paintings. This speed-up of cultural change seems connected with the arrival of modern humans, ''Homo sapiens sapiens''. Additionally, human culture began to become more technologically advanced, in that different populations of humans begin to create novelty in existing technologies. Artifacts such as fish hooks, buttons, and bone needles begin to show signs of variation among different population of humans, something what had not been seen in human cultures prior to 50,000 BP.
+
* Deacon, T. 1998. ''The Symbolic Species: The Co-evolution of Language and the Brain''. W.W. Norton. ISBN 0393038386.  
  
−
The Denisovans are not well delineated anatomically, given the very limited fossils found. The first fossils were discovered in 2008, when a small bone fragment of a finger was found. Two teeth were subsequently found. The lack of fossils has made anatomical representations of the group difficult. However, the DNA was preserved and was able to be extracted and has yielded excellent genetic analysis. As noted in a 2013 article in the ''Dartmouth Undergraduate Journal of Science'', "Although Denisovans are thus far only represented by one finger bone and two teeth, they are currently the most well-known archaic human genetically – including Neanderthals of which there are hundreds of fossil records" (DUJS 2013). As a result, it was found that the Denisovans appear to be a unique group that shares a common origin with Neanderthals. DNA analysis further revealed that the Denisovans lived among and interbred with the ancestors of some present-day modern humans, with up to 6% of the DNA of [[Melanesian]]s and [[Australia]]n [[Aborigines]] deriving from Denisovans (Zimmer 2010; Callaway 2011).  
+
* Goren-Inbar, N., N. Alperson, M. E. Kislev, O. Simchoni, Y. Melamed, A. Ben-Nun, and E. Werker. 2004. Evidence of hominin control of fire at Gesher Benot Ya 'aqov, Israel. ''Science'' 304(5671): 725–727. PMID 15118160.  
  
−
In 2013, [[mitochondria]]l DNA was extracted from a 300,000- to 400,000-year-old sliver of hominin femur bone from [[Spain]], which had been seen as either Neanderthal or ''[[Homo heidelbergensis]]''. An almost complete mitochondrial genome was retrieved, the oldest human DNA sequenced. The DNA surprising yielded ancestral Denisonian DNA (Callaway 2013; Gibbons 2013).
+
* Gray, P. B. 2010. ''The Evolution and Endocrinology of Human Behavior: A Focus on Sex Differences and Reproduction''. Cambridge, UK: Cambridge University Press. ISBN 9780521705103.  
  
 +
* Hazarika, M. 2007. [http://www.himalayanlanguages.org/files/hazarika/Manjil%20Hazarika%20EAA.pdf ''Homo erectus/ergaster'' and Out of Africa: Recent Developments in Paleoanthropology and Prehistoric Archaeology]. ''European Anthropological Association Summer School eBook 1'': 35-41. Retrieved January 22, 2014.
  
−
==Discovery and representative fossils==
+
* Leakey, R., and R. Lewin. 1992. ''Origins Reconsidered: In Search of What Makes Us Human''. Doubleday. ISBN 0385412649.
−
The [[South Africa]]n [[paleontologist|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''.<ref name="Wood2001">{{cite journal|last=Wood|first=Bernard, and Mark Collard|title=The Meaning of ''Homo''|journal=Ludus Vitalis|volume=9|issue=15|year=2001|pages=63–74}}</ref> The name was first applied by [[Colin Groves]] and [[Vratislav Mazák]] to [[KNM ER 992|KNM-ER 992]], a mandible discovered near Lake Rudolf (now Lake Turkana), [[Kenya]] in 1975, which became the [[type specimen|type-specimen]] of the species. The most complete skeleton of ''H. ergaster'' (and one of the most complete extinct hominids to date), [[Turkana Boy|KNM-WT 15000]], was discovered at Lake Turkana, Kenya, in 1984 by [[paleoanthropologist]]s [[Kamoya Kimeu]] and [[Alan Walker (anthropologist)|Alan Walker]]. They nicknamed the 1.6-million-year-old specimen "Turkana Boy".
 
  
−
==Classification and special distinction==
+
* Lordkipanidze, D., M. S. Ponce de León, A. Margvelashvili, et al. 2013. [http://www.sciencemag.org/content/342/6156/326 A complete skull from Dmanisi, Georgia, and the evolutionary biology of early ''Homo'']. ''Science'' 342(6156): 326-331. Retrieved January 22, 2014.
−
Many [[paleoanthropologist]]s still debate the definition of ''H. ergaster'' with ''H. erectus'' as separate species. Some call ''H. ergaster'' the direct African ancestor at ''H. erectus'', proposing that ''H. ergaster'' emigrated out of Africa and into [[Asia]], branching into a distinct species.<ref>{{cite book|last=Tattersall|first=Ian and Jeffrey Schwartz|title=Extinct Humans|year=2001|isbn=0-8133-3482-9|location=Boulder, Colorado|publisher=Westview/Perseus}}</ref> 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 [[Asia]]n populations of  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]],<ref name="McHenry1994">{{cite news|last=McHenry|first=Henry M.|title=Behavioral ecological implications of early hominid body size|year=1994|publisher=Academic Press Limited}}</ref> a smaller, more orthognathous(less protrusive) face, a smaller dental arcade, and a larger [[cranial capacity]] (700–900&nbsp;cm³ in earlier ''ergaster''-[[Biological specimen|specimen]]s, and 900-1100 in later specimens).<ref name="Hazarika2007" /> It is estimated that male ''H. ergaster'' stood 1.89 meters (6&nbsp;ft 2 in) tall{{Citation needed|date=February 2010}}. Remains have been found in [[Tanzania]], [[Ethiopia]], [[Kenya]], and [[South Africa]].
+
* Marshall, M. 2013. [http://www.newscientist.com/article/dn24603-mystery-human-species-emerges-from-denisovan-genome.html#.UqyGK-JFP6o Mystery human species emerges from Denisovan genome]. ''New Scientist'' November 19, 2013. Retrieved January 22, 2014..
  
−
==Divergence==
+
* Mayr, E. 2001. ''What evolution is''. New York: Basic Books. ISBN 0465044255.
−
[[File:Homo ergaster2.jpg|thumb|250px|''Homo ergaster ''skull reconstruction of the ''[[Turkana Boy|Turkana Boy/Nariokotome Boy]]'' from Lake Turkana, Kenya. Museum of Man, [[San Diego, California|San Diego]].]]
 
−
''[[Homo habilis]]'' is generally accepted as the putative ancestor of the genus ''[[Homo]]'',<ref name="Wood2001" /> 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.<ref>{{cite book|last=Urquhart|first=James|title=Finds Test Human Origins Theory|website=news.bbc.co.uk|date=8 August 2007}}</ref>
 
−
It is unclear what genetic influence ''H. ergaster'' had on later hominids. Recent genetic analysis has generally supported the [[Recent African origin of modern humans|Out-of-Africa hypothesis]], and this may designate ''H. ergaster'' the role of ancestor to all later hominids.<ref name="Hazarika2007" />
 
  
−
===Origin and extinction===
+
* McHenry, H. 1994. Behavioral ecological implications of early hominid body size. ''Journal of Human Evolution'' 27 (no. 1/3): 77.
−
''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 from Africa and fathered ''H. erectus'' diverged from the lineage of ''H. ergaster'' almost immediately after this. These early descendants of ''H. habilis'' may have been discovered in [[Homo georgicus|Dmanisi]], [[Georgia (country)|Georgia]].<ref>{{cite news|last=Tattersall|first=Ian|title=An Evolutionary Frameworks for the Acquisition of Symbolic Cognition by ''Homo sapiens''|year=2008}}</ref> ''H. ergaster'' remained [[punctuated equilibrium|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.
 
  
−
==Use of tools==
+
* National Geographic (NG). 2013. [https://genographic.nationalgeographic.com/denisovan/ Why am I denisovan]. ''The Genographic Project''.  January 22, 2014.
−
''Homo ergaster'' used more diverse and sophisticated [[stone tool]]s than its predecessor, ''[[Homo habilis]]''.
 
−
''H. ergaster'' refined the inherited [[Oldowan]]  developing the first [[Acheulean]] bifacial axes:<ref>{{cite book | last = Beck | first = Roger B. | authorlink = | coauthors = Linda Black, Larry S. Krieger, Phillip C. Naylor, Dahia Ibo Shabaka, | title = World History: Patterns of Interaction | publisher = McDougal Littell | year = 1999 | location = Evanston, IL | pages = | url = | doi = | id = | isbn = 0-395-87274-X }}</ref> 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.{{Citation needed|date=April 2010}}
 
  
−
==Sociality==
+
* O'Neil, D. 2013. [http://anthro.palomar.edu/homo2/mod_homo_4.htm Evolution's past is modern human's present]. "Behavioral Sciences Department", Palomar College, San Marcos, California. Retrieved January 22, 2014.
−
Sexual dimorphism in ''H. ergaster'' is greatly reduced from its australopithecine ancestors (around 20%<ref name="McHenry1994" />), but still greater than dimorphism in modern humans. This diminished dimorphism is speculated to be a sign of reduced competition for mates between males,<ref>{{cite article | last = Gray | first= Peter B. | title = The Evolution and Endocrinology of Human Behavior: a Focus on Sex Differences and Reproduction | publisher = Cambridge University Press | year = 2010 | location = Cambridge, UK | pages = 277-292 | isbn = 978-0-521-70510-3}}</ref> which may also correspond to the more modern social practices of ''ergaster'' {{Citation needed|date=July 2011}}.
 
−
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,<ref>{{cite journal|doi=10.1126/science.1095443|last=Goren-Inbar|first=Naama, et al.|last2=Alperson|first2=N|last3=Kislev|first3=ME|last4=Simchoni|first4=O|last5=Melamed|first5=Y|last6=Ben-Nun|first6=A|last7=Werker|first7=E|title=Evidence of Hominin Control of Fire at Gesher Benot Ya 'aqov, Israel|date=30 April 2004|journal=Science|volume=304|issue=5671|pages=725–727|pmid=15118160|bibcode = 2004Sci...304..725G }}</ref> 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{{Dubious|date=June 2011}}, 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.
+
* Reich, D., R. E. Green, M. Kircher, J. Krause, et al. 2010. [http://www.nature.com/nature/journal/v468/n7327/full/nature09710.html?pagewanted=all Genetic history of an archaic hominin group from Denisova Cave in Siberia]. "Nature" 468(7327): 1053–1060. PMID 21179161. Retrieved January 22, 2014.
  
−
===Linguistic use===
+
* Reich, D., N. Patterson, M. Kircher, et. al. 2011. [http://www.cell.com/AJHG/retrieve/pii/S0002929711003958 Denisova admixture and the first modern human dispersals into Southeast Asia and Oceania]. ''The American Journal of Human Genetics'' 89: 516-28. PMID 21944045. Retrieved January 22, 2014.
−
According to the BBC series ''[[Walking With Cavemen]]'', ''Homo ergaster'' was probably the first [[hominid]] to use "what we would recognise as 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 (country)|Georgia]] some 300,000 years older than those of Turkana Boy are well within the normal human range.<ref>{{cite journal|author=Bruce Bower|title=Evolutionary Back Story: Thoroughly Modern Spine Supported Human Ancestor|journal=Science News Online|date=6 May 2006|volume=169| issue = 18|page=275}}</ref>
 
  
−
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<ref>{{cite journal|last=Wong|first=Kate|title=Stranger in a new land|journal=Scientific American|date=November 2003|bibcode=2003SciAm.289e..74W|volume=289|pages=74–83|doi=10.1038/scientificamerican1103-74|issue=5|pmid=14564816}}</ref> (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.
+
* Ruhlen, M. 1994. ''The Origin of Language: Tracing the Evolution of the Mother Tongue. New York: Wiley. ISBN 0471584266.
  
−
There is no archaeological evidence that ''Homo ergaster'' made use of symbolic thought (such as [[paleolithic art|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.{{Dubious|date=April 2010}}
+
* Scientific American (SA). 2005. [http://www.scientificamerican.com/article.cfm?id=fossil-reanalysis-pushes Fossil reanalysis pushes back origin of Homo sapiens]. "Scientific American " February 17, 2005. January 22, 2014.
  
−
==See also==
+
* Shreeve, J. 1995. ''The Neandertal Enigma: Solving the Mystery of Modern Human Origins''. Harper Perennial. ISBN 0670866385.
−
* ''[[Homo erectus]]''
 
−
* ''[[Homo georgicus]]''
 
−
* ''[[Homo habilis]]''
 
−
* ''[[Telanthropus capensis]]''
 
  
−
'''General:'''
+
* Smithsonian National Museum of Natural History. 2014. [http://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus ''Homo erectus'']. ''Smithsonian Institution''. January 22, 2014.
−
* [[List of fossil sites]]
 
−
* [[List of human evolution fossils]]
 
  
−
==Footnotes==
+
* Tattersall, I., and J. Schwartz. 2001. ''Extinct Humans''. Boulder, CO: Westview/Perseus. ISBN 0813334829.
−
{{Reflist|30em}}
 
  
−
==References==
+
* Urquhart, J. 2007. [http://news.bbc.co.uk/2/hi/science/nature/6937476.stm Finds test human origins theory]. ''BBC News'' August 8, 2007. Retrieved January 22, 2014.
−
*{{cite book|title=The Symbolic Species: The Co-evolution of Language and the Brain|last=Deacon|first=Terrence W.|year=1998|publisher=W.W. Norton & Company|isbn=0-393-03838-6}}
 
−
*{{cite book|title=Origins Reconsidered|first= Richard|last=Leakey|authorlink=Richard Leakey |url=http://books.google.com/?id=rGo8AAAACAAJ&dq=origins+reconsidered|isbn=0-385-41264-9|date=1992-09-01}}
 
−
* {{cite book |last=Ruhlen |first=Merritt|title=The origin of language: tracing the evolution of the mother tongue |publisher=Wiley |location=New York |year=1994 |pages= |isbn=0-471-58426-6 |oclc= |doi=}}
 
−
* {{cite book|last=Shreeve|first=James|title=The Neandertal Enigma: Solving the Mystery of Modern Human Origins|year=1995|publisher=Harper Perennial|isbn=0-670-86638-5}}
 
−
* {{cite book|last=Tattersall|first= Ian |coauthors=Jeffrey Schwartz|title=Extinct Humans|publisher= Westview Press|location=[[Boulder, Colorado|Boulder]] and Cumnor Hill|year=2000|isbn=0-8133-3482-9}}
 
−
* {{cite journal|last=Wood|first=Bernard|coauthor=Mark Collard|title=The Meaning of ''Homo''|journal=Ludus Vitalis|volume=9|year=2001}}
 
  
 +
* Watson, T. 2013. [http://www.usatoday.com/story/news/nation/2013/10/17/skull-sheds-light-human-species/2994613/ Skull discovery sheds light on human species]. ''USA Today'' October 17, 2013. Retrieved December 16, 2013.
  
 +
* Wilford, J. N. 2013. [http://www.nytimes.com/2013/10/18/science/fossil-skull-may-rewrite-humans-evolutionary-story.html?_r=0 Skull fossil suggests simpler human lineage.]] ''New York Times'' October 17, 2013. Retrieved December 16, 2013.
  
−
* Mayr, E. 2001. ''What evolution is''. New York: Basic Books. ISBN 0465044255.
+
* Wood, B. and B. G. Richmond. 2000. [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1468107/ Human evolution: Taxonomy and paleobiology]. ''Journal of Anatomy'' 197 (Pt 1): 19–60. PMID 10999270. Retrieved December 19, 2013.
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* Novaresio, P. 1996. ''The Explorers''. Stewart, Tabori & Chang. ISBN 155670495X.
 
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* Sawyer, G. J., and B. Maley. 2005. Neanderthal Reconstructed. ''Anat. Rec.'' (New Anat.) 283B: 23-31.
 
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* Smithsonian National Museum of Natural History. 2007a. [http://www.mnh.si.edu/anthro/humanorigins/ha/erec.html ''Homo erectus'']. ''Smithsonian Institution''. Retrieved March 4, 2007.
 
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* Smithsonian National Museum of Natural History. 2007b. [http://www.mnh.si.edu/anthro/humanorigins/ha/erg.html ''Homo ergaster'']. ''Smithsonian Institution''. Retrieved March 4, 2007.
 
  
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==External links==
+
* Wood, B., and M. Collard. 2001. The meaning of ''Homo''. ''Ludus Vitalis'' 9(15): 63–74.
  
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*[http://www.archaeologyinfo.com/homoergaster.htm Archaeology Info]
+
* Wong, K. 2003. Stranger in a new land. ''Scientific American'' 289: 74–83. PMID 14564816.  
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*[http://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus Smithsonian]
 
  
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<br>
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* Zimmer, C. 2010. Denisovans were Neanderthals' cousins, DNA analysis reveals. ''New York Times''  December 22, 2010.
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{{Human Evolution}}
 
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{{Prehistoric technology}}
 
  
 +
* Zimmer, C. 2013. Toe fossil provides complete Neanderthal genome. ''New York Times'' December 18, 2013.
  
  

Latest revision as of 17:25, 21 February 2014

Homo ergaster
Fossil range: Pleistocene, 1.8–1.3 Ma
↓
Skull KNM-ER 3733 discovered by Bernard Ngeneo in 1975 (Kenya)
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

Homo ergaster is an extinct hominin that lived in eastern and southern Africa from about 1.8 million years ago (mya) to about 1.3 mya. It is variously considered to be (1) a distinct species, perhaps ancestral to the Asian Homo erectus; (2) a subspecies of H. erectus, H. erectus ergaster; or (3) the African variety of H. erectus, with "Homo erectus sensu stricto" for the Asian H. erectus, and "Homo erectus sensu lato" for the larger species comprising both the early African populations and the Asian populations. It is one of the earliest known members of the genus Homo and, although it is unclear what genetic influence H. ergaster had on later hominids, it is widely proposed to be the direct ancestor of such later hominids as Homo heidelbergensis, Homo sapiens, Homo neanderthalensis, and Asian Homo erectus.

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.

Just as various periods are recognized in the geological history of the Earth (eg., Cambrian, Ordovician, and other stages), and in the history of an individual (egg, birth, child, youth, adult, death), various stages are recognized in the evolutionary history of humanity, with primitive humans being the foundation for later stages. However, despite the considerable skulls and partial skeletons of H. ergaster and H. erectus that have been unearthed in Africa, Asia, and eastern Europe, researchers remain uncertain the place these hominids are exactly aligned in the human evolutionary lineage and even whether later findings in Asia are the same species as those attributed to earlier specimens in Africa.

Overview

The earliest delineated member of the genus Homo is H. habilis, which lived from 2.33 to 1.44 million years ago, although some authorities do not consider it should be included in Homo, considering it more worthy, for example, to be retained in Australopithecus (Wood and Richmond 2000). Homo habilis is generally accepted as the putative ancestor of the genus Homo (Wood and Collard 2001) and often of H. ergaster most directly. H. habilis and H. ergaster coexisted for 200,000-300,000 years, possibly indicating that these species diverged from a common ancestor (Urquhard 2007). H. ergaster is believed to have diverged from the lineage of H. habilis between 1.9 and 1.8 million years ago.

Homo ergaster (or Homo erectus) first appears in the fossil record from around 1.8 million years ago. Fossils identified as H. ergaster disappeared from the fossil record about 1.3 to 1.4 million years ago. However, Home erectus, either as synonymous with H. ergaster or as a distinct Asian population or species, survived until about 143,000 years ago. Homo erectus was apparently very successful, considering that fossils of the species have been found in Asia (Indonesia, India, Sri Lanka, and China), and Georgia (Caucasus region of Europe), as well as in Africa as H. ergaster.

There is also support for the idea that that the numerous distinct species being recognized in the fossil record, such as H. erectus and H. habilis, are actually just morphological variation among members of a single evolving lineage among early members of the Homo genus, and that perhaps even only one species with a lot of variability emerged from Africa (Wilford 2013; Watson 2013; Lordkipanidze et al. 2013).

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 (Hazarika 2007). In general, H. ergaster is widely considered to be the direct ancestor of later hominids such as Homo heidelbergensis, Homo sapiens, Neanderthals, Denisovans, and even Asian Homo erectus.

Modern human beings, Neanderthals, and Denisovans are believed to have shared a common ancestor about 400,000 to 500,000 years ago (Marshall 2013; Green et al. 2010). One theory is that these three groups all descended from Homo heidelbergenesis, which lived between 600,000 to 250,000 years ago (Marshall 2013) (other species suggested as ancestral are H. rhodesiensis and H. antecessor). One branch of H. heidelbergenesis are theorized to have left Africa about 400,000 years ago and split shortly thereafter to become Neanderthals, which settled in West Asia and Europe, and Denisovans, which settled farther to the east (NG 2013).

Neanderthals are considered to have lived from perhaps 400,000 years ago, with their appearance in the European fossil record variously put at 200,000 (Zimmer 2013) to 400,000 years ago (Green et al. 2010). Neanderthals disappeared from the fossil record about 30,000 years ago. Based on the DNA sequences for the nuclear genome of Neanderthals and modern humans, the population split between Neanderthals and modern humans took place 270,000 to 440,000 years ago (Reich et al. 2010).

Archaic Homo sapiens, the forerunner of anatomically modern humans, appeared between 400,000 and 250,000 years ago (O'Neil 2013). Anatomically modern humans are believed to have evolved from archaic Homo sapiens in the Middle Paleolithic, about 200,000 to 130,000 years ago (SA 2005; NG 2013), then migrated out of Africa some 50,000 to 100,000 years ago (Recent African Ancestory Theory) and replaced local populations of H. erectus, H. floresiensis, H. heidelbergenesis, and the Denisovan and Neanderthal populations.

Discovery and fossil record

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, although it is now recognized as a member of Homo ergaster (Wood and Collard 2001). 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."

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

H. ergaster remained stable for about 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.

Description and classification

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

The differences between the early populations of H. erectus/H. ergaster in Africa and the later populations found in Asia, Europe, and Africa are substantial enough for the separation by many researchers into the early African H. ergaster and the mainly Asian populations H. erectus (Smithsonian 2014).

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 (McHenry 1994), a smaller, more orthognathous(less protrusive) face, a smaller dental arcade, and a larger cranial capacity (700–900 cm³ in earlier ergaster-specimens, and 900-1100 in later specimens) (Hazarika 2007).

Many paleoanthropologists still debate the definition of H. ergaster with H. erectus as separate species. Some call H. ergaster the direct African ancestor at H. erectus, proposing that H. ergaster emigrated out of Africa and into Asia, branching into a distinct species (Tattersall and Schwartz 2001). Mayr (2001) notes Homo ergaster can be seen as a separate species or as a subspecies of H. erectus, Homo erectus ergaster. 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 larger species H. erectus. The view of palaeoanthropologists who consider H. ergaster to be simply the African variety of H. erectus has led to the use of the term "Homo erectus sensu stricto" for the Asian H. erectus, and "Homo erectus sensu lato" for the larger species comprising both the early African populations (H. ergaster) and the Asian populations (Antón 2003).

Social/cultural aspects

Use of tools

Homo ergaster appears to have used more diverse and sophisticated stone tools than its predecessor, Homo habilis. H. ergaster refined the inherited Oldowan, developing the first Acheulean bifacial axes (Beck et al. 1999). While the use of Acheulean tools began around 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.

Sociality

Sexual dimorphism in H. ergaster is greatly reduced from its Australopithecine ancestors (around 20% according to McHenry 1994), but still greater than dimorphism in modern humans. This diminished dimorphism is speculated to be a sign of reduced competition for mates between males (Gray 2010), which also may correspond to the more modern social practices of ergaster.

Not only was H. ergaster like modern humans in body, but also more in organization 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 (Goren-Inbar et al. 2004), as well as every other hominin sharing a common ancestor with ergaster. The social organization of H. ergaster probably resembled that of modern hunter-gatherer societies. The reduced competition among males and dimorphism also coincided with an increase in brain size and efficiency of stone tools.

Linguistic use

According to the BBC series Walking With Cavemen, Homo ergaster was probably the first hominid to use "what we would recognize as 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 (Bower 2006). 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 (Wong 2003). 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.

References
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  • Antón, S. C. 2003. Natural history of Homo erectus. Am. J. Phys. Anthropol. 122: 126–170.
  • Beck, R. B., L. Black, L. S. Krieger, P. C. Naylor, and D. Ibo Shabaka. 1999. World History: Patterns of Interaction. Evanston, IL: McDougal Littell. ISBN 039587274X.
  • Bower, B. 2006. Evolutionary back story: Thoroughly modern spine supported human ancestor. Science News Online 169(18): 275.
  • Deacon, T. 1998. The Symbolic Species: The Co-evolution of Language and the Brain. W.W. Norton. ISBN 0393038386.
  • Goren-Inbar, N., N. Alperson, M. E. Kislev, O. Simchoni, Y. Melamed, A. Ben-Nun, and E. Werker. 2004. Evidence of hominin control of fire at Gesher Benot Ya 'aqov, Israel. Science 304(5671): 725–727. PMID 15118160.
  • Gray, P. B. 2010. The Evolution and Endocrinology of Human Behavior: A Focus on Sex Differences and Reproduction. Cambridge, UK: Cambridge University Press. ISBN 9780521705103.
  • Leakey, R., and R. Lewin. 1992. Origins Reconsidered: In Search of What Makes Us Human. Doubleday. ISBN 0385412649.
  • McHenry, H. 1994. Behavioral ecological implications of early hominid body size. Journal of Human Evolution 27 (no. 1/3): 77.
  • National Geographic (NG). 2013. Why am I denisovan. The Genographic Project. January 22, 2014.
  • Ruhlen, M. 1994. The Origin of Language: Tracing the Evolution of the Mother Tongue. New York: Wiley. ISBN 0471584266.
  • Shreeve, J. 1995. The Neandertal Enigma: Solving the Mystery of Modern Human Origins. Harper Perennial. ISBN 0670866385.
  • Smithsonian National Museum of Natural History. 2014. Homo erectus. Smithsonian Institution. January 22, 2014.
  • Tattersall, I., and J. Schwartz. 2001. Extinct Humans. Boulder, CO: Westview/Perseus. ISBN 0813334829.
  • Wood, B., and M. Collard. 2001. The meaning of Homo. Ludus Vitalis 9(15): 63–74.
  • Wong, K. 2003. Stranger in a new land. Scientific American 289: 74–83. PMID 14564816.
  • Zimmer, C. 2010. Denisovans were Neanderthals' cousins, DNA analysis reveals. New York Times December 22, 2010.
  • Zimmer, C. 2013. Toe fossil provides complete Neanderthal genome. New York Times December 18, 2013.


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