Athena Review Vol. 5, no. 1
Records of Life: Fossils as Original Sources
44. Homo erectus 1: Africa
Homo erectus
Homo erectus ("upright man") is an archaic human from the P
leistocene, with its earliest occurrence 2-1.8 million years ago. Fossils identified as Homo
erectus span most of the Pleistocene era, a period
which includes the transition to larger-brained hominids, a basic
evolution of tool manufacture and use, and the first widespread
movement of early human populations to distinct
environments. Homo erectus ranged further than any other hominid before
Homo sapiens, from Africa to Indonesia, China, Eurasia, and Western
Europe – and probably, at some intermediate points, back to Africa
(fig.1).Fig.1: Distribution of Homo erectus sites (map: Athena Review 4(1) 2004).
The earliest occurrence outside of Africa is at Dmanisi in the Black Sea region of Georgia, with the relatively primitive Homo erectus georgicus, dating from about 1.8 mya, showing links to Homo habilis. H. erectus reached Sangiran, Java, by 1.6 mya, and and a later population reached Zhoukoudian, China, about 780,000 years ago. Homo erectus persisted for nearly two million years, with the latest examples being the Solo Man fossils from Java dated at 117–108,000 years ago (von Koenisgswald). By about 300,000 years ago, H. erectus had been replaced elsewhere by H. heidelbergensis; who, in turn, led to Homo neanderthalensis.
While the long timespan, regional variability, and far-flung migrations of Homo erectus are generally agreed upon, interpretations of the role of Homo erectus in human evolution are more polarized, and tend to fall into either “Replacement” or “Continuity” theories. Continuity (or Multiregionalist) theories regard Homo erectus as a long-term, coherent species evolving over time into Homo sapiens. Replacement theories, on the other hand, hold that Homo erectus split off from the nearly identical African Homo ergaster (considered the direct ancestor of modern humans), and evolved into one or more separate Asian species, going extinct without contributing to the modern human gene pool. Based on MtDNA and Y-chromosome evidence, as the Replacement Theory holds, all modern humans descended from a group of early Homo sapiens migrating from Africa after 200,000 years ago (Cann et al. 1987; Tattersall 1999, 2000). Replacement theories, however, have had to undergo some modification since the recent revelations (Green et al 2010, Paabo et al.2016) that modern humans share some of the genome of Neanderthals, who descended from Homo erectus.
The bodies and upright posture of H. erectus were relatively similar to those of modern humans, although they were more robust in physique and bone thickness. Brain capacity varied from 546–1,251 cc (compared to the modern human range of 1350-1600 cc). Sexual dimorphism was reduced from that of australopithecines, with men and w
omen closer to the same sizes. H. erectus is associated with the Acheulean stone tool industry, making bifacial tools considerably more sophisticated than those of the earlier Oldowan flake tool industry. The earliest record of Acheuean technology comes from West Turkana, Kenya at 1.76 mya (Lepre et al. 2011). Oldowan unifacial lithics co-occurred at the site for a long time. The earliest records of Achuelean technology outside of Africa do not predate 1 mya, indicating the bifacial techology became widespread via secondary H. erectus dispersals from Africa.
Fig.2: Acheulean handaxes, bifacially flaked tools of chert.
Homo erectus in Africa
The African population of Homo erectus, also known as Homo ergaster, is represented by numerus fossils, mostly from Kenya and Ethiopia at Rift Valley locations including Lake Turkana and Bouri (figs.1 and 3).
By the late
1970s it was evident
that co-occurence of two or more hominid species had occurred in east
Africa between 2.4 and 1.8 mya, including some combination of
australopithecines, Homo habilis, and/or Homo erectus (Walker 1981).
These three taxa are often subdivided on the basis of skull form,
dentition, and other features into at least seven different species,
including the gracile (A. africanus) and robust (A. robustus and A.
boisei) australopithecines, the latter also called Paranthropus; Homo
habilis (split into H. habilis and H. rudolfensis); and Homo erectus
(split into H. erectus and H. ergaster).
Evolution of multiple hominid
species in east Africa within a few hundred thousand years indicates
adaptive radiation which may provide a case of the “punctuated
equilibria” evolutionary model (Eldredge and Gould 1972; Walker 1981).
This would contrast with long periods of relative “stasis” or a lack of
dramatic evolutionary change, as perhaps occurred in the earlier Javan
Homo erectus.Fig.3: Time line of African Homo erectus fossils, correlated with Pleistocene stages.
In 1959, Louis Leakey found remains of a juvenile hominid (OH 5) near flake tools in Olduvai Gorge, Tanzania, for which he created the taxon Homo habilis or “handy man” (Leakey, Tobias and Napier 1964). Nearby in the same Late Pliocene sediments, dated 2.2-2.0 mya were also remains of the large-jawed and smaller brained Australopithecus boisei. The Homo habilis skull had a cranial capacity of about 675 cc, bigger than the still extant australopithecines, but smaller than the later Homo erectus, a partial skull of which Leakey found the next year, 1960, dated at about 1.4-1.25 mya (OH 9). The only other African Homo erectus fossils known ca. 1960 were two mandibles from Ternafine, Algeria dated about 600,000 BP (Arambourg 1957), and the relation between Homo habilis and H. erectus in east Africa remained unresolved.
While Tobias and von Koenigswald both saw links between Olduvai’s Homo habilis and Javan Homo erectus, Leakey and others considered H. erectus an aberrant line largely confined to Asia. The latter position became more difficult to maintain by the mid 1970s, after several more examples of Homo erectus had been found in Africa. These included a partial H. erectus skull and face from Swartkrans in South Africa, discovered in 1969 by Ronald Clark and dated at 1.5 mya (Clark et al. 1970); and a wide range of Homo erectus fossils dated 1.75-1.50 mya from Lake Turkana (fig.4), found amid Australopithecus robustus and Homo habilis remains. More evidence of Homo habilis emerged at Omo, Ethiopia, north of Lake Turkana (Boaz and Howell 1977); and at Koobi Fora (ER 1813), where a combination of rounded skull with large teeth led to a new species designation Homo rudolfensis. Hominid fossils from Omo support a theory of gradual, in situ evolution from Homo habilis to Homo erectus in east Africa from 2.4 to 1.8 mya (Cronin et al. 1981).
The taxon of Homo ergaster was first defined in 1975 by C. Groves and V. Mazak, split from Homo erectus via cladistic analysis on a single mandible from Lake Turkana (KNM-ER 992). Homo ergaster, Greek for “handyman” (equivalent to Louis Leakey’s Homo habilis) has since been used to distinguish Asiatic from African Homo erectus. The replacement theory holds that Homo ergaster is the common ancestor of both African and Asian Homo erectus (the latter, evolving into a separate species) and later forms of Homo leading to modern humans. This distinction has been questioned by recent findings at Bouri, Ethiopia, of Homo erectus skulls from 1 mya. Their similar morphology to Asian Homo erectus indicates there may be no need for the separate African species of Homo ergaster (Asfaw et al. 2002).
Lake Turkana
As at Olduvai and other Rift Valley sites,
the Lake Turkana fossil hominids have been
discovered mainly as surface finds from sediments dated by
potassium/argon methods. Fossil zones on the east side of Lake Turkana include areas of exposed Lower Pleistocene
sediments at Ileret, Koobi Fora, and Allia Bay, the first two well
correlated in date (Walker 1981). Fig.4: Homo erectus skull KNM-ER 3733, viewed from left side (Kenya National Museum, cast)
The nearly complete cranium KNM-ER 3733 from Koobi Fora beside Lake Turkana, was discovered in 1975 by Bernard Ngeneo in a survey led by Richard Leakey. The skull, dated to 1.63±0.15 mya by magnestratigraphy (Lepre and Kent 2010), shows closed cranial sutures and erupted third molars, and represents a mature adult who was probably female. The low cranial vault (also typical of Asian Homo erectus)
has a brain volume of 848
cc.KNM-ER 3733 .has been compared to male fossils KNM-ER 3883 (fig.6) and KNM-WT 15000 (Turkana Boy; fig.7), who were also found at the Koobi Fora site. The features of KNM-ER 3733 are less robust compared to the two male crania. It is considered an adult because of the extensive wear of its teeth, the fact that its third molars were present before the individual died, and because its cranial sutures were fully fused, which is only possible in adult specimen.
Fig.5: Homo erectus skull KNM-ER 3733, frontal view (Kenya Nationa Museum, cast)
Also
from Koobi Fora is the adult male skull KNM-ER 3883. It was
discovered in 1976 at Koobi Fora Area 1 by Richard Leakey and M.
Muluila, and dated to 1.57
mya (fig.6). The brain size of at least 804 cc. is similar to that of KNM-ER 3733.
These individuals are comparable in cranial capacity and some other
aspects of form to several Homo erectus skulls from Sangiran, Java
predating 1.51 mya, as well as to skulls from Dmanisi in Georgia.Fig.6: Homo erectus skull KNM-ER 3883 (Seckenburg Museum, Frankfurt, Germany, cast) .
On the northwest side of Lake Turkana, Lower Pleistocene sediments revealed in 1984-6 the relatively complete fossil skeleton
of
a 10-12 year old Homo erectus youth (KNM-WT 15000), found by Kimoya
Kimeu, Richard Leakey,
and Alan Walker (Leakey et al. 1993). The
skeleton (fig.7), called “Turkana Boy" or "Nariokotome Boy” after the
nearby river, and dated 1.55-1.51 mya, consists of 106 bones and is the
most complete skeleton of a Lower Pleistocene hominin. The individual
was relatively tall (5’3” or 168
cm) with limb bones in the modern range, and would have grown to be about
6 feet tall. The skull of KNM-WT 15000, with a cranial capacity of
880-900 cc, is generally more robust than that of
the slightly earlier KNM-ER 3733 from Koobi Fora, an example of the
physical variability seen in Homo erectus (Walker and Leakey 1993).Material culture associations for Homo erectus at Lake Turkana include detailed cut marks on animal bone which suggests more careful and deliberate meat extraction than might be expected of scavengers. Reduced sexual dimorphism seen in the Koobi Fora hominids may also relate to a meat-enhanced diet (Cachel 2004; Cachel and Harris 1998).
Fig.7: Homo erectus skeleton called the Turkana Boy (KNM-WT 15000) (American Museum of Natural History cast)
Further evidence for long-term variability in Homo erectus comes with the recent discovery of a skull at Olorgesailie, a Middle Pleistocene lakebed site in southern Kenya. The small, relatively gracile Homo erectus cranium shows affinities with both Lake Turkana and Dmanisi hominids (Potts et al. 2004). Dated at 0.9 mya, it is linked with Acheulean technology used in the butchering of lakeside game..
Ethiopia: Bouri
A hominid skullcap or calvaria and postcranial remains recently recovered from the Dakanihylo Member of the Bouri Formation, Middle Awash, Ethiopia, have been identified as Homo erectus remains by Asfaw et al (2002). The Pleistocene sediments containing the fossils, dated at 1.0 mya, also contain abundant early Acheulean stone tools and a diverse vertebrate fauna that indicates a predominantly savannah environment, including numerous species of pigs, bovids similar to the wildebeest or gnu, several types of elephants, hippos, a giant hyena and a large cat.
Despite the lack of the lower part of the skull and the teeth, the calvaria displayed basic characteristics of Homo erectus including a shallow forehead sloping back from massive brow ridges, and an elongated, less spherical brain case. Asfaw et al. (2002) compared these features to those of o
ther Homo erectus fossils and found them similar to contemporary Homo erectus fossils from Asia and Africa.Also found in the same Dakanihylo or "Daka" sedimentary layer of the Bouri formation as the skull were six other Homo erectus fossils, apparently from separate individuals. These included three femurs or thighbones, and a tibia or shin bone, also dated at 1 mya.
The Daka skull's resemblance to Asian counterparts indicates that the early African and Eurasian fossil hominids represent populations of a widespread paleospecies. Daka's anatomical intermediacy between earlier and later African fossils provides evidence of evolutionary change. Its temporal and geographic position indicates that African H. erectus was the ancestor of Homo sapiens.
Fig.8: Homo erectus Daka skull, from Bouri, Ethiopia (American Museum of Natural History cast)
Asfaw et al. (2002) conjecture that the onset of the Ice Ages about 950,000 years ago likely split the Homo erectus populations and led to their divergent evolution. The African population of Homo erectus probably gave rise to modern Homo sapiens, and the European branch may have led to Homo neanderthalensis, while the Asian population perhaps went extinct. By the time Homo erectus disappeared some 400,000 years ago, its various populations had diverged, as evidenced by 400,000-200,00 year-old fossils from Asia compared with African fossils of the same age.
Ethiopia: Konso
Suwa et al. (2007) describe eight craniodental fossils of about 1.4 mya recovered from Konso, Ethiopia, that they attribute to H. erectus. These include KGA10-1, one of the better-preserved H. erectus mandibles known from eastern Africa, and other fragmentary dental and cranial remains.
The Konso H. erectus fossils show a mosaic of primitive and derived features. These include a large and thick mandibular corpus, a moderately developed lateral prominence, a reduced premolar morphology, and a tendency for smaller relative sizes of the posterior molars compared with earlier Homo. In some details of dentition, the Konso fossils differ from eastern African H. erectus of about 1.5 mya. The fragmentary cranial remains, meanwhile, exhibit some similarities with those of eastern African H. erectus examples known from ~1.65 to 1.2 Ma.
The Konso evidence supports an interpretation that African early H. erectus shows morphological continuity within the 1.65 to 1.0 mya time period, with relatively little morphological evolution prior to 1.4 mya and advanced reduction in tooth size occurring sometime thereafter. The evidence also corroborates the hypothesis that the African H. erectus populations represent a variable but continuous evolutionary succession that was a likely source of multiple events of gene flow to the Eurasian continent (Suwa et al. 2007).
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