Introduction: The long journey of an ancient human ancestor
Homo erectus is a major figure in our past. Fossils identified as Homo erectus span most of the 1.9 million year 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 and adaptations 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).
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 (see glossary). Briefly, Continuity (or Multiregionalist) theories regard Homo erectus as a long-term, coherent species evolving over time into Homo sapiens.
[Fig. : Distribution of Homo erectus sites]
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, 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).
Accumulated fossil and site evidence increasingly shows a remarkable adaptability of Homo erectus populations to a wide range of environments during their Pleistocene migrations. The behaviors that evolved during the long span of Homo erectus (i.e., fully bipedal migrations, tool-making, scavenging, hunting) are essentially the earliest human behaviors. This introduction provides the reader with a brief historical background of findings on Homo erectus.
Java Man and the concept of “erectus”: Discovery of the first Homo erectus specimen in southeast Asia was directly inspired by the 19th century “missing link” concept of a bipedal “ape-man” who combined traits of today’s humans and apes (box 1, The Discovery of "Java Man" in 1891). Both Charles Darwin and his disciple Ernst Haeckel believed that upright posture and bipedalism were direct precursors to tool making, by freeing the hands. Few if any Victorian evolutionists, however, could have guessed that a gap of at least 3.5 million years separated the first bipedalism, now known from the Late Miocene (Brunet et al. 2002), from the first stone tools at 2.5 mya. Given today’s knowledge that both apes and humans have evolved for 6-7 million years along different paths from a common ancestor, the notion of Pithecanthropus as a hybrid “ape-man” now appears fancifully naive or misguided. Yet the criteria of erect posture or bipedalism remains the most important morphological trait separating fossil hominids from apes. Bipedal locomotion or walking at first supplemented tree climbing. Its evolutionary advantage most likely concerned energy conservation in travelling (see The paleobiology of Homo erectus and early hominid dispersal, by Susan Cachel). Gradually, by the time of Homo erectus at ca. 1.8 mya, the human anatomy of long legs, tall stature, and full bipedalism had evolved (Wood and Collard 1999).
When Dubois began his fieldwork in the late 1880s, only Neanderthals had been identified as fossil hominids. Neanderthal remains from Germany and Belgium, in terms of skeletal and cranial form, appeared robust but basically modern (Huxley 1863). The quest to find a much earlier, more ape-like human ancestor was a revolutionary step initiated by Dubois.
Revelations at Trinil: Indonesia (then a Dutch colony) was still only tentatively known to contain Pliocene and Pleistocene fossil beds, comparable to better documented zones in the Siwalik Hills of Pakistan. Discovery in 1878 of an extinct Pleistocene chimpanzee called Anthropithecus (“man-ape”) in the Siwalik beds helped convince Dubois of southern Asia’s potential for “missing link”evidence, as did the unique presence of the orangutan in Indonesia.
Pleistocene fossil beds along the Solo River and Kendig Hills in east-central Java (named the Trinil or Kendig zone by Dubois) soon revealed faunal correspondences with the Siwalik Hills, including rhinocerous, hippopotami, a primitive elephant Stegadon, buffalo, deer, hyenas, and large felines. In 1891, the Trinil beds produced a molar resembling Anthropithecus, and then the hominid calvaria (skullcap) now called Trinil 2. The human left femur (thighbone) found in 1892 was at first grouped with both as a kind of advanced, bipedal chimpanzee named Anthropithecus erectus.
The Trinil 2 calvaria (box 1) shows a low, sloping profile with a pinched-in, postorbital constriction contrasting to the domelike form of the modern human skull. Thick walls and heavy brow ridges also appeared apelike. Further study of the skullcap by Dubois, however, with removal of the rock matrix in its cavity revealed a much larger cranial capacity (900 cc), twice that of a chimp (ca. 450 cc). In a tribute to Haeckel, Dubois (1894) renamed the fossil Pithecanthropus erectus, “erect ape-man,” a taxon to be eventually (after discovery of the australopithecines in the 1920s-40s) replaced by Homo erectus .
Further discoveries in Java: Two decades after the Trinil 2 discovery, 1909-10 German excavations led by Margarete Selenka across the Solo River from Trinil recovered Pleistocene fauna of a narrower and mainly later range than those found by Dubois. While the expedition found no hominid remains, it helped refine the Pleistocene biostratigraphy of Java.
Discovery of the next fossil hominids in Java came in the early 1930s at Ngandong, on an upper terrace of the Solo River only ten km from Trinil (fig.2). In 1931-1933 the Dutch Geological Survey under W. F. F. Oppennoorth excavated rich Upper Pleistocene fossil deposits some 20 -24 m above the current level of the Solo. Besides thousands of animal fossils (extinct buffalo, wild oxen, Stegodon, pigs, tigers, etc.), the project recovered 12 hominid calvaria, the largest sample from a single Javan site. The Ngandong remains, named Homo soloensis by Oppennoorth (1932), represent a much-debated group of Upper Pleistocene hominids. They had significantly larger cranial capacities than earlier Javan Homo erectus, averaging 1210 cc compared to 883 cc (Jacob 1981). Massive brow ridges (fig.4) and thick cranial bones, however, make “Solo Man” (dated ca. 200,000-25,000 BP) appear still closely linked to Homo erectus.
[Fig. 2: Map of major Homo erectus sites in east-central Java .]
Soon afterwards, in the mid-to-late1930s, paleontologist Ralph von Koenigswald identified an important series of Lower and Middle Pleistocene Homo erectus fossils collected by Javan farmers. Originally working with the Dutch Geological Survey to classify fossil fauna, von Koenigswald obtained funding from the Carnegie Institute of Washington DC for early hominid site exploration. In the course of these 1930s projects, detailed geological maps were made in Java (Shipman 2001; Huffman 2001).
At Sangiran, one of several large volcanic domes in east-central Java (which ca. 1.5 mya formed a lake shore and riverine zone), von Koenigswald found a Homo erectus mandible (1934); a skullcap called Sangiran 2, similar to Trinil 2 but with a smaller cranial capacity of 815 cc (1937); and several early Homo erectus skulls and mandibles with massive teeth (1938-9). One, Sangiran 6, was at first classed as Paranthropus (or Australopithecus) robustus. Another, Sangiran 4, has an australopithecine-like diastema or gap between the upper canines and incisors. Both are now considered to predate 1.5 mya.
An even earlier Homo erectus fossil of a child’s skull was recovered by von Koenigswald in 1936 in the east Javan village of Perning near Mojokerto, 180 km east of Sangiran on the Brantus River. Now dated as early as 1.8 mya, the Perning skull came from a layer representing an ancient marine deltaic setting. The fossils from Sangiran and Mojokerto demonstrate that initial hominid migrations to southeast Asia came into a diverse range of local environments.
Von Koenigswald took a number of Javan Homo erectus fossils to China in 1939 to compare with the Zhoukoudian hominid remains being studied by Franz Weidenreich. Similarities seen by von Koenigswald and Weidenreich (1939) eventually led to combined use of the Homo erectus taxon for both “Java Man” and “Peking Man” (Mayr 1950).
During World War II, von Koenigswald managed to safeguard many of the Javan fossils even though he was imprisoned by the Japanese from 1942-5. From the 1960s-80s, Tekeu Jacob directed numerous paleoanthropological projects in Java, including excavations at Ngandong, Sambungmachan, and Sangiran revealing several more Homo erectus and H. soloensis skulls (Jacob 1973, 1981). Since the 1990s, work by international teams has progressed at a number of sites including Mojokerto, Ngandong, and Sangiran Dome. Especially interesting finds are Oldowan stone tools and faunal remains with butchery marks recovered in the Bapang Formation in the Ngebung Hills (Semah et al. 1992).
Dating the Java sites: Before the advent of potassium-based geochronology, the dating of fossil deposits in Java was done by biostratigraphy, associating mammalian taxa with geological layers. In 1969, geochronologist Garniss Curtis first applied potassium-argon dating to a volcanic rock from the Mojokerto site, producing a date of 1.9 mya (Swisher et al. 2000). This was basically upheld over 20 years later by more accurate Ar/Ar dates from 1.81-1.6 mya on pumice from the Pucangan (Sangiran) Formation (Swisher et al. 1994). An independent series of dates obtained for the overlying Kabuh (Bapang) Formation in central Java shows a group of five Homo erectus fossils predating 1.51 mya (Larick et al. 2001; Larick et al. 2004).
These early dates remain controversial. If the oldest dates are accurate, correlations with paleomagnetic stratigraphy from the Rift Valley of Africa would show the arrival of hominids in Java as early as the Olduvai subchron (1.98-1.79 mya). Significantly, such early dates suggest the African emergence of Homo and the initial dispersal to subtropical Asia may be directly linked. Conditions favoring this initial migration center on the geologically active Tethys Corridor, a tectonic zone along the south edge of the European continental plate. Environmental change created new subsistence niches at the start of the Pleistocene, while lowered sea-levels due to glaciation exposed the Sunda shelf, over which hominids could walk to southeast Asia.
[Fig. 3: The Sangiran 17 skull, dated at about 1.15 mya (photo: Athena Review, from cast at AMNH).]
Based on this recent dating, the earliest Homo erectus groups settled in Java by 1.8-1.6 mya around coastal deltaic swamps and lakes at the south end of the Sunda shelf, associated with the Sangiran formation and the Ci Saat fauna (including the large carnivore Panthera and bovids such as deer and hippopotami). Homo erectus fossils from this oldest level include the primitive-looking Sangiran 4 found by von Koenigswald, as well as four other individuals (Sangiran 27, 31, 41, and 57) found since 1978. At about 1.5 mya the Sangiran levels were superimposed by river and lake sediments of the Kabuh Formation with associated Trinil Fauna (Dubois’ original Trinil zone). Homo erectus finds include the relatively complete Sangiran 17 cranium (fig. 3) found in 1969; the Sangiran 50 cranium and maxilla found in 1993 at Tanjung (see Larick et al.2004); and the Sangiran 2 skullcap of von Koenigswald, all three dated at 1.25-1.0 mya, slightly earlier than the Trinil 2 calotte.
After 800,000 BP, fossil evidence ceases at the Sangiran Dome. Around this time Homo erectus may have rafted across 25 km of ocean to the island of Flores, east of Bali, where Oldowan tools have been found (Morwood et al. 1998). More recent finds by Morwood and colleagues on Flores show that very late, small Homo erectus-like hominids named Homo floresiensisstill lived there from 95,000-13,000 BP, overlapping the time frame of "Solo Man," and even living into the period of early animal and plant domestication by modern humans in the Near East.
After a hiatus of about 600,000 years after Trinil, the Homo soloensis remains found in the Upper Pleistocene Notopuro and Ngandong Formations represent a much more recent fossil hominid group from Java (fig.2). These problematic fossils are disputed on grounds of their developmental ages, as well as overall taxonomy and chronology (Antón 1999). Prior to the advent of absolute dates, both Oppennoorth and von Koenigwald thought “Solo Man” could have been related to the nearly contemporary Neanderthals, while Weidenreich (1945) considered them an intermediate stage between Homo erectus and Australian aborigines. This latter view is continued today by some multiregionalists, who see similarities in six of the Ngandong crania with a 15,000 year old, anatomically modern human from Willandra Lakes, Australia (Wolpoff and Thorne 1991; Wolpoff et al. 2001).
[Fig. 4: Late Pleistocene Solo 6 skull from Ngandong, Java (photo: Athena Review, from cast at AMNH)]
Uranium-series and electron spin resonance (ESR) dates of 53-27,000 BP have been obtained on bovid teeth from the same Ngandang deposit producing the Homo soloensis skulls (Swisher et al.1997). These dates plus anatomical evidence provide grounds to identify the Ngandong fossils as part of a very late Homo erectus population contemporary with (and a separate species from) Homo sapiens (Antón 2002). The Ngandong fossils remain an important enigma, partly contemporaneous with both the newly found Homo floresiensisof the Indonesian island Flores, and the relatively large-brained fossil skulls from Dali and Mapa in China, representing late Asiatic descendants of Homo erectus.
Homo erectus in China: In the 1920s the famous “Dragon Bone Hill” (Longgushan) quarry site at Zhoukoudian (box 2) yielded hominid fossils identified by Davidson Black as Sinanthropus pekinensis, or “Peking Man”. The Longgushan limestone deposits, originally mined for fossils called “dragon bones,” which were ground up and sold by druggists as aphrodisiacs, eventually provided the largest known sample of Homo erectus fossils. By 1937, when work halted at Zhoukoudian due to Chinese civil war, excavations under W.C. Pei, Lanpo Jia, and colleagues such as Teilhard de Chardin had produced six skullcaps, eleven mandibles, a mixed assortment of facial bones, and about 150 teeth. This sample, while notably lacking in long bones and extremities (see below), represented over 40 individuals of both sexes and different ages, with cranial capacities from 915-1225 cc (Boaz and Ciochon 2004; see book review by Dong Wei).
After Black died suddenly in 1934, Franz Weidenreich, already familiar with some of the Pithecanthropus finds from Java, took over the anatomical work in 1935 and eventually completed a detailed analysis of the Zhoukoudian hominids (1943). Recognizing many similarities with the Java fossil hominids after consultations with von Koenigswald, Weidenreich nevertheless retained in his publications the original, regionally distinct taxa of Sinanthropus pekinensis and Pithecanthropus erectus. He supported, however, combining both as Homo erectus as part of a single, evolving Homo lineage (Mayr 1950).
[Fig. 5: Homo erectus skull from Zhoukoudian, China (photo: Athena Review, from cast at AMNH).]
A mean cranial capacity of about 1050 cc. in the Zhoukoudian skulls shows larger brain size compared to the somewhat earlier Java H. erectus, but many basic similarities. The low-slung, thick-walled skulls from both Java and China are widest at their base, and have large brow ridges, a sagittal keel on top, and a protruding ridge at the rear (occipital) bone (fig. 5; based on the reconstruction by Tattersall and Sawyer 1996). Homo erectus also lacked a chin, and the jaws and teeth are significantly more robust than in modern humans. Chinese facial bones, however, tend to be even more massive than in Java specimens, the skull walls thicker, and the mandibles more robust. These local specializations also vary from the Homo erectus specimens found in Africa (discussed below).
Causes of the very thick skulls of Homo erectus (roughly twice as thick as those of modern humans) may have been a defensive adaptation against trauma from personal violence, including blows from behind (Boaz and Ciochon 2004). This view is supported by at least ten cases of healed depressed fractures found in Zhoukoudian skulls by Weidenreich (1943).
Material culture of Chinese Homo erectus: In excavations which lasted (with wartime interruptions) from 1921-1982, the Longghushan cave site revealed over 100,000 artifacts of worked stone and cut or burned animal bone, the latter often found in the same levels producing Homo erectus fossils. The lithic artifacts, first systematically recorded in 1931, and dominated by quartz flakes, represent a Mode 1 or flake tool industry. Tool forms include retouched or sharpened flakes, scrapers, core tools or choppers, and pointed awls used for piercing. When discovered in the 1920s-30s, these were the first significant artifactual remains to be found in situ with hominid fossils. Since initial descriptions in the late 1930s, however, their interpretation has been rife with controversy (Boaz et al. 2000; Boaz and Ciochon 2004).
An abundance of animal bones found at Zhoukoudian included thousands of deer bones, some charred by fire. Given these apparent food remains, plus numerous stone tools, original interpretations of the cave site portrayed it as a home base for bands of Homo erectus who subsisted by hunting and gathering. Evidence of fire in levels containing burned bone suggested cooking, and the use of fire for warmth seemed consistent with this northernmost settlement area for Homo erectus. Bone artifacts including cut marks from stone tools were identified by Henri Breuil (1939), who visited China several times in the 1930s. Signs of possible cannibalism were also seen by Breuil (1939) and Weidenreich (1943) in breakage and widening of the foramen magna of several skull bases, possibly to remove the brain.
Reexamination of the evidence, however, has significantly altered views about a hunting subsistence for Homo erectus at Zhoukoudian. The overall sample of hominid bones itself provided the first important clues that the caves may have served other functions. Weidenreich (1943) first remarked on the fragmentary nature of the Homo erectus fossil assemblage at Zhoukoudian, which generally lacked long bones and extremities, and where skulls had been broken up apparently even before their deposition in cave sediments. This has been confirmed by recent, detailed examination of the remains at Zhoukoudian locality I by Boaz et al. (2000), revealing that hominid bones made up only half of one percent (0.5%) of the total bones at the site. The high proportion of isolated teeth and skull parts, and the low incidence of long bones or hands and feet, is typical of the bone accumulation in a carnivore den. Some Homo erectus facial bones and crania (as first noted by Weidenreich) show punctures and other marks typical of carnivores, undoubtedly including the large, lion-sized Pleistocene cave hyena Pachycrocuta brevirostris, whose bone remains are the most frequent at the site. Hyenas also seem to have been responsible for the widening of the foramen magnum on H. erectus remains, evidence which could no longer pertain to cannibalism. Other evidence, nevertheless, of cut marks by stone tools on Homo erectus Skull V (first noted by Weidenreich) does show that cannibalism must have occurred at Zhoukoudian (Boaz and Ciochon 2004).
Postcranial bones also exhibit typical hyena tooth marks and breakage, as part of hyaenid scavaging or predation of Homo erectus. Many of the arm and leg bones would have been totally consumed by hyenas or other carnivores, thus accounting for their relative lack in the overall sample. The conclusion inevitably drawn by Boaz et al. (first advanced in 1929 by the archaeologist W. C. Pei ) is that the Zhoukoudian caves, rather than being home bases for hominid hunters, were, for much of the time, dens for the giant cave hyena. Controversy has also persisted over the use of fire at the site. Ash in layers that had been taken as signs of hearth fires showed no evidence of phytoliths (silica particles) typically left by burning wood or other vegetation (Weiner et al. 1998). This has supported the interpretation that most fires at Zhoukoudian were not confined to hearth features, and thus could be due to natural causes (Binford and Stone 1986). Yet some of the main layers with Homo erectusfossils at Zhoukoudian cave (e.g., layer 10) also contain burned bone with stone tools, which would seemingly indicate hominid use of fire, very likely for cooking (Weiner et al. 1998).
[Fig. 6: Approximate dates of Homo erectus finds in four regions.]The flake tool (Mode 1) assemblages contain lithic items useful for defleshing (scrapers and flakes) and for pounding bones to extract marrow (core choppers). Binford and Ho (1985) proposed that Homo erectus subsisted by scavenging, or foraging for meat left on bones in caves occupied primarily by cave hyenas, wolves, or bears. This is supported by close examination of animal bones at Zhoukoudian, which shows that cut marks made by Homo erectus with quartz flakes overlie carnivore bite marks. While the caves at Zhoukoudian often functioned primarily as dens for the cave hyena, they thus also must have served as foraging areas for Homo erectus, who may have camped nearby, possibly making shelters from tree branches (Boaz and Ciochon 2004).
Earlier Chinese sites: In the past decade, several Lower Pleistocene hominid sites have been identified in China (fig. 6). Among the most controversial is Longgupo Cave on the Yangtze River, where a mandible fragment and teeth dated at 1.9 mya by ESR methods have been compared to early African Homo habilis and H. ergaster(Wanpo et al. 1995). Associated with the teeth were pitted and abraided cobble tools of an exotic andesite-porphyrite. Also found at Longgupo were teeth of Gigantopithecus, a huge Plio-Pleistocene ape also occurring with Homo erectus at another Chinese site, Jianshi Cave, and at Tham Khuyen Cave in Vietnam, dated at 475,000 BP (Ciochon et al. 1996). While debate continues on the hominid identification of the Longuppo teeth, the site is of potentially great significance in terms of initial dispersal from Africa.
Other early tool evidence comes from the Nihewan Basin in north China (40 N), a lacustrine region known for Villefranchian-age fauna (Zhu et al. 2001). While the site lacks hominid fossils, a Mode 1 flake tool assemblage of over 3000 items including side- and end-scrapers has been found in layers dated paleomagnetically to 1.36 mya, a relatively early date for hominids in a north-temperate zone.
Some 900 km to the south in Lantian county, a partial cranium from Gongwangling on the Yellow River represents China’s earliest known Homo erectusfossil, dated about 1.15 mya (Etler 1996). By this period, a wide adaptive range is indicated for Chinese Homo erectus. One skull of a female at Lantian, aged about 30, has a cranial capacity of 780 cc, comparable to individuals from Koobi Fora and Sangiran. By 800,000 years ago, bifacial stone tools were being made in the Bose Basin in south China, partly resembling an Acheulean industry but lacking handaxes (Hou Yamei et al. 2000).
Zhoukoudian’s date range is also under revision, along with that of several other Middle Pleistocene Homo erectus sites in China (see information in Etler 2004). In 1985, uranium isotope dating gave absolute dates on hominid-bearing layers at Zhoukoudian’s Localities 1 and 2 from 290,000 - 230,000 BP. Yet the upper strata have recently been redated to be substantially earlier, at 410,000 BP, while the lowest hominid layer is redated at 670,000 BP. Chinese Homo erectus occupations from 670,000-400,000 occurred not only at Zhoukoudian, but also at Tangshan Hill near Nanjing, in Yunxian at Quyuanhekou (both about 620,000-580,000 BP), and the Hexian site at Anhi (over 400,000 BP). The Nanjing and Zhoukoudian Homo erectus specimens seem close in morphology, and Middle Pleistocene faunal assemblages from the two sites are very similar.
[Fig. 7: Skull from Dali, China (photo: Athena Review, from cast at AMNH).]
Later Chinese hominids: Based on these revised dates, fossil evidence of Homo erectus is missing in China between about 400,000 and 280,000 BP. Later hominids then appear with more rounded skulls and (often) larger brain cases, including a young male from Jinniushan dated at 280,000 years ago, with a modern-sized cranium of 1400 cc. At Hexian, a well-preserved Homo cranium (1025 cc) with reduced brow ridges has been dated to about 200,000 BP, contemporary with the Dali cranium (fig. 7), which shows large brow ridges and a flat, high face. The still later Mapa cranium (about 132,000 BP) may be contemporary with Homo soloensis populations from Java’s Ngandong deposits. Controversy persists on whether Homo heidelbergensis populations migrated into China and overlapped the latest Homo erectus groups as a separate species, or there was a more gradual, in situ transition.
Homo habilis and Homo erectus in Africa: 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 provides a convincing case of adaptive radiation as portrayed in 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.
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). (This, and another fragmentary Homo erectus cranium from Olduvai, OH-12, have sometimes been called H. erectus Leakeyi). 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. erectusin 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.3), found amid Australopithecus robustus and Homo habilisremains.
As at Olduvai and other Rift Valley sites, the Lake Turkana fossil hominids (discussed in Cachel 2004) have been discovered mainly as surface finds from sediments dated by potassium/argon methods. Fossil zones on the east side of Lake Turkana (discussed in Cachel 2004) include areas of exposed Lower Pleistocene sediments at Ileret, Koobi Fora, and Allia Bay, the first two well correlated in date (Walker 1981). The nearly complete cranium KNM-ER 3733 from Koobi Fora (fig. 8), found in 1975 by Richard Leakey and dated to 1.75 mya, 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. Also from Koobi Fora is a male skull (KNM-ER 3883) dated to 1.57 mya. The brain size of at least 804 cc. is similar to that of 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 (see below).
[Fig. 8: KNM-ER 3733, a Homo erectus/ergaster skull from Koobi Fora on Lake Turkana, Kenya (photo: Athena Review, from cast at AMNH).]
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.x), called “Nariokotome Boy” after the nearby west Turkana town, and dated 1.55-1.51 mya, is relatively tall (5’3” or 168 cm) with limb bones in the modern range and a cranial capacity of 880-900 cc. The skull of WT 15000 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.
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).
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). Alternatively, based on a low body mass and apparent terrestrial/climbing abilities, Wood and Collard (1999) propose reclassifying the two closely related taxa of H. habilis and H. rudolfensis as australopithecines. The larger Homotaxa, starting with African Homo erectus/ergaster by 1.9 mya, show different adaptations corresponding to larger body mass and specialized bipedal walking abilities.
The identification of Homo ergaster: The taxon of Homo ergasterwas 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).
More 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.
Travels out of Africa: The initial spread of Homo erectus/ ergaster from Africa occurred by about 1.8 mya to Eurasia as well as the Sunda shelf region (Java). The recent discoveries at Dmanisi, Republic of Georgia, of several relatively small-brained hominid remains together with Oldowan tools (Gabunia and Vekua 1995; Gabunia et al. 2000) adds to the argument against any significant time gap between emergence of Homo and large-scale hominid migrations.
In 1984 the Dmanisi Pleistocene deposits yielded their first evidence of stone tools. Subsequent excavations by Georgian and German archaeologists led to the discovery of early hominid remains with Oldowan (Mode 1) stone tools, and 29 species of Villefranchian fauna from the Late Villanian and Early Biharian Mammal Ages, dating from 2.0 to 1.5 mya.
Dmanisi hominids: All of this has transformed Dmanisi into a site of major importance. By 2002, Dmanisi had already produced over twenty fossilized remains of Lower Pleistocene hominids, including three skulls, three lower jaws (mandibles) with intact teeth, and postcranial parts including leg, arm, and finger bones or metatarsals (Vekua et al. 2002). While stature approaches that of Homo erectus/ergaster, brain size is relatively small, at times near the upper range of Homo habilis or even australopithecines.
[Fig. 9: Hominid skull D-2282 from Dmanisi (photo: courtesy David Lordkipanidze).]
The site’s chronology has been determined by the K-Ar date of the Mashavera Basalt underlying the fossils at 1.85 mya, while an upper date of 1.8-1.6 mya is based on volcanic ash dating and faunal analysis. Given the presence of more Palearctic than Paleotropical species, the Lower Pleistocene site, located near the confluence of two rivers, had a moderately dry Mediterranean climate. Two small adult or sub-adult hominid skulls with endocranial volumes below 800 cc were discovered in 1999. The smaller (D-2282), possibly from a female, includes parts of the maxilla and a cranial vault with a capacity of about 650 cc (fig. 9). The larger skull (D-2280), a nearly compete calvaria with a braincase of 775 cc (fig. 103), has more robust brow ridges and may represent a male. A third skull was found in 2001. At first assigned to Homo ergaster, Dmanisi hominid fossils were reclassified in 2002 as a new species, Homo georgicus.
[Fig. 10: Hominid skull D-2280 from Dmanisi (photo: courtesy David Lordkipanidze).]
Oldowan stone tools and subsistence at Dmanisi: Primitive flake and core tools found at Dmanisi, identified as an Oldowan or Mode 1 lithic industry, were made from alluvial cobbles of silicified volcanic tuffs and quartz, found along terraces of the Mashavera and Phinezauri Rivers. Cores fashioned from cobbles or cobble fragments (fig. 11) sometimes show rough striking platforms, with smaller pebble tools resembling the cores. Use wear appears on flake edges as small notches or splinterings, with occasional edge retouch or sharpening, including a burin made from a large flake.
Discoveries at Dmanisi of Mode 1 tools associated with early hominids indicate that the causes of far-ranging migrations before 1.6 mya relate more to enhanced mobility and ecological adaptations, than to any sophistication of stone tool manufacture and related cognitive abilities. In the view of David Lordkipanidze, Deputy Director of the Georgian State Museum (pers. comm.), “the Dmanisi finds invalidate the theory that the development of advanced stone tool technology enabled early humans to finally expand out of Africa.”
[Fig. 11: Stone tools of Oldowan (Mode 1) type from Dmanisi (courtesy David Lordkipanidze).]
Homo erectus in Western Europe: Current evidence shows two distinct phases of Homo erectus in Europe, with the first occurring in the Lower Pleistocene (Milliken 2004). While Dmanisi represents initial hominid migrations from northeastern Africa, another very early northwestern movement came across the Strait of Gibraltar to the Guadix-Baza basin in southeastern Spain. During the past decade, Lower Pleistocene hominid occupations have been revealed at Barranco León-5 and Venta Micena from around 1.7 mya (with fragmentary hominid skeletal remains), and at Fuentenueva-3 from1.6-1.4 mya. Faunal remains and lithic artifacts at these sites suggest positive correlations between the activities of large carnivores such as sabre-tooth cats, and hominid scavenging subsistence using Mode I stone tools.
After a hiatus of at least 500,000 years came a second phase of Homo erectus in Europe (0.9 -0.6 mya), corresponding with the transition from Lower to Middle Pleistocene. Evidence at several sites in Spain (Atapuerca) and Italy (Monte Poggiolo, Isernia la Pineta, and Ceprano) is slightly earlier than, or contemporary with that of Chinese Homo erectus populations at Lantian and the earlier occupations at Zhoukoudian, Nanjing, and Hexian. During the second European phase Homo erectus retained Asiatic, Oldowan tool traditions, probably related to scavenging subsistence modes. In Italy, tool-making episodes at Monte Poggiolo predating 780,000 BP are evidenced by thousands of chert flakes, while at Isernia la Pineta (730,000 BP), abundant bones including those of elephants and bison were defleshed by simple, unretouched flakes. At Atapuerca in northern Spain, bones of deer, boars, and hominids were broken with stone tools for marrow extraction, indicating that by ca. 750,000 BP cannibalism was part of the local diet.
[Fig. 11: Acheulean handaxes, illustrating Mode 2 tools (photo: Athena Review).]
The end of the later European phase coincides with the advent of Homo heidelbergensis and the introduction of Acheulean, Mode 2 stone tools (fig.12) into Europe by about 600,000-500,000 BP. With this came more efficient subsistence practices relating to hunting and gathering. This correlates with a dramatic increase in occupation sites in Europe, which begin to be found as far north as the English Channel (box 3: Saint Acheul, France), indicating significant population growth and expansion of adaptive ranges in Homo groups by 500,000 BP.
[Written and researched by AR editorial staff.]
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