Homo erectus is a major figure in o

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).