Whatever happened to homo erectus science talk
Homo erectus (meaning "upright man", from the Latin ērigere, "to put up, set upright") is an extinct species of hominid that lived throughout most of the Pleistocene geological epoch. Its earliest fossil evidence dates to 1.9 million years ago and the most recent to 70,000 years ago. It is generally thought that H. erectus originated in Africa and spread from there, migrating throughout Eurasia as far as Georgia, India, Sri Lanka, China and Indonesia.
- Whatever happened to homo erectus science talk
- Discovery and representative fossils
- African genesis
- Homo erectus georgicus
- Classification and distinctions
- Interpreting evolution H erectus H ergaster H sapiens
- Use of tools and fire
- Use of fire
- Descendants and subspecies
- Homo erectus
- Related species
- Previously referred taxa
- Individual fossils
Debate also continues about the classification, ancestry, and progeny of Homo erectus, especially vis-à-vis Homo ergaster, with two major positions: 1) H. erectus is the same species as H. ergaster, and thereby H. erectus is a direct ancestor of the later hominins including Homo heidelbergensis, Homo neanderthalensis, and Homo sapiens; or, 2) it is in fact an Asian species distinct from African H. ergaster.
There is also another view—an alternative to 1): some paleoanthropologists consider H. ergaster to be a variety, that is, the "African" variety, of H. erectus, and they offer the labels "Homo erectus sensu stricto" (strict sense) for the Asian species and "Homo erectus sensu lato" (broad sense) for the greater species comprising both Asian and African populations.
A new debate appeared in 2013, with the documentation of the Dmanisi skulls. Considering the large morphological variation among all Dmanisi skulls, researchers now suggest that several early human ancestors variously classified, for example, as Homo ergaster, or Homo rudolfensis, and perhaps even Homo habilis, should instead be designated as Homo erectus.
The first hypothesis of origin is that Homo erectus rose from the Australopithecina in East Africa sometime during—or perhaps even before—the Early Pleistocene geological epoch, which itself dates to 2.58 million years ago (see below, at African genesis, re earlier date at Ledi-Geraru Research Area). From there it migrated, in part, by 2.0 mya, probably as a result of broad desertifying conditions developing then in eastern and northern Africa; it joined the migrations through the "Saharan pump" and dispersed around much of the Old World. The fossil record shows that its development from about 1.8 mya to one mya was widely distributed: in Africa (Lake Turkana and Olduvai Gorge), the Transcaucasus (Dmanisi in Georgia), Indonesia (Sangiran, Central Java and Trinil, East Java), and in Vietnam, China (Zhoukoudian and Shaanxi), and India.
The second hypothesis is that H. erectus evolved in Eurasia and then migrated to Africa. They occupied the Dmanisi site from 1.85 million to 1.77 million years ago, which was about the same time or slightly before their earliest evidence in Africa. There are several proposed explanations of the dispersal of H. erectus georgicus—including whether or not Africa is the source).
Discovery and representative fossils
The Dutch anatomist Eugène Dubois was fascinated by Darwin's theory of evolution especially as it applied to humankind. In 1886, he set out for Asia—which then was the region accepted as the cradle of human evolution despite Darwin's theory of African origin; see Haeckel § Research—to find a human ancestor. In 1891, his team discovered a human fossil on the island of Java, Dutch East Indies (now Indonesia). Excavated from the bank of the Solo River at Trinil, in East Java, he named the species Pithecanthropus erectus—from the Greek πίθηκος, "ape", and ἄνθρωπος, "man"—based on a skullcap (calotte) and a femur like that of Homo sapiens.
Dubois' 1891 find was the first fossil of a Homo-species (or any hominin species) found as result of a directed expedition and search—and which was inspired by Darwin's radical theory that humans, like all other species, evolved from ancestral species, see human evolution. (The first found and recognized human fossil was the accidental discovery of Homo Neanderthalensis in 1856, see List of human evolution fossils.) The Java fossil from Indonesia aroused much public interest. It was dubbed by the popular press as Java Man; but few scientists accepted Dubois' argument that his fossil was the transitional form—the so-called "missing link"—between apes and humans. Java Man is now classified as Homo erectus.
Most of the spectacular discoveries of H. erectus next took place at the Zhoukoudian Project, now known as the Peking Man Site, in Zhoukoudian, China. This site was first discovered by Johan Gunnar Andersson in 1921 and was first excavated in 1921, which produced two human teeth. Canadian anatomist Davidson Black's initial description (1921) of a lower molar as belonging to a previously unknown species (which he named Sinanthropus pekinensis) prompted widely publicized interest. Extensive excavations followed, which altogether uncovered 200 human fossils from more than 40 individuals including five nearly complete skullcaps. German anatomist Franz Weidenreich provided much of the detailed description of this material in several monographs published in the journal Palaeontologica Sinica (Series D).
Nearly all of the original specimens were lost during World War II; however, authentic casts were made by Weidenreich which exist at the American Museum of Natural History in New York City and at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, and are considered to be reliable evidence.
Throughout much of the 20th century, anthropologists debated the role of H. erectus in human evolution. Early in the century, due in part to the discoveries at Java and Zhoukoudian, it was widely accepted that modern humans first evolved in Asia. A few naturalists—Charles Darwin most prominent among them—theorized that humans' earliest ancestors were African: Darwin pointed out that chimpanzees and gorillas, humans' closest relatives, evolved and exist only in Africa.
From the 1950s forward, numerous finds in East Africa confirmed the hypothesis of an African genesis, providing fossil evidence that the earliest hominins originated there. It is now generally accepted that H. erectus descended from either: 1) the earliest hominin genera (such as Australopithecus, and possibly Ardipithecus—of which is still debated whether it is hominin or hominid); or 2) the earliest Homo-species (such as Homo habilis or Homo ergaster). East Africa provided sympatric coexistence for H. erectus and H. habilis for several hundred-thousand years, which tends to confirm the hypothesis that they represent separate lineages from a common ancestor; that is, the ancestral relationship between them was not anagenetic, but was cladogenetic, which here suggests that a subgroup population of habilis—or of a common ancestor of habilis and erectus—became reproductively isolated from the main-group population, eventually evolving into the new species Homo erectus.
In the 1950s, archaeologists John T. Robinson and Robert Broom named Telanthropus capensis; Robinson had discovered a jaw fragment in 1949 in Swartkrans, South Africa. Later, Simonetta proposed to re-designate it to Homo erectus, and Robinson agreed.
In 1961, Yves Coppens discovered a skull of Tchadanthropus uxoris, then the earliest fossil human discovered in north Africa. It was reported that the fossil "had been so eroded by wind-blown sand that it mimicked the appearance of an australopith, a primitive type of hominid". Although at first considered to be a specimen of H. habilis, T. uxoris is no longer considered a valid taxon, and has been subsumed into H. erectus.
In 2013, a fragment of fossilized jawbone, dated to around 2.8 million years ago, was discovered in the Ledi-Geraru Research Area in the Afar depression, Ethiopia. The fossil is considered the earliest evidence of the Homo genus known to date, and seems to be intermediate between Australopithecus and H. habilis. The individual lived just after a major climate shift in the region, when forests and waterways were rapidly replaced by arid savannah, which was a domain favored by the early hominins.
Homo erectus georgicus
Homo erectus georgicus is the subspecies name assigned to fossil skulls and jaws found in Dmanisi, Georgia. First proposed as a separate species, it is now classified within H. erectus. The site was discovered in 1991 by Georgian scientist David Lordkipanidze. Five skulls were excavated from 1991 forward, including a "very complete" skull in 2005. Excavations at Dmanisi have yielded 73 stone tools for cutting and chopping and 34 bone fragments from unidentified fauna. The fossils are about 1.8 million years old.
After their initial assessment, some scientists were persuaded to name the Dmanisi find as a new species, Homo georgicus, which they posited as a descendant of African Homo habilis and an ancestor to Asian Homo erectus. This classification, however, was not supported, and the fossil was instead designated a divergent subgroup of Homo erectus.
The fossil skeletons present a species primitive in its skull and upper body but with relatively advanced spine and lower limbs, inferring greater mobility than the previous morphology. It is now thought not to be a separate species, but to represent a stage soon after the transition between H. habilis to H. erectus; it has been dated at 1.8 mya. The assemblage includes one of the largest Pleistocene Homo mandibles (D2600), one of the smallest Lower Pleistocene mandibles (D211), a nearly complete sub-adult (D2735), and a toothless specimen D3444/D3900.
Two of the skulls—D2700, with a brain volume of 600 cubic centimetres (37 cu in), and D4500 or Dmanisi Skull 5, with a brain volume of about 546 centimetres—present the two smallest and most primitive Hominina skulls from the Pleistocene period. The variation in these skulls were compared to variations in modern humans and within a sample group of chimpanzees. The researchers found that, despite appearances, the variations in the Dmanisi skulls were no greater than those seen among modern people and among chimpanzees. These findings suggest that previous fossil finds that were classified as different species on the basis of the large morphological variation among them—including Homo rudolfensis, Homo gautengensis, H. ergaster, and potentially even H. habilis—should perhaps be re-classified to the same lineage as Homo erectus.
Classification and distinctions
Paleoanthropologists continue to debate the classification of Homo erectus and Homo ergaster as separate species. One school of thought suggests dropping the taxon Homo erectus and equating H. erectus with the archaic H. sapiens. Another calls H. ergaster the direct African ancestor of H. erectus, proposing that erectus emigrated out of Africa to Asia while branching into a distinct species. Some scholars dispense with the species name ergaster, making no distinction between such fossils as the Turkana Boy and Peking Man. Still, "Homo ergaster" has gained some acceptance as a valid taxon, and the two species are still usually defined as distinct African and Asian populations of the greater species H. erectus, that is, "Homo erectus sensu lato".
Some have insisted that Ernst Mayr's biological species definition cannot be used to test the above hypotheses—that is, that the two species might be considered the same. Alternatively, the amount of variation of cranial morphology between known specimens of H. erectus and H. ergaster can be compared to the same variation within an appropriate population of living primates (that is, one of similar geographical distribution or close evolutionary relationship), such that: if the amount of variation between H. erectus and H. ergaster is greater than that within an appropriately selected population, for example, say, macaques, then H. erectus and H. ergaster may be considered as two different species.
Finding an extant (i.e., living) model suitable for field study, analysis, and comparison is very important; and selecting a living sample population of an appropriate species can be difficult. (For example, the morphological variation among the global population of H. sapiens is small, so our own species diversity may not be a trustworthy comparison. Fossils found in Dmanisi, Georgia were originally designated as a separate (but closely related) species; but subsequent specimens showed their variation to be within the range of Homo erectus. and they are now classified as Homo erectus georgicus.)
H. erectus fossils show a cranial capacity greater than that of Homo habilis (although the Dmanisi specimens have distinctively small crania): the earliest fossils show a cranial capacity of 850 cm³, while later Javan specimens measure up to 1100 cm³, overlapping that of H. sapiens.; the frontal bone is less sloped and the dental arcade smaller than that of the australopithecines; the face is more orthognatic (less protrusive) than either the australopithecines or H. habilis, with large brow-ridges and less prominent zygomata (cheekbones). The early hominins stood about 1.79 m (5 ft 10 in)—only 17 percent of modern male humans are taller—and were extraordinarily slender, with long arms and legs.
Sexual dimorphism in H. erectus—males are about 25% larger than females—is slightly greater than seen in the later H. sapiens, but less than that of the earlier genus Australopithecus. Regarding evolution of human physiology, the discovery of the skeleton of "Turkana boy" (Homo ergaster) near Lake Turkana, Kenya, by Richard Leakey and Kamoya Kimeu in 1984—one of the most complete hominin skeletons ever discovered—has contributed greatly to the interpretation.
Interpreting evolution: H. erectus / H. ergaster / H. sapiens
Stringer (2003, 2012) and Reed, et al. (2004) and others have produced schematic graph-models for interpreting the evolution of Homo sapiens from earlier species of Homo, including Homo erectus and/or Homo ergaster, see graphs at right. Blue areas denote the existence of one or more hominin species at a given time and place (that is, region). These and other interpretations differ mainly in the taxonomy and geographical distribution of species.
Stringer (see upper graph-model) depicts the presence of H. erectus as dominating the temporal and geographic development of human evolution; and as persisting broadly throughout Africa and Eurasia for nearly 2 million years, eventually evolving into H. heidelbergensis / H. rhodesiensis, which in turn evolved into H. sapiens. Reed, et al. shows Homo ergaster as the ancestor of Homo erectus; then it is ergaster, or a variety of ergaster, or perhaps a hybrid of ergaster and erectus, which develops into species that evolve into archaic and then modern humans and then out of Africa.
Both models show the Asian variety of Homo erectus going extinct recently. And both models indicate species admixture: early modern humans spread from Africa across different regions of the globe and interbred with earlier descendants of H. heidelbergensis / H. rhodesiensis, namely the Neanderthals, Denisovans, as well as unknown archaic African hominins. See admixture; and see Neanderthal admixture theory.
Use of tools and fire
The Paleolithic Age (Old Stone Age) of prehistoric human history and industry is dated from 2.6 million years ago to about 10,000 years ago; thus it closely coincides with the Pleistocene epoch of geologic time, which is 2.58 million to 11,700 years ago. The beginning of early human evolution reaches back to the earliest innovations of primitive technology and tool culture. H. erectus were the first to use fire to cook and made hand axes out of stone.
Homo ergaster used more diverse and sophisticated stone tools than its predecessors, where early Homo erectus used comparatively primitive tools. This is probably because H. ergaster inherited, used, and created tools first of Oldowan technology and later advanced the technology to the Acheulean. Because the use of Acheulean tools began ca. 1.8 million years ago, and the line of H. erectus diverged some 200,000 years before the general innovation of Acheulean industry in Africa, then it is plausible that the Asian migratory descendants of H. erectus made no use of Acheulean technology. It has been suggested that the Asian H. erectus may have been the first humans to use rafts to travel over bodies of water, including oceans. And the oldest stone tool found in Turkey reveals that hominins passed through the Anatolian gateway from western Asia to Europe approximately 1.2 million years ago—much earlier than previously thought.
Use of fire
East African sites, such as Chesowanja near Lake Baringo, Koobi Fora, and Olorgesailie in Kenya, show potential evidence that fire was utilized by early humans. At Chesowanja, archaeologists found fire-hardened clay fragments, dated to 1.42 mya. Analysis showed that, in order to harden it, the clay must have been heated to about 400 °C (752 °F). At Koobi Fora, two sites show evidence of control of fire by Homo erectus at about 1.5 mya, with reddening of sediment associated with heating the material to 200–400 °C (392–752 °F). At a "hearth-like depression" at a site in Olorgesailie, Kenya, some microscopic charcoal was found—but that could have resulted from natural brush fires.
In Gadeb, Ethiopia, fragments of welded tuff that appeared to have been burned, or scorched, were found alongside H. erectus–created Acheulean artifacts; but such re-firing of the rocks may have been caused by local volcanic activity. In the Middle Awash River Valley, cone-shaped depressions of reddish clay were found that could have been created only by temperatures of 200 °C (392 °F) or greater. These features are thought to be burnt tree stumps such that the fire was likely away from a habitation site. Burnt stones are found in the Awash Valley, but naturally burnt (volcanic) welded tuff is also found in the area.
A site at Bnot Ya'akov Bridge, Israel is reported to evidence that H. erectus or H. ergaster controlled fire there between 790,000 and 690,000 BP; to date this claim has been widely accepted. Some evidence is found that H. erectus was controlling fire less than 250,000 years ago. Evidence also exists that H. erectus were cooking their food as early as 500,000 years ago. Re-analysis of burnt bone fragments and plant ashes from the Wonderwerk Cave, South Africa, has been dubbed evidence supporting human control of fire there by 1 mya.
There is archaeological evidence that Homo erectus cooked their food.
Homo erectus was probably the first hominin to live in a hunter-gatherer society, and anthropologists such as Richard Leakey believe that erectus was socially more like modern humans than the more Australopithecus-like species before it. Likewise, increased cranial capacity generally coincides with the more sophisticated tools occasionally found with fossils.
The discovery of Turkana boy (H. ergaster) in 1984 evidenced that, despite its Homo sapiens-like anatomy, ergaster may not have been capable of producing sounds comparable to modern human speech. It likely communicated in a proto-language lacking the fully developed structure of modern human language but more developed than the non-verbal communication used by chimpanzees. This inference is challenged by the find in Dmanisi, Georgia, of an H. ergaster / erectus vertebrae (at least 150,000 years earlier than the Turkana Boy) that reflects vocal capabilities within the range of H. sapiens. Both brain size and the presence of the Broca's area also support the use of articulate language.
H. erectus was probably the first hominin to live in small, familiar band-societies similar to modern hunter-gatherer band-societies; and is thought to be the first hominin species to hunt in coordinated groups, to use complex tools, and to care for infirm or weak companions.
There has been debate as to whether H. erectus, and possibly the later Neanderthals, may have interbred with anatomically modern humans in Europe and Asia. See Neanderthal admixture theory.
Descendants and subspecies
Homo erectus is the most, or one of the most, long-lived species of Homo, having existed well over one million years and perhaps over two million years; Homo sapiens has existed for about 200,000 years. If considering Homo erectus in its strict sense (that is, as referring to only the Asian variety) no consensus has been reached as to whether it is ancestral to H. sapiens or any later hominins (see above, "Interpreting evolution: ...").
Previously referred taxa
Homo erectus soloensis, who was long assumed to have lived on Java at least as late as about 50,000 years ago but was re-dated in 2011 to a much older age, would be one of them. Some scientists are skeptical of the claim that Homo floresiensis is a descendant of Homo erectus. One explanation holds that the fossils are of a modern human with microcephaly, while another one holds that they are from a group of pygmies.
Some of the major Homo erectus fossils: