Homo erectus

Homo erectus (/ˌhoʊmoʊ əˈrɛktəs/ lit. 'upright man') is an extinct species of archaic human from the Pleistocene, spanning nearly 2 million years. It is the first human species to evolve a humanlike body plan and gait, to leave Africa and colonize Asia and Europe, and to wield fire. H. erectus is the ancestor of later human species, including H. heidelbergensis — the last common ancestor of modern humans, Neanderthals, and Denisovans. As such a widely distributed species both geographically and temporally, H. erectus anatomy varies considerably. Subspecies are sometimes recognized: H. e. erectus, H. e. pekinensis, H. e. soloensis, H. e. ergaster, H. e. georgicus, and H. e. tautavelensis.
The species was first described by Eugène Dubois in 1893 as "Pithecanthropus erectus" using a skullcap, molar, and femur from Java, Indonesia. Further discoveries around East Asia were used to contend that humanity evolved out of Asia. Based on historical race concepts, it was argued that local H. erectus populations directly evolved into local modern human populations (polycentricism) rather than everyone sharing an anatomically modern ancestor (monogenism). As the fossil record improved over the mid-to-late 20th century, "Out of Africa" theory and monogenism became the consensus.
The skull usually has a pronounced brow ridge, a protruding jaw, and large teeth. The bones are extraordinarily thickened. East Asian H. erectus normally have more robust skeletons and larger brain volumes — averaging 1,000 cc (61 cu in), within the range of variation for modern humans. Western H. erectus brain volume got as low as 546 cc (33.3 cu in) in H. e. georgicus. H. erectus probably had a faster apelike growth trajectory, lacking the extended childhood required for language acquisition. Reconstructed adult body dimensions range from 148–167 cm (4 ft 10 in – 5 ft 6 in) in height and about 50 kg (110 lb) in weight.
H. erectus invented the Acheulean industry, a major innovation of large, heavy-duty stone tools. These tools may have been used in butchery, vegetable processing, and woodworking of maybe spears and digging sticks. H. erectus was a major predator of large herbivores on the expanding savannas of the Quaternary glaciation. The species is usually characterized as the first hunter-gatherer and the first to practice sexual division of labor. Fire usage and cave habitation were probably not important aspects of daily life. Similarly, H. erectus may not have often ventured into colder regions or cooked meat. The last occurrence of H. erectus is 117,000 to 108,000 years ago (H. e. soloensis) in Southeast Asia, when the last savannas in the region gave way to jungle.
Despite what Charles Darwin had hypothesized in his 1871 Descent of Man, many late-19th century evolutionary naturalists postulated that Asia (instead of Africa) was the birthplace of humankind. Asia is midway between all continents via land routes or short sea crossings, providing optimal dispersal routes throughout the world. Among the major proponents of "Out of Asia" theory was Ernst Haeckel, who argued that the first human species (which he proactively named "Homo primigenius") evolved on the now-disproven hypothetical continent "Lemuria" from a species he termed "Pithecanthropus alalus" ("speechless ape-man"). "Lemuria" had supposedly sunk below the Indian Ocean, so no fossils could be found to prove this.
Dutch scientist Eugène Dubois joined the Royal Netherlands East Indies Army to search for the "missing link" in Java. At the Trinil site, his team found a skullcap and molar in 1891, and a femur in 1892 (Java Man), which he named "Pithecanthropus erectus" in 1893. He unfruitfully attempted to convince the European scientific community that he had found an upright-walking ape-man dating to the late Pliocene or Early Pleistocene; they dismissed his findings as some kind of malformed non-human ape.
Dubois argued that "P. erectus" was a gibbon-like ape which was the precursor to a more familiar human body plan, but in the 1930s, Jewish-German anatomist Franz Weidenreich noticed a striking similarity with ancient human remains recently being unearthed in China (Peking Man, "Sinanthropus pekinensis"). This characterization became better supported as German-Dutch palaeontologist Gustav Heinrich Ralph von Koenigswald discovered more Indonesian ancient human remains over the decade at Mojokerto, Sangiran, and Ngandong. Weidenreich believed that they were the direct ancestors of the local modern human Homo sapiens subspecies in accord with historical race concepts — that is, Peking Man was the direct ancestor of specifically Chinese people, and Java Man of Aboriginal Australians (polycentricism). As the importance of racial distinction diminished with the development of modern evolutionary synthesis, many fossil human species and genera around Asia, Africa, and Europe (including "Pithecanthropus" and "Sinanthropus") were reclassified as subspecies of Homo erectus.
In the late 20th century, some of the oldest H. erectus fossils were being discovered across Africa, the first being Kenyan archeologist Louis Leakey's Olduvai Hominin 9 in 1960. As the human fossil record expanded, the "Out of Africa" theory and monogenism became the consensus (that all modern humans share a fully anatomically modern common ancestor). H. erectus is now generally considered to be an African species which later dispersed across Eurasia.
By the middle of the 20th century, human taxonomy was in turmoil, with many poorly-defined species and genera described across Europe, Asia, and Africa, which exaggerated how different these fossils actually are from each other. In 1940, Weidenreich was the first to suggest reclassifying "Sinanthropus pekinensis" and "Pithecanthropus erectus" as subspecies of H. erectus. In 1950, German-American evolutionary biologist Ernst Mayr had entered the field of anthropology, and, surveying a "bewildering diversity of names", decided to subsume human fossils into three species of Homo: "H. transvaalensis" (the australopithecines), H. erectus (including "Sinanthropus", "Pithecanthropus", and various other Asian, African, and European taxa), and H. sapiens (including anything younger than H. erectus, such as modern humans and Neanderthals), as had been broadly recommended by various priors. Mayr defined these species as a sequential lineage, with each species evolving into the next (chronospecies). Though later Mayr changed his opinion on the australopithecines (recognizing Australopithecus), his more conservative view of archaic human diversity became widely adopted in the subsequent decades.
In the 1970s, as population genetics was being formulated, the anatomical variation of H. erectus across its wide geographic and temporal range (the basis for the subspecies distinctions) became better understood as clines — different populations which attained some anatomical regionality but were not reproductively isolated. In general, subspecies names for H. erectus are now used for convenience to indicate time and region rather than specific anatomical trends.
If an author uses subspecies, the ones usually recognized can include:
The ancient Georgia fossils have variably been classified as a population of H. e. ergaster (sometimes denoted by a quadrinomial H. e. ergaster georgicus) its own subspecies as H. e. georgicus, or elevated to its own species as H. georgicus. Some authors may also elevate H. ergaster, H. soloensis, and H. pekinensis. Material relegated to H. e. tautavelensis is traditionally assigned to H. heidelbergensis.
H. erectus evolved in Africa from a population of H. habilis (anagenesis). The oldest identified H. erectus specimen is a 2.04 million year old skull, DNH 143, from Drimolen, South Africa, coexisting with the australopithecine Paranthropus robustus. H. erectus dispersed out of Africa soon after evolution, the earliest recorded instances being H. e. georgicus 1.85 to 1.78 million years ago in Georgia and the Indonesian Mojokerto and Sangiran sites 1.8 to 1.6 million years ago. Populations may have pushed into northwestern Europe at around the same time. While H. erectus is usually considered the first hominin to leave Africa, 2.48 and 2.1 million year old stone tools from respectively Zarqa Valley, Jordan, and Shangchen, China, could indicate earlier species left as well. Since H. erectus was first defined in East Asia, those populations are sometimes distinguished as H. erectus sensu stricto ("in the strict sense"), and African and West Eurasian populations as H. erectus sensu lato ("in the broad sense"), but this may not reflect how these populations are actually related to each other.
Once established around the Old World, H. erectus evolved into other later species in the genus Homo, including: H. heidelbergensis, H. antecessor, H. floresiensis, and H. luzonensis. H. heidelbergensis, in turn, is usually placed as the last common ancestor of modern humans (H. sapiens), Neanderthals (H. neanderthalensis), and Denisovans. H. erectus is thus a non-natural, paraphyletic grouping of fossils and does not include all the descendants of a last common ancestor. Despite being designated as different species, H. erectus may have been interbreeding with some of its descendant species, namely the common ancestor of Neanderthals and Denisovans ("Neandersovans").
The dispersal of H. erectus is generally ascribed to the evolution of obligate bipedalism, better technology, and a dietary switch to carnivory. Populations spread out via open grassland and woodland savannas, which were expanding due to a global aridification trend at the onset of the Quaternary glaciation. Most H. erectus sensu lato specimens date to 1.8 to 1 million years ago in the Early Pleistocene before giving way to descendant species. H. erectus sensu stricto persisted much longer than sensu lato, with the youngest population (H. e. soloensis) dating to 117,000 to 108,000 years ago in Late Pleistocene Java. This population appears to have died out when the savannah corridors closed, and tropical jungle took over.
A 2021 phylogeny of some H. erectus fossils using tip dating:
As such a widely distributed species both geographically and through time, the anatomy of H erectus can vary considerably. Among living primates, the degree of regionality achieved by H. erectus (phenotypic plasticity) is only demonstrated in modern humans.
Dubois originally described the species using a skullcap, noting the traits of a low and thickened cranial vault and a continuous bar of bone forming the brow ridge (supraorbital torus). He also used several other traits now considered more typical of H. erectus sensu stricto, such as a sagittal keel running across the midline of the skullcap, a bar of bone across the back of the skull (occipital torus), and a strong crest on the mastoid part of the temporal bone. These traits can be still be found, nonetheless, in a few H. erectus sensu lato specimens, namely the 1.47 million year old Olduvai Hominin 9. Compared to H. erectus sensu lato, the skullcap of sensu stricto narrows considerably at the front, the face is bigger and presumably more prognathic (it juts out more, but the face is poorly documented), and the molars are larger particularly in Indonesian fossils. H. erectus was the first human species with a fleshy nose, which is generally thought to have evolved in response to breathing dry air in order to retain moisture. Compared to earlier Homo, H. erectus has smaller teeth, thinner enamel, and weaker mandibles (jawbone), likely due to a greater reliance on tool use and food processing.
The brain size of H. erectus varies considerably, but is generally smaller in H. erectus sensu lato, as low as 546 cc (33.3 cu in) in Dmanisi skull 5. East Asian H. erectus overall are rather big-brained, averaging roughly 1,000 cc, staying within the range of variation for modern humans. The late-surviving H. e. soloensis has the biggest brain volume with one specimen measuring 1,251 cc (76.3 cu in).
The rest of the body is primarily understood by three partial skeletons from the Kenyan Lake Turkana site, notably Turkana Boy. Other postcranial (any bone aside from the skull) fossils attributed to H. erectus are not associated with a skull, making attribution unverifiable. Though the body plan of earlier Homo is poorly understood, H. erectus has typically been characterized as the first Homo species with a human body plan, distinct from non-human apes. The chest may have been short and barrel-shaped, like other archaic humans. Fossil tracks near Ileret, Kenya, suggest a human gait. This adaptation is implicated in the spread of H. erectus across the Old World.
It is unclear when human ancestors lost most of their body hair. Genetic analysis suggests that high activity in the melanocortin 1 receptor, which would produce dark skin, dates back to 1.2 million years ago. This could indicate the evolution of hairlessness around this time, as a lack of body hair would have left the skin exposed to harmful UV radiation. Populations in higher latitudes potentially developed lighter skin to prevent vitamin D deficiency, though a 500,000 to 300,000 year old Turkish H. erectus specimen presents the earliest case of tuberculous meningitis, which is typically exacerbated by vitamin D deficiency specifically in dark-skinned people living in higher latitudes. Hairlessness is generally thought to have facilitated sweating, but reducing parasite load and sexual selection have also been proposed.
Height reconstructions range approximately 148–167 cm (4 ft 10 in – 5 ft 6 in), with tropical populations typically reconstructed as scoring on the higher end like modern human populations. Adult weight is harder to approximate, but about 50 kg (110 lb) may have been normal. H. erectus is usually thought to be the first human species with little size-specific sexual dimorphism, but the variability of postcranial material makes this unclear.
The Turkana Boy specimen was originally estimated in 1993 to have been roughly 165 cm (5 ft) when it died at about 12 years of age, and predicted to reach 177–193 cm (5 ft 10 in – 6 ft 4 in) had it survived past its pubertal growth spurt and into adulthood — assuming a humanlike growth curve. Further fossil discoveries instead better support an apelike growth curve, making for an adult height of 163 cm (5 ft 4 in) at the age of 16.
The dimensions of a 1.8 million years old adult female H. e. ergaster pelvis from Gona, Ethiopia, suggests that she would have been capable of birthing children with a maximum prenatal brain size of 315 cc (19.2 cu in), about 30–50% of adult brain size, falling between chimpanzees (~40%) and modern humans (28%). Similarly, a 1.5 million year old infant skull from Mojokerto had a brain volume of about 72–84% the size of an adult, which suggests a brain growth trajectory more similar to that of non-human apes. This suggests that the childhood growth and development of H. erectus was intermediate between that of chimpanzees and modern humans, and the faster development rate suggests that altriciality (an extended childhood) evolved at a later stage in human evolution. The faster development rate might also indicate a shorter expected lifespan compared to later Homo.
The bones are extraordinarily thickened, particularly in Homo erectus sensu stricto, so much so that skull fragments have sometimes been confused for fossil turtle carapaces. The medullary canal in the long bones (where the bone marrow is stored, in the limbs) is extremely narrowed (medullary stenosis). This degree of thickening is usually exhibited in semi-aquatic animals which use their heavy (pachyosteosclerotic) bones as ballasts to help them sink, induced by hypothyroidism.
It is unclear what function intense bone thickening could have served. Before more complete skeletons were discovered, Weidenreich suggested H. erectus was a gigantic species. Other explanations include a far more violent and impact-prone lifestyle than other Homo, or pathological nutrient deficiencies. The supraorbital torus thickens with age, and may be a response to bending stresses from habitual loading of the front teeth.
H. erectus was early-on portrayed as the earliest hunter-gatherer and a skilled predator of big game, relying on running. The gradual shift to "top predator" may have led to its dispersal throughout Afro-Eurasia. Though scavenging may have instead played a bigger role at least in some populations, H. erectus fossils are often associated with the butchered remains of large herbivores, especially elephants, rhinos, hippos, bovines, and boars. The complexities of prey behaviors and the nutritional value of meat have been connected to brain volume growth.
H. erectus is usually assumed to have practiced sexual division of labor much like recent hunter-gatherer societies, with men hunting and women gathering. This ideation is supported by a fossil trackway from Ileret, Kenya, made by a probably all-male band of over 20 H. erectus individuals, possibly a hunting party or (similar to chimpanzees) a border patrol group.
Since common modern human tapeworms began to diverge from those of other predators roughly 1.7 million years ago (specifically the pork tapeworm, beef tapeworm, and Asian tapeworm), not only was H. erectus consuming meat regularly enough for speciation to occur in these parasites, but meat was probably consumed raw more often than not. Some populations were collecting aquatic resources, include fish, shellfish, and turtles such as at Lake Turkana and Trinil. Underground storage organs (roots, tubers, etc.) were likely also major dietary components, and traces of the edible plant Celtis have been documented at several H. erectus sites.
Possibly due to overhunting of the biggest game available, the dispersal of H. erectus and descendant species may be implicated in the extinctions of large herbivores and the gradual reduction of average herbivore size over the Pleistocene. H. erectus overhunting has been blamed by some authors for the decline of proboscidean species as well as competing carnivores, but their decline may be better attributed to the spread of grasslands. The giant tortoise Megalochelys may have been driven to extinction by H. erectus in Island Southeast Asia, since species went extinct shortly after the arrival of H. erectus.
H. erectus manufactured Lower Paleolithic technologies, and is credited with the invention of the Acheulean stone tool industry at latest 1.95 million years ago. This was a major technological breakthrough featuring large, heavy-duty tools; most iconically, the handaxe. Over hundreds of thousands of years, the Achuelean eventually replaced its predecessor — the Oldowan (a chopper and flake industry) — in Africa, and spread out across Western Eurasia. This sudden innovation was typically explained as a response to environmental instability in order to process more types of food and broaden the diet, which allowed H. erectus to colonize Eurasia. Despite this characterization of the Acheulean, H. e. georgicus was able to leave Africa despite only manufacturing Oldowan-style tools, and the handaxe does not seem to have been manufactured commonly in East Asia. This conspicuous pattern was first noted by American archaeologist Hallam L. Movius in 1948, who drew the "Movius Line", dividing the East into a "chopping-tool culture" and the West into a "hand axe culture". Movius took this as evidence of inferiority of Far Eastern populations:
H. erectus seems to have been using stone tools in butchery, vegetable processing, and woodworking (maybe manufacturing spears and digging sticks). In Africa, Oldowan sites are typically found alongside major fossil assemblages, but Acheulean sites normally feature more stone tools than fossils, so H. erectus could have been using choppers and handaxes for different activities.
Materials for stone tools were normally sourced locally, and it seems blanks were usually chosen based on size rather than material quality. H. erectus also produced tools from shells at Sangiran and Trinil.
H. erectus is credited as the first human species to wield fire. The earliest claimed fire site is Wonderwerk Cave, South Africa, at 1.7 million years old. While the species' dispersal far out of Africa has often been attributed to fire and cave dwelling, fire does not become common in the archaeological record until 300,000–400,000 years ago, and cave-dwelling about 600,000 years ago. Therefore, H. erectus may have only been scavenging fire opportunistically. Similarly, H. erectus sites usually stay within warmer tropical or subtropical latitudes. The dating of northerly populations (namely Peking Man) could suggest that they were retreating to warmer refugia during glacial periods, but the precise age of the Peking Man fossils is poorly resolved.
Like other primates, H. erectus probably used medicinal plants and infirmed sick group members. The earliest probable example of this is a 1.77 million year old H. e. georgicus specimen who had lost all but one tooth due to age or gum disease (the earliest example of severe chewing impairment) yet still survived for several years afterwards.
H. erectus made long sea crossings to arrive on the islands of Flores, Luzon, and some Mediterranean islands. Some authors have asserted that H. erectus intentionally made these crossings by inventing watercrafts and seafaring so early in time, speaking to advanced cognition and language skills. These populations could have also been founded by natural rafting events instead.
In East Asia, H. erectus is usually represented only by skullcaps, which used to be interpreted as widespread cannibalism and ritual headhunting. This had been reinforced by the historic practice of headhunting and cannibalism in some recent Indonesian, Australian, and Polynesian cultures, which were formerly believed to have directly descended from these H. erectus populations. The lack of the rest of the skeleton is now normally explained by natural phenomena.
Art-making could be evidence of symbolic thinking. An engraved Pseudodon shell DUB1006-fL from Trinil, Java, with geometric markings could possibly be the earliest example of art-making, dating to 546,000 to 436,000 years ago. H. erectus was also the earliest human to collect red-colored pigments, namely ochre. Ochre lumps at Olduvai Gorge, Tanzania, associated with the 1.4 million year old Olduvai Hominid 9 may have been purposefully shaped and trimmed by a hammerstone. Red ochre is normally recognized as bearing symbolic value when associated with modern humans.
The spinal column of the 1.6 million year old Turkana boy would not have supported properly developed respiratory muscles required to produce speech; and a 1.5 million year old infant H. erectus skull from Mojokerto, Java, shows that this population did not have an extended childhood, which is a prerequisite for language acquisition. On the other hand, despite the cochlear (ear) anatomy of Sangiran 2 and 4 retaining several traits reminiscent of australopithecines, the hearing range may have included the higher frequencies used to discern speech.
Given expanding brain size and technological innovation, H. erectus may have been using some basic proto-language in combination with gesturing, and built the basic framework around which fully-fledged languages would eventually be formed.