Homo erectus
Homo erectus 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. Some populations of H. erectus were ancestors 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 evolved directly into local modern human populations rather than all humanity sharing a single anatomically modern ancestor. As the fossil record improved over the mid-to-late 20th century, "Out of Africa" theory and monogenism became the consensus.
The typical skull has a pronounced brow ridge, a protruding jaw, and large teeth. The bones are much thicker than in modern humans. East Asian populations normally have an even more robust skeleton and larger brain volume — averaging. Western H. erectus brain volume could be as low as 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 in height and about in weight.
H. erectus invented the Acheulean tool industry, a major innovation of large, heavy-duty stone tools. These may have been used in butchery, vegetable processing, and woodworking of spears and digging sticks. H. erectus was a major predator of large herbivores on the expanding savannas during 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 known occurrence of H. erectus is 108,000 to 117,000 years ago in Southeast Asia, until the last savannas in the region gave way to jungle.
Taxonomy
Research history
While Charles Darwin had hypothesized in his 1871 Descent of Man that humans most likely evolved in Africa, many late-19th century evolutionary naturalists postulated that Asia 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 evolved on a now-disproven hypothetical continent "Lemuria" from a species he termed Pithecanthropus alalus. "Lemuria" had supposedly sunk below the Indian Ocean, accounting for the lack of fossil evidence.Dutch scientist Eugène Dubois joined the Royal Netherlands East Indies Army to search for the "missing link" of human evolution in Java. At the Trinil site, his team found a skullcap and molar in 1891, and a femur in 1892, which he named "Pithecanthropus erectus" in 1893. He 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 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, German-American anatomist Franz Weidenreich noticed a striking similarity with ancient human remains recently being unearthed in China. 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. As the significance of racial distinction diminished with the development of modern evolutionary synthesis, many fossil human species and genera around Asia, Africa, and Europe were reclassified as subspecies of Homo erectus.
During the late 20th century, some of the oldest H. erectus fossils were 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, with later African populations giving rise to the modern human lineage.
Subspecies
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 the differences among them. 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 entered this field. Surveying a "bewildering diversity of names" and many proposals for consolidation, he decided to reclassify human fossils into three species of Homo: "H. transvaalensis", H. erectus, and H. sapiens. Mayr defined these species as a sequential lineage, each evolving into the next. Though later Mayr changed his opinion on the australopithecines, 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 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.
The more commonly used subspecies are:
- H. e. erectus for earlier Indonesian fossils
- H. e. pekinensis for Chinese fossils
- H. e. soloensis for the latest-surviving Indonesian fossils
- H. e. ergaster for African fossils
- H. e. georgicus for an early group of fossils from Georgia
- H. e. tautavelensis for Western European fossils
Evolution and dispersal
H. erectus evolved in Africa from a population of H. habilis and they coexisted for about half a million years. During this time interval, H. erectus populations could display a mix of more "classically erectus" or "classically habilis" cranial anatomy and a wide range of brain volumes. The oldest identified H. erectus specimen is a 2.04 million year old skull, DNH 134, 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 1.78 to 1.85 million years ago in Georgia and the Indonesian Mojokerto and Sangiran sites 1.6 to 1.8 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, stone tools that possibly date to as far back as 2.48 and 2.1 million year from respectively Zarqa Valley, Jordan, and Shangchen, China, could indicate that an earlier hominin species left Africa. Since H. erectus was first defined in East Asia, those populations are sometimes distinguished as H. erectus sensu stricto, and African and West Eurasian populations as H. erectus sensu lato, 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 Neanderthals, Denisovans, and modern humans. 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 a different species, H. erectus may have interbred with some of its descendant species, namely the common ancestor of Neanderthals and Denisovans.
File:Spreading homo sapiens la.svg|thumb|upright=2.1|Successive dispersals of Homo erectus, Homo neanderthalensis and Homo sapiens
The dispersal of H. erectus is generally ascribed to the evolution of obligate bipedalism, better technology, and adoption of a carnivorous diet. However, the sudden adoption of carnivory could be sampling bias, with earlier species consuming the same amount of meat. 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. H. erectus is usually thought to have occupied the Sahara and West Asia during humid periods, but populations may have persisted into desert periods.
Most H. erectus sensu lato specimens date to 1 to 1.8 million years ago in the Early Pleistocene before giving way to descendant species. The classification of Middle Pleistocene Homo has been a controversial topic, termed "the muddle in the middle". H. erectus sensu stricto persisted much longer than sensu lato, with the youngest population dating to 108,000 to 117,000 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: