Homo erectus

 Homo erectus (meaning "upright man," from the Latin ērigere, "to put up, set upright") is an extinct species of hominin that lived throughout most of the Pleistocene, with the earliest first fossil evidence dating to around 1.9 million years ago and the most recent to around 143,000 years ago. The species originated in Africa and spread as far as Georgia, India, Sri Lanka, China and Java.[1][2]

There is still disagreement on the subject of the classification, ancestry, and progeny of H. erectus, with two major alternative classifications: erectus may be another name for Homo ergaster, and therefore the direct ancestor of later hominids such as Homo heidelbergensis, Homo neanderthalensis, and Homo sapiens; or it may be an Asian species distinct from African ergaster.[1][3][4]

Some palaeoanthropologists consider H. ergaster to be simply the African variety of H. erectus. This leads to the use of the term "Homo erectus sensu stricto" for the Asian H. erectus, and "Homo erectus sensu lato" for the larger species comprising both the early African populations (H. ergaster) and the Asian populations

Origin
The first hypothesis is that H. erectus migrated from Africa during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 2.0 million years ago, and it dispersed throughout much of the Old World. Fossilized remains 1.8 to 1 million years old have been found in Africa (e.g., Lake Turkana[7] and Olduvai Gorge), Georgia, Indonesia (e.g., Sangiran in Central Java and Trinil in East Java), Vietnam, China (e.g., Shaanxi) and India.[8]

The second hypothesis is that H. erectus evolved in Eurasia and then migrated to Africa. The species occupied a Caucasus site called Dmanisi, in Georgia, from 1.85 million to 1.77 million years ago, at the same time or slightly before the earliest evidence in Africa. Excavations found 73 stone tools for cutting and chopping and 34 bone fragments from unidentified creatures.

Discovery and representative fossils
The Dutch anatomist Eugène Dubois, who was especially fascinated by Darwin's theory of evolution as applied to man, set out to Asia (the place accepted then, despite Darwin, as the cradle of human evolution), to find a human ancestor in 1886. In 1891, his team discovered a human fossil on the island of Java, Dutch East Indies (now Indonesia); he described the species as Pithecanthropus erectus (from the Greek πίθηκος,[11] "ape", and ἄνθρωπος,[12] "man"), based on a calotte (skullcap) and a femur like that of H. sapiens found from the bank of the Solo River at Trinil, in East Java. (This species is now regarded as H. erectus).

The find became known as Java Man. Thanks to Canadian anatomist Davidson Black's (1921) initial description of a lower molar, which was dubbed Sinanthropus pekinensis,[13] however, most of the early and spectacular discoveries of this taxon took place at Zhoukoudian in China. 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 Weidenreichian casts do exist at the American Museum of Natural History in New York 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, however, due to discoveries on Java and at Zhoukoudian, it was believed that modern humans first evolved in Asia. A few naturalists (Charles Darwin most prominent among them) predicted that humans' earliest ancestors were African: he pointed out that chimpanzees and gorillas, who are human relatives, live only in Africa.[14]

From the 1950s to 1970s, however, numerous fossil finds from East Africa yielded evidence that the oldest hominins originated there. It is now believed that H. erectus is a descendant of earlier genera such as Ardipithecus and Australopithecus, or early Homo-species such as H. habilis or H. ergaster. H. habilis and H. erectus coexisted for several thousand years, and may represent separate lineages of a common ancestor.[15]

Archaeologist John T. Robinson and Robert Broom named Telanthropus capensis in the 1950s, now thought to belong to Homo erectus.[16] Robinson discovered a jaw fragment, SK 45, in September 1949 in Swartkrans, South Africa. In 1957, Simonetta proposed to re-designate it Homo erectus, and Robinson (1961) agreed.

Homo erectus georgicus
Homo erectus georgicus (Georgian: ქართველი ადამიანი) is the subspecies name sometimes used to describe fossil skulls and jaws found in Dmanisi, Georgia. Although first proposed as a separate species, it is now classified within H. erectus.[22][23][24] A partial skeleton was discovered in 2001. The fossils are about 1.8 million years old. The remains were first discovered in 1991 by Georgian scientist, David Lordkipanidze, accompanied by an international team that unearthed the remains. There have been many proposed explanations of the dispersion of H. erectus georgicus.[25] Implements and animal bones were found alongside the ancient human remains.

At first, scientists thought they had found mandibles and skulls belonging to Homo ergaster, but size differences led them to name a new species, Homo georgicus, which was posited as a descendant of Homo habilis and ancestor of Asian Homo erectus. This classification was not upheld, and the fossil is now considered a divergent subgroup of Homo erectus, sometimes called Homo erectus georgicus.

At around 600 cubic centimetres (37 cu in) brain volume, the skull D2700 is dated to 1.77 million years old and in good condition, offering insights in comparison to the modern human cranial morphology. At the time of discovery the cranium was the smallest and most primitive Hominina skull ever discovered outside of Africa. However, in 2003 a significantly smaller brained hominid was found on the isle of Flores, H. floresiensis. Homo erectus georgicus exhibits strong sexual dimorphism with males being significantly larger than females.

Subsequently, four fossil skeletons were found, showing a species primitive in its skull and upper body but with relatively advanced spines and lower limbs, providing greater mobility. They are now thought not to be a separate species, but to represent a stage soon after the transition between Homo habilis and H. erectus, and have been dated at 1.8 million years before the present, according to the leader of the project, David Lordkipanidze.[23][30] 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 completely toothless specimen (D3900).[31]

A further skull, the only intact skull ever found of an early Pleistocene hominin, was described in 2013.[32] At just under 550 cubic centimetres, the skull had the smallest braincase of all the individuals found at the site. The variations in these skulls prompted the researchers to examine variations in modern human and chimpanzees. The researchers found that while the Dmanisi skulls looked different from one another, the variations were no greater than those seen among modern people and among chimpanzees. These variations therefore suggest that previous fossil finds thought to be of different species on the basis of their variations, such as Homo rudolfensis, Homo gautengensis, H. ergaster and possibly H. habilis, may be alternatively interpreted as belonging to the same lineage as Homo erectus.