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Naming

Contrary to the view Charles Darwin expressed in his 1871 book Descent of Man, many late-19th century evolutionary naturalists postulated that Asia, not Africa, was the birthplace of humankind as it is midway between Europe and America, providing optimal dispersal routes throughout the world (the Out of Asia theory). Among these was German naturalist Ernst Haeckel, who argued that the first human species evolved on the now-disproven hypothetical continent " Lemuria " in what is now Southeast Asia, from a species he termed " Pithecanthropus alalus " ("speechless apeman"). "Lemuria" had supposedly sunk below the Indian Ocean, so no fossils could be found to prove this. Nevertheless, Haeckel's model inspired Dutch scientist Eugène Dubois to journey to the Dutch East Indies. Because no directed expedition had ever discovered human fossils (the few known had all been discovered by accident), and the economy was strained by the Long Depression, the Dutch government refused to fund Dubois. In 1887, he enlisted in the Dutch East India Army as a medical officer, and was able to secure a post in 1887 in the Indies to search for his " missing link " in his spare time. On Java, he found a skullcap in 1891 and a femur in 1892 (Java Man) dating to the late Pliocene or early Pleistocene at the Trinil site along the Solo River, which he named Pithecanthropus erectus ("upright apeman") in 1893. He attempted unsuccessfully to convince the European scientific community that he had found an upright-walking ape-man. Given few fossils of ancient humans had even been discovered at the time, they largely dismissed his findings as a malformed non-human ape.

The significance of these fossils would not be realized until the 1927 discovery of what Canadian paleoanthropologist Davidson Black called " Sinanthropus pekinensis " (Peking Man) at the Zhoukoudian cave near Beijing, China. Black lobbied across North America and Europe for funding to continue excavating the site, which has since become the most productive H. erectus site in the world. Continued interest in Java led to further H. erectus fossil discoveries at Ngandong (Solo Man) in 1931, Mojokerto (Java Man) in 1936, and Sangiran (Java Man) in 1937. The Sangiran site yielded the best preserved Java Man skull. German paleoanthropologist Franz Weidenreich provided much of the detailed description of the Chinese specimens in several monographs. The original specimens were lost during the Second Sino-Japanese War after an attempt to smuggle them out of China for safekeeping. Only casts remain.

Similarities between Java Man and Peking Man led Ernst Mayr to rename both as Homo erectus in 1950. 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, the belief that modern humans first evolved in Asia was widely accepted. A few naturalists— Charles Darwin the most prominent among them—theorized that humans' earliest ancestors were African. Darwin had pointed out that chimpanzees and gorillas, humans ' closest relatives, evolved and exist only in Africa. Darwin did not include orangutans among the great apes of the Old World, likely because he thought of orangutans as primitive humans rather than apes. While Darwin considered Africa as the most probable birthplace of human ancestors, he also made the following statement about the geographic location of human origins in his book The Descent of Man, and Selection in Relation to Sex: "... it is useless to speculate on this subject; for two or three anthropomorphous apes, one the Dryopithecus …, existed in Europe during the Miocene age; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale." (1889, pp. 155–156).

In 1949, the species was reported in Swartkrans Cave, South Africa, by South African paleoanthropologists Robert Broom and John Talbot Robinson, who described it as " Telanthropus capensis ". Homo fossils have also been reported from nearby caves, but their species designation has been a tumultuous discussion. A few North African sites have additionally yielded H. erectus remains, which at first were classified as " Atlantanthropus mauritanicus " in 1951. Beginning in the 1970s, propelled most notably by Richard Leakey, more were being unearthed in East Africa predominantly at the Koobi Fora site, Kenya, and Olduvai Gorge, Tanzania.

Archaic human fossils unearthed across Europe used to be assigned to H. erectus, but have since been separated as H. heidelbergensis as a result of British physical anthropologist Chris Stringer 's work.